Rapid'Sakazakii to Detect Cronobacter spp. in Infant Formula: Certification According to the ISO16140 Standard

Introduction: The RAPID’Sakazakii method is based on a chromogenic principle for Cronobacter spp. detection in infant formula. An ISO 16140 method comparison study was conducted, by analyzing 77 infant formula samples in the relative accuracy, sensitivity and specificity part and showing equivalent performances between the test method and the ISO/TS 22964 methods. The relative detection limits of the RAPID’Sakazakii and the ISO/TS 22964 methods were clearly similar and vary from 0.8 and 1.2 CFU/25g. The selectivity and specificity of the alternative method was assessed by testing 52 target strains and 31 non target strains.

Purpose: An independent inter-laboratory study was conducted at ADRIA, to compare the test methods precision to the ISO/TS 22964 one, as part of the NF Validation approval process and according to the ISO 16140 standard.

Methods: The test method protocol includes an overnight enrichment in BPW. The characteristic colonies are confirmed by running oxydase tests and biochemical galleries. Flexibility is offered by storing the enrichment broth at 5±3°C for 3 days, before streaking onto the selective test method agar.

Results: The alternative method was evaluated in a ring trial involving 16 laboratories. Probiotic infant formula containing Lb. reuteri was contaminated with the wild C. sakazakii strain. Eight blank samples, 8 samples contaminated at a fractional recovery level (0.8 cells/g) and 8 highly contaminated samples (20.6 cells/g) were sent to each collaborator. The calculated relative accuracy, sensitivity and specificity values were, respectively, 97.1, 75.5, and 94.2 %. The results of accordance, concordance, and odds ratio confirm that the test method precision is equivalent to the ISO/TS 22964 standard one.

Significance: Both the ISO 16140 method comparison and inter-laboratory studies clearly show that the test method is a reliable alternative method for Cronobacter spp detection in infant formula, offering important economic savings by reducing time to result and handling time.