Potencial do leite orgânico como fonte de bactérias ácido-láticas produtoras de moléculas bioativas aplicáveis à cadeia produtiva do leite

Abstract

The growing concern about antimicrobial resistance and the search for natural alternatives for food preservation have driven the study of lactic acid bacteria (LAB), widely used in the dairy industry for their ability to produce antimicrobial metabolites, such as organic acids and bacteriocins. This study aimed to isolate, identify, compare antibiotic resistance profiles, and characterize the bioprotective potential of LAB strains from raw milk samples collected from both organic and conventional production systems in the state of Rio de Janeiro, Brazil. A total of 126 bacterial colonies were isolated, of which 67 were presumptively identified as LAB. REP-PCR analysis resulted in 48 genetically distinct strains, later identified by MALDI-TOF as belonging to the genera Enterococcus, Lactococcus, Leuconostoc, and Lactobacillus. Considering the set of strains analyzed, agar diffusion antibiogram assays revealed a higher rate of resistance to the antibiotic cotrimoxazole among LAB strains and universal susceptibility to chloramphenicol, with no detection of the tested resistance genes (ermB, tetO/M/K, blaZ, mecA, aacA-aphD, and vanA/B). All strains, regardless of the production system, were susceptible to at least four of the tested antibiotics. Comparatively, no statistically significant difference was observed between the two systems regarding the susceptibility rates to the tested antibiotics. Antagonism assays using the spot-on-the-lawn technique with LAB strains from organic milk against eight pathogens relevant to the dairy production chain (Enterococcus faecalis, Streptococcus agalactiae, Streptococcus uberis, Streptococcus dysgalactiae, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Listeria monocytogenes) demonstrated at least one potentially bioprotective LAB strain active against each of the tested pathogens. The antimicrobial activity of Enterococcus italicus 06 against E. faecalis ATCC 29212 was sensitive to proteolytic enzymes and stable at pH 4 and 6, as well as at time/temperature combinations of 80 °C for 10 minutes and 121 °C for 15 minutes, indicating that the inhibition by E. italicus is due to the production of a bacteriocin with potential application in food biopreservation. The findings reinforce the relevance of LAB as safe and functional candidates for use in food systems and highlight organic milk as a promising matrix for the discovery of bioprotective cultures.