Colony-forming particles

Tab. 5.1 Certified number concentration of colony forming particles of Enterococcus faecium (WR63) in CRM 506 from artificially contaminated milk powder (Mooijman et al. 1999)...

There are three common ways of assessing, the particulate content of air. One measures dust mass expressed as mg/m3. Another counts particles expressed as number/m3. A third measures bacterial colony-forming particles (BCFP) expressed also as number/m3. 

Fig. 2.7. Selectivity and recovery of microbiological methods. The more selective a method (in particular the culture medium composition), the less competitive microflora will grow but also injured bacteria will form no colonies or only tiny ones (cfp colony-forming particles). Microbiological skill will be based on the ability to select a method with the smallest interferences, the highest recovery for a given type of sample [4].

In this section the terms accuracy, systematic error and precision are defined as proposed by Havelaar et al. [4], These concepts are derived from quantitative analytical chemistry but can just as well be used in quantitative microbiology. According to ISO/DIS 6107-8 [33], accuracy is defined as the degree of similarity between the measurement and the true value of the measured quantity. In a microbiological context the true value is the number of colony-forming particles in the sample. The accuracy is related to the overall error of measurement, that is the difference between the measurement and the true value of the measured quantity. The overall error can be divided into three different components ... 

P.H. in t Veld, N.G.W.M van Strijp-Lockefeer, J.A. van Dommelen, M.E. de Winter, A.H. Havelaar and E.A. Maier, The certification of the number concentration of colony forming particles of Bacillus cereus in artificially contaminated milk powder CRM 528. Report EUR 16272 EN, European Commission, Luxembourg (1995). 

No major decrease in cfp per capsule could be noticed at -20 °C over 200 weeks. Y axis mean number of colony-forming particles of Salmonella typhimurium in one capsule (Ns,cfp). X axis weeks of storage at -20 °C. 

The variation in the number content of colony-forming particles between samples in one reconstituted capsule (Tj) and between samples of different capsules of one batch (T2) were tested separately. Although the T,-value exceeded the critical values twice, the batch was still considered as being of good quality because the deviations of the critical value were small and considered to be of random nature. An additional homogeneity verification was performed using two alternative methods as described in the certification report [38]. 

For the certification of the Salmonella reference material, two different procedures were used. The first procedure determined the number of colony forming particles in one capsule whereas the second procedure determined the presence or absence of Salmonella in one capsule. Both procedures were carried out according to a detailed protocol and Standard Operating Procedures described elsewhere [37]. 

The units are given in number of colony forming particles per ml reconstituted milk... 

Number of colony forming particles of Enterococcus faecium in artificially contaminated... 

After homogenisation for 24 h, both CRM solutions were examined for bacterial contamination. For both CRMs a value far below 100 CFP mL (Colony Forming Particles per mL) was found, which generally is considered to be adequate. 

The determination of MIC of antibiotics was performed by microtiter method. Antimicrobial agents were diluted by serial dilutions MPB in flat-bottomed plates, they were also added to the culture of Staphylococcus aureus, and were incubated for 24 hr at 34°C. The control was culture Staphylococcus aureus without antimicrobial agents. After that mixture sowed on solid nutrient medium Mueller-Hinton agar for calculation of amount of colony forming particles and MIC definitions. The MIC was considered to be the lowest concentration, which retards the growth of Staphylococcus aureus during the incubation period. 

Staphylococcus aureus without antimicrobial agents. After that mixture sowed on solid nutrient medium Mueller-Hinton agar for calculation of amount of colony forming particles and MIC definitions. MIC was considered to be the lowest concentration, which retards the growth of Staphylococcus aureus during the incubation period. 

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