Studies on the survival of Cronobacter sakazakii in powdered infant formula under simulated gastric conditions of newborns
Cronobacter sakazakii can cause severe illnesses in infants, with consumption of contaminated powdered infant formula (PIF) being the major vehicle of infection. This thesis examined the behaviour of C. sakazakii in an acidic environment of a newborn’s stomach and when in the viable but non-culturable (VBNC) state. The SHIME was used to simulate the gastric conditions of newborns. C. sakazakii grew in the stomach portion of the SHIME during a 4-h exposure to pH 4.00, 5.00 and 6.00 by 0.96-1.05, 1.02-1.28 and 1.11-1.73 log CFU/mL, respectively. The gene expression analyses showed that C. sakazakii appeared to develop an acid adaptation response during the 4-h exposure. Altogether, low gastric acidity and lengthy digestion time facilitated the adaptation and survival of C. sakazakii in the newborn’s stomach. An exposure to a thermal treatment of 100°C for 120 seconds, mimicking commercial spray-drying, was sufficient to induce C. sakazakii in artificially-inoculated PIF into the VBNC state. C. sakazakii cells in the VBNC state showed signs of resuscitation and growth after a 4-h incubation in reconstituted PIF at 37°C.