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Catfish Special Edition: Thermal Inactivation of Non-O157:H7 Shiga Toxin Producing Escherichia coli (STEC) on Catfish Fillets

Parvaneh Khosravi, Juan Silva, Christophe H. Sommers and Shiowshuh Sheen

Non-O157:H7 shiga toxin-producing Escherichia coli (non-O157 STEC) strains have emerged as food borne pathogens which have been involved in numerous food borne illness outbreaks worldwide. Seafood (fish) consumption has increased in recent years: it could become more common that STEC outbreaks may be associated with the non-O157 serovars. However, there is a lack of data on thermal inactivation of non-O157 STECs in fish muscle (e.g. catfish). Catfish fillets were inoculated with a six-isolate cocktail of non-O157 STEC serovars, i.e. O26:H11, O45:H2, O103:H2, O111:NM, O121H19, and O145:RM (the Big 6), to determine the impact of thermal treatment (heat) on their survival or thermal inactivation kinetics. The inoculated catfish fillet samples (108-9 cfu/g) were subjected to isothermal heating at 55, 60, and 65°C. The D- and z- values were determined by using linear regression of the survival data. The D- values were found to be 712 sec (R2 = 0.88), 38.8 sec (R2 = 0.97) and 3.6 sec (R2 = 0.91) at 55, 60 and 65°C, respectively. The z-value was 4.4°C, consistent with reported values for STECs  in other food systems. The results of this study showed that the thermal  inactivation effect of non-O157 STECs is not the same as of O157 strains in catfish meat, especially at lower temperature (e.g. 55°C), but becomes similar as temperature increases. The findings will assist risk assessors in providing safer finfish products to consumers.