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Bacillus cereus agar (PEMBA) is used for the selective isolation and enumeration of Bacillus cereus in food samples. It is said to be particularly suitable for the detection of small numbers of Bacillus cereus particularly in the presence of other contaminating organisms. Bacillus cereus agar (PEMBA) is based on the formulation developed by Holbrook and Anderson. The peptone provides the required carbon, nitrogen and vitamins. Mannitol is a fermentable carbohydrate. Bromothymol blue is a pH indicator used to detect mannitol fermentation. Sodium chloride maintains the osmotic balance. Magnesium sulphate provides divalent cations and sulphate. Di-sodium hydrogen phosphate and potassium dihydrogen phosphate are buffering agents. Egg yolk emulsion (BM0140) must be added to this media to assess lecithinase production. Sodium pyruvate is present to improve egg yolk precipitation and enhance B. cereus sporulation. The medium is made selective by the inclusion of polymyxin B sulphate (LS1051). -
Bacitracin Selective Supplement E&O Laboratories Ltd Bacitracin Supplement (LS0012) is an antibiotic supplement used to enhance the isolation of Haemophilus species. -
Bacteriological peptone is an economical source of nutrients provided by a balanced mixture of meat peptones and tryptone.The growth requirements of most non fastidious organisms will be fulfilled by the range of amino acids, peptides and proteoses in this mixture.
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Baird Parker agar is a selective medium for the isolation and presumptive identification of coagulase-positive staphylococci. This medium is used extensively for detecting Staphylococcus aureus in foods, dairy products, and other materials. Enzymatic digest of casein, meat extract and yeast extract provide the required carbon, nitrogen and vitamins. The medium is made selective by the inclusion of lithium chloride and the addition of potassium tellurite. Glycine and sodium pyruvate are included as growth enhancers while the pyruvate also acts as a neutraliser of toxic peroxides. Coagulase positive staphylococci are differentiated by the addition of egg yolk tellurite (BM0530) due to their ability to break down the egg yolk. Clear zones around colonies form due to the proteolytic action of lecithinase. A secondary opaque zone, surrounding presumptive positive colonies, may also form due to lipase activity. Potassium tellurite is reduced by staphylococci giving rise to blackening of colonies. NB: Any black colonies (with halo (typical) or without the halo (atypical)) on this medium must be confirmed as Staphylococcus aureus by further tests (e.g. coagulase test or latex agglutination etc.) Related Supplements : BM0530 Egg Yolk Tellurite
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Bile Aesculin Medium is generally used for the differentiation and presumptive identification of Group D streptococci (enterococci). Enterococci hydrolyse aesculin forming, amongst other products, aesculetin which in turn combines with Ferric ammonium citrate producing a dark brown or black complex. The presence of Bile salts in the medium inhibits gram positive organisms other than enterococci. The medium can also be used for the presumptive identification of certain organisms within the Enterobacteriaceae group such as Klebsiella spp., Enterobacter spp., etc.
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Brucella broth is a non-selective medium for the cultivation of Brucella spp. and other fastidious microorganisms. Brucella broth has been developed from the APHA formulation for Albimi broth. (1&2) The enzymatic digest of casein, enzymatic digest of animal tissues and yeast extract provide the necessary carbon, nitrogen and vitamin sources for this medium. Glucose is a fermentable carbohydrate and sodium chloride maintains the osmotic balance of the medium. Sodium bisulfite is added to enhance growth. References (1) Hausler, W. J. (ed.). 1976. Standard methods for the examination of dairy products, 14th ed. American Public Health Association, Washington, D.C. (2) ISO 10272-1:2006. Microbiology of food and animal feeding stuffs – Horizontal method for detection and enumeration of Campylobacter spp.
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Brucella Medium Base is a general purpose medium for the cultivation of Brucella spp. and other fastidious microorganisms. Brucella Medium Base has been developed from the APHA formulation for Albimi broth. The peptones act as carbon, nitrogen and vitamin source in this medium. Glucose is a fermentable carbohydrate and sodium chloride maintains the osmotic balance of the medium.
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Clostridium difficile agar, when supplemented, is used for the isolation of C. difficile from samples. This formulation is a modification of CCFA (Cycloserine-Cefoxitin-Fructose agar) developed by George et al. The proteose peptone act as carbon, nitrogen and vitamin source in this medium. Fructose is a fermentable carbohydrate. Sodium chloride maintains the osmotic balance of the medium. Disodium hydrogen phosphate and potassium dihydrogen phosphate are buffering agents. The magnesium sulfate acts as a source of inorganic ions and the agar is the solidifying agent. This media requires the addition of defibrinated horse blood and Clostridium difficile selective supplement (LS0022).
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KM0001 Columbia Agar is a modification of the original Columbia Agar formulation described by Ellner et al. from Columbia University and is tested in accordance with ISO 11133:2014. Columbia Agar provides a medium that is suitable for use with both defibrinated horse and sheep blood to support the growth and determining haemolytic reactions of a variety of microorganisms. Columbia Agar with the addition of plain or chocolated blood is recommended by the UK Standards for Microbiology Investigations for various purposes, including as a standard, supplementary or primary isolation medium. Columbia agar with blood is a general-purpose, non-selective medium suitable for isolation and cultivation of most organisms including fastidious anaerobes from clinical specimens. Chocolating the blood provides a highly nutritious medium which supports the growth of a wide range of pathogens including the most fastidious organisms and is particularly useful for the cultivation of Haemophilus and Neisseria species. Chocolate agar is the same as blood agar except that during preparation the red blood cells are lysed when added to molten agar base, which gives the medium a chocolate-brown colouration and from which the agar gets its name. As a result, cell lysis releases intracellular nutrients such as haemoglobin, haemin (X factor), and the coenzyme nicotinamide adenine dinucleotide (NAD or V factor) into the agar. These growth factors are available to fastidious organisms during growth. Related Supplements : Defibrinated Horse Blood, Defibrinated Sheep Blood, Horse Blood Lysed, LS0008 Staph/Strep Selective Supplement, LS0017 Neomycin Selective Supplement, LS0022 Clostridium difficle Selective Supplement, LS0012 Bacitracin Selective Supplement, LS0011 Campylobacter Growth Supplement, LS0009 Campylobacter (Skirrow) Selective Supplement
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This medium is intended for the cultivation and enumeration (via the Miles and Misra technique) of Lactobacillus spp. from a variety of sources and can be used in conjunction with MRS Agar (KM0080). This medium is a modification on the formulation developed by de Man, Rogosa and Sharpe.(1) The peptones, beef extract, yeast extract provides the required carbon, nitrogen and vitamins in this medium. Glucose is a fermentable carbohydrate. 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 magnesium sulphate, manganese sulphate and polysorbate 80 act as growth stimulants. The medium can be made more specific for lactobacilli generally by lowering the pH to between 5.0 and 5.5. This has the effect of inhibiting most streptococci that may otherwise grow on the medium and can be readily confused with lactobacilli.
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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.
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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
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KM0006 Fastidious Anaerobe Agar is a general-purpose medium, when supplemented with blood and any necessary selective agents, can be used for the isolation and culture of fastidious anaerobes from clinical specimens. Anaerobic infections are common infections caused by anaerobic bacteria. These bacteria occur naturally and are the most common flora in the body; in their natural state, they do not cause infection. Anaerobic bacteria can infect deep wounds, tissue, and internal organs where there is little oxygen after injury or surgery. Infection by anaerobic bacteria is normally characterized by formation of abscesses, foul smelling discharge, pus, and free gas in tissue, leading to tissue degradation. KM0006 is recommended as a standard, primary isolation or supplementary medium by the UK Standards for Microbiology Investigations and tested in accordance with the principles of ISO 11133:2014. Related Supplements : LS0015 Actinomycete Selective Supplement, LS0017 Neomycin Selective Supplement, LS0022 Clostridium difficile Selective Supplement, LS0023 Clostridium perfringens Selective Supplement, BM0140 Egg Yolk Emulsion
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Half-Fraser broth is a selective enrichment broth for the identification and isolation of Listeria spp., primarily from food and environmental samples. The antibiotics, nalidixic acid and acriflavine, are already included in the formulation so only ferric ammonium citrate (LS5004) need be added to make the complete Half-Fraser broth. The peptones provide carbon, nitrogen and vitamins, sodium chloride provides osmotic balance and the phosphate buffer system maintains pH. Lithium chloride inhibits enterococci and the antibiotics make the medium highly selective. Listeria spp. hydrolyse aesculin to aesculetin which forms a confirmatory dark brown or black complex with Fe3+ ions.
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KM0215 Half Fraser Broth Complete is used to make Half Fraser Broth enrichment media for the isolation of Listeria species from food and environmental samples.
Developed in 1988 by Fraser (1), the formulation can be made as primary enrichment Half Fraser Broth and secondary enrichment Fraser Broth according to the requirements of ISO 11290-1:2017 (2). KM0215 is recommended by the International Standardization Organization (2) and tested in accordance with the principals of ISO 11133:2014 (3).
The nalidixic acid, acriflavine, and ferric ammonium citrate are already included in the formulation, so no additional supplements are required to make complete Half Fraser Broth.
- Fraser, J. and Sperber, W. (1988) Rapid Detection of Listeria spp. in Food and Environmental Samples by Esculin Hydrolysis. Journal of Food Protection, 51(10), pp.762-765. 2. International Standardization Organization (2017) 11290-1:2017 Microbiology of the food chain - Horizontal method for the detection and enumeration of Listeria monocytogenes and of Listeria spp. - Part 1: Detection method. Geneva: ISO. 3. International Standardization Organization (2014) 11133:2014 Microbiology of food, animal feed and water — Preparation, production, storage and performance testing of culture media. Geneva: ISO.
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Kligler iron agar is used to differentiate between some of the enterobacteriacae on the basis of three reactions: fermentation of lactose and glucose and the production of hydrogen sulphide. Kligler iron agar is a modification of the original formulation developed by Kligler. It incorporates the principles of Russell’s double sugar agar with Kligler ‘s lead acetate agar. The peptone provides the required nitrogen, carbon and vitamins. Lactose and glucose are carbohydrates. Acid production from their fermentation is detected by the phenol red pH indictor. Sodium thiosulphate is reduced to hydrogen sulphide which is detected by the ferric citrate indicator. Sodium chloride maintains the osmotic balance.
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Lauryl Tryptose Broth is a selective medium for the detection of coliforms in water and wastewater. This formulation is based on the Mallmann and Darby formulation. (1) The tryptone provides the required carbon, nitrogen and vitamins in this medium. Lactose is a fermentable carbohydrate. The sodium chloride maintains the osmotic balance whilst the dipotassium hydrogen phosphate and potassium hydrogen phosphate act as buffers. Sodium lauryl sulphate is a selective again used to inhibit non-coliforms. References (1) Mallmann, W. L. and Darby, C. W. 1941. Uses of a lauryl sulphate tryptose broth for the detection of coliform organisms. Am J. Public Health. 31:127
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LB agar (Lennox) is used for the cultivation and maintenance of recombinant strains of Escherichia coli and is based on the formulation stated by Lennox. This medium is typically used in molecular biology procedures such as the detection of phage or plasmid transformed bacteria. LB agar (Lennox) is prepared using 5 g/L of sodium chloride and this level varies from that described by Miller. This allows for additional sodium chloride to be added at the point of preparation if required. Enzymatic digest of casein provides the required nitrogen and carbon for organism growth. Vitamin B complex required by recombinant strains of E. coli are supplied by the yeast extract. Sodium chloride maintains the osmotic balance and provides sodium ions for membrane transport. Related Supplements : LS0035 Ampicillin Selective Supplement, LS0037 Kanamycin Selective Supplement
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Luria Bertani (LB) agar (Miller) is used for the cultivation and maintenance of recombinant strains of Escherichia coli and is based on the formulation stated by Miller. This medium is typically used in molecular biology procedures such as the detection of phage or plasmid transformed bacteria. LB agar (Miller) is prepared using 10 g/L of sodium chloride and this level varies from that described by Lennox. Enzymatic digest of casein provides the required nitrogen and carbon for organism growth. Vitamin B complex required by recombinant strains of E. coli are supplied by the yeast extract. Sodium chloride maintains the osmotic balance and provides sodium ions for membrane transport. Related Supplements : LS0035 Ampicillin Selective Supplement, LS0037 Kanamycin Selective Supplement
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Letheen agar modified is intended for use in the isolation of microorganisms from cosmetics. The casein peptone, meat peptone, beef extract and yeast extract act as carbon, nitrogen and vitamin sources in this medium. Glucose is a fermentable carbohydrate. Sodium chloride maintains the osmotic balance of the medium. The sodium bisulfite, lecithin and polysorbate 80 inactivates quaternary ammonium compounds. Polysorbate 80 neutralises phenols, formalin, hexachlorophene, and in combination with the lecithin, ethanol.
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Letheen broth when prepared with polysorbate 80 is used for the testing of quaternary ammonium compounds for antimicrobial activity. Letheen broth is recommended by the Official Methods of Analysis of the Association of Official Analytical Chemists (AOAC). (1) The enzymatic digest of animal tissue and beef extract act as carbon, nitrogen and vitamin sources in this medium. Sodium chloride maintains the osmotic balance of the medium. Lecithin inactivates quaternary ammonium compounds. Polysorbate 80 must be added to the medium prior to sterilisation. Polysorbate 80 neutralises phenols, formalin, hexachlorophene, and in combination with the lecithin, ethanol. REFERENCE (1) Association of Official Analytical Chemists. 1995. Official methods of analysis, 16th ed. Association of Official Analytical Chemists, Washington, D.C
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Letheen broth modified is intended for use in the isolation of microorganisms from cosmetics. The enzymatic digest of animal tissue, enzymatic digest of casein, yeast extract and beef extract act as carbon, nitrogen and vitamin sources in this medium. Sodium chloride maintains the osmotic balance of the medium. The sodium bisulfite and lecithin inactivates quaternary ammonium compounds. Polysorbate 80 must be added to the medium prior to sterilisation. Polysorbate 80 neutralises phenols, formalin, hexachlorophene, and in combination with the lecithin, ethanol.
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Long and Hammer agar is for the detection of aerobic microorganisms in fish and fish products. This media is recommended for the determination of spoilage organisms in fresh and lightly preserved seafoods. (1) The proteose peptone acts as a nitrogen, carbon and vitamin source. Gelatine is a protein source and solidifying agent. Sodium chloride maintains the osmotic balance and di-potassium hydrogen phosphate is a buffer. 1) Nordic Committee on Food Analysis. (2006) Aerobic count and specific spoilage organisms in fish and fish products. NMKL Method No 184
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MacConkey Agar without Salt and Crystal Violet, based on the formulation by Rappaport and Henig, is a differential medium for the isolation and differentiation of lactose and non-lactose fermenting enteric bacteria while also restricting the swarming of Proteus species. KM0011 is recommended as a differential primary isolation media by the UK Standards for Microbiology Investigations, The Microbiology of Drinking Water and tested in accordance with ISO 11133:2014. Related Supplements : LS0189 Cefotaxime Supplement (1mg/L)
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KM0031 Mannitol Salt Agar is a selective medium for the isolation of Staphylococcus aureus from clinical samples, food, cosmetics and water samples. Chapman showed that adding a higher level of sodium chloride to Mannitol Salt Agar allowed for the recovery of pathogenic staphylococci and inhibits most organisms. Coagulase positive staphylococci (e.g., S. aureus) produce yellow colonies and a surrounding yellow medium while coagulase negative staphylococci produce red colonies and no colour change of the phenol red indicator. The medium conforms to the requirements of the Harmonised EP/USP/JP, is recommended as a primary isolation media by the UK Standards for Microbiology Investigations and tested in accordance with ISO 11133:2014 and Clinical and Laboratory Standards Institute. This medium is also included in the Bacteriological Analytical Manual for cosmetics testing.
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Marine agar is a medium used to support the growth of numerous marine bacteria. Originally formulation by ZoBell (1), its high saline levels are to simulate a close approximation of seawater which allows the marine bacteria to grow (2). The sodium chloride and marine minerals provide the high salinity needed for marine bacteria to thrive and aims to simulate sea water. The peptones provide the necessary nitrogen, amino acids and vitamins for growth. Agar is the solidifying agent. References (1) ZoBell, C.E. 1941. Studies on Marine Bacteria. I. The cultural requirements of heterotrophic aerobes. J. Mar. Res. 4, 42-75. (2) Lyman, J. and Fleming, R. H. 1940. Composition of Seawater. J. Mar. Res. 3, 134-146
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KM0183 Mueller Hinton Agar is used as a base to make various media for antimicrobial susceptibility testing by the disk diffusion method as described by Bauer-Kirby. First described by Mueller and Hinton, Mueller Hinton Agar has been approved as the definitive medium for antimicrobial susceptibility testing by European Committee on Antimicrobial Susceptibility Testing (EUCAST), Clinical and Laboratory Standards Institute (CLSI) and is compliant with ISO16782:2016. KM0183, when prepared as unsupplemented Mueller Hinton Agar, is suggested by EUCAST and CLSI for non-fastidious organisms such as Enterobacterales, Pseudomonas spp., Stenotrophomonas maltophilia, Acinetobacter spp., Staphylococcus spp., Enterococcus spp., Aeromonas spp., Achromobacter xylosoxidans, Vibrio spp., Bacillus spp. and Burkholderia pseudomallei. KM0183, when prepared supplemented with 5% horse blood and nicotinamide adenine dinucleotide (NAD), is suggested by EUCAST and CLSI for fastidious organisms such as Streptococcus pneumoniae, Streptococcus groups A, B, C and G, Viridans group streptococci, Haemophilus influenzae, Moraxella catarrhalis, Listeria monocytogenes, Pasteurella multocida, Campylobacter jejuni and coli, Corynebacterium spp., Aerococcus sanguinicola and urinae and Kingella kingae. Additionally, according to the UK Standards for Microbiology Investigations, when supplemented appropriately, Mueller Hinton Agar can be used in the process of identifying Haemophilus species and the HACEK group of organisms and Helicobacter species from clinical specimens. Related Supplements : LS0005 NAD Supplement (20mgs/L), Defibrinated Horse Blood
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A general-purpose medium for the cultivation of organisms that are less fastidious in their nutritional requirements. The beef extract, peptone and yeast extract act as carbon, nitrogen and vitamin sources in this medium. Sodium chloride maintains osmotic balance.
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Nutrient Broth No.2 is used for the cultivation of fastidious pathogens and other microorganisms. This general use medium, rich in nutrients, allows the growth of bacteria when there is a low level of cells. The medium is particularly suitable as a secondary growth medium for staphylococci to be tested for coagulase production and also be used for sterility testing of aerobic organisms. Beef extract and peptone provide the required carbon, nitrogen and vitamins. Sodium chloride maintains osmotic balance.
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KM0007 Primary UTI Agar is a chromogenic agar that has been developed to allow differentiation and presumptive identification of organisms typically found in urinary tract infections. Urinary Tract Infections (UTI’s) account for 35-40% of all hospital acquired infections in the UK. Gram negative aerobic bacteria are responsible for a considerable proportion of UTI’s with Escherichia coli isolation rates at 80-90% of first-time infections. Various other opportunistic bacterial species can cause UTI’s. KM0007 may be used as a chromogenic medium for the quantification and presumptive identification of bacteria in urine from clinical samples in line with the UK Standards for Microbiology Investigations and tested in accordance with the principles of ISO 11133:2014. Related Supplements : SHS500 Sterile Horse Serum 500ml
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KM0003 Sabouraud Dextrose Agar powder is a general-purpose, non-selective medium which is used for the isolation of yeasts and moulds from clinical, food, pharmaceutical and cosmetic samples. Sabouraud Dextrose Agar is a modification of a medium originally described by Sabouraud. The fungi maintain their typical cultural appearance and thus may be readily identified according to the standard macroscopic characters described by Sabouraud. The formulation conforms to European, United States and Japanese Pharmacopeia requirements. This medium complies with ISO 11133:2014, where it is described as the main reference medium to carry out quantitative testing on culture media intended for fungi. Sabouraud Dextrose Agar is recommended by the UK Standards for Microbiology Investigations for various purposes, including as a standard, supplementary or optional medium. Related Supplements : LS0050 Chloramphenicol Selective Supplement
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Sabouraud dextrose agar with chloramphenicol is a selective media for the isolation of yeasts and fungi suitable for use in all areas of mycology. Sabouraud dextrose agar is a modification of a medium originally described by Sabouraud.(1) The tryptone and meat peptone provides the required nitrogen, carbon and vitamins. The high concentration of dextrose is included as an energy source and in tandem with the acidic pH (5.6) facilitates the growth of fungi whilst providing limited selective properties.(2) Chloramphenicol is included to increase the selectivity of the media inhibiting a range of Gram-positive and Gram-negative bacteria. References (1) Sabouraud, R. 1892. Ann. Dermatol. Syphilol. 3:1061. (2) Jarett, L., and A. C. Sonnenwirth (eds.). 1980. Gradwohl’s and parasitic infections, 7th ed. American Public Health Association, Washington, D.C.
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Sabouraud liquid medium USP is used in sterility testing for the detection of moulds, yeasts and acidophilic microorganisms in pharmaceutical products. This medium is also used for non-sterile testing and for the determination of fungistatic activity. Sabouraud liquid medium USP conforms to the USP and Harmonised Pharmacopeia. The peptic digest of animal tissue and pancreatic digest of casein provides the required nitrogen, carbon and vitamins. The high concentration of dextrose is included as an energy source and in tandem with the acidic pH (5.6) facilitates the growth of fungi whilst providing limited selective properties.
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Developed by Leifson, selenite F broth is a medium for the selective enrichment of Salmonella spp. from both clinical and food samples. The peptone acts as a nitrogen, carbon and vitamin source. Lactose is a fermentable carbohydrate and sodium phosphate is a buffer. The medium is made selective by the addition of sodium biselenite (KM8021). Following overnight incubation subculture(s) are usually made on to one or more of the many selective enteric solid media.
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Selenite mannitol broth is a modification of selenite broth and is for the selective enrichment of Salmonellae spp. from clinical, food and environmental specimens. Comparisons have shown that mannitol selenite broth is better than other enrichment broths for the isolation of Salmonellae spp. The peptone acts as a nitrogen, carbon and vitamin source. Mannitol is a fermentable carbohydrate and sodium phosphate is a buffer. The medium is made selective by the addition of sodium biselenite (KM8021). The fermentation of mannitol by Salmonellae spp. is said to correct the alkaline pH swing which can occur during incubation. Following overnight incubation subculture(s) are usually made on to one or more of the many selective enteric solid media.
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Sheep Blood Agar Base has been developed to provide a nutrient rich medium compatible with sheep blood for the cultivation of many bacteria, especially fastidious Streptococcus spp., without affecting haemolytic reactions. Alternative culture mediums, such as Blood agar base No. 2, can results in mixed haemolytic reactions for some Streptococcus spp. This is thought to occur due to the trace amounts of fermentable carbohydrates in yeast extract and the physiological difference between sheep and horse blood. The tryptone, peptone, and yeast extract provide the required nitrogen, carbon and vitamins in the medium. Sodium chloride maintains the osmotic balance. Related Supplements : LS0008 Staph/Strep Selective Supplement
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For in vitro diagnostic use. KM0159 SIM Medium is a multi-purpose medium for the differentiation of Enterobacteriaceae. This is best described as a multi-purpose medium for the differentiation of Enterobacteriaceae that combines three individual tests into a single medium (hydrogen sulphide production, indole formation and motility). The presence of motility is apparent by the organism tracking out from the line of inoculation and often turning the medium turbid. Non-motile organisms generally grow within the stab line leaving the surrounding medium clear. H₂S positive organisms turn the medium black due to the formation of hydrogen sulphide in the presence of the sodium thiosulfate and ferric ammonium citrate often making it difficult to determine the other parameters. Indole production is tested for by layering a small amount of Indole Reagent (Kovac’s) onto the surface of the medium. A positive result is indicated by the formation of a pink colour at the interface of the reagent and the medium. The enzymatic digest of casein and enzymatic digest of animal tissue provide the required carbon, nitrogen, and vitamins in this medium. Ferric ammonium citrate and sodium thiosulfate are used to detect hydrogen sulphide production. The low concentration of agar allows for a semisolid media which is used for motility detection.
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Trichomonas medium is based on the formula described by Kupferburg, Johnson and Sprince for the selective isolation of Trichomonas spp. (1) The tryptone and liver extract act as carbon, nitrogen and vitamin sources in this medium. Maltose is a fermentable carbohydrate. The agar and cysteine HCl reduce the oxygen tension in the medium which aids the growth of trichmonads. Methylene blue is a redox indictor and allows for the visualisation of any significant oxygen diffusion in the medium. The addition of selective agents such as chloramphenicol is recommended to inhibit bacterial species that may be present in specimens. References 1) Kupferberg, A.B. Johnson, G., and Sprince, H. 1948. Proc. Soc. Exper. Biol. Med., 67:304-308
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Triple sugar iron agar is used to differentiate between some of the enterobacteriacae on the basis of four reactions: fermentation of lactose, glucose and sucrose and the production of hydrogen sulphide. Beef extract, yeast extract and peptone provide the required nitrogen, carbon and vitamins. Lactose, sucrose and glucose are carbohydrates. Acid production from their fermentation is detected by the phenol red pH indictor. Sodium thiosulphate is reduced to hydrogen sulphide which is detected by the ferric citrate indicator. Sodium chloride maintains osmotic balance.
