Multidrug-resistant Klebsiella pneumoniae has emerged as one of the deadliest opportunistic nosocomial pathogens that forms biofilm for the establishment of chronic K. pneumoniae
infections. Herein, we made an attempt to identify the genes involved in biofilm formation in the strain K. pneumoniae ATCC13883. To achieve this, we constructed mini-Tn5 transposon insertion mutants and screened them for biofilm production. We observed that the biofilm formation was enhanced in the mutant where the wcaJ gene was disrupted. WcaJ is the initiating
enzyme of
colanic acid synthesis and loads the first
sugar (glucose-1-P) on the
lipid carrier
undecaprenyl phosphate. The absence of this
glycosyltransferase results in the absence of
colanic acid, which renders a non-mucoid phenotype to the mutant. Further, to determine the effect of mucoidy on
antibiotic susceptibility, we tested the sensitivity of the strains towards different groups of
antibiotics. Unlike the mucoid strains, the resistance of the non-mucoid cells was greater for
polymyxins, but less for
quinolones. Capsular
polysaccharides are known to have a protective effect against phagocytosis, therefore we assessed the role of
colanic acid in virulence by conducting
infection studies on murine macrophages. Surprisingly, the ΔwcaJ strain was less efficient in macrophage activation and was not readily phagocytosed. Thus, the presence of
colanic acid appeared to increase the immunogenicity of K. pneumoniae. Overall, the results indicate that the presence of
colanic acid increases the vulnerability of K. pneumoniae towards both
polymyxins and macrophages, implying that the mucoid strains are less threatening as compared to their high biofilm forming non-mucoid counterparts.