Culture medium for confirmation of penicillin-resistant and penicillinase-producing Neisseria gonorrhoeae

Abstract

A culture method for the isolation and identification of penicillinase (beta-lactamase)-producing Neisseria gonorrhoeae (PPNG) was evaluated in the Philippines where PPNG are common. The method uses plastic biplates containing standard Martin-Lewis gonorrhea culture medium in one side of the biplate and PPNG-selective medium containing 1.5 microgram of penicillin G per ml and a suspension of Sarcina lutea (Micrococcus lutea) that was susceptible to 0.01 microgram of penicillin G per ml in the other side. Penicillin-resistant gonococci grow on both sides of the biplate. The hydrolysis of penicillin by beta-lactamase permits the growth of S. lutea around PPNG colonies. With this medium we successfully identified 11 of 12 PPNG strains growing on primary isolation plates. A 48- to 72-h incubation period was needed, however, for visible growth of S. lutea around PPNG colonies. A unique advantage of this method was the identification of non-PPNG strains which also grew on penicillin-containing medium but did not allow growth of S. lutea. These relatively penicillin-resistant strains were the cause of infections which were not cured by penicillin treatment in 2 of 11 patients.