Fate of Escherichia coli O157:H7 on channel catfish (Ictalurus punctatus) as affected by harvesting and processing schemes
Suhalim, Rico R. Waworuntu
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Survival of Escherichia coli O157:H7 in channel catfish (Ictalurus punctatus), pond, holding tank water, on live catfish and catfish fillet packaged under modified atmosphere (MA) and overwrapped inoculated at 10 5 , 10 6 , and 10 7 CFU/ml was investigated. E. coli O157:H7 were detected by direct plating for 33 d and 69 d in pond and holding tank water, respectively. A rapid decrease of the pathogen was observed in the first two weeks to reach 2 log CFU/ml. The pathogen was isolated by enrichment procedure for approximately another 30 d from pond and holding tank water. The internal organs and skin scrape had 5.5 log and 2.5 log CFU E. coli O157:H7/ml, respectively. E. coli O157:H7 survived in overwrapped and MA packaged fillet for 20 d. There was a significant difference on the survival of the organism between MA and overwrapped packaging at 0ºC and between MA packaged fillets stored at 0º and 10ºC. A 0.5 and 1 log reduction of E. coli O157:H7 in MA packaged fillet was observed after 5 d storage on fillets stored at 10 and 0ºC, respectively. There was no significant difference between the survival of E. coli O157:H7 on fillets with and without skin either in MA or overwrapped packages. Aerobic bacterial populations at the end of the 20 d storage increased by 1 and 3 log CFU/g while psychrotropic populations increased by 2 and 3 log CFU/g for the 0 and 10ºC storage, respectively. E. coli O157:H7 attached to catfish skin mucus as confirmed by confocal scanning laser microscopy (CSLM) images. E. coli O157:H7 were seen at 15 µm into the mucus layer. Plate count revealed a half a log decrease in E. coli O157:H7 population/cm 2 on skin without mucus than on skin with mucus, while a 1-log decrease in population/cm 2 was observed on skin without mucus than on skin with mucus by microscopic count. Approximately 18 and 16% of all the cells observed under CSLM appeared to be dead cells on skin with or without mucus, respectively.