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.