Genotypic evolution in a quinolone-resistant Neisseria gonorrhoeae isolatefrom a patient with clinical failure of levofloxacin treatment

Recently, a reduction in the antimicrobial susceptibility of clinical isola tes of Neisseria gonorrhoeae to newer fluoroquinolones including levofloxac in in vitro has been recognized in Japan. We examined the quinolone resista nce mechanisms in N. gonorrhoeae isolates from a patient with clinical fail ure of levofloxacin treatment. Man with gonococcal urethritis was treated w ith oral 100 mg levofloxacin 3 times daily for 7 days. However, clinical fa ilure of the treatment was observed. The minimum inhibitory concentration o f levofloxacin for the posttreatment isolate (4.0 mu g/ml) was 4-fold highe r than that for the pretreatment isolate (1.0 mu g/ml). To analyze quinolon e resistance mechanisms in the set of isolates, we performed DNA sequencing of the quinolone reisistance-determining regions within the gyrA and parC genes. Moreover, we assayed the intracellular levoflaxacin and norfloxacin accumulation level in these isolates. The pretreatment isolate contained th ree substitutions compared to susceptible wild-type isolate, including seri ne to phenylalanine at position 91 and aspartic acid to asparagine at posit ion 95 in the GyrA protein, and serine to proline at position 88 in the Par C protein. The posttreatment isolate had four substitutions, including the sa me th res substitutions and an additional glutamic acid to glutamine sub stitution at position 91 in ParC. There was no significant difference in th e level of accumulation of levofloxacin and norfloxacin between the pretrea tment and posttreatment isolates. Our results indicate that levofloxacin se lects a mutant having an additional alteration within the gene cording for the: ParC protein during treatment, which may have enhanced quinolone resis tance in the organism.