The indicator bacteria is the type of bacteria used to detect and estimate the level of water faecal contamination. They are not harmful to human health but are used to indicate a health risk.
Every gram of human feces contains about ~ 100 billion ( 1 ÃÆ' - 10 11 ) bacteria. These bacteria may include pathogenic bacterial species, such as Salmonella or Campylobacter, associated with gastroenteritis. In addition, feces can contain pathogenic viruses, protozoa, and parasites. Feces can enter the environment from various sources including wastewater treatment plants, cattle or poultry manure, sanitary landfills, septic systems, sewage sludges, pets and wildlife. If enough quantities are digested, fecal pathogens can cause disease. The variation and frequency of low pathogen concentrations in the environment waters make them difficult to test individually. Therefore, the public body uses the presence of other fecal bacteria more and more easily detected as an indicator of fecal contamination.
Video Indicator bacteria
Criteria for the indicator organism
The US Environmental Protection Agency (EPA) lists the following criteria for organisms being the ideal indicator of fecal contamination:
- Organisms must be present whenever enteric pathogens are present
- Organisms should be useful for all types of water
- The organism must have a longer life-time than the hardest enteric pathogens
- Organisms should not grow in water
- This organism must be found in the intestines of warm-blooded animals.
None of the types of indicator organisms currently used fit all these criteria perfectly, however, when costs are considered, the use of indicators becomes necessary.
Maps Indicator bacteria
Type of indicator organism
Commonly used indicator bacteria include total coliform, or a subset of this group, coliform fecal, which is found in warm intestinal tracts of warm-blooded animals. Total coliform was used as a fecal indicator by public institutions in the US in the early 1920s. These organisms can be identified based on the fact that they all metabolize lactose sugar, generating acids and gases as byproducts. Coliform fecal is more useful as an indicator in recreational waters than total coliforms that include species naturally found in plants and soils; However, there are even some species of fecal coliform that have no fecal origin, such as Klebsiella pneumoniae . Perhaps the biggest drawback to using coliform as an indicator is that they can grow in water under certain conditions.
Escherichia coli ( E. coli ) and enterococci are also used as indicators.
The current detection method
Filtration and membrane culture on selective media
Indicator bacteria can be cultured on specially formulated media to enable the growth of flower species and inhibit the growth of other organisms. Typically, environmental water samples are filtered through a membrane with a small pore size and then the membrane is placed on a selective order. It is often necessary to vary the volume of filtered water samples to prevent too little or too many colonies from forming on a plate. Bacterial colonies can be calculated after 24 to 48 hours depending on the type of bacteria. Counts are reported as colony-forming units per 100 mL (cfu/100 mL).
Quick detection using chromogenic substance
One technique for detecting indicator organisms is the use of chromogenic compounds, which are added to conventional or newly created media which are used to isolate the indicator bacteria. These chromogenic compounds are modified to change color or fluorescence by the addition of specific bacterial enzymes or metabolites. This allows for easy detection and avoids the need for pure culture isolation and confirmation tests.
Application of antibody
Immunological methods using monoclonal antibodies can be used to detect indicator bacteria in water samples. Preactivation in select media should be preliminary detection to avoid detection of dead cells. ELISA antibody technology has been developed to allow for detection that is easy to read by the naked eye for rapid identification of coliform microcolonials. Use of other antibodies in detection using magnetic beads coated with antibodies for the concentration and separation of oocysts and cysts as described below for immunomagnetic separationz (IMS) methods.
IMS/culture and other fast culture-based methods
The immunomagnetic separation involves biotinylated purified antigens and is bound to paramagnetic particles streptoavidin-coated. The raw samples are mixed with beads, then special magnets are used to hold the target organism against the vial wall and the unbound material is poured. This method can be used to restore certain indicator bacteria.
Gene sequence based method
Methods based on the sequence of genes depend on the exclusive gene sequence recognition specific to a particular strain of the organism. Polymerase chain reaction (PCR) and in situ hybridized fluorescence (FISH) are the sequence-based methods currently used to detect certain bacterial indicator strains.
Water quality standards for bacteria
Drinking water standards
The World Health Organization's Guidelines for Drinking Water Quality states that as an indicator organ Escherichia coli provides conclusive evidence of recent faecal pollution and should not be present in water intended for human consumption. In the US, the EPA Total Coliform Rule states that the water system does not comply if more than 5 percent of its monthly water samples contain coliform.
Recreation standard
Initial studies have shown that individuals who swim in waters with mean geometric coliforms mean above 2300/100 mL for three days have higher rates of illness. In the 1960s, these numbers were converted into fecal coliform concentrations with the assumption that 18 percent of the total coliform is feces. Consequently, the US National Technical Advisory Committee recommended the following standard for recreational water in 1968: 10 percent of the total sample during the 30-day period should not exceed 400 fecal coliforms/100 mL or 200/100 mL log averages (based on a minimum of 5 samples taken no more than 30 day period).
Despite criticism, the EPA recommended this criterion again in 1976, however, it began a number of studies in the 1970s and 1980s to address the weaknesses of previous studies. In 1986, the EPA revised its recommendation of bakerologically ambient water quality criteria to include E. coli and enterococci.
The Canadian National Agri-Environmental Standards Approach The initiative to characterize the risks associated with bacterial water quality pollution at farm sites is to compare these sites with people on reference sites away from human or livestock sources. This approach generally results in lower levels if E. coli is used as a standard or "benchmark" based on studies indicating pathogens detected in 80% of water samples with less than 100 cfu E. coli per 100 mL.
Risk assessment for pathogen exposure in recreational waters
Most cases of bacterial gastroenteritis are caused by enteric feeding microorganisms, such as Salmonella and Campylobacter ; however, it is also important to understand the risks of exposure to pathogens through recreational waters. This is especially true in watersheds where human or animal waste is discharged into rivers and down streams used for swimming or other recreational activities. Other important pathogens other than bacteria include viruses such as rotavirus, hepatitis A and hepatitis E and protozoa such as giardia, cryptosporidium and Naegleria fowleri. Due to difficulties associated with monitoring of pathogens in the environment, risk assessment often depends on the use of indicator bacteria.
Epidemiological studies
In the 1950s, a series of epidemiological studies were conducted in the US to determine the relationship between the water quality of the natural waters and the health of the bath. The results show that swimmers are more likely to have gastrointestinal symptoms, eye infections, skin complaints, ears, nose, and throat and respiratory infections than non-swimmers and in some cases higher levels of coliform are correlated with higher incidences of gastrointestinal disease, the sample size in this study is small. Since then, research has been done to confirm the causative relationship between swimming and certain health outcomes. A review of 22 studies in 1998 confirmed that the health risks to swimmers increased as the number of indicator bacteria increased in recreational waters and that E. coli and enterococci concentrations correlated best with the health outcomes among all the indicators studied. The relative risk (RR) disease for swimmers in contaminated freshwater versus swimmers in polluted water is between 1-2 for most of the reviewed data sets. The same study concluded that bacterial indicators were not correlated with viral concentrations.
Pathogen fate and transport
The survival of pathogens in waste, soil, or water materials, depends on many environmental factors including temperature, pH, organic matter content, moisture, exposure to light, and the presence of other organisms. Stool materials can be directly stored, washed into water by ground runoff, transported by soil, or discharged into surface water through drains, pipes, or drainage tiles. The risk of exposure to humans requires: (1) pathogens to survive and present; (2) pathogens to be recreated on the surface of water; and (3) individuals to come into contact with water for sufficient time, or digest sufficient water volume to receive the dose of infection. The mortality rate of bacteria in the environment is often exponential, therefore, the direct deposition of the faeces into the water generally contributes to a higher pathogenic concentration than the material that must be transported by land or through the subsurface.
Human exposure
In general, children, the elderly, and individuals with the immune system require lower doses of pathogenic organisms to contract infections. Currently there are very few studies that are able to measure the amount of time people might spend in recreational waters and how much water they might consume. In general, children swim more often, stay in the water longer, drown their heads more often, and swallow more water. This makes people more afraid of the water at sea because more bacteria will grow around them.
Quantitative microbiological risk assessment
Quantitative microbiological risk assessment (QMRAs) combines the concentration of pathogens in water with dose-response relationships and data that reflects potential exposure to estimate the risk of infection.
Data on water exposure are generally collected using questionnaires, but can also be determined from the actual measurements of water being digested, or estimated from previously published data. Respondents were asked to report frequency and time and location of exposure, detailed information on the amount of water swallowed and head immersion, and basic demographic characteristics such as age, sex, socioeconomic status and family composition. Once enough data is collected and determined to represent the general population, they usually match the distribution, and the distribution parameters are then used in the risk assessment equation. Monitoring data showing pathogens, direct measurements of pathogen concentrations, or estimates obtaining pathogen concentrations from bacterial indicator concentrations, also correspond to distribution. The dose is calculated by multiplying the concentration of pathogens per volume by volume. Dose-response can also be in accordance with the distribution.
Risk management and policy implications
The more assumptions made, the more uncertain the risk estimate associated with pathogens. However, even with great uncertainty, QMRA is a good way to compare various risk scenarios. In a study comparing health risk estimates from exposure to recreational waters affected by human and non-human sources from faecal pollution, QMRA ruled that the risk of gastrointestinal disease from exposure to livestock-affected water was similar to that affected by human waste, and this higher than the water exposed to stool horns, chickens, or pigs. Such studies can be useful for risk managers to determine how best to focus their limited resources, however, risk managers must be aware of the limitations of data used in these calculations. For example, this study used data describing the concentration of Salmonella in chicken droppings published in 1969. Methods for measuring bacteria, changes in animal housing and sanitation practices, and many other factors that may have altered the prevalence of < i>> Salmonella since then. Also, such an approach often ignores the complex fate and transport processes that determine the concentration of bacteria from source to point of exposure.
Overcoming the water quality of bacteria
In the US, each country is allowed to develop their own water quality standards based on the EPA recommendation under the Clean Water Act of 1977. Once water quality standards are approved, countries are tasked with monitoring their surface waters to determine where the disturbance occurs, and water boundaries. a plan called Total Maximum Daily Loads (TMDLs) was developed to direct efforts to improve water quality including changes to bacterial loading permitted by point sources and recommendations for practice changes that reduce nonpoint-source contributions to bacterial loads. Also, many states have coastal monitoring programs to warn swimmers when high-level bacteria indicators are detected.
References
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