Yersinia enterocolitica: Einfluß der Bebrütungstemperatur auf Antibiotika-Resistenz, Beta-Lactamaseproduktion und Wachstumsverhalten

The influence of incubation temperature (37, 30 and 22 degrees C) on antibiotic susceptibility, beta-lactamase activity and growth characteristics was studied on 43 unselected strains of Y. enterocolitica (Serovar O:3 and O:9) freshly isolated from cliical specimens. Antibiotic susceptibility was measured by the disc diffusion technique and by a broth dilution test (MIC). Beta-lactamase activity was detected with chromogenic cephacetrile using standard curves prepared for 37, 30 and 22 degrees C. Continuous increase of beta-lactamase activity was found when incubation temperatures were lowered. All strains were found to be resistant by ampicillin and cephalothin at the three temperatues tested. Some strains showed an intermediate susceptibility to carbenicillin in the disc diffusion test. A temperature reduction of 37 to 30 degrees C significantly decreased the inhibitory zone diameters for the beta-lactam antibiotics ampicillin, carbenicillin and cephalothin, but also for other substances like tetracycline, chloramphenicole and cotrimoxazole. This suggests, that the observed decrease is caused by a better growth of Y. enterocolitica at 30 degrees C rather than increased beta-lactamase production. From 30 to 22 degrees C a further decrease in inhibitory zone diameters was only seen with ampicillin and carbenicillin. This seems to be mainly due to the increased B-lactamase activity observed at 22 degrees C. In contrast the resistance to cephalothin was apparently not influenced by this additional beta-lactamase activity. Resistance to cephalothin therefore depends probably more on other, not beta-lactamase-related, factors such as permeability variations of the outer membrane or modifications of binding proteins involved in the peptidolycan biosynthesis. The correlation between beta-lactamase activity at various incubation temperatures and resistance to beta-lactam antibiotics was less pronounced when the broth dilution test (MIC) was applied. Only carbenicillin showed significantly increasing MIC values from 30 to 22 degrees C. All the Y.e. strains investigated could be divided into two groups with respect to their beta-lactamase production characteristics. The first group showed continuously increasing beta-lactamase values at lower incubation temperatures. In the second group generally lower amounts of beta-lactamase values were found and temperature dependence was not observed. On the other hand variations in cell wall permeability, resulting in a diminished accessability of the cell wall bound enzymes must also be considered.