Plasmid-determined β-lactamases identified in a group of 204 ampicillin-resistant Enterobacteriaceae

Information is presented on the plasmid-determined β-lactamases identified in 204 strains of ampicillin-resistant Enterobacteriaceae. The type most frequently identified was TEM-1 (in 85.3% of the strains), followed by SHV-1 (14.70%). Two types of plasmid-determined β-lactamase were identified in 20 strains; in 18 of them one of the two was TEM-1 and in 13, SHV-1 (the TEM-1+SHV-1 combination was observed in 12 strains). In the 41 Klebsiella strains the most frequently identified enzyme was SHV-1 (in 28 of the strains) and the proportion of strains with two plasmid-determined β-lactamases was higher than in the other species studied.