Azithromycin Resistance Is Coevolving with Reduced Susceptibility to Cephalosporins in Neisseria gonorrhoeae in Ontario, Canada

Abstract

d Azithromycin (AZM) is routinely recommended as a component of dual therapy for gonorrhea in combination with third-generation cephalosporins (3GC). In this study, we examined the prevalence of AZM-resistant (AZM r ) Neisseria gonorrhoeae from July 2010 to February 2013, assessed the rate of concurrent cephalosporin resistance under the current treatment recommendations, and analyzed the clonal distribution of AZM r isolates in Ontario, Canada. Nineteen AZM r clinical isolates (one per patient; MIC, >2 g/ml) were included in the study. Susceptibility profiles of these isolates to 11 antibiotics, molecular typing, characterization of macrolide resistance mechanisms, and penicillin-binding protein 2 (PBP2) patterns were determined for all the isolates. Two groups were defined based on AZM r level; group A isolates displayed high-level resistance (MIC, >2,048 g/ml) due to mutations (A2143G) in the four copies of the 23S rRNA rrl gene, and group B isolates had moderate resistance to AZM (MICs, 2 to 8 g/ml, C2599T mutation in the rrl gene), with a subgroup belonging to sequence type 3158 (ST3158) (n ‫؍‬ 8), which also showed reduced susceptibility to 3GC (MICs, 0.12 to 0.25 g/ml, PBP2 pattern XXXIV). This AZM r phenotype was not observed in previous provincial surveillance in 2008 (the ST3158 clone was found, with AZM MICs of 0.25 to 0.5 g/ml associated with mtrR mutations). We hypothesized that the AZM mutant prevention concentration (MPC) in the ST3158 subpopulation we found in 2008 was higher than the MPC in wild-type isolates (AZM MIC, <0.031 g/ml), increasing the chances of additional selection of AZM r mutations. Full AZM resistance is now emerging in this clone together with reduced susceptibility to 3GC, threatening the future efficacy of these antibiotics as therapeutic options for treatment of gonorrhea.

Whole-Genome Phylogenomic Heterogeneity of Neisseria gonorrhoeae Isolates with Decreased Cephalosporin Susceptibility Collected in Canada between 1989 and 2013

“…AZM resistance is of concern, as it is the recommended cotherapy for gonorrhea (5), and AZM resistance with elevated ESC MICs has recently been described in Ontario (14), Quebec, and British Columbia in Canada (see Table S3 in the supplemental material). In contrast to Grad et al (35) who reported that AZM resistance was clonal in the United States, we observed five geographically separated AZM-resistant strains distributed widely through the phylogenomic tree, indicating that this phenotype is not clonal but arose spontaneously from independent accumulation of mtrR Ϫ35 A deletion and 23S rRNA mutations.…”

“…These results coincide with recent clinical reports of treatment failures to primarily CFM monotherapy in Canada (7,8) and additional global reports of high-level CRO MICs in isolates from Japan and Europe (9-13). Furthermore, isolates with decreased susceptibility to cephalosporins and coresistance to azithromycin (AZM), a recommended cotherapy (5), have recently been identified in Canada (14).Decreased susceptibility to extended-spectrum cephalosporins (ESC-DS) and resistance to AZM have been attributed to several molecular mechanisms. The primary mechanism for ESC-DS is modification of the penA gene (penicillin binding protein 2 [PBP2]) including various mutations of the wild-type gene and a recombinant mosaic allele containing portions of genetic sequences from commensal Neisseria (3,4,9,(15)(16)(17)(18).…”

“…These results coincide with recent clinical reports of treatment failures to primarily CFM monotherapy in Canada (7,8) and additional global reports of high-level CRO MICs in isolates from Japan and Europe (9)(10)(11)(12)(13). Furthermore, isolates with decreased susceptibility to cephalosporins and coresistance to azithromycin (AZM), a recommended cotherapy (5), have recently been identified in Canada (14).…”

Neisseria gonorrhoeae Sequence Typing for Antimicrobial Resistance, a Novel Antimicrobial Resistance Multilocus Typing Scheme for Tracking Global Dissemination of N. gonorrhoeae Strains

“…N. gonorrhoeae has developed resistance to almost all of the antimicrobials previously used for the treatment of gonorrhea, including penicillins, tetracyclines, and fluoroquinolones (2,3); the remaining treatment options are now threatened by the emergence of resistance to third-generation cephalosporins and azithromycin (4)(5)(6)(7)(8)(9)(10)(11)(12)(13).…”

In Vitro Activity of Gepotidacin (GSK2140944) against Neisseria gonorrhoeae

“…However, declining cefixime susceptibility was found to correlate with treatment failures (4) and, in 2012, oral cephalosporins were no longer recommended for treatment in the United States (5). In addition, it has been found that azithromycin resistance has coevolved with cephalosporin resistance, hence compromising combi-nation therapy with these two classes of antibiotics (6). Faced with an already limited and potentially complete lack of treatment options in the future, there is an urgent need to research and develop new antimicrobial agents to treat gonococcal infections.…”