Comparison of prevalence of virulence factors for Klebsiella pneumoniae liver abscesses between isolates with capsular K1/K2 and non-K1/K2 serotypes

Decoding virulence and resistance in Klebsiella pneumoniae: Pharmacological insights, immunological dynamics, and in silico therapeutic strategies

Klebsiella pneumoniae (K. pneumoniae) has become a serious global health concern due to its rising virulence and antibiotic resistance. As one of the leading members of ESKAPE pathogens, it plays a major role in a wide range of infections that cause pneumonia, urinary tract infections, and bacteremia, especially in immunocompromised and hospitalized patients. The recent increase in multidrug-resistant (MDR) and hypervirulent (hvKP) strains due to the production of extended-spectrum beta-lactamases (ESBLs) and carbapenemases, has greatly limited therapeutic options that highlights the need for novel approaches to combat the pathogen. This review outlines the virulence mechanisms, profiles of antibiotic resistance, and immune evasion strategies in K. pneumoniae. Also, it points out the role of capsular polysaccharides, lipopolysaccharides, and fimbriae in host colonization and immune evasion. Additionally, the review discusses the emerging therapeutic strategies of vaccine development, computational drug discovery, and the use of artificial intelligence (AI). The progress achieved in reverse vaccinology and structural biology enables the identification of new drug and vaccine targets, whereas AI and machine learning (ML) stand out as powerful candidates for high-throughput screening and drug design. However, challenges with antigenic variability, safety, and the need to collaborate globally still exist. This review focuses on the need for interdisciplinary approaches involving molecular biology and immunology with computational sciences to address K. pneumoniae infections and provide appropriate therapies in the era of antibiotic resistance.

Hypervirulent Klebsiella pneumoniae: Insights into Virulence, Antibiotic Resistance, and Fight Strategies Against a Superbug

Community-acquired infections caused by Klebsiella pneumoniae (K. pneumoniae) have become a significant global health concern, particularly with the emergence of hypervirulent strains (hvKP). These strains are associated with severe infections, such as pyogenic liver abscesses, even in otherwise healthy individuals. Initially reported in Taiwan in the 1980s, hvKP has now spread worldwide. The pathogenicity of hvKP is attributed to an array of virulence factors that enhance its ability to colonize and evade host immune defenses. Additionally, the convergence of hypervirulence with antibiotic resistance has further complicated treatment strategies. As a member of the ESKAPE group of pathogens, K. pneumoniae exhibits high resistance to multiple antibiotics, posing a challenge for healthcare settings. This review provides a comprehensive overview of hvKP, highlighting its structural and pathogenic differences from classical K. pneumoniae strains, key virulence factors, mechanisms of antibiotic resistance, and the increasing threat of multidrug-resistant hvKP. Lastly, we discuss current treatment guidelines and emerging therapeutic strategies to combat this formidable pathogen.

Weberviruses are gut-associated phages that infect Klebsiella spp

Weberviruses are bacteriophages (phages) that can infect and lyse clinically relevant, multidrug-resistant (MDR) strains of Klebsiella. They are an attractive therapeutic option to tackle Klebsiella infections due to their high burst sizes, long shelf life, and associated depolymerases. In this study, we isolated and characterized seven new lytic phages and compared their genomes with those of their closest relatives. Gene-sharing network, ViPTree proteome, and terL gene-sequence-based analyses incorporating all publicly available webervirus genomes [n = 258 from isolates, n = 65 from metagenome-assembled genome (MAG) datasets] confirmed the seven phages as members of the genus Webervirus and identified a novel genus (Defiantjazzvirus) within the family Drexlerviridae. Using our curated database of 265 isolated phage genomes and 65 MAGs (n = 330 total), we found that weberviruses are distributed globally and primarily associated with samples originating from the gut: sewage (154/330, 47%), wastewater (83/330, 25%), and human faeces (66/330, 20%). We identified three distinct clusters of potential depolymerases encoded within the 330 genomes. Due to their global distribution, frequency of isolation and lytic activity against the MDR clinical Klebsiella strains used in this study, we conclude that weberviruses and their depolymerases show promise for development as therapeutic agents against Klebsiella spp.

A systematic review of hypervirulent Klebsiella pneumoniae research: bibliometric and topic modeling perspectives

Background/objective

Hypervirulent Klebsiella pneumoniae (hvKP) is an emerging global health threat, exhibiting increased virulence and multidrug resistance compared to classic K. pneumoniae. Understanding the research landscape surrounding hvKP is crucial for developing effective control strategies. This study aimed to comprehensively analyze the global research trends in hvKP from 2013 to 2024 using bibliometric and topic modeling techniques.

Methods

Data from 1,014 articles on hvKP, retrieved from the Web of Science Core Collection, were analyzed using Bibliometrix, CiteSpace, and VOSviewer to assess publication trends, collaborations, geographical distribution, and keyword co-occurrence. Latent Dirichlet Allocation (LDA) topic modeling was employed to identify key research themes.

Results

The analysis revealed a steadily increasing volume of hvKP research, with China and the United States as major contributors. Four primary research themes emerged: high virulence phenotypes and mechanisms; drug resistance and treatment strategies; genetic and molecular mechanisms; and epidemiological and transmission characteristics. Research hotspots included virulence mechanisms, drug resistance, genomic detection approaches, and epidemiological features.

Conclusion

This bibliometric analysis provides a comprehensive overview of hvKP research, highlighting key trends and research gaps. The identified research hotspots inform future research directions and contribute to the development of effective strategies for combating hvKP infections. The increasing research volume underscores the urgent need for continued investigation into this significant public health threat.

Insights into the roles of macrophages in Klebsiella pneumoniae infections: a comprehensive review

Klebsiella pneumoniae (KP) infections represent a significant global health challenge, characterized by severe inflammatory sequelae and escalating antimicrobial resistance. This comprehensive review elucidates the complex interplay between macrophages and KP, encompassing pathogen recognition mechanisms, macrophage activation states, cellular death pathways, and emerging immunotherapeutic strategies. We critically analyze current literature on macrophage pattern recognition receptor engagement with KP-associated molecular patterns. The review examines the spectrum of macrophage responses to KP infection, including classical M1 polarization and the newly described M(Kp) phenotype, alongside metabolic reprogramming events such as glycolytic enhancement and immune responsive gene 1 (IRG1)-itaconate upregulation. We systematically evaluate macrophage fate decisions in response to KP, including autophagy, apoptosis, pyroptosis, and necroptosis. Furthermore, we provide a critical assessment of potential future therapeutic modalities. Given the limitations of current treatment paradigms, elucidating macrophage-KP interactions is imperative. Insights gained from this analysis may inform the development of novel immunomodulatory approaches to augment conventional antimicrobial therapies, potentially transforming the clinical management of KP infections.

Bacteriophage-derived depolymerase: a review on prospective antibacterial agents to combat Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram-negative bacterium that colonizes mucosal surfaces and is a common cause of nosocomial infections. The emergence of antimicrobial resistance in K. pneumoniae, particularly carbapenem-resistant strains, poses a significant threat to human health, with high mortality rates and healthcare costs. Another major problem is that hypervirulent K. pneumoniae tends to form biofilms. Bacteriophage-derived depolymerases, a class of enzymes that degrade diverse bacterial surface carbohydrates, have been exploited as antibiofilm and antimicrobial adjuvants because of their high stability, specificity, strong antimicrobial activity, and low incidence of bacterial resistance. This review presents a summary of the structure and properties of depolymerase, as well as an overview of both in vitro and in vivo studies of depolymerase therapy for multidrug-resistant or biofilm-forming K. pneumoniae infections. These studies employed a range of approaches, including utilizing a single depolymerase or combinations of depolymerase and phages or antibiotics. Furthermore, this review outlines the current challenges facing depolymerase therapy and potential future approaches for treating K. pneumoniae infections.

Virulence determinants in Klebsiella pneumoniae associated with septicaemia outbreaks in neonatal pigs

Klebsiella pneumoniae is recognized as an opportunistic pathogen in pigs causing pneumonia, mastitis and diarrhoea, but can also cause mortalities due to septicaemia and meningitis in previously healthy piglets. This study aimed to identify virulence genes present in K. pneumoniae that caused outbreaks of septicaemia in neonatal pigs. The genomes of thirty-eight Australian K. pneumoniae isolates from pigs with septicaemia, meningitis, myocarditis, pneumonia, enteritis and healthy cohorts were sequenced. The presence of antimicrobial resistance, siderophore and enhanced capsule production genes were identified by sequence analysis and verified by either PCR or phenotypic tests. An additional 52 international K. pneumoniae genomes from healthy and clinically affected pigs (28), humans (16), birds (3), one rodent and environmental isolates (4) were included in a pangenome analysis. Porcine septicaemic K. pneumoniae genomes from the UK and Australia clustered together and had higher virulence scores than all other clinical and non-clinical isolates. Septicaemic isolates were predominantly ST25, had enhanced capsule polysaccharide production with K2 capsule type and contained genes for the siderophores aerobactin, salmochelin and yersiniabactin. Septicaemic K. pneumoniae were more likely to have genes encoding the assembly of LPS, fimbriae and adhesins, and enzymes needed for the integration of mobile genetic elements. No single virulence gene was solely associated with isolates causing septicaemia. These findings indicate that there may be genotypes associated with clinical disease outcomes for K. pneumoniae. In the absence of some virulence genes, K. pneumoniae was still able to cause significant disease if the pig's immune system was immature or compromised.

Sensitive and specific LAMP and multiplex qRT-PCR assays for detection of hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKP) pose significant challenges to clinical anti-infective treatment and has emerged as a major threat to global public health. In this study, we employed the loop-mediated isothermal amplification (LAMP) assays with OTG (orange to green) visual dye and multiplex quantitative real-time PCR (qRT-PCR) assay to rapidly detect hvKP. We determined the detection limits of the LAMP methods for K. pneumoniae, iroB, and iucA genes and the qRT-PCR assay for iroB, iucA, rmpA and rmpA2. Additionally, we assessed the sensitivity and specificity (both over 95 %) of the LAMP and qRT-PCR methods. The LAMP and qRT-PCR methods established in this study have been proven to be simpler and more reliable than traditional PCR methods, making them an improved choice for laboratory diagnosis.

Emergence of mcr-8.1-bearing MDR-hypervirulent Klebsiella pneumoniae ST307

We report for the first time whole-genome sequencing of four multidrug-resistant sequence type (ST) 307 Klebsiella pneumoniae recovered from patients in two hospitals in Armenia. Comparative genomic analysis revealed that the isolates were closely related, with a maximum of 39 single nucleotide polymorphism (SNP) differences in the core genome. All Armenian isolates carried the integrative and conjugative element ICEKp4, which bears the yersiniabactin locus, and shared a common evolutionary origin, diverging around 2005 (95% CI: 1999 to 2011). Antibiotic susceptibility testing showed resistance to several antibiotics, including ampicillin, amoxicillin-clavulanic acid, cefepime, ceftazidime, norfloxacin, levofloxacin, and chloramphenicol. Specifically, isolates designated as ARM03 and ARM06 were resistant to piperacillin-tazobactam, ARM04 and ARM05 had intermediate resistance to both piperacillin-tazobactam and imipenem, and ARM03 showed intermediate resistance to amikacin. We further identified antimicrobial resistance (AMR) genes in four Armenian isolates, including blaOXA-1, blaTEM-1D, blaSHV-28, dfrA14, tet(A), sul2, qnrB1, aac(6´)-Ib-cr, strA, strB and the extended-spectrum β-lactamase gene blaCTX-M-15. Additionally, ARM03 and ARM06 also obtained dfrA5, sul1, sul3, cmlA1, mphA, aph3-Ia and the unique colistin resistance gene mcr-8.1, which was absent in all other publicly available ST307 isolates. These two isolates also acquired aerobactin siderophore-encoding gene clusters (iucABCD-iutA) and the hypermucoidy locus rmpADC (ARM06 had rmpA fragment). ARM04 and ARM05, as well as ARM03 and ARM06, had nearly identical AMR and virulence genes, along with similar plasmid replicon profiles, respectively. Our findings suggest that a transmission event occurred between the two hospitals in Armenia, likely facilitated by patients or community members, during which K. pneumoniae ST307 isolates acquired plasmids carrying AMR and virulence genes.IMPORTANCEMultidrug-resistant (MDR) Klebsiella pneumoniae sequence type (ST) 307 has emerged as a high-risk clone associated with hospital- and community-acquired infections, posing a major threat to global public health. We report in-depth comparative genomics analyses of K. pneumoniae ST307 isolates recovered from patients in Armenia. The unique colistin resistance gene mcr-8.1 identified in ARM03 and ARM06 was absent in all other ST307 isolates obtained from the publicly available data sets. ARM03 and ARM06 also acquired aerobactin siderophore-encoding gene clusters (iucABCD-iutA) and the hypermucoidy locus rmpADC (ARM06 possessed incomplete rmpA fragment). Our findings suggest that a transmission event has occurred between two hospitals in Armenia either through patients or community members. In addition, the Armenian isolates obtained plasmids carrying virulence and AMR genes during the transmission event. Our study emphasises the importance of genomic surveillance of this emerging MDR-hypervirulent pathogen to provide early interventions.

Detection of virulent Klebsiella pneumoniae strains causing intestinal and extraintestinal infections during the 80s and 90s in Brazil

Klebsiella pneumoniae is an important pathogen that causes several human infections, which is currently among the main bacterial species of clinical importance. Given the importance of understanding the characteristics of this pathogen and its evolutionary aspects, in this study, we sought to characterize strains of K. pneumoniae recovered in the 1980s and 1990s in São Paulo, Brazil. Our analyses included 48 strains recovered from diarrheagenic stools and extraintestinal infections. These strains were submitted to screening for virulence and ESβL-encoding genes, antimicrobial susceptibility tests, biofilm formation, and hypermucosity and hemolytic activity tests. Our results revealed that among the studied virulence genes, the most frequent were entB (100%), followed by iutA (100%), mrkD (98%), and ycfM (72%). Phenotypic tests revealed that the strains were non- hemolytic, and two strains were positive for the hypermucoviscosity phenotype but did not have the genetic markers associated with this phenotype. Furthermore, 17% of the isolates proved to be strong biofilm producers. Antimicrobial susceptibility testing demonstrated that most strains were susceptible to the tested antimicrobials, with the exception of five isolates that produced CTX-M-2. Our findings indicate that the collection of strains studied showed variability in virulence factors, as well as biofilm production. Still, a minority of the strains showed clinically significant resistance mechanisms. As far as we know, this is the oldest collection of K. pneumoniae studied in the country.Keywords: Bacterial virulence; Ancient bacterial strains; Enterobacterales; Bacterial infection; Diarrhea.

Antimicrobial resistance, virulence genes profiles and molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae strains from captive giant pandas (Ailuropoda melanoleuca)

BACKGROUND

Carbapenem-resistant Klebsiella pneumoniae (CRKP) increases the difficulty of clinical treatment of giant pandas. This study aimed to investigate the antibiotic susceptibility, antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), virulence genes, and molecular epidemiology of CRKP strains isolated from giant pandas. A total of 187 nonduplicated Klebsiella pneumoniae (KP) isolates were collected from fresh feces of captive giant pandas at the Chengdu Research Base of Giant Panda Breeding. Then CRKP were isolated and identified through carbapenase Carba NP assay. Subsequently, the antimicrobial susceptibility testing and antibiotic resistance genes of CRKP isolates were studied by disk diffusion (K-B) and HT-qPCR, respectively. Then both the MGEs and virulence genes of CRKP isolates were analyzed by PCR. In addition, molecular epidemiology was analyzed among the CRKP strains using pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST).

RESULTS

Eight strains of CRKP (4.5%) were isolated and identified among the 187 KP strains, and seven of eight CRKP strains both exhibited resistance to imipenem, while one strain showed resistance to meropenem, and one demonstrated multiple resistance; eight CRKP strains carried a large amount of ARGs, among which ampC/blaDHA, blaSHV-01, blaSHV-02, tetB-01, tetB-02, tetC-01, and tetC-02 were the most abundant. The MGEs analysis revealed the presence of intI1 in all strains, while the detection rates of other MGEs varied, and strain 24 exhibited the highest diversity of MGE species. Seven virulence genes, including wabG, uge, ycf, entB, kpn, alls, and wcaG, showed positive results with different proportions across the strains. In addition, PFGE patterns indicated a high level of genetic diversity among the CRKP strains. MLST analysis classified the strains into different sequence types (STs).

CONCLUSIONS

This study highlighted the diversity of CRKP strains isolated from giant panda feces, which exhibited varying levels of antibiotic resistance along with multiple ARGs, MGEs and virulence genes present. These findings emphasized the importance of monitoring and researching antibiotic resistance within wildlife populations to protect the health status of these conservation dependent animals.

Co-existence of antibiotic resistance and virulence factors in carbapenem resistant Klebsiella pneumoniae clinical isolates from Alexandria, Egypt

BACKGROUND

The emergence and spread of carbapenem resistance among Enterobacteriaceae, particularly Klebsiella pneumoniae, constitute a serious threat to public health, since carbapenems are the last line of defense in the treatment of life-threatening infections caused by drug-resistant Enterobacteriaceae. The current study investigated the co-existence of different virulence factors and carbapenemases in carbapenem-resistant Klebsiella pneumoniae clinical isolates from Alexandria, Egypt.

RESULTS

Phenotypic characterization of virulence factors indicated that 41.5% of the isolates were strong biofilm producers, while hypermucoviscosity was detected in 14.9% of the isolates. All isolates harbored five or more virulence factor encoding genes. entB, ycfM, mrkD and fimH were detected in all isolates, while only one isolate was negative for ybtS. uge, iutA, rmpA and kpn were detected in 61 (64.8%), 55 (58.5%), 41 (43.6%) and 27 (28.7%) isolates, respectively, while all isolates lacked magA and k2A. Phenotypic detection of carbapenemases was explored by performing CarbaNP and mCIM/eCIM. CarbaNP test showed positive results in 98.9% of the isolates and positive mCIM tests were observed in all isolates, while 68 (72.3%) isolates showed positive eCIM tests. blaNDM was the most prevalent carbapenemase encoding gene (92.5%) followed by the blaOXA-48 (51.1%), while blaKPC was detected in only one (1.06%) isolate. blaVIM, blaIMP and blaGES were not detected in any of the tested isolates.

CONCLUSIONS

The widespread of carbapenem-resistant Klebsiella pneumoniae represents a major problem in health care settings. A significant association between certain virulence factors and carbapenemase-encoding genes was observed. Antibiotic stewardship programs and infection control policies should be effectively implemented especially in hospitals to limit the spread of such highly virulent pathogens.

Peritonsillar abscess caused by hypervirulent Klebsiella pneumoniae: A case report and literature review

Klebsiella pneumoniae is a pathogenic bacterium responsible for otorhinolaryngology-head and neck infections. Hypervirulent K. pneumoniae (hvKp), an alarming subtype of K. pneumoniae, causes life-threatening hematogenous infection. However, there are few reports on the character of hvKp strain in the field of otorhinolaryngology-head and neck surgery. We report the case of a 60-year-old Japanese man with a peritonsillar abscess caused by hvKp. K. pneumoniae isolated from pus was positive in a string test. Genetic analysis revealed that the strain had K2, rmpA and aerobactin genes. There was no evidence of hematogenous infections such as bacteremia and liver abscess, and there was improvement by surgical drainage and intravenous antimicrobial treatment. To the best of our knowledge, this is the first reported case of peritonsillar abscess caused by hvKp that did not have hematogenous infections. The string test is a simple and inexpensive method for screening hvKp. This case highlights the need for strategies to inhibit the spread of these highly virulent strains by early drainage and appropriate antimicrobial treatment.

Macrophage-depleted young mice are beneficial in vivo models to assess the translocation of Klebsiella pneumonia from the gastrointestinal tract to the liver in the elderly

Pathobionts are commensal intestinal microbiota capable of causing systemic infections under specific conditions, such as environmental changes or aging. However, it is unclear how pathobionts are recognized by the intestinal mucosal immune system under physiological conditions. This study demonstrates that the gut pathobiont Klebsiella pneumoniae causes injury to the epithelium and translocates to the liver in specific pathogen-free mice treated with clodronate-liposomes that depleted macrophages. In the clodronate-liposome-treated mice, indigenous classical K. pneumoniae (cKp) with non-K1/K2 capsular serotypes were isolated from the liver, indicating that gut commensal cKp translocated from the gastrointestinal tract to the liver due to the depletion of intestinal macrophages. Oral inoculation of isolated cKp to clodronate-liposome-treated mice significantly reduced the survival rates compared to that of non-treated mice. Our findings demonstrate that intestinal mucosal macrophages play a pivotal role in sensing commensal cKp and suppressing their translocation to the liver. This study demonstrates that clodronate-liposome-treated mouse models are effective for screening and evaluating drugs that prevent the translocation of cKp to the liver, providing new insights into the development of preventive protocols against K. pneumoniae infection.

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.

Deciphering the relative importance of genetic elements in hypervirulent Klebsiella pneumoniae to guide countermeasure development

BACKGROUND

Quantitating the contribution of phenotype-responsible elements in hypervirulent Klebsiella pneumoniae is needed.

METHODS

Isogenic mutants of four hypervirulent clinical isolates that produced K1 (ST23), K2 (ST86), K20 (ST1544), or K54 (ST29) capsules (mean 2.2 log10 LD50 (range 1.5-2.9)) were created to measure the effects on LD50 in a murine model of the hypervirulence-associated plasmid (pVir), iucA, prmpA, prmpA2 (truncated), irp2, and clbBC.

FINDINGS

Curing pVir had the greatest increase in survival (mean LD50 to 7.6 (range 7.0-9.0, p ≤ 0.0001), a dosage comparable to classical K. pneumoniae. Results also showed increased mean LD50s for ΔprmpA (5.9, p ≤ 0.0001), ΔiucA (3.6, p ≤ 0.0001), Δirp2 (3.4), ΔrmpAΔiucA (6.3, p ≤ 0.0001), and ΔpVirΔirp2 (8.7, p ≤ 0.0001). Notably ΔpVir had an additional mean LD50 increase of 1.3 compared to the pVir-encoded ΔprmpAΔiucA (p ≤ 0.01), suggesting presence of additional pVir-virulence genes. Truncated pRmpA2 did not contribute to virulence. Odd ratios in the absence of pVir/yersiniabactin, pVir, pRmpA/aerobactin, pRmpA, aerobactin, yersiniabactin, and colibactin demonstrated a 250-fold, 67-fold, 20-fold, 16.7-fold, 9.6-fold, and 1.7-fold decrease in lethality respectively.

INTERPRETATION

These data can guide countermeasure development.

FUNDING

This work was supported by NIH R21 AI123558-01 and 1R21AI141826-01A1 (Dr. Russo) and the Department of Veterans Affairs VA Merit Review (I01 BX004677-01) (Dr. Russo). This study was also partially funded by the U.S. Defense Health Program (DHP) Operations and Maintenance.

Relationship between virulence and carbapenem resistance phenotype of Klebsiella pneumoniae from blood infection: identification of a carbapenem-resistant and hypervirulent strain

OBJECTIVES

To investigate the relationship between the virulence and the carbapenem resistance phenotype of Klebsiella pneumoniae from blood infection, and to identify carbapenem-resistant and hypervirulent Klebsiella pneumoniae (CR-HVKP)strains.

METHODS

A total of 192 Klebsiella pneumoniae strains were isolated from blood culture of patients with bloodstream infections from 2016 to 2019, of which 96 isolates were carbapenem-resistant Klebsiella pneumoniae (CRKP) and 96 were carbapenem-sensitive Klebsiella pneumoniae (CSKP). The drug susceptibility was detected by VITEK-2 automatic microbial analyzer; carbapenemase genes, virulence genes and capsule typing were detected by polymerase chain reaction; the high viscosity phenotype of strains was detected by string test, and the genome characteristics of CR-HVKP were detected by whole genome sequencing. Serum killing and biofilm formation test were used to further verify the virulence of CR-HVKP.

RESULTS

There were significant differences in drug resistance to common antibiotics, except for minocycline between CSKP and CRKP isolates (all P<0.05). 92 out of 96 CRKP isolates carried carbapenemase genes, mainly blaKPC-2. The string tests were positive in 4 isolates of CRKP and 36 isolates of CSKP (P<0.05). The detection rates of virulence genes Kfu, aerobictin, iutA, ybtS, rmpA, magA, allS, and capsule antigen K1 and K2 in CSKP group were significantly higher than those in CRKP group (all P<0.05). One HVKP strain was detected in the CRKP group (CR-HVKP) and 36 HVKP was detected in the CSKP group (P<0.05). The CR-HVKP strain belonged to the MLST412, serotype K57, expressed iutA, entB, mrkD, fimH, and rmpA virulence genes, and showed strong biofilm formation and significantly increased serum resistance. Whole genome sequencing results showed that this CR-HVKP isolate carried blaSHV-145, blaTEM-1, blaCTX-M-3, fosA6, oqxA5, oqxB26, and aac(3)-IId resistance genes, accompanied by abnormalities in outer membrane protein K (OmpK) 35 and OmpK36.

CONCLUSIONS

The drug resistance of CRKP is significantly higher than that of CSKP, while CRKP carrying fewer virulence genes in both number and types compared to CSKP. A new MLST type of carbapenem-resistant and hypervirulent Klebsiella pneumoniae strain has been detected, which requires clinical awareness and epidemiological monitoring.

Virulence Factors and Carbapenem-Resistance Mechanisms in Hypervirulent Klebsiella Pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKP) has emerged as a novel variant of K. pneumoniae, exhibiting distinct phenotypic and genotypic characteristics that confer increased virulence and pathogenicity. It is not only responsible for nosocomial infections but also community-acquired infections, including liver abscesses, endophthalmitis, and meningitis, leading to significant morbidity and mortality. HvKP has been reported all over the world, but it is mainly prevalent in Asia Pacific, especially China. Moreover, hvKP can acquire carbapenemase genes resulting in the emergence of carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKP), which possesses both high virulence and drug resistance capabilities. Consequently, CR-hvKP poses substantial challenges to infection control and presents serious threats to global public health. In this paper, we provide a comprehensive summary of the epidemiological characteristics, virulence factors, and mechanisms underlying carbapenem resistance in hvKP strains with the aim of offering valuable insights for practical prevention strategies as well as future research.

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

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

[Carbapenemase Genes, Virulence Genes, and Molecular Epidemiology of Carbapenem-Resistant Klebsiella pneumoniae Derived From Bloodstream Infections]

Objective

To investigate the clinical characteristics and molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolated from patients with bloodstream infections in a large tertiary-care general hospital in Southwest China.

Methods

A total of 131 strains of non-repeating CRKP were collected from the blood cultures of patients who had bloodstream infections in 2015-2019. The strains were identified by VITEK-2, a fully automated microbial analyzer, and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. The minimum inhibitory concentration (MIC) was determined by microbroth dilution method. The common carbapenemase resistant genes and virulence factors were identified by PCR. Homology analysis was performed by multilocus sequencing typing. Whole genome sequencing was performed to analyze the genomic characteristics of CRKP without carbapenemase.

Results

The 131 strains of CRKP showed resistance to common antibiotics, except for polymyxin B (1.6% resistance rate) and tigacycline (8.0% resistance rate). A total of 105 (80.2%) CRKP strains carried the Klebsiella pneumoniae carbapenemase (KPC) resistance gene, 15 (11.4%) strains carried the New Delhi Metallo-β-lactamase (NDM) gene, and 4 (3.1%) isolates carried both KPC and NDM genes. Sequence typing (ST) 11 (74.0%) was the dominant sequence type. High detection rates for mrkD (96.2%), fimH (98.5%), entB (100%), and other virulence genes were reported. One hypervirulent CRKP strain was detected. The seven strains of CRKP that did not produce carbapenemase were shown to carry ESBL or AmpC genes and had anomalies in membrane porins OMPK35 and OMPK36, according to whole genome sequencing.

Conclusion

In a large-scale tertiary-care general hospital, CRKP mainly carries the KPC gene, has a high drug resistance rate to a variety of antibiotics, and possesses multiple virulence genes. Attention should be paid to CRKP strains with high virulence.

Capsules and their traits shape phage susceptibility and plasmid conjugation efficiency

Bacterial evolution is affected by mobile genetic elements like phages and conjugative plasmids, offering new adaptive traits while incurring fitness costs. Their infection is affected by the bacterial capsule. Yet, its importance has been difficult to quantify because of the high diversity of confounding mechanisms in bacterial genomes such as anti-viral systems and surface receptor modifications. Swapping capsule loci between Klebsiella pneumoniae strains allowed us to quantify their impact on plasmid and phage infection independently of genetic background. Capsule swaps systematically invert phage susceptibility, revealing serotypes as key determinants of phage infection. Capsule types also influence conjugation efficiency in both donor and recipient cells, a mechanism shaped by capsule volume and conjugative pilus structure. Comparative genomics confirmed that more permissive serotypes in the lab correspond to the strains acquiring more conjugative plasmids in nature. The least capsule-sensitive pili (F-like) are the most frequent in the species' plasmids, and are the only ones associated with both antibiotic resistance and virulence factors, driving the convergence between virulence and antibiotics resistance in the population. These results show how traits of cellular envelopes define slow and fast lanes of infection by mobile genetic elements, with implications for population dynamics and horizontal gene transfer.

Higher Virulence Renders K2 Klebsiella pneumoniae a Stable Share Among Those from Pyogenic Liver Abscess

Objective

To explore why serotype K2 accounts for a stable share in Klebsiella pneumoniae from pyogenic liver abscess (PLA).

Methods

Totally 15 K2 K. pneumoniae strains from PLA, 21 K2 from non-PLA, and 31 K1 from PLA were collected from China. Sequence typing, molecular serotyping, regular PCR, and Galleria mellonella lethality were performed. A total of 12 virulence genes were detected: peg-344, allS, p-rmpA, p-rmpA2, c-rmpA, fimH, mrkD, iucA, iroN, irp2, entB, and wzi. The differences between K2 K. pneumoniae strains from PLA and non-PLA were investigated along with K1 ones.

Results

Significant differences were found between K2 strains from PLA and non-PLA for the rates of virulence genes peg-344 and iucA. The latter group also showed more diverse sequence types than the former. Significant differences were only found for virulence genes allS and irp2 between K1 and K2 strains from PLA. Based on the equal virulence factors backgrounds other than serotypes, K2 strain is more virulent than K1 as G. mellonella lethality confirmed. Gene p-rmpA only brings equal virulence to p-rmpA plus p-rmpA2 in K2 strain.

Conclusion

Based on the same virulence factors backgrounds except serotypes, K2 K. pneumoniae is more virulent than K1 from PLA, which provides a survival advantage to maintain a stable share.

Occurrence and characteristics of extended-spectrum-β-lactamase- and pAmpC-producing Klebsiella pneumoniae isolated from companion animals with urinary tract infections

This study examined 70 Klebsiella pneumoniae isolates derived from companion animals with urinary tract infections in Taiwan. Overall, 81% (57/70) of the isolates carried extended-spectrum β-lactamase (ESBL) and/or plasmid-encoded AmpC (pAmpC) genes. ESBL genes were detected in 19 samples, with blaCTX-M-1, blaCTX-M-9, and blaSHV being the predominant groups. pAmpC genes were detected in 56 isolates, with blaCIT and blaDHA being the predominant groups. Multilocus sequence typing revealed that sequence types (ST)11, ST15, and ST655 were prevalent. wabG, uge, entB, mrkD, and fimH were identified as primary virulence genes. Two isolates demonstrated a hypermucoviscosity phenotype in the string test. Antimicrobial susceptibility testing exhibited high resistance to β-lactams and fluoroquinolones in ESBL-positive isolates but low resistance to aminoglycosides, sulfonamides, and carbapenems. Isolates carrying pAmpC genes exhibited resistance to penicillin-class β-lactams. These findings provide valuable insights into the role of K. pneumoniae in the context of the concept of One Health.

Structural analysis of molybdate binding protein ModA from Klebsiella pneumoniae

Klebsiella pneumoniae, a facultative anaerobe, relies on acquiring molybdenum to sustain growth in anaerobic conditions, a crucial factor for the pathogen to establish infections within host environments. Molybdenum plays a critical role in pathogenesis as it forms an essential component of cofactors for molybdoenzymes. K. pneumoniae utilizes the ABC (ATP-Binding-Cassette) transporter encoded by the modABC operon for uptake of the group VI elements molybdenum and tungsten. In this study, we determined the X-ray crystal structures of both the molybdenum-free and molybdenum-bound substrate-binding protein (SBP) ModA from Klebsiella pneumoniae to 2.00 Å and 1.77 Å resolution respectively. ModA crystallizes in the space group P222 with a single monomer in one asymmetric unit. The purified protein remained soluble and specifically bound molybdate and tungstate with Kd values of 6.3 nM and 5.2 nM, respectively. Tungstate competes with molybdate by binding to ModA, resulting in enhanced antimicrobial activity. These data provide a starting point for structural and functional analyses of molybdate transport in K. pneumoniae.

Virulence, antimicrobial resistance, and molecular characteristics of carbapenem-resistant Klebsiella pneumoniae in a hospital in Shijiazhuang City from China

Carbapenem-resistant Klebsiella pneumoniae (CRKP), as one of the most common drug-resistant bacteria threatening human health, is hyper-resistant to multiple antimicrobial drugs and carbapenems, which can be dealt with only limited clinical treatment options. This study described the epidemiological characteristics of CRKP in this tertiary care hospital from 2016 to 2020. Specimen sources included blood, sputum, alveolar lavage fluid, puncture fluid, secretions from a burn wound, and urine. Among the 87 carbapenem-resistant strains, ST11 was the predominant isolate, followed by ST15, ST273, ST340, and ST626. These STs were in broad agreement with the STs defined by pulsed-field gel electrophoresis clustering analysis in discriminating clusters of related strains. Most CRKP isolates contained the blaKPC-2 gene, some isolates carried the blaOXA-1, blaNDM-1, and blaNDM-5 genes, and the isolates carrying carbapenem resistance genes were more resistant to the antimicrobials of β-lactams, carbapenems, macrolides, and fluoroquinolone. The OmpK35 and OmpK37 genes were detected in all CRKP strains, and the Ompk36 gene was detected in some CRKP strains. All detected OmpK37 had 4 mutant sites, and OmpK36 had 11 mutant sites, while no mutant sites were found in OmpK35. More than half of the CRKP strains contained the OqxA and OqxB efflux pump genes. The virulence genes were most commonly combined with urea-wabG-fimH-entB-ybtS-uge-ycf. Only one CRKP isolate was detected with the K54 podoconjugate serotype. This study elucidated the clinical epidemiological features and molecular typing of CRKP, and grasped the distribution of drug-resistant genotypes, podocyte serotypes, and virulence genes of CRKP, providing some guidance for the subsequent treatment of CRKP infection.

Virulence, antimicrobial resistance, and molecular characteristics of carbapenem-resistant Klebsiella pneumoniae in a hospital in Shijiazhuang City from China

Carbapenem-resistant Klebsiella pneumoniae (CRKP), as one of the most common drug-resistant bacteria threatening human health, is hyper-resistant to multiple antimicrobial drugs and carbapenems, which can be dealt with only limited clinical treatment options. This study described the epidemiological characteristics of CRKP in this tertiary care hospital from 2016 to 2020. Specimen sources included blood, sputum, alveolar lavage fluid, puncture fluid, secretions from a burn wound, and urine. Among the 87 carbapenem-resistant strains, ST11 was the predominant isolate, followed by ST15, ST273, ST340, and ST626. These STs were in broad agreement with the STs defined by pulsed-field gel electrophoresis clustering analysis in discriminating clusters of related strains. Most CRKP isolates contained the blaKPC-2 gene, some isolates carried the blaOXA-1, blaNDM-1, and blaNDM-5 genes, and the isolates carrying carbapenem resistance genes were more resistant to the antimicrobials of β-lactams, carbapenems, macrolides, and fluoroquinolone. The OmpK35 and OmpK37 genes were detected in all CRKP strains, and the Ompk36 gene was detected in some CRKP strains. All detected OmpK37 had 4 mutant sites, and OmpK36 had 11 mutant sites, while no mutant sites were found in OmpK35. More than half of the CRKP strains contained the OqxA and OqxB efflux pump genes. The virulence genes were most commonly combined with urea-wabG-fimH-entB-ybtS-uge-ycf. Only one CRKP isolate was detected with the K54 podoconjugate serotype. This study elucidated the clinical epidemiological features and molecular typing of CRKP, and grasped the distribution of drug-resistant genotypes, podocyte serotypes, and virulence genes of CRKP, providing some guidance for the subsequent treatment of CRKP infection.

Characterization of Klebsiella pneumoniae Extracellular Polysaccharides

Klebsiella pneumoniae is a clinically significant, Gram-negative pathogen in which the production of extracellular polysaccharides is a key virulence factor. Extracellular polysaccharides such as the capsule and its mucoviscosity play a significant role in K. pneumoniae infection. In this article, we explain several standard protocols used to characterize the extracellular polysaccharides of K. pneumoniae. Several of these protocols are adapted specifically for K. pneumoniae and describe methods to purify and quantify the extracellular polysaccharide of K. pneumoniae. We also present a standardized protocol to quantify K. pneumoniae mucoviscosity, a unique feature of K. pneumoniae extracellular polysaccharide. These protocols will help create uniformity in standard protocols used in K. pneumoniae extracellular polysaccharide studies. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Extracellular polysaccharide isolation and purification Basic Protocol 2: Large-scale isolation and purification of extracellular polysaccharide Basic Protocol 3: Uronic acid quantification of extracellular polysaccharide Basic Protocol 4: Extracellular polysaccharide visualization by SDS-PAGE Basic Protocol 5: Klebsiella pneumoniae mucoviscosity measurement by sedimentation resistance assay Alternate Protocol 5: 96-well plate-based Klebsiella pneumoniae sedimentation resistance assay Support Protocol 5: Determination of plate to cuvette conversion factor.

Interaction of multidrug-resistant hypervirulent Klebsiella pneumoniae with components of human innate host defense

IMPORTANCE

Klebsiella pneumoniae strains with a combination of multidrug resistance and hypervirulence genotypes (MDR hvKp) have emerged as a cause of human infections. The ability of these microbes to avoid killing by the innate immune system remains to be tested fully. To that end, we compared the ability of a global collection of hvKp and MDR hvKp clinical isolates to survive in human blood and resist phagocytic killing by human neutrophils. The two MDR hvKp clinical isolates tested (ST11 and ST147) were killed in human blood and by human neutrophils in vitro, whereas phagocytic killing of hvKp clinical isolates (ST23 and ST86) required specific antisera. Although the data were varied and often isolate specific, they are an important first step toward gaining an enhanced understanding of host defense against MDR hvKp.

Klebsiella pneumoniae: adaptive immune landscapes and vaccine horizons

Klebsiella pneumoniae is among the most common antibiotic-resistant pathogens causing nosocomial infections. Additionally, it is a leading cause of neonatal sepsis and childhood mortality across the globe. Despite its clinical importance, we are only beginning to understand how the mammalian adaptive immune system responds to this pathogen. Further, many studies investigating potential K. pneumoniae vaccine candidates or alternative therapies have been launched in recent years. Here, we review the current state of knowledge on the adaptive immune response to K. pneumoniae infections and progress towards developing vaccines and other therapies to combat these infections.

Widespread Detection of Yersiniabactin Gene Cluster and Its Encoding Integrative Conjugative Elements (ICEKp) among Nonoutbreak OXA-48-Producing Klebsiella pneumoniae Clinical Isolates from Spain and the Netherlands

In this study, we determined the presence of virulence factors in nonoutbreak, high-risk clones and other isolates belonging to less common sequence types associated with the spread of OXA-48-producing Klebsiella pneumoniae clinical isolates from The Netherlands (n = 61) and Spain (n = 53). Most isolates shared a chromosomally encoded core of virulence factors, including the enterobactin gene cluster, fimbrial fim and mrk gene clusters, and urea metabolism genes (ureAD). We observed a high diversity of K-Locus and K/O loci combinations, KL17 and KL24 (both 16%), and the O1/O2v1 locus (51%) being the most prevalent in our study. The most prevalent accessory virulence factor was the yersiniabactin gene cluster (66.7%). We found seven yersiniabactin lineages-ybt 9, ybt 10, ybt 13, ybt 14, ybt 16, ybt 17, and ybt 27-which were chromosomally embedded in seven integrative conjugative elements (ICEKp): ICEKp3, ICEKp4, ICEKp2, ICEKp5, ICEKp12, ICEKp10, and ICEKp22, respectively. Multidrug-resistant lineages-ST11, ST101, and ST405-were associated with ybt 10/ICEKp4, ybt 9/ICEKp3, and ybt 27/ICEKp22, respectively. The fimbrial adhesin kpi operon (kpiABCDEFG) was predominant among ST14, ST15, and ST405 isolates, as well as the ferric uptake system kfuABC, which was also predominant among ST101 isolates. No convergence of hypervirulence and resistance was observed in this collection of OXA-48-producing K. pneumoniae clinical isolates. Nevertheless, two isolates, ST133 and ST792, were positive for the genotoxin colibactin gene cluster (ICEKp10). In this study, the integrative conjugative element, ICEKp, was the major vehicle for yersiniabactin and colibactin gene clusters spreading. IMPORTANCE Convergence of multidrug resistance and hypervirulence in Klebsiella pneumoniae isolates has been reported mostly related to sporadic cases or small outbreaks. Nevertheless, little is known about the real prevalence of carbapenem-resistant hypervirulent K. pneumoniae since these two phenomena are often separately studied. In this study, we gathered information on the virulent content of nonoutbreak, high-risk clones (i.e., ST11, ST15, and ST405) and other less common STs associated with the spread of OXA-48-producing K. pneumoniae clinical isolates. The study of virulence content in nonoutbreak isolates can help us to expand information on the genomic landscape of virulence factors in K. pneumoniae population by identifying virulence markers and their mechanisms of spread. Surveillance should focus not only on antimicrobial resistance but also on virulence characteristics to avoid the spread of multidrug and (hyper)virulent K. pneumoniae that may cause untreatable and more severe infections.

Molecular characteristics and virulence factors of carbapenem-resistant Klebsiella pneumoniae among pediatric patients in Shanghai, China

We retrospectively investigated CRKP isolates among 92 pediatric patients (32 neonates and 60 non‑neonates) in 2019 and 2020 (59 and 33 isolates, respectively) to investigate the molecular characteristics and virulence factors of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolated from pediatric patients,. All the CRKP isolates were subjected to antimicrobial susceptibility testing, string testing, molecular typing of virulence and carbapenemase genes, and multilocus sequence typing. Hypervirulent K. pneumoniae (Hvkp) was defined based on the detection of the regulator of mucoid phenotype A (rmpA).Sequence type 11 (ST11) accounted for the majority of infections in both neonates (37.5%) and non‑neonates (43.3%) (P > 0.05), whereas it increased from 30.5% (18/59) in 2019 to 60.6% (20/33) in 2020 (P < 0.05). Carbapenemase gene KPC-2 was predominant in both neonates and non‑neonates (46.9% vs. 51.7%, respectively), followed by New Delhi metallo-beta-lactamase 1 (NDM-1) (34.4% vs. 28.3%, respectively) (all P > 0.05). Compared to 2019, the proportion of bla_NDM-1 decreased (44.1% vs. 6.1%) (P < 0.001), while that of bla_KPC-2 increased (40.7% vs. 66.7%) (P = 0.017) in 2020. ybtS and iutA had a higher positivity rate in KPC-2 and ST11 producers (all P < 0.05); the KPC-2-, ybtS-, and iutA-positive isolates showed relatively higher resistance to fluoroquinolones and aminoglycosides, nitrofurantoin, and piperacillin/tazobactam, respectively. Furthermore, the combined expression (95.7%, 88/92) of carbapenemase and virulence-associated genes was detected, with the carbapenemase genes bla_KPC-2 and bla_TEM-1 combined with virulence-associated genes entB, mrkD, and ybtS accounting for the highest percentage (20.7%).Carbapenemase gene mutations in the CRKP strain from 2019 to 2020 highlight the importance of dynamic monitoring. The spread of hypervirulence-associated genes in CRKP strains and the high positivity rates of ybtS and iutA in KPC-2- and ST11-producing ones signify their high virulence potential in pediatric patients.

Identification of three capsule depolymerases in a bacteriophage infecting Klebsiella pneumoniae capsular types K7, K20, and K27 and therapeutic application

BACKGROUND

Klebsiella pneumoniae capsular types K1, K2, K5, K20, K54, and K57 are prevalent hypervirulent types associated with community infections, and worrisomely, hypervirulent strains that acquired drug resistance have been found. In the search for alternative therapeutics, studies have been conducted on phages that infect K. pneumoniae K1, K2, K5, and K57-type strains and their phage-encoded depolymerases. However, phages targeting K. pneumoniae K20-type strains and capsule depolymerases capable of digesting K20-type capsules have rarely been reported. In this study, we characterized a phage that can infect K. pneumoniae K20-type strains, phage vB_KpnM-20.

METHODS

A phage was isolated from sewage water in Taipei, Taiwan, its genome was analyzed, and its predicted capsule depolymerases were expressed and purified. The host specificity and capsule-digesting activity of the capsule depolymerases were determined. The therapeutic effect of the depolymerase targeting K. pneumoniae K20-type strains was analyzed in a mouse infection model.

RESULTS

The isolated Klebsiella phage, vB_KpnM-20, infects K. pneumoniae K7, K20, and K27-type strains. Three capsule depolymerases, K7dep, K20dep, and K27dep, encoded by the phage were specific to K7, K20, and K27-type capsules, respectively. K20dep also recognized Escherichia coli K30-type capsule, which is highly similar to K. pneumoniae K20-type. The survival of K. pneumoniae K20-type-infected mice was increased following administration of K20dep.

CONCLUSIONS

The potential of capsule depolymerase K20dep for the treatment of K. pneumoniae infections was revealed using an in vivo infection model. In addition, K7dep, K20dep, and K27dep capsule depolymerases could be used for K. pneumoniae capsular typing.

E. coli allantoinase is activated by the downstream metabolic enzyme, glycerate kinase, and stabilizes the putative allantoin transporter by direct binding

Allantoin is a good source of ammonium for many organisms, and in Escherichia coli it is utilized under anaerobic conditions. We provide evidence that allantoinase (AllB) is allosterically activated by direct binding of the allantoin catabolic enzyme, glycerate 2-kinase (GlxK) in the presence of glyoxylate. Glyoxylate is known to be an effector of the AllR repressor which regulates the allantoin utilization operons in E. coli. AllB has low affinity for allantoin, but its activation by GlxK leads to increased affinity for its substrate. We also show that the predicted allantoin transporter YbbW (re-named AllW) has allantoin specificity and the protein-protein interaction with AllB. Our results show that the AllB-dependent allantoin degradative pathway is subject to previously unrecognized regulatory mechanisms involving direct protein-protein interactions.

Capsular polysaccharide inhibits vaccine-induced O-antigen antibody binding and function across both classical and hypervirulent K2:O1 strains of Klebsiella pneumoniae

Klebsiella pneumoniae presents as two circulating pathotypes: classical K. pneumoniae (cKp) and hypervirulent K. pneumoniae (hvKp). Classical isolates are considered urgent threats due to their antibiotic resistance profiles, while hvKp isolates have historically been antibiotic susceptible. Recently, however, increased rates of antibiotic resistance have been observed in both hvKp and cKp, further underscoring the need for preventive and effective immunotherapies. Two distinct surface polysaccharides have gained traction as vaccine candidates against K. pneumoniae: capsular polysaccharide and the O-antigen of lipopolysaccharide. While both targets have practical advantages and disadvantages, it remains unclear which of these antigens included in a vaccine would provide superior protection against matched K. pneumoniae strains. Here, we report the production of two bioconjugate vaccines, one targeting the K2 capsular serotype and the other targeting the O1 O-antigen. Using murine models, we investigated whether these vaccines induced specific antibody responses that recognize K2:O1 K. pneumoniae strains. While each vaccine was immunogenic in mice, both cKp and hvKp strains exhibited decreased O-antibody binding in the presence of capsule. Further, O1 antibodies demonstrated decreased killing in serum bactericidal assays with encapsulated strains, suggesting that the presence of K. pneumoniae capsule blocks O1-antibody binding and function. Finally, the K2 vaccine outperformed the O1 vaccine against both cKp and hvKp in two different murine infection models. These data suggest that capsule-based vaccines may be superior to O-antigen vaccines for targeting hvKp and some cKp strains, due to capsule blocking the O-antigen.

Different regulatory mechanisms of the capsule in hypervirulent Klebsiella pneumonia: "direct" wcaJ variation vs. "indirect" rmpA regulation

Introduction

Hypervirulent Klebsiella pneumoniae produce an increased amount of capsular substance and are associated with a hypermucoviscous phenotype. Capsule production is regulated by capsular regulatory genes and capsular gene cluster variations. In the present study, we focus on the effect of rmpA and wcaJon capsule biosynthesis.

Methods

Phylogenetic trees were constructed to analyze wcaJ and rmpA sequence diversity in different serotypes hypervirulent strains. Then mutant strains (K2044ΔwcaJ, K2044K1wcaJ, K2044K2wcaJand K2044K64wcaJ) were used to verify the effects of wcaJ and its diversity on capsule synthesis and strain virulence. Furthmore, the role of rmpA in capsular synthesis and its mechanisms were detected in K2044ΔrmpA strain.

Results

RmpA sequences are conversed in different serotypes. And rmpA promoted the production of hypercapsules by simultaneously acting on three promoters in cps cluster. Whereas wcaJ, its sequences are different in different serotypes, and its loss result in the termination of capsular synthesis. Moreover, the results verified that K2 wcaJ could form hypercapsule in K2044 strains (K1 serotype), but K64 wcaJ could not.

Discussion

The interaction of multiple factors is involved in capsule synthesis, including wcaJ and rmpA. RmpA, an known conserved capsular regulator gene, acts on cps cluster promoters to promote the production of the hypercapsule. WcaJ as initiating enzyme of CPS biosynthesis, its presence determines the synthesis of capsule. Besides, different from rmpA, wcaJ sequence consistency is limited to the same serotype, which cause wcaJ functioning in different serotype strains with sequence recognition specificity.

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

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

Phagocytosis is a primary determinant of pulmonary clearance of clinical Klebsiella pneumoniae isolates

Introduction

Klebsiella pneumoniae (Kp) is a common cause of hospital-acquired pneumonia. Although previous studies have suggested that evasion of phagocytic uptake is a virulence determinant of Kp, few studies have examined phagocytosis sensitivity in clinical Kp isolates.

Methods

We screened 19 clinical respiratory Kp isolates that were previously assessed for mucoviscosity for their sensitivity to macrophage phagocytic uptake, and evaluated phagocytosis as a functional correlate of in vivo Kp pathogenicity.

Results

The respiratory Kp isolates displayed heterogeneity in the susceptibility to macrophage phagocytic uptake, with 14 out of 19 Kp isolates displaying relative phagocytosis-sensitivity compared to the reference Kp strain ATCC 43816, and 5 out of 19 Kp isolates displaying relative phagocytosis-resistance. Intratracheal infection with the non-mucoviscous phagocytosis-sensitive isolate S17 resulted in a significantly lower bacterial burden compared to infection with the mucoviscous phagocytosis-resistant isolate W42. In addition, infection with S17 was associated with a reduced inflammatory response, including reduced bronchoalveolar lavage fluid (BAL) polymorphonuclear (PMN) cell count, and reduced BAL TNF, IL-1β, and IL-12p40 levels. Importantly, host control of infection with the phagocytosis-sensitive S17 isolate was impaired in alveolar macrophage (AM)-depleted mice, whereas AM-depletion had no significant impact on host defense against infection with the phagocytosis-resistant W42 isolate.

Conclusion

Altogether, these findings show that phagocytosis is a primary determinant of pulmonary clearance of clinical Kp isolates.

Virulence analysis and antibiotic resistance of Klebsiella pneumoniae isolates from hospitalised patients in Poland

Klebsiella pneumoniae (KP) is a nosocomial pathogen causing difficult-to-treat infections. The presence of virulence genes and antibiotic resistance of 109 KP isolates from hospitalized patients were investigated. Among them, 68.8% were multi-drug resistant (MDR) and 59.6% produced extended-spectrum beta-lactamases (ESBLs). Metallo-β-lactamases (MBLs) were produced by 22% of isolates (mainly from anus), including 16.5% of isolates producing New Delhi metallo-β-lactamase (NDM-1). The genes encoding adhesins (fimH-91.7%, mrkD-96.3%), enterobactin (entB-100%) and yersiniabactin (irp-1-88%) were frequently identified. The genes encoding salmochelin (iroD-9.2%, iroN-7.3%) and colibactin (clbA, clbB-0.9%) were identified rarely. Iron acquisition system-related kfu gene and wcaG gene involved in capsule production were identified in 6.4% and 11% of isolates, respectively. The rmpA gene associated with hypermucoviscosity was present in 6.4% of isolates. In 19.2% of isolates magA gene was detected, specific for K1 capsule serotype, while 22.9% of isolates showed K2 capsule serotype. The rmpA, iroD or iroN genes being diagnostic biomarkers for hypervirulent KP (hvKP) were detected in 16.5% of isolates. We found that 55.5% of hvKP were MDR and produced ESBLs, thus hospital KP isolates pose a serious threat to the healthcare system.

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

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

Multidrug resistant Klebsiella Pneumoniae reservoir and their capsular resistance genes in cow farms of district Peshawar, Pakistan

Klebsiella pneumoniae is a major zoonotic pathogen that causes a variety of severe illnesses as well as mastitis. The distribution of mastitis-causing K. Pneumoniae and its virulence factors vary by country and geographical location. The present study aimed to find out the occurrence of Multidrug-resistant (MDR) K. Pneumoniae and their capsular resistance genes which were undocumented previously in cow farms of district Peshawar, Pakistan. A total of 700 milk samples from symptomatic mastitic cows were screened for MDR K. Pneumoniae. Furthermore, the characterization of capsular resistance genes was done by molecular techniques. Among these samples, K. pneumoniae was found 180/700 (25.7%), while MDR K. pneumoniae was found 80/180 (44.4%). The antibiogram analysis revealed high resistance to Vancomycin (95%) while highly sensitive to Ceftazidime (80%). The distribution of capsular genes shows the most common serotype K2 gene 39/80 (48.7%), followed by serotype K1 gene 34/80 (42.5%), serotype K5 17/80 (21.2%), and serotype K54 13/80 (16.2), respectively. Moreover, the co-occurrence of serotypes K1+K2 was found at 11.25%, KI+K5 was 05%, K1+K54 was 3.75%, and K2+K5 was 7.5%, respectively. A statistically significant association (p ≤ 0.05) was found between predicted and discovered K. pneumoniae values. In conclusion, the presence of MDR K. pneumoniae in combination with capsular genes may be a possible threat to dairy farm animals and humans in Peshawar, Pakistan. It may give us special attention to follow up on hygienic practices in livestock management.

The Antibacterial Effect of Boron Compounds and Evaluation of the Effects on Biofilm Formation in the Infection Model of Klebsiella pneumoniae on the HepG2 Cell Line

Aim: Klebsiella pneumoniae causes hospital-acquired pneumonia, urinary tract infection and bacteremia in immunocompromised patients. Klebsiella pneumoniae, which has become more common recently, causes antibiotic resistance as well as pyogenic liver abscesses and hematogenous metastatic spread in humans. Developing antibiotic resistance complicates the treatment of liver infections. In our study, we aimed to evaluate the effect of boron compounds in an infection model created by Klebsiella pneumoniae 700603. Materials and Methods: Minimum inhibitory concentration and fractional inhibitory concentration studies, resistance gene levels, and HepG2 cell analyses were performed and evaluated. Results: We determined the low and high minimum inhibitory concentration values of boron components, sodium perborate monohydrate and etidote, respectively. In addition, sodium perborate monohydrate is also effective on biofilm formation and resistance genes. Our findings have shown that boron compounds are more effective when used in a combination. In the toxicity model created in the cellular study, the boron compounds cytotoxic effect decreased due to their antibacterial effects. Conclusion: İt seems that boron compounds are effective, and the positive effect increases when used together.

Clinical and genomic analysis of hypermucoviscous Klebsiella pneumoniae isolates: Identification of new hypermucoviscosity associated genes

Introduction

Hypermucoviscous Klebsiella pneumoniae (HmKp) poses an emerging and highly pathogenic global health threat. This study aimed to investigate the clinical and genomic characteristics of HmKp isolates to better understand the virulence mechanisms of the hypermucoviscous (HMV) phenotype.

Methods

From May 2018 to August 2021, 203 non-repeat K. pneumoniae isolates causing invasive infections were collected from a hospital in Beijing, China. Isolates were divided into HmKp (n=90, 44.3%) and non-HmKp (n=113, 55.7%) groups according to string test results.

Results

Multivariate regression showed that diabetes mellitus (odds ratio [OR]=2.20, 95% confidence interval (CI): 1.20-4.05, p=0.010) and liver abscess (OR=2.93, CI 95%:1.29-7.03, p=0.012) were associated with HmKp infections. K. pneumoniae was highly diverse, comprising 87 sequence types (STs) and 54 serotypes. Among HmKp isolates, ST23 was the most frequent ST (25/90, 27.8%), and the most prevalent serotypes were KL2 (31/90, 34.4%) and KL1 (27/90, 30.0%). Thirteen virulence genes were located on the capsular polysaccharide synthesis region of KL1 strains. HmKp isolates were sensitive to multiple antibiotics but carried more SHV-type extended spectrum β-lactamase (ESBL) resistance genes (p<0.05), suggesting that the emergence of ESBL-mediated multidrug resistance in HmKp should be monitored carefully during treatment. Phylogenetic analysis disclosed that HmKp isolates were highly diverse. Comparative genomic analysis confirmed that the HMV phenotype is a plasmid-encoded virulence factor. Seventeen HmKp genes were highly associated with HmKp, and included rmpAC, 7 iron-acquisition-related genes, and pagO, which may promote liver abscess formation.

Discussion

This investigation provides insight into the mechanisms producing the HMV phenotype.

Sewage from a secondary hospital in Ribeirão Preto, southeastern Brazil: a source of multidrug-resistant Enterobacteriaceae

Antimicrobial resistance is one of the severe threats to global health. Hospital sewage can serve as a reservoir for multi-resistant bacteria and promote the spread of antimicrobial resistance. This study aimed to investigate the antimicrobial susceptibility and the pathogenic potential of Enterobacteriaceae isolated from the sewage of a secondary hospital in Ribeirão Preto, a city in southeastern Brazil. The strains were isolated by membrane filtration and identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF). The antimicrobial susceptibility profile was performed by disk diffusion. Polymerase chain reaction (PCR) assays were used to detect virulence genes among the strains. Twenty-eight isolates were obtained, with Klebsiella pneumoniae being the predominant species (71.4%, n = 20). All isolates were classified as multidrug-resistant, including four isolates that were non-susceptible to at least 50% of the tested antibiotics. All isolates were also non-susceptible to cefuroxime and sulfonamides antibiotics; however, they were susceptible to norfloxacin, ofloxacin, amikacin, gentamicin, netilmicin, ertapenem, cefazolin, cefaclor, and cefotetan. The virulence genes ycfM, fimH, mrkD, kfu, and entB were detected in several isolates. Our study showed that even in a secondary hospital, without the routine of major surgeries and intensive care admissions, the hospital sewage can harbor a high percentage of multidrug-resistant bacteria with pathogenic potential. This leads to the worrying risk of public health and environmental contamination.

First Report of Potentially Pathogenic Klebsiella pneumoniae from Serotype K2 in Mollusk Tegillarca granosa and Genetic Diversity of Klebsiella pneumoniae in 14 Species of Edible Aquatic Animals

Klebsiella pneumoniae can cause serious pneumonitis in humans. The bacterium is also the common causative agent of hospital-acquired multidrug-resistant (MDR) infections. Here we for the first time reported the genetic diversity of K. pneumoniae strains in 14 species of edible aquatic animals sampled in the summer of 2018 and 2019 in Shanghai, China. Virulence-related genes were present in the K. pneumoniae strains (n = 94), including the entB (98.9%), mrkD (85.1%), fimH (50.0%), and ybtA (14.9%) strains. Resistance to sulfamethoxazole-trimethoprim was the most prevalent (52.1%), followed by chloramphenicol (31.9%), and tetracycline (27.7%), among the strains, wherein 34.0% had MDR phenotypes. Meanwhile, most strains were tolerant to heavy metals Cu2+ (96.8%), Cr3+ (96.8%), Zn2+ (91.5%), Pb2+ (89.4%), and Hg2+ (81.9%). Remarkably, a higher abundance of the bacterium was found in bottom-dwelling aquatic animals, among which mollusk Tegillarca granosa contained K. pneumoniae 8-2-5-4 isolate from serotype K2 (ST-2026). Genome features of the potentially pathogenic isolate were characterized. The enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR)−based genome fingerprinting classified the 94 K. pneumoniae strains into 76 ERIC genotypes with 63 singletons, demonstrating considerable genetic diversity in the strains. The findings of this study fill the gap in the risk assessment of K. pneumoniae in edible aquatic animals.

The making of hypervirulent Klebsiella pneumoniae

Klebsiella pneumoniae is a notorious bacterium in clinical practice. Virulence, carbapenem-resistance and their convergence among K. pneumoniae are extensively discussed in this article. Hypervirulent K. pneumoniae (HvKP) has spread from the Asian Pacific Rim to the world, inducing various invasive infections, such as pyogenic liver abscess, endophthalmitis, and meningitis. Furthermore, HvKP has acquired more and more drug resistance. Among multidrug-resistant HvKP, hypervirulent carbapenem-resistant K. pneumoniae (Hv-CRKP), and carbapenem-resistant hypervirulent K. pneumoniae (CR-HvKP) are both devastating for their extreme drug resistance and virulence. The hypervirulence of HvKP is primarily attributed to hypercapsule, macromolecular exopolysaccharides, or excessive siderophores, although it has many other factors, for example, lipopolysaccharides, fimbriae, and porins. In contrast with classical determination of HvKP, that is, animal lethality test, molecular determination could be an optional and practical method after improvement. HvKP, including Hv-CRKP and CR-HvKP, has been progressing. R-M and CRISPR-Cas systems may play pivotal roles in such evolutions. Hv-CRKP and CR-HvKP, in particular the former, should be of severe concern due to their being more and more prevalent.

Comparison of the therapeutic potential of bacteriophage KpV74 and phage-derived depolymerase (β-glucosidase) against Klebsiella pneumoniae capsular type K2

Bacteriophages and phage polysaccharide-degrading enzymes (depolymerases) are garnering attention as possible alternatives to antibiotics. Here, we describe the antimicrobial properties of bacteriophage KpV74 and phage depolymerase Dep_kpv74 specific to the hypervirulent Klebsiella pneumoniae of the K2 capsular type. The depolymerase Dep_kpv74 was identified as a specific glucosidase that cleaved the K2 type capsular polysaccharides of the K. pneumoniae by a hydrolytic mechanism. This depolymerase was effective against thigh soft tissue K. pneumoniae infection in mice without inducing adverse behavioral effects or toxicity. The depolymerase efficiency was similar to or greater than the bacteriophage efficiency. The phage KpV74 had a therapeutic effect only for treating the infection caused by the phage-propagating K. pneumoniae strain and was completely inactive against the infection caused by the K. pneumoniae strain that did not support phage multiplication. The depolymerase was effective in both cases. A mutant resistant to phage and depolymerase was isolated during the treatment of mice with bacteriophage. A confirmed one-base deletion in the flippase-coding wzx gene of this mutant is assumed to affect the polysaccharide capsule, abolishing the KpV74 phage adsorption and reducing the K. pneumoniae virulence.

MDR carbapenemase-producing Klebsiella pneumoniae of the hypervirulence-associated ST23 clone in Poland, 2009-19

OBJECTIVES

To characterize carbapenemase-producing isolates of the Klebsiella pneumoniae hypervirulent (hvKp) clone ST23 in Poland.

METHODS

Fifteen K. pneumoniae ST23 isolates were identified by the Polish surveillance of carbapenemase-producing Enterobacterales. These comprised a cluster with KPC-2 + NDM-1 (n = 7), KPC-2 (n = 1) or NDM-1 (n = 1) enzymes from one hospital from 2018, and sporadic isolates with KPC-2 (n = 1), NDM-1 (n = 1), VIM-1 (n = 1) or OXA-48 (n = 3), recovered from 2009 to 2019 in different towns. The isolates were sequenced by Illumina MiSeq, followed by MinION for six representatives. Clonality, phylogeny, serotypes, virulomes, resistomes and plasmids of the isolates were analysed and compared with international ST23 strains, using various bioinformatic tools.

RESULTS

Only two diverse isolates with KPC-2 or VIM-1 were of typical hvKp ST23 serotypes K1 and O1v.2, and its predominant phylogenetic clade. These contained multiple chromosomal (ybt, clb) and pK2044/KpVP-1 plasmid (iuc, iro, rmpADC, rmpA2) virulence loci, whereas carbapenemase and other antimicrobial resistance (AMR) genes were on single additional plasmids. All remaining isolates were of K57 and O2v.2 serotypes, and a minor, distant clade of unclear phylogeny, including also ∼10 isolates from other European countries. These had fewer virulence loci (ybt, iuc, rmpADC, rmpA2) but abounded in plasmids, which with several chromosomal AMR mutations conferred more extensive MDR phenotypes than in K1 O1v.2. Lower clonal diversity than in K1, and numerous common characteristics of the isolates supported the hypothesis of the emerging character of the ST23 K57 clade.

CONCLUSIONS

A new MDR ST23 lineage has emerged in Europe, causing a potential threat to public health.

Identification and Characterization of Plasmids and Genes from Carbapenemase-Producing Klebsiella pneumoniae in Makkah Province, Saudi Arabia

Klebsiella pneumoniae (K. pneumoniae) is involved in several hospital and community-acquired infections. The prevalence of K. pneumoniae-producing-carbapenemase (KPC) resistance genes rapidly increases and threatens public health worldwide. This study aimed to assess the antibiotic resistance level of K. pneumoniae isolates from Makkah Province, Saudi Arabia, during the Islamic ‘Umrah’ ritual and to identify the plasmid types, presence of genes associated with carbapenem hydrolyzing enzymes, and virulence factors. The phenotypic and genotypic analyses based on the minimum inhibitory concentration (MIC), biofilm formation, PCR, and characterization of KPC-encoding plasmids based on the replicon typing technique (PBRT) were explored. The results showed that most isolates were resistant to carbapenem antibiotics and other antibiotics classes. This study identified sixteen different replicons of plasmids in the isolates and multiple genes encoding carbapenem factors, with blaVIM and blaOXA-48 being the most prevalent genes identified in the isolates. However, none of the isolates exhibited positivity for the KPC production activity. In addition, this study also identified six virulence-related genes, including kfu, wabG, uge, rmpA, fimH, and a capsular polysaccharide (CPS). Together, the data reported in this study indicate that the isolated K. pneumoniae during the pilgrimage in Makkah were all resistant to carbapenem antibiotics. Although the isolates lacked KPC production activity, they carried multiple carbapenem-resistant genes and virulence factors, which could drive their resistant phenotype. The need for specialized methods for KPC detection, monitoring the possibility of nosocomial transmission, and diverse therapeutic alternatives are necessary for controlling the spreading of KPC. This study can serve as a reference for clinicians and researchers on types of K. pneumoniae commonly found during religious gathering seasons in Saudi Arabia.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Siderophore iucA of hypermucoviscous Klebsiella pneumoniae promotes liver damage in mice by inducing oxidative stress

The hypermucoviscosity/hypervirulent K. pneumoniae (hvKP) is a dominant cause of pyogenic liver abscess (PLA) and has contributed to the endemicity of disease in Asian country. The siderophore aerobactin (iucA) is highly expressed in hvKP and acting virulence role during hvKP infection. However, its role in the PLA is poorly understood. We constructed iucA deletion mutant (ΔiucA-hvKP852) and used animal study to characterize the role of siderophore iucA in K. pneumoniae liver abscess. The animal experiments showed that ΔiucA-hvKP852 strain had lower virulence in mice compared to hvKP852 wild type strain. At 24 h after infection, only two of ten mice developed liver abscess during infection with ΔiucA-hvKP852 strain, while nine of ten mice infected with wild type hvKP852 strain showed multiple lesions of liver abscess. The liver tissue infected with ΔiucA-hvKP852 exhibited low reactive oxygen stress levels compared to those infected by wild type hvKP852 strain (P < 0.05). The results suggest that siderophore iucA play an important role in the liver abscess by inducing oxidative stress.

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iucA positive strains produces more siderophore than iucA negative hvK. pneumoniae.

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Siderophore production is positively related with Oxidative stress in hvK. pneumoniae.

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iucA enhances oxidative stress in liver and forms liver abscess during hvK. pneumoniae infection.