Determination of single cell lag times of Cronobacter spp. strains exposed to different stress conditions: Impact on detection

• Lag time was calculated from time to detection values determined from OD data.
• Acid stress caused the longest lag times and desiccation stress caused the greatest inactivation.
• There was no correlation of lag time and inactivation caused by heat and acid stresses.
• Simulations of growth after extended lag indicated that some strains might not reach the limit of detection.
• Increasing the number of samples increases the probability of detecting Cronobacter spp. in food products.

The variability of stress resistance and lag time of single cells can have a big impact on their growth and therefore on the probability of their detection in food. In this study, six strains of Cronobacter spp. were subjected to heat, acid and desiccation stress and single cell lag times were determined using optical density measurements. The duration of lag time was highest after acid stress and did not correlate to stress resistance. The effect that the inactivation caused by stress and an extended lag time had on the projected cfu level reached after enrichment was simulated in different scenarios. For most strains, an enrichment time of 18 h was sufficient for stressed cells to reach the suggested minimum level of cell inoculum for the Cronobacter screening broth detection. Particular strains may require longer recovery periods. Further, probability calculations showed that the number of samples taken from a batch may have an important effect on detection probability, especially at low contamination rates. Therefore, in addition to increasing the recovery period, increasing the number of samples is a suitable strategy to improve detection.