Intrinsic penicillin resistance in penicillinase-producing Neisseria gonorrhoeae strains.
The minimal inhibitory concentrations (MICs) of ampicillin for fifty strains of beta-lactamase-producing Neisseria gonorrhoeae (PPNG) isolated in Japan ranged from 1.56 to 200 micrograms/ml, and all the strains harbored a 4.5 megadalton plasmid. These strains were classified into two groups: dicloxacillin-susceptible (28%) and -resistant group (72%). A linear correlation was found in the dicloxacillin-susceptible strains between their beta-lactamase activity and the susceptibility to ampicillin, but not in the dicloxacillin-resistant strains. This suggests that the high ampicillin resistance in PPNG is due not only to acquiring the beta-lactamase producing plasmid, but also to some intrinsic resistance of the strains. To investigate a cause of the high ampicillin resistance, the beta-lactamase-producing plasmid, pTMS1, was transferred by conjugation to a penicillin-susceptible gonococcal strain as well as to its isogenic multiply antibiotic-resistant transformants, and the susceptibility of the transconjugants to ampicillin was determined. Acquisition of pTMS1 by a penicillin-susceptible strain resulted in a 32-fold increase in resistance to ampicillin, whereas the increase was 128-fold for its isogenic strains which contain some chromosomal mutations. These results suggest that reduced permeability of the outer membrane to ampicillin underlies the high ampicillin resistance of PPNG.
Ikeda
F
F
Department of Microbiology, Toho University School of Medicine, Tokyo.
D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D008826:Microbial Sensitivity Tests; D009344:Neisseria gonorrhoeae / Q000187:drug effects* / Q000201:enzymology; D010403:Penicillin Resistance; D010405:Penicillinase / Q000096:biosynthesis*; D010957:Plasmids; D014170:Transformation, Genetic
D004269:DNA, Bacterial; D010405:Penicillinase