Plasmid carriage and antibiotic susceptibility of Neisseria meningitidis strains isolated in Sweden 1981-1990.

A random selection of Neisseria meningitidis strains isolated in Sweden in the period 1981-1990 were investigated for plasmid carriage and susceptibility to antimicrobial agents commonly used for treatment and prophylaxis of meningococcal disease. The MICs were determined by the agar dilution method for penicillin V, penicillin G, rifampicin, sulfadiazine, erythromycin and tetracycline. In 13% of the invasive strains the MIC of penicillin V was > or = 0.5 mg/l which may cause concern regarding the usefulness of penicillin V in prophylaxis. In strains isolated from the urogenital tract the MICs of penicillin V and penicillin G were higher than in the invasive strains. In about 82% of the strains isolated in 1987-1988 the MIC of tetracycline was > or = 0.5 mg/l whereas no such strains were found in 1981-1982. Plasmids were found in 2 of 119 invasive strains, in 1 of 50 strains from the respiratory tract and in 1 of 19 strains from the urogenital tract. The plasmid sizes were 1.3, 2.6, 25 and 40 Mda. None of these strains were beta-lactamase producing and no relation to a high degree antibiotic resistance was observed.