Neisseria gonorrhoeae with decreased susceptibility to ciprofloxacin: pulsed-field gel electrophoresis typing of strains from North America, Hawaii, and the Philippines

Ciprofloxacin and ofloxacin are among the antibiotics recommended by the Centers for Disease Control and Prevention and are widely used to treat uncomplicated gonorrhea in adults. Strains of Neisseria gonorrhoeae which are less susceptible or resistant to fluoroquinolones have been reported in several countries. Criteria for classifying gonococcal ciprofloxacin susceptibilities have been proposed as follows: MIC greater than or equal to 1.0 mu g/ml, resistant; MIC of 0.125 to 0.5 mu g/ml, decreased susceptibility; and MIC less than or equal to 0.06 mu g/ml, susceptible. In this study, we assumed that isolates having pulsed-field gel electrophoresis (PFGE) patterns which differed by the presence or absence of a single band were closely related while those that had PFGE patterns which differed by greater than or equal to 2 bands were likely to be less closely related. This is a more stringent criterion for interpreting PFGE patterns than what has been proposed. We found genetic relatedness as well as diversity among Pro/IB-5,7 and Pro/IB-1 N. gonorrhoeae isolates recovered over a 2-year time period from various geographic locations. Phenotypic properties such as auxotype/serotype class, presence of beta -lactamase or plasmids, and antibiotic susceptibility have been used to group N. gonorrhoeae isolates. In this study, the PFGE groups did not always correlate with groups based on phenotype. An example is the first nine isolates in Table 1, which share common PFGE patterns but differed in their susceptibility to ciprofloxacin and carriage of the beta -lactamase plasmid. Similarly, 92-032894 (Pro/IB-5,7) shared PFGE patterns with Pro/IB-1 isolates rather than Pro/IB-5,7. This suggests that PFGE analysis can be a useful addition in grouping isolates into genetic clusters which can be used to trace the movement of particular genotypes over time and into different social and geographical settings.