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Biosensors: a Potential Tool for Detection of Microbial Contaminants for Food Safety
Published in Megh R Goyal, Sustainable Biological Systems for Agriculture, 2018
Anurag Jyoti, Rajesh Singh Tomar
Enterohemorrhagic E. coli (EHEC) is exploited in sorbitol MacConkey agar (SMAC). The International Organization for Standardization (ISO) protocol (ISO 16654) recommends that addition of Cefixime and potassium tellurite to SMAC (CT-SMAC) may increase the selectivity in samples. E. coli O157 generally produces colorless colonies when cultured on this media, thus distinguishing it from other EHEC serogroups. EHEC O157:H7 colonies are confirmed with biochemical tests and immunoassays having the O157 somatic antigen and H7 flagellar antigen (Figure 6.1).
Sanitary status and water quality of some drinking water sources and antibiogram of Shiga toxin-producing Escherichia coli O157:H7 isolated from Shika, Zaria, Nigeria
Published in International Journal of Environmental Health Research, 2022
Osayande Obanor, Seniyat Larai Afegbua, Joseph Baba Ameh
The total coliform and faecal coliform present in 100 mL of each water sample were assessed with the membrane filtration technique and cultured on membrane lactose glucuronide agar (Oxoid, UK) at 37ºC and 45ºC, respectively. The resulting colonies were recorded as colony-forming unit (CFU) per 100 mL of the water sample (Cheesbrough 2006). The yellow colonies from membrane lactose glucuronide agar were subcultured onto the Cefixime-tellurite Sorbitol MacConkey agar (CT-SMAC) (Oxoid, UK) plate and incubated aerobically at 37ºC for 24 h. Transparent and colourless colonies, characteristic of E. coli O157:H7, were then sub-cultured onto nutrient agar slants at 37°C for 24 h and stored at 4°C prior to further characterization by Gram staining and biochemical tests (Indole, MR-VP, citrate utilization and β-glucuronidase) (Oxoid, UK) and serological analysis (Cheesbrough 2006). A serological identification of E. coli O157:H7 was achieved by using Latex Agglutination test kit (Oxoid, UK) according to the manufacturer’s instructions.
Supercritical CO2 for the drying and microbial inactivation of apple’s slices
Published in Drying Technology, 2021
Alessandro Zambon, Siméon Bourdoux, Maria F. Pantano, Nicola Maria Pugno, Francesca Boldrin, Gerard Hofland, Andreja Rajkovic, Frank Devlieghere, Sara Spilimbergo
Microbial load before and after the treatment was analyzed by means of the standard plate count techniques. In stomacher bags, treated samples were diluted in steril MIlliQ water with a ratio of 1:10. After stomaching for 1 min, 10-fold dilutions were prepared and plated on the selective media. The appropriate dilutions were spread-plated on Cefixime-Tellurite Sorbitol MacConkey Agar (CT-SMAC, Sacco, Italy) containing nalidixic acid (50 µg/mL, Sigma-Aldrich, Germany) and CT-SMAC containing kanamycin (100 µg/mL, Sigma-Aldrich) for E. coli O157:H7. Salmonella was enumerated on Xylose Lysine Deoxycholate agar (XLD, Biolife, Italy) containing nalidixic acid (50 µg/mL), XLD containing kanamycin (100 µg/mL), and XLD containing streptomycin (100 µg/mL, Sigma-Aldrich). Listeria monocytogenes was enumerated on Listeria Agar (Liofilchem, Italy). The use of antibiotics for Salmonella and E. coli O157:H7 permitted the enumeration of the specific strain based on their antibiotic resistance.[8] The incubation was performed at 37 °C for 24 h for E. coli O157:H7 and Salmonella, and at 37 °C for 48 h for L. monocytogenes. The enumeration was referred to the weight of initial fresh product and expressed in log10 CFU/g. The limit of detection (LOD) for the spread plate was 100 CFU/g, respectively. In the case that the results of quantitative microbial analysis were below of LOD, the plating was also done from the first dilution of the sample that was incubated for 24 h at 37 °C providing the enriched sample decreasing the detection limit up to 1 CFU/g.