Inhibition of Vaginal Lactobacilli by a Bacteriocin‐Like InhibitorProduced by Enterococcus faecium 62‐6: Potential Significancefor Bacterial Vaginosis

Abstract

Objective: Bacterial vaginosis (BV) is characterized by a shift in vaginal tract ecology, which includes a decrease in the concentration and/or prevalence of facultative lactobacilli. Currently, mechanisms which could account for the disappearance of lactobacilli are not well understood. The objective of this study was to determine whether vaginal streptococci/enterococci can produce bacteriocin-like inhibitors antagonistic to vaginal lactobacilli. Methods: Seventy strains of vaginal streptococci or enterococci were tested for antagonistic activities against vaginal lactobacilli using the deferred antagonism technique. Results: One strain, Enterococcus faecium 62-6, which strongly inhibited growth of lactobacilli was selected for further characterization. The spectrum of inhibitory activity of strain 62-6 included Gram-positive organisms from the vaginal environment, although native lactobacilli from the same host were resistant to inhibitor action. Following growth in MRS broth the strain 62-6 inhibitor was shown to be heat-(100°C, 30 minutes), cold-(4°C, less than 114 days) and pH-(4-7) stable. The sensitivity of inhibitor-containing supernatants to pepsin and α-chymotrypsin suggested an essential proteinaceous component. The inhibitor was sensitive to lipase but resistant to lysozyme. Dialysis of inhibitor-containing culture supernatants suggested a molecular mass greater than 12 000 Da. All physicochemical properties were consistent with its classification as a bacteriocin-like inhibitor. Kinetic assays demonstrated a sharp onset of inhibitor production coinciding with a concentration of 62-6 of 10 7 cfu/ml, suggesting that production may be regulated by quorum sensing. Conclusions: These results may have clinical significance as a novel mechanism to account for the decline of vaginal Lactobacillus populations and contribute to both the establishment and recurrence of BV.

Characterization of a novel bacteriocin produced by Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish

“…The enzyme sensitivity tests demonstrated that this strain was a novel sakacin, based on its sensitivity to lipase; other known bacteriocins produced by L. sakei were not sensitive to lipase, although the bacteriocin-like inhibitory substances from pathogenic Vibrio harveyi VIB 571 and Enterococcus faecium 62-6 were sensitive to lipase (Kelly, Mequio, & Pybus, 2003;Prasad, Morris, Hansen, Meaden, & Austin, 2005). These results suggest that sakacin LSJ618 may be a lipoprotein whose lipidic moiety is an important factor for its antibacterial activity.…”

Purification and characterization of enterocin 62-6, a two-peptide bacteriocin produced by a vaginal strain ofEnterococcus faecium: Potential significance in bacterial vaginosis

“…We previously reported production of a bacteriocin-like inhibitor by E. faecium strain 62-6, which was antagonistic to the growth of 16 of 32 lactobacilli tested (including known hydrogen peroxide producers) as well as other Gram-positive bacteria of vaginal origin (5). The growth inhibitory effects of E. faecium 62-6 against the lactobacilli were shown to be independent of conditions of low pH alone and hydrogen peroxide production (5).…”

“…By contrast, our interest focuses on the possible significance of bacteriocins in the ecology of the human vaginal tract. Specifically, we are investigating the hypothesis that the introduction of Gram-positive bacteriocinproducing organisms into the vaginal tract may inhibit the growth of bacteria associated with the healthy vagina, particularly the lactobacilli, and thus be one mechanism that could potentially pave the way for the establishment of the abnormal microbiota associated with the vaginal tract syndrome, bacterial vaginosis (BV) (5).…”

“…Since sexual activity has been a well-documented risk factor for BV acquisition (8,16) and sexual contact provides the opportunity for introduction of microorganisms into the vagina, we are investigating whether the introduction of bacteriocin-producing bacteria into the healthy vaginal tract could affect the ecology by causing the decline in concentration of lactobacilli. We have been evaluating bacteriocin production against vaginal strains of lactobacilli by genera of bacteria associated with the healthy vaginal tract, in particular streptococci and enterococci, since they would have the potential to establish a new host in the vagina (5).…”

Prevention and treatment of urogenital infections and complications: lactobacilli's multi-pronged effects

“…Fluctuations in estrogen levels and glycogen, induced by estrogen stimulation are factors (9), as is the possible influx of phages (10) and production by pathogens of anti-lactobacilli bacteriocins (11). The fact that women can have BV at different times of the menstrual cycle (12), suggests that hormones are not the main factor responsible for an altered microbiota.…”