O19.1 Azithromycin and Doxycycline Resistance Profiles of Mycoplasma Genitalium and Association with Treatment Outcomes
- P A Totten1,
- N L Jensen1,
- C M Khosopour1,
- C W Gillespie1,
- J S Jensen2,
- G K Kenny1,
- M R Golden1,
- L E Manhart1
Background Antibiotic resistance profiles of recent Mycoplasma genitalium (MG) isolates have not been extensively evaluated nor correlated with treatment outcomes for NGU. Urine specimens from men with NGU enrolled in a treatment trial in Seattle, WA were used to culture MG strains and assess the association of their susceptibility to azithromycin and doxycycline with treatment outcomes.
Methods Urines from all MG-positive (by PCR) men were co-cultured with VERO cells. MG growth was detected by an increase in genomes using an MG-specific quantitative PCR (qPCR); minimum inhibitory concentrations (MICs) were defined by the antibiotic concentration that resulted in 99% growth inhibition. MICs were measured at baseline (V1), 3-week (V2) and 6-week follow-up (V3). Clinical cure (V2, V3) was defined < 5 PMNs/HPF, no urethral discharge or symptoms; microbiologic cure was defined by a negative MG-specific PCR result.
Results Viable MG strains were recovered from 141 (92%) of 153 MG PCR-positive specimens; MICs were determined on 103 isolates. Azithromycin MICs were clearly bimodal; 46% (48/103) were ≤ 0.001–0.5 μg/ml, considered susceptible, and 54% (55/103) were ≥ 8 μg/ml considered resistant. Except for two strains with MICs of ≥ 8 μg/ml doxycycline, MICs were < 0.125–2 μg/ml. Doxycycline MICs did not correlate with treatment outcomes. At baseline, 33/57 (57.9%) of isolates had azithromycin MICs that were resistant. Of men in the azithromycin arm with MIC data and treatment outcomes at V2, 11/13 clinical failures (84.6%) and 16/20 microbiologic failures (80.0%) had azithromycin resistant isolates at baseline. After receiving azithromycin, 9/10 V2 clinical failures (90%) and 12/13 microbiologic failures (92.3%) had V2 azithromycin resistant MICs. All V3 clinical (7/7) and microbiologic (10/10) failures had V3 azithromycin resistant MICs.
Conclusion Approximately 60% of MG strains were resistant to azithromycin at baseline; azithromycin treatment failures occurred in 90–100% of men who received azithromycin. Development of new antimicrobial therapies for MG is essential.