Colony counting/enumeration

IDF (1991). Enumeration of microorganisms colony count technique at 30 °C, Standard lOOB. 

Work Item D enumeration of Clostridium perfringens - colony count technique. 

Work Item F general guidance for enumeration of Bacillus cereus - colony count technique at 30°C. 

Savings in time and materials can be made by removing the need for the dilution series in the standard plate colony count. Various methods based on the Thompson plate loop method have been described. In the technique, two loops that retain 0.01 and 0.001 ml are dipped into the sample. A Petri dish is positioned under each loop and the loops are flushed with diluent, agar is then added, and the contents of the Petri dish are mixed. These machines can plate 10 and 10 dilutions from 300 samples per hour. The technique is suitable for enumerating bacteria in the range 3000-300 000 ml Manufacturers of one commercially available automated plate loop machine (PetriFoss) claim that the relationship with the reference method has a correlation coefficient of 0.99. 

Table 1 Examples of some conventional colony count methods that may be used to enumerate microorganisms from a variety of samples...

International Standard, ISO 6888 (1983). Microbiology—General guidance for enumeration of Staphylococcus aureus—Colony count technique. International Organization for Standardization, Geneva, Switzerland. 

Most pulmonary tumor colonies in mice are in the pleura. Therefore, pigmented colonies (such as melanomas) can be counted without lung dissection. However, it may be more facile, especially when there are extensive pulmonary metastases, to dissect the lungs into the individual four or five lobes which are then enumerated individually using a dissecting microscope. 

From the English Channel, 84 samples were counted. Most of the samples were preserved and colonies of Phaeocystis were enumerated in the total sample volume collected (100-250 ml). The samples were settled for minimum 24 h, then gently concentrated by removing surface water with a plastic syringes (ca. 10 mm diameter), passed through a 5 pm nylon mesh. All volume of concentrated subsamples (5-10 ml) was observed in 1 ml-Naumann counting chamber (Naumann 1922). 

Colonies When a viable cell is deposited on the surface of a solidified agar medium, it reproduces and forms a cluster (or colony) of cells, which are counted for enumeration. However, these colonies may also initially arise from pairs, chains, or clumps of cells depending on the morphology of the microorganism. In these cases, the population should be recorded as Solony-forming units per mL (CFU/mL) rather than cells per mL. 

---