Characterization of Food-Borne Outbreak Isolates

The isolates from the food-borne outbreak comprised two from food: FC1 and FC2 (obtained from the leftover pasta sauce: mussels and smoked mackerel in garlic butter sauce) and five from the vomit of one patient: FC6, FC7, FC8, FC9, and FC10. They were isolated on Polymyxin Pyruvate Egg-Yolk Mannitol Bromothymol-Blue Agar (PEMBA), which was incubated at 37 °C for 48 h. The isolates were examined using phase-contrast microscopy and biochemically characterized using the API 20E and API 50 CHB systems (BioMérieux, Marcy-l’Étoile, France). Growth at 40 °C, 42 °C, 45 °C, 48 °C, and 50 °C, was also observed in Tryptone Soy Broth (Oxoid, Basingstoke, UK) cultures incubated in water baths. B. cereus F4810/72 (also known as strain B0358 in the Logan Bacillus Collection at Glasgow) was used as a reference emetic toxin-producing strain. All bacterial cultures were maintained on Tryptone Soy Agar (TSA) (Oxoid, Basingstoke, UK), stored at 4 °C, or in lyophilized form.