Concurrent outbreaks of extended-spectrum beta-lactamase-producing organisms of the family Enterobacteriaceae in a Warsaw hospital

The increasing use of broader-spectrum cephalosporins in the first half of the 1990s has become one of the major factors responsible for the high rate of selection of extended-spectrum beta-lactamase (ESBL)-producing microorg anisms in Polish hospitals. Thirty-five isolates of seven different species of the family Enterobacteriaceae were identified as ESBL producers, over a 4 month period, in one of Warsaw's hospitals between the end of 1996 and t he beginning of 1997. Sixteen per cent of all Klebsiella pneumoniae isolate s, 16% of Citrobacter freundii isolates and 32% of Serratia marcescens isol ates collected by the hospital microbiology laboratory at that time were ex pressing these enzymes. The majority of these (27 isolates) were found to e xpress CTX-M-type ESBLs (pl 8.4). This outbreak was due to both plasmid dis semination among unrelated strains and clonal spread of some strains in sev eral wards of the hospital. The remaining isolates produced ESBLs (pl 8.2) belonging to the SHV family of beta-lactamases and demonstrated a high degr ee of genetic diversity.