The in vitro activity of norfloxacin, ofloxacin and ciprofloxacin and other antibiotics in current use against Neisseria gonorrhoeae.

One hundred non-beta-lactamase-producing and 50 beta-lactamase-producing strains of Neisseria gonorrhoeae serogroup WI and WII/III were tested in vitro by an agar dilution method against a panel of antibiotics including ciprofloxacin, ofloxacin and norfloxacin. All strains irrespective of beta-lactamase production and serogroup allocation, were inhibited by 0.125 mg/l of all quinolones. Ciprofloxacin turned out to be most active followed by ofloxacin and norfloxacin. All strains were also inhibited by low concentrations of cefotaxime (MIC less than 0.25 mg/l). Many strains mostly among the beta-lactamase-producing strains were resistant (MIC greater than 4 mg/l) to doxycycline. Ampicillin is still active against the majority of non-beta-lactamase-producing strains. The majority of the strains belonged to serogroup WII/III which are known to be less sensitive to penicillin G and ampicillin.