Colony count determination

If the colony count determined lies above 100, the figures are rounded down... 

After the experiments, 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 in an eppendorf tube. 50 pi of sample was 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 show no viable bacterial and fungal colonies were present in the interior parts of the Prototype Unit. Viable colonies are found on the external surface of the unit. This suggests that air passing through the Prototype Unit was sterilized by the action of the formulated catalyst. 

Colony forming ability of the fetal liver cells was determined in the medium comprised 1.3% methylcellulose, 4.0 mM glutamine, 10 U/ml penicillin/-streptomycin, 100 U/ml GM-CSF, 100 U/ml IL-3, 50 ng/ml stem cell factor and 10 U/ml erythropoietin in IMDM. An aliquot of 10 cells was transferred to a 35 mm sterile plastic Petri dish and incubated at 37 C in a fully humidified atmosphere of 5% CO2 in air. The final colony count was performed on day 14 of culture, the colony types being defined by general morphological criteria. 

The 35 mm dish assay detects compounds that are cytotoxic to or alter proliferation of the multipotent stem cells, but the main limitation of the 35 mm dish CFU assay is the need to microscopically identify and count the colonies to determine the compound concentration that decreased the number of colonies by 50% (IC50) or 90% (IC90). The European Community for Validation of Alternative Methods (ECVAM) supported the recommendation of using the mouse and human CFU-GM IC90 with... 

Fig. 7. IC50 vs. LC50 values for HeLa cells treated with a series of platinum complexes. LC50 was determined by a colony-counting assay. /C50 was the platinum concentration at which EGFP expression was reduced to 50% of control.

Use the dilution factors and colony counts to determine the total number of viable cells (Trp+ plus Trp-) present per milliliter of undiluted culture in tubes 1 and 2. Assuming that all of the Trp+ cells are transformants and assuming that the total number of viable cells in tubes 2 through 6 is the same, calculate the efficiency of transformation in tubes 2 to 6. Interpret all your results in terms of the contents of each tube and your knowledge of the process of transformation. Which tubes served as controls for the experiment Explain. 

As one example the case of a bacterial mutagenicity test may be cited, where hundreds of petri dishes with the bacterial colonies grown as a result of the test, and which may be considered to constitute the test system as well as the primary data. After the end of the incubation period these petri dishes cannot be stored for too long a time, since either the bacteria (and any contaminant germs) will continue to grow, or the layer of agar growth medium will dry out, and both of these events will render the plates useless for further evaluation after some time. The petri dishes will therefore have to be discarded shortly after the end of the experiment. The actual raw data of the study to be archived are, however, the bacterial colony counts, whether they have been manually determined or automatically recorded. Thus, if it can be ascertained... 

These bacteria were cultivated in each product for 24 h at 37 °C and each cultured broth sample was serially diluted into the corresponding aseptic products. The total colony count was determined with Plate Count Agar (MERCK). Bioluminescent Assay... 

The coefficient of determination is = 84.6% between X2 and Xi and the value = 71.63, P < 0.0001. A plot of the logio colony counts, X2, vs. media concentration, X3, is presented in Figure 6.1. Plainly, the two variables are collinear the greater the media concentration, the greater the logio colony counts. 

Example 10.1 A researcher was interested in determining the logio microbial cotmts obtained from a contaminated 2.3 cm coupon at different temperatures and media concentrations. The researcher thought that temperature variation from 20°C to 45°C and media concentration would affect the microbial colony counts. 

The following morning, count colonies and determine the mean ( standard deviation) colony-forming unit (CFU) titers for the two GAS strains. Typical titers are 2 X 10 CPUs per mL. 

In order to determine the colony count, 1 ml of water in each case is pipetted into a sterile Petri culture dish and mixed with sterile nutrient gelatine or sterile nutrient agar. Nutrient gelatine is liquefied in a water bath at 33 °C and cooled to about 30 C before pouring into the culture dish. Nutrient agar is liquefied in boiling water and cooled to 6 2 C... 

The membrane filter process and the dip slide process are unofficial methods of determining the colony count. 

The ability of biocide-treated biofilms to utilise nutritional substrates can be determined by a direct viable count (DVC), which is measured by the effect of nalidixic acid (Lisle et al., 1999). A further method described by Holtmann and Sell (2001) for indirectly measuring the metabolic activity of biocide-treated bacteria is the determination of redox potential in the biofilm with microelectrodes. It can be shown that the increase of redox potential is correlated with a reduction in the colony count and the dehydrogenase activity. Microelectrodes are proposed as a way of monitoring the success of biocide treatments. 

Kwon-Chung, K. J. Tewari, R. P. Determination of viability of Histoplasma capsulatum yeast cells grown in vitro comparison between dye and colony count methods. J. Med. Vet. Mycol. 1987, 25, 107-114. 

In a parallel test with water instead of disinfectant the colony forming units (cfu) of surviving bacteria are determined and the reduction in viable counts is calculated. 

Duplicate counts are made using serial dilutions up to 10-6 and drop plates. Solutions are then spotted onto blood agar plates and incubated at 37 °C for 18 hours after which the number of colony forming units is determined. To pass the BA Challenge Test there must be no growth from the aliquots taken at 15 minutes or more from the 1 400 and 1 1600 dilutions. 

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