Comparison of resistance to metals, beta-lactam antibiotics and hydrolysis of beta-lactams by Yersinia enterocolitica and Yersinia kristensenii

The resistance to metals, antibiotics and hydrolytic activity of crude extracts to beta-lactams was compared in Yersinia sp. (39 strains) of different origin (patients, pigs, small terrestrial mammals), and serovar. Y. enterocolitica serovar 3 showed the highest levels of resistance (> 256 mg/l) to ampicillin (AMP), carbenicillin (CAR) and cefazolin (CFZ), as well as the highest susceptibility to cefoxitin (COX, < 1 - 8). Other serovars of Y. enterocolitica and Y. frederiksenii also reached high levels of resistance to AMP and CAR, but in the majority of strains it was 64 mg/l. Susceptibility of the strains to CFZ ranged within < 8 - 16 mg/l. Y. kristensenii was sensitive to CFZ and displayed threshold levels of resistance to AMP and CAR (< 8 - 16 mg/l). Except for Y. enterocolitica serovar 3, resistance to COX was increased. Isolates were resistant to Pb2+, Co2+, Ni2+ and Cd2+. Resistance to Ag and Hg was rare and low. Ail crude extracts displayed low hydrolytic activity to AMP and CFZ. After repeated cultivation in the presence of subMIC Cd2+ (0.4 mM) hydrolysis of beta-lactams was negative, but phenotypic tolerance to CFZ was increased.