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Antimicrobial Agents and Chemotherapy, September 2002, p. 3020-3025, Vol. 46, No. 9
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.9.3020-3025.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Mutation in 23S rRNA Associated with Macrolide Resistance in Neisseria gonorrhoeae

Lai-King Ng,* Irene Martin, Gary Liu, and Louis Bryden

National Laboratory for Sexually Transmitted Diseases, National Microbiology Laboratory, Population and Public Health Branch, Health Canada, Winnipeg, Manitoba, Canada

Received 9 January 2002/ Returned for modification 17 April 2002/ Accepted 20 June 2002

Fifty-six azithromycin-resistant (MICs, 2.0 to 4.0 µg/ml) Neisseria gonorrhoeae strains with cross-resistance to erythromycin (MICs, 2.0 to 64.0 µg/ml), isolated in Canada between 1997 and 1999, were characterized, and their mechanisms of azithromycin resistance were determined. Most (58.9%) of them belonged to auxotype-serotype class NR/IB-03, with a 2.6-mDa plasmid. Based on resistance to crystal violet (MICs >= 1 µg/ml), 96.4% of these macrolide-resistant strains appeared to have increased efflux. Nine of the eleven strains selected for further characterization were found to have a promoter region mtrR mutation, a single-base-pair (A) deletion in the 13-bp inverted repeat, which is believed to cause overexpression of the mtrCDE-encoded efflux pump. The two remaining macrolide-resistant strains (erythromycin MIC, 64.0 µg/ml; azithromycin MIC, 4.0 µg/ml), which did not have the mutation in the mtrR promoter region, were found to have a C2611T mutation (Escherichia coli numbering) in the peptidyltransferase loop in domain V of the 23S rRNA alleles. Although mutations in domain V of 23S rRNA alleles had been reported in other bacteria, including E. coli, Streptococcus pneumoniae, and Helicobacter pylori, this is the first observation of these mutations associated with macrolide resistance in N. gonorrhoeae.

* Corresponding author. Mailing address: National Microbiology Laboratory, Population and Public Health Branch, Health Canada, 1015 Arlington St., Room H2380, Winnipeg, MB, R3E 3R2 Canada. Phone: (204) 789-2131. Fax: (204) 789-2140. E-mail: Lai_King_Ng {at}hc-sc.gc.ca.

Antimicrobial Agents and Chemotherapy, September 2002, p. 3020-3025, Vol. 46, No. 9
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.9.3020-3025.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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