-
This medium is used for the cultivation and enumeration of Lactobacillus spp. MRS agar is based on the formulation by de Man, Rogosa and Sharpe. The peptone, yeast extract and beef extract provides the reuired carbon, nitrogen and vitamin source. Glucose is a fermentable carbohydrate. The magnesium sulphate and manganese sulphate act as growth stimulants. Potassium phosphate is a buffering agent. Selectivity of the medium is achieved through the use of ammonium citrate and sodium acetate, inhibiting microorganisms such as streptococci and moulds. The addition of the surfactant Tween 80 is required to facilitate the uptake of nutrients from Lactobacillus spp. -
This is a selective medium for the isolation of Salmonella spp. and Shigella spp. from clinical specimens and environmental samples. This formulation was developed by Hynes through a modification of Leifson’s DCA medium. The peptone provides the required carbon, nitrogen and vitamins. Lactose is a fermentable carbohydrate and neutral red is a pH indicator. Sodium thiosulphate and ferric citrate are used to detect hydrogen sulphide production indicated by the black centred colonies of hydrogen sulphite positive organisms. Sodium deoxycholate and sodium citrate inhibit most Gram-positive organisms.
-
A selective medium for the isolation and detection of dermatophytic fungi originally developed by Taplin et al. Dermatophytes appear as fluffy colonies with reddening of the medium while other fungi cause the medium to become yellow due to acid production. Yeasts will also grow on this medium but are readily distinguished by their distinct white/creamy colonies and distinctive smell. Soy peptone provides the required carbon, nitrogen and vitamins. Glucose is a fermentable carbohydrate. The inclusion of phenol red assists in the differentiation between saprophytic and environmental fungi. Although the low pH (pH 5.5) of the medium inhibits most bacteria chloramphenicol and cycloheximide are often added to further reduce the risk when processing material that may be more heavily contaminated. NB: Prolonged incubation should be avoided as this may cause fungi other than dermatophytes to turn the medium red. Related Supplements : LS0050 Chloramphenicol Selective Supplement
-
Dichloran Rose Bengal Chloramphenicol (DRBC) agar is based on the formulation described by King et al. and is used for the selective isolation and enumeration of yeasts and moulds from food samples. The peptone provides the required carbon, nitrogen and vitamins. Glucose is a fermentable carbohydrate. Potassium di-hydrogen phosphate is a buffering agent and magnesium sulfate is a source of divalent ions and sulfate. In order to curtail the size of the colony diameters of spreading fungi, the antifungal agent dichloran is added to the base and the pH is reduced to 5.6. Rose Bengal suppresses growth of bacteria and restricts the size and height of colonies of more rapidly growing molds. The inclusion of chloramphenicol ensures the suppression of bacteria present in environmental and food samples. Rose Bengal is absorbed by yeast and mold colonies and this further aids in their enumeration. Occasionally reduced recovery of yeasts may be encountered due to the increased activity of Rose Bengal at pH 5.6.
-
DNase agar is used primarily in clinical laboratories to differentiate pathogenic Staphylococcus aureus from other staphylococci based on deoxyribonuclease (DNase) activity. The tryptone provides the required carbon, nitrogen and vitamins. Sodium chloride maintains the osmotic balance. The addition of DNA to the base medium provides a simple method to check for DNase activity. Following incubation of the inoculated medium, the surface of the medium is flooded with a small quantity of 1M hydrochloric acid to precipitate the DNA. This results in the medium turning opaque. Organisms that can produce sufficient quantity of a DNase enzyme will hydrolyse the DNA resulting in a clear area around the colonies. Whereas DNase negative organisms will not produce clearing. NB: As with most tests of this type a positive result should not be taken in isolation and other appropriate tests, e.g. coagulase test, latex agglutination etc., should be carried out.
-
DNase agar is used primarily in clinical laboratories to differentiate pathogenic Staphylococcus aureus from other staphylococci based on deoxyribonuclease (DNase) activity. The tryptone provides the required carbon, nitrogen and vitamins. Sodium chloride maintains the osmotic balance. The addition of DNA to the base medium provides a simple method to check for DNase activity. The methyl green fades into a colourless compound if the DNA in the medium is depolymerised. Organisms that can produce sufficient quantity of a DNase enzyme will hydrolyse the DNA resulting in a clear area around the colonies. Whereas DNase negative organisms will not produce clearing. NB: As with most tests of this type a positive result should not be taken in isolation and other appropriate tests, e.g. coagulase test, latex agglutination etc., should be carried out.
-
Edwardsiella ictaluri medium is a selective medium for the isolation of Edwardsiella spp. based on the formulation by Shotts et al. (1) Edwardsiella spp. may be differentiated from other microorganisms on this medium due to its colony morphology. The peptones provide the required carbon, nitrogen and vitamins. Sodium chloride maintains the osmotic balance. Colistin and bile salts are selective agents to inhibit most Gram-negative and Gram- positive organisms. Mannitol is a fermentable carbohydrate and bromthymol blue is a pH indicator. Phenylalanine and ferric citrate are used to detect phenylalanine deaminase activity in Proteus spp. Agar is a solidifying agent. Shotts et al. (1) noted Proteus spp. swarming can overgrow on a mixed cultured sample. Therefore, a selective supplement (LS0021) may be added to the medium to restrict Proteus spp. swarming
-
E.E. Broth is recommended as an enrichment medium when examining food and feedstuffs for Enterobacteriaceae. It is a modification of Brilliant Green Bile Broth, with an improved buffering capacity to encourage early growth and prevent autosterilization. E.E. Broth uses glucose instead of lactose to make the medium a test for all enterobacteria including non-lactose fermenting organisms. This formulation complies with the Harmonized USP/EP/JP. Nitrogen is supplied by the gelatin peptone whilst glucose serves as the fermentable carbohydrate source. Oxbile and brilliant green are the selective agents helping to suppress Gram-positive non- target organisms. Auto sterilisation is prevented through the buffer system composed of potassium dihydrogen phosphate and disodium hydrogen phosphate.
