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Aims Hypervirulent Klebsiella pneumoniae (hvKp) causes invasive community-acquired infections in healthy individuals, and hypermucoviscosity (HMV) is the main phenotype associated with hvKp. This study investigates the impact of microaerobic environment availability on the mucoviscosity of K. pneumoniae. Methods and results By culturing 25 clinical strains under microaerobic and aerobic environments, we observed a notable reduction in mucoviscosity in microaerobic environments. RNA sequencing and qRT-PCR revealed downregulated expressions of capsule synthesis genes (galf, orf2, wzi, wza, wzb, wzc, wcaj, manC, manB , and ugd) and regulatory genes (rmpA, rmpD , and rmpC) under microaerobic conditions. Transmission electron microscopy and Indian ink staining analysis were performed, revealing that the capsular thickness of K. pneumoniae decreased by half in microaerobic conditions compared to aerobic conditions. Deletion of rmpD and rmpC caused the loss of the HMV phenotype in both aerobic and microaerobic conditions. However, compared to wild-type strain in microaerobic condition, only rmpD overexpression strain, and not rmpC overexpression strain, displayed a significant increase in capsule thickness in microaerobic conditions. Conclusions Microaerobic conditions can suppress the mucoviscosity of K. pneumoniae , but this suppression can be overcome by altering the expression of rmpD , indicating a specific function for rmpD in the oxygen environmental adaptation of K. pneumoniae. [ABSTRACT FROM AUTHOR]

This study aimed to screen antibiotic resistance and virulence genes in carbapenem‐resistant hypermucoviscous Klebsiella pneumoniae isolates from an Egyptian hospital. Among 38 previously confirmed carbapenem‐nonsusceptible K. pneumoniae isolates, a string test identified three isolates as positive for hypermucoviscosity. Phenotypic characterization and molecular detection of carbapenemase‐ and virulence‐encoding genes were performed. PCR‐based multilocus sequence typing and phylogenetics were used to determine the clonality and global epidemiology of the strains. The coexistence of virulence and resistance genes in the isolates was analyzed statistically using a chi‐square test. Three isolates showed the presence of carbapenemase‐encoding genes (blaNDM, blaVIM, and blaIMP), adhesion genes (fim‐H‐1 and mrkD), and siderophore genes (entB); the isolates belonged to sequence types (STs) 101, 1310, and 1626. The relatedness between these sequence types and the sequence types of globally detected hypermucoviscous K. pneumoniae that also harbor carbapenemases was determined. Our analysis showed that the resistance and virulence profiles were not homogenous. Phylogenetically, different clones clustered together. There was no significant association between the presence of resistance and virulence genes in the isolates. There is a need for periodic surveillance of the healthcare settings in Egypt and globally to understand the true epidemiology of carbapenem‐resistant, hypermucoviscous K. pneumoniae. [ABSTRACT FROM AUTHOR]

Hypervirulent Klebsiella pneumoniae (KP) is defined according to hypermucoviscosity or various virulence factors and is clinically associated with community-acquired liver abscess (CLA). In this study, we investigated the clinical and microbiological characteristics of KP and significant factors associated with hypervirulence. The clinical characteristics, antimicrobial susceptibility, hypermucoviscosity, serotypes, hypervirulence-related genes, and biofilm formation of 414 KP isolates collected from the Keimyung University Dongsan Hospital between December 2013 and November 2015 were analyzed according to CLA. Significant risk factors for hypervirulent KP (HvKP) associated with CLA were investigated using logistic regression analysis. Notably, 155 (37.4%) isolates were hypermucoviscous, and 170 (41.1%) harbored aerobactin. CLA was present in 34 cases (8.2%). Epidemiology and treatment outcomes did not differ significantly between the CLA and non-CLA groups. The CLA group had significantly higher antibiotic susceptibility, K1/K2, rmpA, magA, allS, kfu, iutA, string test-positive result, and biofilm mass. Multivariate logistic regression revealed rmpA (OR, 5.67; 95% CI, 2.09–15.33; p = 0.001), magA (OR, 2.34; 95% CI, 1.01–5.40; p = 0.047), and biofilm mass >0.80 (OR, 2.13; 95% CI, 1.00–4.56; p = 0.050) as significant risk factors for CLA. rmpA was identified as the most significant risk factor for CLA among KP strains, implying that it is an important factor associated with HvKP. [ABSTRACT FROM AUTHOR]

Background: The development of tigecycline resistance in hypervirulent Klebsiella pneumoniae strains has resulted in decreased virulence that is associated with reduced production of capsular polysaccharides (CPS). In this study, we investigated the mechanisms that link tigecycline susceptibility to decreased virulence. Methods: We compared transcriptomes from tigecycline-susceptible wild-type strains and tigecycline-resistant mutants using mRNA sequencing. ompR-overexpressed and ompR-deleted mutants were constructed from wild-type strains and tigecycline-resistant mutants, respectively. Antibiotic susceptibility tests were performed, and string tests and precipitation assays were conducted to identify phenotypic changes related to tigecycline susceptibility and ompR expression. Bacterial virulence was assessed by serum resistance and Galleria mellonella infection assays. Results: Transcriptomic analyses demonstrated a significant decrease in the expression of ompK35 in the tigecycline-resistant mutants. We observed that tigecycline-resistant mutants overexpressed ompR, and that the expression of ompK35 was regulated negatively by ompR. While tigecycline-resistant mutants and ompR-overexpressed mutants exhibited reduced hypermucoviscosity and virulence, deletion of ompR from tigecycline-resistant mutants restored their hypermucoviscosity and virulence. Conclusions: In hypervirulent K. pneumoniae strains, ompR expression, which is regulated by exposure to tigecycline, may affect the production of CPS, leading to bacterial virulence. [ABSTRACT FROM AUTHOR]

Background: Hypervirulent Klebsiella pneumoniae (hvKP) is a virulent subtype of K. Pneumoniae. It commonly causes a serious community acquired infections, but it can also cause hospital acquired (nosocomial) infections. Emergence of antimicrobial resistance in hvKP ia a cause of concern. Objective: Phenotypic and molecular characterization and differentiation of classical and hypervirulent klebsiella pneumoniae isolated from Benha University Hospital. Subjects and Methods: Klebsiella pneumoniae was isolated by cultivation on Mac-Conkey agar media. Identified phenotypically and subjected to antibiotic sensitivity test. Conventional PCR was performed for detection of RmpA and RmpA2 virulence genes. Results: Eight strains out of 70 (11.4%) K.Pneumoniae were identified as probable hvKP by detection of RmpA2 that was detected in all hvKP while rmpA was detected in 2 out of 8 hvKP isolates. Both cKP and hvKP isolates exhibited high resistance rates for most of the tested antibiotics. Conclusion: Particularly in the presence of antibiotic resistance, HvKP pose a new hazard. Both Rmp A and Rmp A2 virulence genes were strongly associated with hvKP. [ABSTRACT FROM AUTHOR]

• Disinfectant tolerance of hvKP with HMV is stronger than that of lvKP and E. coli. • Virulence plasmid contributes to disinfectant tolerance of hvKP in water. • CPS and mitigating oxidative stress contribute to disinfectant tolerance of hvKP. • Disinfection strategy should be strengthened to control hvKP in water environment. Due to the strong pathogenicity of hypervirulent Klebsiella pneumoniae (hvKP), its performance against disinfectants in water should be understood to protect public health and ecological environment. Unfortunately, the disinfectant tolerance of hvKP with a hypermucoviscosity (HMV) phenotype is a critical underexplored area. Here, the tolerance of K. pneumoniae isolates to common disinfectants was evaluated, and its underlying mechanisms were clarified. Results showed that hvKP strains with HMV exhibited remarkable tolerance to triclosan (TCS), sodium hypochlorite (NaClO), and benzalkonium bromide (BB), surpassing that of low-virulent K. pneumoniae (lvKP) and Escherichia coli , which is the microbial indicator of drinking water quality. Ct value of NaClO reached 4.41 mg/L·min to kill 4-log hvKP, while the values were 2.52 and 2.28 mg/L·min to achieve 4-log killing of lvKP and E. coli , respectively. The curing of the virulence plasmid from hvKP strain K2044 revealed that capsular polysaccharide (CPS) synthesis, driven by the virulence plasmids, helped mitigate cell membrane injury and bacterial inactivation under NaClO stress; consequently, it provided a protective advantage to hvKP. Enhancing the antioxidative stress system to reduce ROS production and mitigate oxidative stress caused by NaClO further improved the disinfectant resistance of hvKP strains with HMV. This study emphasized that hvKP strains with HMV posed a considerable challenge to disinfection procedure of water treatment. It also revealed that an improved dosage of NaClO ensures bacteria killing, indicating the optimization of the design of water treatment processes involving disinfection strategies and technical parameters should be considered. [Display omitted] [ABSTRACT FROM AUTHOR]

Hypervirulent Klebsiella pneumoniae (hvKp) raised concern worldwide. We studied 22 hvKp clinical invasive isolates referred to the Belgian national reference laboratory between 2014 and 2020. Sixty-four percent of the isolates expressed K2 capsular serotype and belonged to 7 different MLST lineages, while 32% expressed K1 (all belonging to ST23) and were associated with liver abscesses. Primary extra-hepatic infections were reported in 36% and sepsis for 95% of the patients with 30% of deaths. Improved clinical and microbiological diagnostics are required as hvKp may represent an underestimated cause of community-acquired invasive infections in Belgium. [ABSTRACT FROM AUTHOR]

Hypervirulent Klebsiella pneumoniae (HvKP), which causes highly fatal infections, is a new threat to human health. In an attempt to investigate the underlying mechanisms of resistance to neutrophil-mediated killing and hence expression of high-level virulence by HvKP, we tested the binding affinity of HvKP strains to various types of human cells. Our data showed that HvKP exhibited weaker binding to both lung epithelial cells, intestinal Caco-2 cells and macrophages when compared to the classic, non-hypervirulent strains (cKP). Consistently, transconjugants that have acquired a rmpA or rmpA2-bearing plasmid were found to exhibit decreased adhesion to various types of human cells, and hence higher survival rate upon exposure to neutrophil cells. We further found that over production of hypermucoviscosity (HMV), but not capsular polysaccharide (CPS), contributed to the reduced binding and phagocytosis. The effect of hypermucoviscosity on enhancing HvKP virulence was further shown in human serum survival assays and animal experiments. Findings in this study therefore confirmed that rmpA/A2-mediated hypermucoviscosity in HvKP plays a key role in the pathogenesis of this organism through conferring the ability to evade neutrophil binding and phagocytosis. [ABSTRACT FROM AUTHOR]

Background: Klebsiella spp. are important pathogens associated with bacteremia among admitted children and is among the leading cause of death in children < 5 years in postmortem studies, supporting a larger role than previously considered in childhood mortality. Herein, we compared the antimicrobial susceptibility, mechanisms of resistance, and the virulence profile of Klebsiella spp. from admitted and postmortem children.Methods: Antimicrobial susceptibility and virulence factors of Klebsiella spp. recovered from blood samples collected upon admission to the hospital (n = 88) and postmortem blood (n = 23) from children < 5 years were assessed by disk diffusion and multiplex PCR.Results: Klebsiella isolates from postmortem blood were likely to be ceftriaxone resistant (69.6%, 16/23 vs. 48.9%, 43/88, p = 0.045) or extended-spectrum β-lactamase (ESBL) producers (60.9%, 14/23 vs. 25%, 22/88, p = 0.001) compared to those from admitted children. blaCTX-M-15 was the most frequent ESBL gene: 65.3%, 9/14 in postmortem isolates and 22.7% (5/22) from admitted children. We found higher frequency of genes associated with hypermucoviscosity phenotype and invasin in postmortem isolates than those from admitted children: rmpA (30.4%; 7/23 vs. 9.1%, 8/88, p = 0.011), wzi-K1 (34.7%; 8/23 vs. 8%; 7/88, p = 0.002) and traT (60.8%; 14/23 vs. 10.2%; 9/88, p < 0.0001), respectively. Additionally, serine protease auto-transporters of Enterobacteriaceae were detected from 1.8% (pic) to 12.6% (pet) among all isolates. Klebsiella case fatality rate was 30.7% (23/75).Conclusion: Multidrug resistant Klebsiella spp. harboring genes associated with hypermucoviscosity phenotype has emerged in Mozambique causing invasive fatal disease in children; highlighting the urgent need for prompt diagnosis, appropriate treatment and effective preventive measures for infection control. [ABSTRACT FROM AUTHOR]

Given the increasing incidence of multidrug-resistant (MDR) Klebsiella pneumoniae infections, it is of great interest to investigate the risk of transmission associated with the prevalence of this pathogen. Some studies have described fresh raw poultry meat as a reservoir of MDR K. pneumoniae , including clinically relevant sequence types (ST) and extended-spectrum β-lactamase (ESBL) strains, indicating possible consumer exposure. This study compared 47 MDR strains of K. pneumoniae from poultry meat and human clinical isolates to assess similarities, including analysis of antimicrobial resistance profiles and virulence factors involved in infection. In addition, several biofilm culture methods were evaluated for reproducible assessment of biofilm formation in K. pneumoniae strains. Globally, no association between strain origin and STs, hypermucoviscosity, biofilm formation or serum resistance could be found between isolates of food and clinical origin, nor an associated AMR pattern, suggesting overlapping populations. We found that LB supplemented with glucose in microaerobiosis was the best discrimination condition for biofilm formation in the active attachment biofilm cultivation model. The biofilm formation capacity was strongly dependent on culture conditions, with a strain-specific response, but only a minor increase in biofilm levels was recorded in clinical K. pneumoniae populations. Our results suggest that a similar risk of zoonosis transmission from potentially virulent foodborne strains previously observed in E. coli is also present in this high-priority pathogen. This study further confirms that foodborne isolates of K. pneumoniae pose a risk to consumers and therefore this pathogen should be included in the surveillance of foodborne pathogens with high risk of MDR infections and therapeutic failure. • The zoonotic potential of foodborne isolates of K. pneumoniae is confirmed. • AMR-profile analysis revealed overlapping clinical and foodborne populations. • Culture conditions strongly affect biofilm formation and hypermucoviscosity. • No correlation was found between strain origin or ST and phenotypic traits related to virulence. • K. pneumoniae should be included in the surveillance of MDR foodborne pathogens. [ABSTRACT FROM AUTHOR]

Hypervirulent Klebsiella pneumoniae (HvKP), which causes highly fatal infections, is a new threat to human health. In an attempt to investigate the underlying mechanisms of resistance to neutrophil-mediated killing and hence expression of high-level virulence by HvKP, we tested the binding affinity of HvKP strains to various types of human cells. Our data showed that HvKP exhibited weaker binding to both lung epithelial cells, intestinal Caco-2 cells and macrophages when compared to the classic, non-hypervirulent strains (cKP). Consistently, transconjugants that have acquired a rmpA or rmpA2-bearing plasmid were found to exhibit decreased adhesion to various types of human cells, and hence higher survival rate upon exposure to neutrophil cells. We further found that over production of hypermucoviscosity (HMV), but not capsular polysaccharide (CPS), contributed to the reduced binding and phagocytosis. The effect of hypermucoviscosity on enhancing HvKP virulence was further shown in human serum survival assays and animal experiments. Findings in this study therefore confirmed that rmpA/A2-mediated hypermucoviscosity in HvKP plays a key role in the pathogenesis of this organism through conferring the ability to evade neutrophil binding and phagocytosis. [ABSTRACT FROM AUTHOR]

Background: Hypervirulent Klebsiella pneumoniae (HVKp) infections have distinct clinical manifestations from classical K. pneumoniae infections. The hallmark of HVKp infections are liver abscess formation and metastatic infections. Due to the severe sequelae of these complications, method to identify patients at-risk of HVKp infections should be developed. Results: A retrospective cohort study of 222 patients with K. pneumoniae bloodstream infections (BSIs) was performed. Patient demographics, clinical manifestations, and bacterial characteristics were investigated. Ten cases of liver abscesses were identified. Characteristics such as community-onset BSIs, hypermucoviscosity phenotype, and capsular serotype K1 were identified as risk factors for HVKp infections. A scoring system was developed based on the risk factors. The area under the receiver operating characteristic curve for the scoring system was 0.90. A score of ≥ 2 points provided sensitivity and specificity of 0.70 and 0.94, respectively. Conclusions: Simple scoring system was developed for the diagnosis of HVKp infections. The system allows early identification of patients with K. pneumoniae BSIs in whom hypervirulent infections should be evaluated. Prospective evaluation is expected. [ABSTRACT FROM AUTHOR]

The convergence of carbapenem-resistance and hypervirulence genes in Klebsiella pneumoniae has led to the emergence of highly drug-resistant superbugs capable of causing invasive disease. We analyzed 556 carbapenem-resistant K. pneumoniae isolates from patients in Singapore hospitals during 2010-2015 and discovered 18 isolates from 7 patients also harbored hypervirulence features. All isolates contained a closely related plasmid (pKPC2) harboring blaKPC-2, a K. pneumoniae carbapenemase gene, and had a hypervirulent background of capsular serotypes K1, K2, and K20. In total, 5 of 7 first patient isolates were hypermucoviscous, and 6 were virulent in mice. The pKPC2 was highly transmissible and remarkably stable, maintained in bacteria within a patient with few changes for months in the absence of antimicrobial drug selection pressure. Intrapatient isolates were also able to acquire additional antimicrobial drug resistance genes when inside human bodies. Our results highlight the potential spread of carbapenem-resistant hypervirulent K. pneumoniae in Singapore. [ABSTRACT FROM AUTHOR]

Introduction: The rapid spread of Hypervirulent Klebsiella pneumoniae (hvKP) and Multi Drug Resistant (MDR) strains among the clinical isolates of K.pneumoniae is a great deal of concern. The drug resistance and limited treatment options are the major threats. However, the spread of drug resistant strains is through plasmid which may carry virulence determinants such as capsular antigens. Aim: To know the occurrence of hvKP; to study the occurrence of various capsular serotypes such as K1, K2, K3 and K4 among the isolates of K. pneumoniae using Co-agglutination (Co-A) test; to know the occurrence of beta lactamase genes (bla genes) among the K1, K2, K3 and K4 positive serotypes of K. pneumoniae. The study also tried to assess the reproducibility of Co-A test by comparing the result with PCR. Materials and Methods: A prospective study was carried with a total of 60 consecutive, non-duplicate isolates of K. pneumoniae recovered from various clinical specimens obtained from both outpatients and inpatients between April to December 2017. To determine the occurrence of hvKP by string test, the identification of various serotypes was done by Co-A test and PCR. The determination of beta lactamase genes such as blaTEM, blaSHV and blaCTX-M among the capsular serotypes was done by PCR study. Results: Rate of typability by Co-A was found to be 13(21.67%), 0(0%), 32(53.33%), 7(11.67%) for K1, K2, K3 and K4, respectively. Eight (13.33%) of them remained untypable. The rate of typability among the K. pneumoniae K1 serotype by Co-A test and PCR remained somewhat similar. Conclusion: Co-A test is a good method of serotyping and can be used not only for diagnostic purpose but also for epidemiological study. [ABSTRACT FROM AUTHOR]

Klebsiella spp. isolates from community-acquired infections were characterized. A total of 39 Klebsiella spp. isolates were obtained from outpatients at four rural hospitals in Mexico (2013–2014). The biochemical tests identified all as being K. pneumoniae . The molecular multiplex-PCR test identified 36 (92.4%) K. pneumoniae isolates and one (2.5%) K. variicola isolate, and phylogenetic analysis of the rpoB gene identified two isolates (5.1%) belonging to K. quasipneumoniae subsp. quasipneumoniae and K. quasivariicola . The last one was confirmed by phylogenetic analysis of six-loci concatenated genes. Mostly the isolates were multidrug resistant; however, a minority were extended-spectrum β-lactamase producing (10.2%). The extended-spectrum β-lactamase CTX-M-15 gene was identified in these isolates. Analysis of biofilm production and the hypermucoviscosity phenotype showed a total of 35 (92.3%) and seven (17.9%) of the isolates were positive for these phenotypes respectively. The K2 (4/39, 10.2%), K5 (2/39, 5.1%) and K54 (1/39, 2.5%) serotypes were identified in seven (17.9%) of the isolates, and only 28.5% (2/7) hypermucoviscous isolates were positive for the K2 and K5 serotypes. In general, the sequence type (ST) analysis and phylogenetic analysis of seven multilocus sequence typing loci were heterogeneous; however, ST29 was the most prevalent ST in the analysed isolates, accounting for 19% (4/21) of the total isolates. Two of the four ST29 isolates had the hypermucoviscosity phenotype. The virulence factors for fimbriae were the most prevalent, followed by siderophores. Community-acquired infections are caused by various species from Klebsiella genus, with different profiles of antibiotic resistance and heterogeneous virulence factors. [ABSTRACT FROM AUTHOR]

Hypermucoviscous (HV) strains of capsular types K1, K2 and K57 are the most virulent representatives of the Klebsiella pneumoniae species. Eight novel bacteriophages lytic for HV K. pneumoniae were isolated and characterized. Three bacteriophages, KpV41, KpV475, and KpV71 were found to have a lytic activity against mainly K. pneumoniae of capsular type K1. Two phages, KpV74, and KpV763 were lytic for K2 capsular type K. pneumoniae , and the phage KpV767 was specific to K57-type K. pneumoniae only. Two more phages, KpV766, and KpV48 had no capsular specificity. The phage genomes consist of a linear double-stranded DNA of 40,395–44,623 bp including direct terminal repeats of 180–246 bp. The G + C contents are 52.3–54.2 % that is slightly lower than that of genomes of K. pneumoniae strains being used for phage propagation. According to the genome structures, sequence similarity and phylogenetic data, the phages are classified within the genus Kp32virus and Kp34virus of subfamily Autographivirinae, family Podoviridae . In the phage genomes, genes encoding proteins with putative motifs of polysaccharide depolymerase were identified. Depolymerase genes of phages KpV71 and KpV74 lytic for hypermucoviscous K. pneumoniae of K1 and K2 capsular type, respectively, were cloned and expressed in Escherichia coli , and the recombinant gene products were purified. The specificity and polysaccharide-degrading activity of the recombinant depolymerases were demonstrated. [ABSTRACT FROM AUTHOR]

Since the hypermucoviscous variants of Klebsiella pneumoniae were first reported, many cases of primary liver abscesses and other invasive infections caused by this pathogen have been described worldwide. Hypermucoviscosity is a phenotypic feature characterized by the formation of a viscous filament ≥5 mm when a bacterial colony is stretched by a bacteriological loop; this is the so-called positive string test. Hypermucoviscosity appears to be associated with this unusual and aggressive type of infection, and therefore, the causal strains are considered hypervirulent. Since these first reports, the terms hypermucoviscosity and hypervirulence have often been used synonymously. However, new evidence has suggested that hypermucoviscosity and hypervirulence are 2 different phenotypes that should not be used synonymously. Moreover, it is important to establish that a negative string test is insufficient in determining whether a strain is or is not hypervirulent. On the other hand, hypervirulence- and hypermucoviscosity-associated genes must be identified, considering that these phenotypes correspond to 2 different phenomena, regardless of whether they can act in synergy under certain circumstances. Therefore, it is essential to quickly identify the genetic determinants behind the hypervirulent phenotype to develop effective methodologies that can diagnose in a prompt and effective way these hypervirulent variants of K. pneumoniae. [ABSTRACT FROM AUTHOR]

We investigated the implications of hypervirulence determinants on clinical features of 48 adult patients with bacteremia caused by extended-spectrum β-lactamase-producing Klebsiella pneumoniae. Isolates in the hypervirulence group included any of the following virulence determinants: K1/K2 capsule serotypes, hypermucoviscosity phenotype, rmpA gene, or rmpA2 gene. Nonhypervirulence group isolates were negative for all of the above virulence factors. In this study, all isolates used were non-K1/K2 strains. Statistically significant differences were observed in clinical features of patients between the two groups. The hypervirulent isolates ( n = 19), including 11 isolates with the hypermucoviscosity phenotype, 15 with the rmpA gene, and 16 with the rmpA2 gene, were more commonly recovered from diabetic patients and mainly manifested as secondary bacteremia (such as pneumonia, urinary tract infections, or other localized infections). The nonhypervirulent isolates ( n = 29) were more commonly recovered from patients after prolonged hospital stays (>30 days) and mostly manifested as primary bacteremia. The overall in-hospital mortality was 56.3%. Hazard ratio (HR) analysis revealed the following positive predictors for mortality: nosocomial infection, stay in an intensive care unit, no removal of the central venous catheter, Charlson comorbidity score, and APACHE II score (≧15). The negative predictors were initial appropriate antibiotic therapy (HR 0.42) and urinary tract infection (HR 0.19). Charlson score was an independent confounder based on multivariate analysis (HR 1.43, 95% confidence interval 1.04-1.99). In conclusion, hypervirulence determinants played a role in causing secondary infections in diabetic patients; however, the presence of morbidity cofactors could themselves influence mortality, despite the absence of hypervirulence determinants. [ABSTRACT FROM AUTHOR]

Background:Klebsiella pneumoniaewith hypermucoviscosity (HM) phenotype is generally more virulent than HM-negative strains. The aim of this study was to investigate the prevalence of HM phenotype among urinary isolates and to compare the virulence factors, antimicrobial susceptibility patterns and clinical characteristics of HM-positive and -negativeK. pneumoniaeisolated from urine of hospitalized patients. Methods:From June to October 2013, a total of 81 non-repetitiveK. pneumoniaestrains were isolated from urine. HM phenotype was determined by a string test. The K1 and K2 genotypes, theallS,kfu,rmpA,rmpA2andwabG, aerobactin gene were detected by polymerase chain reaction. Results:Of the 81K. pneumoniaeisolates, 12.3% produced a positive string test. The aerobactin (80.0%[8/10] vs. 15.5%[11/71],p = .0001),allS(40.0%[4/10] vs. 9.9%[7/71],p = .009),rmpA(70.0%[7/10] vs. 14.1%[10/71],p = .0001) andrmpA2(60.0%[6/10] vs. 16.9%[12/71],p = .002) genes were more prevalent in HM positive than in HM negative strains. The K1 (20.0%[2/10) vs. 8.5%[6/71]] and K2 (30.0%[3/10] vs. 4.2%[3/71]) capsular serotypes were more common in HM strains than in non-HM strains (p = .0001). HM-positiveK. pneumoniaeisolates were more susceptible to amoxicillin/clavulanic acid (p = .02), cefazolin (p = .03), cefotaxime (p = .02) and ciprofloxacin (p = .03) than HM-negative isolates. Multivariate analysis showed that HM phenotype (OR, 23.87; 95% CI, 3.91–145.4,p < .01) and age >60 years (OR, 8.33; 95% CI, 1.25–55.31,p = .03) were significant risk factors for concurrent bacteraemia. Conclusion:Klebsiella pneumoniaewith expression of HM phenotype isolated from urine were more likely to be associated with concurrent bacteraemia than isolates without the HM phenotype, and were more susceptible to antibiotics. Physicians have to be aware of the possibility of bacteraemia in patients withK. pneumoniaebacteriuria, especially if strains are HM positive and the patient is >60 years old. [ABSTRACT FROM PUBLISHER]

Transformation efficiency is very low in hypermucoviscous Kllebsiella pneumoniae owing to high amount of capsular polysaccharide. Here, we propose a method to improve the transformation in hypermucoviscous K. pneumoniae using citric acid. An increased number of recovered transformants was observed in the strains cultured in the presence of citric acid. • Transformation in hypermucoviscous Klebsiella pneumoniae strains have frequently resulted in very low efficiency of transformation, because of the high amount of capsular polysaccharides. • We show that electroporation method using citric acid for transforming hypermucoviscous K. pneumoniae is efficient by reducing the amount of capsular polysaccharide. • The time constant value, an indicator of transformation efficiency was optimized when K. pneumoniae is treated citric acid. [ABSTRACT FROM AUTHOR]

Background: Klebsiella pneumoniae is a prominent nosocomial pathogen that accounts for up to 10% of all hospital-acquired infections. It is a frequent cause of ventilator-associated pneumonia (VAP). The purpose of this study was to investigate the clinical characteristics of K. pneumoniae-associated VAP and the molecular characteristics of K. pneumoniae strains. Methods: We retrospectively reviewed 70 mechanically ventilated patients with K. pneumoniae isolated. All K. pneumoniae strains were examined to determine hypermucoviscosity (HV) phenotype, capsular serotypes, virulence genes, multilocus sequence typing and antimicrobial susceptibility. Results: Hypermucoviscosity was found in 14 of 70 (20%) isolates of K. pneumoniae. Among the 70 patients, 43 cases (61.4%) developed VAP. Furthermore, VAP was more frequently induced by HV-positive K. pneumoniae (14/14, 100%) than by HV-negative strains (29/56, 51.7%). HV-positive K. pneumoniae-associated VAP patients were more inclined to develop bacteremia and had a higher mortality rate than HV-negative strains VAP patients. Antibiotic resistance was more frequent in HV- negative strains- than in HV- positive strains-infected patients. The prevalence of rmpA and aerobactin genes were 85.7% and 85.7% respectively, and serotypes K1 and K2 accounted for 14.3% and 28.6% of the hypermucoviscosity strains, respectively. Strains carrying rmpA and aerobactin genes were significantly associated with HV-phenotype, and rmpA and aerobactin coexisted in HV-positive strains. Multilocus sequence typing analysis identified 24 different sequence types from K. pneumoniae VAP samples. Conclusions: HV-phenotype is the major virulence determinant for mechanically ventilated patients. There was a specific sequence typing (ST) distribution between HV-positive and HV-negative strains. [ABSTRACT FROM AUTHOR]

Cases of infection with hypervirulent Klebsiella pneumoniae are gradually increasing in number, and cause life-threatening community-acquired infection even in immunocompetent patients. A 14-year-old boy developed septic hip arthritis due to hypervirulent K. pneumoniae (sequence type 23, serotype K1, magA positive). The patient initially seemed to have been successfully treated with antibiotics and surgical intervention, but septic arthritis developed into osteomyelitis of the femoral head and myositis, which required long-term antibiotic therapy and additional surgical intervention. This is the first pediatric case of hypervirulent K. pneumoniae septic hip arthritis. Treatment plans should mainly consist of antibiotic therapy and surgical intervention. Clinicians, even pediatricians, in developed countries should be aware of the increasing incidence of hypervirulent Klebsiella pneumoniae infection. [ABSTRACT FROM AUTHOR]

In recent years, an emergent Klebsiella pneumoniae hypermucoviscosity (HMV) phenotype has been associated with increased invasiveness and pathogenicity in primates. In this project, bacteria recovered from infected African green monkeys (AGM) ( Chlorocebus aethiops sabaeus ) were screened for HMV phenotype, and were compared to non-HMV isolates in in vitro , serum, and oxidative-mediated killing assays. Complement-mediated killing was assessed utilizing freshly collected serum from healthy AGM. Oxidative-mediated killing was investigated utilizing sodium hypochlorite and hydrogen peroxide. Compared to non-HMV isolates, HMV isolates were more resistant to serum-mediated and oxidative killing ( p < 0.05). Phagocytosis resistance was evaluated using AGM peripheral blood monocytes (PBMC), and results indicated that non-HMV isolates associated with the AGM PBMC to a greater extent than HMV isolates ( p < 0.001). Measurement of lactate dehydrogenase release showed that HMV isolates were more cytotoxic to AGM PBMC than non-HMV isolates ( p < 0.001). Thus, the hypermucoid phenotype appears to be an important virulence factor that promotes evasion of innate immune defenses. [ABSTRACT FROM AUTHOR]

Klebsiella pneumoniae (KP) with the hypermucoviscosity (hV) phenotype has abundant capsular polysaccharides (cPs) and usually causes an invasive syndrome. sialic acid (sia), a component of cPs in KP strains with the hV phenotype, may be anti-phagocytic. sia-binding immunoglobulin-like lectin-9 (siglec-9) act as an Mhc class-I receptor on neutrophils that recognizes sia and sends a signal to dampen inflammatory response. Three clinical KP strains with KP-M1 (hV-positive, capsular serotype K1), KP-14 (hV-negative, capsular serotype non-K1/K2), and DT-X (hV-negative, capsular serotype K1) were studied. We assessed total sia in cPs extracts using enzymatic methods and phagocytosis by neutrophils of neuraminidase-treated bacteria using flow cytometry. Neutrophil killing was evaluated in the presence and absence of antibodies against siglec-9. The concentration of sia was significantly higher in the cPs extract of KP-M1 (56.75 ± 6.75 µmole/109 cfu) than in the cPs extract of KP-14 (0.02 ± 0.01 µmole/109 cfu) and DT-X (a negligible value). The KP-M1 (compared with the KP-14 and DT-X) was more resistant to neutrophil phagocytosis. Both the hV phenotype and resistance to phagocytosis of KP-M1 were significantly decreased after sia removal with neuraminidase treatment. Fluorescence microscopy with an antibody against human siglec-9 showed attachment of KP-M1 (but were absent of KP-14 and DT-X) to the surface of neutrophils and colocalization with human siglec-9. engagement of siglec-9 via sia enhanced neutrophils killing of KP-M1 by ex vivo human neutrophils bactericidal activity assay. The result showed that sia might be a constituent of KP-M1 cPs responsible for hV, thereby contributing to anti-phagocytic activity of this pathogen. [ABSTRACT FROM AUTHOR]

Purpose/Aim: Klebsiella pneumoniae causes a blinding infection called endogenous endophthalmitis. The role of innate immune recognition of K. pneumoniae in the eye during infection is not known. We hypothesized that intraocular recognition of K. pneumoniae was mediated by Toll-like receptor (TLR)-4 and may be dependent on MagA-regulated hypermucoviscosity. Materials and Methods: Experimental endophthalmitis was induced in C57BL/6J or TLR4−/− mice by intravitreal injection of 100 CFU of wild type or ΔmagA K. pneumoniae. Infection and inflammation were quantified by determining viable K. pneumoniae per eye, retinal responses via electroretinography, myeloperoxidase activity of infiltrating neutrophils and the proinflammatory cytokine and chemokine response. Results: C57BL/6J and TLR4−/− mice could not control intraocular wild-type K. pneumoniae growth. TLR4−/− mice were less able than C57BL/6J to control the intraocular growth of ΔmagA K. pneumoniae. Retinal function testing suggested that infection with ΔmagA K. pneumoniae resulted in less retinal function loss. There was a TLR4-dependent delay in initial neutrophil recruitment, regardless of the infecting organism. The proinflammatory cytokine/chemokine data supported these results. These findings were not due to an inability of TLR4−/− neutrophils to recognize or kill K. pneumoniae. Conclusions: These studies suggest that TLR4 is important in the early intraocular recognition and host response to K. pneumoniae. However, the role of MagA in TLR4-mediated intraocular recognition and subsequent inflammation is less clear. [ABSTRACT FROM AUTHOR]

Background Klebsiella pneumoniae (KP) expressing hypermucoviscosity phenotype (HV-KP) has abundant capsular polysaccharide (CPS) and is capable of causing invasive syndrome. Sodium salicylate (SAL) reduces the production of CPS. The study was aimed to investigate the relationship between aspirin usage and KP-mediated invasive syndrome and the effect of SAL on HV-KP. Methods Patients with community-acquired KP bacteraemia were prospectively enrolled. KP-M1, a serotype-K1 HV-KP clinical isolate, was used in the following experiments: CPS production, HV-KP phenotype, and the effect of SAL on neutrophils phagocytosis. The effect of oral aspirin intake on the leukocyte bactericidal activity was evaluated. Results Patients infected by HV-KP and diabetic patients with poor glycemic control were at an increased risk for invasive syndrome (p < 0.01); those who had recent use of aspirin (p = 0.02) were at a lower risk. CPS production was significantly reduced in the presence of SAL. The HV-KP phenotype and resistance to neutrophil phagocytosis were both significantly reduced in the KP-M1 after incubation with SAL (p < 0.01). Aspirin treatment significantly enhanced the killing of KP-M1 by leukocytes (p < 0.01). Conclusion Treatment with SAL significantly reduces CPS production in HV-KP, thereby contributing to leukocyte phagocytosis and bactericidal activity against this pathogen. [ABSTRACT FROM AUTHOR]

A 59-year-old Japanese diabetic woman was admitted to a small private hospital with general malaise, fever, and a 1-month history of low back pain. A computed tomography scan of the abdomen revealed left abdominal necrotizing fasciitis with suspected left psoas muscle abscess. She was transferred to Gunma University Hospital, received antibiotic therapy, and underwent debridement of the infected subcutaneous tissue, fascia, and necrotic left psoas muscle. She was transferred to the intensive care unit to receive mechanical ventilation and inotropic support. Blood culture showed growth of Klebsiella pneumoniae, from which hypermucoviscosity was detected by the string test. She was extubated on day 5 of hospitalization and transferred to a general ward on day 14. Free skin grafting was performed on day 76, and she was discharged on day 134 without any complications. [ABSTRACT FROM AUTHOR]

Abstract: Hypermucoviscosity, rmpA (regulator of mucoid phenotype), aerobactin (an iron siderophore), kfu (an iron uptake system), allS (associated with allantoin metabolism), and K1/K2 capsules are important virulence determinants in Klebsiella pneumoniae for liver abscesses. We determined the prevalence of these virulence factors of 50 nonrepeat K. pneumoniae isolates recovered from patients with primary liver abscesses who were treated at 2 medical centers in Taiwan. Virulence genes were surveyed by polymerase chain reaction analysis. The prevalence of hypermucoviscosity phenotype, plasmid-born rmpA, aerobactin, kfu, and allS genes revealed 96%, 100%, 100%, 100%, and 100% in 26 capsular K1 isolates; 90%, 100%, 100%, 0%, and 0% in 10 K2 isolates; and 79%, 86%, 93%, 50%, and 0% in 14 non-K1/K2 isolates; respectively. When injected into mice intraperitoneally, regardless of any capsule K serotype, K. pneumoniae isolates with hypermucoviscosity phenotype as well as presence of rmpA and aerobactin genes exhibited high virulence for mouse lethality (LD50, <102 CFU). Without significant difference in the prevalence of expressing hypermucoviscosity phenotype and carriage of rmpA and aerobactin genes, these virulent non-K1/K2 isolates are as capable as K1/K2 isolates of causing primary liver abscesses. [Copyright &y& Elsevier]

Background. Klebsiella pneumoniae, a Gram-negative bacillus usually forming glistening mucoid colonies with viscid consistency on the culture plate, is a common pathogen causing various clinical infection patterns. However, little is known about the clinical implications of this mucoid character. Objective. The purposes of this study, therefore, were to investigate the frequency of hypermucoviscosity (HV) in bacteraemic isolates of K. pneumoniae, and determine the significance of any association between HV and various clinical manifestations. Design. Retrospective observational study. Patients. Patients diagnosed with K. pneumoniae bacteraemia at a community-based university hospital between June 1999 and June 2001 were enrolled in this analysis. Measurements. Clinical data concerning comorbid diseases and infection patterns was collected. K. pneumoniae bacteraemic isolates were examined for the presence of HV using a modified string test. The clinical impact of HV and risk factors for the invasive syndrome were assessed using statistical analysis. Polymerase chain reaction (PCR) was performed to detect magA, a gene related to HV phenotype. Results. Overall, 200 (64.9%) of the 308 cases of K. pneumoniae bacteraemia were community-acquired infections. Compared with hospital-acquired K. pneumoniae bacteraemia (HA-KpB), community-acquired K. pneumoniae bacteraemia (CA-KpB) was more likely to be monomicrobial in nature (83.5% vs. 64.8%; P < 0.001) and caused by HV strains (41.5% vs. 14.8%; P < 0.001). The prevalence rate of magA among HV phenotypical K. pneumoniae strains was 24.1%. Patients infected with HV-positive strains were more likely to have the distinctive invasive syndrome (i.e. liver abscess, meningitis, pleural empyaema or endophthalmitis) than those infected with HV-negative variants (37.3% vs. 6.8%; P < 0.001). Multivariate logistic regression analysis, adjusted for age, showed that HV phenotype in K. pneumoniae strains (OR 8.86; 95% CI, 3.70–21.25; P < 0.001) was positively associated with the development of the invasive syndrome in CA-KpB cases. Conclusions. The HV phenotype of K. pneumoniae bacteraemic isolates was associated with the development of a distinctive invasive syndrome. Identification of the HV phenotype should prompt clinicians to initiate aggressive investigations for invasive diseases. [ABSTRACT FROM AUTHOR]

The authors deal with the association of the pathogen Klebsiella pneumoniae with community-acquired bacteremia and its ability to express hypermucoviscosity (HV). Topics include the virulence factors that contribute to K. pneumoniae pathogenesis, controversies regarding the ability of K. pneumoniae to express the HV phenotype and its association with rmpA/rmpA2 gene prevalence, and the possibility that K. pneumoniae isolates causing pyogenic liver abscess can raise resistance to antimicrobials.

Summary: Objectives: To investigate the association between Klebsiella pneumoniae-mediated invasive syndrome and underlying diseases in patients and/or K. pneumoniae characteristics, including the rmpA, rmpA2, and magA genes, capsular polysaccharide (cps) K1 or K2 serotypes, hypermucoviscosity (HV) phenotype, and extended-spectrum β-lactamase (ESBL) production. Methods: This was a prospective cross-sectional study. Results: The invasive syndrome was detected in 19 of 91 patients (20.9%) with K. pneumoniae infections, and diabetes mellitus was the most common underlying disease (9 of 19). The presence of rmpA or rmpA2 was found in 91.4% of the 35 isolates with the HV phenotype, while in only 17.9% of the 56 isolates without HV phenotype. Multivariate logistic regression analysis showed that the HV phenotype was an independent risk factor for K. pneumoniae-mediated invasive syndrome (odds ratio (OR) 58.24, 95% confidence interval (CI) 7.23–468.87; p < 0.001) and was negatively associated with ESBL production (OR 0.042, 95% CI 0.005–0.331; p =0.003). Binary logistic regression analysis revealed that the invasive syndrome was not influenced by the presence of diabetes mellitus among patients infected with K. pneumoniae positive for the rmpA or rmpA2 gene, HV phenotype, or cps K1/K2 serotype. Conclusions: The HV phenotype of K. pneumoniae contributes to invasive syndrome and is a negative predictor for K. pneumoniae acquisition of ESBLs. [Copyright &y& Elsevier]