Vaginal Lactobacilli Reduce Neisseria gonorrhoeae Viability through Multiple Strategies: An in Vitro Study

Abstract

The emergence and spread of antimicrobial resistance in Neisseria gonorrhoeae (GC) underline the need of “antibiotic-free” strategies for the control of gonorrhea. The aim of this study was to assess the anti-gonococcal activity of 14 vaginal Lactobacillus strains, belonging to different species (L. crispatus, L. gasseri, L. vaginalis), isolated from healthy pre-menopausal women. In particular, we performed “inhibition” experiments, evaluating the ability of both lactobacilli cells and culture supernatants in reducing GC viability, at two different contact times (7 and 60 min). First, we found that the acidic environment, associated to lactobacilli metabolism, is extremely effective in counteracting GC growth, in a pH- and time-dependent manner. Indeed, a complete abolishment of GC viability by lactobacilli supernatants was observed only for pH values < 4.0, even at short contact times. On the contrary, for higher pH values, no 100%-reduction of GC growth was reached at any contact time. Experiments with organic/inorganic acid solutions confirmed the strict correlation between the pH levels and the anti-gonococcal effect. In this context, the presence of lactate seemed to be crucial for the anti-gonococcal activity, especially for pH values in the range 4.4–5.3, indicating that the presence of H+ ions is necessary but not sufficient to kill gonococci. Moreover, experiments with buffered supernatants led to exclude a direct role in the GC killing by other bioactive molecules produced by lactobacilli. Second, we noticed that lactobacilli cells are able to reduce GC viability and to co-aggregate with gonococci. In this context, we demonstrated that released-surface components with biosurfactant properties, isolated from “highly-aggregating” lactobacilli, could affect GC viability. The antimicrobial potential of biosurfactants isolated from lactobacilli against pathogens has been largely investigated, but this is the first report about a possible use of these molecules in order to counteract GC infectivity. In conclusion, we identified specific Lactobacillus strains, mainly belonging to L. crispatus species, able to counteract GC viability through multiple mechanisms. These L. crispatus strains could represent a new potential probiotic strategy for the prevention of GC infections in women.

C4BP-IgM protein as a therapeutic approach to treat Neisseria gonorrhoeae infections

“…Considering that untreatable gonorrhea cases might soon become a reality, identifying new prevention and treatment options is crucial. In addition to new antibiotics or a novel combination of the currently used ones, new therapies have been suggested to prevent recurrence of the infection: IL-12 to promote Th1-driven adaptive immune response (34), vaginal lactobacillus strains to counteract gonococcal growth (35), and fatty acid derivatives for a fast anti-gonococcal activity targeting membrane disruption (36). Here we present a potentially novel therapeutic approach that targets a virulence mechanism of bacteria -its ability to bind the complement inhibitor C4BP.…”

Lactobacillus crispatus BC5 Interferes With Chlamydia trachomatis Infectivity Through Integrin Modulation in Cervical Cells

“…A normal vaginal microbiota, dominated by lactobacilli, is crucial for the prevention of several urogenital and sexually transmitted infections, including Chlamydia ( Gupta et al, 1998 ; Spurbeck and Arvidson, 2008 ; Parolin et al, 2015 ; Nardini et al, 2016 ; Foschi et al, 2017 ; Ñahui Palomino et al, 2017 ). This aspect is strengthened by the demonstration that in case of bacterial vaginosis, a clinical condition characterized by the depletion of lactobacilli, a higher risk of STI transmission and acquisition is reported ( Taha et al, 1998 ; Martin et al, 1999 ; Wiesenfeld et al, 2003 ; Abbai et al, 2015 ).…”

Selective Inhibition of Neisseria gonorrhoeae by a Dithiazoline in Mixed Infections with Lactobacillus gasseri

“…To expand our consideration of species-specific differences and explore a potential environment in which DTZ would be clinically useful (the lower female reproductive tract), we tested the efficacy of DTZ against a representative vaginal commensal, Lactobacillus gasseri. L. gasseri has been previously shown to block N. gonorrhoeae-epithelial cell interactions (28,29), and lactobacilli in general maintain a low pH in the vagina that is an important determinant of discouraging Neisseria growth (30). We found that L. gasseri is greatly reduced in sensitivity to DTZ compared to that of N. gonorrhoeae as well as the previously described E. coli and Salmonella enterica (17).…”

“…Concentrations of 250 and 500 M were able to delay the initiation of growth, although growth proceeded at a normal rate throughout exponential phase, plateauing at a much higher A 540 value than lower-concentration DTZ treatments. Observation of the cultures at the end of growth suggests that the increased optical density is due to biofilm formation (data not shown (30,37). For an antimicrobial agent to be effective against N. gonorrhoeae infection, it will need to function in the context of both interbacterial competition and host cell infection.…”

“…Lactobacilli are the most abundant residents of the lower female reproductive tract, and their colonization of tissues serves as a barrier to competing bacteria, including N. gonorrhoeae (28). Previous work has determined that lactobacilli inhibit N. gonorrhoeae adherence to cervical cells (39), produce bacteriocins (40), and establish an acidic environment that discourages N. gonorrhoeae growth (30). Infections of mucosal surfaces rarely happen in sterile isolation, which is why we set out to consider what effects DTZ may have on a model vaginal commensal.…”