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Growth and toxin production of Bacillus cereus strains in reconstituted initial infant milk formula

Bursová, Šárka, Necidová, Lenka, Haruštiaková, Danka
Food control 2018 v.93 pp. 334-343
Bacillus cereus, bacteria, diarrhea, dried milk, enterotoxins, foodborne illness, hemolysins, infant formulas, inoculum, microbial growth, milk, models, reconstituted milk, risk, shelf life, spores, temperature
Bacillus cereus may cause two different types of foodborne illness: diarrheal and emetic syndromes. Dried infant formulae are at risk of contamination by the B. cereus, which is reflected by the requirement for the microbiological examination of foods listed in Regulation (EC) 2073/2005, as amended. This study evaluates the growth and toxin production potential of B. cereus in reconstituted dried infant milk formula. Powdered milk was inoculated with approximately 1 log and 3 log cfu g−1 of spore suspension of toxigenic B. cereus strains and then stored as reconstituted milk for 48 h at 8 °C, 15 °C, and 24 °C. The growth of B. cereus, tested by the plate method, and production of the emetic toxin and enterotoxins, tested by the gold-labelled immunosorbent assay, were regularly detected during 48 h of storage. The Baranyi-Roberts model was used to study the growth potential of B. cereus strains. In reconstituted infant milk, B. cereus did not grow at 8 °C during 48 h of storage. B. cereus multiplied and formed toxins only at 15 °C and 24 °C. The growth curve of the bacteria stored at 15 °C included the lag and exponential phases, and the growth was not completed during the period. The growth of B. cereus at 24 °C was completed, peaking within 27 and 20 h, with the low and high inoculum sizes, respectively. Detectable amounts of toxins were formed during the bacterial growth of around 5 log cfu ml−1 (non-hemolytic enterotoxin) and 7 log cfu ml−1 (hemolysin BL and emetic toxin). Model experiments evaluated consumer risk from B. cereus toxins resulting from extended storage of reconstituted infant milk formula at improper temperatures.