Volume 31, Number 10—October 2025
Research Letter
Neonatal Gonococcal Conjunctivitis Caused by Fluoroquinolone-Resistant Neisseria gonorrhoeae
Table
MICs of antimicrobial drugs for Neisseria gonorrhoeae isolate B196-JP22 from a case of neonatal gonococcal conjunctivitis caused by fluoroquinolone-resistant N. gonorrhoeae, Japan
| Antimicrobial drug | MIC, mg/L | Interpretation* | Antimicrobial resistance genes (mutation details) |
|---|---|---|---|
| Penicillin G |
1 |
Reduced susceptibility |
mtrR (mtrR_A39T),† mtrR (mtrR_promoter_a-57del),‡ ponA (ponA_L421P),† penA gene§ |
| Piperacillin/tazobactam |
<0.01 |
Susceptible |
|
| Ceftriaxone |
0.05 |
Susceptible |
|
| Meropenem |
0.01 |
Susceptible |
|
| Levofloxacin |
12 |
Resistant |
gyrA (gyrA_S91F/D95N),† parC (parC_S87I)† |
| Azithromycin | 0.75 | Elevated MIC¶ | mtrA, macA, macB, farA# |
*Antimicrobial MIC tested by using Etest (bioMérieux, https://www.biomerieux.com). Interpretation according to Clinical and Laboratory Standards Institute (CLSI) standards (4). CLSI cutoff for susceptible is MIC <0.06 μg/mL, for intermediate is MIC 0.12–1 μg/mL, for resistant is MIC >2 μg/mL. A MIC of 1 was described as reduced susceptibility. †Missense mutation. ‡Promoter deletion. §The penA gene that encodes the PBP2 shared 99.77% identity with the penA encoded by the World Health Organization Alfa strain. However, it could not be classified by using the NG-STAR platform (https://ngstar.canada.ca) because of 2 gaps in the sequence, and the closest NG STAR type was the nonmosaic allele 18.001. ¶MIC 0.75 μg/mL was within susceptible range, although elevated compared with local reference strains. CLSI MIC cutoff for N. gonorrhoeae azithromycin susceptibility is MIC <1 μg/mL. However, CLSI has set a susceptible only interpretive breakpoint at this value, with the recommendation that this applies when azithromycin (1 g single dose) is used in combination with another antimicrobial, such as ceftriaxone. #Efflux pumps encoded in this strain include mtrA, macA, macB, and farA.