Indicator organisms are used as a proxy to monitor conditions in a particular environment, ecosystem, area, habitat, or consumer product. Certain bacteria, fungi and helminth eggs are being used for various purposes. Types Indicator bacteria Certain bacteria can be used as indicator organisms in particular situations, such as when present in bodies of water. Indicator bacteria themselves may not be pathogenic but their presence in waste may indicate the presence of other pathogens. Similar to how there are various types of indicator organisms, there are also various types of indicator bacteria. The most common indicators are total coliforms, fecal coliforms, E. coli, and enterococci. The presence of bacteria commonly found in human feces, termed coliform bacteria (e.g. E. coli), in surface water is a common indicator of faecal contamination. The means by which pathogens found in fecal matter can enter recreational bodies of water include, but are not limited to, sewage, septic systems, urban runoff, coastal recreational waste, and livestock waste. For this reason, sanitation programs often test water for the presence of these organisms to ensure that drinking water systems are not contaminated with feces. This testing can be done using several methods which generally involve taking samples of water, or passing large amounts of water through a filter to sample bacteria, then testing to see if bacteria from that water grow on selective media such as MacConkey agar. MacConkey agar will only allow the growth of gram-negative bacteria and the bacteria will grow differently according to how it metabolizes lactose or its lack of ability to metabolize it. Alternatively, the sample can be tested to see if it utilizes various nutrients in ways characteristic of coliform bacteria. Coliform bacteria selected as indicators of faecal contamination must not persist in the environment for long periods of time following efflux from the intestine, and their presence must be closely correlated with contamination by other faecal organisms. Indicator organisms need not be pathogenic. Non-coliform bacteria, such as Streptococcus bovis and certain clostridia may also be used as an index of faecal contamination. The presence of indicator bacteria is measured in a variety of ecosystems and sometimes alongside other measurements. In the Great Lakes, a study was conducted testing for both fecal indicator bacteria (FIB) concentrations and pathogen gene markers. The FIB measured in this study included fecal coliform bacteria, E. coli, and enterococci. FIB were collected via membrane filtration and serial