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  • Title: Inhibition of vaginal lactobacilli by a bacteriocin-like inhibitor produced by Enterococcus faecium 62-6: potential significance for bacterial vaginosis.
    Author: Kelly MC, Mequio MJ, Pybus V.
    Journal: Infect Dis Obstet Gynecol; 2003; 11(3):147-56. PubMed ID: 15022875.
    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 degrees C, 30 minutes), cold- (4 degrees C, less than 114 days) and pH- (4-7) stable. The sensitivity of inhibitor-containing supernatants to pepsin and alpha-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.
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