ANALYSIS OF QUINOLONE RESISTANCE MECHANISMS IN A SPARFLOXACIN-RESISTANT CLINICAL ISOLATE OF NEISSERIA-GONORRHOEAE

Background and Objectives: Recently, a reduction in the susceptibility of clinical isolates of Neisseria gonorrhoeae to newer fluoroquinolon es including sparfloxacin in vitro has been recognized in Japan. The q uinolone resistance mechanisms in gonococcal isolates from a patient w ith clinical failure of sparfloxacin treatment was investigated. Goal: To report a man with gonococcal urethritis in whom clinical failure o f sparfloxacin treatment occurred and to examine the quinolone resista nce mechanisms in gonococcal isolates from the patient. Study Design: A man crith gonococcal urethritis was treated with oral 100 mg sparflo xacin three times daily for 5 days, However, clinical failure of the s parfloxacin treatment was observed. The antimicrobial susceptibilities of pretreatment and posttreatment isolates to sparfloxacin and other agents were measured. To analyze quinolone resistance mechanisms in th e set of isolates, DNA sequencing of the genes corresponding to the qu inolone resistance-determining regions within the GyrA and ParC protei ns nas performed. We also assayed the intracellular sparfloxacin accum ulation level in these gonococcal cells. Moreover, we performed pulsed -field gel electrophoresis analysis to determine whether the pretreatm ent and posttreatment isolates were isogenic. Results: The minimum inh ibitory concentration of sparfloxacin for the posttreatment isolate (4 mu g/ml) was 16 times higher than that for the pretreatment isolate ( 0.25 mu g/ml). The pretreatment isolate contained three mutations, inc luding a Ser-91 to Phe mutation and an Asp-95 to Asn mutation in GyrA and a Ser-88 to Pro mutation in ParC, The posttreatment isolate had fo ur mutations, including the same three mutations and an additional Glu -91 to Gly mutation in ParC, The sparfloxacin accumulation level withi n 30 minutes in the posttreatment isolate was four times less than tha t in the pretreatment isolate. There were no differences in the pulsed -field gel electrophoresis patterns between the pretreatment and postt reatment isolates from the patient. Conclusions: The emergence of a fl uoroquinolone-resistant N. gonorrhoeae isolate with multiple mutations involving GyrA and ParC reduced the response to sparfloxacin treatmen t. Multiple dosing and long-term treatment with sparfloxacin seems to induce a mutation in ParC and an alteration leading to reduced drug ac cumulation that contribute to increasing the fluoroquinolone resistanc e level.