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

Objectives: Chlorhexidine digluconate (chlorhexidine) and Listerine® mouthwashes are being promoted as alternative treatment options to prevent the emergence of antimicrobial resistance in Neisseria gonorrhoeae. We performed in vitro challenge experiments to assess induction and evolution of resistance to these two mouthwashes and potential cross-resistance to other antimicrobials. Methods: A customized morbidostat was used to subject N. gonorrhoeae reference strain WHO-F to dynamically sustained Listerine® or chlorhexidine pressure for 18 days and 40 days, respectively. Cultures were sampled twice a week and minimal inhibitory concentrations (MICs) of Listerine®, chlorhexidine, ceftriaxone, ciprofloxacin, cefixime and azithromycin were determined using the agar dilution method. Isolates with an increased MIC for Listerine® or chlorhexidine were subjected to whole genome sequencing to track the evolution of resistance. Results: We were unable to increase MICs for Listerine®. Three out of five cultures developed a 10-fold increase in chlorhexidine MIC within 40 days compared to baseline (from 2 to 20 mg/L). Increases in chlorhexidine MIC were positively associated with increases in the MICs of azithromycin and ciprofloxacin. Low-to-higher-level chlorhexidine resistance (2-20 mg/L) was associated with mutations in NorM. Higher-level resistance (20 mg/L) was temporally associated with mutations upstream of the MtrCDE efflux pump repressor (mtrR) and the mlaA gene, part of the maintenance of lipid asymmetry (Mla) system. Conclusion: Exposure to sub-lethal chlorhexidine concentrations may not only enhance resistance to chlorhexidine itself but also cross-resistance to other antibiotics in N. gonorrhoeae. This raises concern regarding the widespread use of chlorhexidine as an oral antiseptic, for example in the field of dentistry.

Molecular epidemiological analysis of Mycoplasma genitalium shows low prevalence of azithromycin resistance and a well-established epidemic in South Africa.

OBJECTIVES: Macrolide resistance in Mycoplasma genitalium is emerging globally. There is paucity of data from sub-Saharan Africa where syndromic management is used to treat sexually transmitted infections (STIs). We conducted a molecular epidemiological study to determine the prevalence of azithromycin resistance and epidemic diversity of M. genitalium infections in South Africa. METHODS: We analysed 90 M. genitalium-positive specimens that had been collected consecutively from men and women (50% symptomatic) from geographically diverse communities across the northern part of South Africa between 2015 and 2019. Melting curve analysis followed by targeted sequencing of the 23S rRNA gene was performed to detect azithromycin resistance. Molecular typing was done through single nucleotide polymorphism (SNP) analysis of the MG191 gene and short tandem repeats (STR) assessment of the MG309 gene. An overview of all published M. genitalium sequence types was generated and novel sequence types identified in this study were allocated numbers accordingly. RESULTS: Azithromycin resistance was detected in 1/90 M. genitalium-positive specimens (1.1%; 95% CI 0% to 3.3%) as conferred by A2071G mutation; this strain also harboured a C234T mutation in the parC gene with wild type gyrA gene. SNP typing and STR assessment was successful in 38/90 specimens (42%) and showed a genetically diverse epidemic, without geographic clustering, with eight novel sequence types identified. CONCLUSION: This is the first study that determines resistance in M. genitalium infection since introduction of azithromycin in the syndromic management regimen for STIs in South Africa in 2015. Despite a well-established epidemic, azithromycin-resistant M. genitalium infection is still uncommon in the public healthcare sector. However, it has the potential to undermine the effectiveness of syndromic management. Introduction of molecular diagnostics and continuous surveillance are warranted for early detection emergence of resistance.

Commensal Neisseria Are Shared between Sexual Partners: Implications for Gonococcal and Meningococcal Antimicrobial Resistance.

Antimicrobial resistance in pathogenic Neisseria parallels reduced antimicrobial susceptibility in commensal Neisseria in certain populations, like men who have sex with men (MSM). Although this reduced susceptibility can be a consequence of frequent antimicrobial exposure at the individual level, we hypothesized that commensal Neisseria are transmitted between sexual partners. We used data from a 2014 microbiome study in which saliva and tongue swabs were taken from 21 couples (42 individuals). Samples were analyzed using 16S rRNA gene sequencing. We compared intimate partners with unrelated individuals and found that the oral Neisseria communities of intimate partners were more similar than those of unrelated individuals (average Morisita-Horn dissimilarity index for saliva samples: 0.54 versus 0.71, respectively (p = 0.005); and for tongue swabs: 0.42 versus 0.63, respectively (p = 0.006)). This similarity presumably results from transmission of oral Neisseria through intimate kissing. This finding suggests that intensive gonorrhea screening in MSM may, via increased antimicrobial exposure, promote, rather than prevent, the emergence and spread of antimicrobial resistance in Neisseria. Non-antibiotic strategies such as vaccines and oral antiseptics could prove more sustainable options to reduce gonococcal prevalence.