Resumo

Lactic Acid Bacteria isolated from bulgarian goat yoghurt, produced in South Africa, were screened for the production of bacteriocins, with the aim of investigating the interaction of the LAB and their bacteriocins with mastitis causing pathogenic bacteria. From a total of 23 isolates screened, three produced bacteriocins active against a narrow spectrum of Gram-positive bacteria, including Streptococcus agalactiae, Streptococcus uberis, Staphylococcus epidermidis (isolated from the milk of infected cows) and Lactobacillus sakei. The bacteriocin producer strains were identified as members of the genera Streptococcus. Bacteriocin ST91KM, produced by S. macedonicus ST91KM, is approximately 2.3 – 2.5 kDa in size as determined by trycine-SDS PAGE. The bacteriocin remained stable after incubation for 2h at pH 2.0 to 10.0. No decrease in activity was recorded after treatment at 100°C for 100 min, but the peptide was inactivated at 121°C for 20 min. No change in activity was recorded after treatment with SDS, urea, Tween 20, Tween 80 and EDTA. Treatment with pronase, pepsin and trypsin inactivated the bacteriocin. Activity was not reduced after treatment with α-amylase, suggesting that the peptide is not glycosylated. The mode of activity is bactericidal, as observed against S. agalactiae and L. sakei. Bacteriocin ST91KM was produced at 1600 AU ml-1 in MRS medium at pH 6.0, in presence of Vit. C, Vit. B1, Vit B12 or DL-6,8-thioctic acid. Meat extract (20 g/l) as single nitrogen source increased production of bacteriocin ST91KM to 3 200 AU/ml. Mannose (20.0 g/l) results in 6 400 AU/ml bacteriocin activity. Medium supplemented with KH2HPO4 or K2HPO4 at 10.0 g/l yielded 3 200 AU/ml bacteriocin ST91KM. Glycerol (5 g/l) increased production of bacteriocin ST91KM. Tween 80 at 2.0 g/l results in 100% increase of bacteriocin production.