Extreme care is required to ensure the purity of plasmodium cultures
the importance of maintaining cultures of malarial parasite called plasmodium is evident in the wake of growing menace of malaria. The cultures help in carrying basic biological research that can later be used for designing effective therapies for the disease. Majority of the research involves characterising the dna of the parasite, patterns of gene expression, and the proteins synthesised by it.
But a recent finding may pose serious setbacks to laboratory approaches towards the study of plasmodium biology. F Turrini and his colleagues at the University of Torino, Italy, report that more than one supposedly pure culture of plasmodium has been found to be contaminated by a smaller parasite of its own called mycoplasma. The parasite makes a whole range of enzymes and secondary metabolites that can effect cell growth (Parasitology Today , Vol 13, No 10).
Mycoplasma is considered to be the smallest organisms capable of self-replication. They resemble other bacteria in some respects but also differ in some respect as they lack a cell wall. Many of the organisms are known to be responsible for infections of the respiratory and urinary tracts. The basic technique used by Turrini and his colleagues, was the polymerase chain reaction that can be used to amplify and characterise very small fractions of 'foreign' dna within a background of 'native' dna .
The scientists discovered that the plasmodium cultures did not contain viable mycoplasma cells in some cases. However, they contained both dna and enzymes that are derived from mycoplasma. There were significant levels of activity of the mycoplasma enzyme called arginine deiminase that can inhibit the growth of other cells in culture. The finding arouses suspicion about all observations in which blood cell growth was inhibited by plasmodial factors because the inhibition may have been caused by mycoplasmal arginine deiminase .
Mycoplasma contamination was passed on from one generation of cell culture to another and persisted in spite of freezing the cultures in liquid nitrogen. The standard sterility precautions proved ineffective in preventing the contamination of 'clean' cultures that were handled in the same laboratory as infected ones. But special precautions including the use of specific antibiotics were found to be effective.
The study suggests for taking appropriate actions so that the purity of plasmodium cultures could be maintained. The ill effects of mycoplasma can be erroneously attributed to the plasmodium itself. Consequently, there is a risk of wasting time, effort and money in developing potential therapies that deal with mycoplasma.
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