Abstract
AIMS: To investigate the evolution of chromosomal and plasmid mediated resistance for ampicillin and tetracycline of N gonorrhoeae strains in Stockholm during 1982-1993. METHODS: A total of 404 gonococcal strains isolated in 1982, 1987, 1990, 1992, 1993 were analysed for minimal inhibitory concentrations (MIC) of ampicillin and tetracycline and for plasmid content. MIC values were determined by the agar dilution method and plasmid preparations were performed using alkaline lysis. To detect additional gonococcal strains with tet(M) plasmids all strains isolated in 1988-1989 and 1991, in all 234 isolates, were analysed retrospectively for MIC values of tetracycline. If an MIC value of > or = 4.0 mg/l was recorded plasmid analysis was performed. RESULTS: Increased proportions of chromosomally mediated resistance to tetracycline (p < 0.001) as well as plasmid mediated resistance to both ampicillin (p < 0.02) and tetracycline were found in the later part of the study. In 1991 the first gonococcus with tet(M) plasmid was isolated in Sweden. The proportion of strains with chromosomally mediated resistance for ampicillin did not change during the study period. The proportion of gonococcal strains with the 39 kb conjugative plasmid was increased in the later part of the study. CONCLUSIONS: The increased proportion of N gonorrhoeae strains with resistance to ampicillin and tetracycline is most likely due to importation of strains from areas with high prevalence of antibiotic resistant gonococci. The proportion of N gonorrhoeae strains with tet(M) plasmids is low in Sweden, but might increase in the same way as the proportion of PPNG strains has increased during 1982-1993.