Acquired macrolide resistance genes and the 1 bp deletion in the mtrR promoter in Neisseria gonorrhoeae

The presence of macrolide-lincosamide-streptogramin B resistance genes erm(B), erm(C) and erm(F), the macrolide resistance mef(A) gene, and the DNA sequence of a 13 bp repeat in the promoter region of the mtrR gene, were determined in 62 Neisseria gonorrhoeae isolates collected between 1992 and 1999 in Seattle, Washington, USA. Eleven isolates with erythromycin and azithromycin MICs of less than or equal to0.06 mg/L, had no acquired genes or deletions in the 13 bp repeat region. Among 44 isolates with erythromycin MICs 1.0-16.0 mg/L, and azithromycin MICs 0.06-4.0 mg/L, 16 carried the 1 bp deletion in the mtrR promoter region alone, nine carried one or more of the four acquired macrolide resistance genes alone, and 14 carried both acquired macrolide resistance genes plus the 1 bp deletion in the mtrR promoter region. Three isolates with erythromycin MICs greater than or equal to 8 mg/L, and azithromycin MICs of 4.0 mg/L, carried only erm genes. Five isolates with MICs of 1-2 mg/L did not carry the 1 bp deletion, or any of the acquired resistance genes examined. Our data suggest that the 1 bp deletion in the mtrR promoter region is not found in all erythromycin-resistant (MIC greater than or equal to 1.0 mg/L) N. gonorrhoeae.