7. All culture growth should be characterized based on

morphology, AFB stain and biochemical tests.

Liquid media: Such as Middlebrook 7H9, Dubos

Tween albumin broth and Kirchner medium have been

developed for the enrichment of growth of small number

of mycobacteria. They are valuable in isolating bacteria

from uncontaminated specimen such as CSF, pleura

and peritoneal fluids. There is an increased growth

rate of Mycobacterium tuberculosis in liquid medium.

Inclusion of antibiotic cocktails such as PACT (Polymyxin

B, Ampho-tericin B, Carbenicillin, Trimethoprim) or

PANTA (Polymyxin B, Amphotericin B, Nalidixic Acid,

Trimethoprim, Azlocillin) is required to make the liquid

media sufficiently inhibitory to the growth of other

bacteria and fungi especially when sputum specimens are

used.

It is recommended internationally that specimen for

mycobacterial culture should be inoculated in both types

of media. According to most acceptable guidelines at least

three different media should be inoculated, and at least

one of them being a liquid medium.

The different composition of the media and combination of different media have an impact on the yield and

positive cultures, thereby increasing sensitivity of culture

and mycobacterial isolation.

Recent Indian studies have also indicated that

‘Lowenstein-Jensen’ medium and ‘Kirchner’s liquid

medium are the best combination for the isolation of

mycobacteria from specimens other than sputum.

Ideally the cultures are incubated at 36 ± 10oC; with

an atmosphere of 5–10% of CO2 being stimulating to the

growth of mycobacteria.