Antimicrobial activity of bacteriocin-producing Yersinia spp. against foodborne pathogenic bacterial strains

Abstract

Bacteriocins (BAC) are bacterial metabolites that act by inhibiting the growth of related or unrelated species; thus, BAC have been studied as biocontrollers of foodborne pathogens as these compounds are also considered GRAS (generally recognized as safe). Non-pathogenic Yersinia species, such as Y. intermedia, Y. frederiksenii, and Y. enterocolitica biotype 1A use to be BAC producers exhibiting inhibitory effect against pathogenic Y. enterocolitica strains (biotypes 1B, 2-5). The aims of this work were: i) to evaluate the antimicrobial activity of BAC produced non-pathogenic Yersinia strains against foodborne pathogens bacterial strains, and ii) to evaluate this activity at different temperatures. For this purpose, four Y. intermedia (10, 79, 85, 96), two Y. fredericksenii (73, 74), and two Y. enterocolitica 1A (66, 89) strains were used as bacteriocin-producing strains (BPS). As indicator strains (IS) eight pathogens were tested: Salmonella sp., Shigella flexneri, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Bacillus cereus, Listeria monocytogenes and Y. enterocolitica 1B. The spot-plate technique was performed on a double-layer agar. BPS and IS were cultured in Luria Bertani broth (LB) at 25°C for 18 h. Inocula were adjusted to a concentration corresponding to a DO610 of 0.2 and 10 μl of each BPS were spot plated onto semisolid agar previously inoculated with IS. Plates were incubated at 10°C, 25°C and 37°C for 18 h, in duplicate. The sensitivity of the IS was evident by the presence of halos around the BPS; in addition, the diameters of the halos (mm) were measured. Among the eight BPS tested, only two Y. intermedia (96 and79) and two Y. enterocolitica 1A (66 and 89) were active against L. monocytogenes and Y. enterocolitica 1B. For L. monocytogenes the inhibition at 10°C was: BPS 66:14.25±1.25 mm, BPS 79: 14±0 mm, BPS 89: 14.5±1 mm, BPS 96: 15±1.5 mm; at 25°C was: BPS 66: 10.75±0.25 mm, BPS 79: 14.25±0.25 mm, BPS 89: 14.5±2 mm, BPS 96: 13.15±0.35 mm. For Y. enterocolitica the inhibition at 10°C was: BPS 66: 16.5±0.5 mm, BPS 79: 16±1 mm, BPS 89: 16±1 mm, BPS 96: 15.25±1.75 mm; at 25°C was: BPS 66: 15±0 mm, BPS 79: 13.5±2 mm, BPS 89: 15.5±0.5 mm, BPS 96: 15.75±0.75 mm. At 10°C and at 25°C there was inhibition, while at 37°C there was no inhibition. These results encourage the hypothesis that bacteriocins produced by non-pathogenic Yersinia strains could be involved in the reduction or elimination of pathogenic strains responsible for causing spoilage or foodborne illness even at refrigeration temperatures.