Evaluation of the antimicrobial activity of bacteriocins produced by regional Yersinia strains

Abstract

Bacteriocins are extracellular peptides of ribosomal origin and encoded at the plasmid level. Pathogenic Yersinia enterocoliticastrains belonging to biotypes (B) 1 to 5 are cause of gastrointestinal symptoms and immunological sequelae in humans byconsumption of contaminated foods. Y. frederiksenii, Y. intermedia and strains of Y. enterocolitica B1A do not carry thevirulence markers that characterize pathogenic Y. enterocolitica strains; however, they may produce bacteriocins that inhibitthe growth or destroy these pathogenic strains. To contribute to food safety and the human health, the use of bacteria asbiocontrol agents in food has been proposed since they offer safe advantages to the consumer. The aim of this study was toevaluate the antimicrobial activity of bacteriocins produced by Yersinia strains on pathogenic Y. enterocolitica strains isolatedfrom various foods in our region by the plate titration method. Two Y. intermedia B1 (named 79 and 26), one Y. intermediaB6 (10) and three Y. enterocolitica B1A (66, 89, 90) were tested as bacteriocin-producing strains (BPS), and three Y.enterocolitica strains belonging to B2, B3 and B4 were used as indicator strains (IS) of the antimicrobial effect. The spottechnique was performed on a double layer agar. BPS and IS were cultured in Luria Bertani broth (LB) with shaking at 25°Cfor 18 h, and inocula were adjusted to a concentration corresponding to an ODʎ610 0.2. From BPS, two-fold dilutions weremade in LB, and 10 μl of each one was placed on Petri plates with semisolid agar previously inoculated with IS. Plates wereincubated at 25°C and at 10°C for 18 h. The reciprocal of the highest dilution of BPS that produced total inhibition of IS wasconsidered as the titer and expressed in arbitrary units per ml (AU ml -1). Results represent the average of three differentexperiments. At 25°C, the highest inhibition titers were observed for Y. enterocolitica B1A (90) on Y. enterocolitica B2 andB4, with values of 12,800 + 0 AU ml-1and 10,667 + 3,695 AU ml-1(p > 0.05), respectively. At 10 ° C, the highest inhibitiontiters were shown by Y. intermedia B1 (79) on Y. enterocolitica B2 and B4, with values of 9,262 + 3,695 AU ml-1and 6,400+ 0 AU ml-1 (p > 0.05), respectively. All BPS showed lower titers on Y. enterocolitica B3 than on Y. enterocolitica B2 and B4(p < 0.05) at both temperatures. When comparing the two temperatures, most of titles produced by BPS were higher at 25°Cthan at 10°C (p < 0.05). Results obtained in this study demonstrate the capacity of regional Y. intermedia and Y. enterocoliticaB1A strains to produce significant amounts of bacteriocins with inhibitory effect on pathogenic Y. enterocolitica strains, andhighlight the great potential of these substances as antagonists of pathogenic or spoilage bacteria in food, even at refrigerationtemperatures.