Most organisms grow best at or near room and body temperature. These are mesophiles. The nature of a solution based on its acidity or alkalinity is described as pH. The pH scale ranges from 0, strongly acidic, to 14, strongly basic. Neutral solutions are pH 7, the pH of pure water. Most bacteria require near neutral conditions for optimal growth with minimums and maximums between 4 and 9.
Many organisms change the pH of their substrate by producing by-products during growth.
They can change conditions such that the environment can no longer support their growth. Yeasts and molds are more tolerant of lower pH than the bacteria and may outgrow them under those conditions. Many treatments such as hydrogen peroxide and chlorine can kill or injure microbes. Under certain conditions those given a sublethal treatment are injured, but can recover. Growth Characteristic growth patterns can be illustrated on a graph.