The development of mouthwashes without anti-gonococcal activity for controlled clinical trials: an in vitro study

Abstract

Background: The oropharynx plays a major role in the development and spread of antimicrobial resistant Neisseria gonorrhoeae among men who have sex with men. Trials are currently assessing the efficacy of bactericidal mouthwashes as possible therapeutic or preventive options against these pharyngeal gonococcal infections. Controlled clinical trials require the use of a placebo mouthwash without anti-gonococcal activity. So far, no such placebo mouthwash has been described. We describe the development of a mouthwash for this purpose. Methods: The in vitro anti-gonococcal activity of Corsodyl®, Listerine Cool Mint®, Biotene®, phosphate buffered saline and six in-house placebo mouthwashes was evaluated. Three gonococcal isolates from patients with pharyngeal infection were exposed to the mouthwashes for a duration ranging from 30 seconds to 60 minutes. Isolates were then plated in duplicate onto blood agar (5% horse blood) and incubated for 24 hours (5-7% CO 2, 35 ± 2°C). Growth of N. gonorrhoeae was scored on a five-point scale (0 = no growth, to 4 = confluent growth of colonies). Results: Corsodyl® and Listerine Cool Mint® were bactericidal to all isolates. For the other mouthwashes, the median growth score after 60 minutes of exposure was 4 (interquartile range 4-4) for phosphate buffered saline; 1 (interquartile range 1-3) for Biotene®; and ranged between 0 and 2 for the in-house composed mouthwashes. An in-house composed mouthwash (Placebo 6) performed best, with a growth score of 2.5 (interquartile range 1-3). Conclusions: All the evaluated potential placebo mouthwashes were bacteriostatic after gonococcal exposure of 30 to 60 minutes. In-house composed Placebo 6 showed less inhibition on gonococcal growth than Biotene® and the other in-house placebos and demonstrates, in our opinion, a good trade-off between anti-gonococcal properties and taste.

The Impact of Mouthwash on the Oropharyngeal Microbiota of Men Who Have Sex with Men: a Substudy of the OMEGA Trial

“…For example, chlorhexidine is an antiseptic that has broad-spectrum antibacterial activity ( 39 ); therefore, one may expect a chlorhexidine mouthwash to have more impact on the oral microbiome compared to milder mouthwashes. Additionally, while exposure to Listerine Zero for 10 s or longer has been shown to inhibit the growth of N. gonorrhoeae in vitro , short-term exposure to Biotène (i.e., 5 min or less) has limited activity against N. gonorrhoeae ( 15 , 17 ). This may indicate that the two mouthwashes have different antimicrobial activity, which could explain, in part, why we observed differences in how the two mouthwashes affected the oropharyngeal microbiota composition.…”

“…Because of this, the use of antiseptic mouthwash has been proposed as an intervention to reduce gonorrhea transmission in MSM ( 7 , 13 ). Previous in vitro studies have shown that antiseptic mouthwash can inhibit N. gonorrhoeae growth ( 14 , 15 ), and a small number of clinical trials have examined the use of mouthwash for the prevention and/or treatment of oropharyngeal gonorrhea ( 14 , 16 – 19 ).…”

Sub-Inhibitory Concentrations of Chlorhexidine Induce Resistance to Chlorhexidine and Decrease Antibiotic Susceptibility in Neisseria gonorrhoeae

“…Its antibacterial mechanism of action is based on damaging the bacterial cytoplasmic membrane and subsequent leakage of cytoplasmic components ( Cieplik et al, 2019 ). In vitro studies have established that N. gonorrhoeae is highly susceptible to killing by chlorhexidine ( Rabe and Hillier, 2000 ; Victoria et al, 2018 ; Van Dijck et al, 2020 ). However, a recent clinical trial was ended early since twice daily gargling with chlorhexidine for six days failed to eradicate N. gonorrhoeae in the oropharynx ( Van Dijck et al, 2021a ).…”

Chlorhexidine Mouthwash Fails to Eradicate Oropharyngeal Gonorrhea in a Clinical Pilot Trial (MoNg)

“…[1][2][3] As a consequence, several authors have proposed that antiseptic mouthwashes may be used to prevent or treat oropharyngeal gonorrhea. 1,4,5 In vitro studies have established that Ng is highly susceptible to killing by mouthwashes such as Listerine 6,7 and chlorhexidine, [8][9][10] and a randomized controlled trial in men with culture-positive oropharyngeal gonorrhea found that Ng could not be cultured in a significant proportion of men 5 minutes after a single gargling session with Listerine. 7 Despite these initial encouraging results, 3 randomized clinical trials have found that Listerine failed to prevent (PReGo 4 and OMEGA1 11 ) or treat (OMEGA2 5 ) oropharyngeal gonorrhea.…”

“…Nevertheless, chlorhexidine's strong in vitro bactericidal effect suggests that it could be more effective than Listerine in killing Ng in the oropharynx. 6,8,13,14 The aim of this single-arm, open-label pilot study was therefore to assess whether a chlorhexidine mouthwash could eradicate Ng from the oropharynx of asymptomatic men.…”