Identification of organisms

摘要

1. Although often referred to as non-selective media, all media used for HPC determinations, along with respective time and temperature conditions, are "selective" for those bacteria that can grow under those specific conditions. 2. There is no single medium or method that will recover or enumerate all bacteria in the water being analyzed. 3. Many heterotrophic bacteria that are present in water are not culturable at present. 4. The choice of culture medium, temperature, and incubation time are important with regard to HPC results from a given water sample. (1) Both high-nutrient and low-nutrient media are used for HPC determinations. (2) High-nutrient media are better for enumeration of bacteria from animals and humans. (3) Low-nutrient media are better for enumeration of water-based bacteria, including drinking water. The most commonly employed heterotrophic medium is R2A. It was designed specifically as a low-nutrient, low-ionic strength formulation to isolate bacteria that have a water-based, rather than mammalian lifestyle.