Activity of clavulanate combinations against TEM-1 β-lactamase-producing Escherichia coli isolates obtained in 1982 and 1989

Abstract

Recent reports of decreased susceptibility to amoxycillin/clavulanate and ticarcillin/ clavulanate combinations amongst Escherichia coli isolates have been attributed to an increased frequency of hyperproduction of TEM-1 β-lactamase. To test this claim we compared the activities of clavulanate combinations against consecutive E. coli isolates producing TEM-1 β-lactamase that were obtained from clinical material at The London Hospital during 1982 (n = 50) and 1989 (n = 46). Enzyme production was quantified and related to the level of clavulanate required to potentiate amoxycillin and ticarcillin. The levels of TEM-1 enzyme production varied 150-fold amongst the isolates, partly because of variation in the gene copy number. A clear correlation existed between enzyme quantity and levels of resistance to the clavula nate combinations. However, there was no significant difference (P > 0.05, Mann-Whitney U test) between the isolates obtained in 1982 and 1989 in terms of the clavulanate concentrations required to potentiate the penicillins, or in the distribution of β-lactamase activities present.