[ESBL-positive strains of the Bacteroides fragilis group isolated from patients at the regional hospital center in Płock (Poland)].

The aim of this study was to confirm a presumptive qualification of clinical B. fragilis group strains isolated in Płock as ESBL-positive strains and to determine some properties of these strains. Twenty four clinical strains belonging to the B. fragilis group, isolated first of all from surgical patients, were received for testing. Identification of strains was performed in the automatic ATB Expression system (bioMerieux sa, France) using biochemical API 20 A strips. Strains were tested for the production of catalase (ID Color Catalase test, bioMerieux sa) and beta-lactamase (Cefinase, BBL, Becton Dickinson, USA). Susceptibility of strains to four antimicrobial agents: clindamycin, metronidazole, amoxicillin/clavulanic acid and imipenem was determined by Etest (AB Biodisk, Sweden). ESBLs were detected with the use of two disc diffusion methods: the double-disc synergy test (DDST) according to Jarlier et al. and the diagnostic disc (DD) test according to Appleton. Seventeen of examined strains belonged to the species Bacteroides fragilis, three--to B. ovatus/thetaiotaomicron, two--to B. distasonis, one--to B. uniformis and one--to B. stercoris/eggerthii. One strain (B. uniformis) did not produce catalase, whereas all strains produced beta-lactamases. Examined strains were susceptible in vitro to metronidazole, amoxicillin/clavulanic acid and imipenem. One clindamycin-resistant strain was detected (B. fragilis). Occurrence of ESBL-type enzymes was confirmed in 22 strains of following species: B. fragilis (17 strains), B. ovatus/thetaiotaomicron (3), B. distasonis (1) and B. uniformis (1). Clinical strains of the B. fragilis group with a new mechanism of resistance to beta-lactam antibiotics appeared during last years in Poland. They produce extended-spectrum beta-lactamases (ESBLs), so they are resistant to penicillins, cephalosporins and monobactams. Monitoring of infections caused by these threatening strains in hospital patients is very important.