Biofilm formation and antibiotic resistance inKlebsiella pneumoniaeurinary strains

Multidrug‐resistant Klebsiella pneumoniae has become a relevant healthcare‐associated pathogen. Capsule, type 1 and 3 fimbriae (mrkA gene), type 2 quorum‐sensing system (luxS), synthesis of D‐galactan I (wbbM), LPS transport (wzm) and poly‐beta‐1,6‐N‐acetyl‐D‐glucosamine (pgaA) seem involved in K. pneumoniae biofilm. Nonenzymatic antibiotic resistance is related to nonexpression or mutation of porins (OmpK35 and OmpK36), and efflux pump (acrB) overexpression. The aim of this study was to analyse some virulence factors of K. pneumoniae isolates, and to evaluate possible correlations between their antibiotic resistance profile and ability to form biofilm. Quantitative biofilm production assay, congo red agar test and string test were performed on 120 isolates clustered in 56 extensively drug‐resistant (XDR), 40 MDR and 24 susceptible (S) strains. Nine representative strains were analysed by real‐time RT‐PCR for the expression of antibiotic resistance (OmpK35, OmpK36, acrB) and biofilm production genes (mrkA, luxS, pga, wbbM, wzm) during planktonic and sessile growth. XDR isolates showed a higher ability to form biofilm (91·07%) and to produce polysaccharides (78·57%) when compared to MDR and S strains. In biofilm‐growing XDR strains, seven of eight genes were upregulated, with the only exception of OmpK36. XDR strains exhibited phenotypic and genotypic features supporting a significant growth as biofilm. This study produces new findings that highlight a positive correlation between antibiotic resistance profile and biofilm‐forming ability in XDR K. pneumoniae strains. These new evidences might contribute to the progress in selection of therapeutic treatments of infections caused by K. pneumoniae resistant also to the ‘last line of defence’ antibiotics, that is, carbapenems.