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Sorbitol MacConkey with Cefixime & Tellurite (CT-Smac) This is a selective differential medium for the isolation of Escherichia coli 0157:H7. It differs from other MacConkey medium in that Lactose has been replaced by Sorbitol. As Escherichia coli 0157:H7 does not ferment Sorbitol it produces pale translucent colonies whereas most other strains of Escherichia coli are Sorbitol positive and produce pink colonies. The medium is made more selective by the addition of the antimicrobial Cefixime and Potassium Tellurite. -
Thiosulphate Citrate Bile Salts Sucrose (TCBS) Agar TCBS is a selective isolation medium for culture of pathogenic Vibrio spp. from clinical samples. The formulation was developed by Kobayashi, Enomoto, Skazaki and Kuwahara. This medium inhibits most enterobacteriacae for at least 24 hours. For the isolation of Vibrio spp. other than V.cholerae in environmental bacteriology, it is advisable to incubate at the lower temperature range of 20°C – 30°C. NB - It is not recommended to perform an oxidase test on any presumptive positive isolates directly from TCBS medium. -
This is a medium to detect Thermo-Stable-Nuclease from Staphylococcus aureus after heat inactivation of the organism. After boiling and centrifugation the supernatant is placed in a well in the plate and incubated for 4 hours. If present, the enzyme breaks down the DNA in the medium and produces a zone of clearing indicating a positive reaction. -
This is a medium for determining the mutagenicity of a chemical reagent using the Ames Test. A histidine requiring strain (His- ) of Salmonella typhimurium is inoculated into a mixture of salt agar, histidine solution and the test reagent, which is mixed and then used to overlay the media. Following incubation if the test reagent is mutagenic it will reverse the His- phenotype allowing growth to occur at a higher level than the control. -
Originally introduced as an aid to recovery of Shigella spp. XLD is also a first class medium for recovery of Salmonella spp. It differs from other media of this type in that it has less Sodium Desoxycholate as its selective agent. The indicator system is somewhat complex taking advantage of the fermentation or otherwise of three carbohydrates (Lactose Sucrose and Xylose) together with Lysine Decarboxylase and Sodium Thiosulphate as an indication of the presence or absence of Hydrogen Sulphide. -
Xylose Lysine Deoxycholate (XLD) Agar is used for the isolation and detection of Salmonella and Shigella spp. It differs from other media of this type in that it has less sodium deoxycholate as its selective agent. The indicator system is somewhat complex taking advantage of the fermentation or otherwise of three carbohydrates (lactose, sucrose and xylose) together with lysine decarboxylase and sodium thiosulphate as an indication of the presence or absence of hydrogen sulphide. The addition of novobiocin (20mg/L) improves the inhibition of Proteus spp. -
This is a selective medium for the isolation and enumeration of Yersinia spp. in clinical and food samples. It is made selective by the inclusion of Sodium desoxycholate, Crystal violet and the antimicrobials Cefsulodin, Novobiocin and Irgasan. Mannitol is also included which Yersinia ferments giving a colony that produces a ‘Bull’s Eye’ appearance. The majority of other enteric organisms are inhibited but if they do grow they produce a large pinkish colony with an opaque halo.
