Middlebrook 7H10 Agar Slant

Principle And Interpretation

Dubos and Middlebrook (1) developed various formulations containing oleic acid and albumin, which protect Mycobacterium from toxic agents, helping for the growth of tubercle bacilli. Middlebrook 7H10 Agar Base was formulated as per Middlebrook, Cohn et al (6) reformed the original oleic acid-albumin agar and observed rapid and luxuriant growth of Mycobacterium species, which they called as 7H10. Kubica and Dye (5) reported less contamination on 7H10 Agar than egg-based media commonly used for the cultivation of Mycobacteria. Middlebrook 7H10 Agar Base is also used for isolation, cultivation and sensitivity testing of M. tuberculosis on enrichment with OADC Growth Supplement (FD018) and glycerol. Middlebrook media consists of many inorganic salts, which help, in growth of Mycobacteria. Citric acid formed from sodium citrate helps in retaining inorganic cations in solution. Glycerol supplies carbon and energy. Middlebrook OADC Growth Supplement (FD018) contains oleic acid, bovine albumin, sodium chloride, dextrose and catalase. Oleic acid and other long chain fatty acids are essential for metabolism of Mycobacteria. Some free fatty acids are toxic to Mycobacteria but albumin binds to those fatty acids and prevents toxic action on Mycobacteria. Dextrose serves as an energy source. Catalase neutralizes toxic peroxides. Malachite green partially inhibits other bacteria (2,7). Mycobacteria are strict aerobes and therefore increased CO2 tension and aerobic conditions must be provided during incubation. Care should be taken while decontamination of the specimen. Also proper specimen collection (sputum and not saliva) should be ensured. Samples should be carefully handled to avoid contamination.