Listeria monocytogenes Occurrence and Growth at Refrigeration Temperatures in Fresh Blue Crab (Callinectes sapidus) Meat

Abstract

In this study, 126 samples of freshly cooked and picked blue crab (Callinectes sapidus) meat collected from different processing facilities were analyzed for the presence of Listeria spp. Thirteen samples (10%) were positive for Listeria, with 10 samples positive for L. monocytogenes and 3 samples positive for L. innocua. Fraser broth was used in a 5-tube most probable number (MPN) enumeration, in duplicate, of Listeria in 25-g samples incubated at 36°C for 24 h and plated in modified Oxford agar and blood agar with API strip confirmation. The levels of Listeria cells found in fresh blue crab meat were always less than 100/g with only one exception, in which the MPN index was 1,100/g. A L. monocytogenes strain (168) isolated from fresh blue crab meat was inoculated (less than 50 CFU/g) into pasteurized crab meat and incubated at 1.1, 2.2, and 5°C for 21 days. Growth curves were obtained by analyzing 2-g samples at intervals of 0, 8, 10, 12, 14, 16, 19, and 21 days. When inoculated into pasteurized blue crab meat, L. monocytogenes had an increased growth rate as the storage temperature increased, with approximately a 7-log10-unit increase in population at 5°C and only a 2.5-log10-unit increase in population at 1.1°C after the 21 days of incubation.