Distribution of beta lactamases in Enterobacteriaceae: indoor versus outdoor strains.

The distribution of beta-lactamases of indoor and outdoor origin was studied over a 9-month period. We consecutively selected 37 indoor and 48 outdoor strains of the following genera of the Enterobacteriaceae family: Escherichia (species coli), Enterobacter, Proteus, and Klebsiella. All isolates were resistant to amoxicillin and/or cephalothin and/or cefamandole. All strains showed beta-lactamase activity. We characterized the enzymes by an isoelectric focusing method and by a disc diffusion test. For both indoor and outdoor isolates we found that plasmid-mediated beta-lactamases were encountered mostly in the E. coli and Klebsiella species, whereas chromosomally mediated enzymes predominated in the Proteus and Enterobacter species. No significant difference in distribution of beta-lactamases could be found comparing both groups, but it was noted that chromosomally mediated beta-lactamases predominated in the Department of Urology, while plasmid-mediated beta-lactamases prevailed in other departments (p less than 0.05).