Sputum culture

Clinical description

This is a bacteriologic confirmatory test for MTB. It is highly sensitive technique that can detect as few as 100 viable bacilli per ml of sputum. Because culture facilities are located centrally, the time between collection and processing should be 3 days or less and not more than five days when kept in a cold chain (2-8oC).

• Solid culture media: (Löwenstein-Jensen) is a culture media which has several advantages

over liquid media, including ease of preparation, low cost and low contamination rate.

However, the length of time it takes to culture and conduct drug susceptibility testing (DST) as well as the turnaround time for results limits its use in peripheral laboratories.

• Liquid culture media: (MGIT 960 system) is a specially enriched culture media developed

to shorten the time required for bacillary growth to 5-15 days. It has an additional 10% sensitivity over LJ solid media. However, the method is prone to a higher contamination rate.

Advantages of MTB culture

• Detects small numbers of organisms (as few as 10 bacilli).
• Is often 30-50% more sensitive (than smear microscopy) in diagnosing TB than

microscopy.

• Allows species identification and drug susceptibility testing.
• Recommended for monitoring the treatment response of drug-resistant TB patients.

National Tuberculosis Control Programme 35 Limitations of MTB culture

• Results can take 4-8 weeks to be issued, especially when solid culture is used
• High installation and maintenance cost.
• High biosafety level requirement.
• Requires well-trained personnel.
• Requires an efficient sample transportation system.