Appearance in Japan of highly macrolide-resistant Escherichia coli producing macrolide 2'-phosphotransferase II.

Escherichia coli CU1, a clinical isolate recovered in Japan in 1997, was found to be highly-resistant to both 14-membered and 16-membered ring macrolide antibiotics. A crude extract prepared from strain CU1 inactivated 14-, 15- and 16-membered ring macrolides in the presence of ATP and the Rf value of inactivated oleandomycin was identical to that of oleandomycin 2'-phosphate. This suggested that strain CU1 produced the enzyme macrolide 2'-phosphotransferase [MPH(2')]. Substrate specificity of the crude enzyme from strain CU1 against 14-, 15- and 16-membered ring macrolides was basically similar to that of MPH(2')II from strain BM2506, differing in that the former more effectively inactivated roxithromycin and tylosin. Subsequent attempts were made to clone the novel mph gene encoding for MPH(2') in strain CU1. The mph gene carried by strain CU1 was located on nontransmissible plasmid DNA, designated pCU001. Its molecular weight, estimated by agarose electrophoresis, was approximately 57 kD. The DNA sequence of the cloned mph gene from the Japanese isolate CU1 was identical to that of mphB, which until now had only been recovered in France. The variance in the substrate specificity of MPH(2')II from each strain led us to speculate that other factors in the reaction affect the enzymatic inactivation activity.