Search

Abstract Background In recent years, there has been a growing interest in phage therapy as an effective therapeutic tool against colibacillosis caused by avian pathogenic Escherichia coli (APEC) which resulted from the increasing number of multidrug resistant (MDR) APEC strains. Methods In the present study, we reported the characterization of a new lytic bacteriophage (Escherichia phage AG- MK-2022. Basu) isolated from poultry slaughterhouse wastewater. In addition, the in vitro bacteriolytic activity of the newly isolated phage (Escherichia phage AG- MK-2022. Basu) and the Escherichia phage VaT-2019a isolate PE17 (GenBank: MK353636.1) were assessed against MDR- APEC strains (n = 100) isolated from broiler chickens with clinical signs of colibacillosis. Results Escherichia phage AG- MK-2022. Basu belongs to the Myoviridae family and exhibits a broad host range. Furthermore, the phage showed stability under a wide range of temperatures, pH values and different concentrations of NaCl. Genome analysis of the Escherichia phage AG- MK-2022. Basu revealed that the phage possesses no antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and any E. coli virulence associated genes. In vitro bacterial challenge tests demonstrated that two phages, the Escherichia phage VaT-2019a isolate PE17 and the Escherichia phage AG- MK-2022. Basu exhibited high bactericidal activity against APEC strains and lysed 95% of the tested APEC strains. Conclusions The current study findings indicate that both phages could be suggested as safe biocontrol agents and alternatives to antibiotics for controlling MDR-APEC strains isolated from broilers.

Background: In recent years, there has been a growing interest in phage therapy as an effective therapeutic tool against colibacillosis caused by avian pathogenic Escherichia coli (APEC) which resulted from the increasing number of multidrug resistant (MDR) APEC strains. Methods: In the present study, we reported the characterization of a new lytic bacteriophage (Escherichia phage AG- MK-2022. Basu) isolated from poultry slaughterhouse wastewater. In addition, the in vitro bacteriolytic activity of the newly isolated phage (Escherichia phage AG- MK-2022. Basu) and the Escherichia phage VaT-2019a isolate PE17 (GenBank: MK353636.1) were assessed against MDR- APEC strains (n = 100) isolated from broiler chickens with clinical signs of colibacillosis. Results : Escherichia phage AG- MK-2022. Basu belongs to the Myoviridae family and exhibits a broad host range. Furthermore, the phage showed stability under a wide range of temperatures, pH values and different concentrations of NaCl. Genome analysis of the Escherichia phage AG- MK-2022. Basu revealed that the phage possesses no antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and any E. coli virulence associated genes. In vitro bacterial challenge tests demonstrated that two phages, the Escherichia phage VaT-2019a isolate PE17 and the Escherichia phage AG- MK-2022. Basu exhibited high bactericidal activity against APEC strains and lysed 95% of the tested APEC strains. Conclusions: The current study findings indicate that both phages could be suggested as safe biocontrol agents and alternatives to antibiotics for controlling MDR-APEC strains isolated from broilers. [ABSTRACT FROM AUTHOR]

Avian pathogenic Escherichia coli (APEC) is a major bacterial pathogen responsible for the most widespread form of colibacillosis, resulting in substantial economic losses within the poultry sector and posing a potential public health risk. From July to September 2021, our study investigated the antibiotic resistance pattern of Escherichia coli (E. coli) and the presence of virulence-associated genes (iucD, iutA, iss, and ompT) linked to APEC using 105 broiler meat samples comprising liver, thigh, and breast muscle, in Chitwan, Nepal. E. coli was isolated and identified by culturing samples on MacConkey's agar, Eosin-methylene blue (EMB) agar and performing different biochemical tests. Antibiotic resistance patterns of E. coli were determined by the Kirby-Bauer disc diffusion method. Following the isolation of E. coli, the molecular detection of APEC was performed using conventional polymerase chain reaction (PCR). Out of the 105 samples analyzed, 61 (58.1 %) tested positive for E. coli. In antibiotic susceptibility test (AST), gentamicin and tetracycline exhibited the highest resistance rates, with 90.2 % and 67.2 %, respectively and 29.5 % of the E. coli isolates displayed multidrug-drug resistance. Out of 61 confirmed E. coli isolates, iutA was detected in 47 (77.0 %) samples, iucD in 46 (75.4 %), iss in 53 (86.8 %), and ompT in 39 (63.9 %) samples. This study reports the occurrence of MDR E. coli in meat samples, together with virulence genes associated with APEC which poses a public health threat. Continuous surveillance is vital for monitoring APEC transmission within poultry farms, coupled with efforts to raise awareness of food safety among consumers of broiler meat.

Avian pathogenic Escherichia coli (APEC) belonging to extraintestinal pathogenic E. coli (ExPEC) can cause severe infections in extraintestinal tissues in birds and humans, such as the lungs and blood. MprA (microcin production regulation, locus A, herein renamed AbsR, a blood survival regulator), a member of the MarR (multiple antibiotic resistance regulator) transcriptional regulator family, governs the expression of capsule biosynthetic genes in human ExPEC and represents a promising druggable target for antimicrobials. However, a deep understanding of the AbsR regulatory mechanism as well as its regulon is lacking. In this study, we present a systems-level analysis of the APEC AbsR regulon using ChIP-Seq (chromatin immunoprecipitation sequencing) and RNA-Seq (RNA sequencing) methods. We found that AbsR directly regulates 99 genes and indirectly regulates 667 genes. Furthermore, we showed that: 1) AbsR contributes to antiphagocytotic effects by macrophages and virulence in a mouse model for systemic infection by directly activating the capsular gene cluster; 2) AbsR positively impacts biofilm formation via direct regulation of the T2SS (type II secretion system) but plays a marginal role in virulence; and 3) AbsR directly upregulates the acid tolerance signaling system EvgAS to withstand acid stress but is dispensable in ExPEC virulence. Finally, our data indicate that the role of AbsR in virulence gene regulation is relatively conserved in ExPEC strains. Altogether, this study provides a comprehensive analysis of the AbsR regulon and regulatory mechanism, and our data suggest that AbsR likely influences virulence primarily through the control of capsule production. Interestingly, we found that AbsR severely represses the expression of the type I-F CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR associated) systems, which could have implications in CRISPR biology and application.

Abstract Avian pathogenic Escherichia coli (APEC) is the cause of colibacillosis outbreaks in young poultry chicks, resulting in acute to peracute death. The high morbidity and mortality caused by colibacillosis results in poor animal welfare, reduced sustainability and economical loss worldwide. To advance the understanding of the molecular epidemiology, genomic relatedness and virulence traits of APEC, we performed systematic sampling from 45 confirmed colibacillosis broiler flocks with high first week mortality (FWM) during 2018–2021. From these flocks, 219 APEC isolates were whole genome sequenced (WGS) and bioinformatic analyses were performed. The bioinformatic analyses included sequence typing (ST), serotyping, detection of virulence-associated genes (VAGs) and phylogenetic analysis. Our results showed a high prevalence of ST23, ST429 and ST95 among APEC isolates from Norwegian broiler flocks, and identified ST23, ST429, ST117 and ST371 to cause disease more often alone, compared to ST95, ST69 and ST10. Phylogenetic analyses, together with associated metadata, identified two distinct outbreaks of colibacillosis across farms caused by ST429 and ST23 and gave insight into expected SNP distances within and between flocks identified with the same ST. Further, our results highlighted the need for combining two typing methods, such as serotyping and sequence typing, to better discriminate strains of APEC. Ultimately, systematic sampling of APEC from multiple birds in a flock, together with WGS as a diagnostic tool is important to identify the disease-causing APEC within a flock and to detect outbreaks of colibacillosis across farms.

An experimental group of one-day-old chicken from a commercial hatchery was given a defined mixture of 7 gut anaerobes. The next day the chicks were inoculated by an APEC strain O78:H4-ST117 resistant to ciprofloxacin, alongside with the control group and monitored for 4 wk after the inoculation for the presence of the colonizing strains and ciprofloxacin-resistant E. coli. Significant reduction of colonization rates in the first 2 wk was recorded in the experimental group for the numbers of ciprofloxacin-resistant E. coli. The results show that colonization of chicken by defined anaerobic mixtures may provide a decisive protection during the critical period of the chicken intestinal microflora development.

Avian pathogenic Escherichia coli (APEC) is the cause of colibacillosis outbreaks in young poultry chicks, resulting in acute to peracute death. The high morbidity and mortality caused by colibacillosis results in poor animal welfare, reduced sustainability and economical loss worldwide. To advance the understanding of the molecular epidemiology, genomic relatedness and virulence traits of APEC, we performed systematic sampling from 45 confirmed colibacillosis broiler flocks with high first week mortality (FWM) during 2018–2021. From these flocks, 219 APEC isolates were whole genome sequenced (WGS) and bioinformatic analyses were performed. The bioinformatic analyses included sequence typing (ST), serotyping, detection of virulence-associated genes (VAGs) and phylogenetic analysis. Our results showed a high prevalence of ST23, ST429 and ST95 among APEC isolates from Norwegian broiler flocks, and identified ST23, ST429, ST117 and ST371 to cause disease more often alone, compared to ST95, ST69 and ST10. Phylogenetic analyses, together with associated metadata, identified two distinct outbreaks of colibacillosis across farms caused by ST429 and ST23 and gave insight into expected SNP distances within and between flocks identified with the same ST. Further, our results highlighted the need for combining two typing methods, such as serotyping and sequence typing, to better discriminate strains of APEC. Ultimately, systematic sampling of APEC from multiple birds in a flock, together with WGS as a diagnostic tool is important to identify the disease-causing APEC within a flock and to detect outbreaks of colibacillosis across farms. [ABSTRACT FROM AUTHOR]

Among various diseases, colibacillosis is one of the most important diseases, which causes heavy economic losses in broilers as well as in layers. It is caused by pathotype avian pathogenic E. coli (APEC). The present research work was carried out to detect and characterize the 60 Escherichia coli isolates. All the preserved isolates were obtained from various poultry farms located in and around Anand, Gujarat. All the isolates were revived and confirmed by polymerase chain reaction using phoA gene followed by characterization of the isolates based on seven virulence associated genes, viz., astA, iss, vat, papC, iucD, irp2 and tsh. Out of the 60 E. coli isolates analysed, the overall highest positive percentage was for gene iss (93.34%), followed by iucD (60.00%), irp2 (46.67%), astA (40%), tsh (33.33%), vat (26.67%) and papC (15.00%), respectively. [ABSTRACT FROM AUTHOR]

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avians, resulting in considerable losses in the poultry industry. APEC showed zoonotic potential initially related to the fact that APEC serves as the reservoir of virulence genes and antibiotic resistance genes for other E. coli. Thus, we determine the serotypes, phylogenetic groups, virulence genes distribution, and antibiotic resistance profiles of APEC isolates in eastern China. A total of 230 APEC were isolated from diseased chicken and duck with typical colibacillosis symptoms. Serotyping identified that O78 (44.78%) was the predominant serotype. The majority of APEC isolates were classified into B2 (29.57%), A (26.96%), D (20.00%), and B1 (18.26%), respectively. Among the 15 virulence genes, a high prevalence of ibeB (99.57%), fimC (91.74%), mat (91.30%), ompA (83.04%), and iss (80.43%) genes was observed. Except for low resistance rates for imipenem (1.7%) and polymyxin B (0.4%), most of the APEC isolates were resistant to erythromycin (98.7%), enrofloxacin (96.1%), tetracycline (95.2%), doxycycline (93.9%), lincomycin (90.0%), and streptomycin (90.0%). Moreover, all APEC exhibit multi-drug resistance. This study indicated that APEC isolates harbor a variety of virulence genes and showed multi-antibiotic resistance profiles, providing proof for understanding the epidemiological background and zoonotic potential of APEC in poultry farms. [ABSTRACT FROM AUTHOR]

Pathogenic strains of Escherichia coli infecting poultry, commonly called avian pathogenic E. coli (APEC) present significant risks, to the health of both poultry and the general public. This systematic review aimed to examine the prevalence of APEC serotypes, sequence types (ST), phylogenetic groups, virulence factors and antibiotic resistance patterns based on 189 research papers sourced from PubMed, Web of Science, and ProQuest. Then, data were extracted from the selected studies and analyzed to assess the global distribution and characteristics of APEC strains. The metaprop codes in the Meta and Metafor packages of R as implemented in RStudio were then used to conduct meta-analysis. Among APEC strains identified from these different research reports serogroup O78 had the highest overall prevalence (16 %), followed by serogroups O2 (10 %), and O117 (8 %). The most common ST profiles were ST117 (20 %), ST140 (15 %), ST95 (12 %), and ST131 (9 %). ST117 and ST140 are known reservoirs for pathogenic E. coli in humans. Moreover, phylogenetic assessment highlighted the prevalence of phylogroups A, A1, F, D, and B2 among APEC strains indicating diversity in phylogenetic origin within poultry populations. The presence of antimicrobial resistance was notable among APEC strains against antibiotics such as tetracyclines, penicillins, and cephalosporins. This resistance may be linked to use of antimicrobials in poultry production in certain regions presenting challenges for both animal health management and human infection control. Analysis of sequences linked to adherence or virulence indicated that genes encoding adhesins (csg, fimC), iron/metal uptake (sitB, sitC, iroD) and cytotoxicity (estB, hlyF), and serum resistance (traT, iss) were highly prevalent. These factors have been reported to contribute to APEC host colonization and virulence in poultry. In summary, this overview of the characteristics of APEC highlights the pressing importance of monitoring and implementing management approaches to reduce antimicrobial resistance considering that a phylogenetic diversity of E. coli strains causes infections in both poultry and humans and represents a risk to both animal and public health. Further, determining the major conserved aspects and predominant mechanisms of virulence of APEC is critical for improving diagnostics and developing preventative measures to reduce the burden of infection caused by pathogenic E. coli in poultry and lower risks associated with foodborne transmission of E. coli to humans through poultry and poultry products. • High prevalence of O78, O2 and O117 among APEC strains isolated from clinical cases. • ST117, ST140, and ST95 are the most common ST profiles among APEC strains. • Phylogenetic group A, A1, F, D, and B1 are predominant among APEC strains. • A high level of antimicrobial resistance is observed among APEC strains. • Csg, fimC, sitB, sitC, iroD, estB, and hlyF genes are prevalent among APEC strains. [ABSTRACT FROM AUTHOR]

This study was carried out to evaluate the effects of supplemental zinc methionine (Zn–Met) on growth performance, immune function, and intestinal health of meat ducks challenged with avian pathogenic Escherichia coli (APEC). A total of 480 1-day-old Cherry Valley male ducks were randomly assigned to 8 treatments with 10 replicates, each replicate containing 10 ducks. A 4 × 2 factor design was used with four dietary zinc levels (0, 30, 60, 120 mg Zn/kg in the form Zn–Met was added to the corn–soybean basal diet) and challenged with or without APEC at 8-days-old ducks. The trial lasted for 14 days. The results showed that a dietary Zn–Met supplementation significantly increased body weight (BW) of 14 days and BW gain, and decreased mortality during 7–14-days-old ducks (p < 0.05). Furthermore, dietary 30, 60, 120 mg/kg Zn–Met supplementation noticeably increased the thymus index at 2 days post-infection (2 DPI) and 8 DPI (p < 0.05), and 120 mg/kg Zn–Met enhanced the serum IgA at 2 DPI and IgA, IgG, IgM, C3 at 8 DPI (p < 0.05). In addition, dietary 120 mg/kg Zn–Met supplementation dramatically increased villus height and villus height/crypt depth (V / C) of jejunum at 2 DPI and 8 DPI (p < 0.05). The TNF- α and IFN- γ mRNA expression were downregulated after supplemented with 120 mg/kg Zn–Met in jejunum at 8 DPI (p < 0.05). Moreover, dietary 120 mg/kg Zn–Met supplementation stimulated ZO-3 , OCLN mRNA expression at 2 DPI and ZO-2 mRNA expression in jejunum at 8 DPI (p < 0.05), and improved the MUC2 concentration in jejunum at 2 DPI and 8 DPI (p < 0.05). At the same time, the cecal Bifidobacterium and Lactobacillus counts were increased (p < 0.05), and Escherichia coli counts were decreased (p < 0.05) after supplemented with Zn–Met. In conclusion, inclusion of 120 mg/kg Zn–Met minimizes the adverse effects of APEC challenge on meat ducks by improving growth performance and enhancing immune function and intestinal health. [ABSTRACT FROM AUTHOR]

The CTX-M-55 type extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae is increasing in prevalence worldwide without the transmission mechanism being fully clarified, which threatens public and livestock health. Outer membrane vesicles (OMVs) have been shown to mediate the gene horizontal transmission in some species. However, whether blaCTX-M-55 can be transmitted horizontally through OMVs in avian pathogenic Escherichia coli (APEC) has not been reported yet. To test this hypothesis, an ESBL-producing APEC was isolated and whole-genome sequencing (WGS) was performed to analyze the location of blaCTX-M-55. Ultracentrifugation and size exclusion chromatography was used to isolate and purify OMVs, and the transfer experiment of blaCTX-M-55 via OMVs was performed finally. Our results showed that the blaCTX-M-55 was located on an IncI2 plasmid. The number and diameter of OMVs secreted by ESBL-producing APEC treated with different antibiotics were significantly varied. The transfer experiment showed that the OMVs could mediate the horizontal transfer of blaCTX-M-55, and the frequency of gene transfer ranged from 10−5 to 10−6 CFU/mL with the highest frequency observed in the Enrofloxacin treatment group. These findings contribute to a better understanding of the antibiotics in promoting and disseminating resistance in the poultry industry and support the restrictions on the use of antibiotics in the poultry industry. [ABSTRACT FROM AUTHOR]

This study was carried out to evaluate the effects of supplemental zinc methionine (Zn–Met) on growth performance, immune function, and intestinal health of meat ducks challenged with avian pathogenic Escherichia coli (APEC). A total of 480 1-day-old Cherry Valley male ducks were randomly assigned to 8 treatments with 10 replicates, each replicate containing 10 ducks. A 4 × 2 factor design was used with four dietary zinc levels (0, 30, 60, 120 mg Zn/kg in the form Zn–Met was added to the corn–soybean basal diet) and challenged with or without APEC at 8-days-old ducks. The trial lasted for 14 days. The results showed that a dietary Zn–Met supplementation significantly increased body weight (BW) of 14 days and BW gain, and decreased mortality during 7–14-days-old ducks (p < 0.05). Furthermore, dietary 30, 60, 120 mg/kg Zn–Met supplementation noticeably increased the thymus index at 2 days post-infection (2 DPI) and 8 DPI (p < 0.05), and 120 mg/kg Zn–Met enhanced the serum IgA at 2 DPI and IgA, IgG, IgM, C3 at 8 DPI (p < 0.05). In addition, dietary 120 mg/kg Zn–Met supplementation dramatically increased villus height and villus height/crypt depth (V/C) of jejunum at 2 DPI and 8 DPI (p < 0.05). The TNF-α and IFN-γ mRNA expression were downregulated after supplemented with 120 mg/kg Zn–Met in jejunum at 8 DPI (p < 0.05). Moreover, dietary 120 mg/kg Zn–Met supplementation stimulated ZO-3, OCLN mRNA expression at 2 DPI and ZO-2 mRNA expression in jejunum at 8 DPI (p < 0.05), and improved the MUC2 concentration in jejunum at 2 DPI and 8 DPI (p < 0.05). At the same time, the cecal Bifidobacterium and Lactobacillus counts were increased (p < 0.05), and Escherichia coli counts were decreased (p < 0.05) after supplemented with Zn–Met. In conclusion, inclusion of 120 mg/kg Zn–Met minimizes the adverse effects of APEC challenge on meat ducks by improving growth performance and enhancing immune function and intestinal health.

Avian pathogenic Escherichia coli (APEC) is a major bacterial pathogen responsible for the most widespread form of colibacillosis, resulting in substantial economic losses within the poultry sector and posing a potential public health risk. From July to September 2021, our study investigated the antibiotic resistance pattern of Escherichia coli ( E. coli ) and the presence of virulence-associated genes ( iucD , iutA , iss , and ompT ) linked to APEC using 105 broiler meat samples comprising liver, thigh, and breast muscle, in Chitwan, Nepal. E. coli was isolated and identified by culturing samples on MacConkey's agar, Eosin-methylene blue (EMB) agar and performing different biochemical tests. Antibiotic resistance patterns of E. coli were determined by the Kirby-Bauer disc diffusion method. Following the isolation of E. coli , the molecular detection of APEC was performed using conventional polymerase chain reaction (PCR). Out of the 105 samples analyzed, 61 (58.1 %) tested positive for E. coli . In antibiotic susceptibility test (AST), gentamicin and tetracycline exhibited the highest resistance rates, with 90.2 % and 67.2 %, respectively and 29.5 % of the E. coli isolates displayed multidrug-drug resistance. Out of 61 confirmed E. coli isolates, iutA was detected in 47 (77.0 %) samples, iucD in 46 (75.4 %), iss in 53 (86.8 %), and ompT in 39 (63.9 %) samples. This study reports the occurrence of MDR E. coli in meat samples, together with virulence genes associated with APEC which poses a public health threat. Continuous surveillance is vital for monitoring APEC transmission within poultry farms, coupled with efforts to raise awareness of food safety among consumers of broiler meat., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

The Escherichia coli (E. coli) nirC gene encodes a nitrite transporter, which involved in transporting toxic nitrite (NO2−) from the environment into the bacteria. Although the deletion of nirC gene could cause changes in motility, adhesion in the previous study, and the virulence involved in the specified mechanism for pathogenic E. coli remains to be known. In the present work, we aimed to evaluate the role of NirC in a serotype O2:K1:H7 avian pathogenic Escherichia coli (APEC) strain. For this purpose, we generated a NirC-deficient mutant of APEC XM strain and examined its biological characteristics. The nirC gene deletion mutant enhanced ability of motility, decreased in biofilm formation, and it markedly reduced ability to adhere mouse brain microvascular endothelial cell b.End3 cells. For understanding its mechanism, sequentially we detected and found the stress regulator rpoS and its downstream genes csrA were up-regulated in NirC-deficient mutant while diguanylate cyclase gene dgcT was down-regulated. By high-performance liquid chromatography (HPLC) experiment, we demonstrated the concentration of intracellular 3′,5′-cyclic diguanosine monophosphate (c-di-GMP) significantly decrease in nirC gene deletion mutant. Taken data together, we may make a conclusion with a possible signal pathway clue, due to NirC mutation, environmental NO2− accumulation leads to nitrite stress and inactivates c-di-GMP synthesis by stimulating the stress regulator RpoS, resulting in changes of biological characteristics. [ABSTRACT FROM AUTHOR]

Abstract Background Avian pathogenic Escherichia coli (APEC) isolated from avian cellulitis lesions produces a toxin, named Escherichia coli vacuolating factor (ECVF), that causes cell vacuolization and induces inflammatory response in broiler chicken. Methods We investigated the intracellular activities of ECVF in avian fibroblasts using fluorescence staining, electron microscopy, MTT and LDH measurements. As ECVF act specifically in avian cells, we performed blotting assay followed by mass spectrometry to better understand its initial intracellular protein recognition. Results ECVF induced actin contraction, mitochondrial damage and membrane permeability alterations. Ultrastructural analysis showed intracellular alterations, as nuclear lobulation and the presence of degraded structures inside the vacuoles. Moreover, ECVF induced cell death in fibroblasts. ECVF-biotin associates to at least two proteins only in avian cell lysates: alpha-actinin 4 and vinculin, both involved in cytoskeleton structure. Conclusion These findings demonstrated that ECVF plays an important role in avian cellulitis, markedly in initial steps of infection. Taken together, the results place this toxin as a target for drug and/or vaccine development, instead of the use of large amounts antibiotics.

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avians, resulting in considerable losses in the poultry industry. APEC showed zoonotic potential initially related to the fact that APEC serves as the reservoir of virulence genes and antibiotic resistance genes for other E. coli. Thus, we determine the serotypes, phylogenetic groups, virulence genes distribution, and antibiotic resistance profiles of APEC isolates in eastern China. A total of 230 APEC were isolated from diseased chicken and duck with typical colibacillosis symptoms. Serotyping identified that O78 (44.78%) was the predominant serotype. The majority of APEC isolates were classified into B2 (29.57%), A (26.96%), D (20.00%), and B1 (18.26%), respectively. Among the 15 virulence genes, a high prevalence of ibeB (99.57%), fimC (91.74%), mat (91.30%), ompA (83.04%), and iss (80.43%) genes was observed. Except for low resistance rates for imipenem (1.7%) and polymyxin B (0.4%), most of the APEC isolates were resistant to erythromycin (98.7%), enrofloxacin (96.1%), tetracycline (95.2%), doxycycline (93.9%), lincomycin (90.0%), and streptomycin (90.0%). Moreover, all APEC exhibit multi-drug resistance. This study indicated that APEC isolates harbor a variety of virulence genes and showed multi-antibiotic resistance profiles, providing proof for understanding the epidemiological background and zoonotic potential of APEC in poultry farms.

The CTX-M-55 type extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae is increasing in prevalence worldwide without the transmission mechanism being fully clarified, which threatens public and livestock health. Outer membrane vesicles (OMVs) have been shown to mediate the gene horizontal transmission in some species. However, whether blaCTX-M-55 can be transmitted horizontally through OMVs in avian pathogenic Escherichia coli (APEC) has not been reported yet. To test this hypothesis, an ESBL-producing APEC was isolated and whole-genome sequencing (WGS) was performed to analyze the location of blaCTX-M-55. Ultracentrifugation and size exclusion chromatography was used to isolate and purify OMVs, and the transfer experiment of blaCTX-M-55 via OMVs was performed finally. Our results showed that the blaCTX-M-55 was located on an IncI2 plasmid. The number and diameter of OMVs secreted by ESBL-producing APEC treated with different antibiotics were significantly varied. The transfer experiment showed that the OMVs could mediate the horizontal transfer of blaCTX-M-55, and the frequency of gene transfer ranged from 10−5 to 10−6 CFU/mL with the highest frequency observed in the Enrofloxacin treatment group. These findings contribute to a better understanding of the antibiotics in promoting and disseminating resistance in the poultry industry and support the restrictions on the use of antibiotics in the poultry industry.

Abstract Background Avian pathogenic Escherichia coli (APEC) are causative agent of extraintestinal infections, collectively known as colibacillosis, which results significant losses in poultry industries. The extraintestinal survival of E. coli is facilitated by numerous virulence factors which are coded by virulence genes. This study was conducted to find out the pattern of antibiotic resistance and virulence genes content in the APEC strains isolated from broiler chickens at National Avian Disease Investigation Laboratory and Veterinary Teaching Hospital, Rampur, Chitwan, Nepal. Results A total of 50 E. coli strains were isolated from 50 colibacillosis suspected broiler chickens. Out of 50 isolates of E. coli, 47 (94%) showed resistant to three or more antimicrobials. The highest levels (22%) of multidrug-resistant E. coli were observed for five different types of antimicrobials. Antibiogram profiles of 50 E. coli strains showed the maximum resistance to ampicillin (98%), followed by co-trimoxazole (90%), and doxycycline (62%). The highest intermediate resistance was shown by colistin (50%) and the highest sensitivity was against amikacin (84%), followed by nitrofurantoin (55%). Based on the genetic criteria, 45 (90%) E. coli isolates were considered as pathogenic (APEC) which contained more than five virulence genes. Out of total APEC genes detected, we found the combination of iss, iucD, hlyF, ompT, iroN, and iutA genes were mostly associated with the APEC and additionally, to some lesser extent irp2, papC, Cva/cvi, and tsh genes showed the critical role for virulent traits of APEC strains. Conclusion In this study, high prevalent of antimicrobial resistant pattern was found with avian pathogenic E. coli strains isolated from broiler chickens. To our knowledge, this is the first molecular analysis which confirmed the prevalence of APEC strains in poultry sector in Nepal. These finding suggest the need of surveillance and intervention system to control misuse of antibiotics and APEC outbreak in the poultry farm.

This study aimed to optimize the colistin-based antibacterial therapy to prevent antimicrobial resistance related to biofilm formation in avian pathogenic Escherichia coli (APEC) in chicken. Of all the bacterial isolates (n = 136), 69 were identified as APEC by polymerase chain reaction (PCR). Through a series of antibiotic susceptibility tests, susceptibility to colistin (50 concentration (1.00 μg/mL), and regrowth was not inhibited even during multiple exposures. However, upon exposure to 8 μg/mL—a concentration that was close to the MPC—the growth of APEC was inhibited, including in the resistant strains. Additionally, colistin-induced resistant strains showed a slower growth compared with the susceptible ones. Colistin-induced resistant APEC strains did not show colistin resistance gene (mcr-1). However, the expression of higher mgrB and phoQ levels was observed in the resistant strains. Furthermore, these strains showed increased formation of biofilm. Hence, the present study indicated that colistin could induce resistance through the increased formation of biofilm in APEC strains by enhancing the expression of phoQ.

Type VI secretion system (T6SS) is a secretory system found in Gram‐negative bacteria. One of the main structures for T6SS is Hcp (hemolysin co‐regulation protein) pipeline. To investigate the role of Hcp major sub‐unit genes hcp1 and hcp2, we deleted hcp1 and hcp2 genes for constructing the in‐frame gene deletion mutants. The properties of biofilm formation and the adhesion to chicken embryo fibroblasts cells (DF1 cells) were reduced in the hcp2 mutant. The knockout of hcp1 and hcp2 genes reduced the ability of the avian pathogenic Escherichia coli (APEC) strain CE129 to infect developing chicken embryos. The expression of quorum sensing (QS)‐associated genes luxS, lsrR, and pfs were down‐regulated in the hcp1 mutant, and the expression of type 1 fimbriae gene fimA and the adhesion‐related genes fimC and papC were decreased in the hcp2 mutant, as well as the expression of anti‐serum survival factor genes ompA and iss were inhibited in both hcp1 and hcp2 mutants. These results described above from this study help to further elaborate the role of HCP in APEC. [ABSTRACT FROM AUTHOR]

Background: Avian pathogenic Escherichia coli (APEC) are causative agent of extraintestinal infections, collectively known as colibacillosis, which results significant losses in poultry industries. The extraintestinal survival of E. coli is facilitated by numerous virulence factors which are coded by virulence genes. This study was conducted to find out the pattern of antibiotic resistance and virulence genes content in the APEC strains isolated from broiler chickens at National Avian Disease Investigation Laboratory and Veterinary Teaching Hospital, Rampur, Chitwan, Nepal. Results: A total of 50 E. coli strains were isolated from 50 colibacillosis suspected broiler chickens. Out of 50 isolates of E. coli, 47 (94%) showed resistant to three or more antimicrobials. The highest levels (22%) of multidrug-resistant E. coli were observed for five different types of antimicrobials. Antibiogram profiles of 50 E. coli strains showed the maximum resistance to ampicillin (98%), followed by co-trimoxazole (90%), and doxycycline (62%). The highest intermediate resistance was shown by colistin (50%) and the highest sensitivity was against amikacin (84%), followed by nitrofurantoin (55%). Based on the genetic criteria, 45 (90%) E. coli isolates were considered as pathogenic (APEC) which contained more than five virulence genes. Out of total APEC genes detected, we found the combination of iss, iucD, hlyF, ompT, iroN, and iutA genes were mostly associated with the APEC and additionally, to some lesser extent irp2, papC, Cva/cvi, and tsh genes showed the critical role for virulent traits of APEC strains. Conclusion: In this study, high prevalent of antimicrobial resistant pattern was found with avian pathogenic E. coli strains isolated from broiler chickens. To our knowledge, this is the first molecular analysis which confirmed the prevalence of APEC strains in poultry sector in Nepal. These finding suggest the need of surveillance and intervention system to control misuse of antibiotics and APEC outbreak in the poultry farm. [ABSTRACT FROM AUTHOR]

An experimental group of one-day-old chicken from a commercial hatchery was given a defined mixture of 7 gut anaerobes. The next day the chicks were inoculated by an APEC strain O78:H4-ST117 resistant to ciprofloxacin, alongside with the control group and monitored for 4 wk after the inoculation for the presence of the colonizing strains and ciprofloxacin-resistant E. coli. Significant reduction of colonization rates in the first 2 wk was recorded in the experimental group for the numbers of ciprofloxacin-resistant E. coli. The results show that colonization of chicken by defined anaerobic mixtures may provide a decisive protection during the critical period of the chicken intestinal microflora development. [ABSTRACT FROM AUTHOR]

Fosfomycin, a broad-spectrum antibiotic against both Gram-positive and Gram-negative bacteria, is very important in the clinic but many fosfomycin-resistant bacteria have been isolated from patients. In this study, the resistance mechanism of three fosfomycin-resistant avian pathogenic Escherichia coli (APEC) strains (JE1, IF7 and CD11) isolated from septicemic chickens were analyzed. The results showed that their fosfomycin-resistance mechanisms were different. An alteration in the glpT transport system was the main reason of the fosfomycin-resistance mechanisms of strain IF7. Compared with the control stain BL21, the capacity of fosfomycin-uptake was low in all these three stains (JE1>IF7>CD11). Sequence results of murA showed that there were more than 10 sites of nucleotide mutation, but only one amino acid mutation T116A showed in CD11. Real-time detection test showed that the expression level of the murA gene of the three stains was significantly increased (four times increase in strain CD11 and two times increase in strains JE1 and IF7). The transformation and recombinant test showed that the recombinant bacteria with the murA of JE1 and CD11 showed high minimal inhibitory concentration (MIC) against fosfomycin. From the results of this research, it showed that most of the fosfomycin-resistance mechanisms once showed in patient bacteria have appeared in the APEC strains and the fosfomycin-resistance mechanism of the three APEC isolates was different.

Poultry colibacillosis due to Avian Pathogenic Escherichia coli (APEC) is responsible for several extra-intestinal pathological conditions, leading to serious economic damage in poultry production. The most commonly associated pathologies are airsacculitis, colisepticemia, and cellulitis in broiler chickens, and salpingitis and peritonitis in broiler breeders. In this work a total of 66 strains isolated from dead broiler breeders affected with colibacillosis and 61 strains from healthy broilers were studied. Strains from broiler breeders were typified with serogroups O2, O18, and O78, which are mainly associated with disease. The serogroup O78 was the most prevalent (58%). All the strains were checked for the presence of 11 virulence genes: 1) arginine succinyltransferase A (astA); ii) E.coli hemeutilization protein A (chuA); iii) colicin V A/B (cvaA/B); iv) fimbriae mannosebinding type 1 (fimC); v) ferric yersiniabactin uptake A (fyuA); vi) iron-repressible high-molecular-weight proteins 2 (irp2); vii) increased serum survival (iss); viii) iron-uptake systems of E.coli D (iucD); ix) pielonefritis associated to pili C (papC); x) temperature sensitive haemaglutinin (tsh), and xi) vacuolating autotransporter toxin (vat), by Multiplex-PCR. The results showed that all genes are present in both commensal and pathogenic E. coli strains. The iron uptake-related genes and the serum survival gene were more prevalent among APEC. The adhesin genes, except tsh, and the toxin genes, except astA, were also more prevalent among APEC isolates. Except for astA and tsh, APEC strains harbored the majority of the virulenceassociated genes studied and fimC was the most prevalent gene, detected in 96.97 and 88.52% of APEC and AFEC strains, respectively. Possession of more than one iron transport system seems to play an important role on APEC survival. [ABSTRACT FROM AUTHOR]

The article discusses a study which analyzed in silico phylogenetic and virulence gene profile of avian pathogenic Escherichia coli (APEC) genome sequences. Topics highlighted include the zoonotic risk attributed to APEC trains, phylogenetic maximum likelihood tree, multi-locus sequence typing (MLST) and allele sequences of housekeeping genes. Also mentioned are Pathogenic islands (PAIs) and Gene Cluster 3.0 software.

A collection of 46 avian pathogenic Escherichia coli (APEC) isolates was examined for the presence of mutators by determining the rate of mutation to rifampicin resistance. The collection included 34 E. coli isolates obtained in pure culture from chronic lesions of salpingitis and peritonitis in 34 broiler breeders, of which 12 were associated with the development of secondary septicemia. Twelve additional isolates were obtained from a clonal outbreak (ST95) of E. coli peritonitis syndrome (EPS), the lesions of which changed gradually over time into a subacute/chronic form. The hypothesis of the present study was that mutation rates would be higher for chronic infection isolates than for isolates from acute infections/exacerbations. The distribution of mutation rates followed a pattern similar to that found for other clinical isolates of E. coli, with a modal/median value of 1.47×10−8. Of the 46 isolates, 24% (n =11) were weakly hypermutable (2.00×10−8 ≤ μ <2.00×10−7), however, no strong mutators were detected (μ ≥2.00×10−7). Chronic salpingitis isolates had the highest proportion (45%, P =0.001) of weak mutators and also, significantly higher mutation rates (P =0.003) compared to isolates that caused septicemia (4%). In addition, mutation rates were significantly lower among ST95 isolates (P <0.0005), and among isolates from the same clonal group as ST95 (P =0.027), when compared to isolates from other groups. Although a clear association with the time phase of infection (as lesions of EPS became more chronic) could not be observed (ρ =0.523, P =0.081), a higher frequency of weak mutators among chronic infection isolates suggests that increased mutation rates play a role in adaptation of APEC to long-term persistence in an infected host environment. [ABSTRACT FROM AUTHOR]

Avian pathogenic Escherichia coli (APEC) can cause the acute and sudden death of poultry, which leads to serious economic losses in the poultry industry. Biofilm formation contributes to the persistence of bacterial infection, drug resistance, and resistance to diverse environmental stress. Many transcription regulators in APEC play an essential role in the formation of biofilm and could provide further insights into APEC pathogenesis. YjjQ has an important role in the pathogenicity of bacteria by regulating the expression of virulence factors, such as flagellar and iron uptake. However, YjjQ regulates other virulence factors, and their role in the overall regulatory network is unclear. Here, we further evaluate the function of YjjQ on APEC biofilm formation and motility. In this study, we successfully constructed mutant (AE27∆yjjQ) and complement (AE27ΔyjjQ-comp) strains of the wild-type strain AE27. Inactivation of the yjjQ gene significantly increased biofilm-forming ability in APEC. Scanning electron microscopy showed that the biofilm formation of the AE27 was single-layered and flat, whereas that of the AE27∆yjjQ had a porous three-dimensional structure. Moreover, the deletion of the yjjQ gene inhibited the motility of APEC. RNA-sequencing was used to further investigate the regulatory mechanism of YjjQ in APEC. The results indicate that YjjQ regulates biofilm formation and flagellar genes in AE27∆yjjQ. RT-qPCR shows that YjjQ affects the transcriptional levels of genes, including flagella genes (flhD, flhC and flgE), and biofilm formation genes (pstA, uhpC, nikD, and ygcS). These results confirm that the transcription regulator YjjQ is involved in APEC biofilm formation and motility, and provide new evidence for the prevention and control of APEC., Competing Interests: Declaration of Competing Interest The authors have no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

• Sampling of three birds from a flock to identify the major disease-causing APEC. • Liver is a well suited organ for identifying APEC from systemic infection in broiler. • Little sequence diversity between APEC from different organs within a bird. Avian pathogenic E. coli (APEC) cause high first week mortality (FWM) in broiler chickens worldwide. In order to investigate the epidemiologic aspects of colibacillosis in broiler flocks it is important to develop reliable and cost-effective sampling guidelines. In this context, it is particularly important to define the minimum number of samples required to reliably identify the causative APEC clone during outbreaks of colibacillosis. This study describes the diversity of E. coli isolates between and within three flocks with high FWM due to colibacillosis. Each flock was represented by five animals, showing typical lesions of colibacillosis, and spleen, liver and one other organ from each animal was sampled for APEC. A total of 47 E. coli isolates, one per organ, and approximately 15 isolates per flock were whole genome sequenced and compared by multilocus sequence typing (MLST), serotyping and phylogenetic analysis to deduce their relationship. The results revealed that within individual birds there was little or no sequence type (ST) or serotype diversity between APEC isolates from different organs. Based on phylogenetic analysis, isolates belonging to the same ST and serotype showed a low number of single nucleotide polymorphisms (SNPs) across more than 95 % of the genome. Isolates from the liver always represented the major disease-causing APEC in individual birds, even when more than one ST was detected within an individual bird and flock. This study guides us towards an economically efficient way of sampling for future epidemiological studies on colibacillosis, by determining the causative APEC-clone at flock level. [ABSTRACT FROM AUTHOR]

Highlights: [•] Immunoproteomics was applied to identify immunogenic proteins of APEC for the first time. [•] Two predominant immunogenic components, OmpA and Flic, were identified. [•] GroEL and other 8 proteins are reported as immunoreactive proteins in APEC for the first time. [•] GroEL stimulated antibody responses and supported protective efficacy against infections of heterogeneous APEC strains. [ABSTRACT FROM AUTHOR]

The article presents a case study of 43 one-day-old red-legged partridge chicks that died. It states that avian pathogenic Escherichia coli (APEC) strains were detected and isolated from cloacal swabs and tissues origination from these birds. The study highlights that APEC strains are linked to colibacillosis in partridges and confirmed that patridges are fecal carriers and potential spreaders of APEC.

The article assesses the prevalence of Escherichia coli, Salmonella spp., and Mycobacterium avium subsp. paratuberculosis isolated from the feces of wild European starlings humanely trapped at a feedlot in central Kansas. The National Antimicrobial Resistance Monitoring System panels were used to test all E. coli and Salmonella isolates recovered for antimicrobial susceptibility. The E. coli isolates were classified as to their content of genes associated with pathogenic E. coli of birds and cattle. Resistance to antimicrobial agents was shown by about half of the E. coli isolates, while resistance to tetracycline was shown by 96 percent of the isolates. The criteria established for identification as avian pathogenic E. coli O157 were met by five percent of the E. coli isolates.

• O145 may be emerging as a predominant serogroup of APEC in China. • The reasons for the prevalence and neglect of APEC O145 from the genetic perspective. • Pangenome were performed to assess the potential threats of APEC O145 to humans. • Our attention should away from the serogroups of O1, O2, and O78 among APEC. Among the numerous serotypes of Avian pathogenic Escherichia coli (APEC), O1, O2 and O78 have long been considered the predominant serogroups. O145, a pivotal serogroup in non-O157 Shiga toxin-producing Escherichia coli , has never been considered an important serogroup among APEC. The prevalence of APEC O145 was determined from the results of molecular serogrouping based on 42 sequenced isolates from Jiangsu and Guangxi Provinces in China. After realizing the potential importance of O145, 224 APEC isolates isolated from Jiangsu, Guangxi, Anhui, Shandong, Henan, Yunnan and Fujian provinces were screened using PCR amplification. The results showed that the proportion of O145 detected was 37.9 % (85/224), which was higher than those of the three traditional APEC serogroups. The virulence evaluation experiment showed that this serogroup may have stronger pathogenicity. Here, we report for the first time that O145 may be emerging as a predominant serogroup of APEC in China. The possible reasons for its prevalence and oversight were analyzed through genomic analysis. Furthermore, pangenome analysis with STEC O145 was performed to assess the potential threat to humans. The discovery of the ubiquity of O145 may not be coincidental, which may also account for the failure of vaccines that target the three major serogroups. Therefore, this newly predominant serogroup should be paid more attention and the focus should not be limited to the so-called three major APEC serogroups. [ABSTRACT FROM AUTHOR]

Recent studies by DNA–DNA hybridisation assays conducted on a large collection of Escherichia coli strains isolated from chickens, ducks and turkeys suffering from colibacillosis, showed that 76% of the strains were negative for the presence of the pap gene cluster. The objective of this paper was to study the virulence associated with the avian E. coli strains negative for the P fimbriae, but carrying the f17 or the afa-8 gene cluster coding for adhesins associated with strains pathogenic for mammals. Three strains carrying the f17 fimbriae and three carrying the afa-8 adhesin-encoding gene cluster were studied in three in vivo experimental models of avian colibacillosis: subcutaneous inoculation of 1-day-old chicks, inoculation of specific-pathogen-free (SPF) chickens via the intra-thoracic air sac, and intra-tracheal inoculation of axenic chickens. The results showed that the six P-negative E. coli isolates carrying the f17 or the afa-8 gene cluster were lethal for 1-day-old chicks. They were also able to reproduce clinical signs and lesions of colibacillosis (aerosacculitis, pericarditis, perihepathitis), with bacteraemia and septicaemia, in SPF chickens inoculated via the thoracic air sacs as well as in axenic chickens inoculated by the intra-tracheal route. Further studies with f17 and afa-8 allelic mutants constructed by disruption must be performed to confirm a role of F17 fimbrial and Afa-VIII afimbrial adhesins in the pathogenesis of avian colibacillosis. [Copyright &y& Elsevier]

This study aimed to optimize the colistin-based antibacterial therapy to prevent antimicrobial resistance related to biofilm formation in avian pathogenic Escherichia coli (APEC) in chicken. Of all the bacterial isolates (n = 136), 69 were identified as APEC by polymerase chain reaction (PCR). Through a series of antibiotic susceptibility tests, susceptibility to colistin (<2 μg/mL) was confirmed in all isolates. Hence, a mutant selection window (MSW) was determined to obtain colistin-induced resistant bacteria. The minimum inhibitory concentration (MIC) of colistin against the colistin-induced resistant APEC strains ranged from 8 to 16 μg/mL. To identify the inhibitory activity of colistin against the resistant strains, the mutant prevention concentration (MPC) was investigated for 72 h, and the single and multi-dose colistin activities were determined through the time-kill curve against APEC strains. Bacterial regrowth occurred after 12 h at a double MIC50 concentration (1.00 μg/mL), and regrowth was not inhibited even during multiple exposures. However, upon exposure to 8 μg/mL—a concentration that was close to the MPC—the growth of APEC was inhibited, including in the resistant strains. Additionally, colistin-induced resistant strains showed a slower growth compared with the susceptible ones. Colistin-induced resistant APEC strains did not show colistin resistance gene (mcr-1). However, the expression of higher mgrB and phoQ levels was observed in the resistant strains. Furthermore, these strains showed increased formation of biofilm. Hence, the present study indicated that colistin could induce resistance through the increased formation of biofilm in APEC strains by enhancing the expression of phoQ. [ABSTRACT FROM AUTHOR]

Background: Avian pathogenic Escherichia coli (APEC) isolated from avian cellulitis lesions produces a toxin, named Escherichia coli vacuolating factor (ECVF), that causes cell vacuolization and induces inflammatory response in broiler chicken., Methods: We investigated the intracellular activities of ECVF in avian fibroblasts using fluorescence staining, electron microscopy, MTT and LDH measurements. As ECVF act specifically in avian cells, we performed blotting assay followed by mass spectrometry to better understand its initial intracellular protein recognition., Results: ECVF induced actin contraction, mitochondrial damage and membrane permeability alterations. Ultrastructural analysis showed intracellular alterations, as nuclear lobulation and the presence of degraded structures inside the vacuoles. Moreover, ECVF induced cell death in fibroblasts. ECVF-biotin associates to at least two proteins only in avian cell lysates: alpha-actinin 4 and vinculin, both involved in cytoskeleton structure., Conclusion: These findings demonstrated that ECVF plays an important role in avian cellulitis, markedly in initial steps of infection. Taken together, the results place this toxin as a target for drug and/or vaccine development, instead of the use of large amounts antibiotics., Competing Interests: Competing interests: The authors declare that they have no competing interests.

Type VI secretion system (T6SS) is a secretory system found in Gram-negative bacteria. One of the main structures for T6SS is Hcp (hemolysin co-regulation protein) pipeline. To investigate the role of Hcp major sub-unit genes hcp 1 and hcp 2 , we deleted hcp 1 and hcp 2 genes for constructing the in-frame gene deletion mutants. The properties of biofilm formation and the adhesion to chicken embryo fibroblasts cells (DF1 cells) were reduced in the hcp 2 mutant. The knockout of hcp 1 and hcp 2 genes reduced the ability of the avian pathogenic Escherichia coli (APEC) strain CE129 to infect developing chicken embryos. The expression of quorum sensing (QS)-associated genes luxS, lsrR, and pfs were down-regulated in the hcp 1 mutant, and the expression of type 1 fimbriae gene fimA and the adhesion-related genes fimC and papC were decreased in the hcp 2 mutant, as well as the expression of anti-serum survival factor genes ompA and iss were inhibited in both hcp 1 and hcp 2 mutants. These results described above from this study help to further elaborate the role of HCP in APEC., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Avian colibacillosis is one of the most common infectious diseases caused partially or entirely by avian pathogenic Escherichia coli (APEC) in birds. In addition to spontaneous infection, APEC can also cause secondary infections that result in greater severity of illness and greater losses to the poultry industry. In order to assess the role of 2', 3'-cyclic phosphodiesterase (cpdB) in APEC on disease physiology and pathogenicity, an avian pathogenic Escherichia coli-34 (APEC-34) cpdB mutant was obtained using the Red system. The cpdB mutant grew at a slower rate than the natural strain APEC-34. Scanning electron microscopy (SEM) indicated that the bacteria of the cpdB mutant were significantly longer than the bacteria observed in the natural strain (P<0.01), and that the width of the cpdB mutant was significantly smaller than its natural counterpart (P<0.01). In order to evaluate the role of cpdB in APEC in the colonization of internal organs (lung, liver and spleen) in poultry, seven-day-old SPF chicks were infected with 10 9 CFU/chick of the cpdB mutant or the natural strain. No colonizations of cpdB mutants were observed in the internal organs 10days following the infection, though numerous natural strains were observed at 20days following infection. Additionally, the relative expression of division protein ftsZ, outer membrane protein A ompA, ferric uptake regulator fur and tryptophanase tnaA genes in the mutant strain were all significantly lower than in the natural strain (P<0.05 or P<0.01). These results suggested that cpdB is involved in the long-term colonization of APEC in the internal organs of the test subjects. The deletion of the cpdB gene also significantly affected the APEC growth and morphology., (Copyright © 2016. Published by Elsevier Ltd.)