Resistência térmica de Escherichia coli produtora de toxina Shiga em carne bovina brasileira

Abstract

Shiga toxin-producing Escherichia coli (STEC) is an important pathogen in public health as it related to severe food-borne infections. The risk of these infections increases when STEC have high thermal resistance (between 60° and 71°C). Studies have shown the occurrence of gene markers inserted in a mobile island called locus of heat resistance (LHR) in a significant portion of highly heat-resistant strains, but there is no data of LHR incidence in Brazil. So, in this study we performed the first characterization of STEC heat resistance in Brazil with detection of LHR. For this, 22 strains of E. coli STEC randomly selected from carcasses and beef were grown in Luria Bertani broth (LB) under different survival challenges (60 °C/ 0, 6, 12, 18 and 24 min and 71 °C/ 0 and 6 min). The concentration of viable bacteria was determined before and after the challenge periods, with PCR analysis conducted to detect the LHR in all isolates. The LHR was in 4/22 strains (18.18%), with 2 of these strains having the highest heat resistance of all isolates evaluated and the other two having moderate heat resistance. For heat-sensitive strains, we determined that they could be identified by incubating only for the time required for the culture to reach 60 °C, which would speed identification of heat-resistant isolates in future studies. However, all strains that showed high resistance (60 °C up to 6 min) were sensitive to 71 °C (temperature established as safe for food cooking according to USDA and close to that established for food cooking in ANVISA- Brazil). In our study, we identified a high proportion of LHR-positive isolates compared to studies in colder climates may indicate selection for heat resistance by the tropical climate of Brazil. This study represents a first evaluation of STEC heat resistance in Brazil and demonstrates that heat-resistant strains could survive in ready-to-eat foods stored at 60 °C.