Factors associated with antimicrobial resistance among clinical isolates of Klebsiella pneumoniae: 1-year survey in a French university hospital

Klebsiella pneumoniae is an opportunistic pathogen responsible for nosocomial infections. Both resistance to multiple antibiotics and the expression of virulence factors are likely to be involved in the physiopathological process. In this study, 227 isolates of K. pneumoniae collected over a 1-year period in a teaching hospital in Clermont-Ferrand, France, were investigated for their antibiotic resistance pattern and the presence of several potential virulence traits. Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) indicated that most of the isolates were phylogenetically unrelated. When tested in an in vitro adhesion assay with Int-407 intestinal cells, the median adhesion index was 5.5×10⁴ bacteria/cm² (range, 2.0×10²–3.4×10⁵). Isolates resistant to cefoxitin, chloramphenicol, and quinolones showed significantly lower adhesion indexes. The frequency of mutagenesis conferring resistance to rifampicin was low for most of the isolates. The median mutagenesis frequency was 1.0×10^–8 (range, 2.5×10^–9–3.2×10^–6) at 24 h and 1.1×10^–8 (range, 1.8×10^–9–1.2×10^–5) at 7 days. In contrast, isolates resistant to cefoxitin, chloramphenicol, and tetracycline showed a significantly greater ability to mutate. These results suggest a link between adhesion capabilities and resistance to certain antibiotics. They furthermore indicate that strains with a high mutagenesis capacity are more likely to acquire antibiotic resistance genes. The high pathogenicity island of Yersinia was detected in 16.3% of the strains and was more often associated with isolates resistant to nalidixic acid and augmentin.