Correlation of β-lactamase production and resistance to β-lactam antibiotics in enterobacteriaceae

Abstract

Incidence of β-lactamase production (using the Nitrocefin test and isoelectric focusing) was evaluated on 284 strains of ampicillin-resistant Enterobacteriaceae. Production of the various β-lactamases was correlated with the resistance to different β-lactam antibiotics. No obvious correlation between the β-lactamase production and the resistance pattern was found. The most striking result was the lack of β-lactamase production in 42.6% of the strains. About 50% or more of the Proteus morganii, Proteus vulgaris, Serratia and Enterobacter strains produced no β-lactamases, in contrast to E. coli, Klebsiella, and Proteus rettgeri strains which produced β-lactamases extensively. The predominant enzyme was TEM 1, while TEM 2 enzyme was extremely common in Proteus mirabilis and Proteus rettgeri. Finally, it can be concluded from our results that the production of β-lactamases can be regarded as an important but not the sole determinant of resistance of β-lactam antibiotics.