Virulence potential of Bacillus cereus isolates isolated from Italian infant formulae

Introduction: Several international studies have confirmed the sporadic presence of pathogenic bacteria and have enumerated spoilage organisms in commercial powdered formula products, including Bacillus cereus. Purpose: This study aimed to investigate the prevalence and counts of Bacillus cereus in powdered formulae for infants marketed on the Italian market. Methods: 83 samples, including 23 infant formulae (PIF), 42 follow-on formulae (FOF), and 18 formulae for special medical purposes (SMP) were analyzed, enumerating B. cereus by spreading aliquots onto PEMBA agar. Genomic DNA from B. cereus isolates was extracted. To determine the presence of toxin-encoding genes in B. cereus, conventional PCR was performed. Target genes included sphingomyelinase (sph), enterotoxin Bcet (bcet), enterotoxin FM (entFM), phosphatidylinositol-specific phospholipase C (plcA), cytotoxin K (cytK), and the non-hemolytic enterotoxin components (nheA, nheB, nheC) and cereulide-ces. B. cereus isolates were submitted to antimicrobial susceptibility testing by broth microdilution using the Sensititre™ automated system. Results: B. cereus was detected in 45.8% of samples, but counts detectable (1 log CFU/g) in just three samples. 42 presumptive B. cereus were isolated. All the strains were able to produce proteases, 21 strains secreted PC-PLC and 28 produced the tripartite hemolysin HBL. Among toxin-encoding genes, the most prevalent was sph (97.7%), followed by nheA, nheB, nheC (76.2%), entFM (64.3%) and bcet (45.2%). Only 7.1% of the isolates carried cytK gene. ces was in 28.6% of the isolates. Antimicrobial resistance pattern of the isolates showed high resistance rates to β-lactams and a moderate resistance to erythromycin. Significance: The prevalence, virulence potential, and antibiotic resistance profiles of B. cereus isolates raise important concerns especially considering the vulnerability of the target population.