-
Sodium Hydroxide (4%) with Phenol Red is a reagent used in the digestion and decontamination of sputum samples prior to culture for mycobacteria. Most clinical specimens submitted for acid-fast bacilli isolation are contaminated with more quickly developing commensal microbial flora. Additionally, acid-fast bacilli may be retained in respiratory secretions and not released for culture until the material is liquefied. Respiratory specimens, such as sputum, contain mucin which may trap microorganisms. Decontamination and digestion of the mucous components kills contaminating normal flora and allows slower growing mycobacteria to grow. Timely neutralization prevents potential loss of mycobacteria caused by high pH levels of decontaminants, resulting in the preservation of more viable organisms. Phenol red is used to indicate changes in pH. BM1320 is recommended by the UK Standards for Microbiology Investigations as part of their decontamination/digestion protocol; it is generally used in conjunction with Sputum Neutralising Buffer without Phenol Red (BM1324). -
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.
