ANTAGONISM AND PRIMARY in vitro PROBIOTIC EVALUATION OF LACTIC ACID BACTERIA (LAB) RECOVERED FROM Ergo

Ergo is a naturally processed indigenous fermented dairy product, which is commonly prepared at household level and consumed in Ethiopia. The fermentation of this product is lactic acid bacterial dominated process. During this study 500 lactic acid bacterial isolates were recovered from ergo and tested for antagonism against four foodborne pathogens (E. coli O57:H7, Salmonella typhimurium DT104, Shigella shigelea SH10-1 and Staphylococcus aureus MERSA). Based on screening agar spot test method, 41.8% of LAB formed lysis zone against the test foodborne pathogens on modified MRS agar medium. Crude extracts of 40 lactic acid bacteria (LAB) that inhibited the test pathogens with ≥ 10 mm lysis zone were tested against the pathogens. Of these 40 LABS, 55% (22 LAB isolates) of extracts were observed inhibitory to the test pathogens with the well diffusion method. Purified extracts (ammonium sulfate precipitated) of 72% (16 isolates) of those shown active with crude extracts test were exhibited inhibitory activity against the test foodborne pathogens. From inhibitory LAB of purified extracts, 17.5% were found antagonistic to three or four of the test foodborne pathogens. The same 16 LAB isolates with antagonistic characteristics were tested for acid tolerance at pH 2.0, 2.5 and 3.0 for 3 and 6 hrs. Of these 16, none of the LAB isolates survived exposure to pH 2.0 for 3 hrs. Only 7 LAB isolates survived (with survival rate of >50%) the exposure at pH 2.5 for 3 and further incubation for 6 hours. All 16 isolates tolerated pH 3.0 for 3 hours. Further incubation for 6 hours reduced the survivors to 12. The 7 LAB isolates those survived exposure to pH 2.5 for 6 hrs were tolerated 0.3% bile (with survival rate of >95%) for 48 hours. The study indicated that the LAB isolates that are observed antagonistic to foodborne pathogens with purified extract could serve to formulate starter culture that can produce bioprotective ergo.