Abstract
A bacteriocin produced by a vaginal isolate of Enterococcus faecium strain 62-6, designated enterocin 62-6, was characterized following purification and DNA sequence analysis and compared to previously described bacteriocins. Enterocin 62-6 was isolated from brain heart infusion (BHI) culture supernatants using ammonium sulfate precipitation followed by elution from a Sepharose cation exchange column using a continuous salt gradient (0.1-0.7 M NaCl). SDS-PAGE of an active column fraction resulted in an electrophoretically pure protein, which corresponded to the growth inhibition of the sensitive Lactobacillus indicator strain in the gel overlay assay. Purified enterocin 62-6 was shown to be heat- and pH-stable, and sensitive to the proteolytic enzymes alpha-chymotrypsin and pepsin. Results from mass spectrometry suggested that it comprised two peptides of 5206 and 5219+/-1 Da, which was confirmed by DNA sequence analysis. The characteristics of enterocin 62-6 as a small, heat- and pH-stable, cationic, hydrophobic, two-peptide, plasmid-borne bacteriocin, with an inhibitory spectrum against a broad range of Gram-positive but not Gram-negative bacteria, were consistent with its classification as a class IIc bacteriocin. Furthermore, its wide spectrum of growth inhibitory activity against Gram-positive bacteria of vaginal origin including lactobacilli, and stability under the acidic conditions of the vagina, are consistent with our hypothesis that it could have potential significance in disrupting the ecology of the vaginal tract and pave the way for the establishment of the abnormal microbiota associated with the vaginal syndrome bacterial vaginosis. This is the first class IIc bacteriocin produced by a strain of E. faecium of vaginal origin to be characterized.
Highlights
There is currently a resurgence of interest in the small, ribosomally synthesized antimicrobial peptide bacteriocins produced by lactic acid bacteria [1,2]
We are investigating the hypothesis that the introduction of Gram-positive bacteriocin-producing organisms into the vaginal tract may inhibit the growth of bacteria associated with the healthy vagina, the lactobacilli, and 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]
The current study describes the purification and characterization of the first class IIc enterococcal bacteriocin from an isolate of E. faecium of vaginal origin, enterocin 62-6
Summary
There is currently a resurgence of interest in the small, ribosomally synthesized antimicrobial peptide bacteriocins produced by lactic acid bacteria [1,2]. Many of these bacteriocins have an inhibitory spectrum against a broad range of Gram-positive bacteria. We are investigating the hypothesis that the introduction of Gram-positive bacteriocin-producing organisms into the vaginal tract may inhibit the growth of bacteria associated with the healthy vagina, the lactobacilli, and 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]
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