Relationship between beta-lactamases production and resistance to beta-lactam antibiotics in clinical isolates of Enterobacteriaceae.

288 clinical isolates of Enterobacteriaceae were assayed for beta-lactamase production in order to assess the role played by beta-lactamases in resistance to beta-lactam antibiotics. The data obtained showed that beta-lactamase production is undoubtedly a fundamental determinant for resistance. In fact, there was a significant correlation between the specific activity of the enzyme and the MIC of the strains considered. However, the role played by permeability barriers and/or other factors should be stressed, especially in determining resistance to cephalosporins. The validity of the nitrocefin test for detection of beta-lactamase production in Enterobacteriaeae from clinical isolates was also investigated.