ANALYSIS OF BETA-LACTAMASE PRODUCTION IN AMPICILLIN-RESISTANT ESCHERICHIA-COLI ISOLATED FROM BLOOD CULTURES 1983-1989

From 1983 to 1989, 520 Escherichia coli blood culture pathogens were isolated from two hospitals in Turku, Finland. Ampicillin resistance (MIC greater-than-or-equal-to 16-mu-g/ml) of these isolates increased from 33 % in 1983 to 66 % in 1987, but decreased to 38-49 % in 1988-1989. Occurrence of TEM-1 beta-lactamase producing isolates increased only slightly from 14 % in 1983 to 25 % in 1989 among all Escherichia coli strains studied. Strains with ampicillin MIC values of 16-mu-g/ml and 32-mu-g/ml were mostly responsible for the increase in resistance. Among these isolates, TEM-1 or any other of the well known plasmid-mediated beta-lactamases were not found by hybridization or isoelectric focusing.