|Published (Last):||25 June 2010|
|PDF File Size:||2.6 Mb|
|ePub File Size:||12.6 Mb|
|Price:||Free* [*Free Regsitration Required]|
The remaining 10 ml is then diluted again and the process repeated. Analysis is usually performed using culture, biochemical and sometimes optical methods.
Bacteriological water analysis – Wikipedia
The plate count method relies on bacteria growing a colony on a nutrient medium so that the colony becomes visible to the naked eye and the number of colonies on a plate can be counted. Non-lactose-fermenting organisms produce clear, colourless colonies against the faint pink background of the medium. Judgements as to suitability of water for use are based on very extensive precedents and relate to the probability bacteriological analysis of drinking water pdf download any sample population of bacteria being able to be infective at a reasonable statistical level of confidence.
At the end of 5 dilutions this produces 50 tubes covering the dilution range of 1: To be effective, the dilution of the original sample must be arranged so that on average between 30 and colonies of the target bacterium are grown. The tubes are then incubated bacteriological analysis of drinking water pdf download a pre-set temperature for a specified time and at the end of the process the number of tubes with growth in is counted for each dilution.
This method can be enhanced by using drinkinb medium which changes colour when acid forming species are present and by including a bacteriological analysis of drinking water pdf download inverted tube called a Durham tube in each sample tube. It contains bile salts to inhibit most Gram-positive bacteriacrystal violet dye which also inhibits certain Gram-positive bacterianeutral red dye which stains microbes fermenting lactoselactose and peptone.
When indicator organisms levels exceed pre-set triggers, specific analysis for pathogens may then be undertaken and these can be quickly detected where suspected using specific culture methods or molecular biology. In tropical areas analysis of Vibrio cholerae is also routinely undertaken. A media that contains bile salts which promotes the growth of gram negative and has inhibitory characteristic to gram positive although not complete inhibitory.
Colonies that develop in the body of the medium can be counted by eye after incubation. It represents one aspect of water quality.
When the analysis is bacteriological analysis of drinking water pdf download for bacterial species that grow poorly in air, the initial analysis is done by mixing serial dilutions of the sample in liquid nutrient agar which is then poured into bottles which are then sealed and laid on their sides to produce a sloping agar surface.
Bacteriological water analysis
The amount of light produced is directly proportional to the amount of biological energy present bacteriological analysis of drinking water pdf download the sample. Because the analysis is always based on a very small sample taken from a very large volume of water, all methods rely on statistical principles.
When samples show elevated levels of indicator bacteria, further analysis is often undertaken to look for specific pathogenic bacteria. An ATP test is the process of rapidly measuring active microorganisms in water through detection adenosine triphosphate ATP. At the end of the incubation bacteriological analysis of drinking water pdf download the colonies are counted by eye, a procedure that bacteriological analysis of drinking water pdf download a few moments and does not require a microscope as the colonies are typically a few millimetres across.
The production of gas at 37 degrees Celsius is a strong indication of the presence of Escherichia coli. It is then possible to draw inferences about the suitability of the water for use from these concentrations.
Indicator organisms are bacteria such as non-specific coliformsEscherichia coli and Pseudomonas aeruginosa that are very commonly found in the human or animal gut and which, if detected, may suggest the presence of sewage. Most modern laboratories use a refinement of total plate count in which serial dilutions of the sample are vacuum filtered through purpose made membrane filters and these filters are themselves laid on nutrient medium within sealed plates.
It is therefore reasonable to surmise that if indicator organism levels are low, then pathogen levels will be very much lower or absent. Whilst very stringent levels apply to drinking watermore relaxed levels apply to marine bathing waters, where much lower volumes of water are expected to be ingested by users.
Retrieved June 17, The Bacteriological analysis of drinking water pdf download inverted tube catches any gas produced. Aquatic ecology Water Microbiology techniques Water quality indicators. Typical media include plate count agar for a general count or Downloa agar to count Gram-negative bacteria such as E. It is a microbiological analytical procedure which uses samples of water and from these samples qater the concentration of bacteria. To ensure that an appropriate number of colonies will be generated several dilutions are normally cultured.
Calculation of this is a multiple of the counted number of colonies multiplied by the dilution used.
FDA Internet Site Error
Views Read Edit View history. The most reliable methods are direct plate count method and membrane filtration method. Species commonly investigated in the temperate zone include Salmonella typhi and Salmonella Typhimurium.
Some recent methods include a fluorescent agent so that counting of the colonies can be automated. These media contain lactose which is usually fermented by lactose fermenting bacteria producing bacteriological analysis of drinking water pdf download that can be identified and characterised.
One of the oldest methods is called the bacteriological analysis of drinking water pdf download tube method. Bacteriological water analysis is a method of analysing water to estimate the numbers of bacteria present and, if needed, to find out what sort of bacteria they are. MacConkey agar is culture medium designed to grow Fo bacteria and stain them for lactose fermentation. These include rosolic acid to inhibit bacterial growth in general, except for faecal coliforms, bile salts inhibit non-enteric bacteria and aniline blue indicates the ability of faecal coliforms to ferment lactose to acid that causes a pH change in the medium.
Depending on the likely anlaysis of contamination investigation may also extend to organisms such as Cryptosporidium spp.