Variable thermotolerance of Cronobacter sakazakii strains at elevated temperatures in powdered infant formula.

Despite advancements in food safety standards and control measures, Cronobacter sakazakii continues to be a serious public health concern, particularly in Powdered Infant Formula (PIF). This study aims to characterise the ability of C. sakazakii to tolerate high temperatures (90 °C) in a commercial dry PIF matrix using distinct strains (n = 6). Multi-locus sequence typing (MLST) analysis identified the six strains as belonging to ST1, ST4, and ST8 MLST types. All strains were able to tolerate exposure to the high temperature in the powder matrix with significant variation (p < 0.05) in the Weibull scale parameter δ, representing the time associated with a 1-log₁₀ reduction, with values ranging from 8.30 ± 3.92 to 0.87 ± 1.02 min. A total of 43 known thermotolerance-related genes were present across all genomes. Among these genes, the presence of three genes (hspA, yadV_1, and yadV_2) was associated with enhanced thermotolerance in the powder matrix. Additionally, a complete putative thermotolerance genomic island (thrB-Q) was present in tested strains exhibiting enhanced ability to tolerate exposure to the elevated temperature. While all strains were able to tolerate exposure to high temperature in powdered infant formula, there was significant strain-specific variability and the strain-specific differences may be linked to their genetic content. Such variations in thermotolerance, linked to strain-specific genetic determinants, are an important consideration for designing effective control strategies.