Six-plate test

Apart from detection, some microbial inhibitor tests including the three-plate and the six-plate tests are further suitable for tentative confirmation of... 

In the six-plate test, the sample is brought in a punch hole or a paper disc on each of the six test plates that have been inoculated with Bacillus cereus. Bacillus subtilis (pH 6), Bacillus subtilis (pH 8), Sarcina lutea, Escherichia coli, and Bacillus stearothermophilus, respectively (33). Once the samples have been introduced, the plates are incubated for the required time at the required temperature. If, on one of the plates, a zone of inhibition of 1.0 mm is observed around the disks or holes, the result of the test is considered positive, provided that interferences have been excluded. 

Samples for cell viability tests were taken three times during the different batch and fed-batch fermentations. A sample of 1 mL was diluted 104-105 times and 0.1 mL of diluted sample was applied to an agar plate. Five to six plates were prepared for every sample, and the plates were incubated for 24 h at 30°C. The total cell concentration in the reactor sample was determined with microscopy using a Biirker counting chamber. The viability, expressed as the fraction of cells able to form colonies, was calculated by dividing the concentration of colony-forming cells by the total cell concentration. 

Westinghouse Electric Corp. initiated a program to develop air-cooled PAFC stacks, containing cooling plates at six-ceU intervals. Full size 100-kW stacks (468 cells, 0.12-m electrode area) were built, and a module containing four of these stacks was tested. An air-cooled stack operated at 0.480 MPa yielded a cell voltage of 0.7 V at 267 m A /cm (187 mW/cm ). Demonstration of this technology is plarmed for a site in Norway. 

Tissue Culture Assay. Kogure et al. (48) report a novel tissue culture assay for detecting several types of sodium channel blockers. The mouse neuroblastoma cell line ATCC CCL 131 is grown in RPMI 1640 supplemented with 13.5% fetal bovine serum and 100 pg/ml gentamycin, in an atmosphere of 5% C0 95% air at 37 C. Ninety-six well plates are seeded with 1 x 10 cells in 200 pi of medium containing 1 mM ouabain and 0.075 mM veratridine. Veratridine and ouabain cause neuroblastoma cells to round-up and die. In the presence of sodium channel blockers (e.g., TTXs or STXs), the lethal action of veratridine is obviated and cells retain normal morphology and viability. An important feature of this assay is that a positive test for sodium channel blockers results in normal cell viability. Since bacterial extracts can contain cytotoxic components, this assay offers an advantage over tests that use cell death as an endpoint. The minimum detectable level of TTX is approximately 3 nM, or approximately 1/1000 mouse unit. 

After the six-month field test, the Prototype Unit was disassembled and the component parts were individually swabbed with sterilized cotton wools (4 cm2). Each samples were stored in 1 ml sterilized distilled water and 50 pi of samples were transferred to TSA and MEA plates. The TSA plates were incubated at 37 °C for 24 h and bacterial colonies were counted. The number of fungal colonies was determined from the MEA plates after incubating at 30 °C for 5 days. The results of the test are shown in Table 12.9-7. The results show that bacteria and fungi thrived near the air intake where they deposited on the grills, panel and around the intake slots. However once the microorganisms are drawn through the catalyst-coated desiccant wheel, the number of viable... 

Various incubation systems have also been tested using human liver shces, these inclnde the 24-well plates with magnetic stirrers [38,66,69], the six-well plates in a shaker [52] and the DOC roller system [70,71], but no direct comparison has been made as yet. Human hver slices can be cultured for 72 h in DOC and maintain their ability to respond to specific inducers of cytochrome P450 such asmethylclofenapate and Aroclor 1254 [71]. 

---