Cronobacter sakazakii is an emerging food borne pathogen which has been associated with outbreaks of a rare form of infant meningitis. Although the origin of the microorganism has not been established, several
infection cases have been associated with the consumption of contaminated powdered infant formula (PIF). In the present study, growth characteristics of three C. sakazakii strains isolated from PIF samples and C.
muytjensii strain ATCC 51329, which was formerly the ATCC Preceptrol™ strain for the quality control of
‘Enterobacter sakazakii’ prior to the taxonomic revision, were investigated in Tryptone Soya broth (TSB) and
reconstituted PIF at 4, 10, 25, 37, 45 and 50ºC. The viability of heat treated cells of Cronobacter strains was
evaluated by plating on Violet Red Bile Glucose agar (VRBGA) and the Druggan-Forsythe-Iversen (DFI)
chromogenic agar followed by incubation at 37ºC. These strains were also subjected to higher temperatures
between 52 to 60ºC to measure their thermal tolerance. The mean generation time of all Cronobacter strains
were slightly lower in PIF than in TSB. C. muytjensii ATCC 51329 showed lower generation time in all culture
media and all temperatures compared to the Cronobacter food isolates, but the results were not significantly
different (P>0.05). The results also indicated that combination of PIF: DFI culture media had higher recovery at
all temperatures compared to other combinations. Survival study also indicated that C. muytjensii ATCC 51329
had higher D-value compared to food isolates at all incubation temperatures.
A total of 90 samples comprising powdered infant formulas (n=51), follow-up formulas (n=21), and infant foods (n=18) from 15 domestic and imported brands were purchased from various retailers in Klang Valley, Malaysia and evaluated in terms of microbiological quality and the similarity of rehydration instructions on the product label to guidelines set by the World Health Organization. Microbiological analysis included the determination of aerobic plate count (APC) and the presence of Enterobacteriaceae and Cronobacter spp. Isolates of interest were identified using ID 32E (bioMérieux France, Craponne, France). In this study, 87% of powdered infant formulas, follow-up formulas, and infant foods analyzed had an APC below the permitted level of <10(4) cfu/g. These acceptable APC ranged between <10(2) to 7.2×10(3) cfu/g. The most frequently isolated Enterobacteriaceae was Enterobacter cloacae, which was present in 3 infant formulas and 1 infant food tested. Other Enterobacteriaceae detected from powdered infant and follow-up formulas were Citrobacter spp., Klebsiella spp., and other Enterobacter spp. No Cronobacter species were found in any samples. Rehydration instructions from the product labels were collated and it was observed that none directed the use of water with a temperature >70°C for formula preparation, as specified by the 2008 revised World Health Organization guidelines. Six brands instructed the use of water at 40 to 55°C, a temperature range that would support the survival and even growth of Enterobacteriaceae.