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The probiotic strain Enterococcus mundtii ST4SA, isolated from soy beans, produces a broad-spectrum antimicrobial peptide. The aim of this study was to determine if peptide ST4SA could withstand conditions simulating those found in the gastro-intestinal tract (GIT). Antimicrobial activity of peptide ST4SA has been monitored by growth inhibition of Enterococcus faecium on plates and leakage of β-galactosidase from damaged cells. The ability of peptide ST4SA to adhere to target cells, which is the first step in cell destruction, has been determined by calculating the percentage of active peptide that remained in the cell-free supernatant. Seventy-five percent of peptide ST4SA adhered to E. faecium HKLHS at 37 °C, 88% adhered to the cells at pH 8.0 and 10.0, and 75% adhered to the cells at pH 4.0 and 6.0 at 37 °C. Complete adherence of peptide ST4SA to E. faecium HKLHS was recorded in the presence of 3.0%, 5.0% and 10.0% (v/v) pancreatic juice, 0.3%, 0.5% and 1.0% (v/v) oxbile and 1% (w/v) NaCl, MgCl(2) and KCl. Peptide ST4SA survived conditions associated with the GIT and may be used to prevent or retard the growth of intestinal microbiota.

Bacteriocin ST15 (bacST15), produced by Enterococcus mundtii ST15, inhibited the growth of a variety of bacteria, including exopolysaccharide (EPS)-producing strains isolated from biofilms in stainless steel pipes. Maximal production of bacST15 (51200 AU/ml) was recorded after 20 h of growth in MRS broth (Biolab), which was maintained throughout fermentation. Only 12800 AU/ml bacST15 has been recorded in MRS filtrate with components smaller than 8000 Da, suggesting that nutrients larger than 8000 Da are required for optimal bacST15 production. Cation-exchange chromatography yielded an active peptide, which is 3944.00 Da, according to electron-spray mass spectrometry and tricin-SDS PAGE. BacST15 is smaller than the 4287 Da reported for bacteriocins ATO6 and KS produced by E. mundtii . The iso-electric point of bacST15 is between 7 and 9, and similar to that reported for pediocin PD-1.

Klebsiella oxytoca is a Gram-negative bacterium found in faecal microbiota and known to cause several infections in humans, including antibiotic-associated hemorrhagic colitis. We present here a case of colitis caused by K. oxytoca toxin producing strains that evolved in chronic diarrhea successfully treated by fecal microbiota transplant.

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