CONICET | Buscador de Institutos y Recursos Humanos

Food-grade phosphates are used in the meat, poultry and seafood processing industry, fruit and vegetable applications, and dairy and beverage manufacturing to improve chemical and organoleptic properties of the final product. They have also demonstrated antimicrobial activity on bacteria and fungi. The foodborne enteropathogens, Shiga toxin-producing Escherichia coli (STEC), Salmonella Enteritidis (SE) and Yersinia enterocolitica (YE), could be inhibited by these compounds. In the present study, the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) of trisodium phosphate (TSP), sodium acid pyrophosphate (SAPP, Na2H2P2O7), tetrasodium pyrophosphate (TSPP, Na4P2O7) and sodium tripolyphosphate (STPP, Na5P3O10) against the three pathogens were determined by the broth microdilution test. The microplates contained Mueller Hinton broth plus 0.01% of a colorimetric indicator of bacterial growth, serial two-fold dilutions of each compound, and standardized inoculum of each microorganism. They were incubated at 37ºC for 24 h. MIC was the lowest concentration of each phosphate where no growth was observed. Later, subcultures from dilutions without turbidity were performed on trypticase soy agar (TSA). MBC was defined as the lowest phosphate concentration that showed no bacterial growth on TSA. MIC and MBC increased in this order: TSP < TSPP = SAPP < STPP. Regarding the microbial susceptibility, YE was the most sensitive microorganism with CIM values of 3.12 (SAPP), 6.25 (TSP and TSPP) and 12.5 (STPP) mg/ml, which were similar to those observed for SE [6.25 (TSPP), 12.5 (TSP) and 25 (SAPP and STPP) mg/ml]. STEC was the most resistant pathogen with MIC values of 12.5 (TSP), 50 (SAPP and TSPP) and 100 (STPP) mg/ml (p < 0.05). Similar trends were observed for MBC values. Phosphate levels < 5 mg/ml are admitted in food industry, so that only YE could be effectively inhibited by SAPP

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