Toxigenic Potential of Bacillus cereus Strains Isolated from Retail Dairy Products in Egypt

Isolation, Identification, and Characterization of Bacillus cereus Group Bacteria Isolated from the Dairy Farm Environment and Raw Milk in Tunisia

Members of the Bacillus cereus group are well-known opportunistic foodborne pathogens. In this study, the prevalence, hemolytic activity, antimicrobial resistance profile, virulence factor genes, genetic diversity by enterobacterial repetitive intergenic consensus (ERIC)-polymerase chain reaction (PCR) genotyping, and adhesion potential were investigated in isolates from a Tunisian dairy farm environment and raw milk. A total of 200 samples, including bedding, feces, feed, liquid manure, and raw bovine milk, were examined. Based on PCR test targeting sspE gene, 59 isolates were detected. The prevalence of B. cereus group isolates in bedding, feces, liquid manure, feed, and raw milk was 48%, 37.8%, 20%, 17.1%, and 12.5%, respectively. Out of the tested strains, 81.4% showed β-hemolytic on blood agar plates. An antimicrobial resistance test against 11 antibiotics showed that more than 50% of the isolates were resistant to ampicillin and novobiocin, while a high sensitivity to other antibiotics tested was observed in most isolates. The distribution of enterotoxigenic genes showed that 8.5% and 67.8% of isolates carried hblABCD and nheABC, respectively. In addition, the detection rate of cytotoxin K (cytk), enterotoxin T (bceT), and ces genes was 72.9%, 64.4%, and 5.1%, respectively. ERIC-PCR fingerprinting genotype analysis allowed discriminating 40 different profiles. The adhesion potential of B. cereus group on stainless steel showed that all isolates were able to adhere at various levels, from 1.5 ± 0.3 to 5.1 ± 0.1 log colony-forming unit (CFU)/cm2 for vegetative cells and from 2.6 ± 0.4 to 5.7 ± 0.3 log CFU/cm2 for spores. An important finding of the study is useful for updating the knowledge of the contamination status of B. cereus group in Tunisia, at the dairy farm level.

Phenotypic diagnosis and genotypic identification of Bacillus cereus causing subclinical mastitis in cows

Background and Aims

Bovine mastitis is a disease that affects dairy cows and impacts the global dairy industry. Bacillus spp. can infect the mammary gland during lactation, intramammary treatment, or dry cow therapy. This study aimed to isolate and identify Bacillus spp. in raw milk samples from cows with subclinical mastitis from dairy farms in Beheira, Giza, Alexandria, and Menoufia Governorate, Egypt. We also investigated their antibiotic sensitivity and detected the enterotoxigenic and antibiotic resistance genes.

Materials and Methods

A total of 262 milk samples (15-20 ml each) were examined microscopically, biochemically, and phenotypically. A polymerase chain reaction was used for genotypic identification and detecting antibiotic-resistance and enterotoxigenic genes. Antibiotic sensitivity was tested using the agar well diffusion test.

Results

Bacillus cereus was identified in 47.7% of samples. Nhe and hblD enterotoxin genes were found in 93.64% (103/110) and 91.82% (101/110) of the samples, respectively. Tetracycline and β-lactam antibiotic-resistance genes were present in 0% (0/110) and 98.18% (108/110), respectively, of the samples. All isolates were resistant to cefepime, cefixime, and oxacillin, while they were susceptible to amoxicillin-clavulanic, chloramphenicol, ampicillin/sulbactam, and levofloxacin.

Conclusion

These results highlight the need to promote awareness regarding B. cereus, the most common pathogen causing mastitis in Egyptian dairy cows. We also emphasized that antibiotic misuse during mastitis is a potential public health threat.

Characterization and spoilage potential of Bacillus cereus isolated from farm environment and raw milk

Bacillus cereus sensu lato (B. cereus sl) is important spoilage bacteria causing milk structure and flavor changes and is ubiquitous in the environment. This study addresses the biodiversity, toxicity, and proteolytic activity of B. cereus sl from 82 environmental samples and 18 raw bovine milk samples from a dairy farm in the region of Tianjin. In sum, 47 B. cereus sl isolates were characterized through biochemical tests, 16S rRNA gene sequencing, and panC gene analysis. Fourteen sequence types (STs) of B. cereus sl were found in raw bovine milk samples, and five new STs (ST2749, ST2750, ST2751, ST2752, and ST2753) were identified in this study. ST1150 was the dominant ST, associated with fecal, air, drinking water, teat skin, teat cup, and teat dip cup. The results of toxin gene analyses showed that 12.77% and 8.51% of isolates carried hblACD and nheABC operons, respectively. In addition, the detection rate of emetic cesB gene was 21.28%. B. cereus sl demonstrated high spoilage potentials even at 7°C, which has the proteolytic activity of 14.32 ± 1.96 μmol of glycine equivalents per ml. Proteolytic activities were significantly (p < 0.05) decreased after the heat treatment. The residual activity of protease produced at 7°C was significantly higher than that produced at 25°C and 37°C after treatment at 121°C for 10 s and 135°C for 5 s (p < 0.01). Together, the results provide insights into the characteristics of B. cereus sl from farm environment and raw bovine milk and revealed that B. cereus sl contamination should also be monitored in raw milk for ultra-high temperature (UHT) products. This knowledge illustrates that strict cleaning management should be implemented to control B. cereus sl and assure high-quality milk products.

Midguts of Culex pipiens L. (Diptera: Culicidae) as a potential source of raw milk contamination with pathogens

Despite their importance, only few studies focused on the mosquitoes borne microbial diseases, especially bacterial and fungal diseases, their vectorial capacity toward microorganisms, and their important role in raw milk contamination with pathogens in some unsanitary dairy farms. In Egypt, where Culex pipiens is the historical main vector of lymphatic filariasis, only few studies discussed the isolation of pathogens from the midguts of different stages of C. pipiens. This study aims to isolate and identify the pathogenic symbiotic microorganisms inside the midgut of adult female C. pipiens as well as investigate its ability to transmit their midgut pathogens to raw milk. A total of 750 field strain C. pipiens larvae of the second and third larval instars were collected from ponds water around the livestock farms in Mariotteya, Giza, Egypt, for microbial pathogen isolation and identification. All collected larval instars were transported to the laboratory at the Research and Training Center on Vectors of Diseases (RTC), Ain Shams University, where they were maintained for further studies. Six groups of C. pipiens were tested for the incidence of various pathogenic microorganisms in their midguts and their possibility to contaminate commercial sterilized milk. Traditional PCR assays and sequencing method detected and identified 16srRNA genes of the predominant hemolytic isolates from milk and midguts of female C. pipiens. The phylogenetic analyses of the obtained isolates were performed based on NCBI data. Three strains of Bacillus anthracis strain CPMESA 2021, Staphylococcus warneri strain CPSAME 2021, and Bacillus cereus strain CPSEMA 2021, which represent most food pathogens, were found in the midguts of C. pipiens and were submitted to the GenBank database with the accession numbers OK585071, OK576651, and OK585052, respectively. The isolation of these strains from mosquitoes raises contemporary issues concerning milk safety, such as bacterial isolates, the degree of the vectorial capacity of mosquitoes, milk production and processing conditions, and human pathogenicity. Such serious issues need further investigation.