In-vitro antimicrobial susceptibility of Neisseria gonorrhoeae in New Zealand.

Four hundred and forty-two isolates of Neisseria gonorrhoeae were tested by an agar dilution method for their susceptibility to penicillin, ampicillin, tetracycline, cephaloridine, and spectinomycin. Of these isolates, 295 were tested for their susceptibility to sulphamethoxazole and to trimethoprim by the same method, using Oxoid diagnostic sensitivity test agar plus 7.5% laked horse blood instead of Proteose No. 3 agar plus 1% IsoVitaleX and 1% haemoglobin. One hundred (22.6%) of the isolates were found to be relatively resistant to penicillin (minimum inhibitory concentration (MIC) less than 0.1 iu/ml), but only 1.1% had a MIC of 1 iu/ml or higher. Ampicillin was slightly more active than penicillin in that all isolates were inhibited by 0.5 microgram/ml or less. For 3.7% of isolates the MIC of tetracycline was 2 microgram/ml or higher. All isolates were sensitive to spectinomycin. By calculating the Spearman rank correlation coefficient (rs), a high correlation (rs greater than 0.5) was found between susceptibility to penicillin and susceptibility to ampicillin, tetracycline, and cephaloridine. Low correlation (rs less than 0.2) was found between susceptibility to penicillin and susceptibility to spectinomycin, sulphamethoxazole, and trimethoprim.