Plasmids related to beta-lactamase in Bacteroides fragilis

Abstract

Bacteroides fragilis is the most frequently isolated anaerobe from the clinical specimens. Most B. fragilis produces beta-lactamase enzyme that hydrolyse penicillin and ampicillin. The study on 90 strains of B. fragilis group revealed that 85 strains produced beta-lactamase enzyme. The minimum inhibitory concentration (MIC) to ampicillin and penicillin G of the majority of strain was between 16 and 32 g./ml. Cefoxitin which was beta-lactamase stable antibiotic had lower MIC than ampicillin and penicillin i.e. 4-8 g./ml. three strains of B. ovatus were able to transfer ampicillin resistance to a strain of non-beta-lactamase producing B. vulgatus by filter mating technique. The transconjugants had a substantial increasing in beta-lactamase activity and the MIC of ampicillin and penicillin G. The property of beta-lactamase (pI) from the transconjugants was 4.3 similar to their donors. However there was no plasmid found in the donor, and the transconjugants, except the two strains of donor contained some small plasmids. The beta-lactamase of B. fragilis group focused in the acid range (pI 4.3-4.9) which were unusually lower than beta-lactamase from most aerobic bacteria. Most B. fragilis produced beta-lactamase with pI 4.9 and a few strains of B. fragilis produced beta-lactamase with another minor band at pH 5.1. These B. fragilis strains did not transfer the ampicillin resistant to the ampicillin susceptible recipient by conjugation. This may due to the unappropriate recipient or the ampicillin resistant determinant was located on the chromosome.