Aerobic spore-forming bacteria in powdered infant formula: Enumeration, identification by MALDI-TOF mass spectrometry (MS), presence of toxin genes and rpoB gene typing

This study aimed to assess the counts and biodiversity characterization of aerobic sporeforming bacteria (ASB) in powdered infant formula (PIF). Fifty-four (n = 54) samples of PIF of three brands were analyzed for mesophilic aerobic bacteria, and ASB counts. ASB isolated from PIF were assessed for their ability to produce spoilage enzymes and hemolytic activity and further identified by MALDI-TOF mass spectrometry. Then, the isolates were subjected to rpoB gene typing and assessment of bceT, entFM, nhe (A, B, C), and hbl (A, B, C) toxin genes. The main species isolated were B. licheniformis (54%), followed by B. cereus (33%) and B. subtilis (5%). The ASB counts ranged from 1 to 4 log CFU/g, and the mean was 2.9 log CFU/g for mesophilic aerobic sporeforming bacteria (MSC) and 2.5 log CFU/g for thermophilic aerobic sporeforming bacteria (TSC). Most PIF samples presented MSC and TSC counts between 2 and 3 log CFU/g. A total of 13%, 50%, and 37% of the samples presented MSC counts from