Characteristics of Hypervirulent Klebsiella pneumoniae: Does Low Expression of rmpA Contribute to the Absence of Hypervirulence?

Antibiotic resistance rates in hypervirulent Klebsiella pneumoniae strains: A systematic review and meta-analysis

OBJECTIVES

In response to the growing global concerns regarding antibiotic resistance, we conducted a meta-analysis to assess the prevalence of antibiotic resistance in hypervirulent Klebsiella pneumoniae (hvKp) strains.

METHODS

We conducted a meta-analysis of antibiotic resistance in the hvKp strains. Eligible studies published in English until April 10, 2023, were identified through a systematic search of various databases. After removing duplicates, two authors independently assessed and analysed the relevant publications, and a third author resolved any discrepancies. Data extraction included publication details and key information on antibiotic resistance. Data synthesis employed a random-effects model to account for heterogeneity, and various statistical analyses were conducted using R and the metafor package.

RESULTS

This meta-analysis of 77 studies from 17 countries revealed the prevalence of antibiotic resistance in hvKp strains. A high resistance rates have been observed against various classes of antibiotics. Ampicillin-sulbactam faced 45.3% resistance, respectively, rendering them largely ineffective. The first-generation cephalosporin cefazolin exhibited a resistance rate of 38.1%, whereas second-generation cefuroxime displayed 26.7% resistance. Third-generation cephalosporins, cefotaxime (65.8%) and ceftazidime (57.1%), and fourth-generation cephalosporins, cefepime (51.3%), showed substantial resistance. The last resort carbapenems, imipenem (45.7%), meropenem (51.0%) and ertapenem (40.6%), were not spared.

CONCLUSION

This study emphasizes the growing issue of antibiotic resistance in hvKp strains, with notable resistance to both older and newer antibiotics, increasing resistance over time, regional disparities and methodological variations. Effective responses should involve international cooperation, standardized testing and tailored regional interventions.

Molecular epidemiology of string test-positive Klebsiella pneumoniae isolates in Huzhou, China, 2020-2023

Objective

This study used whole-genome sequencing (WGS) to explore the genetic diversity, virulence factors, and antimicrobial resistance determinants of string test-positive Klebsiella pneumoniae (KP) over a 4-year surveillance period in Huzhou, China.

Methods

In total, 632 clinical isolates were collected via hospital surveillance from 2020 to 2023; 100 were positive in the string test and these 100 strains were subjected to antimicrobial susceptibility testing using an agar dilution method followed by WGS.

Results

The resistance rates to cefotaxime (77.0%), trimethoprim-sulfamethoxazole (67.0%), and nalidixic acid (64.0%) were high. Multilocus sequence typing revealed high genetic diversity; there were 33 sequence types (STs) and 15 capsular serotypes. The most common ST was ST23 (16.0%) and the most common capsular serotype was K1 (22.5%). Virulome analysis revealed among-strain differences in virulence factors that affected bacterial adherence, efflux pump action, iron uptake, nutritional factors, metabolic regulation, the secretion system, and toxin production. The Kleborate strain-specific virulence scores of all 100 string test-positive KPs were derived: 28 strains scored 5, 28 scored 4, 21 scored 3, 12 scored 1, and 11 scored 0. All 77 strains with scores of 3 to 5 contained the iucA gene. The phylogeny based on whole-genome single nucleotide polymorphisms (wgSNPs) indicated high clonality; the string test-positive KP strains were grouped into six clades. Closely related isolates in each genetic cluster usually shared STs.

Conclusion

The present study highlights the significance of the KP iucA gene in terms of hypervirulence and the diverse genotypes of string test-positive KP strains isolated in Huzhou hospitals.

Complete genome sequence, phenotypic correlation and pangenome analysis of uropathogenic Klebsiella spp

Urinary tract infections (UTI) by antibiotic resistant and virulent K. pneumoniae are a growing concern. Understanding the genome and validating the genomic profile along with pangenome analysis will facilitate surveillance of high-risk clones of K. pneumoniae to underpin management strategies toward early detection. The present study aims to correlate resistome with phenotypic antimicrobial resistance and virulome with pathogenicity in Klebsiella spp. The present study aimed to perform complete genome sequences of Klebsiella spp. and to analyse the correlation of resistome with phenotypic antimicrobial resistance and virulome with pathogenicity. To understand the resistome, pangenome and virulome in the Klebsiella spp, the ResFinder, CARD, IS Finder, PlasmidFinder, PHASTER, Roary, VFDB were used. The phenotypic susceptibility profiling identified the uropathogenic kp3 to exhibit multi drug resistance. The resistome and in vitro antimicrobial profiling showed concordance with all the tested antibiotics against the study strains. Hypermucoviscosity was not observed for any of the test isolates; this phenotypic character matches perfectly with the absence of rmpA and magA genes. To the best of our knowledge, this is the first report on the presence of ste, stf, stc and sti major fimbrial operons of Salmonella enterica serotype Typhimurium in K. pneumoniae genome. The study identifies the discordance of virulome and virulence in Klebsiella spp. The complete genome analysis and phenotypic correlation identify uropathogenic K. pneumoniae kp3 as a carbapenem-resistant and virulent pathogen. The Pangenome of K. pneumoniae was open suggesting high genetic diversity. Diverse K serotypes were observed. Sequence typing reveals the prevalence of K. pneumoniae high-risk clones in UTI catheterised patients. The study also highlights the concordance of resistome and in vitro susceptibility tests. Importantly, the study identifies the necessity of virulome and phenotypic virulence markers for timely diagnosis and immediate treatment for the management of high-risk K. pneumoniae clones.

Virulence Factors in Klebsiella pneumoniae: A Literature Review

Klebsiella pneumoniae, a member of the autochthonous human gut microbiota, utilizes a variety of virulence factors for survival and pathogenesis. Consequently, it is responsible for several human infections, including urinary tract infections, respiratory tract infections, liver abscess, meningitis, bloodstream infections, and medical device-associated infections. The main studied virulence factors in K. pneumoniae are capsule-associated, fimbriae, siderophores, Klebsiella ferric iron uptake, and the ability to metabolize allantoin. They are crucial for virulence and were associated with specific infections in the mice infection model. Notably, these factors are also prevalent in strains from the same infections in humans. However, the type and quantity of virulence factors may vary between strains, which defines the degree of pathogenicity. In this review, we summarize the main virulence factors investigated in K. pneumoniae from different human infections. We also cover the specific identification genes and their prevalence in K. pneumoniae, especially in hypervirulent strains.

Molecular Characteristics of Virulence Genes in Carbapenem-Resistant and Carbapenem-Sensitive Klebsiella Pneumoniae in Relation to Different Capsule Serotypes in Ningbo, China

Background

Klebsiella pneumoniae (KP) is a common nosocomial pathogen. Capsules are an important component of KP's virulence, among which the K1, K2, K5, K20, K54, and K57 serotypes are predominant and exhibit varying degrees of virulence.

Methods

The capsule and virulence genes of 150 carbapenem-resistant Klebsiella pneumoniae (CRKP) and 213 carbapenem-sensitive Klebsiella pneumoniae (CSKP) isolates were examined by polymerase chain reaction (PCR). The isolates were tested for hypermucoviscosity by string tests. Phylogenetic relationships between KP isolates were analyzed using multilocus sequence typing (MLST) and a Galleria mellonella infection model confirmed the differences in virulence.

Results

A total of 111 of 363 isolates of KP were detected, the highest detected serotypes were K1, K5, and K2, and CSKP was detected more frequently than CRKP. There was a greater prevalence of K1 and K2 serotypes in CSKP, while in CRKP, K5 serotypes were more prevalent. K1 isolates had the highest detection rates for hypermucoviscosity Klebsiella pneumoniae (hmKP) and hypervirulent Klebsiella pneumoniae (hvKP), and carried the most virulence genes. K54 isolates had the lowest detection rate of hmKP while K5 isolates had the lowest detection rate of hvKP and carried the fewest virulence genes. MLST results for serotypes K1, K20, and K57 showed significant homogeneity, while those for serotypes K2, K5, and K54 showed diversity. The Galleria mellonella infection model showed that the K1 serotype was the most virulent and the K54 serotype was the weakest.

Conclusion

CSKP isolates were detected more frequently than CRKP isolates for capsular serotype detection. K1 isolates had the most virulence gene and strongest virulence, K5 isolates carried the fewest virulence genes, and K54 isolates had the weakest virulence. Furthermore, significant homogeneity was observed among K1, K20, and K57 isolates.

Clinical and Microbiologic Analysis of Klebsiella pneumoniae Infection: Hypermucoviscosity, Virulence Factor, Genotype, and Antimicrobial Susceptibility

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.

Bacterial Infections in Intensive Care Units: Epidemiological and Microbiological Aspects

Intensive care units constitute a critical setting for the management of infections. The patients' fragilities and spread of multidrug-resistant microorganisms lead to relevant difficulties in the patients' care. Recent epidemiological surveys documented the Gram-negative bacteria supremacy among intensive care unit (ICU) infection aetiologies, accounting for numerous multidrug-resistant isolates. Regarding this specific setting, clinical microbiology support holds a crucial role in the definition of diagnostic algorithms. Eventually, the complete patient evaluation requires integrating local epidemiological knowledge into the best practice and the standardization of antimicrobial stewardship programs. Clinical laboratories usually receive respiratory tract and blood samples from ICU patients, which express a significant predisposition to severe infections. Therefore, conventional or rapid diagnostic workflows should be modified depending on patients' urgency and preliminary colonization data. Additionally, it is essential to complete each microbiological report with rapid phenotypic minimum inhibitory concentration (MIC) values and information about resistance markers. Microbiologists also help in the eventual integration of ultimate genome analysis techniques into complicated diagnostic workflows. Herein, we want to emphasize the role of the microbiologist in the decisional process of critical patient management.

Differences in molecular characteristics and expression of virulence genes in carbapenem-resistant and sensitive Klebsiella pneumoniae isolates in Ningbo, China

Background

In recent years, Klebsiella pneumoniae has attracted attention because of its increasing drug resistance. At the same time, the migration and pathogenicity caused by its virulence genes also bring many difficulties to the diagnosis and treatment of clinical infections. However, it is currently unclear whether there are differences in virulence and pathogenicity with changes in drug resistance.

Objective

To understand the differences in molecular characteristics and expression of virulence genes in carbapenem-resistant Klebsiella pneumoniae (CRKP) and carbapenem-sensitive Klebsiella pneumoniae (CSKP).

Methods

Using polymerase chain reaction (PCR), we examined capsule polysaccharide-related genes and virulence genes in 150 clinical isolates of CRKP and 213 isolates of CSKP from the local area in Ningbo, China. Multilocus sequence typing (MLST) was used to analyze the phylogenetic relationships of clinical Klebsiella pneumoniae isolates. Furthermore, real-time quantitative PCR (RT-qPCR) was used to analyze the expression differences of common virulence genes in CSKP and CRKP, and the virulence was further verified by the larval model of Galleria mellonella.

Results

The study found that the detection rates of genes rmpA, iroB, peg-344, magA, aerobactin, alls, kfu, and entB were significantly higher in CSKP compared to CRKP. The capsule gene types K1 and K2 were more common in CSKP, while K5 was more common in CRKP. Hypervirulent Klebsiella pneumoniae (hvKP) was predominantly from CSKP. CRKP strains exhibited noticeable homogeneity, with ST11 being the predominant sequence type among the strains. CSKP strains showed greater diversity in ST types, but ST23 was still the predominant sequence type. Carbapenem-sensitive hypervirulent Klebsiella pneumoniae (CS-hvKP) had higher expression of rmpA and rmpA2 genes compared to carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP). In the wax moth virulence model, the survival rate of CS-hvKP was significantly lower than that of CR-hvKP.

Conclusion

There is a significant difference in the distribution of virulence genes between CSKP and CRKP, with CSKP carrying a significantly greater number of virulence genes. Furthermore, compared to CSKP, CRKP strains exhibit noticeable homogeneity, with ST11 being the predominant sequence type among the strains. Additionally, in terms of virulence gene expression efficiency and virulence, CSKP is significantly higher than CRKP.

Clinical and Genomic Characterization of a Cohort of Patients With Klebsiella pneumoniae Bloodstream Infection

BACKGROUND

The clinical and microbial factors associated with Klebsiella pneumoniae bloodstream infections (BSIs) are not well characterized. Prior studies have focused on highly resistant or hypervirulent isolates, limiting our understanding of K. pneumoniae strains that commonly cause BSI. We performed a record review and whole-genome sequencing to investigate the clinical characteristics, bacterial diversity, determinants of antimicrobial resistance, and risk factors for in-hospital death in a cohort of patients with K. pneumoniae BSI.

METHODS

We identified 562 patients at Massachusetts General Hospital with K. pneumoniae BSIs between 2016 and 2022. We collected data on comorbid conditions, infection source, clinical outcomes, and antibiotic resistance and performed whole-genome sequencing on 108 sequential BSI isolates from 2021 to 2022.

RESULTS

Intra-abdominal infection was the most common source of infection accounting for 34% of all BSIs. A respiratory tract source accounted for 6% of BSIs but was associated with a higher in-hospital mortality rate (adjusted odds ratio, 5.4 [95% confidence interval, 2.2-12.8]; P < .001 for comparison with other sources). Resistance to the first antibiotic prescribed was also associated with a higher risk of death (adjusted odds ratio, 5.2 [95% confidence interval, 2.2-12.4]; P < .001). BSI isolates were genetically diverse, and no clusters of epidemiologically and genetically linked cases were observed. Virulence factors associated with invasiveness were observed at a low prevalence, although an unexpected association between O-antigen type and the source of infection was found.

CONCLUSIONS

These observations demonstrate the versatility of K. pneumoniae as an opportunistic pathogen and highlight the need for new approaches for surveillance and the rapid identification of patients with invasive antimicrobial-resistant K. pneumoniae infection.

Whole proteome analysis of MDR Klebsiella pneumoniae to identify mRNA and multiple epitope based vaccine targets against emerging nosocomial and lungs associated infections

Klebsiella pneumonia is a Gram negative facultative anaerobic bacterium involved in various community-acquired pneumonia, nosocomial and lungs associated infections. Frequent usage of several antibiotics and acquired resistance mechanisms has made this bacterium multi-drug resistance (MDR), complicating the treatment of patients. To avoid the spread of this bacterium, there is an urgent need to develop a vaccine based on immuno-informatics approaches that is more efficient than conventional method of vaccine prediction or development. Initially, the complete proteomic sequence of K. pneumonia was picked over for specific and prospective vaccine targets. From the annotation of the whole proteome, eight immunogenic proteins were selected, and these shortlisted proteins were interpreted for CTL, B-cells, and HTL epitopes prediction, to construct mRNA and multi-epitope vaccines. The Antigenicity, allergenicity and toxicity analysis validate the vaccine's design, and its molecular docking was done with immuno-receptor the TLR-3. The docking interaction showed a stronger binding affinity with a minimum energy of -1153.2 kcal/mol and established 23 hydrogen bonds, 3 salt bridges, 1 disulfide bond, and 340 non-binding contacts. Further validation was done using In-silico cloning which shows the highest CAI score of 0.98 with higher GC contents of 72.25% which represents a vaccine construct with a high value of expression in E. coli. Immune Simulation shows that the antibodies (IgM, IgG1, and IgG2) production exceeded 650,000 in 2 to 3 days but the response was completely neutralized in the 5th day. In conclusion, the study provides the effective, safe and stable vaccine construct against Klebsiella pneumonia, which further needs in vitro and in vivo validations.Communicated by Ramaswamy H. Sarma.

"Superbugs" with hypervirulence and carbapenem resistance in Klebsiella pneumoniae: the rise of such emerging nosocomial pathogens in China

Although hypervirulent Klebsiella pneumoniae (hvKP) can produce community-acquired infections that are fatal in young and adult hosts, such as pyogenic liver abscess, endophthalmitis, and meningitis, it has historically been susceptible to antibiotics. Carbapenem-resistant K. pneumoniae (CRKP) is usually associated with urinary tract infections acquired in hospitals, pneumonia, septicemias, and soft tissue infections. Outbreaks and quick spread of CRKP in hospitals have become a major challenge in public health due to the lack of effective antibacterial treatments. In the early stages of K. pneumoniae development, HvKP and CRKP first appear as distinct routes. However, the lines dividing the two pathotypes are vanishing currently, and the advent of carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKP) is devastating as it is simultaneously multidrug-resistant, hypervirulent, and highly transmissible. Most CR-hvKP cases have been reported in Asian clinical settings, particularly in China. Typically, CR-hvKP develops when hvKP or CRKP acquires plasmids that carry either the carbapenem-resistance gene or the virulence gene. Alternatively, classic K. pneumoniae (cKP) may acquire a hybrid plasmid carrying both genes. In this review, we provide an overview of the key antimicrobial resistance mechanisms, virulence factors, clinical presentations, and outcomes associated with CR-hvKP infection. Additionally, we discuss the possible evolutionary processes and prevalence of CR-hvKP in China. Given the wide occurrence of CR-hvKP, continued surveillance and control measures of such organisms should be assigned a higher priority.

Phenotypic and genetic characterization of hypervirulent Klebsiella pneumoniae in patients with liver abscess and ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) and pyogenic liver abscess (PLA) due to Klebsiella pneumoniae infection can trigger life-threatening malignant consequences, however, there are few studies on the strain-associated clinical pathogenic mechanisms between VAP and PLA. A total of 266 patients consist of 129 VAP and 137 PLA were included for analysis in this study. We conducted a comprehensive survey for the two groups of K. pneumoniae isolates, including phenotypic experiments, clinical epidemiology, genomic analysis, and instrumental analysis, i.e., to obtain the genomic differential profile of K. pneumoniae strains responsible for two distinct infection outcomes. We found that PLA group had a propensity for specific underlying diseases, especially diabetes and cholelithiasis. The resistance level of VAP was significantly higher than that of PLA (78.57% vs. 36%, P < 0.001), while the virulence results were opposite. There were also some differences in key signaling pathways of biochemical processes between the two groups. The combination of iucA, rmpA, hypermucoviscous phenotype, and ST23 presented in K. pneumoniae infection is more important and highly prudent for timely treatment. The present study may contribute a benchmark for the K. pneumoniae clinical screening, epidemiological surveillance, and effective therapeutic strategies.

Characterization of novel bacteriophage PSKP16 and its therapeutic potential against β-lactamase and biofilm producer strain of K2-Hypervirulent Klebsiella pneumoniae pneumonia infection in mice model

BACKGROUND

Severe infections caused by β- lactamase producers, hypervirulent Klebsiella pneumoniae (BhvKp) with K2 serotype, highlight emergency need for new therapeutic strategies against this pathogen. We aimed to assess the efficacy of a novel phage, PSKP16, in the treating of pneumonia induced by BhvKp in mice models.

METHOD

Genome sequences of PSKP16 were analyzed, and associated information can be found in NCBI. We applied treatment in two ways: by using mice for immediate and delayed treatments. Moreover, acute pneumonia obtained by BhvKp with intranasal method, was characterized in terms of histopathology of pulmonary lesions, biomarkers of inflammation level, leukocytes cells infiltration extent in mice, and was assessed treatment of them with PSKP16 multiplicity of infection (MOI: 10), either individually or in combination with gentamicin. Assessment of the ability of PSKP16 to inhibit BhvKp biofilm was studied.

RESULTS

PSKP16 was associated with the Drexlerviridae family, and had a genome size of 46,712 bp, and 67 predicted ORFs. Herein, prompt phage administration's efficacy to decrease bacterial load and improve the survival rate in pneumonia models was faster than the synergism model with delay, but both almost displayed similar endpoints. The distribution of BhvKp strains in the lung was consistent with the histopathological findings, simultaneous inflammation, and level of serum tumor necrosis factor-α (TNF α). The phage treatment presented a lack of severe lesions and alveolar edema, reduction of inflammatory cell infiltration, which not only was it not associated with an over-inflammation but also provided a faster correction of blood cell count abnormalities compared to gentamicin. Phage with a high concentration in in vitro model effectively eliminated biofilms.

CONCLUSION

It is essential to raise clinical awareness and management of BhvKp infections, signaled as the next superbug in waiting. The results of our study underscore the importance of PSKP16 as a phage with promising therapeutic potential in treating BhvKp-induced pneumonia.

Genomic Insights Into Molecular Characteristics and Phylogenetic Linkage Between the Cases of Carbapenem-Resistant Klebsiella pneumoniae From a Non-tertiary Hospital in China: A Cohort Study

Background: Carbapenem-resistant Klebsiella pneumoniae (CRKP) strains have been listed as one of the major clinical concerns. Objectives: We investigated CPKP isolates from non-tertiary hospitals to find disseminated clones and analyze extensive phenotypic and genetic diversity in this study. Methods: In this cohort study, a total of 49 CRKP isolates from 3 hospitals in the same region were collected in 2021. The prevalence and antimicrobial susceptibility patterns were analyzed. Clinical data were retrieved from electronic medical record systems. The molecular types, antimicrobial resistance (AMR) profiles, plasmid replicons, and virulence factors were analyzed. The maximum-likelihood phylogenetic tree and transmission networks were constructed using single-nucleotide polymorphisms (SNPs). Results: The median age of patients (N = 49) was 66.0 years, and 85.7% were male. The most common CRKP infection was nosocomial pneumonia (75.5%), followed by bacteremia (10.2%). More than 53% of isolates were resistant to ceftazidime-avibactam (CAZ/AVI). Forty-five isolates were successfully sequenced; the predominant carbapenem-resistant gene was blaKPC-2 (93.3%). The 30-day mortality in our cohort was 24.5%. The most dominant sequence type (ST) was ST11 (60.0%), followed by ST15 (13.3%). Whole genome sequencing (WGS) analysis exhibited dissemination of ST11 strain clones, ST420, and ST15 clones, both within and outside the given hospital. Conclusions: In this surveillance study, several dissemination chains of CRKP were discovered in the hospital and the region, as ST11 was the main epidemic clone. Our findings suggest that effective infection control practices and antimicrobial stewardship are needed in non-tertiary hospitals in China.

Occurrence and Molecular Study of Hypermucoviscous/Hypervirulence Trait in Gut Commensal K. pneumoniae from Healthy Subjects

Hypervirulent Klebsiella pneumoniae (hvKp) is emerging worldwide. Hypermucoviscousity is the characteristic trait that distinguishes it from classic K. pneumoniae (cKp), which enables Kp to cause severe invasive infections. This research aimed to investigate the hypermucoviscous Kp (hmvKp) phenotype among gut commensal Kp isolated from healthy individuals and attempted to characterize the genes encoding virulence factors that may regulate the hypermucoviscosity trait. Using the string test, 50 identified Kp isolates from healthy individuals’ stool samples were examined for hypermucoviscosity and investigated by transmission electron microscopy (TEM). Antimicrobial susceptibility profiles of Kp isolates were determined using the Kirby Bauer disc method. Kp isolates were tested for genes encoding different virulence factors by PCR. Biofilm formation was assayed by the microtiter plate method. All Kp isolates were multidrug-resistant (MDR). Phenotypically, 42% of isolates were hmvKp. PCR-based genotypic testing revealed the hmvKp isolates belonged to capsular serotype K2. All study Kp isolates harbored more than one virulence gene. The genes magA and rmpA were not detected, while the terW gene was present in all isolates. The siderophores encoding genes entB and irp2 were most prevalent in hmvKp isolates (90.5%) and non-hmvKp (96.6%), respectively. hmvKp isolates harbored the genes wabG and uge with rates of 90.5% and 85.7%, respectively. The outcomes of this research highlight the potential health risk of commensal Kp to cause severe invasive diseases, owing to being hmvKp and MDR, and harboring multiple virulence genes. The absence of essential genes related to hypermucoviscosity such as magA and rmpA in hmvKp phenotypes suggests the multifactorial complexity of the hypermucoviscosity or hypervirulence traits. Thus, further studies are warranted to verify the hypermucoviscosity-related virulence factors among pathogenic and commensal Kp in different colonization niches.

Relationship Between Drug Resistance Characteristics and Biofilm Formation in Klebsiella Pneumoniae Strains

Objective

To conduct epidemiological analysis of Klebsiella pneumoniae (K. pneumoniae) with hypervirulence, and to investigate its drug resistance phenotype, Extended-spectrum β-lactamase (ESBLs) gene, virulence factor, capsular serotype and biofilm formation, so as to provide theoretical basis for further understanding of the drug resistance mechanism of K. pneumoniae with hypervirulence.

Methods

K. Pneumoniae were isolated from clinical samples collected from inpatients. All strains were identified by VITEK2 Compact using fully automatic microbial analyzer, the minimal inhibitory concentration (MIC) of antibiotics was determined by microbroth dilution test. The double disk diffusion method was used to detect the production of ESBLs, modified carbapenem inactivation method (mCIM) was used to detect the production of carbapenemase, and hypermucoviscosity phenotype was detected by wire drawing test. PCR was used to detect ESBLs gene, virulence factor and capsular serotype. Crystal violet staining was used to detect the ability of biofilm formation.

Results

The ESBLs genes detected in this study included strains blaTEM 35 (36.5%), blaSHV 51 (53.1%), and blaCTX-M 49 (51.0%). Most strains carried multiple ESBLs genes, but not all of them produce ESBLs. K1 and K2 accounted for 14.6% and 11.5% respectively. Most (91.7%) strains carried the fimH gene, and the other virulence genes were ybtS (53.1%), entB (46.9%), rmpA (41.7%), aerobactin (32.3%), allS (15.6%), kfu (15.6%). Of all the Klebsiella pneumoniae strains, 33 (34.4%) exhibited ESBLs phenotype, 16 (16.7%) were carbapenemase-producing, and 20 (20.8%) with ESBLs phenotype tested were resistant to all four drugs. The correlation between ESBLs-producing strains and biofilm formation was significantly increased compared to strains without ESBLs phenotype (P=0.035).

Conclusion

Compared to hypervirulent Klebsiella pneumoniae (hvKP), classical Klebsiella pneumoniae (cKP) has a tendency to acquire antibiotic resistance. Our study showed that genes encoding rmpA, K1 or K2, and kfu were highly associated with hvKP.

Phenotypic and Genomic Characterization of Nine String-Positive Carbapenem-Resistant Acinetobacter baumannii Isolates from Israel

A positive "string test" indicates the ability of bacterial colonies grown on agar plates to form viscous strings of >5 mm when stretched. This phenotype is strongly associated with hypervirulence in Klebsiella pneumoniae but has never been described in carbapenem-resistant Acinetobacter baumannii (CRAB), an emerging human pathogen of high clinical significance. In this work, we screened 1,000 CRAB isolates, among which we identified and characterized 9 string-positive CRAB (stCRAB) isolates. Phenotypic and genotypic analyses revealed that the isolates were not phylogenetically related and possessed different antibiotic resistance and virulence profiles. Transmission electron microscopy (TEM) showed the presence of capsule in string-positive isolates. String-positive isolates were more motile but did not form more biofilm than non-string-positive isolates. They were less virulent in a murine thigh fitness model and a Galleria mellonella survival assay. In conclusion, here, we describe string-positive A. baumannii isolates and their phenotypic and molecular characteristics. We found that unlike K. pneumoniae, stCRAB isolates were not associated with increased virulence. IMPORTANCE Acinetobacter baumannii has been considered a major health care threat in recent years. Despite many efforts, the pathogenesis and molecular mechanism of A. baumannii virulence remain poorly understood. Moreover, the plasticity of its genome frequently gives rise to new and more virulent isolates. Our current study is of significant importance as it concerns a previously undescribed A. baumannii phenotype. The string-positive phenotype is strongly associated with increased fitness and virulence in other Gram-negative bacteria such as K. pneumoniae. Although no clear correlation with virulence or fitness was found in our 9 stCRAB isolates, this could have been due to the limited statistical power of our research. We suggest that this phenotype should be taken into consideration as due to its genome plasticity, the next change can give rise to string-positive and hypervirulent strains, as is known for K. pneumoniae. Additional future research is needed regarding its possible consequences.

Evaluation of biosynthesized silver nanoparticles effects on expression levels of virulence and biofilm-related genes of multidrug-resistant Klebsiella pneumoniae isolates

The emergence of multidrug-resistant (MDR) strains of Klebsiella pneumoniae is associated with high morbidity and mortality due to limited treatment options. This study attempts to biologically synthesize silver nanoparticles (AgNPs) and investigate their effect on expression levels of virulence and biofilm-related genes in clinically isolated K. pneumoniae. In this study, biofilm formation ability, antibiotic resistance pattern, extended-spectrum β-lactamases (ESBLs), and carbapenemases production were investigated for 200 clinical isolates of K. pneumoniae using phenotypic methods. Polymerase chain reaction (PCR) was used to detect virulence and biofilm-related genes, ESBL-encoding genes, and carbapenem resistance genes. AgNPs were synthesized using the bio-reduction method. The antibacterial effects of AgNPs were investigated by microdilution broth. In addition, the cytotoxic effect of AgNPs on L929 fibroblast cell lines was determined. The effects of AgNPs on K. pneumoniae virulence and biofilm-related genes (fimH, rmpA, and mrkA) were determined using quantitative real-time PCR. Thirty percent of the isolates produced a strong biofilm. The highest and lowest levels of resistance were observed against amoxicillin/clavulanic acid (95.4%) and tigecycline (96%), respectively. About 31% of isolates were considered positive for carbapenemases, and 75% of the isolates produced an ESBLs enzyme. Different frequencies of mentioned genes were observed. The synthesized AgNPs had a spherical morphology and varied in size. AgNPs inhibited the growth of MDR K. pneumoniae at 128 µg/ml. In addition, AgNPs downregulated the expression of fimH, rmpA, and mrkA genes by 10, 7, and 14-fold, respectively (p < 0.05), also exerted no cytotoxic effect on L929 fibroblast cell lines. It was revealed that AgNPs lead to a decrease in expression levels of virulence and biofilm-related genes; therefore, it was concluded that AgNPs had an excellent antibacterial effect on MDR K. pneumoniae.

Determination of Mutational Timing of Colistin-Resistance Genes through Klebsiella pneumoniae Evolution

The emergence and dissemination of carbapenem-resistant Klebsiella pneumoniae (KP), one of the carbapenem-resistant Enterobacteriaceae (CRE), is now an emerging cause of antibiotic-resistant nosocomial infections associated with high rates of morbidity and mortality. Colistin, or polymyxin E, is a last-resort peptide antibiotic used to treat multidrug-resistant (MDR) Gram-negative bacterial infections including KP. Unfortunately, resistance to colistin is rising with increasing use in the clinical setting. Although clinical evidence links certain mutations to colistin resistance (COL-R) in KP, the origination and association of the mutations remain unclear. We hypothesize that the timing of COL-R mutations influences the development and progression of KP resistance to colistin. We performed planktonic and biofilm in vitro experimental evolutions of KP strain ATCC 43816 under increasing colistin concentrations to characterize the temporal regulation of critical COL-R mutations throughout COL-R progression. The resistance generation and mutation profiles of independently evolved bacterial populations with different lifestyles were compared. Genes with various functions theorize the timeline in which key mutations are generated and their roles in the progression of COL-R. Our results aim to advance the research and development of effective therapeutics to treat MDR bacterial infection as the dissemination of CRE continues to be a severe public health threat.

Antibiotic Resistance, Molecular Characteristics and Risk Factors of Carbapenem-Resistant Klebsiella pneumoniae in Clinical Isolates

BACKGROUND

The global epidemic of carbapenem-resistant Klebsiella pneumonia (CRKP) has become a significant public health challenge. This study aimed to investigate the antibiotic resistance and molecular characteristics of CRKP and the clinical characteristics of infected patients.

METHODS

Sixty-two clinically isolated CRKP strains were collected for the first time from the First Affiliated Hospital of Zhejiang Chinese Medical University in Zhejiang Province. The carbapenemase gene, virulence-associated gene, capsular serotype gene and fenestra protein gene were detected by PCR. Univariate logistic regression and multivariate logistic regression analyses were performed to predict the risk factors for the prognosis of CRKP infection.

RESULTS

All CRKP isolates were resistant to meropenem, piperacillin-tazobactam, and ceftazidime (100%, 62/62), and all but one CRKP isolate was resistant to imipenem and cefepime (96.8%, 61/62). The rate of colistin resistance was the lowest (11.9%, 8/62). For CRKP in the ICU, the rates of resistance to various antibiotics were significantly higher than those in general ward patients. Fifty strains carried the carbapenemase gene bla KPC, and 3 strains carried both the bla KPC and bla NDM genes. The virulence genes uge, wabG, ycf, entB, ureA and fimH were detected in more than 90% of the 62 CRKP strains. Two strains had Ompk35, Ompk36 and Hcp gene deletions. The bla KPC, rmpA and rmpA2 genes had the highest positive rate in blood samples, and bla NDM had the highest positive rate in stool samples. Multivariate analysis showed that pulmonary disease affected the prognosis of CRKP infection.

CONCLUSION

The prevalence and molecular characteristics of CRKP clinical isolates in Zhengjiang Province in China were described, and the antibiotic resistance rate was higher. Additionally, relevant genes of CRKP strains and clinical characteristics of patients are related to the progression and prognosis of CRKP infection.

Emergence of a NDM-1-producing ST25 Klebsiella pneumoniae strain causing neonatal sepsis in China

Carbapenem-resistant Klebsiella pneumoniae (CRKP) seriously threaten the efficacy of modern medicine with a high associated mortality rate and unprecedented transmission rate. In this study, we isolated a clinical K. pneumoniae strain DY1928 harboring bla_NDM-1 from a neonate with blood infection. Antimicrobial susceptibility testing indicated that DY1928 was resistant to various antimicrobial agents, including meropenem, imipenem, ceftriaxone, cefotaxime, ceftazidime, cefepime, piperacillin-tazobactam, and amoxicillin-clavulanate. S1 nuclease-pulsed field gel electrophoresis (S1-PFGE), southern blot and conjugation experiment revealed that the bla_NDM-1 gene was located on a conjugative plasmid of IncA/C2 type with a 147.9 kb length. Whole-genome sequencing showed that there was a conservative structure sequence (bla_NDM-1-ble-trpF-dsbD) located downstream of the bla_NDM-1 gene. Multilocus sequence typing (MLST) classified DY1928 as ST25, which was a hypervirulent K. pneumoniae type. Phylogenetic analysis of genomic data from all ST25 K. pneumoniae strains available in the NCBI database suggested that all bla_NDM-1 positive strains were isolated in China and had clinical origins. A mouse bloodstream infection model was constructed to test the virulence of DY1928, and 11 K. pneumoniae strains homologous to DY1928 were isolated from the feces of infected mice. Moreover, we found that DY1928 had a tendency to flow from the blood into the intestine in mice and caused multiple organ damage. To our knowledge, this is the first study to report an infection caused by bla_NDM-1-positive ST25 K. pneumoniae in the neonatal unit. Our findings indicated that stricter surveillance and more effective actions were needed to reduce the risk of disseminating such K. pneumoniae strains in clinical settings, especially in neonatal wards.

Hypervirulent carbapenem-resistant Klebsiella pneumoniae causing highly fatal meningitis in southeastern China

Klebsiella pneumoniae (K. pneumoniae) is one of the most common causes of bacterial meningitis worldwide. The purpose of this study was to investigate the clinical and microbiological characteristics of K. pneumoniae meningitis, as well as the association of antimicrobial resistance, virulence, and patient prognosis. The clinical data of patients with K. pneumoniae meningitis from 2014 to 2020 in a tertiary teaching hospital were retrospectively evaluated. Antimicrobial susceptibility profiles were performed by the agar dilution method and broth microdilution method. The isolates were detected for virulence-related genes, resistance genes, capsular serotypes, and molecular subtypes. A total of 36 individuals with K. pneumoniae meningitis were included in the study, accounting for 11.3% (36/318) of all cases of bacterial meningitis. Of the 36 available isolates, K1, K47, and K64 were tied for the most frequent serotype (7/36, 19.4%). MLST analysis classified the isolates into 14 distinct STs, with ST11 being the most common (14/36, 38.9%). Carbapenem resistance was found in 44.4% (16/36) of the isolates, while hypervirulent K. pneumoniae (HvKP) was found in 66.7% (24/36) of the isolates. The isolates of hypervirulent carbapenem-resistant K. pneumoniae (Hv-CRKP) were then confirmed to be 36.1% (13/36). Importantly, individuals with meningitis caused by Hv-CRKP had a statistically significant higher mortality than the other patients (92.3%, 12/13 vs. 56.5%, 13/23; P < 0.05). The high percentage and fatality of K. pneumoniae-caused meningitis, particularly in Hv-CRKP strains, should be of significant concern. More effective surveillance and treatment solutions will be required in future to avoid the spread of these life-threatening infections over the world.

Epidemiological characteristics and molecular evolution mechanisms of carbapenem-resistant hypervirulent Klebsiella pneumoniae

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP), a type of Klebsiella pneumoniae (KP) that exhibits hypervirulence and carbapenem resistance phenotypes, can cause severe infections, both hospital- and community-acquired infections. CR-hvKP has brought great challenges to global public health and is associated with significant morbidity and mortality. There are many mechanisms responsible for the evolution of the hypervirulence and carbapenem resistance phenotypes, such as the horizontal transfer of the plasmid carrying the carbapenem resistance gene to hypervirulent Klebsiella pneumoniae (hvKP) or carbapenemase-producing Klebsiella pneumoniae (CRKP) acquiring a hypervirulence plasmid carrying a virulence-encoding gene. Notably, KP can evolve into CR-hvKP by acquiring a hybrid plasmid carrying both the carbapenem resistance and hypervirulence genes. In this review, we summarize the evolutionary mechanisms of resistance and plasmid-borne virulence as well as the prevalence of CR-hvKP.

Phenotypic Characterization of Virulence Factors and Antibiogram of Klebsiella pneumoniae Isolates from Various Clinical Samples – A Cross Sectional Study

K. pneumoniae is known to cause hospital and community acquired infections. It is usually associated with upper & lower respiratory infections, septicaemia, urinary tract infection, wound infections, neonatal sepsis, meningitis, and endophthalmitis. The virulence factors play a role in its existence in different environmental conditions and therefore help in establishing Klebsiella pneumoniae infection in the human body. Multi drug resistant Klebsiella pneumoniae is an increasing threat to human health. Klebsiella pneumoniae is one of the species recognized as nosocomial pathogens that exhibit multidrug resistance and virulence in ESKAPE group as per WHO. The study was conducted to determine the various virulence factors & the antimicrobial pattern of Klebsiella pneumoniae isolates. A cross sectional observational study, conducted in Department of Microbiology of R.L. Jalappa Hospital and Research Centre, Kolar, Sample size of 150. All 150 Klebsiella pneumoniae isolates collected for the study, The Klebsiella pneumoniae isolates which were positive for various virulence factors were as follows on hemolysis 7(4.66%), capsule 150(100%), Hypermucoviscosity formation 66(44%), biofilm production 81(54%), siderophore production 110(73.33%), protease 135(90%), gelatinase 126(84%), lipase production 119(79.33%), lecithinase activity 82(54.66%). The drug resistance klebsiella pneumoniae were as follows: ESBL producers 24(16.67%), AmpC producers were 22(14.67%), MDR 116(74.20%), extensive drug resistant (XDR) 30(20%), pan drug resistant (PDR) 42(28%), Carbapenem resistance 65.33% reported. The increasing coexistence of virulence factors & antimicrobial resistance pattern is of particular concern. Hence active surveillance for antimicrobial resistance & virulence determinants is imperative now to implement effective control measures to prevent the rapid spread of drug resistance.

Characterization of Hypervirulent Klebsiella pneumoniae (Hv-Kp): Correlation of Virulence with Antimicrobial Susceptibility

Introduction

Hypervirulent K. pneumoniae (Hv-Kp) is an emerging variant of classical K. pneumoniae (C-Kp) that exhibits hypermucoviscocity and possesses multiple siderophores as virulence factors and is known to cause serious debilitating infections in immunocompetent individuals. Aim and objective. The aim of this study is to identify C-Kp and Hv-Kp strains and detect their virulence factors and antimicrobial susceptibility patterns.

Materials and Methods

A total of 129 K. pneumoniae isolates from different clinical samples were used for the identification and differentiation of classical K. pneumoniae (C-Kp) and hypervirulent K. pneumoniae (Hv-Kp) to correlate their virulence with antimicrobial susceptibility patterns and identify their risk factors. Hypermucoviscosity was determined by a string test (>5 mm of string length). The aerobactin gene was detected by PCR. Results and Conclusion. In total, 13.9% (18/129) were Hv-Kp and 86.1% (111/129) were C-Kp. Only 50% (9/18) of the Hv-Kp isolates were hypermucoviscous. C-Kp was significantly more resistant to antimicrobials than Hv-Kp. Among C-Kp, 75.7% were ESBL producers and 76.6% were multidrug resistant while in Hv-Kp, 44.44% were both ESBL producers and multidrug-resistant which is statistically significant (P < 0.01). Diabetes was a common risk factor for C-Kp infections whereas, respiratory disorders like COPD and prolonged ICU stay were the risk factors for Hv-Kp infections. The mortality rate among patients with Hv-Kp infections (87.5%) was significantly high when compared to that of C-Kp infections (35.7%) (P < 0.001). A majority of hypermucoviscous K. pneumoniae isolates were multidrug resistant (65.2%). Although the prevalence of Hv-Kp infections was low, a high percentage of them were multidrug resistant with a significantly high mortality rate. Hence, it is important to efficiently identify Hv-Kp strains from clinical samples and determine their antimicrobial susceptibility patterns, so as to provide immediate and effective treatment and to prevent possible outbreaks.

Molecular and clinical characterization of hypervirulent Klebsiella pneumoniae isolates from individuals with urinary tract infections

Despite being a significant public health concern, hypervirulent Klebsiella pneumoniae (hvKP) has rarely been investigated in urinary tract infections (UTIs). To investigate the molecular and clinical characterization of hvKP in UTIs, we collected K. pneumoniae strains and clinical data from patients with UTIs. HvKP was confirmed by virulence-related genes and the Galleria mellonella model and sequenced by next-generation sequencing. Our data showed that 30/121 isolates were hvKP [17 carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKP), 12 hvKP, and 1 extended-spectrum β-lactamase-producing hvKP]; these had higher resistance to most antimicrobials and were more likely to cause complicated UTIs (cUTIs). Notably, the mucoid phenotype-regulating genes _prmpA and _prmpA2 were truncated in 3 and 19 hvKP, respectively. Eight serotypes were detected and divided into three groups: K64 (n = 17), K1/K2 (n = 6), and others (n = 7). Furthermore, 16/17 K64 hvKP isolates were CR-hvKP but with a lower mortality rate of G. mellonella as the truncated _prmpA/_prmpA2 incurred high fitness cost to the isolates. In addition, all K64 isolates belonged to ST11 with the same cluster, and in two of these strains (KP88 and KP92) bla_KPC-2 gene was successfully transferred to EC600. Genetic environment analysis showed that IS26–tnpR–ISKpn27–bla_KPC−2–ISKpn6 may be the core structure in the horizontal transfer of bla_KPC-2. The highest mortality rate among the infected G. mellonella was observed in the K1/K2 group. In conclusion, hvKP had a higher resistance rate and was more likely to lead to cUTIs. Convergence of hypervirulence and carbapenem resistance in a transmissible ST11 clone of K64 K. pneumoniae was mediated by a plasmid in UTIs. Therefore, surveillance of hvKP in UTIs should be strengthened.

Bacteriological characteristics of hypervirulent Klebsiella pneumoniae rmpA gene (hvKp-rmpA)-harboring strains in the south of Iran

Background and Objectives

To provide data on the occurrence of classical K. pneumoniae (cKp) and hypervirulent Klebsiella pneumoniae (hvKp) strains harboring the gene encoding regulator of mucoid phenotype A (rmpA) and evaluated characteristics of virulence biomarkers, carbapenemase, extended-spectrum-β-lactamase (ESBL)-producing, and capsule serotypes among K. pneumoniae clinical isolates collected in the south of Iran.

Materials and Methods

A total of 400 K. pneumoniae isolates were collected. First, the K. pneumoniae isolates were screened for rmpA gene by PCR, and then they were characterized for the presence of the virulence genes (pagO, iucA, iroB, luxR), capsular serotype genes (K1, K2, K5, K20, K54, and K57), carbapenemase (bla _NDM, bla _IMP, bla _VIM, bla _KPC, bla _SPM, bla _OXA-48, and bla _OXA-181) and ESBL (bla _CTX-M, bla _SHV and bla _TEM) genes. For all K. pneumoniae isolates phenotypic tests include of string test and disk diffusion test were performed.

Results

In total, 16 (4%) hvKp-rmpA+ and 384 (96%) cKp were observed. Of hvKp-rmpA+ strains, 16 (100%) were carried pagO, iroB, and luxR genes, and 13 (81.3%) strains harbored iucA gene. The most prevalent capsular type genes were K1 (62%) and K2 (19%) in hvKp-rmpA+ strains. The incidence of bla _SHV gene in hvKp and cKp was 94% (15/16) and 87.5% (336/384), respectively. The cKp isolates carried bla _NDM (30/384; 7.8%) gene.

Conclusion

Our data suggest that the incidence of hvKp was low. Also, hvKp-rmpA+ strains have less antibiotic resistance than cKp isolates. Serotypes K1 and K2, and bla _SHV gene were strongly associated with hvKp-rmpA+.

Epidemiological Features of Klebsiella pneumoniae Infection in the Hepatobiliary System of Patients in Yantai, China, Based on Clinical and Genetic Analyses

Purpose

To investigate the epidemiological features of Klebsiella pneumoniae infection of the hepatobiliary system of patients in Yantai, China.

Methods

This retrospective study was conducted from January to December 2019 in Yantai Yuhuangding Hospital. Patients for whom K. pneumoniae was isolated from the hepatobiliary system were considered for inclusion. The clinical features and genetic analyses were conducted to explore the epidemiological characteristics.

Results

A total of 88 cases were enrolled, including 69 cases of hypervirulent K. pneumoniae (hvKP) and 19 cases of classical K. pneumoniae (cKP). Community-acquired infections, fever, liver abscess, and C-reactive protein (CRP) and procalcitonin (PCT) levels were significantly higher, while biliary tract disease was lower in the hvKP group compared with the cKP group. Among the 69 hvKP infections, 61 developed a liver abscess. Community-acquired infections, fever, and CRP and PCT levels were higher, whereas biliary tract disease and malignancy were lower in the liver abscess group compared with the non-liver abscess group. All strains were susceptible to the majority of antibiotics tested. All hvKP strains possessed the bla_SHV, oqxA, oqxB and fosA resistance genes. K1 and K2 accounted for 78% of hvKP strains. K1 strains belonged to sequence types ST23 and ST700, whereas K2 strains belonged to ST65, ST86 and ST5212. K1 isolates possessed the most virulence determinants, followed by K2 and non-K1/K2 isolates. K2 isolates lacked the allS gene, which was rare in non K1/K2 isolates, but present in most K1 isolates. The mceG gene was only detected in K1 isolates. AllS and virulence determinants were significantly more prevalent in the liver abscess group than in the non-liver abscess group.

Conclusion

The prevalence of hvKP among K. pneumoniae infections of the hepatobiliary system is high in Yantai, China. Greater vigilance of hvKP infection is required in clinical and microbiological laboratories.

Clinical and Molecular Analysis of ST11-K47 Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae: A Strain Causing Liver Abscess

Klebsiella pneumoniae has been the predominant pathogen of liver abscess, but ST11-K47 carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) has rarely been studied as the causative organism. We identified an ST11-K47 CR-hvKP (HvKp-su1) from the drainage fluid of a liver abscess in a Chinese man who was diagnosed with liver abscess combined with diabetes, pneumonia, pleural infection, abdominal abscess, and splenic abscess. HvKp-su1 was non-hypermucoviscous and lacked the magA and rmpA genes and pLVPK plasmid but exhibited high virulence, with a high mortality rate (90%) to wax moth larvae (G. mellonella), similar to the hypervirulent Klebsiella pneumoniae ATCC43816 (91.67%). Whole-genome sequencing and bioinformatics analysis indicated that HvKp-su1 possesses a plasmid similar to a type of pLVPK-like plasmid (JX-CR-hvKP-2-P2), which is an uncommon plasmid in CR-hvKP. HvKp-su1 carried multiple resistance genes, including bla_KPC-2. bla_TEM-1, bla_SHV-55, and bla_CTX-M-65; hypervirulence genes such as aerobactin (iutA), salmochelin (iroEN), and yersiniabactin (ybtAEPQSTUX); and the type 3 fimbriae-encoding system (mrkACDF). Moreover, v_5377 and v_5429 (cofT, CFA/III (CS8)) located on plasmid 1 were simultaneously predicted to be virulence genes. After the long-term combination use of antibiotics, the patient successfully recovered. In summary, our study clarified the clinical and molecular characteristics of a rare ST11-K47 CR-hvKP (HvKp-su1), raising great concerns about the emergence of ST11-K47 CR-hvKP with multidrug resistance and hypervirulence, and providing insights into the control and treatment of liver abscess caused by ST11-K47 CR-hvKP.

Early Response of Antimicrobial Resistance and Virulence Genes Expression in Classical, Hypervirulent, and Hybrid hvKp-MDR Klebsiella pneumoniae on Antimicrobial Stress

Klebsiella pneumoniae is an increasingly important hospital pathogen. Classical K. pneumoniae (cKp) and hypervirulent K. pneumoniae (hvKp) are two distinct evolutionary genetic lines. The recently ongoing evolution of K. pneumoniae resulted in the generation of hybrid hvKP-MDR strains. K. pneumoniae distinct isolates (n = 70) belonged to 20 sequence types with the prevalence of ST395 (27.1%), ST23 (18.6%), ST147 (15.7%), and ST86 (7.1%), and 17 capsular types with the predominance of K2 (31.4%), K57 (18.6%), K64 (10.0%), K1 (5.7%) were isolated from patients of the Moscow neurosurgery ICU in 2014-2019. The rate of multi-drug resistant (MDR) and carbapenem-resistant phenotypes were 84.3% and 45.7%, respectively. Whole-genome sequencing of five selected strains belonging to cKp (ST395^K47 and ST147^K64), hvKp (ST86^K2), and hvKp-MDR (ST23^K1 and ST23^K57) revealed bla_SHV, bla_TEM, bla_CTX, bla_OXA-48, and bla_NDM beta-lactamase genes; acr, oqx, kpn, kde, and kex efflux genes; and K. pneumoniae virulence genes. Selective pressure of 100 mg/L ampicillin or 10 mg/L ceftriaxone induced changes of expression levels for named genes in the strains belonging to cKp, hvKp, and hybrid hvKp-MDR. Obtained results seem to be important for epidemiologists and clinicians for enhancing knowledge about hospital pathogens.

Emergence of Colistin Resistance in Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae Under the Pressure of Tigecycline

Colistin and tigecycline are the last options against carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP). Intersecting resistance determinants have been detected between these antibiotics; however, there is only limited evidence of such association. Here, we describe a colistin-resistant CR-hvKP isolated from a patient with severe neonatal bacteremia treated with tigecycline as opposed to colistin before isolation of this strain, providing a clinical clue to colistin resistance under tigecycline pressure. Furthermore, an ST11-K64 KPC-2–producing, colistin-susceptible CR-hvKP strain was subjected to experimental evolution toward colistin resistance under tigecycline and colistin pressure to verify this phenomenon in vitro. The biological impact of acquiring colistin resistance on fitness and virulence was also studied. As expected, the parental strain rapidly developed colistin resistance under both tigecycline and colistin selection. However, different from the colistin resistance mechanism in the clinical strain that was due to an ISKpn26 insertion in the mgrB gene, the mutants in this study developed colistin resistance through a ∼4.4 or ∼4.6 kb deletion including the mgrB locus as well as the kdgR, yobH, yebO, yobF, cspC, ftsI, and rlmA genes. Although the virulence of the colistin-resistant mutants, as determined in the Galleria mellonella model, decreased compared with that of the parent strain, it was still higher than that of NTUH-K2044. This suggests a slight virulence cost when CR-hvKP develops colistin resistance under tigecycline or colistin pressure. Together, our results provide clinical and experimental evidence for the association between colistin resistance and tigecycline pressure in CR-hvKP, highlighting a critical issue in the clinical setting.

Emergence of Tigecycline Nonsusceptible and IMP-4 Carbapenemase-Producing K2-ST65 Hypervirulent Klebsiella pneumoniae in China

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) poses a significant public health challenge worldwide, but research on IMP-producing CR-hvKP and its tigecycline resistance is extremely scarce. We report herein the recovery of two IMP-4–producing, capsular serotype K2, sequence type 65 (K2-ST65), hypervirulent K. pneumoniae isolates (C1672 and C2051), which caused severe and fatal infections in ICU patients, after retrospectively screening 3,285 carbapenem-resistant K. pneumoniae isolates from 26 provinces in China. Notably, C2051 also demonstrated tigecycline nonsusceptibility, mediated by a frameshift mutation in the TetR/AcrR family transcriptional regulator. Both strains harbored bla_IMP-4 and critical plasmid-borne virulence genes (rmpA/rmpA2, iucA, and iroN) and demonstrated high virulence in Galleria mellonella, indicating CR-hvKP. The bla_IMP-4 gene was located on the IncU- and IncN-type plasmids, which showed high stability in C1672 and C2051 after serial passage for 5 days, with retention rates of 87% and 93.7%, respectively. No significant differences in growth rates were observed among the parental strains and the corresponding resistance plasmid-cured mutants (P = 0.5273), suggesting that strains carrying the bla_IMP and virulence plasmids have the potential to exist for a long time without compromising fitness. The genetic environments of the bla_IMP-4 gene in both strains were similar, and it has been inferred that the genetic regions of bla_IMP-4 were inserted into different backbones. Several conjugal transfer genes, such as traO, traE, traN, and traBCD, were identified in the bla_IMP-4-bearing plasmid of C2051, suggesting a higher ability for plasmid transmission. The convergence of IMP carbapenemase and tigecycline nonsusceptibility in a classic hypervirulent K. pneumoniae lineage highlights the need to enhance clinical awareness and epidemiologic surveillance.

IMPORTANCE To date, research on IMP-producing CR-hvKP is extremely scarce. Only one case of urinary tract infection caused by an IMP-6–producing K1-ST23 hypervirulent K. pneumoniae isolate in Japan was recorded, with a limited description of clinical information and genomic features. None of the published studies examined the virulence of the reported strains or the stability and fitness of resistance plasmids or presented a phylogenetic analysis. This dearth of data is notable because CR-hvKP infections are increasingly identified, but critical characteristics of the emerging resistance mediated by IMP carbapenemases in CR-hvKP remain unknown. Here, we report the emergence of two IMP-4 carbapenemase-producing K2-ST65 hypervirulent K. pneumoniae isolates that caused severe and fatal infections in clinical settings in China. Notably, one of them also demonstrated tigecycline nonsusceptibility. These strains carrying bla_IMP and virulence plasmids had the potential to exist for a long time without compromising their fitness, highlighting the urgent need to enhance clinical awareness and epidemiologic surveillance to prevent their dissemination.

Multidrug-Resistant Klebsiella pneumoniae Causing Severe Infections in the Neuro-ICU

The purpose of this study was the identification of genetic lineages and antimicrobial resistance (AMR) and virulence genes in Klebsiella pneumoniae isolates associated with severe infections in the neuro-ICU. Susceptibility to antimicrobials was determined using the Vitek-2 instrument. AMR and virulence genes, sequence types (STs), and capsular types were identified by PCR. Whole-genome sequencing was conducted on the Illumina MiSeq platform. It was shown that K. pneumoniae isolates of ST14^K2, ST23^K57, ST39^K23, ST76^K23, ST86^K2, ST218^K57, ST219^KL125/114, ST268^K20, and ST2674^K47 caused severe systemic infections, including ST14^K2, ST39^K23, and ST268^K20 that were associated with fatal incomes. Moreover, eight isolates of ST395^K2 and ST307^{KL102/149/155} were associated with manifestations of vasculitis and microcirculation disorders. Another 12 K. pneumoniae isolates of ST395^K2,KL39, ST307^{KL102/149/155}, and ST147^K14/64 were collected from patients without severe systemic infections. Major isolates (n = 38) were XDR and MDR. Beta-lactamase genes were identified: bla_SHV (n = 41), bla_CTX-M (n = 28), bla_TEM (n = 21), bla_OXA-48 (n = 21), bla_NDM (n = 1), and bla_KPC (n = 1). The prevalent virulence genes were wabG (n = 41), fimH (n = 41), allS (n = 41), and uge (n = 34), and rarer, detected only in the genomes of the isolates causing severe systemic infections-rmpA (n = 8), kfu (n = 6), iroN (n = 5), and iroD (n = 5) indicating high potential of the isolates for hypervirulence.

Clinical and Molecular Characteristics of Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae Isolates in a Tertiary Hospital in Shanghai, China

Background

The convergence of carbapenem-resistance and hypervirulence in Klebsiella pneumoniae has led to a significant public health challenge. In recent years, there have been more and more reports on carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) isolates.

Materials and Methods

Clinical data of patients infected with CR-hvKP from January 2019 to December 2020 in a tertiary hospital were retrospectively evaluated. The number of isolates of Klebsiella pneumoniae, hypermucoviscous Klebsiella pneumoniae (hmKP), carbapenem-resistant hypermucoviscous Klebsiella pneumoniae (CR-hmKP) and carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) collected during the period of 2 years was calculated. The antimicrobial resistance gene, virulence-associated gene, capsular serotype gene and multilocus sequence typing (MLST) of CR-hvKP isolates were detected by PCR.

Results

During the study period, a total of 1081 isolates of non-repeat Klebsiella pneumoniae were isolated, including 392 isolates of hypermucoviscous Klebsiella pneumoniae (36.3%), 39 isolates of CR-hmKP (3.6%), and 16 isolates of CR-hvKP (1.5%). About 31.2% (5/16) of CR-hvKP were isolated from 2019, and 68.8% (11/16) of CR-hvKP were isolated from 2020. Among the 16 isolates of CR-hvKP, 13 isolates were ST11 and serotype K64, 1 isolate was ST11 and serotype K47, 1 isolate was ST23 and serotype K1, and 1 isolate was ST86 and serotype K2. The virulence-associated genes entB, fimH, rmpA2, iutA, iucA were present in all of 16 CR-hvKP isolates, followed by mrkD (n=14), rmpA (n=13), aerobactin (n=2), allS (n=1). Sixteen CR-hvKP isolates all carry carbapenemase gene bla _KPC-2 and extended-spectrum β-lactamase gene bla _SHV. ERIC-PCR DNA fingerprinting results showed that 16 CR-hvKP isolates were highly polymorphic, and there were significant differences in bands among the isolates, presenting a sporadic state.

Conclusion

Although CR-hvKP was sporadically distributed, it showed an increasing trend year by year. Therefore, clinical attention should be paid, and necessary measures should be taken to avoid the cloning and transmission of superbacterium CR-hvKP.

Virulence Factors in Hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKP) has spread globally since first described in the Asian Pacific Rim. It is an invasive variant that differs from the classical K. pneumoniae (cKP), with hypermucoviscosity and hypervirulence, causing community-acquired infections, including pyogenic liver abscess, pneumonia, meningitis, and endophthalmitis. It utilizes a battery of virulence factors for survival and pathogenesis, such as capsule, siderophores, lipopolysaccharide, fimbriae, outer membrane proteins, and type 6 secretion system, of which the former two are dominant. This review summarizes these hvKP-associated virulence factors in order to understand its molecular pathogenesis and shed light on new strategies to improve the prevention, diagnosis, and treatment of hvKP-causing infection.

Hypervirulent and hypermucoviscous extended-spectrum β-lactamase-producing Klebsiella pneumoniae and Klebsiella variicola in Chile

Convergence of virulence and antibiotic-resistance has been reported in Klebsiella pneumoniae, but not in Klebsiella variicola. We, hereby, report the detection and genomic characterization of hypervirulent and hypermucoviscous K. pneumoniae and K.variicola recovered in Chile from health-care associated infections, which displayed resistance to broad-spectrum cephalosporins. One hundred forty-six K. pneumoniae complex isolates were screened by hypermucoviscosity by the “string test.” Two hypermucoid isolates, one hypermucoviscous K. pneumoniae (hmKp) and one K. variicola (hmKv), were further investigated by whole-genome sequencing. In vivo virulence was analyzed by the Galleria mellonella killing assay. In silico analysis of hmKp UCO-494 and hmKv UCO-495 revealed the presence of multiple antibiotic-resistance genes, such as bla_CTX-M-1, bla_DHA-1 and bla_LEN-25 among others clinically relevant resistance determinants, including mutations in a two-component regulatory system related to colistin resistance. These genetic features confer a multidrug-resistant (MDR) phenotype in both strains. Moreover, virulome in silico analysis confirmed the presence of the aerobactin gene iutA, in addition to yersiniabactin and/or colicin V encoding genes, which are normally associated to high virulence in humans. Furthermore, both isolates were able to kill G. mellonella and displayed higher virulence in comparison with the control strain. In summary, the convergence of virulence and the MDR-phenotype in K. pneumoniae complex members is reported for the first time in Chile, denoting a clinical problem that deserves special attention and continuous surveillance in South America.