Comparison of resistance types in Enterobacter cloacae 1977 and 1985

A collection of Enterobacter cloacae strains from Odense University Hospital from 1977 were compared with a collection from 1985 as regards acquired resistance traits. Among the strains with carbenicillin (Ca) resistance, the number of multiresistant strains decreased while the number with sole Ca-resistance increased. In 1977, a high proportion of the Ca-resistant (Ca-r) strains had plasmid-mediated beta-lactam resistance, but in 1985 the Ca-r strains were completely dominated by organisms with elevated amounts of chromosomally-mediated beta-lactamase. The latter, but not the former, strains were resistant to the newer cephalosporins (e.g. cefotaxime (Ctax)). The consumption of Ctax and cefuroxime increased from 0 kg in 1977 to 7.0 kg in 1985. It is therefore probable that this increase was the cause of the change in occurrence of the resistance types. Ninety-one % of the Ca-r strains were isolated from urinary samples in 1977. The percentage was only 31 in 1985. This change, concomitant with the increase in Ctax-r strains, can probably be explained by the better conditions for selection of Ctax-r mutants, producing greater amounts of chromosomal beta-lactamase, in wounds and respiratory tract than in urine.