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Published on: October 6, 2010
Hypervirulent Klebsiella pneumoniae serotype K1 clinical isolates form robust biofilms at the air-liquid interface
Meritxell Cubero1,2, Sara Marti1,2, Mª Ángeles Domínguez1,3,4
1Department of Microbiology, Hospital Universitari de Bellvitge, Instituto de Investigación Biomédica de Bellvitge (IDIBELL), Barcelona, Spain.
Abstract:
The prevalence of a new hypervirulent and hypermucoviscous K. pneumoniae phenotype (Hmv) is increasing worldwide, mainly linked to serotypes K1 and K2. Since capsular thickness can directly affect the capability to form biofilms, we aimed to evaluate the association between the Hmv phenotype with adhesion and biofilm formation in a collection of clinical K. pneumoniae isolates. We selected 38 Hmv clinical isolates [15 serotype K1; 9 serotype K2; 3 non-K1/K2 (rmpA+); 11 non-K1/K2 (rmpA-)] and 7 non-Hmv clinical isolates. The Hmv phenotype was assessed through the mucoviscosity test. Serum resistance was determined by bacterial viability tests in pooled human serum. Adhesion was evaluated with the Biofilm Ring Test®, and biofilm formation was identified by crystal violet staining (Solid-Liquid, SLI-biofilm) or visual examination (Air-Liquid, ALI-biofilm). This study linked for the first time the formation of robust ALI-biofilm plugs by K. pneumoniae to the capsular serotype K1, a group of hypervirulent strains which are generally highly susceptible to the antimicrobial agents. Among all the studied isolates, the capsular serotype K1 presented lower initial adhesion despite having the adhesins mrkD and fimH but higher ALI-biofilm formation than isolates with other capsular serotypes (K2 or non-K1/K2). This structure might confer increased resistance to a group of hypervirulent K. pneumoniae serotype K1.
Insights
Hypervirulent Klebsiella pneumoniae strains with a hypermucoviscous (Hmv) phenotype show increased biofilm formation. Serotype K1 strains form robust air-liquid biofilms, potentially enhancing resistance in these hypervirulent bacteria.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Infectious Diseases
Background:
- The hypervirulent and hypermucoviscous (Hmv) Klebsiella pneumoniae phenotype is globally increasing, primarily associated with serotypes K1 and K2.
- Capsular polysaccharide thickness is a key factor influencing bacterial adhesion and biofilm formation capabilities.
Purpose of the Study:
- To investigate the association between the Hmv phenotype and bacterial adhesion and biofilm formation in clinical Klebsiella pneumoniae isolates.
- To characterize biofilm formation in relation to capsular serotypes (K1, K2, non-K1/K2) and the presence of rmpA gene.
Main Methods:
- Mucoviscosity testing to assess the Hmv phenotype.
- Serum resistance assays using pooled human serum.
- Biofilm Ring Test® for adhesion evaluation.
- Crystal violet staining and visual examination for solid-liquid (SLI) and air-liquid (ALI) biofilm quantification.
Main Results:
- Capsular serotype K1 Klebsiella pneumoniae isolates demonstrated robust ALI-biofilm plug formation, a novel finding.
- Despite possessing adhesins (mrkD, fimH), K1 isolates exhibited lower initial adhesion compared to other serotypes.
- K1 isolates showed significantly higher ALI-biofilm formation than K2 or non-K1/K2 isolates.
- The Hmv phenotype was confirmed in 38 clinical isolates, with 15 being K1, 9 K2, and 3 rmpA+ non-K1/K2.
Conclusions:
- Capsular serotype K1 is strongly linked to the formation of substantial air-liquid biofilms in Klebsiella pneumoniae.
- This ALI-biofilm structure may contribute to the increased resistance and virulence of hypervirulent K1 strains.
- Understanding these mechanisms is crucial for developing targeted interventions against emerging Klebsiella pneumoniae infections.
