In Vitro Antimicrobial Characterization of Lactobacillus Isolates Towards Their Use as Probiotic Alternatives to Antibiotic Growth Promoters

In the present study, the probiotic potential of Lactobacillus isolates selected from fecal samples of farmyard chickens and ducks was scientifically validated for their use as alternatives to antibiotics in poultry. A total of 129 Lactobacillus isolates were characterized of which four produced inhibitory substances with antimicrobial activities. They were further identified on the basis of their carbohydrate fermentation profile and High-Resolution Melting analysis as Lactobacillus paracasei MW-37CGZ, Lactobacillus paracasei MW-38CGZ, Lactobacillus plantarum MW-48CGZ and Lactobacillus plantarum MW-18CGZ. The obtained results revealed that L. plantarum MW-18CGZ and L. paracasei MW-37CGZ showed strong antagonistic activities against human (nine) and zoonotic pathogens (eleven). The antimicrobial substance produced by L. plantarum MW-18CGZ was found to be proteinaceous, thus indicating that this substance may belong to a group of potent antimicrobial peptides produced by some microorganisms including lactic acid bacteria (LAB). Both viable and non-viable cells of the four isolates demonstrated good hydrophobicity in xylene with L. plantarum MW-48CGZ exhibiting higher hydrophobicity than other isolates (77.64±5.18%). They were susceptible to chloramphenicol, clindamycin, ampicilin and erythromycin with Minimum Inhibitory Concentration (MIC) below cut-off values established by the European Food Safety Authority (EFSA). Among the four Lactobacillus, L. plantarum MW-18CGZ and L. paracasei MW-37CGZ displayed high autoaggregation and coaggregation towards pathogens and all isolates survived in low-pH, high bile salt concentrations and none exhibited virulent factors. According to the obtained results, L. plantarum MW-18CGZ and L. paracasei MW-37CGZ could be considered as future biotherapeutic substitutes for antibiotics to reduce antibiotic residues in food derived from poultry as well as the generation and spread of antibiotic resistance.