A collaborative study to evaluate qualitatively powdered baby food validation samples artificially contaminated with Salmonella anatum

Nineteen laboratories participated in a collaborative study to evaluate the performance of validation samples consisting of powdered infant formula and cereal-based weaning food artificially contaminated with low levels of Salmonella anatum. The Standard method BS EN ISO 6579:2002 was to be followed for the trial. Salmonella counts in each baby food were around 10 CFU/25 g (low) or 10 CFU/g (high level). Trial participants received five samples of each sample type and five blank samples. All samples contained Pseudomonas aeruginosa and Lactobacillus spp. at concentrations between 104 and 105 CFU/g as background flora. Precision data for the powdered infant formula were similar for the solid selective plating-out medium xylose–lysine–deoxycholate (XLD) and a 2nd choice of agar suitable to isolate Salmonella spp. The sensitivity was 91.3%, accordance 82.5% and concordance 83.9% for the low and 100% for the high level in all cases. For the cereal-based weaning food, the precision data for the high level were similar for XLD and the 2nd choice medium (98.8%, 97.5% and 97.5%). A slight difference was observed for the low level where XLD obtained values of 82.5%, 73.8%, 70.6% for sensitivity, accordance and concordance and the second choice medium values of 81.5%, 72.5% and 69%. The specificity, accordance and concordance of blanks for the infant formula and cereal-based weaning food were 100%.