Background: The emergence of isolates with decreased susceptibilities to the cephalosporins and reports of treatment failures in Canada and around the world has made the concept of untreatable gonorrhea infections a future possibility. Alternative therapies such as gentamicin and ertapenem need to be evaluated for future therapeutic use.
Methods: Neisseria gonorrhoeae were collected by Canadian provincial public health laboratories in 2012 and submitted to the National Microbiology Laboratory for testing. Neisseria gonorrhoeae multi-antigen sequence types (NG-MAST or STs) and minimum inhibitory concentrations (MICs) were determined using the Etest for gentamicin (n=334) and ertapenem (n=378). Five reference cultures were also tested and their results were compared to established MICs. Currently there are no ertapenem or gentamicin interpretation criteria for N. gonorrhoeae.
Results: The MICs of gentamicin ranged from 1 mg/L to 6 mg/L with a modal MIC of 4 mg/L. The MICs of ertapenem ranged from <0.002 mg/L to 0.064 mg/L with a modal MIC of 0.008 mg/L. Isolates with decreased susceptibilities to ceftriaxone and cefixime had a modal MIC for ertapenem of 0.047 mg/L. The gentamicin modal MIC for these isolates remained the same. There were 139 different STs identified among the 378 isolates tested. ST-1407 was found to have the highest prevalence [10.% (n=39)] with ST-3158, ST-3307, ST-4709 and ST-7986 following at 5.3% (n=18) each. The modal MICs for the ST-1407 isolates were 0.032 mg/L for ertapenem and 3 mg/L for gentamicin.
Conclusions: Modal MICs to gentamicin and ertapenem in a collection of diverse Canadian N. gonorrhoeae isolates are similar to that reported in other countries. Gentamicin is already used for gonorrhea treatment in other countries and may be a future option for treatment in combination with azithromycin in Canada. Ertapenem MICs remained low but are slightly elevated in the isolates with decreased susceptibilities to ceftriaxone and cefixime.