Survival and detection ofBacillus cereusin the presence ofEscherichia coli,Salmonella enteritidis, Staphylococcus aureus, Pseudomonas aeruginosaandCandida albicansafter rechallenge in make-up removers

Effect of Sublethal Concentrations of Zinc Oxide Nanoparticles on Bacillus cereus

Zinc oxide nanoparticles (ZnONPs), which are produced on a large scale, pose a potential threat to various environments because they can interact with the microbial populations found in them. Bacteria that are widespread in soil, water, and plant material include the Bacillus cereus group, which plays an important role in biodegradation and the nutrient cycle and is a major factor determining ecological balance. This group includes, among others, the foodborne pathogen B. cereus sensu stricto (herein referred to as B. cereus). The aim of this study was a comprehensive assessment of the effects of commercially available ZnONPs on B. cereus. The MIC (minimum inhibitory concentration) for B. cereus was 1.6 mg/mL, and the MBC (minimum bactericidal concentration) was 1.8 mg/mL. Growth of B. cereus was inhibited by a concentration of ZnONPs lower than or equal to MIC50. Concentrations from 0.2 to 0.8 mg/mL inhibited the growth of these bacteria in liquid media, induced symptoms of oxidative stress, and stimulated an environmental stress response in the form of biofilm and endospore formation. In addition, ZnONPs negatively affected the ability of the bacteria to break down the azo dye Evans Blue but enhanced the antimicrobial properties of phenolic compounds. Sublethal concentrations of ZnONPs generally decreased the activity of B. cereus cells, especially in the presence of phenolics, which indicates their potential toxicological impact, but at the same time they induced universal defence responses in these cells, which in the case of potential pathogens can hinder their removal.

qPCR detection of viable Bacillus cereus group cells in cosmetic products

Reference methods for microbiological safety assessments of cosmetics rely on culture methods that reveal colonies of live microorganisms on growth media. Rapid molecular technologies, such as qPCR, detects the presence of target DNA in samples from dead and viable cells. DNA intercalating dyes, such as propidium monoazide (PMAxx), are capable of restricting PCR amplification to viable microbial cells. Here we developed singleplex and multiplex real time (qPCR) assays for the detection of Bacillus cereus (B. cereus) using 16S rRNA and phosphatidylcholine-specific phospholipase C (PLC) gene specific sequences coupled with PMAxx. The limit of detection was determined to be ~ 1 log CFU/ml for 16S rRNA and 3 log CFU/ml for PLC detection in pure culture using an eye shadow isolate, B. cereus 3A. We assessed the inclusivity and exclusivity of our qPCR assays using 212 strains, including 143 members of B. cereus, 38 non- B. cereus. and 31 non-Bacillus species; inclusivity was 100% for the 16S rRNA and 97.9% for the PLC targets; the exclusivity was 100% for 16S rRNA and 98.6% for PLC targets. These qPCR assays were then used to assess samples of commercial cosmetics: one set of liquid face toners (N = 3), artificially contaminated with B. cereus 3A, and one set of powdered cosmetics (N = 8), previously determined to be contaminated with B. cereus. For some samples, test portions were analyzed by qPCR in parallel, with and without PMAxx treatment. All test portions were simultaneously streaked on BACARA plates to confirm viable cells of B. cereus, according to the culture method. We found no difference in sensitivity between the singleplex and the multiplex qPCR assays (P > 0.05). Inoculated samples that did not recover B. cereus on plates still showed amplification of the DNA targets. However, that amplification was significantly delayed in PMAxx -treated samples (P < 0.0001) with C_T value differences of 7.82 for 16S rRNA and 7.22 for PLC. Likewise, amplification delay was significant (P < 0.0001) with inoculated samples that recovered B. cereus on plates with C_T value differences of 2.96 and 2.36 for 16S rRNA and PLC, respectively, demonstrating the presence of dead cells in the samples. All our qPCR results correlated with detection on BACARA plates (kappa, k = 0.99), independently of the presence of PMAxx in the PCR assays. Nevertheless, the amplification threshold with PMAxx dyes was significantly higher than the non-PMAxx dyes. Our findings confirm qPCR can be used for more rapid detection of microorganisms in cosmetics, including B. cereus, and selective detection of viable cells can be improved using PMAxx dyes.

Genomic characterization of Bacillus cereus sensu stricto 3A ES isolated from eye shadow cosmetic products

BACKGROUND

The Bacillus cereus group, also known as B. cereus sensu lato (s.l.) contains ubiquitous spore-forming bacteria found in the environment including strains from the B. cereus sensu stricto (s.s.) species. They occur naturally in a wide range of raw materials and in consumer products. Characterizing isolates that have survived in consumer products allows us to better understand the mechanisms that permit spores to persist and potentially cause illness. Here we characterize the draft genome sequence of B. cereus s. s. 3A-ES, originally isolated from eye shadow and since investigated in several cosmetic studies and compared it to other top ten published complete genome sequences of B. cereus s.l. members.

RESULTS

The draft genome sequence of B. cereus s.s. 3A ES consisted of an average of 90 contigs comprising approximately 5,335,727 bp and a GC content of 34,988%, and with 5509 predicted coding sequences. Based on the annotation statistics and comparison to other genomes within the same species archived in the Pathosystems Resource Integration Center (PATRIC), this genome "was of good quality. Annotation of B. cereus s.s. 3A ES revealed a variety of subsystem features, virulence factors and antibiotic resistant genes. The phylogenetic analysis of ten B. cereus group members showed B. cereus s.s. 3A-ES to be a closely related homolog of B. cereus s.s. ATCC 14,579, an established reference strain that is not adapted for cosmetic microbiological studies. Survival of 3A-ES in eye shadow could be linked to predicted stress-response genes and strengthened by additional stress-response genes such as VanB-type, VanRB, CAT15/16, BcrA, BcrB, Lsa(B), and recA that are lacking in B. cereus s.s. ATCC 14,579.

CONCLUSION

Our genomic analysis of B. cereus s.s. 3A-ES revealed genes, which may allow this bacterium to withstand the action of preservatives and inhibitors in cosmetics, as well as virulence factors that could contribute to its pathogenicity. Having a well-characterized strain obtained from eye-shadow may be useful for establishing a reference strain for cosmetics testing.

Rapid Detection of Bacillus cereus Using Cross-Priming Amplification

Bacillus cereus is a spore-forming gastrointestinal pathogen that can cause life-threatening diseases. Here, a simple and effective assay to detect B. cereus was developed, using cross-priming amplification (CPA). Amplicons were detected using disposable cartridges that contained nucleic acid detection strips. The sensitivity of CPA assay for B. cereus was assessed using serial dilutions of genomic DNA, which indicated a detection limit of 3.6 × 10¹ CFU/mL. No cross-reactions were detected when genomic DNA extracted from 12 different B. cereus strains and 20 other bacterial foodborne strains were tested, suggesting that the assay is highly specific. Finally, we evaluated the practical applications of the CPA assay for the detection of B. cereus in 150 food samples and found that its sensitivity and specificity, compared with real-time PCR, were approximately 98.18 and 100%, respectively. In conclusion, CPA combined with nucleic acid detection strips is easy to perform, requires simple equipment, and offers highly specific and sensitive B. cereus detection.