Two cases of acute gastroenteritis occurred in 5-month-old infants hospitalized in a mother-and-child hospital in Queretaro, Mexico, on 24 January 2010. C. sakazakii was recovered from the powdered infant formula (PIF), rehydrated PIF (R-PIF) fed to infants, and their fecal samples. The microorganism was present at levels of 0.33 most probable number (MPN)/g and 24 MPN/ml in PIF and R-PIF, respectively. The total ingested dose for the day before the onset of the diarrheic syndrome ranged between 2,160 and 3,600 MPN/ml. All strains of C. sakazakii recovered from the three sources (R-PIF, PIF, and fecal matter) showed identical biotypes, adhesion and invasiveness factors, and pulsed-field gel electrophoresis profiles. No deaths were observed. Salmonella, Shigella, and enterotoxigenic Escherichia coli were not found in food or fecal samples.

Introduction: Certain strains of Cronobacter sakazakii can cause serious invasive infections in children, mainly those less than 2 months old and fed with powdered infant formula (PIF). The infectious dose of C. sakazakii is unknown but evidence suggests that it is approximately 1000 CFU. Powdered infant formula is currently considered safe if its end-product C. sakazakii level is <1 CFU/g. In this study, we determined the lag time, generation time, and growth rate of five pooled C. sakazakii isolates to evaluate the factors affecting contamination levels in reconstituted PIF. Methods: 1.71 log CFU/ml of C. sakazakii were inoculated into 100 ml and 3000 ml of reconstituted PIF and incubated at 22 °C and 35 °C. Growth was evaluated over a 24-h period. ComBase was used for modeling. Results: In 3000 ml, the growth rate was 0.45 ± 0.02 log CFU/h with a lag phase of 3±0.05 h and generation time of 0.67 h at 22 °C, while the growth rate was 0.73 ± 0.01 log CFU/h with a lag phase of 0.45±0.03 h and generation time of 0.41 h at 35 °C. Conclusions: C. sakazakii grows rapidly in reconstituted PIF, especially at 35 °C.

A combination of different hurdles, such as mild heat (54 ℃ for 10 min) or pulsed electric field (25 pulses; 25 kV/cm; 3.35 kJ/cm per pulse) treatments and essential oils constituents (carvacrol, citral, and (+)-limonene), to reduce spoiling bacteria and yeasts in apple juice was evaluated. For this purpose, the heat and pulsed electric field resistances of five strains of Leuconostoc spp. and five Saccharomyces spp. strains were assayed, achieving different inactivation levels for each treatment and strain. For instance, Leuconostoc fallax 74, the most heat-resistant strain, was the second-most sensitive strain to pulsed electric field. The most resistant strains were exposed to combined processes of heat or pulsed electric field and 0.2 µl/ml essential oils constituents. The combination of heat and essential oils constituents proved to be synergistic against both microorganisms in apple juice. The most effective was the combination of mild heat and carvacrol, which caused the inactivation of 99% of L. fallax 74 and 99.99% of Saccharomyces cerevisiae CECT 1172 cells. Therefore, this study shows the great potential of carvacrol, citral, and (+)-limonene in combined treatments with mild heat to achieve a higher degree of inactivation of spoiling microorganisms in apple juice, and thus, to extend its shelf life.