Enterotoxigenic Staphylococcus aureus in Brazilian artisanal cheeses: Occurrence, counts, phenotypic and genotypic profiles.

The present study aimed to assess the occurrence and counts of Staphylococcus aureus in Brazilian artisanal cheeses (BAC) produced in five regions of Brazil: Coalho and Manteiga (Northeast region); Colonial and Serrano (South); Caipira (Central-West); Marajó (North); and Minas Artisanal cheeses, from Araxá, Campos das Vertentes, Cerrado, Serro and Canastra microregions (Southeast). The resistance to chlorine-based sanitizers, ability to attach to stainless steel surfaces, and antibiogram profile of a large set of S. aureus strains (n = 585) were assessed. Further, a total of 42 isolates were evaluated for the presence of enterotoxigenic genes (sea, seb, sec, sed, see, seg, sei, sej, and ser) and submitted to typing using pulsed-field gel electrophoresis (PFGE). BAC presented high counts of S. aureus (3.4-6.4 log CFU/g), varying from 25 to 62.5%. From the S. aureus strains (n = 585) assessed, 16% could resist 200 ppm of sodium hypochlorite, whereas 87.6% produced strong ability to attach to stainless steel surfaces, corroborating with S. aureus ability to persist and spread in the environment. Furthermore, the relatively high frequency (80.5%) of multidrug-resistant S. aureus and the presence of enterotoxin genes in 92.6% of the strains is of utmost attention. It reveals the lurking threat of SFP that can survive when conditions are favorable. The presence of enterotoxigenic and antimicrobial-resistant strains of S. aureus in cheese constitutes a potential risk to public health. This result calls for better control of cheese contamination sources, and taking hygienic measures is necessary for food safety. More attention should be paid to animal welfare and hygiene practices in some dairy farms during manufacturing to enhance the microbiological quality of traditional cheese products.

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 <2 log CFU/g, between 2 and 3 log CFU/g and between 3 and 4 log CFU/g, respectively. Among the ASB isolates, 97% had protease, 84% hydrolyzed starch, 66% had hemolytic activity, and 61% had lecithinase activity. A total of 44 out of 120 isolates harbored at least one toxin gene; 56% for B. cereus, 34% for B licheniformis, and less than 5% for B. subtilis, B pumilus, and L. sphaericus. All B. cereus isolates harbored the nhe gene, 60% entFM, 44% cytK, 32% bceT, and 28% hbl genes. Besides, 17% of B. licheniformis harbored nhe. A small proportion of B. subtilis, B. pumilus, and L. sphaericus carried toxin genes. The rpoB based phylogenetic tree provided high resolution among Bacillus species. The findings of this study provide insights into the phenotypic and genotypic biodiversity of Bacillus present in PIF.

Ohmic heating increases inactivation and morphological changes of Salmonella sp. and the formation of bioactive compounds in infant formula.

The effect of ohmic heating (OH) (50, 55, and 60 °C, 6 V/cm) on the inactivation kinetics (Weibull model) and morphological changes (scanning electron microscopy and flow cytometry) of Salmonella spp. in infant formula (IF) was evaluated. In addition, thermal load indicators (hydroxymethylfurfural and whey protein nitrogen index, HMF, and WPNI) and bioactive compounds (DPPH, total phenolics, ACE, α-amylase, and α-glucosidase inhibitory activities) were also studied. OH presented a more intense inactivation rate than conventional heating, resulting in a reduction of about 5 log CFU per mL at 60 °C in only 2.91 min, being also noted a greater cell membrane deformation, higher formation of bioactive compounds, and lower values for the thermal load parameters. Overall, OH contributed to retaining the nutritional value and improve food safety in IF processing.