Characterization of Infant Formulae Marketed in Italy and Virulence Potential of Bacillus cereus Isolates

This study aimed to evaluate the microbiological quality and safety of powdered formulae intended for infant consumption on the Italian market. A total of 83 samples, including 23 infant formulae (PIF), 42 follow-on formulae (FOF), and 18 formulae for special medical purposes (SMPs), were taken between 2023 and 2024. Low total viable counts were highlighted with all SMP samples, 87.0% of PIF samples and 97.6% of FOF samples being compliant with the threshold set by the Code of Hygienic Practice for Powdered Formulae for Infants and Young Children (2.70 Log CFU/g). High contamination levels (>4 Log CFU/g) were found exclusively in PIF (8.7%) and FOF samples (2.4%). Considering potential pathogenic bacteria, the presence of <i>Listeria monocytogenes</i>, <i>Yersinia enterocolitica</i>, <i>Salmonella</i> spp., <i>Bacillus cereus</i>, and <i>Cronobacter sakazakii</i> was investigated. Enumeration of <i>Bacillus cereus</i>, <i>Staphylococcus aureus</i>, and <i>Clostridia</i> was also performed. Only presumptive <i>B. cereus</i> was detected (37 samples, and in 3 samples was enumerated with counts equal to 1 Log CFU/g). A total of 42 presumptive <i>B. cereus</i> isolates were tested for the production of hemolysin BL, phosphatidylcholine-specific phospholipase C, proteases, and for the presence of chromosomal toxin-encoding genes, showing a relevant prevalence of virulence factors and highlighting a potential concern for infants. The antimicrobial resistance pattern of the isolates showed high resistance rates to β-lactams and a moderate resistance to erythromycin. A chemical-physical characterization of the formulae was also performed showing high heterogeneity in terms of pH, Aw, and concentration of organic acids. The results obtained provide useful information for monitoring the potential exposition of infants to microbial populations and to evaluate the safety of the products available on the market.