Escherichia coli O157:H7 is a serotype of the bacterial species Escherichia coli and is one of the Shiga-like toxin–producing types of E. coli. It is a cause of disease, typically foodborne illness, through consumption of contaminated and raw food, including raw milk and undercooked ground beef. Infection with this type of pathogenic bacteria may lead to hemorrhagic diarrhea, and to kidney failure; these have been reported to cause the deaths of children younger than five years of age, of elderly patients, and of patients whose immune systems are otherwise compromised.
An agar plate is a Petri dish that contains a growth medium solidified with agar, used to culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics.
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagnostic methods used as research tools in molecular biology.
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. It represents one aspect of water quality. It is a microbiological analytical procedure which uses samples of water and from these samples determines the concentration of bacteria. It is then possible to draw inferences about the suitability of the water for use from these concentrations. This process is used, for example, to routinely confirm that water is safe for human consumption or that bathing and recreational waters are safe to use.
Proteus vulgaris is a rod-shaped, nitrate-reducing, indole-positive and catalase-positive, hydrogen sulfide-producing, Gram-negative bacterium that inhabits the intestinal tracts of humans and animals. It can be found in soil, water, and fecal matter. It is grouped with the Morganellaceae and is an opportunistic pathogen of humans. It is known to cause wound infections and other species of its genera are known to cause urinary tract infections.
Proteus mirabilis is a Gram-negative, facultatively anaerobic, rod-shaped bacterium. It shows swarming motility and urease activity. P. mirabilis causes 90% of all Proteus infections in humans. It is widely distributed in soil and water. Proteus mirabilis can migrate across the surface of solid media or devices using a type of cooperative group motility called swarming. Proteus mirabilis is most frequently associated with infections of the urinary tract, especially in complicated or catheter-associated urinary tract infections.
Coliform bacteria are defined as either motile or non-motile Gram-negative non-spore forming bacilli that possess β-galactosidase to produce acids and gases under their optimal growth temperature of 35–37 °C. They can be aerobes or facultative aerobes, and are a commonly used indicator of low sanitary quality of foods, milk, and water. Coliforms can be found in the aquatic environment, in soil and on vegetation; they are universally present in large numbers in the feces of warm-blooded animals as they are known to inhabit the gastrointestinal system. While coliform bacteria are not normally the cause of serious illness, they are easy to culture, and their presence is used to infer that other pathogenic organisms of fecal origin may be present in a sample, or that said sample is not safe to consume. Such pathogens include disease-causing bacteria, viruses, or protozoa and many multicellular parasites. Every drinking water source must be tested for the presence of these total coliform bacteria.
Eosin methylene blue is a selective and differential media used for the identification of Gram-negative bacteria, specifically the Enterobacteriaceae. EMB inhibits the growth of most Gram-positive bacteria. EMB is often used to confirm the presence of coliforms in a sample. It contains two dyes, eosin and methylene blue in the ratio of 6:1. EMB is a differential microbiological media, which inhibits the growth of Gram-positive bacteria and differentiates bacteria that ferment lactose from those that do not. Organisms that ferment lactose appear dark/black or green often with "nucleated colonies"—colonies with dark centers. Organisms that do not ferment lactose will appear pink and often mucoid.
A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss Physcomitrella patens. Different types of media are used for growing different types of cells.
Burkholderia cepacia complex (BCC) is a species complex consisting of Burkholderia cepacia and at least 20 different biochemically similar species of Gram-negative bacteria. They are catalase-producing and lactose-nonfermenting. Members of BCC are opportunistic human pathogens that most often cause pneumonia in immunocompromised individuals with underlying lung disease. Patients with sickle-cell haemoglobinopathies are also at risk. The species complex also attacks young onion and tobacco plants, and displays a remarkable ability to digest oil.
Sorbitol-MacConkey agar is a variant of traditional MacConkey agar used in the detection of E. coli O157:H7. Traditionally, MacConkey agar has been used to distinguish those bacteria that ferment lactose from those that do not. This is important because gut bacteria, such as Escherichia coli, can typically ferment lactose, while important gut pathogens, such as Salmonella enterica and most shigellas are unable to ferment lactose. Shigella sonnei can ferment lactose, but only after prolonged incubation, so it is referred to as a late-lactose fermenter.
CLED agar is a valuable non-inhibitory growth medium used in the isolation and differentiation of urinary microbes. It contains cystine and lactose and is electrolyte-deficient; the latter trait prevents the swarming of Proteus species. Cystine promotes the formation of cystine-dependent dwarf colonies. Bromothymol blue is the indicator used in the agar, it changes to yellow in case of acid production during fermentation of lactose or changes to deep blue in case of alkalinization. Lactose-positive bacteria build yellow colonies. Bacteria which decarboxylate L-cystine cause an alkaline reaction and build deep blue colonies.
Xylose Lysine Deoxycholate agar is a selective growth medium used in the isolation of Salmonella and Shigella species from clinical samples and from food. The agar was developed by Welton Taylor in 1965. It has a pH of approximately 7.4, leaving it with a bright pink or red appearance due to the indicator phenol red. Sugar fermentation lowers the pH and the phenol red indicator registers this by changing to yellow. Most gut bacteria, including Salmonella, can ferment the sugar xylose to produce acid; Shigella colonies cannot do this and therefore remain red. After exhausting the xylose supply Salmonella colonies will decarboxylate lysine, increasing the pH once again to alkaline and mimicking the red Shigella colonies. Salmonellae metabolise thiosulfate to produce hydrogen sulfide, which leads to the formation of colonies with black centers and allows them to be differentiated from the similarly coloured Shigella colonies.
Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. It contains a high concentration of salt (NaCl) which is inhibitory to most bacteria - making MSA selective against most Gram-negative and selective for some Gram-positive bacteria that tolerate high salt concentrations. It is also a differential medium for mannitol-fermenting staphylococci, containing the sugar alcohol mannitol and the indicator phenol red, a pH indicator for detecting acid produced by mannitol-fermenting staphylococci. Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce small pink or red colonies with no colour change to the medium. If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow. It is used for the selective isolation of presumptive pathogenic (pp) Staphylococcus species.
De Man–Rogosa–Sharpe agar, often abbreviated to MRS, is a selective culture medium designed to favour the luxuriant growth of Lactobacilli for lab study. Developed in 1960, this medium was named for its inventors, Johannes Cornelis de Man, Morrison Rogosa, and Margaret Elisabeth Sharpe. It contains sodium acetate, which suppresses the growth of many competing bacteria. This medium has a clear brown colour.
Hektoen enteric agar is a selective and differential agar primarily used to recover Salmonella and Shigella from patient specimens. HEA contains indicators of lactose fermentation and hydrogen sulfide production; as well as inhibitors to prevent the growth of Gram-positive bacteria. It is named after the Hektoen Institute in Chicago, where researchers developed the agar.
Endo agar is a microbiological growth medium with a faint pink colour. Originally developed for the isolation of Salmonella typhi, it is now used mostly as a coliform medium. Most gram-negative organisms grow well in this medium, while growth of gram-positive organisms is inhibited. Coliform organisms ferment the lactose in this medium, producing a green metallic sheen, whereas non-lactose-fermenting organisms produce clear, colourless colonies, i.e. Salmonella species.
Thiosulfate–citrate–bile salts–sucrose agar, or TCBS agar, is a type of selective agar culture plate that is used in microbiology laboratories to isolate Vibrio species. TCBS agar is highly selective for the isolation of V. cholerae and V. parahaemolyticus as well as other Vibrio species. Apart from TCBS agar, other rapid testing dipsticks like immunochromatographic dipstick is also used in endemic areas such as Asia, Africa and Latin America. Though, TCBS agar study is required for confirmation. This becomes immensely important in cases of gastroenteritis caused by campylobacter species, whose symptoms mimic that of cholera. Since no yellow bacterial growth is observed in case of campylobacter species on TCBS agar, chances of incorrect diagnosis can be rectified. TCBS agar contains high concentrations of sodium thiosulfate and sodium citrate to inhibit the growth of Enterobacteriaceae. Inhibition of gram-positive bacteria is achieved by the incorporation of ox gall, which is a naturally occurring substance containing a mixture of bile salts and sodium cholate, a pure bile salt. Sodium thiosulfate also serves as a sulfur source and its presence, in combination with ferric citrate, allows for the easy detection of hydrogen sulfide production. Saccharose (sucrose) is included as a fermentable carbohydrate for metabolism by Vibrio species. The alkaline pH of the medium enhances the recovery of V. cholerae and inhibits the growth of others. Thymol blue and bromothymol blue are included as indicators of pH changes.
The NYC medium or GC medium agar is used for isolating Gonococci.
Columbia Nalidixic Acid (CNA) agar is a growth medium used for the isolation and cultivation of bacteria from clinical and non-clinical specimens. CNA agar contains antibiotics that inhibit Gram-negative organisms, aiding in the selective isolation of Gram-positive bacteria. Gram-positive organisms that grow on the media can be differentiated on the basis of hemolysis.
