Screening and Identification of Goat-Milk-Derived Lactic Acid Bacteria with Bacteriocin-like Activity and Probiotic Potentials

Abstract

In the current study, we screened 46 isolates of lactic acid bacteria (LAB) derived from goat milk for bacteriocin producers that can inhibit common foodborne pathogens (Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus). The following three strains that showed antimicrobial activity against all indicators were identified: Enterococcus faecalis DH9003 and DH9012, and Lactococcus lactis DH9011. Their antimicrobial products exhibited typical bacteriocin characteristics, such as heat stability and proteinase nature. The bacteriostatic activity of concentrated bacteriocins produced by these LAB was observed at low concentrations (half-minimum inhibitory concentration [MIC50] and 4MIC50), whereas complete inhibition activity against Listeria monocytogenes was detected at high concentrations (16MIC50) of the two Enterococcus faecalis strains (DH9003 and DH9012). Furthermore, the probiotic potentials of the three strains were investigated and described. The results revealed that none of the strains had hemolytic activity, whereas all: were sensitive to ampicillin (50 mg/mL) and streptomycin sulfate (100 mg/mL); were resistant to bile, artificial simulated intestinal tract, and gastric juice at different pH levels (2.5, 3.0, 3.5); and had β-galactosidase activity. Furthermore, all strains exhibited an auto-aggregating phenotype, with self-aggregation ranging from 30% to 55%. DH9003 and DH9012 co-aggregated well with Listeria monocytogenes and Escherichia coli (52.6% and 63.2%, 68.5% and 57.6%, respectively), whereas DH9011 co-aggregated poorly with Listeria monocytogenes (15.6%) and did not co-aggregate with Escherichia coli. Furthermore, our results showed that all three isolates exhibited strong antibacterial activity, tolerance to bile and simulated gastrointestinal environments, adhesion capability, and safety. Finally, DH9003 was selected and used for gavage in rats. By observing the pathological characteristics of rat intestinal and liver tissue sections, DH9003 showed no harmful effects on the intestine and liver of rats, but rather resulted in a denser and longer intestinal mucosa, as well as improving the intestinal mucosa of rats. Considering their substantial prospective applications, we concluded that these three isolates are potential probiotic candidates.