Serratia marcescens isolated in 2005 from clinical specimens from patients with diminished immunity.

Serratia marcescens is an important agent in hospital infections. The aim of this paper was to compare the resistance patterns of S. marcescens strains isolated during 1 year from patients of various wards of the Institute of Transplantology. The mechanisms of beta-lactam antibiotic resistance were of especial interest. We investigated the 81 strains of S. marcescens, isolated during 2005 from patients on 3 wards and 1 clinic of the Transplantation Institute. An unusually high resistance to most antibiotics was observed among S. marcescens strains. Extended spectrum beta-lactamases (ESBLs) were probably produced by 63.2% to 84.6% of strains, depending on the ward. Additionally, about 30% of them were probably derepressed AmpC producers. The patterns of resistance indicated that at least 2 resistant clones of S. marcescens spread among the patients. One of the clones demonstrated both ESBL and derepressed AmpC production and was susceptible only to carbapenems. The second, producing ESBL, was susceptible to piperacillin/tazobactam and carbapenems. All investigated strains were resistant to nitrofurantoin. Strains of the second group were rarely susceptible to other antibiotics: aminoglycosides, ciprofloxacin, cotrimoxazole, or fosfomycin.