Within-host resistance evolution of a fatal ST11 hypervirulent carbapenem-resistant Klebsiella pneumoniae

A novel mutation of ramR involved in tigecycline resistance in Klebsiella pneumoniae

This study aims to investigate the novel potential tigecycline resistance mechanism in Klebsiella pneumoniae and provide new insights for the clinical treatment of infections caused by carbapenem-resistant Klebsiella pneumoniae. In vitro experiments were conducted to induce tigecycline resistance in Klebsiella pneumoniae, simulating potential genetic mutations that may arise under the selective pressure of tigecycline in clinical settings. Next-generation sequencing and real-time quantitative PCR (RT-qPCR) were employed to analyze bacterial genomic mutations and the transcription of related genes, respectively. Gene knockout technology, broth microdilution method, and resistance stability tests were utilized to further validate the function of the identified gene mutation sites. A novel two-base pair deletion mutation (position 517-518) in the ramR gene (g. 517_518 del) was identified in Klebsiella pneumoniae strains cultured in broth medium containing progressively increasing concentrations of tigecycline (4, 8, and 16 mg/L). The impact of this mutation on tigecycline resistance was characterized. The RT-qPCR analysis revealed a consistent upregulation of ramR expression across all tigecycline-induced strains, with significant elevation observed at various concentrations (0.5, 1, 2, 4, 8, and 16 mg/L). Furthermore, the g. 517_518 del mutation in ramR was associated with sustained tigecycline resistance. This study illustrated a novel ramR mutation, leading to tigecycline resistance in Klebsiella pneumoniae.

IMPORTANCE

In this study, a novel missense mutation (g. 517_518 del GC) was detected in the ramR of tigecycline-induced Klebsiella pneumoniae, which was conducted in vitro, and the effects of anti-tigecycline caused by this mutation in ramR were confirmed. A high expression of ramR was observed in all tigecycline-induced strains. In addition, g. 517_518 del GC in ramR maintained tigecycline resistance. In summary, we illustrated a novel mutation of ramR, leading to tigecycline resistance in Klebsiella pneumoniae.

Emergence and clinical challenges of ST11-K64 carbapenem-resistant Klebsiella pneumoniae: molecular insights and implications for antimicrobial resistance and virulence in Southwest China

BACKGROUND

In clinical practice, the emergence of ST11-K64 carbapenem-resistant Klebsiella pneumoniae (ST11-K64 CRKP) has become increasingly alarming. Despite this trend, limited research has been conducted to elucidate the clinical and molecular characteristics of these strains.

OBJECTIVES

This study aimed to comprehensively investigate the clinical characteristics, antimicrobial resistance patterns, resistance and virulence-associated genes, and molecular epidemiology of ST11-K64 CRKP in Southwest China.

METHODS

A retrospective analysis was performed on patients infected with carbapenem-resistant Klebsiella pneumoniae (CRKP) in a tertiary care hospital between July 2021 and May 2022. A total of 69 CRKP strains were isolated, with clinical data collected for detailed analysis. Laboratory assessments included antimicrobial susceptibility testing, hypermucoviscosity string testing, genotypic characterization of antimicrobial resistance and virulence genes, and multi-locus sequence typing. Statistical analyses were conducted using SPSS, with significance set at P < 0.05.

RESULTS

Among the 69 CRKP isolates, 36 strains (52.2%) were identified as ST11-K64 CRKP. Hematological diseases were less associated with ST11-K64 CRKP infection compared to non-ST11-K64 strains (P = 0.012). However, central intravenous catheter use (P = 0.001), mechanical ventilation (P = 0.002), tracheal intubation (P = 0.006), and tracheotomy (P = 0.041) were significantly more common in ST11-K64 CRKP cases. Resistance rates to amikacin (P < 0.001), gentamicin (P = 0.004), tobramycin (P = 0.034), and sulfamethoxazole (P < 0.001) were significantly higher in ST11-K64 CRKP. Additionally, resistance-associated genes such as blaKPC-2 (P < 0.001) and virulence-associated genes including rmpA (P < 0.001), iucA (P < 0.001), rmpA2 (P < 0.001), and iutA (P = 0.001) were detected at significantly higher rates in ST11-K64 strains compared to non-ST11-K64 strains. Furthermore, compared to ST11-K47 CRKP, ST11-K64 CRKP harbored more virulence genes, such as rmpA (P = 0.007), iucA (P = 0.001), and iutA (P = 0.003).

CONCLUSION

Our findings underscore the rising prevalence of ST11-K64 CRKP, characterized by high levels of antimicrobial resistance and the presence of potent resistance and virulence genes. This strain poses a significant clinical and therapeutic challenge, necessitating heightened vigilance, stringent infection control measures, and robust clinical management strategies.

Analysis of the virulence of a lethal, carbapenem-resistant hypervirulent KPC-33-producing Klebsiella pneumoniae: Emergence of ST11-KL64 hv-CRKP in ICU

OBJECTIVE

Hypervirulent and carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) poses a serious threat to public health. Here, we analyse a case of systemic infection caused by a hv-CRKP, which ultimately led to the patient's death from sepsis. And a total of 30 CRKPs were analyzed to elucidate the molecular epidemiological features of CRKPs in the hospital, and to provide a basis for clinical anti-infective therapy.

METHODS

In this case, a total of 7 K. pneumoniae strains were isolated from the blood, sputum, urine, and feces of the patient. The Vitek-2 compact system was used to identify the strains and perform antimicrobial susceptibility testing. Biofilm formation, siderophore production assays and Galleria mellonella infection model were used to verify the virulence phenotypes of the strains in the case. Whole-genome sequencing was conducted on the four hv-CRKP isolated from different samples in the case and 26 other CRKP collected in our hospital from September to November in 2022, using the Illumina Hiseq 6000 high-throughput sequencing platform to analyse the resistance and virulence genes.

RESULTS

In the case, after 7 days of treatment with ceftazidime-avibactam (CZA), the resistance profile of the strains changed. The strain that was initially sensitive to CZA developed to resistant, resistant to imipenem (IPM) developed to sensitive, and resistant to meropenem (MEM) developed to intermediate. Whole-genome sequencing revealed that the four strains in the case were all ST11-KL64 K. pneumoniae, and the change in resistance phenotype was due to the mutation from blaKPC-2 to blaKPC-33. KPN7 had a total of six plasmids, with siderophore-related genes iucABCD and iutA, and mucoid phenotype-related gene rmpA2 located on plasmid p4-KPN7; resistance genes blaKPC-33, blaTEM-1B, and blaCTX-M-65 located on plasmid p5-KPN7; and virulence genes fim, irp, iutA, and ybt located on the chromosome. Biofilm formation and siderophore production assays confirmed that the seven K. pneumoniae strains isolated in this case had strong biofilm formation and siderophore production capabilities. Galleria mellonella Infection Model showed that KPN4 and KPN7 was phenotypically highly virulent and KPN7 performed lower virulence compared to KPN4. Apart from the 4 hv-CRKP strains, other 26 CRKP strains all carried blaKPC-2, and 69.2% (18/26) were ST-11 and 30.8%(8/26) were ST-15. And 83.3% (15/18) were ST11-KL64 strains, followed by ST11-KL25 strains 11.1%(2/18) and ST11-KL47 strain 5.6%(1/18). All the eight ST-15 strains were KL-19.

CONCLUSION

The ST11-KL64 hv-CRKP clone spread widely in ICU carried numerous resistance and virulence genes, and under antibiotic pressure, they easily underwent mutations resulting in changes in resistance phenotypes, especially in mutations of blaKPC-2 gene in acquiring resistance to CZA. Therefore, clinical attention should be paid to such strains, and the use of antibiotics should be adjusted promptly based on the susceptibility of the strains to antimicrobial agents.

Virulence phenotype alteration impacts nosocomial pathogen persistence on inanimate surfaces in hospital settings

The hospital setting serves as a critical conduit for pathogen dissemination, particularly amid the escalating concern of nosocomial infections in China. Currently, most studies use metagenomics to investigate microbial communities in hospital settings, with less focus on the transmission strategies of individual bacteria. In our study, we identified two Klebsiella pneumoniae strains exhibiting different mucoid characteristics. The strain designated as KPE was obtained from a well sanitized ward, while the strain KPH was isolated from the sputum samples of patients within the identical ward. We characterized the KPE strain as not lethal to mice and showed a distinct hypomuciod phenotype, strikingly different from the virulent KPH isolate. Two strains harbored the single nucleotide polymorphism (SNP) mutations in the virulence-related gene rmpA and wcaJ promoter regions, resulting in the downregulation of mucoid regulatory gene rmpA and capsule synthesis genes. Consequently, this led to diminished production of capsular polysaccharides and weakened virulence in the KPE strain. Furthermore, the KPE strain exhibited an elevated capacity for acquiring antibiotic-resistant plasmids and greater material survival ability. These findings indicated that mucoid changes enable K. pneumoniae strains to survive better on inanimate surfaces, promoting their persistence ward environment and further transmission in patients.

Molecular characterization of ST15 carbapenem-resistant Klebsiella pneumoniae isolated in a single patient

BACKGROUND

The carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a serious threat to antibiotic applicability and public health. During treatment, K. pneumoniae (KP) frequently exhibits shifts in drug-resistant phenotypes, complicating clinical treatment as it transitions from sensitivity to resistance. In this study, we analysed the clinical and molecular characteristics of drug resistance changes in KP strains isolated from a single patient, and the potential mechanisms underlying these resistance changes.

METHODS

Antimicrobial susceptibility test and string test were conducted to evaluate the resistant and virulent characterization of the strains. Pulsed-field gel electrophoresis (PFGE) was used to investigate the homology relationship between the strains. The whole genome sequencing and phylogenetic analysis of 9 representative isolates was also performed. The transfer ability of the drug-resistant plasmid was studied by plasmid conjugation experiment. The transconjugants were verified by polymerase chain reaction amplification of specific genes, antimicrobial susceptibility test and PFGE.

RESULTS

Our results revealed that 9 KP strains, isolated from the same patient, exhibited 'resistance-sensitivity-resistance-sensitivity' alternately to carbapenems. The differences in DNA fingerprint bands among the nine KP isolates were ≤3, which can be classified as the same PFGE type. Phylogenetic analysis showed that these 9 strains constituted a distinct branch within the phylogenetic tree. All nine KP strains belonged to the ST15-KL19 clone. Six of the strains were classified as CRKP, all of which carried 11 drug resistance genes: oqxB, oqxA, fosA6, aac(3)-lld, blaSHV-28, blaKPC-2, blaOXA-1, mph(A), tet(A), catB3 and aac(6')-lb-cr, mediating drug resistance to quinolones, fosfomycin, aminoglycosides, β-lactam, carbapenems, macrolides and chloramphenicol, belonging to multi-drug resistant bacteria. The carbapenem-resistant plasmid p2-KP3762-1 was found to transfer within species, from CRKP to hypervirulent KPRJF293HA, carbapenem-sensitive KP KP3657 and Escherichia coli C600 at a frequency of (1.19 ± 1.58) ×10-6, (1.09 ± 1.38) ×10-7 and (10.9 ± 9.53) ×10-6 respectively, resulting in the dissemination of carbapenem resistance genes.

CONCLUSIONS

In this study, KP strains isolated from a single patient exhibited an alternating phenotype of resistant-sensitive-resistant-sensitive to carbapenems. The 9 KP isolates share a high degree of genetic similarity. The plasmid p2-KP3762-1, harbouring the carbapenem resistance gene blaKPC-2, may undergo inter-strain and inter-clone transfer via conjugation in the patient during treatment. Furthermore, our findings suggest that the pathogens in this patient are likely to have a common ancestral origin.

Genomic characterization of ST11-KL25 hypervirulent KPC-2-producing multidrug-resistant Klebsiella pneumoniae from China

The global prevalence of ST11 hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) isolates has been increasingly documented, yet genomic characterization of this clone remains insufficiently explored. Here, we report a clinical ST11-KL25 hv-CRKP strain (KP156) that exhibited resistance to multiple antibiotics and demonstrated hypervirulence in a mouse infection model. Whole-genome sequencing revealed that KP156 harbored one virulence plasmid (pKP156-Vir) and two resistance plasmids (pKP156-KPC and pKP156-tetA). The pKP156-Vir contains several virulence factors, including rmpA2 and iucABCD, which are critical contributors to its hypervirulence. The bla KPC-2 and bla CTX-M-65 genes, located within the Tn6296 transposon of pKP156-KPC, along with a multidrug-resistant (MDR) region containing multiple transposons and conjugative elements in pKP156-tetA, are associated with the transfer of resistance genes. Phylogenetic analysis indicates that KP156 shares high homology with other ST11 hv-CRKPs, suggesting potential transmission of this clone. Our study informs the development of genomic surveillance and control strategies for this strain.

ESKAPE in China: epidemiology and characteristics of antibiotic resistance

The escalation of antibiotic resistance and the diminishing antimicrobial pipeline have emerged as significant threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria, demanding urgently effective therapies. Despite the introduction of various new antibiotics and antibiotic adjuvants, such as innovative β-lactamase inhibitors, these organisms continue to pose substantial therapeutic challenges. People's Republic of China, as a country facing a severe bacterial resistance situation, has undergone a series of changes and findings in recent years in terms of the prevalence, transmission characteristics and resistance mechanisms of antibiotic resistant bacteria. The increasing levels of population mobility have not only shaped the unique characteristics of antibiotic resistance prevalence and transmission within People's Republic of China but have also indirectly reflected global patterns of antibiotic-resistant dissemination. What's more, as a vast nation, People's Republic of China exhibits significant variations in the levels of antibiotic resistance and the prevalence characteristics of antibiotic resistant bacteria across different provinces and regions. In this review, we examine the current epidemiology and characteristics of this important group of bacterial pathogens, delving into relevant mechanisms of resistance to recently introduced antibiotics that impact their clinical utility in China.

Hypervirulent and carbapenem-resistant Klebsiella pneumoniae: A global public health threat

The evolution of hypervirulent and carbapenem-resistant Klebsiella pneumoniae can be categorized into three main patterns: the evolution of KL1/KL2-hvKp strains into CR-hvKp, the evolution of carbapenem-resistant K. pneumoniae (CRKp) strains into hv-CRKp, and the acquisition of hybrid plasmids carrying carbapenem resistance and virulence genes by classical K. pneumoniae (cKp). These strains are characterized by multi-drug resistance, high virulence, and high infectivity. Currently, there are no effective methods for treating and surveillance this pathogen. In addition, the continuous horizontal transfer and clonal spread of these bacteria under the pressure of hospital antibiotics have led to the emergence of more drug-resistant strains. This review discusses the evolution and distribution characteristics of hypervirulent and carbapenem-resistant K. pneumoniae, the mechanisms of carbapenem resistance and hypervirulence, risk factors for susceptibility, infection syndromes, treatment regimens, real-time surveillance and preventive control measures. It also outlines the resistance mechanisms of antimicrobial drugs used to treat this pathogen, providing insights for developing new drugs, combination therapies, and a "One Health" approach. Narrowing the scope of surveillance but intensifying implementation efforts is a viable solution. Monitoring of strains can be focused primarily on hospitals and urban wastewater treatment plants.

Gut colonization with antibiotic-resistant Escherichia coli pathobionts leads to disease severity in ulcerative colitis

BACKGROUND

Escherichia coli is a Gram-negative commensal of human gut. Surprisingly, the role of E. coli in the pathogenesis of ulcerative colitis (UC) has not been explored until now.

METHODS

Human gut microbiota composition and meta-gut resistome were evaluated using metagenomics. Antibiotic susceptibility of E. coli isolates against different class of antibiotics was investigated. Further, the genome sequence analysis of E. coli isolates was performed to gain insight into the antimicrobial resistance (AMR) mechanism and virulence factors. Gut proteome of UC and non-UC was examined to understand the effect of resistant bacteria on host physiology.

RESULTS

In UC patients, meta-gut resistome was found to be dominated by AMR genes (829) compared to healthy controls (HC) [518]. The metagenome study revealed a higher prevalence of AMR genes in the rural population (378 in HC; 607 in UC) compared to the urban (340 in HC; 578 in UC). Approximately, 40% of all E. coli isolates were multi-drug resistant (MDR), with higher prevalence in UC (43.75%) compared to HC (33.33%). Up-regulated expression of antimicrobial human proteins (lactotransferrin, azurocidin, cathepsin G, neutrophil elastase, and neutrophil defensin 3) and inflammatory mediator (Protein S100-A9 and Protein S100-A8) suggest microbial infection in UC gut.

CONCLUSIONS

In addition to the conventional culturomics method, a multi-omics strategy provides deeper insights into the disease etiology, emergence of MDR pathobionts, and their roles in the disruption of the healthy gut environment in UC patients.

Clinical and laboratory insights into the threat of hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKP) typically causes severe invasive infections affecting multiple sites in healthy individuals. In the past, hvKP was characterized by a hypermucoviscosity phenotype, susceptibility to antimicrobial agents, and its tendency to cause invasive infections in healthy individuals within the community. However, there has been an alarming increase in reports of multidrug-resistant hvKP, particularly carbapenem-resistant strains, causing nosocomial infections in critically ill or immunocompromised patients. This presents a significant challenge for clinical treatment. Early identification of hvKP is crucial for timely infection control. Notably, identifying hvKP has become confusing due to its prevalence in nosocomial settings and the limited predictive specificity of the hypermucoviscosity phenotype. Novel virulence predictors for hvKP have been discovered through animal models or machine learning algorithms, while standardization of identification criteria is still necessary. Timely source control and antibiotic therapy have been widely employed for the treatment of hvKP infections. Additionally, phage therapy is a promising alternative approach due to escalating antibiotic resistance. In summary, this narrative review highlights the latest research progress in the development, virulence factors, identification, epidemiology of hvKP, and treatment options available for hvKP infection.

Genomic study substantiates the intensive care unit as a reservoir for carbapenem-resistant Klebsiella pneumoniae in a teaching hospital in China

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has recently emerged as a notable public health concern, while the underlying drivers of CRKP transmission among patients across different healthcare facilities have not been fully elucidated. To explore the transmission dynamics of CRKP, 45 isolates were collected from both the intensive care unit (ICU) and non-ICU facilities in a teaching hospital in Guangdong, China, from March 2020 to August 2023. The collection of clinical data and antimicrobial resistance phenotypes was conducted, followed by genomic data analysis for these isolates. The mean age of the patients was 75.2 years, with 18 patients (40.0%) admitted to the ICU. The predominant strain in hospital-acquired CRKP was sequence type 11 (ST11), with k-locus type 64 and serotype O1/O2v1 (KL64:O1/O2v1), accounting for 95.6% (43/45) of the cases. The CRKP ST11 isolates from the ICU exhibited a low single nucleotide polymorphism (SNP) distance when compared to isolates from other departments. Genome-wide association studies identified 17 genes strongly associated with SNPs that distinguish CRKP ST11 isolates from those in the ICU and other departments. Temporal transmission analysis revealed that all CRKP isolates from other departments were genetically very close to those from the ICU, with fewer than 16 SNP differences. To further elucidate the transmission routes among departments within the hospital, we reconstructed detailed patient-to-patient transmission pathways using hybrid methods that combine TransPhylo with an SNP-based algorithm. A clear transmission route, along with mutations in potential key genes, was deduced from genomic data coupled with clinical information in this study, providing insights into CRKP transmission dynamics in healthcare settings.

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.

Adaptive evolution of carbapenem-resistant hypervirulent Klebsiella pneumoniae in the urinary tract of a single patient

The emergence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) is a growing concern due to its high mortality and limited treatment options. Although hypermucoviscosity is crucial for CR-hvKp infection, the role of changes in bacterial mucoviscosity in the host colonization and persistence of CR-hvKp is not clearly defined. Herein, we observed a phenotypic switch of CR-hvKp from a hypermucoviscous to a hypomucoviscous state in a patient with scrotal abscess and urinary tract infection (UTI). This switch was attributed to decreased expression of rmpADC, the regulator of mucoid phenotype, caused by deletion of the upstream insertion sequence ISKpn26. Postswitching, the hypomucoid variant showed a 9.0-fold decrease in mice sepsis mortality, a >170.0-fold reduction in the ability to evade macrophage phagocytosis in vitro, and an 11.2- to 40.9-fold drop in growth rate in normal mouse serum. Conversely, it exhibited an increased residence time in the mouse urinary tract (21 vs. 6 d), as well as a 216.4-fold boost in adhesion to bladder epithelial cells and a 48.7% enhancement in biofilm production. Notably, the CR-hvKp mucoid switch was reproduced in an antibiotic-free mouse UTI model. The in vivo generation of hypomucoid variants was primarily associated with defective or low expression of rmpADC or capsule synthesis gene wcaJ, mediated by ISKpn26 insertion/deletion or base-pair insertion. The spontaneous hypomucoid variants also outcompeted hypermucoid bacteria in the mouse urinary tract. Collectively, the ISKpn26-associated mucoid switch in CR-hvKp signifies the antibiotic-independent host adaptive evolution, providing insights into the role of mucoid switch in the persistence of CR-hvKp.

Adaptive attenuation of virulence in hypervirulent carbapenem-resistant Klebsiella pneumoniae

The emergence of nosocomial infections caused by hypervirulent and carbapenem-resistant K. pneumoniae (hv-CRKP) has become a significant public health challenge. The genetic traits of virulence and resistance plasmids in hv-CRKP have been extensively studied; however, research on the adaptive evolution strategies of clinical strains inside the host was scarce. This study aimed to understand the effects of antibiotic treatment on the phenotype and genotype characteristics of hv-CRKP. We investigated the evolution of hv-CRKP strains isolated from the same patient to elucidate the transition between hospital invasion and colonization. A comparative genomics analysis was performed to identify single nucleotide polymorphisms in the rmpA promoter. Subsequent validation through RNA-seq and gene deletion confirmed that distinct rmpA promoter sequences exert control over the mucoid phenotype. Additionally, biofilm experiments, cell adhesion assays, and animal infection models were conducted to illuminate the influence of rmpA promoter diversity on virulence changes. We demonstrated that the P12T and P11T promoters of rmpA possess strong activity, which leads to the evolution of CRKP into infectious and virulent strains. Meanwhile, the specific sequence of polyT motifs in the rmpA promoter led to a decrease in the lethality of hv-CRKP and enhanced cell adhesion and colonization. To summarize, the rmpA promoter of hv-CRKP is utilized to control capsule production, thereby modifying pathogenicity to better suit the host's ecological environment.IMPORTANCEThe prevalence of hospital-acquired illness caused by hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) is significant, leading to prolonged antibiotic treatment. However, there are few reports on the phenotypic changes of hv-CRKP in patients undergoing antibiotic treatment. We performed a comprehensive examination of the genetic evolutionary traits of hv-CRKP obtained from the same patient and observed variations in the promoter sequences of the virulence factor rmpA. The strong activity of the promoter sequences P11T and P12T enhances the consistent production of capsule polysaccharides, resulting in an invasive strain. Conversely, weak promoter activity of P9T and P10T is advantageous for exposing pili, hence improving bacterial cell attachment ability and facilitating bacterial colonization. This finding also explains the confusion of some clinical strains carrying wild-type rmpA but exhibiting a low mucoid phenotype. This adaptive alteration facilitates the dissemination of K. pneumoniae within the hospital setting.

Global prevalence of mutation in the mgrB gene among clinical isolates of colistin-resistant Klebsiella pneumoniae: a systematic review and meta-analysis

Background

Colistin is used as a last resort for managing infections caused by multidrug-resistant bacteria. However, the high emergence of colistin-resistant strains has restricted the clinical use of this antibiotic in the clinical setting. In the present study, we evaluated the global prevalence of the mutation in the mgrB gene, one of the most important mechanisms of colistin resistance in Klebsiella pneumoniae.

Methods

Several databases, including Scopus, Medline (via PubMed), and Web of Science, were searched (until August 2023) to identify those studies that address the mgrB mutation in clinical isolates of K. pneumoniae. Using Stata software, the pooled prevalence of mgrB mutation and subgroup analyses for the year of publication, country, continent, mgrB mutation types, and detection methods of mgrB mutation were analyzed.

Results

Out of the 115 studies included in the analysis, the prevalence of mgrB mutations in colistin-resistant K. pneumoniae isolates was estimated at 65% of isolates, and mgrB variations with insertional inactivation had the highest prevalence among the five investigated mutations with 69%. The year subgroup analysis indicated an increase in mutated mgrB from 46% in 2014 to 61% in 2022. Europe had the highest prevalence of mutated mgrB at 73%, while Africa had the lowest at 54%.

Conclusion

Mutations in the mgrB gene are reported as one of the most common mechanisms of colistin resistance in K. pneumoniae, and the results of the present study showed that 65% of the reported colistin-resistant K. pneumoniae had a mutation in this gene.

Antibacterial Activity and Action Mechanism of Bacteriocin Paracin wx7 as a Selective Biopreservative against Vancomycin-Resistant Enterococcus faecalis in Fresh-Cut Lettuce

Fresh-cut vegetables are widely consumed, but there is no food preservative available to selectively inhibit vancomycin-resistant E. faecalis, which is a serious health menace in fresh-cut vegetables. To develop a promising food biopreservative, a bacteriocin, paracin wx7, was synthesized, showing selective inhibition against E. faecalis with MIC values of 4-8 μM. It showed instant bactericidal mode within 1 h at high concentrations with concomitant cell lysis against vancomycin-resistant E. faecalis. Its lethal effect was visualized in a dose-dependent manner by PI/SYTO9 staining observation. The results of an in vivo control experiment carried out on E. faecalis in fresh-cut lettuce showed that 99.97% of vancomycin-resistant E. faecalis were dead after 64 μM paracin wx7 treatment for 7 days without influencing total bacteria. Further, the action mechanism of paracin wx7 was investigated. Confocal microscopy showed that paracin wx7 was located both on the cell envelope and in cytoplasm. For the cell envelope, the studies of membrane permeability using SYTOX Green dyeing and DNA leakage revealed that paracin wx7 damaged the membrane integrity of E. faecalis. Simultaneously, it exhibited membrane depolarization after analysis using DiSC3(5). Damage to the cell envelope resulted in cell deformation observed by scanning electron microscopy. On entering the cytoplasm, the paracin wx7 induced the production of endogenous reactive oxygen species.

Dynamic within-host cefiderocol heteroresistance caused by blaSHV-12 amplification in pandrug-resistant and hypervirulent Klebsiella pneumoniae sequence type 11

AIMS

Although cefiderocol (FDC) is not prescribed in China, FDC-resistant pandrug-resistant hypervirulent Klebsiella pneumoniae (PDR-hvKp) is emerging. In this study, we performed FDC susceptibility testing of clinical Kp isolates to explore the prevalence of FDC-resistant isolates and the mechanism of FDC-resistance.

METHODS

We retrospectively selected 151 carbapenem-resistant Kp isolates to assess FDC susceptibility. Seven isolates harboring blaSHV-12 from two patients were enrolled for whole-genome sequencing. The antimicrobial resistance, virulence, blaSHV-12 expression, and fitness costs in different media were examined. The amplification of blaSHV-12 was further investigated by qPCR and long-read sequencing.

RESULTS

The 151 isolates showed a low MIC50/MIC90 (1/4 mg/L) of FDC. The seven isolates were ST11 PDR-hvKp, and two represented FDC-resistance (MIC=32 mg/L). The IncR/IncFII plasmids of two FDC-resistant isolates harbored 6 and 15 copies of blaSHV-12, whereas four FDC-susceptible isolates carried one copy and one harbored three copies. These blaSHV-12 genes concatenated together and were located within the same 7.3 kb fragment flanked by IS26, which contributed to the increased expression and FDC resistance without fitness costs. The amplification of blaSHV-12 and FDC resistance could be induced by FDC in vitro and reversed during continuous passage.

CONCLUSIONS

The amplification of blaSHV-12 and the consequent dynamic within-host heteroresistance are important concerns for the rational application of antibiotics. Long-read sequencing might be a superior way to detect resistance gene amplification rapidly and accurately.

Presence of hypervirulence-associated determinants in Klebsiella pneumoniae from hospitalised patients in Germany

BACKGROUND

Klebsiella (K.) pneumoniae is a ubiquitous Gram-negative bacterium and a common coloniser of animals and humans. Today, K. pneumoniae is one of the most persistent nosocomial pathogens worldwide and poses a severe threat/burden to public health by causing urinary tract infections, pneumonia and bloodstream infections. Infections mainly affect immunocompromised individuals and hospitalised patients. In recent years, a new type of K. pneumoniae has emerged associated with community-acquired infections such as pyogenic liver abscess in otherwise healthy individuals and is therefore termed hypervirulent K. pneumoniae (hvKp). The aim of this study was the characterisation of K. pneumoniae isolates with properties of hypervirulence from Germany.

METHODS

A set of 62 potentially hypervirulent K. pneumoniae isolates from human patients was compiled. Inclusion criteria were the presence of at least one determinant that has been previously associated with hypervirulence: (I) clinical manifestation, (II) a positive string test as a marker for hypermucoviscosity, and (III) presence of virulence associated genes rmpA and/or rmpA2 and/or magA. Phenotypic characterisation of the isolates included antimicrobial resistance testing by broth microdilution. Whole genome sequencing (WGS) was performed using Illumina® MiSeq/NextSeq to investigate the genetic repertoire such as multi-locus sequence types (ST), capsule types (K), further virulence associated genes and resistance genes of the collected isolates. For selected isolates long-read sequencing was applied and plasmid sequences with resistance and virulence determinants were compared.

RESULTS

WGS analyses confirmed presence of several signature genes for hvKp. Among them, the most prevalent were the siderophore loci iuc and ybt and the capsule regulator genes rmpA and rmpA2. The most dominant ST among the hvKp isolates were ST395 capsule type K2 and ST395 capsule type K5; both have been described previously and were confirmed by our data as multidrug-resistant (MDR) isolates. ST23 capsule type K1 was the second most abundant ST in this study; this ST has been described as commonly associated with hypervirulence. In general, resistance to beta-lactams caused by the production of extended-spectrum beta-lactamases (ESBL) and carbapenemases was observed frequently in our isolates, confirming the threatening rise of MDR-hvKp strains.

CONCLUSIONS

Our study results show that K. pneumoniae strains that carry several determinants of hypervirulence are present for many years in Germany. The detection of carbapenemase genes and hypervirulence associated genes on the same plasmid is highly problematic and requires intensified screening and molecular surveillance. However, the non-uniform definition of hvKp complicates their detection. Testing for hypermucoviscosity alone is not specific enough to identify hvKp. Thus, we suggest that the classification of hvKp should be applied to isolates that not only fulfil phenotypical criteria (severe clinical manifestations, hypermucoviscosity) but also (I) the presence of at least two virulence loci e.g. iuc and ybt, and (II) the presence of rmpA and/or rmpA2.

Metagenomics next-generation sequencing (mNGS) reveals emerging infection induced by Klebsiella pneumoniaeniae

OBJECTIVES

The increasing emergence of hypervirulent Klebsiella pneumoniae (hv-Kp) and carbapenem-resistant K. pneumoniae (CR-Kp) is a serious and substantial public health problem. The use of the last resort antimicrobials, tigecycline and polymyxin to combat infections is complicated by the expanding repertoire of newly-identified CR-hvKp. The transmission and co-occurrence of the corresponding antimicrobial resistance and virulence determinants are largely unknown. The aim of this study was to investigate the dissemination and dynamics of CR-Kp and its antibiotic resistance in a hospitalised patient.

METHODS

Metagenomic next-generation sequencing (mNGS) was conducted for different specimens collected from an elderly male hospitalised patient. CR-Kp strains were examined using antibiotic susceptibility and string testing. Antimicrobial and virulence genes were annotated using whole-genome sequencing (WGS).

RESULTS

A clinical case of a patient infected with a variety of CR-Kp isolates was reported. The co-occurrence of KPC-2 and NDM-1 in the patient was revealed. The CR-Kp isolates, such as BALF2, and Sputum T1 and T3, were classified into ST11 and ST147, respectively. The genetic signature (iuc operon) of hypervirulence was identified in strain T1, although string testing indicated its intermediate virulence.

CONCLUSIONS

In this study, multiple infections of CR-Kp isolates were revealed by mNGS, and their dissemination was attributed to plasmid variations, mgrB inactivation and integrative conjugative elements (ICEs). Furthermore, the finding indicated one likely convergence to form CR-hvKp, different from acquisition of carbapenem-resistance determinants in hvKp. A combination of mNGS and WGS is beneficial for clinical diagnosis and anti-infection therapy, and facilitates a better understanding of genetic variants conferring antimicrobial and virulence properties.

Increase in antioxidant capacity associated with the successful subclone of hypervirulent carbapenem-resistant Klebsiella pneumoniae ST11-KL64

The acquisition of exogenous mobile genetic material imposes an adaptive burden on bacteria, whereas the adaptational evolution of virulence plasmids upon entry into carbapenem-resistant Klebsiella pneumoniae (CRKP) and its impact remains unclear. To better understand the virulence in CRKP, we characterize virulence plasmids utilizing a large genomic data containing 1219 K. pneumoniae from our long-term surveillance and publicly accessible databases. Phylogenetic evaluation unveils associations between distinct virulence plasmids and serotypes. The sub-lineage ST11-KL64 CRKP acquires a pK2044-like virulence plasmid from ST23-KL1 hypervirulent K. pneumoniae, with a 2698 bp region deletion in all ST11-KL64. The deletion is observed to regulate methionine metabolism, enhance antioxidant capacity, and further improve survival of hypervirulent CRKP in macrophages. The pK2044-like virulence plasmid discards certain sequences to enhance survival of ST11-KL64, thereby conferring an evolutionary advantage. This work contributes to multifaceted understanding of virulence and provides insight into potential causes behind low fitness costs observed in bacteria.

Within-Host Resistance and Virulence Evolution of a Hypervirulent Carbapenem-Resistant Klebsiella pneumoniae ST11 Under Antibiotic Pressure

Background

Hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) has recently aroused an extremely severe health challenge and public concern. However, the underlying mechanisms of fitness costs that accompany antibiotic resistance acquisition remain largely unexplored. Here, we report a hv-CRKP-associated fatal infection and reveal a reduction in virulence due to the acquisition of aminoglycoside resistance.

Methods

The bacterial identification, antimicrobial susceptibility, hypermucoviscosity, virulence factors, MLST and serotypes were profiled.The clonal homology and plasmid acquisition among hv-CRKP strains were detected by XbaI and S1-PFGE. The virulence potential of the strains was evaluated using Galleria mellonella larvae infection model, serum resistance assay, capsular polysaccharide quantification, and biofilm formation assay. Genomic variations were identified using whole-genome sequencing (WGS).

Results

Four K. pneumoniae carbapenemase (KPC)-producing CRKP strains were consecutively isolated from an 86-year-old patient with severe pneumonia. Whole-genome sequencing (WGS) showed that all four hv-CRKP strains belonged to the ST11-KL64 clone. PFGE analysis revealed that the four ST11-KL64 hv-CRKP strains could be grouped into the same PFGE type. Under the pressure of antibiotics, the antimicrobial resistance of the strains increased and the virulence potential decreased. Further sequencing, using the Nanopore platform, was performed on three representative isolates (WYKP586, WYKP589, and WYKP594). Genomic analysis showed that the plasmids of these three strains underwent a large number of breaks and recombination events under antibiotic pressure. We found that as aminoglycoside resistance emerged via acquisition of the rmtB gene, the hypermucoviscosity and virulence of the strains decreased because of internal mutations in the rmpA and rmpA2 genes.

Conclusion

This study shows that ST11-KL64 hv-CRKP can further evolve to acquire aminoglycoside resistance accompanied by decreased virulence to adapt to antibiotic pressure in the host.

"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.

Role of the ISKpn element in mediating mgrB gene mutations in ST11 hypervirulent colistin-resistant Klebsiella pneumoniae

Background

Colistin has emerged as a last-resort therapeutic against antibiotic-resistant bacterial infections, particularly those attributed to carbapenem-resistant Enterobacteriaceae (CRE) like CRKP. Yet, alarmingly, approximately 45% of multidrug-resistant Klebsiella pneumoniae strains now manifest resistance to colistin. Through our study, we discerned that the synergy between carbapenemase and IS elements amplifies resistance in Klebsiella pneumoniae, thereby narrowing the existing therapeutic avenues. This underscores the instrumental role of IS elements in enhancing colistin resistance through mgrB disruption.

Methods

From 2021 to 2023, 127 colistin-resistant Klebsiella pneumoniae isolates underwent meticulous examination. We embarked on an exhaustive genetic probe, targeting genes associated with both plasmid-mediated mobile resistance-encompassing blaKPC, blaNDM, blaIMP, blaVIM, blaOXA-48-like, and mcr-1 to mcr-8-and chromosome-mediated resistance systems, including PhoP/Q, PmrA/B, and mgrB. PCR amplification revealed the presence of virulence-associated genes from the pLVPK plasmid, such as rmpA, rmpA2, iucA, iroB, and peg344. mgrB sequencing was delegated to Sangon Biotech, Shanghai, and the sequences procured were validated using BLAST. Our search for IS elements was navigated through the IS finder portal. Phenotypically, we harnessed broth microdilution (BMD) to ascertain the MICs of colistin. To sketch the clonal lineage of mgrB-mutated CoR-Kp isolates, sophisticated methodologies like MLST and PFGE were deployed. S1-PFGE unraveled the intrinsic plasmids in these isolates. Our battery of virulence assessment techniques ranged from the string test and capsular serotyping to the serum killing assay and the Galleria mellonella larval infection model.

Results

Among the 127 analyzed isolates, 20 showed an enlarged mgrB PCR amplicon compared to wild-type strains. These emerged over a three-year period: three in 2021, thirteen in 2022, and four in 2023. Antimicrobial susceptibility tests revealed that these isolates consistently resisted several drugs, notably TCC, TZP, CAZ, and COL. Additionally, 85% resisted both DOX and TOB. The MICs for colistin across these strains ranged between 16 to 64 mg/L, with a median of 40 mg/L. From a genetic perspective, MLST unanimously categorized these mgrB-mutated CoR-hvKp isolates as ST11. PFGE further delineated them into six distinct clusters, with clusters A and D being predominant. This distribution suggests potential horizontal and clonal genetic transmission. Intriguingly, every mgrB-mutated CoR-hvKP isolate possessed at least two virulence genes akin to the pLVPK-like virulence plasmid, with iroB and rmpA2 standing out. Their virulence was empirically validated both in vitro and in vivo. A pivotal discovery was the identification of three distinct insertion sequence (IS) elements within or near the mgrB gene. These were:ISKpn26 in eleven isolates, mainly in cluster A, with various insertion sites including +74, +125, and an upstream -35.ISKpn14 in four isolates with insertions at +93, -35, and two upstream at -60.IS903B present in five isolates, marking positions like +74, +125, +116, and -35 in the promoter region. These diverse insertions, spanning six unique locations in or near the mgrB gene, underscore its remarkable adaptability.

Conclusion

Our exploration spotlights the ISKpn element's paramount role in fostering mgrB gene mutations in ST11 hypervirulent colistin-resistant Klebsiella pneumoniae. Employing MLST and PFGE, we unearthed two primary genetic conduits: clonal and horizontal. A striking observation was the ubiquitous presence of the KPC carbapenemase gene in all the evaluated ST11 hypervirulent colistin-resistant Klebsiella pneumoniae strains, with a majority also harboring the NDM gene. The myriad mgrB gene insertion locales accentuate its flexibility and the overarching influence of IS elements, notably the pervasive IS5-like variants ISKpn26 and IS903B. Our revelations illuminate the escalating role of IS elements in antibiotic resistance within ST11 hypervirulent colistin-resistant Klebsiella pneumoniae, advocating for innovative interventions to counteract these burgeoning resistance paradigms given their profound ramifications for prevailing treatment modalities.

Hypervirulent Klebsiella pneumoniae detection methods: a minireview

Hypervirulent Klebsiella pneumoniae (hvKp), characterized by high virulence and epidemic potential, has become a global public health challenge. Therefore, improving the identification of hvKp and enabling earlier and faster detection in the community to support subsequent effective treatment and prevention of hvKp are an urgent issue. To address these issues, a number of assays have emerged, such as String test, Galleria mellonella infection test, PCR, isothermal exponential amplification, and so on. In this paper, we have collected articles on the detection methods of hvKp and conducted a retrospective review based on two aspects: traditional detection technology and biomarker-based detection technology. We summarize the advantages and limitations of these detection methods and discuss the challenges as well as future directions, hoping to provide new insights and references for the rapid detection of hvKp in the future. The aim of this study is to focus on the research papers related to Hypervirulent Klebsiella pneumoniae involving the period from 2012 to 2022. We conducted searches using the keywords "Hypervirulent Klebsiella pneumoniae, biomarkers, detection techniques" on ScienceDirect and Google Scholar. Additionally, we also searched on PubMed, using MeSH terms associated with the keywords (such as Klebsiella pneumoniae, Klebsiella Infections, Virulence, Biomarkers, diagnosis, etc.).

Complete genetic characterization of carbapenem-resistant Acinetobacter johnsonii, co-producing NDM-1, OXA-58, and PER-1 in a patient source

The emergence of carbapenemase-producing Acinetobacter spp. has been widely reported and become a global threat. However, carbapenem-resistant A. johnsonii strains are relatively rare and without comprehensive genetic structure analysis, especially for isolates collected from human specimen. Here, one A. johnsonii AYTCM strain, co-producing NDM-1, OXA-58, and PER-1 enzymes, was isolated from sputum in China in 2018. Antimicrobial susceptibility testing showed that it was resistant to meropenem, imipenem, ceftazidime, ciprofloxacin, and cefoperazone/sulbactam. Whole-genome sequencing and bioinformatic analysis revealed that it possessed 11 plasmids. bla OXA-58 and bla PER-1 genes were located in the pAYTCM-1 plasmid. Especially, a complex class 1 integron consisted of a 5' conserved segment (5' CS) and 3' CS, which was found to carry sul1, arr-3, qnrVC6, and bla PER-1 cassettes. Moreover, the bla NDM-1 gene was located in 41,087 conjugative plasmids and was quite stable even after 70 passages under antibiotics-free conditions. In addition, six prophage regions were identified. Tracking of closely related plasmids in the public database showed that pAYTCM-1 was similar to pXBB1-9, pOXA23_010062, pOXA58_010030, and pAcsw19-2 plasmids, which were collected from the strains of sewage in China. Concerning the pAYTCM-3 plasmids, results showed that strains were collected from different sources and their hosts were isolated from various countries, such as China, USA, Japan, Brazil, and Mexico, suggesting that a wide spread occurred all over the world. In conclusion, early surveillance is warranted to avoid the extensive spread of this high-risk clone in the healthcare setting.

Clinical and Molecular Characteristics and Antibacterial Strategies of Klebsiella pneumoniae in Pyogenic Infection

Treatment of Klebsiella pneumoniae causing pyogenic infections is challenging. The clinical and molecular characteristics of Klebsiella pneumoniae causing pyogenic infections are poorly understood, and antibacterial treatment strategies are limited. We analyzed the clinical and molecular characteristics of K. pneumoniae from patients with pyogenic infections and used time-kill assays to reveal the bactericidal kinetics of antimicrobial agents against hypervirulent K. pneumoniae (hvKp). A total of 54 K. pneumoniae isolates were included, comprising 33 hvKp and 21 classic K. pneumoniae (cKp) isolates, and the hvKp and cKp isolates were identified using five genes (iroB, iucA, rmpA, rmpA2, and peg-344) that have been applied as hvKp strain markers. The median age of all cases was 54 years (25th and 75th percentiles, 50.5 to 70), 62.96% of individuals had diabetes, and 22.22% of isolates were sourced from individuals without underlying disease. The ratios of white blood cells/procalcitonin and C-reactive protein/procalcitonin were potential clinical markers for the identification of suppurative infection caused by hvKp and cKp. The 54 K. pneumoniae isolates were classified into 8 sequence type 11 (ST11) and 46 non-ST11 strains. ST11 strains carrying multiple drug resistance genes have a multidrug resistance phenotype, while non-ST11 strains carrying only intrinsic resistance genes are generally susceptible to antibiotics. Bactericidal kinetics revealed that hvKp isolates were not easily killed by antimicrobials at susceptible breakpoint concentrations compared with cKp. Given the varied clinical and molecular features and the catastrophic pathogenicity of K. pneumoniae, it is critical to determine the characteristics of such isolates for optimal management and effective treatment of K. pneumoniae causing pyogenic infections. IMPORTANCE Klebsiella pneumoniae may cause pyogenic infections, which are potentially life-threatening and bring great challenges for clinical management. However, the clinical and molecular characteristics of K. pneumoniae are poorly understood, and effective antibacterial treatment strategies are limited. We analyzed the clinical and molecular features of 54 isolates from patients with various pyogenic infections. We found that most patients with pyogenic infections had underlying diseases, such as diabetes. The ratio of white blood cells to procalcitonin and the ratio of C-reactive protein to procalcitonin were potential clinical markers for differentiating hypervirulent K. pneumoniae strains from classical K. pneumoniae strains that cause pyogenic infections. K. pneumoniae isolates of ST11 were generally more resistant to antibiotics than non-ST11 isolates. Most importantly, hypervirulent K. pneumoniae strains were more tolerant to antibiotics than classic K. pneumoniae isolates.

Role of efflux pumps, their inhibitors, and regulators in colistin resistance

Colistin is highly promising against multidrug-resistant and extensively drug-resistant bacteria clinically. Bacteria are resistant to colistin mainly through mcr and chromosome-mediated lipopolysaccharide (LPS) synthesis-related locus variation. However, the current understanding cannot fully explain the resistance mechanism in mcr-negative colistin-resistant strains. Significantly, the contribution of efflux pumps to colistin resistance remains to be clarified. This review aims to discuss the contribution of efflux pumps and their related transcriptional regulators to colistin resistance in various bacteria and the reversal effect of efflux pump inhibitors on colistin resistance. Previous studies suggested a complex regulatory relationship between the efflux pumps and their transcriptional regulators and LPS synthesis, transport, and modification. Carbonyl cyanide 3-chlorophenylhydrazone (CCCP), 1-(1-naphthylmethyl)-piperazine (NMP), and Phe-Arg-β-naphthylamide (PAβN) all achieved the reversal of colistin resistance, highlighting the role of efflux pumps in colistin resistance and their potential for adjuvant development. The contribution of the efflux pumps to colistin resistance might also be related to specific genetic backgrounds. They can participate in colistin tolerance and heterogeneous resistance to affect the treatment efficacy of colistin. These findings help understand the development of resistance in mcr-negative colistin-resistant strains.

Molecular evaluation of aminoglycosides resistance and biofilm formation in Klebsiella pneumoniae clinical isolates: A cross-sectional study

Background and Aims

Resistance to antibiotics and the capability to develop biofilm as two main virulent determinants of Klebsiella pneumoniae have important role in infection persistence. The aim of the study was to evaluate the association between the prevalence of aminoglycoside resistance and virulence genes and biofilm formation capacity in K. pneumoniae strains isolated from hospitalized patients in South-West of Iran.

Methods

A total of 114 non-duplicate clinical isolates of K. pneumoniae collected from Ahvaz teaching hospitals. Identification of species was performed by biochemical tests and then confirmed by polymerase chain reaction (PCR) of rpoB gene. The susceptibility to antibiotics was determined by Kirby-Bauer disk diffusion method. Biofilm formation was assessed by microtiter plate method. Finally, PCR was conducted to detect virulence gene determinants including fimbrial genes, aminoglycoside modifying enzymes- and 16S rRNA methylase (RMTase) genes.

Results

Totally, all collected strains were carbapenem resistant and showed multidrug- and extensively drug-resistance phenotype (75% and 25%, respectively). Seventy-one percent (n = 81) of isolates were non-susceptible to aminoglycosides. Among aminoglycoside antibiotics, K. pneumoniae isolates showed the highest and lowest resistance rates to tobramycin (71%) and the amikacin (25%), respectively. All biofilm producer strains were positive for the presence virulence determinants including ecpA, fimA, mrkD, and mrkA. Of 81 aminoglycosides non-susceptible isolates 33% were positive for the presence ant (2″)-Ia as the most prevalent gene followed by aac (3')-IIa and armA (27%), aac (6')-Ib (18%), and aph (3')-Ia (15%).

Conclusion

K. pneumoniae isolates showed the highest and the lowest aminoglycoside resistance rates to tobramycin and amikacin, respectively. Majority of isolates were biofilm producers and there was significant association between antibiotic resistance pattern and the strength of biofilm production. The ant(2″)-Ia, aac (3')-IIa, and armA genes in aminoglycoside-resistant isolates.