Beta-lactamases in hospital strains of gram-negative bacteria.

A collection of 98 strains of enteric Gramnegative bacteria isolated in routine investigations in a hospital laboratory all showed beta-lactamase activity, and 39 of them (40%) produced sufficient enzyme to allow determination of their relative activities against benzylpenicillin, ampicillin and cephaloridine (substrate profiles). The commonest type of beta-lactamase, detected in 33 of the 39 strains, was an "all-purpose" enzyme that showed similar activity against the penicillins and the cephalosporins. All 39 were resistant to multiple antibiotics. They were examined for their ability to transfer the beta-lactamase gene during R-factor transfer, and transferability of the beta-lactamase gene was demonstrated in 13 strains out of 32.