Middlebrook 7H11 HiVeg™ Agar Base

Principle And Interpretation

Solid media for Mycobacterial cultivation may be egg-based (Lowenstein Jensen Media) or agar-based (Middlebrook Media) (1). Dubos and Middlebrook (2) developed various formulations containing oleic acid and albumin, which protect Mycobacterium from toxic agents, helping for the growth of tubercle bacilli. Middlebrook 7H11 Agar is a modification of Middlebrook 7H10 Agar (3) used for the isolation, cultivation and sensitivity testing of M. tuberculosis. It was shown by Cohn et al (4) that the addition of HiVeg™ hydrolysate enhanced the growth of more fastidious M. tuberculosis strains, which in turn was helpful in drug susceptibility testing (5). The media is enriched by the addition of Middlebrook 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 (6,1). Middlebrook 7H11 HiVeg™ Agar Base is prepared by completely replacing animal based peptone with vegetable peptones to avoid BSE/TSE risks associate with animal peptones. 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.