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Alishvandi A, Barancheshemeh M, Firuzpour F, Aram C, Kamali MJ, Keikha M. Decoding virulence and resistance in Klebsiella pneumoniae: Pharmacological insights, immunological dynamics, and in silico therapeutic strategies. Microb Pathog 2025; 205:107691. [PMID: 40355055 DOI: 10.1016/j.micpath.2025.107691] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2025] [Revised: 05/07/2025] [Accepted: 05/09/2025] [Indexed: 05/14/2025]
Abstract
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.
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Affiliation(s)
- Ali Alishvandi
- Student Research Committee, Iranshahr University of Medical Sciences, Iranshahr, Iran; Department of Immunology, School of Medicine, Iranshahr University of Medical Sciences, Iranshahr, Iran
| | | | - Faezeh Firuzpour
- Research Committee, Babol University of Medical Sciences, Babol, Iran; Cancer Research Center, Babol University of Medical Sciences, Babol, Iran
| | - Cena Aram
- Department of Cell & Molecular Biology, Faculty of Biological Sciences, Kharazmi University, Tehran, Iran
| | - Mohammad Javad Kamali
- Department of Medical Genetics, School of Medicine, Babol University of Medical Sciences, Babol, Iran
| | - Masoud Keikha
- Tropical and Communicable Diseases Research Center, Iranshahr University of Medical Sciences, Iranshahr, Iran; Department of Medical Microbiology, School of Medicine, Iranshahr University of Medical Sciences, Iranshahr, Iran.
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Desai D, Misra RN, Gandham NR, Das NK, Mukhida S, Mirza S. First Report of Virulence Factors in Carbapenem-resistant Klebsiella pneumoniae from Maharashtra, India. JOURNAL OF DATTA MEGHE INSTITUTE OF MEDICAL SCIENCES UNIVERSITY 2024; 19:729-735. [DOI: 10.4103/jdmimsu.jdmimsu_374_24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2024] [Accepted: 09/25/2024] [Indexed: 05/11/2025]
Abstract
Introduction:
Klebsiella pneumoniae (KPN) is a major multidrug-resistant (MDR) organism all over the world which can cause various infections. These variations in the infections are due to the presence or expression of virulence factors along with the presence of antimicrobial resistance. These virulence factors play an important role in adherence, invasion, spread, and in turn the range of infections. Various virulence factors such as capsules, lipopolysaccharides, siderophores, and fimbriae (FimH) are reported.
Objective:
Molecular screening of the multidrug-resistant KPN (MDR KPN) for the most common multidrug resistant gene to characterize the virulence factors in the clinical isolates and find out their prevalence in the Maharashtra region of India.
Materials and Methods:
The study was conducted for 2 years at a tertiary care teaching hospital in western Maharashtra. A total of 931 extended-spectrum beta-lactamase (ESBL)-producing MDR KPN were isolated. Polymerase chain reaction (PCR) was performed for 45 purified isolates to check the presence of various multidrug-resistant (MDR) genes and to detect virulence factors.
Results:
Multiplex PCR was performed on 45 isolates, and the presence of ESBLs genes was detected in majority of the isolates. Among these, 97.8% harbored blaTEM and blaSHV genes, and blaCTX-M gene was found in 88.9% of isolates, whereas enterobactin (entB) and FimH genes contributed to 93.33% (14 of 15 isolates). However, all these isolates did not harbor mucoid phenotype regulator, K2, and Aerobactin genes screened for. The majority of the isolates expressed both entB and FimH simultaneously.
Conclusion:
The current study observed that the MDR isolates of KPN-producing β-lactamases harbor multiple types of virulence genes and virulence factors. Prevalence of entB and FimH virulence factors was found while other virulence factors may be absent in the Maharashtra region for MDR KPN.
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Affiliation(s)
- Deepali Desai
- Department of Microbiology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
| | - Rabindra Nath Misra
- Department of Microbiology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
| | - Nageswari R Gandham
- Department of Microbiology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
| | - Nikunja Kumar Das
- Department of Microbiology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
- Department of Microbiology, MAEER MIT Pune’s MIMER Medical College and Dr. BSTR Hospital, Pune, Maharashtra, India
| | - Sahjid Mukhida
- Department of Microbiology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
| | - Shahzad Mirza
- Department of Microbiology, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pune, Maharashtra, India
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Monteiro ADSS, Cordeiro SM, Reis JN. Virulence Factors in Klebsiella pneumoniae: A Literature Review. Indian J Microbiol 2024; 64:389-401. [PMID: 39011017 PMCID: PMC11246375 DOI: 10.1007/s12088-024-01247-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Accepted: 02/28/2024] [Indexed: 07/17/2024] Open
Abstract
Klebsiella pneumoniae, a member of the autochthonous human gut microbiota, utilizes a variety of virulence factors for survival and pathogenesis. Consequently, it is responsible for several human infections, including urinary tract infections, respiratory tract infections, liver abscess, meningitis, bloodstream infections, and medical device-associated infections. The main studied virulence factors in K. pneumoniae are capsule-associated, fimbriae, siderophores, Klebsiella ferric iron uptake, and the ability to metabolize allantoin. They are crucial for virulence and were associated with specific infections in the mice infection model. Notably, these factors are also prevalent in strains from the same infections in humans. However, the type and quantity of virulence factors may vary between strains, which defines the degree of pathogenicity. In this review, we summarize the main virulence factors investigated in K. pneumoniae from different human infections. We also cover the specific identification genes and their prevalence in K. pneumoniae, especially in hypervirulent strains.
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Affiliation(s)
- Adriano de Souza Santos Monteiro
- Laboratory of Pathology and Molecular Biology (LPBM), Gonçalo Moniz Research Institute, Oswaldo Cruz Foundation (FIOCRUZ), Salvador, Bahia Brazil
| | | | - Joice Neves Reis
- Laboratory of Pathology and Molecular Biology (LPBM), Gonçalo Moniz Research Institute, Oswaldo Cruz Foundation (FIOCRUZ), Salvador, Bahia Brazil
- Faculty of Pharmacy, Federal University of Bahia, Salvador, Bahia Brazil
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Jati AP, Sola-Campoy PJ, Bosch T, Schouls LM, Hendrickx APA, Bautista V, Lara N, Raangs E, Aracil B, Rossen JWA, Friedrich AW, Navarro Riaza AM, Cañada-García JE, Ramírez de Arellano E, Oteo-Iglesias J, Pérez-Vázquez M, García-Cobos S, The Dutch and Spanish Collaborative Working Groups on Surveillance on Carbapenemase-Producing Enterobacterales. Widespread Detection of Yersiniabactin Gene Cluster and Its Encoding Integrative Conjugative Elements (ICE Kp) among Nonoutbreak OXA-48-Producing Klebsiella pneumoniae Clinical Isolates from Spain and the Netherlands. Microbiol Spectr 2023; 11:e0471622. [PMID: 37310221 PMCID: PMC10434048 DOI: 10.1128/spectrum.04716-22] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 05/22/2023] [Indexed: 06/14/2023] Open
Abstract
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.
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Affiliation(s)
- Afif P. Jati
- University of Groningen, University Medical Center Groningen, Department of Medical Microbiology and Infection Prevention, Groningen, The Netherlands
- Indonesian Society of Bioinformatics and Biodiversity, Indonesia
| | - Pedro J. Sola-Campoy
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Thijs Bosch
- Infectious Diseases Research, Diagnostics and Laboratory Surveillance, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
| | - Leo M. Schouls
- Infectious Diseases Research, Diagnostics and Laboratory Surveillance, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
| | - Antoni P. A. Hendrickx
- Infectious Diseases Research, Diagnostics and Laboratory Surveillance, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
| | - Verónica Bautista
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Noelia Lara
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Erwin Raangs
- University of Groningen, University Medical Center Groningen, Department of Medical Microbiology and Infection Prevention, Groningen, The Netherlands
| | - Belén Aracil
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
- CIBER de Enfermedades Infecciosas, Spanish Network for Research in Infectious Diseases, Instituto de Salud Carlos III, Madrid, Spain
| | - John W. A. Rossen
- University of Groningen, University Medical Center Groningen, Department of Medical Microbiology and Infection Prevention, Groningen, The Netherlands
- Laboratory of Medical Microbiology and Infectious Diseases, Isala Hospital, Zwolle, The Netherlands
- Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah, USA
| | - Alex W. Friedrich
- University of Groningen, University Medical Center Groningen, Department of Medical Microbiology and Infection Prevention, Groningen, The Netherlands
- University Hospital Münster, Institute of European Prevention Networks in Infection Control, Münster, Germany
| | - Ana M. Navarro Riaza
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Javier E. Cañada-García
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - Eva Ramírez de Arellano
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
- CIBER de Enfermedades Infecciosas, Spanish Network for Research in Infectious Diseases, Instituto de Salud Carlos III, Madrid, Spain
| | - Jesús Oteo-Iglesias
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
- CIBER de Enfermedades Infecciosas, Spanish Network for Research in Infectious Diseases, Instituto de Salud Carlos III, Madrid, Spain
| | - María Pérez-Vázquez
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
- CIBER de Enfermedades Infecciosas, Spanish Network for Research in Infectious Diseases, Instituto de Salud Carlos III, Madrid, Spain
| | - Silvia García-Cobos
- University of Groningen, University Medical Center Groningen, Department of Medical Microbiology and Infection Prevention, Groningen, The Netherlands
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
| | - The Dutch and Spanish Collaborative Working Groups on Surveillance on Carbapenemase-Producing Enterobacterales
- University of Groningen, University Medical Center Groningen, Department of Medical Microbiology and Infection Prevention, Groningen, The Netherlands
- Indonesian Society of Bioinformatics and Biodiversity, Indonesia
- Laboratorio de Referencia e Investigación en Resistencia a Antibióticos e Infecciones Relacionadas con la Asistencia Sanitaria, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
- Infectious Diseases Research, Diagnostics and Laboratory Surveillance, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
- CIBER de Enfermedades Infecciosas, Spanish Network for Research in Infectious Diseases, Instituto de Salud Carlos III, Madrid, Spain
- Laboratory of Medical Microbiology and Infectious Diseases, Isala Hospital, Zwolle, The Netherlands
- Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah, USA
- University Hospital Münster, Institute of European Prevention Networks in Infection Control, Münster, Germany
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Kuo CH, Lin WF, Liu CJ, Wang ZC, Liu TY, Peng HL. Role of the stress-responsive two-component system CpxAR in regulating fimbriae expression in Klebsiella pneumoniae CG43. JOURNAL OF MICROBIOLOGY, IMMUNOLOGY, AND INFECTION = WEI MIAN YU GAN RAN ZA ZHI 2023:S1684-1182(23)00040-3. [PMID: 36898943 DOI: 10.1016/j.jmii.2023.02.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 02/06/2023] [Accepted: 02/18/2023] [Indexed: 02/27/2023]
Abstract
BACKGROUND CpxAR is a two-component system that allows bacteria to reorganize envelope structures in response to extracellular stimuli. CpxAR negatively affects type 1 fimbriae expression in Klebsiella pneumoniae CG43, a hypervirulent strain. The involvement of CpxAR in the regulation of type 3 fimbriae expression was investigated. METHODS cpxAR, cpxA, and cpxR gene-specific deletion mutants were generated. The deletion effects on the expression of type 1 and type 3 fimbriae were analyzed via measuring the promoter activity, mannose sensitive yeast agglutination activity, biofilm formation, and the production of the major pilins FimA and MrkA respectively. RNA sequencing analysis of CG43S3, ΔcpxAR, ΔcpxR and Δfur was employed to study the regulatory mechanism influencing the expression of type 3 fimbriae. RESULTS Deletion of cpxAR increased type 1 and type 3 fimbrial expression. Comparative transcriptomic analysis showed that the expression of oxidative stress-responsive enzymes, type 1 and type 3 fimbriae, and iron acquisition and homeostasis control systems were differentially affected by cpxAR or cpxR deletion. Subsequent analysis revealed that the small RNA RyhB negatively affects the expression of type 3 fimbriae, while CpxAR positively controls ryhB expression. Finally, the site-directed mutation of the predicted interacting sequences of RyhB with the mRNA of MrkA attenuated the RyhB repression of type 3 fimbriae. CONCLUSION CpxAR negatively regulates the expression of type 3 fimbriae by modulating cellular iron levels thereafter activating the expression of RyhB. The activated RyhB represses the expression of type 3 fimbriae by base-pairing binding to the 5'region of mrkA mRNA.
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Affiliation(s)
- Chih-Hao Kuo
- Department of Biological Science and Technology, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Wei-Feng Lin
- Institute of Molecular Medicine and Bioengineering, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Chia-Jui Liu
- Department of Biological Science and Technology, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Zhe-Chong Wang
- Department of Biological Science and Technology, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Ting-Yi Liu
- Institute of Molecular Medicine and Bioengineering, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Hwei-Ling Peng
- Department of Biological Science and Technology, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan; Institute of Molecular Medicine and Bioengineering, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan.
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Conserved FimK Truncation Coincides with Increased Expression of Type 3 Fimbriae and Cultured Bladder Epithelial Cell Association in Klebsiella quasipneumoniae. J Bacteriol 2022; 204:e0017222. [PMID: 36005809 PMCID: PMC9487511 DOI: 10.1128/jb.00172-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Klebsiella spp. commonly cause both uncomplicated urinary tract infection (UTI) and recurrent UTI (rUTI). Klebsiella quasipneumoniae, a relatively newly defined species of Klebsiella, has been shown to be metabolically distinct from Klebsiella pneumoniae, but its type 1 and type 3 fimbriae have not been studied. K. pneumoniae uses both type 1 and type 3 fimbriae to attach to host epithelial cells. The type 1 fimbrial operon is well conserved between Escherichia coli and K. pneumoniae apart from fimK, which is unique to Klebsiella spp. FimK contains an N-terminal DNA binding domain and a C-terminal phosphodiesterase (PDE) domain that has been hypothesized to cross-regulate type 3 fimbriae expression via modulation of cellular levels of cyclic di-GMP. Here, we find that a conserved premature stop codon in K. quasipneumoniae fimK results in truncation of the C-terminal PDE domain and that K quasipneumoniae strain KqPF9 cultured bladder epithelial cell association and invasion are dependent on type 3 but not type 1 fimbriae. Further, we show that basal expression of both type 1 and type 3 fimbrial operons as well as cultured bladder epithelial cell association is elevated in KqPF9 relative to uropathogenic K. pneumoniae TOP52. Finally, we show that complementation of KqPF9ΔfimK with the TOP52 fimK allele reduced type 3 fimbrial expression and cultured bladder epithelial cell attachment. Taken together these data suggest that the C-terminal PDE of FimK can modulate type 3 fimbrial expression in K. pneumoniae and its absence in K. quasipneumoniae may lead to a loss of type 3 fimbrial cross-regulation. IMPORTANCE K. quasipneumoniae is often indicated as the cause of opportunistic infections, including urinary tract infection, which affects >50% of women worldwide. However, the virulence factors of K. quasipneumoniae remain uninvestigated. Prior to this work, K. quasipneumoniae and K. pneumoniae had only been distinguished phenotypically by metabolic differences. This work contributes to the understanding of K. quasipneumoniae by evaluating the contribution of type 1 and type 3 fimbriae, which are critical colonization factors encoded by all Klebsiella spp., to K. quasipneumoniae bladder epithelial cell attachment in vitro. We observe clear differences in bladder epithelial cell attachment and regulation of type 3 fimbriae between uropathogenic K. pneumoniae and K. quasipneumoniae that coincide with a structural difference in the fimbrial regulatory gene fimK.
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Lin WF, Hu RY, Chang HY, Lin FY, Kuo CH, Su LH, Peng HL. The role of urease in the acid stress response and fimbriae expression in Klebsiella pneumoniae CG43. JOURNAL OF MICROBIOLOGY, IMMUNOLOGY, AND INFECTION = WEI MIAN YU GAN RAN ZA ZHI 2022; 55:620-633. [PMID: 35367140 DOI: 10.1016/j.jmii.2022.02.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Revised: 01/26/2022] [Accepted: 02/07/2022] [Indexed: 06/14/2023]
Abstract
BACKGROUND/PURPOSE Two urease operons were identified in Klebsiella pneumoniae CG43, ure-1 and ure-2. This study investigates whether a differential regulation of the expression of ure-1 and ure-2 exists and how urease activity influences the acid stress response and expression of type 1 and type 3 fimbriae. METHODS The ureA1 and ureA2 gene specific deletion mutants were constructed. Promoter activity was assessed using a LacZ reporter system. The sensitivity to acid stress was determined by assessing the survival after pH 2.5 treatment. The influence on type 1 and type 3 fimbriae expression was assessed using western blotting and mannose-sensitive yeast agglutination and biofilm formation assay, respectively. RESULTS Bacterial growth analysis in mM9-U or modified Stuart broth revealed that ure-1 was the principal urease system, and ure-2 had a negative effect on ure-1 activity. Deletion of the fur or nac gene had no apparent effect on the activity of Pure1, Pure2-1, and Pure2-2. The Pure2-2 activity was enhanced by deletion of the hns gene. ureA1 deletion increased acid stress sensitivity, whereas the deleting effect of ureA2 was notable without hns. Deletion of ureA1 or ureA2 significantly induced the expression of type 1 fimbriae but decreased MrkA production and biofilm formation. CONCLUSION ure-1 is the primary expression system in K. pneumoniae CG43, while ure-2 is active in the absence of hns. Impairment of urease activity increases the sensitivity to acid stress, and the accumulation of urea induces the expression of type 1 fimbriae but represses type 3 fimbriae expression.
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Affiliation(s)
- Wei-Feng Lin
- Institute of Molecular Medicine and Bioengineering, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Rong-Yu Hu
- Institute of Molecular Medicine and Bioengineering, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Hwan-You Chang
- Institute of Molecular Medicine, National Tsing Hua University, Hsin Chu, Taiwan
| | - Fang-Yu Lin
- Institute of Molecular Medicine, National Tsing Hua University, Hsin Chu, Taiwan
| | - Chih-Hao Kuo
- Department of Biological Science and Technology, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Li-Hsin Su
- Institute of Molecular Medicine and Bioengineering, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan
| | - Hwei-Ling Peng
- Institute of Molecular Medicine and Bioengineering, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan; Department of Biological Science and Technology, School of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsin Chu, Taiwan.
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Gomes AÉI, Pacheco T, Dos Santos CDS, Pereira JA, Ribeiro ML, Darrieux M, Ferraz LFC. Functional Insights From KpfR, a New Transcriptional Regulator of Fimbrial Expression That Is Crucial for Klebsiella pneumoniae Pathogenicity. Front Microbiol 2021; 11:601921. [PMID: 33552015 PMCID: PMC7861041 DOI: 10.3389/fmicb.2020.601921] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 12/03/2020] [Indexed: 12/17/2022] Open
Abstract
Although originally known as an opportunistic pathogen, Klebsiella pneumoniae has been considered a worldwide health threat nowadays due to the emergence of hypervirulent and antibiotic-resistant strains capable of causing severe infections not only on immunocompromised patients but also on healthy individuals. Fimbriae is an essential virulence factor for K. pneumoniae, especially in urinary tract infections (UTIs), because it allows the pathogen to adhere and invade urothelial cells and to form biofilms on biotic and abiotic surfaces. The importance of fimbriae for K. pneumoniae pathogenicity is highlighted by the large number of fimbrial gene clusters on the bacterium genome, which requires a coordinated and finely adjusted system to control the synthesis of these structures. In this work, we describe KpfR as a new transcriptional repressor of fimbrial expression in K. pneumoniae and discuss its role in the bacterium pathogenicity. K. pneumoniae with disrupted kpfR gene exhibited a hyperfimbriated phenotype with enhanced biofilm formation and greater adhesion to and replication within epithelial host cells. Nonetheless, the mutant strain was attenuated for colonization of the bladder in a murine model of urinary tract infection. These results indicate that KpfR is an important transcriptional repressor that, by negatively controlling the expression of fimbriae, prevents K. pneumoniae from having a hyperfimbriated phenotype and from being recognized and eliminated by the host immune system.
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Affiliation(s)
- Ana Érika Inácio Gomes
- Laboratório de Biologia Molecular de Microrganismos, Universidade São Francisco, Bragança Paulista, Brazil
| | - Thaisy Pacheco
- Laboratório de Biologia Molecular de Microrganismos, Universidade São Francisco, Bragança Paulista, Brazil
| | | | - José Aires Pereira
- Laboratório de Biologia Molecular e Celular de Tumores, Universidade São Francisco, Bragança Paulista, Brazil
| | - Marcelo Lima Ribeiro
- Laboratório de Imunofarmacologia e Biologia Molecular, Universidade São Francisco, Bragança Paulista, Brazil
| | - Michelle Darrieux
- Laboratório de Biologia Molecular de Microrganismos, Universidade São Francisco, Bragança Paulista, Brazil
| | - Lúcio Fábio Caldas Ferraz
- Laboratório de Biologia Molecular de Microrganismos, Universidade São Francisco, Bragança Paulista, Brazil
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9
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Lin TH, Chen Y, Kuo JT, Lai YC, Wu CC, Huang CF, Lin CT. Phosphorylated OmpR Is Required for Type 3 Fimbriae Expression in Klebsiella pneumoniae Under Hypertonic Conditions. Front Microbiol 2018; 9:2405. [PMID: 30369914 PMCID: PMC6194325 DOI: 10.3389/fmicb.2018.02405] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 09/20/2018] [Indexed: 11/28/2022] Open
Abstract
OmpR/EnvZ is a two-component system that senses osmotic signals and controls downstream gene expression in many species of Enterobacteriaceae. However, the role of OmpR/EnvZ in Klebsiella pneumoniae remains unknown. In this study, we found that production of MrkA, the major subunit of type 3 fimbriae, was decreased under hypertonic conditions. A deletion mutant of ompR and a site-directed mutant with a single amino acid substitution of aspartate 55 to alanine (D55A), which mimics the unphosphorylated form of OmpR, markedly reduced MrkA production under hypertonic conditions. These results indicate that K. pneumoniae type 3 fimbriae expression is activated by the phosphorylated form of OmpR (OmpR∼P). Although no typical OmpR∼P binding site was found in the PmrkA sequence, mrkA mRNA levels and PmrkA activity were decreased in the ΔompR and ompRD55A strains compared with the wild type (WT) strain, indicating that OmpR∼P mediates type 3 fimbriae expression at the transcriptional level. Previous reports have demonstrated that a cyclic-di-GMP (c-di-GMP) related gene cluster, mrkHIJ, regulates the expression of type 3 fimbriae. We found that both the ompR and ompRD55A mutants exhibited decreased mrkHIJ mRNA levels, intracellular c-di-GMP concentration, and bacterial biofilm amount, but increased total intracellular phosphodiesterase activity in response to hypertonic conditions. These results indicate that OmpR∼P regulates type 3 fimbriae expression to influence K. pneumoniae biofilm formation via MrkHIJ and modulation of intracellular c-di-GMP levels. Taken together, we herein provide evidence that OmpR∼P acts as a critical factor in the regulation of the c-di-GMP signaling pathway, type 3 fimbriae expression, and biofilm amount in K. pneumoniae in response to osmotic stresses.
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Affiliation(s)
- Tien-Huang Lin
- Department of Urology, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan.,School of Post-Baccalaureate Chinese Medicine, Tzu Chi University, Hualian, Taiwan
| | - Yeh Chen
- Department of Biotechnology, Hungkuang University, Taichung, Taiwan
| | - Jong-Tar Kuo
- Department of Biological Science and Technology, China University of Science and Technology, Taipei, Taiwan
| | - Yi-Chyi Lai
- Department of Microbiology and Immunology, Chung-Shan Medical University, Taichung, Taiwan
| | - Chien-Chen Wu
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan
| | - Chun-Fa Huang
- School of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Ching-Ting Lin
- School of Chinese Medicine, China Medical University, Taichung, Taiwan
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10
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Selection and validation of reference genes for gene expression studies in Klebsiella pneumoniae using Reverse Transcription Quantitative real-time PCR. Sci Rep 2018; 8:9001. [PMID: 29899556 PMCID: PMC5998039 DOI: 10.1038/s41598-018-27420-2] [Citation(s) in RCA: 76] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/23/2018] [Indexed: 12/27/2022] Open
Abstract
For reliable results, Reverse Transcription Quantitative real-time Polymerase Chain Reaction (RT-qPCR) analyses depend on stably expressed reference genes for data normalization purposes. Klebsiella pneumoniae is an opportunistic Gram-negative bacterium that has become a serious threat worldwide. Unfortunately, there is no consensus for an ideal reference gene for RT-qPCR data normalization on K. pneumoniae. In this study, the expression profile of eleven candidate reference genes was assessed in K. pneumoniae cells submitted to various experimental conditions, and the expression stability of these candidate genes was evaluated using statistical algorithms BestKeeper, NormFinder, geNorm, Delta CT and RefFinder. The statistical analyses ranked recA, rho, proC and rpoD as the most suitable reference genes for accurate RT-qPCR data normalization in K. pneumoniae. The reliability of the proposed reference genes was validated by normalizing the relative expression of iron-regulated genes in K. pneumoniae cells submitted to iron-replete and iron-limited conditions. This work emphasizes that the stable expression of any potential reference candidate gene must be validated in each physiological condition or experimental treatment under study.
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11
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High Levels of Cyclic Di-GMP in Klebsiella pneumoniae Attenuate Virulence in the Lung. Infect Immun 2018; 86:IAI.00647-17. [PMID: 29158434 DOI: 10.1128/iai.00647-17] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Accepted: 11/15/2017] [Indexed: 01/22/2023] Open
Abstract
The bacterial second messenger bis-(3'-5')-cyclic dimeric GMP (c-di-GMP) has been shown to influence the expression of virulence factors in certain pathogenic bacteria, but little is known about its activity in the increasingly antibiotic-resistant pathogen Klebsiella pneumoniae Here, the expression in K. pneumoniae of a heterologous diguanylate cyclase increased the bacterial c-di-GMP concentration and attenuated pathogenesis in murine pneumonia. This attenuation remained evident in mice lacking the c-di-GMP sensor STING, indicating that the high c-di-GMP concentration exerted its influence not on host responses but on bacterial physiology. While serum resistance and capsule expression were unaffected by the increased c-di-GMP concentration, both type 3 and type 1 pili were strongly upregulated. Importantly, attenuation of K. pneumoniae virulence by high c-di-GMP levels was abrogated when type 1 pilus expression was silenced. We conclude that increased type 1 piliation may hamper K. pneumoniae virulence in the respiratory tract and that c-di-GMP signaling represents a potential therapeutic target for antibiotic-resistant K. pneumoniae in this niche.
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12
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Lin CT, Lin TH, Wu CC, Wan L, Huang CF, Peng HL. CRP-Cyclic AMP Regulates the Expression of Type 3 Fimbriae via Cyclic di-GMP in Klebsiella pneumoniae. PLoS One 2016; 11:e0162884. [PMID: 27631471 PMCID: PMC5025149 DOI: 10.1371/journal.pone.0162884] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 08/30/2016] [Indexed: 12/18/2022] Open
Abstract
Klebsiella pneumoniae is the predominant pathogen isolated from liver abscesses of diabetic patients in Asian countries. However, the effects of elevated blood glucose levels on the virulence of this pathogen remain largely unknown. Type 3 fimbriae, encoded by the mrkABCDF genes, are important virulence factors in K. pneumoniae pathogenesis. In this study, the effects of exogenous glucose and the intracellular cyclic AMP (cAMP) signaling pathway on type 3 fimbriae expression regulation were investigated. The production of MrkA, the major subunit of type 3 fimbriae, was increased in glucose-rich medium, whereas cAMP supplementation reversed the effect. MrkA production was markedly increased by cyaA or crp deletion, but slightly decreased by cpdA deletion. In addition, the mRNA levels of mrkABCDF genes and the activity of PmrkA were increased in Δcrp strain, as well as the mRNA levels of mrkHIJ genes that encode cyclic di-GMP (c-di-GMP)-related regulatory proteins that influence type 3 fimbriae expression. Moreover, the activities of PmrkHI and PmrkJ were decreased in ΔlacZΔcrp strain. These results indicate that CRP-cAMP down-regulates mrkABCDF and mrkHIJ at the transcriptional level. Further deletion of mrkH or mrkI in Δcrp strain diminished the production of MrkA, indicating that MrkH and MrkI are required for the CRP regulation of type 3 fimbriae expression. Furthermore, the high activity of PmrkHI in the ΔlacZΔcrp strain was diminished in ΔlacZΔcrpΔmrkHI, but increased in the ΔlacZΔcrpΔmrkJ strain. Deletion of crp increased the intracellular c-di-GMP concentration and reduced the phosphodiesterase activity. Moreover, we found that the mRNA levels of multiple genes related to c-di-GMP metabolism were altered in Δcrp strain. These indicate that CRP regulates type 3 fimbriae expression indirectly via the c-di-GMP signaling pathway. In conclusion, we found evidence of a coordinated regulation of type 3 fimbriae expression by the CRP-cAMP and c-di-GMP signaling pathways in K. pneumoniae.
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Affiliation(s)
- Ching-Ting Lin
- School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China
- * E-mail: (CTL); (HLP)
| | - Tien-Huang Lin
- Division of Urology, Taichung Tzu Chi Hospital, The Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, Republic of China
- Tzu Chi University School of Post-Baccalaureate Chinese Medicine, Hualien, Taiwan, Republic of China
| | - Chien-Chen Wu
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
| | - Lei Wan
- School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China
| | - Chun-Fa Huang
- School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China
| | - Hwei-Ling Peng
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
- * E-mail: (CTL); (HLP)
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13
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Wang ZC, Liu CJ, Huang YJ, Wang YS, Peng HL. PecS regulates the urate-responsive expression of type 1 fimbriae in Klebsiella pneumoniae CG43. MICROBIOLOGY-SGM 2015; 161:2395-409. [PMID: 26385366 DOI: 10.1099/mic.0.000185] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In the Klebsiella pneumoniae CG43 genome, the divergently transcribed genes coding for PecS, the MarR-type transcription factor, and PecM, the drug metabolite transporter, are located between the type 1 and type 3 fimbrial gene clusters. The intergenic sequence pecO between pecS and pecM contains three putative PecS binding sites and a CpxR box. Electrophoretic mobility shift assay revealed that the recombinant PecS and CpxR could specifically bind to the pecO sequence, and the specific interaction of PecS and pecO could be attenuated by urate. The expression of pecS and pecM was negatively regulated by CpxAR and PecS, and was inducible by exogenous urate in the absence of cpxAR. Compared with CG43S3ΔcpxAR, the derived mutants CG43S3ΔcpxARΔpecS and CG43S3ΔcpxARΔpecSΔpecM exerted similar levels of sensitivity to H2O2 or paraquat, but higher levels of mannose-sensitive yeast agglutination activity and FimA production. The promoter activity and transcript levels of fimA in CG43S3ΔcpxAR were also increased by deleting pecS. However, no binding activity between PecS and the fimA promoter could be observed. Nevertheless, PecS deletion could reduce the expression of the global regulator HNS and release the negative effect of HNS on FimA expression. In CG43S3ΔcpxAR, the expression of FimA as well as PecS was inducible by urate, whilst urate-induced FimA expression was inhibited by the deletion of pecS. Taken together, we propose that K. pneumoniae PecS indirectly and negatively regulates the expression of type 1 fimbriae, and the regulation is urate-inducible in the absence of CpxAR.
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Affiliation(s)
- Zhe-Chong Wang
- 1 Department of Biological Science and Technology, School of Biological Science and Technology, National Chiao Tung University, Hsin Chu, ROC
| | - Chia-Jui Liu
- 1 Department of Biological Science and Technology, School of Biological Science and Technology, National Chiao Tung University, Hsin Chu, ROC
| | - Ying-Jung Huang
- 2 Division of Hematology-Oncology, Chang Gung Memorial Hospital, Tao Yuan, ROC
| | - Yu-Seng Wang
- 1 Department of Biological Science and Technology, School of Biological Science and Technology, National Chiao Tung University, Hsin Chu, ROC
| | - Hwei-Ling Peng
- 1 Department of Biological Science and Technology, School of Biological Science and Technology, National Chiao Tung University, Hsin Chu, ROC
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14
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Rosen DA, Hilliard JK, Tiemann KM, Todd EM, Morley SC, Hunstad DA. Klebsiella pneumoniae FimK Promotes Virulence in Murine Pneumonia. J Infect Dis 2015; 213:649-58. [PMID: 26347570 DOI: 10.1093/infdis/jiv440] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Accepted: 08/10/2015] [Indexed: 11/15/2022] Open
Abstract
Klebsiella pneumoniae, a chief cause of nosocomial pneumonia, is a versatile and commonly multidrug-resistant human pathogen for which further insight into pathogenesis is needed. We show that the pilus regulatory gene fimK promotes the virulence of K. pneumoniae strain TOP52 in murine pneumonia. This contrasts with the attenuating effect of fimK on urinary tract virulence, illustrating that a single factor may exert opposing effects on pathogenesis in distinct host niches. Loss of fimK in TOP52 pneumonia was associated with diminished lung bacterial burden, limited innate responses within the lung, and improved host survival. FimK expression was shown to promote serum resistance, capsule production, and protection from phagocytosis by host immune cells. Finally, while the widely used K. pneumoniae model strain 43816 produces rapid dissemination and death in mice, TOP52 caused largely localized pneumonia with limited lethality, thereby providing an alternative tool for studying K. pneumoniae pathogenesis and control within the lung.
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Affiliation(s)
- David A Rosen
- Division of Pediatric Infectious Diseases, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri
| | - Julia K Hilliard
- Division of Pediatric Infectious Diseases, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri
| | - Kristin M Tiemann
- Division of Pediatric Infectious Diseases, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri
| | - Elizabeth M Todd
- Division of Pediatric Infectious Diseases, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri
| | - S Celeste Morley
- Division of Pediatric Infectious Diseases, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, Missouri
| | - David A Hunstad
- Division of Pediatric Infectious Diseases, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri
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15
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Li B, Zhao Y, Liu C, Chen Z, Zhou D. Molecular pathogenesis of Klebsiella pneumoniae. Future Microbiol 2015; 9:1071-81. [PMID: 25340836 DOI: 10.2217/fmb.14.48] [Citation(s) in RCA: 225] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Typical Klebsiella pneumoniae is an opportunistic pathogen, which mostly affects those with weakened immune systems and tends to cause nosocomial infections. A subset of hypervirulent K. pneumoniae serotypes with elevated production of capsule polysaccharide can affect previously healthy persons and cause life-threatening community-acquired infections, such as pyogenic liver abscess, meningitis, necrotizing fasciitis, endophthalmitis and severe pneumonia. K. pneumoniae utilizes a variety of virulence factors, especially capsule polysaccharide, lipopolysaccharide, fimbriae, outer membrane proteins and determinants for iron acquisition and nitrogen source utilization, for survival and immune evasion during infection. This article aims to present the state-of-the-art understanding of the molecular pathogenesis of K. pneumoniae.
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Affiliation(s)
- Bei Li
- Department of Dermatology, Taihe Hospital, Hubei University of Medicine, Shiyan, Hubei, China
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16
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Positive autoregulation of mrkHI by the cyclic di-GMP-dependent MrkH protein in the biofilm regulatory circuit of Klebsiella pneumoniae. J Bacteriol 2015; 197:1659-67. [PMID: 25733612 DOI: 10.1128/jb.02615-14] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2015] [Accepted: 02/22/2015] [Indexed: 01/07/2023] Open
Abstract
UNLABELLED Klebsiella pneumoniae is an important cause of nosocomial infections, primarily through the formation of surface-associated biofilms to promote microbial colonization on host tissues. Expression of type 3 fimbriae by K. pneumoniae facilitates surface adherence, a process strongly activated by the cyclic di-GMP (c-di-GMP)-dependent transcriptional activator MrkH. In this study, we demonstrated the critical importance of MrkH in facilitating K. pneumoniae attachment on a variety of medically relevant materials and demonstrated the mechanism by which bacteria activate expression of type 3 fimbriae to colonize these materials. Sequence analysis revealed a putative MrkH recognition DNA sequence ("MrkH box"; TATCAA) located in the regulatory region of the mrkHI operon. Mutational analysis, electrophoretic mobility shift assay, and quantitative PCR experiments demonstrated that MrkH binds to the cognate DNA sequence to autoregulate mrkHI expression in a c-di-GMP-dependent manner. A half-turn deletion, but not a full-turn deletion, between the MrkH box and the -35 promoter element rendered MrkH ineffective in activating mrkHI expression, implying that a direct interaction between MrkH and RNA polymerase exists. In vivo analyses showed that residues L260, R265, N268, C269, E273, and I275 in the C-terminal domain of the RNA polymerase α subunit are involved in the positive control of mrkHI expression by MrkH and revealed the regions of MrkH required for DNA binding and transcriptional activation. Taken together, the data suggest a model whereby c-di-GMP-dependent MrkH recruits RNA polymerase to the mrkHI promoter to autoactivate mrkH expression. Increased MrkH production subsequently drives mrkABCDF expression when activated by c-di-GMP, leading to biosynthesis of type 3 fimbriae and biofilm formation. IMPORTANCE Bacterial biofilms can cause persistent infections that are refractory to antimicrobial treatments. This study investigated how a commonly encountered hospital-acquired pathogen, Klebsiella pneumoniae, controls the expression of MrkH, the principal regulator of type 3 fimbriae and biofilm formation. We discovered a regulatory circuit whereby MrkH acts as a c-di-GMP-dependent transcriptional activator of both the gene cluster of type 3 fimbriae and the mrkHI operon. In this positive-feedback loop, whereby MrkH activates its own production, K. pneumoniae has evolved a mechanism to ensure rapid MrkH production, expression of type 3 fimbriae, and subsequent biofilm formation under favorable conditions. Deciphering the molecular mechanisms of biofilm formation by bacterial pathogens is important for the development of innovative treatment strategies for biofilm infections.
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