Ascorbate as an induction inhibitor of β-lactamase in a strain of Enterobacter cloacae

H.A. SHOEB, H.I. AL-SHORA AND T. ABDEL-SALAM. 1995. The effect of ascorbate and anaerobiosis of β-lactamase content (constitutive and inducible) in relation to the susceptibility of a standard strain of Enterobacter cloacae to ampicillin was studied. Enterobacter cloacae ATCC 13047 showed increasing susceptibility to ampicillin when incubated anaerobically in the presence of increasing concentrations of ascorbic acid. The inducible β-lactamase activity in the cell-free extracts of Ent. cloacae decreased when the bacterium was grown aerobically in the presence of ascorbic acid. Under anaerobic growth conditions, however, ascorbic acid abrogated the induction of the enzyme completely. On the other hand, the constitutive enzymatic activity was markedly decreased as the bacterium was grown anaerobically. Thus under these growth conditions, ascorbate-anaerobiosis, the total β-lactamase level in the presence of ampicillin as inducer fell below the basal constitutive activity observed in the absence of ampicillin.