Survival characteristics of environmental and clinically derived strains of Cronobacter sakazakii in infant milk formula (IMF) and ingredients.

AIMS: The study aimed to compare survival of Cronobacter sakazakii strains in plant-derived infant milk formula (IMF) ingredients and their thermotolerance in reconstituted IMF. METHODS AND
RESULTS: Inulin and lecithin were inoculated with isolates of C. sakazakii including the typed clinical strains, NCTC 11467(T) and BAA 894; a mutant strain in which the wcaD gene had been disrupted; and two environmental strains isolated from IMF processing facilities. Samples were stored and examined for C. sakazakii. All strains were still detectable in both matrices after 338 days storage, except for the mutant strain that was no longer detectable at that time. Higher numbers of the environmental strains were recoverable after 338 days than the clinical strains. The thermotolerance of the five strains was investigated in reconstituted IMF at 55, 60 and 65°C. The clinically derived type strain, NCTC 11467(T), and the mutant strain were shown to be significantly more thermotolerant than other strains tested.
CONCLUSIONS: Environmental strains were more persistent than the clinical strains in inulin and lecithin, indicating that patho-adaptation may have contributed to a reduction in the desiccation tolerance phenotype. However, the thermotolerance results could indicate that the ability to produce extracellular polysaccharide decreases thermotolerance. SIGNIFICANCE AND IMPACT OF THE STUDY: These results indicate that desiccation resistance may play a role in survival of C. sakazakii in dry IMF ingredients and processing plants; however, this trait may be of less importance in clinical environs.