New Mutation in 23S rRNA Gene Associated with High Level of Azithromycin Resistance in Neisseria gonorrhoeae

We evaluated the activity of solithromycin against 196 clinical gonococcal isolates collected at the Public Health Ontario Laboratories, Toronto, Canada, including isolates with different levels of azithromycin resistance, as well as the role of pH in MIC determinations using pH-adjusted agar plates (pH range, 5.6 to 7.6). In vitro invasion assays were performed using monolayers of HeLa epithelial cells and clinical gonococci displaying different azithromycin MICs; infected cultures were treated with solithromycin, and its intracellular activity was determined by CFU assays after 3 and 20 h of exposure. Solithromycin displayed a MIC 50 and MIC 90 of 0.0625 and 0.125 g/ml, respectively, making its activity at least 4-fold higher than that of azithromycin. Clinical isolates with elevated MICs for azithromycin (MICs of >2,048 g/ml and 4 to 8 g/ml) showed solithromycin MIC values of 8 and 0.5 g/ml, respectively. In contrast to azithromycin, solithromycin MICs were not significantly affected by acidic pHs, suggesting more stability at lower pH. Moreover, when intracellular Neisseria gonorrhoeae isolates were incubated with solithromycin at 4 times, 1 times, and one-fourth of the MIC, the exposure to solithromycin resulted in the progressive loss of viability of most isolates over time. The intracellular activity of solithromycin, combined with the low MICs to this agent, indicates that it may be an attractive option for gonorrhea treatment if clinical trials in development reveal that this drug can be used safely in adult indications, especially when multidrug-resistant clinical isolates are now emerging.

Section: Antigonococcal Activity Of Solithromycinmentioning

confidence: 99%

Determination of In Vitro Activities of Solithromycin at Different pHs and Its Intracellular Activity against Clinical Isolates of Neisseria gonorrhoeae from a Laboratory Collection

Mallegol

Fernandes

Seah

et al. 2013

“…Case reports of AZM-resistant N. gonorrhoeae have been described in many countries, including Canada and the United States (10)(11)(12)(13)(14)(15)(16)(17)(18), but only rarely has AZM-resistant N. gonorrhoeae been reported to be associated with concurrent reduced susceptibility to 3GC (16,17). In Canada, AZM-resistant N. gonorrhoeae was first identified in 1997, and the first AZM-resistant isolates were identified in Ontario in 1998 (10).…”

mentioning

confidence: 99%

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

Allen

Seah

Martín

et al. 2014

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.

“…Three different mechanisms involved in macrolide resistance were described in N. gonorrhoeae: efflux systems (30,45), modification of the ribosomal target by methylases (43), and ribosomal modification by point mutations in the macrolide targets (18,19,34). Here, the presence of 23S rRNA methylases (ermA, ermB, ermC, and ermF genes), a plasmid-mediated efflux pump (mefA/E genes), macrolide 2Ј-phosphotransferase (mphA gene), ERY esterases (ereA and ereB genes), and possible mutations in the mtrR gene/promoter and riboproteins L4 and L22 (rplD and rplV genes) were tested in all the isolates with ERY rs .…”

Section: Resultsmentioning

confidence: 99%

“…During 2006, 28% of N. gonorrhoeae isolates were resistant to ciprofloxacin in Ontario, Canada (38). Clinical strains displaying intermediate susceptibility or resistance to azithromycin (AZM) are now emerging (9,18,19,32,40,46,60).…”

mentioning

confidence: 99%

Molecular Analysis of Antimicrobial Resistance Mechanisms in Neisseria gonorrhoeae Isolates from Ontario, Canada

Allen

Farrell

Rebbapragada

et al. 2011

Surveillance of gonococcal antimicrobial resistance and the molecular characterization of the mechanisms underlying these resistance phenotypes are essential in order to establish correct empirical therapies, as well as to describe the emergence of new mechanisms in local bacterial populations. To address these goals, 149 isolates were collected over a 1-month period (October-November 2008) at the Ontario Public Health Laboratory, Toronto, Canada, and susceptibility profiles (8 antibiotics) were examined. Mutations in previously identified targets or the presence of some enzymes related to resistance (r), nonsusceptibility (ns) (resistant plus intermediate categories), or reduced susceptibility (rs) to the antibiotics tested were also studied. A significant proportion of nonsusceptibility to penicillin (PEN) (89.2%), tetracycline (TET) (72.3%), ciprofloxacin (CIP) (29%), and macrolides (erythromycin [ERY] and azithromycin; 22.3%) was found in these strains. Multidrug resistance was observed in 18.8% of the collection. Although all the strains were susceptible to spectinomycin and extended-spectrum cephalosporins (ESC) (ceftriaxone and cefixime), 9.4% of them displayed reduced susceptibility to extended-spectrum cephalosporins. PBP 2 mosaic structures were found in all of these ESC rs isolates. Alterations in the mtrR promoter, MtrR repressor (TET r , PEN ns , ESC rs , and ERY ns ), porin PIB (TET r and PEN ns ), and ribosomal protein S10 (TET r ) and double mutations in gyrA and parC quinolone resistance-determining regions (QRDRs) (CIP r ) were associated with and presumably responsible for the resistance phenotypes observed. This is the first description of ESC rs in Canada. The detection of this phenotype indicates a change in the epidemiology of this resistance and highlights the importance of continued surveillance to preserve the last antimicrobial options available.