In-vitro Effect of Iron on the Growth Density of Mycobacterium tuberculosis and Drug Susceptibility Testing.
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Date
2014-05
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Abstract
This work was carried out to study the effect of iron on the growth density of Mycobacterium
tuberculosis as well as drug susceptibility testing. Fifty two smear-positive acid fast bacilli
out of 100 sputum specimens were obtained from patients who were referred to National
Health Laboratory, Federal Ministry of Health, Sudan. The smear positive specimens were
cultured onto control LJ medium and other three sets of LJ medium containing ferrous
sulfate (iron) with different concentration; 100 mg/l, 200 mg/l and 400 mg/l. The growth was
graded as negative (0 = no growth), +1 (1-19 colonies), +2 (20-100 colonies) +3 (100-200
colonies), +4 (200-500 colonies) and +5 (more than 500 colonies). At the same time,
proportion method was applied to test susceptibility of mycobacterial isolates (20 isolates)
to anti-tuberculosis drugs; isoniazid (INH), rifampicin (RIF), ethambutol (EMB) and
streptomycin (STM) in the presence and absence of ferrous sulfate. Chi squire test was
used to analyze categorical variables and the significance level was set at P = .05.
Collectively, the results showed that the growth density of M. tuberculosis increased
significantly when ferrous sulfate was added to LJ medium. Resistance to the four first line
anti-tuberculosis drugs (INH, RIF, EMB, STM), INH and EMB were also respectively
increased from 10% to 15℅, 20% to 40% and 10% to 15% in the presence of ferrous sulfate. Contrary to other findings, it was observed that addition of ferrous sulfate to LJ
medium enhanced the activity of STM while no effect was seen on RIF and multi-drug
resistance (INH and RIF).
The study concluded that the growth density of M. tuberculosis can be enhanced by
supplementing LJ medium with 100-200 mg/l iron. This would be useful in recovery of the
organisms from specimens with a low bacterial load particularly in laboratories in low
income setting. Supplementation of LJ medium with iron must be avoided if drug
susceptibility testing is required.
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Keywords
Mycobacterium tuberculosis, iron, growth, culture, drug susceptibility
Citation
Abdalla Rasheeda H, Eleragi Ali M S, Hassan Salaheddin O, Ibrahim Nuha Y, Sanousi Mohamed S El. In-vitro Effect of Iron on the Growth Density of Mycobacterium tuberculosis and Drug Susceptibility Testing. British Microbiology Research Journal. 2014 May; 4(5): 523-529.