Growth and survival of Cronobacter species as measured by media performance
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 PreceptrolTM 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.