Effect OF Iron on Growth Characterization and Drug Susceptibility OF Mycobacterium Tuberculosis

Abstract

This prospective experimental study was conducted on sputum samples that were sent to the National Health Laboratory during the period from October 2005 to October 2006. It was formulated to study the effect of ferrous sulphate (iron) on the growth of M. tuberculosis and its effect on susceptibility to the first line anti-tuberculous drugs Isoniazid (INH) , Rifampicin (RIF), Streptomycin (SM) and Ethambutol(EMB), as well as its impact on nitratase enzyme and catalase activity at 68 o C. The effect of ferrous sulphate on the molecular identification of M. Tuberculosiswas also investigated. Hundred specimens confirmed as acid fast bacilli (AFB) were cultured on plain Loweinstein Jensen media (L J media) and on Loweinstein Jensen media supplemented with ferrous sulphate in the following concentrations 100mg/L, 200mg/L and 400mg/L respectively. (52 samples out of 100 showed growth in the culture media). It was found that the growth density of M. tuberculosisincreased significantly (p-value < 0.05) whenthe concentration of ferrous sulphate was increased in the L J media. The effect of iron on susceptibility of M. tuberculosis to the first-line anti-tuberculosis drugs was studied intwo ways. Firstly, 20 isolates were cultured on plain L J mediumand on L J medium containing ferrous sulphate. Then, the recovered bacilli were subjected to susceptibility testing. It was found that the percentage of resistance to INH was less for the isolates that were cultured on media containing ferrous sulphate (25%) than that of the isolates cultured on plain L J media (30%), this difference was statistically insignificant (pvalue=1.00). For SM, it was found that the resistance was IV insignificantly increased (p-value=0.25) from 35% (on plain L J media) to 50% for those who were cultured on iron containing media. In case of RIF there was no detectable change in the resistance, but EMB resistance was increased insignificantly (p-value=0.69) from 10% (on plain L J media) to 20%on iron containing media. Secondly by adding ferrous sulphate to the L J media that contained the anti-tuberculosis drugs, then comparing resistance of the isolates to the anti-tuberculous drugs beforeand after the addition of ferrous sulphate. Among the first twenty isolates that were subjected to the susceptibility tests, it was found that, the resistance to INH had increased insignificantly(p-value = 0.25) whenferrous sulphate was added to the media containing INH;It was increased from 20% before the addition of iron to 40% after adding the iron. Moreover, the resistance against EMB had increased from 10% to 15% after the addition of iron, this increase was also found to be statistically insignificant (p-value=1.00). However for SM there was an insignificant decrease in the resistance from 35% before adding iron to 30% after adding iron (p-value=1.00). RIF susceptibility was not affected before and after adding ferrous sulphate where the percentage of isolate resistance remained as it is 20%. The effect of iron on nitratase enzyme and catalase activity at 68 o C, was not affected in the presence orabsence of iron on the medium. At the molecular level, there was no any effect of iron on the identification capacity of these molecular tools.