Nalidixic acid disk for laboratory detection of ciprofloxacin resistance in Neisseria meningitidis.

Recently the CLSI recommended a disk diffusion method and breakpoints for meningococci which include breakpoints derived for nalidixic acid which serve as surrogate markers for gyrase A mutations associated with diminished fluoroquinolone susceptibility. This study presents the application of this methodology to a panel of 57 meningococcal strains isolated in Spain that include all levels of susceptibility to ciprofloxacin. In conclusion, the most useful method to predict isolates with gyrA mutations that decrease the activity of fluoroquinolones is the use of 30-μg nalidixic acid disks.