Inhibition of food-related bacteria by antibacterial substances produced by Pseudomonas sp. strains isolated from pasteurized milk

In this work, the production of antimicrobial substances by strains of Pseudomonas sp. isolated from pasteurized milk and their potential action against food-related bacteria were investigated. Samples of pasteurized milk were purchased from arbitrarily chosen commercial establishments in the city of Rio de Janeiro, Brazil. Of the four samples analyzed, three presented several typical colonies of Pseudomonas. About 100 colonies were chosen and subjected to biochemical tests for confirmation of their identity. Eighteen strains of the Pseudomonas genus were identified and submitted to tests for the production of antimicrobial substances. Twelve strains (66.7%) were identified as Pseudomonas fluorescens, four (22.2%) as P. aeruginosa, one (5.5%) as P. mendocina and one (5.5%) as P. pseudoalcaligenes. Only two P. fluorescens strains were unable to produce any antimicrobial substance against any of the indicator strains tested. Most of the strains presented a broad spectrum of action, inhibiting reference and food-related strains such as Proteus vulgaris, Proteus mirabilis, Hafnia alvei, Yersinia enterocolitica, Escherichia coli and Salmonella typhi. Five antimicrobial substance-producing strains, which presented the broadest spectrum of action, were also tested against Staphylococcus aureus reference strains and 26 Staphylococcus sp. strains isolated from foods, some of which were resistant to antibiotics. The producer strains 8.1 and 8.3, both P. aeruginosa, were able to inhibit all the staphylococcal strains tested. The antimicrobial substances produced by strains 8.1 and 8.3 did not seem to be typical bacteriocins, since they were resistant to the three proteolytic enzymes tested. Experiments involving the characterization of these substances are being carried out in order to evaluate their biotechnological application. Neste trabalho, a produção de substâncias antimicrobianas por estirpes de Pseudomonas sp. isoladas de leite pasteurizado e seu potencial de ação contra bactérias associadas a alimentos foram investigados. As amostras de leite pasteurizado foram adquiridas em estabelecimentos comerciais, arbitrariamente escolhidos, da cidade do Rio de Janeiro-RJ, Brasil. Dentre as quatro amostras analisadas, três apresentaram várias colônias típicas de Pseudomonas. Cerca de cem colônias foram escolhidas e submetidas a testes bioquímicos para confirmação da identificação. Dezoito estirpes do gênero Pseudomonas foram identificadas e submetidas aos testes de pro