[Resistance of gram negative bacteria to new generation cephalosporins and the role of beta-lactamases in this type of resistance].

In this study, by using the microbroth dilution method, in vitro susceptibilities of gram negative bacteria to new generation cephalosporins were examined, and among these, 40 bacteria which showed resistance against at least two antibiotics were tested for beta-lactamase production. Beta-lactamase production was positive in all of them. However, this type of resistance could not be transferred to susceptible recipients by conjugation experiments. Our results suggest that the resistance to beta-lactam antibiotics in these strains are related with chromosomally mediated beta-lactamases.