Molecular analysis of antimicrobial resistance mechanisms in Neisseria gonorrhoeae isolates from Ontario, Canada

Abstract

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.

FIG. 1.

Multidrug resistance observed in this study (including ERY^rs isolates).

FIG. 2.

Deduced amino acid sequences of PBP 2 from 14 ESC^rs N. gonorrhoeae isolates found in this study compared with the sequence from the wild-type strain LM306 (GenBank accession no. M32091). Active sites are highlighted in gray. The numbers of isolates with each pattern are shown in parentheses. The periods represent amino acid residues identical to those of LM306; the dashes are blanks. PBP 2 type XXXIV, GenBank accession number ADE22248; XXXV, ZP_04719537; XXXVI, ZP_04723776.