Search

Escherichia coli O157 belongs to a diverse serogroup including different H serotypes. E. coli O157: H7 is the most common serotype that can cause acute gastroenteritis, hemorrhagic colitis (HC), and hemolytic-uremic syndrome (HUS) in humans. In recent years, some E. coli O157:non-H7 strains have been reported to cause sporadic cases and outbreaks of diarrheal diseases. However, the phenotypic and genotypic characteristics of E. coli O157:non-H7 are poorly understood. In this study, E. coli O157:non-H7 strains were isolated from retail food sold on markets in 13 cities in China during 2012-2016 and characterized systematically in terms of their H serotypes, virulence genes, antibiotic resistance, and genotypes. Six H serotypes (H26, H42, H11, H38, H4, and H5) were identified, of which, O157:H42 (31.4 %) and O157:H26 (28.6 %) were the most prevalent. Most of the isolates (82.9 %) carried virulence genes. Ten isolates (28.6 %) carried the eae gene and were identified as atypical enteropathogenic E. coli. Multilocus sequence typing showed that the E. coli O157:non-H7 strains demonstrated diverse sequence types with different evolutionary trends than E. coli O157:H7. All the isolates exhibited multidrug resistance. The isolates showed a high prevalence of resistance to AMC, AMP, CTX, CIP, T/S, TE, and FFC. The predominant antibiotic-resistance genes were TEM-1 (40.0 %), CTX-M-55 (34.3 %), aadA (74.3 %), sul2 (62.9 %), floR (91.4 %), tetA (85.7 %), qnrS (37.1 %), oqxA (62.9 %), and oqxB (62.9 %). For the first time, we identified IncI2 plasmid-mediated colistin-resistant strains (six O157:H26 and one O157:H4). These strains co-harbored plasmid-mediated mcr-1 gene, CTX-M-55, OXA-4, PMQR, and other resistant genes, which is of great concern. Colistin and cefotaxime are generally used as the last defense to treat complicated infections. The emergence of virulent and multidrug resistant strains in food poses a serious threat to human health. The strict monitoring and surveillance of multiple-drug resistant strains in food are needed to prevent their dissemination to humans.

Food-derived Staphylococcaceae species with severe antimicrobial resistance, especially Staphylococcus aureus, is a major threat to public health. Macrococcus caseolyticus (M. caseolyticus) is a member of the Staphylococcaceae family which plays a vital role in fermented products and disease causation in animals. In our previous study, several Staphylococcus aureus antibiotic-resistant island msr (SaRI

Staphylococcus aureus encodes numerous toxins that are known or strongly suspected to cause specific diseases or symptoms. Panton-Valentine leukocidin (PVL) is one of these important toxins that is associated with high mortality rates. In our previous study, 1581 S. aureus strains were isolated from 4300 samples of retail foods obtained from most of the provincial capitals in China from 2011 to 2016. This study aimed to investigate the prevalence of PVL-positive S. aureus isolates from retail foods in China and characterize these isolates by antibiotic resistance testing, spa typing, multilocus sequence typing (MLST) and enterotoxin gene analyses. In total, seventy-two isolates (72/1581, 4.6%) possessed pvl genes, including 24.1% MRSA isolates (26/108) and 3.1% MSSA isolates (46/1473), covering different types of food. The strains were divided into seventeen sequence types (STs) and twenty-seven spa types, and 43.1% (31/72) of the PVL-positive S. aureus isolates belonged to CC59-t437. These isolates contained at least one of the following enterotoxin genes: sei (97.2%), sem (86.1%), seq (80.6%), seg (68.1%), sek (68.1%), seb (62.5%), sel (52.8%), sej (50.0%), seh (48.6%), sep (45.8%), sea (38.9%), ser (37.5%), sen (27.8%), sec (16.7%), see (16.7%), sed (6.9%), seo (6.9%) and seu (6.7%). A total of 87.5% of the S. aureus isolates (63/72) harboured the classic SE genes (sea, seb, sec, sed, and see), whereas all the S. aureus isolates harboured the genes of the egc cluster (seg, sei, sem, sen, seo, and seu). In antimicrobial susceptibility tests, 98.6% of the isolates (71/72) exhibited resistance to at least one antibiotic, including 47 multi-drug-resistant isolates. Resistance to penicillin (94.4%), erythromycin (83.4%), clindamycin (63.9%), kanamycin (61.1%), telithromycin (58.3%), streptomycin (51.4%), tetracycline (47.2%), chloramphenicol (27.8%), fusidic acid (27.8%) and other antibiotics (

Antibiotic-resistant bacteria in food pose an important threat to public health. Multidrug-resistant strains in ready-to-eat (RTE) foods can be transferred to humans through diet, which increases their health risk. This study systematically investigated antibiotic resistance and antibiotic resistance genes in E. coli isolated from retail RTE foods and characterized plasmid-mediated colistin-resistant E. coli strains. A total of 1118 RTE food samples were collected from markets in 39 cities in China, and 126 E. coli strains, >95% of which were multidrug-resistant, were isolated. The isolates showed a high prevalence of resistance to tetracycline (95.24%), ampicillin (82.54%), trimethoprim-sulfamethoxazole (77.78%), nalidixic acid (74.60%), cephalothin (72.22%), chloramphenicol (66.67%), and streptomycin (53.97%). Twenty-two extended-spectrum β-lactamase (ESBL)-producing E. coli and four colistin-resistant E. coli were identified. The resistance genes TEM, CTX-M, tetA, sul2, strA/strB, aadA, and qnrS were the most frequently detected. CTX-M-55 and CTX-M-14 were the predominant CTX-M types. All the four colistin-resistant E. coli isolates were positive for mcr-1. The mcr-1 gene can be transferred to E. coli C600 through conjugation and transformation. Whole-genome sequencing revealed that the mcr-1 genes were found in IncX4 and IncHI2 plasmids. To the best of our knowledge, this is the first report of IncHI2/IncX4 plasmid-bearing mcr-1-positive E. coli strains in RTE foods sold in markets, and the first report of the isolation of the international epidemic E. coli clone ST101 and mcr-1-carrying ESBL-producing E. coli from RTE foods. These results provide valuable information for assessing antibiotic-resistant E. coli infections and controlling antibiotic-resistant E. coli.

The abundant information provided by the pan-genome analysis approach reveals the diversity among Listeria monocytogenes serotypes. The objective of this study was to mine novel target genes using pan-genome analysis for multiplex PCR detection and differentiation of the major L. monocytogenes serotypes present in food. Pan-genome analysis and PCR validation revealed a total of 10 specific targets: one for lineage I, two for serogroup I.1, one for serogroup I.2, two for lineage II, one for serogroup II.1, three for lineage III. Primers for the novel targets were highly specific in individual reactions. The detection limits were 103–104 colony-forming units (CFU)/mL in pure bacterial cultures, meeting the requirements of molecular detection. Based on these novel targets, two new “lineage” multiplex PCR assays were developed to simultaneously distinguish between three lineages (I, II, and III) and five major serotypes (1/2a, 1/2b, 1/2c, 4b, and 4c) of L. monocytogenes. The detection limits of lineage I and lineage II&III mPCRs were 0.771 pg/μL and 1.76 pg/μL genomic DNA, respectively. The specificity of the mPCRs was robustly verified using other L. monocytogenes and non-L. monocytogenes serotypes. These results suggest that the two “lineage” multiplex PCRs based on novel targets offer a promising approach for accurate, sensitive, and rapid identification of L. monocytogenes serotypes.

Staphylococcus aureus is an important food-related pathogen associated with bacterial poisoning that is difficult to treat due to its multidrug resistance. The cfr and lsa(E) genes both cause multiple drug resistance and have been identified in numerous Staphylococcus species, respectively. In this study, we found that a methicillin-resistant S. aureus (MRSA) strain, 2868B2, which was isolated from a sample of frozen dumplings in Hangzhou in 2015, co-carried these two different multidrug resistance genes. Further analysis showed that this strain was resistant to more than 18 antibiotics and expressed high-level resistance to florfenicol, chloramphenicol, clindamycin, tiamulin, erythromycin, ampicillin, cefepime, ceftazidime, kanamycin, streptomycin, tetracycline, trimethoprim-sulfamethoxazole and linezolid (MIC = 8 μg/mL). Whole genome sequencing was performed to characterize the genetic environment of these resistance genes and other genomic features. The cfr gene was located on the single plasmid p2868B2 (39,159 bp), which demonstrated considerable similarity to many plasmids previously identified in humans and animals. p2868B2 contained the insertion sequence (IS) element IS21-558, which allowed the insertion of cfr into Tn558 and played an important role in the mobility of cfr. Additionally, a novel multidrug resistance region (36.9 kb) harbouring lsa(E) along with nine additional antibiotic resistance genes (ARGs) (aadD, aadE, aacA-aphD, spc, lnu(B), lsa(E), tetL, ermC and blaZ) was identified. The multidrug resistance region harboured four copies of IS257 that were active and can mediate the formation of four circular structures containing ARGs and ISs. In addition, genes encoding various virulence factors and affecting multiple cell adhesion properties were identified in the genome of MRSA 2868B2. This study confirmed that the cfr and lsa(E) genes coexist in one MRSA strain and the presence of plasmid and IS257 in the multi-ARG cluster can promote both ARG transfer and dissemination. Furthermore, the presence of so many ARGs and virulence genes in food-related pathogens may seriously compromise the effectiveness of clinical therapy and threaten public health, its occurrence should pay public attention and the traceability of these genes in food-related samples needs further surveillance.

Cronobacter spp. are important foodborne pathogens that infections occur in all age groups, especially cause serious life-threatening diseases in infants. This study aimed to acquire data on Cronobacter spp. contamination of meat and meat products (n = 588) in China during 2011 to 2016, and investigated the use of CRISPR typing technology as an approach for characterizing the genetics of Cronobacter spp. The overall contamination rate for Cronobacter spp. was determined to be 9.18% (54/588). Of the positive samples, 90.74% (49/54) had

Vibrio parahaemolyticus is the leading cause of foodborne bacterial poisoning in China. The aim of this research is to conduct a study on the prevalence, virulence, and antimicrobial resistance of V. parahaemolyticus from different types of food samples in 12 different cities of China. Since fluoroquinolones are the major choice of treatment for V. parahaemolyticus infections, the genetic basis for fluoroquinolone resistance in V. parahaemolyticus were also investigated. V. parahaemolyticus was detected in 163 of the 784 food samples collected from 12 different cities in China, resulting in a prevalence of 20.79%. The prevalence of V. parahaemolyticus in ready-to-eat (RTE) food (4.96%) was much lower than those of shrimp (32.62%) and fish (22.00%). Virulence gene screening showed that 44 (27.00%) V. parahaemolyticus strains carried at least one virulence gene. Four isolates from shrimp and three isolates from fish contained both the virulence genes tdh and trh. In addition, the trh was firstly detected in one isolate collected from RTE food. All isolates exhibited relatively high resistance rates to ampicillin (82.21%), gentamicin (19.63%), and tetracycline (14.11%), while

The aim of this study is to investigate the prevalence of integrons and integron-associated antibiotic resistance in V. parahaemolyticus strains collected from RTE foods in China, and to carry out a comprehensive analysis on the molecular characterization of V. parahaemolyticus strains carrying bla

The plasmid-mediated colistin resistance gene mcr-1 has been identified in various Enterobacteriaceae species, which poses a great challenge to the public health. The present study aimed to investigate the prevalence of mcr-1 in Vibrio parahaemolyticus isolated from food samples in China, and to conduct a comprehensive analysis on the molecular characterization of V. parahaemolyticus isolate carrying mcr-1-harboring plasmid. A total of 646 V. parahaemolyticus strains isolated from 2531 food samples collected in retail markets in 34 different cities in China were screened for colistin resistance. Of the 646 V. parahaemolyticus isolates tested, 25 (2.5%) exhibited colistin resistance. The mcr-1 gene was detected in one colistin-resistant V. parahaemolyticus isolate, VP181, obtained from a shrimp sample collected in Hong Kong. The mcr-1 gene was located on a transferable IncX4 plasmid with size of ~40 kb. A Class A β-lactamase gene, blaCARB-17 and the plasmid-mediated quinolone resistance (PMQR) gene qnrVC5 were detected in the mcr-1-positive V. parahaemolyticus isolate VP181. Virulence gene assays indicated that tdh was detected in VP181 by PCR. This is the first report of the occurrence of plasmid-encoded mcr-1 in virulent V. parahaemolyticus strain. Our findings indicate horizontal transfer of this gene to non-Enterobacteriaceae gram-negative bacteria, which warrants further investigation because of the public health threat it poses.

Cronobacter species (Cronobacter spp.) are important foodborne pathogens that can infect and cause serious life-threatening diseases in infants and immunocompromised elderly. This study aimed to acquire data on Cronobacter spp. contamination of aquatic products in China from 2011 to 2016. In total, 800 aquatic products were tested, and the overall contamination rate for Cronobacter spp. was 3.9% (31/800). The average contamination level of the positive samples was 2.05 MPN/g. Four species and nine serotypes were identified among 33 isolates, of which the C. sakazakii serogroup O1 (n = 9) was the primary serotype. The majority of Cronobacter spp. strains harbored highest resistance against cephalothin (84.8%), followed by tetracycline (6.1%), trimethoprim/sulfameth-oxazole (3.0%) and chloramphenicol (3.0%). Two isolates were resistant to three antibiotics. In total, 26 sequence types and 33 CRISPR types (including 6 new STs and 26 new CTs) were identified, which indicates the extremely high diversity of Cronobacter spp. in aquatic products. Pathogenic C. sakazakii ST4, ST1, and C. malonaticus ST7 were also observed. Overall, this large-scale study revealed the relatively low prevalence and high genetic diversity of Cronobacter spp. in aquatic products in China, and the findings provide valuable information that can guide the establishment of effective measures for the control and precaution of Cronobacter spp. in aquatic products during production processes.

The aim of this study is to investigate the prevalence of integrons and integron-associated antibiotic resistance in V. parahaemolyticus strains collected from RTE foods in China, and to carry out a comprehensive analysis on the molecular characterization of V. parahaemolyticus strains carrying blaVEB-1-positive class 1 integron. Of the 51 V. parahaemolyticus strains isolated from RTE food samples, none of the isolates was found to carry integrase genes intI2 and IntI3. However, all 51 strains were positive to integrase gene intI1, and only 2 of 51 (3.92%) intI1-positive isolates yielded polymerase chain reaction (PCR) products of gene cassette amplification. Sequence data and BLAST analysis indicated the gene cassette arrays of class 1 integron in VP007 is dfrA14-blaVEB-1-aadB, while the gene cassette arrays of class 1 integron in V187 is blaVEB-1-aadB-arr2-cmlA-blaOXA-10-aadA1. Antimicrobial susceptibility testing showed that the two V. parahaemolyticus isolates harboring class 1 integrons exhibited multi-drug resistance to various antibiotics. S1-PFGE and Southern blot analysis confirmed the class 1 integron harboring blaVEB-1 gene in V187 was located on the plasmid of ~175 kb and transferrable to the recipient strain by conjugation. This is the first detection of class 1 integrons harboring the ESBL gene blaVEB-1 in V. parahaemolyticus. To the best of our knowledge, this is also the first report of VEB-producing V. parahaemolyticus from RTE foods. Our findings revealed that class 1 integron on conjugative plasmid contributes significantly to the dissemination of VEB-producing V. parahaemolyticus, which warrants further investigation because of the public health threat it poses.