Introduction Studies have found that oral sex plays a major role in the transmission of Neisseria gonorrhoeae (NG) in men who have sex with men (MSM) populations. We aimed to establish in vitro the concentration and exposure time of Chlorhexidine mouthwash (Corsodyl â) that can inhibit the growth of NG to less than 102 Colony Forming Units (CFU) per ml.

Method Four NG strains isolated from pharyngeal specimens were selected for this exercise. Three were isolated from women, and all four were susceptible to ceftriaxone, cefixime, and spectinomycin, three were less susceptible (intermediate) to azithromycin and two were resistant to ciprofloxacin. None of the strains produced penicillinase. The antibiotic susceptibility was obtained using the agar dilution method and European Committee on Antimicrobial Susceptibility Testing breakpoints were used. Of each of the isolates a suspension of approximate 108 CFU/ml (0.5Mc Farland) was prepared in Phosphate-Buffered Saline (PBS)(positive control) and in serial dilutions of Chlorhexidine in PBS- 0.2%, 0.1% and 0.05%. Following 30 and 60 s of exposure at ambient temperature a volume of 10 µl of each of the suspensions was plated onto BBLTMColumbia blood agar (5% horse blood) and incubated for 48 hours (5%–7% CO2, 35±2°C). The colony growth was recorded and the number of CFU was counted, if appropriate. All experiments were conducted in triplicate.

Results Abundant growth was obtained with all PBS control suspensions. Zero CFU/ml were retrieved for all experiments using 0.2% chlorhexidine and 60 s of contact time. In only one of the 12 experiments using 0.2% chlorhexidine and 30 s of contact time a NG growth of 100 CFU/ml was obtained. Lower concentrations of chlorhexidine inhibited the growth of NG but to a lesser degree than 0.2%. The longer contact time inhibited the growth more frequently compared to the 30 s of contact time.

Conclusion The efficacy of the inexpensive and widely available 0.2% chlorhexidine mouthwash in preventing or treating pharyngeal NG merits consideration in clinical trials.