Chromosomally-mediated beta-lactamases produced by Levinea amalonatica with activity against methoxyimino-cephalosporins.

Levinea amalonatica strain A2370 was isolated from the blood culture of a patient hospitalized in Charles Nicolle hospital (Tunis) during July 1986 and had decreased susceptibility to cefotaxime. Isoelectric focusing of crude extracts from this strain demonstrated three bands of beta-lactamase activity which focused at pH 5.4, 5.5 and 6.05. The three bands were separated and analysed for their kinetic properties. One enzyme (pI 5.4) had the properties of a TEM-1 beta-lactamase and did not confer resistance to third-generation cephalosporins. The two other bands, named B1 and B2, had pIs of 6.05 and 5.5 respectively, hydrolysed cefotaxime and similar cephalosporins, and were produced constitutively. After prolonged storage (six months at -20 degrees C) of the highly purified B1 enzyme, a mixture of B1/B2, with the B2 band predominating, was obtained. This observation suggested that the B2 enzyme was derived from B1. These enzymes appeared to differ from the MJ-2 beta-lactamase described previously in L. amalonatica.