Infection with Carbapenem-resistant Hypervirulent Klebsiella Pneumoniae: clinical, virulence and molecular epidemiological characteristics

Molecular epidemiology and emergence of sequence type 25 hypervirulent Klebsiella pneumoniae in pigs in the Netherlands (2013-2020): a global comparative analysis with human and pig isolates

Klebsiella pneumoniae (Kp), a ubiquitous pathogen found in diverse ecological niches, poses a threat to human and animal health. Hypervirulent Kp (hvKp) is concerning for its acquisition of virulence and antimicrobial resistance genes through plasmids. This study investigates hvKp as a cause of septicaemia in piglets in the Netherlands and examines the role of plasmids in virulence and host association. We collected 41 Kp isolates cultured from necropsies submitted from 15 different farms (2013-2020) and sequenced them using long-read sequencing. We identified sequence type (ST) 25 as the dominant Kp (67%, 10/15 farms) associated with septicaemia in pigs in the Netherlands. ST25 isolates displayed a hypervirulent profile, including the K2 hyper-capsule type and carried an iuc3 virulence plasmid. Further analysis revealed two ST25 clonal groups: CG25 and CG3804, a novel porcine clone. Multidrug resistance was identified in CG25 isolates from five pig farms. There was one colistin-resistant isolate carrying mcr-1 on a plasmid. Comparative genomic analysis was performed by including a large dataset of related publicly available Kp genomes from ST25 humans (n=230) and pigs (n=12) of all STs for phylogenetic and plasmid analysis. Pangenomic analysis revealed significantly higher iuc3 prevalence in global CG25 pig isolates (98%, 40/41) compared to humans (10%, 24/234) correlating with their enhanced virulence (scores 3-4 vs 0-1). The study highlights ST25 hvKp causing septicaemia in piglets in the Netherlands for the first time. Aerobactin lineage iuc3 on a plasmid is associated with infections in pigs and is responsible for an increased virulence score.

Emergence and evolution of rare ST592 bla NDM-1-positive carbapenem-resistant hypervirulent Klebsiella pneumoniae in China

Objectives

This study aimed to characterize the genomes of two rare ST592 Klebsiella pneumoniae isolates and to explore their evolution into carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKp).

Methods

The minimum inhibitory concentrations (MICs) were determined using a VITEK 2 compact system. Conjugation experiments were conducted using film matings. Whole-genome sequencing (WGS) was performed using the Illumina and Nanopore platforms. The antimicrobial resistance determinants were identified using the ABRicate program in the ResFinder database. Insertion sequences were identified using ISFinder and the bacterial virulence factors identified using the Virulence Factor Database (VFDB). The K and O loci were examined using Kleborate. Multilocus sequence typing (MLST) and replicon type identification were performed by the Center for Genomic Epidemiology. Conjugation-related elements were predicted using oriTfinder. The plasmid structure was visualized using Circos, and a possible evolutionary model was constructed using BioRender.

Results

Isolates KPZM6 and KPZM16 were identified as ST592 and KL57, respectively, and were collected from the same department. The antimicrobial susceptibility testing data revealed that KPZM16 possesses an extensively drug-resistant (XDR) profile, whereas KPZM6 is a susceptible K. pneumoniae. The hybrid assembly showed that both KPZM6 and KPZM16 have one pLVPK-like virulence plasmid carrying the rmpA, rmpA2, and iucABCD-iutA gene clusters. However, strain KPZM16 harbors one IncN plasmid carrying the carbapenem resistance genes bla NDM-1, dfrA14, and qnrS1. The results of the conjugation experiments demonstrated that the plasmid could be transferred to the recipient strain. It is possible that the NDM-1-producing plasmid was transferred from KPZM6 to KPZM16 via conjugation, leading to the formation of CR-hvKp.

Conclusions

This is the first study in which complete genomic characterization of the rare NDM-1-producing ST592 K. pneumoniae clinical isolate was performed. This study provides a possible evolutionary hypothesis for the formation of CR-hvKp via conjugation. Early detection is recommended to avoid the extensive spread of this clone.

Global trends of ceftazidime-avibactam resistance in gram-negative bacteria: systematic review and meta-analysis

BACKGROUND

The emergence of antimicrobial resistance in Gram-negative bacteria (GNB) is a major global concern. Ceftazidime-avibactam (CAZ-AVI) has been identified as a potential treatment option for complicated infections.

OBJECTIVES

This meta-analysis aimed to evaluate the global resistance proportions of GNB to CAZ-AVI comprehensively.

METHODS

Studies were searched in Scopus, PubMed, and EMBASE (until September 2024), and statistical analyses were conducted using STATA software (version 20.0).

RESULTS

CAZ-AVI resistance proportions were determined in 136 studies, with 25.8% (95% CI 22.2-29.7) for non-fermentative gram-negative bacilli and 6.1% (95% CI 4.9-7.4) for Enterobacterales. The CAZ-AVI resistance proportion significantly increased from 5.6% (95% CI 4.1-7.6) of 221,278 GNB isolates in 2015-2020 to 13.2% (95% CI 11.4-15.2) of 285,978 GNB isolates in 2021-2024. Regionally, CAZ-AVI resistance was highest in Asia 19.3% (95% CI 15.7-24.23.4), followed by Africa 13.6% (95% CI 5.6-29.2), Europe 11% (95% CI 7.8-15.2), South America 6.1% (95% CI 3.2-11.5) and North America 5.3% (95% CI 4.2-6.7). Among GNB resistance profiles, colistin-resistant isolates and XDR isolates exhibited the highest resistance proportions (37.1%, 95% CI 14-68 and 32.1%, 95% CI 18.5-49.6), respectively), followed by carbapenem-resistant isolates and MDR isolates [(25.8%, 95% CI 22.6-29.3) and (13%, 95% CI 9.6, 17.3)].

CONCLUSION

A high proportion of GNB isolates from urinary tract infections remained susceptible to CAZ-AVI, indicating its potential as a suitable treatment option. However, the increasing resistance trends among GNB are concerning and warrant continuous monitoring to maintain CAZ-AVI's effectiveness against GNB infections.

Hypervirulent Klebsiella pneumoniae: Epidemiology outside Asian countries, antibiotic resistance association, methods of detection and clinical management

Two main Klebsiella pneumoniae pathotypes are of public health concern, classical K. pneumoniae (cKP), with high antibiotic resistance acquisition capacity, and hypervirulent K. pneumoniae (hvKP). The emergence of hypervirulent and antibiotic-resistant K. pneumoniae, especially carbapenem resistance, is worrisome and require effective methods for detection and treatment. Different evolutionary paths contribute to the emergence of hypervirulence and antibiotic resistance, commonly via the acquisition of resistance plasmids by hvKP (CR-hvKP) or the acquisition of virulence plasmids by CRKp (hv-CRKp). ST11-KL64 together with blaKPC-2, is the most extended hv-CRKP lineage acquiring virulence plasmids with associated biomarkers, rmpA, rmpa2, iroBCDEN, iucABCDiutA, and peg344. In addition to ST11, other hv-CRKP clones have been reported in Europe such as ST101, ST147 and ST512, highlighting the association of ST147 with OXA-48 and NDM carbapenemases. Although still very rare in Spain, hvKP cases are increasing in recent years, mainly due to ST23-K1, ST380-K2 and ST86-K2. Management of hvKP infections requires active antibiotic therapy based primarily on antibiotic susceptibility patters and site of infection.

Antibiotic Susceptibility Patterns and Virulence Profiles of Classical and Hypervirulent Klebsiella pneumoniae Strains Isolated from Clinical Samples in Khyber Pakhtunkhwa, Pakistan

The emergence of hypervirulent and carbapenem-resistant hypermucoviscous Klebsiella pneumoniae strains presents a significant public health challenge due to their increased virulence and resistance to multiple antibiotics. This study evaluates the antibiotic susceptibility patterns and virulence profiles of classical and hypervirulent K. pneumoniae strains isolated from various clinical samples. A total of 500 clinical samples were collected from patients at the Mardan Medical Complex and Ayub Medical Complex in KPK between July 2022 and June 2024. Among these, 64 K. pneumoniae strains were isolated and subsequently subjected to antimicrobial susceptibility testing (AST) and phenotypic virulence detection. Among the 64 isolates, 21 (32.8%) exhibited hypermucoviscosity, a characteristic associated with increased pathogenicity. Hemagglutination was observed in 35 (54.1%) of the isolates, indicating the presence of surface adhesins that facilitate bacterial adherence to host tissues. A high prevalence of biofilm formation was noted, with 54 (84%) isolates capable of forming biofilms, which are known to protect bacteria from antibiotics and the host immune response. Most isolates (59/64, 92.1%) were resistant against ampicillin, highlighting its limited efficacy against these strains. Conversely, the lowest resistance was observed for tigecycline, with only 15% (10/64) of the isolates showing resistance, indicating its potential utility as a treatment option. The study also found that 38 (59.3%) of the isolates were extended-spectrum beta-lactamase (ESBL) producers, 42 (65.6%) were multidrug-resistant (MDR), 32 (50%) were extensively drug-resistant (XDR), and 13 (20.3%) were resistant to carbapenems. The genetic study revealed biofilm producer and enhancer genes (mrkD, pgaABCD, fimH, treC, wzc, pilQ, and luxS) mainly in the hypervirulent strains. These hypervirulent strains also show a high number of resistance genes. The findings of this study underscore the critical need for the active surveillance of antimicrobial resistance and virulence determinants in K. pneumoniae. The coexistence of high levels of antibiotic resistance and virulence factors in these isolates poses a severe threat to public health, as it can lead to difficult-to-treat infections and increased morbidity and mortality.

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.

Epidemiology, antimicrobial resistance profile, associated risk factors and management of carbapenem resistant Klebsiella pneumoniae in children under 5 with suspected sepsis in Ethiopia

BACKGROUND

Early detection and treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) could reduce the risk of developing life-threatening sepsis in childhood. However, little is known about sepsis caused by CRKP in children under-5 in developing countries. This study aimed to determine the epidemiology, antimicrobial resistance profile, associated risk factors and management of CRKP in children under-5 with sepsis in Ethiopia.

METHODS

This prospective multicenter study was conducted from June 2021 to December 2023 in three tertiary hospitals in Ethiopia. Samples collection and processing, identification and antimicrobial susceptibility testing were performed according to CLSI guidelines. Sociodemographic data were collected using structured questionnaires. Data were analyzed using STATA-21 and logistic regression to determine associated risk factors. A p-value < 0.05 was considered statistically significant.

RESULTS

Among 2483 children under-5 who were suspected of having sepsis, 530 (21.3%) were infected with K. pneumoniae. Infants and newborns were the most vulnerable age categories, with incidences of 25.3% and 34.2%, respectively. About 92.1% and 47.4% of the isolates were confirmed to produce ESBLs and -carbapenemases, respectively. Thus, isolates were resistant to cephalosporins(91-100%), gentamicin(83.7%), meropenem(49.1%), tigecycline(39%), and amikacin(21%). The prevalence rates of MDR, XDR, and PDR strains were 95.7%, 25.9%, and 11.4%, respectively. Combining amikacin with meropenem or tigecycline was used as a treatment option for XDR and PDR strains. . Regarding risk factors for sepsis caused by K. pneumoniae included prematurity [AOR = 7.1; 95%CI: 2.3-10.3], prolonged hospitalization [AOR = 4.4;95%CI = 1.9-8.2], admission to the ICU [AOR = 6.2;95% CI:2.8-9.2], pneumonia [AOR = 5.1;95%CI:1.6-13.2], meningitis [AOR = 15.3;95%CI:8.1-29.9], UTI [AOR = 2.1; 95%CI = 1.2-4.2], invasive procedures [AOR = 4.8; 95%CI:1.4-15.5], comorbidities [AOR = 4.2;95%CI = 2.2-13.2], parturition [AOR = 5.4;95%CI:2.5-13.3], and membrane rupture [AOR = 12.1; 95%CI = 2.3-26.2].

CONCLUSIONS

The prevalence of bacterial sepsis caused by CRKP in children under 5 is high and became a serious public health concern that requires immediate attention and action.Therefore, it is crucial to revise treatment guidelines and improve IPC practices to reduce children's morbidity and mortality from those superbugs and beyond.

A Decade-Long Review of the Virulence, Resistance, and Epidemiological Risks of Klebsiella pneumoniae in ICUs

Klebsiella pneumoniae, a major opportunistic pathogen, causes severe infections in both community and healthcare settings, especially in intensive care units (ICUs), where multidrug-resistant (MDR) strains, such as carbapenem-resistant K. pneumoniae (CRKP), pose significant treatment challenges. The rise in hypervirulent K. pneumoniae (hvKP) with enhanced virulence factors complicates management further. The ST11 clone, prevalent in China, exhibits both resistance and virulence traits, contributing to hospital outbreaks. ICU patients, particularly those with comorbidities or prior antibiotic exposure, are at higher risk. Treatment is complicated by limited antibiotic options and the increasing prevalence of polymicrobial infections, which involve resistant pathogens like Pseudomonas aeruginosa and Acinetobacter baumannii. Combination therapies offer some promise, but mortality rates remain high, and resistance to last-resort antibiotics is growing. Infection control measures and personalized treatment plans are critical, alongside the urgent need for vaccine development to combat the rising threat of K. pneumoniae, particularly in vulnerable populations. Effective management requires improved diagnostic tools, antimicrobial stewardship, and innovative treatment strategies to reduce the burden of this pathogen, especially in resource-limited settings. This review aims to provide a comprehensive analysis of the virulence, resistance, and epidemiological risks of K. pneumoniae in ICUs over the past decade, highlighting the ongoing challenges and the need for continued efforts to combat this growing threat.

A Decade-Long Review of the Virulence, Resistance, and Epidemiological Risks of Klebsiella pneumoniae in ICUs

Klebsiella pneumoniae, a major opportunistic pathogen, causes severe infections in both community and healthcare settings, especially in intensive care units (ICUs), where multidrug-resistant (MDR) strains, such as carbapenem-resistant K. pneumoniae (CRKP), pose significant treatment challenges. The rise in hypervirulent K. pneumoniae (hvKP) with enhanced virulence factors complicates management further. The ST11 clone, prevalent in China, exhibits both resistance and virulence traits, contributing to hospital outbreaks. ICU patients, particularly those with comorbidities or prior antibiotic exposure, are at higher risk. Treatment is complicated by limited antibiotic options and the increasing prevalence of polymicrobial infections, which involve resistant pathogens like Pseudomonas aeruginosa and Acinetobacter baumannii. Combination therapies offer some promise, but mortality rates remain high, and resistance to last-resort antibiotics is growing. Infection control measures and personalized treatment plans are critical, alongside the urgent need for vaccine development to combat the rising threat of K. pneumoniae, particularly in vulnerable populations. Effective management requires improved diagnostic tools, antimicrobial stewardship, and innovative treatment strategies to reduce the burden of this pathogen, especially in resource-limited settings. This review aims to provide a comprehensive analysis of the virulence, resistance, and epidemiological risks of K. pneumoniae in ICUs over the past decade, highlighting the ongoing challenges and the need for continued efforts to combat this growing threat.

Overexpression of KPC contributes to ceftazidime-avibactam heteroresistance in clinical isolates of carbapenem-resistant Klebsiella pneumoniae

Ceftazidime-avibactam (CZA) is one of the effective antibiotics used for the treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) infections, but its resistance rate has increased recently. Previous studies have focused on the mechanisms of CZA resistance, while its heteroresistance in CRKP remains poorly understood. This study aimed to investigate the characteristics and mechanisms of CZA heteroresistance in CRKP isolates. A total of 311 CRKP clinical strains were collected in China from 2020 to 2022. The MICs of CZA and other antibiotics against K. pneumoniae were determined by broth microdilution method. The occurrence of CZA heteroresistance in CRKP was evaluated with population analysis profiling (PAP) and their characteristics were detected by polymerase chain reaction (PCR). The underlying mechanism of CZA heteroresistance in CRKP strains was investigated by molecular sequencing, whole genome sequencing (WGS), quantitative real-time PCR (qRT-PCR), and in vitro functional experiments. Strategies for preventing the emergence of CZA heteroresistance and alternative treatment options for strains exhibiting CZA heteroresistance were further explored. Thirty-four (12.4%) CZA-susceptible CRKP isolates were found to exhibit heteroresistance to CZA. All heteroresistant strains belonged to KPC-2 (97.1%) or KPC-3 (2.9%). The dominant multilocus sequence typing (MLST) was ST11 (64.7%) and the prevalent capsular serotypes were KL47 (38.2%) and KL64 (32.4%). Imipenem-relebactam and meropenem-vaborbactam still exhibited excellent antimicrobial activity against the resistant subpopulations of CZA heteroresistant strains. No significant mutations were found in KPC, OmpK35/36, PBP2/3, and LamB in resistant subpopulations. The relative expression and copy number of bla KPC were significantly upregulated in 47.1% and 35.3% of the resistant subpopulations compared with their parental strains, respectively. Silencing bla KPC expression significantly decreased the CZA MIC in resistant subpopulations with high bla KPC expression and hindered the emergence of CZA heteroresistance in their parental strains. Moreover, increasing the avibactam concentration to 8 or 16 mg/L or combining CZA with 0.5 × MIC tigecycline significantly suppressed the formation of CZA heteroresistance (P<0.05). In conclusion, we identified the occurrence of CZA heteroresistance in CRKP in China, which was attributed to the overexpression of KPC. Increasing the concentration of avibactam or combining CZA with tigecycline could effectively prevent the development of CZA heteroresistance in CRKP isolates. Besides, imipenem-relebactam and meropenem-vaborbactam may serve as alternative therapeutic options when clinical isolates with CZA heteroresistance are detected.

Phenotypic and Genotypic Detection of Hypervirulent Klebsiella pneumoniae Isolated from Hospital-Acquired Infections

Hypervirulent Klebsiella pneumoniae is a highly pathogenic variant of Klebsiella pneumonae, which represents a global public health issue because it is very virulent and spreads easily. The objectives of this study were to assess the predominance of hvKp among health care-associated infections in intensive care units of Tanta University Hospital and to compare hvKp with classical K. pneumoniae (cKp) in terms of antibiotic resistance, virulence, and molecular features. The study included 300 patients suffering from HAIs from different ICUs of Tanta University Hospitals. K. pneumoniae isolates were identified and subjected to string testing and antibiotic susceptibility testing, and the tissue culture assay for biofilm formation and polymerase chain reaction (PCR) tests were performed for the identification of capsular genes (K1, K2, K57) and virulence genes (rmpA, rmpA2, iuc A). Fifty-seven K. pneumonaie isolates were isolated. A total of 21 (36.8%) of them were hvKp and 36 (63.15%) were cKp. Significantly higher antibiotic resistance was detected in the cKp group. There was a significant difference between biofilm formation between cKp and hvKp isolates (p < 0.004*). iucA, rmpA2, and K1 genes were significantly associated with hvKp. The string test shows 100% sensitivity and negative predictive value for the detection of hvKp. Consequently, using the string test alone for the screening of hvKp is required. However, combining aerobactin-positive with hypermucoviscous isolates while screening for hvKp is crucial.

Molecular characteristics and pathogenic mechanisms of KPC-3 producing hypervirulent carbapenem-resistant Klebsiella pneumoniae (ST23-K1)

Objective

This study aimed to comprehensively investigate hypervirulent carbapenem-resistant Klebsiella pneumoniae (CR-hvKP) in the Ningbo region. Importantly, we sought to elucidate its molecular characteristics and pathogenic mechanisms. This information will provide evidence-based insights for preventing and controlling nosocomial infections and facilitate improved clinical diagnosis and treatment in this region.

Methods

96 carbapenem-resistant Klebsiella pneumoniae strains were collected from the Ningbo region between January 2021 and December 2022. Whole genome sequencing and bioinformatic methods were employed to identify and characterize CR-hvKP strains at the molecular level. The minimum inhibitory concentrations (MICs) of common clinical antibiotics were determined using the VITEK-2 Compact automatic microbiological analyzer. Plasmid conjugation experiments evaluated the transferability of resistance plasmids. Finally, mouse virulence assays were conducted to explore the pathogenic mechanisms.

Results

Among the 96 strains, a single CR-hvKP strain, designated CR-hvKP57, was identified, with an isolation frequency of 1.04%. Whole-genome sequencing revealed the strain to be ST23 serotype with a K1 capsule. This strain harbored three plasmids. Plasmid 1, a pLVPK-like virulence plasmid, carried multiple virulence genes, including rmpA, rmpA2, iroB, iucA, and terB. Plasmid 2 contained transposable element sequences such as IS15 and IS26. Plasmid 3, classified as a resistance plasmid, harbored the bla KPC-3 carbapenem resistance gene. Mouse virulence assays demonstrated a high mortality rate associated with CR-hvKP57 infection. Additionally, there was a significant increase in IL-1β, IL-6, and TNF-α levels in response to CR-hvKP57 infection, indicating varying degrees of inflammatory response. Western blot experiments further suggested that the pathogenic mechanism involves activation of the NF-κB signaling pathway.

Conclusion

This study confirms the emergence of hypervirulent CR-hvKP in the Ningbo region, which likely resulted from the acquisition of a pLVPK-like virulence plasmid and a bla KPC-3 resistance plasmid by the ST23-K1 type Klebsiella pneumoniae. Our findings highlight the urgent need for more judicious use of antibiotics to limit the emergence of resistance. Additionally, strengthening infection prevention and control measures is crucial to minimize the spread of virulence and resistance plasmids.

Antibiotic resistance and epidemiological characteristics of polymyxin-resistant Klebsiella pneumoniae

OBJECTIVES

The emergence of polymyxin-resistant Klebsiella pneumoniae (KPN) in clinical settings necessitates an analysis of its antibiotic resistance characteristics, epidemiological features, and risk factors for its development. This study aims to provide insights for the prevention and control of polymyxin-resistant KPN infections.

METHODS

Thirty clinical isolates of polymyxin-resistant KPN were collected from the Third Xiangya Hospital of Central South University. Their antibiotic resistance profiles were analyzed. The presence of carbapenemase KPC, OXA-48, VIM, IMP, and NDM was detected using colloidal gold immunochromatography. Hypervirulent KPN was initially screened using the string test. Biofilm formation capacity was assessed using crystal violet staining. Combination drug susceptibility tests (polymyxin B with meropenem, tigecycline, cefoperazone/sulbactam) were conducted using the checkerboard method. Polymyxin-related resistance genes were detected by PCR. Multi-locus sequence typing (MLST) was performed for genotyping and phylogenetic tree construction. The study also involved collecting data from carbapenem-resistant (CR)-KPN polymyxin-resistant strains (23 strains, experimental group) and CR-KPN polymyxin-sensitive strains (57 strains, control group) to analyze potential risk factors for polymyxin-resistant KPN infection through univariate analysis and multivariate Logistic regression. The induction of resistance by continuous exposure to polymyxin B and colistin E was also tested.

RESULTS

Among the 30 polymyxin-resistant KPN isolates, 28 were CR-KPN, all producing KPC enzyme. Four isolates were positive in the string test. Most isolates showed strong biofilm formation capabilities. Combination therapy showed additive or synergistic effects. All isolates carried the pmrA and phoP genes, while no mcr-1 or mcr-2 genes were detected. MLST results indicated that ST11 was the predominant type. The phylogenetic tree suggested that polymyxin-resistant KPN had not caused a hospital outbreak in the institution. The use of two or more different classes of antibiotics and the use of polymyxin were identified as independent risk factors for the development of polymyxin-resistant strains. Continuous use of polymyxin induced drug resistance.

CONCLUSIONS

Polymyxin-resistant KPN is resistant to nearly all commonly used antibiotics, making polymyxin-based combination therapy a viable option. No plasmid-mediated polymyxin-resistant KPN has been isolated in the hospital. Polymyxin can induce resistance in KPN, highlighting the need for rational antibiotic use in clinical settings to delay the emergence of resistance.