Virulence and plasmid transferability of KPC Klebsiella pneumoniae at the Veterans Affairs Healthcare System of New Jersey

Study on Virulence Genes, Drug Resistance and Molecular Epidemiology of Klebsiella pneumoniae with High Virulence in Inner Mongolia, China

Objective

The purpose of this study was to analyse the clinical, microbiological and molecular epidemiological characteristics of patients with pyogenic liver abscess (PLA) caused by Klebsiella pneumoniae (KPN) in Inner Mongolia, China.

Methods

The KPN isolates from 78 KPN-PLA cases admitted to a tertiary teaching hospital in Baotou, Inner Mongolia, from 2016 to 2019 were studied systematically and described comprehensively. The virulence factors, drug resistance and sequence types of KPN in different samples were identified by a wire-drawing test, polymerase chain reaction, a drug susceptibility test and multi-site sequence typing.

Results

There were more male than female KPN-PLA patients (P<0.05). The mortality rate was 2.5%, and KPN-PLA was significantly associated with diabetes mellitus (P<0.05). Most of the KPN isolates in the puncture fluid of patients with KPN-PLA were hypervirulent KPN (HvKP). The positive rate of the KPN-PLA specimens was higher than that of the blood and urine specimens. The KPN isolates of the urine specimens had higher drug resistance than the other two (P<0.05). The hypermucoviscous KPN, aerobic actin (aero) (+), K1 and K2 serotypes accounted for 80.8%, 89.7%, 56.4% and 26.9%, respectively. In addition to ironB (3.8%), the detection rates of virulence factors rmpA, irp2, entB, iucD, aero, wcaG, iutA, kfu, ybtA, iron, fimH and mrkD were higher (69.2%-100.0%). The positive rate of KPN isolates of the KPN-PLA puncture fluid was higher than that of the blood and urine samples (P<0.05). In addition, ST23 was found to be the dominant ST (32.1%) of KPN-PLA in the Baotou region.

Conclusion

In the KPN-PLA specimens, the KPN isolates were more virulent than those in the blood and urine specimens, and a carbapenem-resistant HvKP strain emerged. This research will help improve the understanding of HvKP and provide useful suggestions for KPN-PLA treatments.

Prevalence of High-Risk β-Lactam Resistance Genes in Family Livestock Farms in Danjiangkou Reservoir Basin, Central China

The propagation of antibiotic resistance genes (ARGs) from domestic livestock manure is an unnegligible important environmental problem. There is an increasing need to understand the role of domestic livestock manure in causing antibiotic resistance in the environment to minimize risks to human health. Here, we targeted β-lactam resistance genes (bla genes), primarily discovered in clinical settings, to compare the high-risk ARG profile and their main spreading vectors of 26 family livestock farms in China and analyze the effects of domestic livestock manure on their receiving farmland environments. Results showed that the high-risk bla genes and their spreading carriers were widely prevalent in livestock and poultry manure from family farms. The bla_ampC gene encoding extended-spectrum AmpC β-lactamases, as well as its corresponding spreading carrier (class-1 integron), had the highest occurrence level. The bla gene abundance in family chicken farms was higher than that in family swine and cattle farms, while the bla gene contamination in the feces of laying hens or beef cattle was worse than that in corresponding broiler chickens or dairy cattle. Notably, the application from domestic livestock manure led to substantial emission of bla genes, which significantly increased the abundance of high-risk resistance genes in farmland soil by 12–46 times. This study demonstrated the prevalence and severity of high-risk resistance genes in domestic livestock and poultry manure; meanwhile, the discharge of bla genes also highlighted the need to mitigate the persistence and spread of these elevated high-risk genes in agricultural systems.

Klebsiella pneumoniae Harboring Carbapenemase Genes in Taiwan: Its Evolution over 20 Years, 1998-2019

Klebsiella pneumoniae (K. pneumoniae) is an important pathogen causing various types of human infections in Taiwan. Carbapenemases have increasingly been reported in Enterobacterales in the past two decades. Carbapenemase-producing K. pneumoniae (CPKP), a major resistance concern that has emerged during the last decade, has become a global threat, with its related infections associated with high morbidity and mortality; however, therapeutic options for CPKP-associated infections are limited. Carbapenemases - including K. pneumoniae carbapenemases (KPC)-2, New Delhi metallo-β-lactamase (NDM)-1, Verona integron-encoded metallo-β-lactamase (VIM)-1, imipenemase (IMP)-1, and oxacillinase (OXA)-48 - have been reported worldwide, with a marked prevalence in different countries or areas of the world. Understanding the epidemiology of carbapenemase producers is important for the prevention of their expansion. This review examined the evolution of CPKP in the last two decades to better understand the role of CPKP in Taiwan. It discovered that the endemicity has changed from IMP-8, NDM-1 and VIM-1 to the most common KPC-2 and rapidly emerging OXA-48. Resistance epidemiology, genetic background, virulence factors, therapy, and outcomes are discussed in this paper.

Characterisation of virulence genes associated with pathogenicity in Klebsiella pneumoniae

Purpose

This study was undertaken to characterise the virulence factors in clinical strains of Klebsiella pneumoniae and analyse their association with various infections caused and also to determine the association between virulence factors and antimicrobial resistance profile.

Materials and Methods

A total number of 370 clinically significant, non-duplicate isolates of K. pneumoniae isolated from both hospitalised patients and patients attending clinics were included in this study. Polymerase chain reaction (PCR) was carried out for the detection of various virulence genes such as mucoviscosity-associated gene A (magA), gene associated with allantoin metabolism (allS), Klebsiella ferric iron uptake(Kfu), capsule-associated gene A (K2A), regulator of mucoid phenotype A (rmpA), enterobactin (entB), yersiniabactin (YbtS), aerobactin, Fimbrial adhesin (FimH) and uridine-diphosphate galacturonate 4-epimerase (uge). Antimicrobial susceptibility testing and PCR-based detection of beta-lactamase-encoding genes such as extended-spectrum beta-lactamases, AmpCs and carbapenemases were performed. Univariate analysis was done to find the association between virulence genes and mortality.

Results

The siderophore, entB, was present in most (90.5%) of the isolates. Of the 370 isolates, 345 carried multiple virulence genes; 15 harboured single virulence genes and 10 did not harbour any of the studied virulence genes. The most common combination of occurrence was entB and FimH. A mortality rate of 12.75% (38/298) was observed among hospitalised patients. None of the virulence genes had any significant association with mortality.

Conclusion

Pathogenic K. pneumoniae can harbour single to multiple virulence genes. Invasive infection with even a single virulence gene-harbouring K. pneumoniae can lead to poor outcomes. Both multidrug-resistant (MDR) and non-MDR K. pneumoniae can harbour a variety of virulence genes. None of the virulence genes have a significant association with mortality.

High Prevalence of Multidrug-Resistant Klebsiella pneumoniae Harboring Several Virulence and β-Lactamase Encoding Genes in a Brazilian Intensive Care Unit

Klebsiella pneumoniae is an important opportunistic pathogen that commonly causes nosocomial infections and contributes to substantial morbidity and mortality. We sought to investigate the antibiotic resistance profile, pathogenic potential and the clonal relationships between K. pneumoniae (n = 25) isolated from patients and sources at a tertiary care hospital's intensive care units (ICUs) in the northern region of Brazil. Most of K. pneumoniae isolates (n = 21, 84%) were classified as multidrug resistant (MDR) with high-level resistance to β-lactams, aminoglycosides, quinolones, tigecycline, and colistin. All the 25 isolates presented extended-spectrum beta-lactamase-producing (ESBL), including carbapenemase producers, and carried the bla KPC (100%), bla TEM (100%), bla SHV variants (n = 24, 96%), bla OXA-1 group (n = 21, 84%) and bla CTX-M-1 group (n = 18, 72%) genes. The K2 serotype was found in 4% (n = 1) of the isolates, and the K1 was not detected. The virulence-associated genes found among the 25 isolates were mrkD (n = 24, 96%), fimH-1 (n = 22, 88%), entB (100%), iutA (n = 10, 40%), ybtS (n = 15, 60%). The genes related with efflux pumps and outer membrane porins found were AcrAB (100%), tolC (n = 24, 96%), mdtK (n = 22, 88%), OmpK35 (n = 15, 60%), and OmpK36 (n = 7, 28%). ERIC-PCR was employed to determine the clonal relationship between the different isolated strains. The obtained ERIC-PCR patterns revealed that the similarity between isolates was above 70%. To determine the sequence types (STs) a multilocus sequence typing (MLST) assay was used. The results indicated the presence of high-risk international clones among the isolates. In our study, the wide variety of MDR K. pneumoniae harboring β-lactams and virulence genes strongly suggest a necessity for the implementation of effective strategies to prevent and control the spread of antibiotic resistant infections.

Virulence and resistance determinants of Klebsiella pneumoniae isolated from a Portuguese tertiary university hospital centre over a 31-year period

INTRODUCTION

The rapid and complex evolution of bacterial resistance mechanisms in Klebsiella pneumoniae producing extended-spectrum β-lactamases and carbapenemases in Klebsiella pneumoniae is one of the most significant threats to public health. However, questions and controversies regarding the interactions between resistance and virulence in multidrug-resistant K. pneumoniae isolates remain unclear.

METHODS

A retrospective cohort study was performed with 100 K. pneumoniae isolates recovered from a tertiary care university hospital centre in Lisbon over a 31-year period. Resistance and virulence determinants were screened using molecular methods (PCR, M13-PCR and MLST).

RESULTS

The predominant virulence profile (fimH, mrkD_v1, khe) was shared by all isolates, indicative of an important role of type 1 and 3 fimbrial adhesins and haemolysin, regardless of the type of β-lactamase produced. However, accumulation of virulence factors was identified in KPC-3-producers, with a higher frequency (p<0.05) of capsular serotype K2 and iucC aerobactin when compared with non-KPC-3 β-lactamases or carbapenemases. Additionally, 9 different virulence profiles were found, indicating that the KPC-3 carbapenemase producers seem to adapt successfully to the host environment and maintain virulence via several pathways.

CONCLUSION

This study describes an overlapping of multidrug-resistance and virulence determinants in ST-14^K2 KPC-3 K. pneumoniae clinical isolates that may impose an additional challenge in the treatment of infections caused by this pathogen.

Dissemination of carbapenem-resistant Klebsiella pneumoniae harboring KPC-carrying plasmid pKPC_P16, a pKPC_LK30 variant, in northern Taiwan

The prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) was up to 30% between 2014 and 2016 in the study hospital. Of these 77 CRKP isolates, 22 isolates with sequence type ST11 carried the new pKPC_P16 plasmid, a pKPC_LK30 variant, and were widely disseminated between 2014 and 2015 in northern Taiwan.

Endotoxin neutralization by an O-antigen specific monoclonal antibody: A potential novel therapeutic approach against Klebsiella pneumoniae ST258

Klebsiella pneumoniae ST258 is a globally distributed multi-drug resistant pathogen responsible for severe invasive infections. In this study, the different virulence potential of K. pneumoniae ST258 isolates in endotoxin susceptible versus resistant animal models was shown. Furthermore, ST258 clinical isolates were found highly sensitive to the bactericidal effect of naive animal and human serum. These observations imply that LPS, released from the rapidly lysed bacteria, may contribute to the high mortality associated with ST258 bacteremia cases.

A humanized version (mAb A1102) of a previously described murine mAb specific for the conserved LPS O-antigen, was tested for endotoxin neutralization. A1102 was able to neutralize TLR-4 activation by ST258-derived LPS in vitro with an efficacy exceeding that of polymyxin B by 3 orders of magnitude. Passive immunization with A1102 afforded a significant level of protection in a galactosamine-sensitized mouse model of endotoxemia, induced by ST258-derived LPS, or upon challenge with live bacteria. Efficacy was retained using an aglycosylated IgG, as well as upon complement depletion, suggesting that Fc-independent endotoxin neutralization may be the main protective mechanism in this model, in spite of the complement-dependent bactericidal and opsonic activities additionally observed for A1102 in vitro. Furthermore, rabbits that are naturally highly susceptible to endotoxin, were also significantly protected by low doses of A1102 when challenged with an ST258 strain.

Given this unique mode of action and the high protective efficacy of this mAb, passive immunization, as prophylactic or adjunct therapeutic approach for the treatment of infections caused by ST258 isolates should be considered.

CD36 Provides Host Protection Against Klebsiella pneumoniae Intrapulmonary Infection by Enhancing Lipopolysaccharide Responsiveness and Macrophage Phagocytosis

Klebsiella pneumoniae remains an important cause of intrapulmonary infection and invasive disease worldwide. K. pneumoniae can evade serum killing and phagocytosis primarily through the expression of a polysaccharide capsule, but its pathogenicity is also influenced by host factors. We examined whether CD36, a scavenger receptor that recognizes pathogen and modified self ligands, is a host determinant of K. pneumoniae pathogenicity. Despite differences in serum sensitivity and virulence of 3 distinct K. pneumoniae (hypermucoviscous K1, research K2, and carbapenemase-producing ST258) strains, the absence of CD36 significantly increased host susceptibility to acute intrapulmonary infection by K. pneumoniae, regardless of strain. We demonstrate that CD36 enhances LPS responsiveness to K. pneumoniae to increase downstream cytokine production and macrophage phagocytosis that is independent of polysaccharide capsular antigen. Our study provides new insights into host determinants of K. pneumoniae pathogenicity and raises the possibility that functional mutations in CD36 may predispose individuals to K. pneumoniae syndromes.

Horizontal Transfer of Carbapenemase-Encoding Plasmids and Comparison with Hospital Epidemiology Data

Carbapenemase-producing organisms have spread worldwide, and infections with these bacteria cause significant morbidity. Horizontal transfer of plasmids carrying genes that encode carbapenemases plays an important role in the spread of multidrug-resistant Gram-negative bacteria. Here we investigate parameters regulating conjugation using an Escherichia coli laboratory strain that lacks plasmids or restriction enzyme modification systems as a recipient and also using patient isolates as donors and recipients. Because conjugation is tightly regulated, we performed a systematic analysis of the transfer of Klebsiella pneumoniae carbapenemase (blaKPC)-encoding plasmids into multiple strains under different environmental conditions to investigate critical variables. We used four blaKPC-carrying plasmids isolated from patient strains obtained from two hospitals: pKpQIL and pKPC-47e from the National Institutes of Health, and pKPC_UVA01 and pKPC_UVA02 from the University of Virginia. Plasmid transfer frequency differed substantially between different donor and recipient pairs, and the frequency was influenced by plasmid content, temperature, and substrate, in addition to donor and recipient strain. pKPC-47e was attenuated in conjugation efficiency across all conditions tested. Despite its presence in multiple clinical species, pKPC_UVA01 had lower conjugation efficiencies than pKpQIL into recipient strains. The conjugation frequency of these plasmids into K. pneumoniae and E. coli patient isolates ranged widely without a clear correlation with clinical epidemiological data. Our results highlight the importance of each variable examined in these controlled experiments. The in vitro models did not reliably predict plasmid mobilization observed in a patient population, indicating that further studies are needed to understand the most important variables affecting horizontal transfer in vivo.

Carbapenem-resistant Enterobacteriaceae colonization and infection in critically ill patients: a retrospective matched cohort comparison with non-carriers

OBJECTIVES

To examine whether carbapenem-resistant Enterobacteriaceae (CRE) carriage is associated with incidence of clinical infection as a means of assessing whether the morbidity and mortality associated with these bacteria are mediated by underlying conditions or intrinsic properties of CRE.

METHODS

This retrospective matched cohort study compared the incidence of invasive infections in CRE-colonized patients and matched non-carriers in the intensive care unit (ICU). The primary outcome was infection caused by CRE of the same species as the colonizing strain among CRE carriers, and infections caused by carbapenem-sensitive strains of the same organism in non-carriers. Hospital discharge and death were considered as competing events. Competing-risks hazard analysis was performed for the entire cohort and for a nested cohort matched by Acute Physiology and Chronic Health Evaluation (APACHE) II scores, stratified by matching.

RESULTS

In total, 146 CRE carriers were compared with 292 non-carriers. Patients were well matched for most risk factors for Enterobacteriaceae infection, including age, renal failure, previous invasive infection, previous hospitalization, APACHE II score, length of mechanical ventilation, length of hospitalization and CRE carriage. On regression analysis, colonization with CRE was independently associated with Enterobacteriaceae infection {cause-specific hazard ratio (CSHR) 2.06 [95% confidence interval (CI) 1.03-4.09]}. On regression analysis of the APACHE-II-matched cohort (N=284), colonization with CRE remained significantly associated with Enterobacteriaceae infection [CSHR 3.32 (95% CI 1.31-8.43)].

CONCLUSIONS

Colonization with CRE was associated with at least a two-fold increased risk of infection by the colonizing strain amongst ICU patients.

Prevalence and Fate of Carbapenemase Genes in a Wastewater Treatment Plant in Northern China

Carbapenemase-producing strains of bacteria, which were primarily found in the medical field, have increasingly been found in the environment, thus posing potential risks to public health. One possible way for carbapenemase genes to enter the environment is via wastewater. Therefore, the goal of this study was to determine the occurrence and fate of five high-risk carbapenemase genes in a wastewater treatment plant (WWTP) in northern China using real-time qPCR. Results showed that the bla_KPC-2, bla_GES-1, and bla_IMP-1 genes prevailed throughout all processing stages (even in the chlorination disinfection unit) in the WWTP, whereas the bla_VIM-2 and bla_OXA-48 genes were not detected in all samples. Worryingly, considerable amounts of carbapenemase genes ((1.54 ± 0.61) × 10³ copies/mL to (2.14± 0.41) × 10⁵ copies/mL) were detected in WWTP effluent samples, while the majority of the carbapenemase genes were transported to the dewatered sludge with concentrations from (6.51 ± 0.14) × 10⁹ copies/g to (6.18 ± 0.63) × 10¹⁰ copies/g dry weight. Furthermore, a total of 97 KPC-2-producing strains, belonging to 8 bacterial genera, were isolated from the WWTP. Sequencing of 16S rRNA revealed that most of KPC-2 producing isolates were opportunistic pathogens, including Klebsiella spp. (10.3%), Enterococcus spp. (11.3%), Acinetobacter spp. (19.6%), Escherichia spp. (12.4%), Shigella spp. (17.5%), Stenotrophomonas spp. (10.3%) and Wautersiella spp. (9.3%). Moreover, bla_KPC-2 genes were identified for the first time in Paenibacillus spp. isolates (an indigenous bacteria), indicating an increased risk of horizontal transfer between clinical pathogens and environmental bacteria. Indeed, a conjugation experiment demonstrated transfer of the bla_KPC-2 gene to an E.coli J53 strain from a Klebsiella strain isolated from the WWTP. To our knowledge, this is the first study to obtain Paenibacillus spp. isolates carrying the carbapenemase gene and to quantify the abundance of carbapenemase genes in the environment.

Nested Russian Doll-Like Genetic Mobility Drives Rapid Dissemination of the Carbapenem Resistance Gene blaKPC

The recent widespread emergence of carbapenem resistance in Enterobacteriaceae is a major public health concern, as carbapenems are a therapy of last resort against this family of common bacterial pathogens. Resistance genes can mobilize via various mechanisms, including conjugation and transposition; however, the importance of this mobility in short-term evolution, such as within nosocomial outbreaks, is unknown. Using a combination of short- and long-read whole-genome sequencing of 281 bla_KPC-positive Enterobacteriaceae isolates from a single hospital over 5 years, we demonstrate rapid dissemination of this carbapenem resistance gene to multiple species, strains, and plasmids. Mobility of bla_KPC occurs at multiple nested genetic levels, with transmission of bla_KPC strains between individuals, frequent transfer of bla_KPC plasmids between strains/species, and frequent transposition of bla_KPC transposon Tn4401 between plasmids. We also identify a common insertion site for Tn4401 within various Tn2-like elements, suggesting that homologous recombination between Tn2-like elements has enhanced the spread of Tn4401 between different plasmid vectors. Furthermore, while short-read sequencing has known limitations for plasmid assembly, various studies have attempted to overcome this by the use of reference-based methods. We also demonstrate that, as a consequence of the genetic mobility observed in this study, plasmid structures can be extremely dynamic, and therefore these reference-based methods, as well as traditional partial typing methods, can produce very misleading conclusions. Overall, our findings demonstrate that nonclonal resistance gene dissemination can be extremely rapid, presenting significant challenges for public health surveillance and achieving effective control of antibiotic resistance.

Correlation between antimicrobial resistance and virulence in Klebsiella pneumoniae

Klebsiella pneumoniae is responsible for a wide range of infections, including urinary tract infections, pneumonia, bacteremia, and liver abscesses. In addition to susceptible clinical isolates involved in nosocomial infections, multidrug-resistant (MDR) and hypervirulent (hvKP) strains have evolved separately in distinct clonal groups. The rapid geographic spread of these isolates is of particular concern. However, we still know little about the virulence of K. pneumoniae except for hvKP, whose secrets are beginning to be revealed. The treatment of K. pneumoniae infections is threatened by the emergence of antimicrobial resistance. The dissemination of resistance is associated with genetic mobile elements, such as plasmids that may also carry virulence determinants. A proficient pathogen should be virulent, resistant to antibiotics, and epidemic. However, the interplay between resistance and virulence is poorly understood. Here, we review current knowledge on the topic.

Quantification and comparison of virulence and characteristics of different variants of carbapenemase-producing Klebsiella pneumoniae clinical isolates from Taiwan and the United States

BACKGROUND/PURPOSE

The emergence of Klebsiella pneumoniae carbapenemase (KPC)-producing strains is a challenge for clinicians. The characteristics and virulence of variants of KPC-producing K. pneumoniae isolates were evaluated.

METHODS

Five clinical isolates-three KPC subtypes from Taiwan (KPC2-TW, KPC3-TW, and KPC17-TW) and two clinical strains from the United States (US; KPC2-US, KPC3-US)-were included. Virulent traits and capsular serotypes were analyzed by Polymerase Chain Reaction (PCR). Serum killing, neutrophil phagocytosis, and mice lethargy studies were performed to evaluate virulence.

RESULTS

Multilocus sequence typing (MLST) demonstrated that KPC2-TW and KPC17-TW belonged to sequence type (ST)11, and KPC2-US, KPC3-US, and KPC3-TW to ST258. KPC3-TW expressed capsular serotype K1, whereas the others were non-K1/K2/K5 isolates. MLST analysis indicated that ST11 strains were serum resistant, whereas ST258 isolates were serum sensitive. ST11 isolates exhibited significantly higher 15-minute phagocytic rates than ST258 isolates (70.28 ± 16.68% vs. 34.88 ± 10.52%, p < 0.001). The capsular serotype K1 strain was more resistant to neutrophil phagocytosis than non-K1/K2/K5 isolates (27.1 ± 10.23% vs. 54.46 ± 20.94%, p = 0.050). All KPC-producing strain variants from Taiwan and the US demonstrated less virulence in a mouse lethality study, where the LD50 ranged from approximately 10(6) colony-forming units (CFU) to >10(7) CFU. Immunological responses were not significantly correlated with KPC subtype; however, responses were associated with MLST and capsular serotype.

CONCLUSION

Production of KPC itself was not associated with increased virulence despite different variants of KPC. The ST11 KPC-producing strain was resistant to serum killing, whereas capsular ss K1 was associated with resistance to neutrophil phagocytosis.

Interactions of Klebsiella pneumoniae with the innate immune system vary in relation to clone and resistance phenotype

Apart from inadequate antimicrobial treatment, specific virulence factors contribute to the high attributable mortality of infections caused by multidrug-resistant (MDR) Klebsiella pneumoniae. We explored the roles of MDR and clones as virulence determinants of K. pneumoniae and their interaction with innate immunity. Twenty isolates were studied and characterized by resistance phenotype and multilocus sequence type (MLST). Human peripheral blood mononuclear cells (PBMCs) were stimulated for the production of proinflammatory cytokines by live and heat-killed isolates and plasmid DNA; modulation by cellular pathway inhibitors was explored. Survival of 30 mice was recorded after intraperitoneal challenge with susceptible and K. pneumoniae carbapenemase (KPC)-producing isolates. Splenocytes of mice were stimulated for the production of pro- and anti-inflammatory cytokines. Isolates were divided into different patterns of production of tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) poststimulation in relation to both the MLST clone and resistance phenotype. The sequence type 383 (ST383) clone producing Verona integron-encoded metallo-β-lactamase (VIM) stimulated high production of both TNF-α and IL-1β. Clone ST17 producing KPC elicited low TNF-α production; this was reversed by Toll-like receptor 9 (TLR9) antagonists, indicating an effect of plasmid DNA. This isolate was linked with early death of mice compared to high-TNF-α-producing isolates. We conclude that KPC-producing isolates seem to be highly virulent in a low-TNF-α-release environment, suggesting an immunoparalysis induction mechanism. KPC plasmids may directly contribute to the immune system stimulation.

Mortality burden related to infection with carbapenem-resistant Gram-negative bacteria among haematological cancer patients: a retrospective cohort study

OBJECTIVES

Carbapenem-resistant Gram-negative bacteria (CRGNB) pose a clinical challenge. We attempted to estimate the mortality burden of CRGNB among haematological cancer patients.

METHODS

This was a retrospective cohort study. We included adult patients hospitalized in the haemato-oncological/bone marrow transplantation departments for chemotherapy, between 2008 and 2014, with Gram-negative aerobic bacteraemia. We compared patients with CRGNB and carbapenem-susceptible Gram-negative bacteraemia (CSGNB). The primary outcome was 14 day all-cause mortality. In addition, we assessed 1 year survival. Multivariable logistics regression analysis and adjusted Cox regression analysis were conducted. Analyses were adjusted to the propensity for CRGNB bacteraemia.

RESULTS

The cohort included mostly young patients (mean age 50.1 years) with acute leukaemia (264/423, 62.4%) and the median absolute neutrophil count at bacteraemia onset was 0 × 10(9)/L. The unadjusted 14 day mortality rate was higher for patients with CRGNB compared with CSGNB [45.6% (47/103) versus 15% (48/320), respectively (P < 0.001)]. Adjusting to baseline prognostic factors, infection characteristics and the propensity score retained a significant association between CRGNB and 14 day mortality (OR 5.14, 95% CI 2.32-11.38). Including only the first bacteraemic episode per patient, 1 year mortality was 74.7% (68/91) for patients with CRGNB versus 49.8% (119/239) for patients with CSGNB (P < 0.001). Adjusting for risk factors associated with 1 year mortality, the HR for mortality with CRGNB was 1.48 (95% CI 1-2.2). CRGNB bacteraemia was associated with several risk factors for mortality, including inappropriate empirical antibiotic treatment and less effective definitive antibiotics.

CONCLUSIONS

This study demonstrated a significant adjusted association between CRGNB and mortality up to 1 year among haemato-oncological patients receiving chemotherapy.

Carbapenemase-producing Klebsiella pneumoniae: molecular and genetic decoding

Klebsiella pneumoniae carbapenemases (KPCs) were first identified in 1996 in the USA. Since then, regional outbreaks of KPC-producing K. pneumoniae (KPC-Kp) have occurred in the USA, and have spread internationally. Dissemination of blaKPC involves both horizontal transfer of blaKPC genes and plasmids, and clonal spread. Of epidemiological significance, the international spread of KPC-producing K. pneumoniae is primarily associated with a single multilocus sequence type (ST), ST258, and its related variants. However, the molecular factors contributing to the success of ST258 largely remain unclear. In this review, we discuss the recent progresses in understanding KPC-producing K. pneumoniae that are contributing to our knowledge of plasmid and genome composition and structure among the KPC epidemic clone, and we identify possible factors that influence its epidemiological success.

Expansion and evolution of a virulent, extensively drug-resistant (polymyxin B-resistant), QnrS1-, CTX-M-2-, and KPC-2-producing Klebsiella pneumoniae ST11 international high-risk clone

In this study, we report the early expansion, evolution, and characterization of a multiresistant Klebsiella pneumoniae clone that was isolated with increasing frequency from inpatients in a tertiary-care university hospital in Brazil. Seven carbapenem- and quinolone-resistant and polymyxin B-susceptible or -resistant K. pneumoniae isolates isolated between December 2012 and February 2013 were investigated. Beta-lactamase- and plasmid-mediated quinolone resistance (PMQR)-encoding genes and the genetic environment were investigated using PCR, sequencing, and restriction fragment length polymorphism (RFLP). Clonal relatedness was established using XbaI-pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and phylogenetic group characterization. Plasmid analyses included PCR-based replicon typing (PBRT) and hybridization of the S1-PFGE product, plasmid MLST, and conjugation experiments. Virulence potential was assessed by PCR by searching for 10 virulence factor-encoding genes (ureA, fimH, kfuBC, uge, wabG, magA, mrkD, allS, rmpA, and cf29a) and by phenotypic tests to analyze the hypermucoviscous phenotype. The genetic context of a multidrug-resistant and extensively drug-resistant K. pneumoniae ST11-KpI clone harboring IncFIIk-Tn4401a-blaKPC-2, qnrS1, and blaCTX-M-2 was found. Moreover, three isolates displayed high resistance to polymyxin B (MICs = 32, 32, and 128 mg/liter) as well as mucous and hypermucoviscous phenotypes. These bacteria also harbored ureA, fimH, uge, wabG, and mrkD, which code for virulence factors associated with binding, biofilm formation, and the ability to colonize and escape from phagocytosis. Our study describes the association of important coresistance and virulence factors in the K. pneumoniae ST11 international high-risk clone, which makes this pathogen successful at infections and points to the quick expansion and evolution of this multiresistant and virulent clone, leading to a pandrug-resistant phenotype and persistent bacteria in a Brazilian hospital.

Single or in combination antimicrobial resistance mechanisms of Klebsiella pneumoniae contribute to varied susceptibility to different carbapenems

Resistance to carbapenems has been documented by the production of carbapenemase or the loss of porins combined with extended-spectrum β-lactamases or AmpC β-lactamases. However, no complete comparisons have been made regarding the contributions of each resistance mechanism towards carbapenem resistance. In this study, we genetically engineered mutants of Klebsiella pneumoniae with individual and combined resistance mechanisms, and then compared each resistance mechanism in response to ertapenem, imipenem, meropenem, doripenem and other antibiotics. Among the four studied carbapenems, ertapenem was the least active against the loss of porins, cephalosporinases and carbapenemases. In addition to the production of KPC-2 or NDM-1 alone, resistance to all four carbapenems could also be conferred by the loss of two major porins, OmpK35 and OmpK36, combined with CTX-M-15 or DHA-1 with its regulator AmpR. Because the loss of OmpK35/36 alone or the loss of a single porin combined with bla CTX-M-15 or bla DHA-1-ampR expression was only sufficient for ertapenem resistance, our results suggest that carbapenems other than ertapenem should still be effective against these strains and laboratory testing for non-susceptibility to other carbapenems should improve the accurate identification of these isolates.

KPC-2-encoding plasmids from Escherichia coli and Klebsiella pneumoniae in Taiwan

OBJECTIVES

Two plasmids carrying bla(KPC-2) isolated from carbapenem-resistant Escherichia coli (CR-EC) and carbapenem-resistant Klebsiella pneumoniae (CR-KP), respectively, were completely sequenced. The CR-KP strain was selected from an outbreak in 2012, and the CR-EC strain was the first blaKPC-2-carrying E. coli identified in the same carbapenem resistance monitoring programme in Taiwan.

METHODS

Antimicrobial susceptibility tests, multilocus sequence typing (MLST) and the conjugal transfer of plasmids were performed. Complete sequencing of the plasmids was performed using a shotgun approach.

RESULTS

The CR-EC and CR-KP strains in this study were determined to be ST410 and ST11, respectively, by MLST. From CR-EC, we identified a 145 kb conjugative plasmid that carries bla(KPC-2), bla(CMY-2), bla(CTX-M-3) and bla(TEM-1). The plasmid is a chimera composed of three regions related to IncI, IncN and RepFIC replicons. From CR-KP, we identified an 86.5 kb plasmid, pKPC-LK30, which carries bla(KPC-2) and bla(SHV-11). The plasmid is very similar to two bla(KPC-2)-carrying IncFII(K) plasmids, but lacks one of the replication origins and cannot conjugate.

CONCLUSIONS

The differences in cross-species transferability of the two plasmids can be explained by genetic differences between their backbones and could have resulted in the confined bla(KPC-2)-carrying CR-KP outbreak in Taiwan. Plasmid pKPC-LKEc is the first bla(KPC-2)-carrying plasmid identified from CR-EC in Taiwan. With relatively high transferability it should be closely monitored.

KPC-producing, multidrug-resistant Klebsiella pneumoniae sequence type 258 as a typical opportunistic pathogen

The virulence of a KPC-producing Klebsiella pneumoniae sequence type 258 (ST258) strain representing those circulating in Greece was assessed in a mouse septicemia model. The strain was virtually avirulent (50% lethal dose, >10(8) and 5 × 10(7) CFU for immunocompetent and neutropenic animals, respectively). Also, it was highly susceptible to serum killing, rapidly phagocytosed in vitro, and classified as K41, which is not among the virulent capsular types. The findings indirectly support the notion that high ST258-associated mortality is largely due to inefficient antimicrobial treatment.

Virulence of Klebsiella pneumoniae isolates harboring bla KPC-2 carbapenemase gene in a Caenorhabditis elegans model

Klebsiella pneumoniae carbapenemase (KPC) is a carbapenemase increasingly reported worldwide in Enterobacteriaceae. The aim of this study was to analyze the virulence of several KPC-2-producing K. pneumoniae isolates. The studied strains were (i) five KPC-2 clinical strains from different geographical origins, belonging to different ST-types and possessing plasmids of different incompatibility groups; (ii) seven transformants obtained after electroporation of either these natural KPC plasmids or a recombinant plasmid harboring only the bla_KPC-2 gene into reference strains K. pneumoniae ATCC10031/CIP53153; and (iii) five clinical strains cured of plasmids. The virulence of K. pneumoniae isolates was evaluated in the Caenorhabditis elegans model. The clinical KPC producers and transformants were significantly less virulent (LT50: 5.5 days) than K. pneumoniae reference strain (LT50: 4.3 days) (p<0.01). However, the worldwide spread KPC-2 positive K. pneumoniae ST258 strains and reference strains containing plasmids extracted from K. pneumoniae ST258 strains had a higher virulence than KPC-2 strains belonging to other ST types (LT50: 5 days vs. 6 days, p<0.01). The increased virulence observed in cured strains confirmed this trend. The bla_KPC-2 gene itself was not associated to increased virulence.