ANALYSIS OF GENETIC-POLYMORPHISM IN THE PHOSPHOLIPASE REGION OF MYCOBACTERIUM-TUBERCULOSIS

mtp40 was originally identified as a short genomic region that was fou nd in strains of Mycobacterium tuberculosis but not in Mycobacterium b ovis, Subsequent studies have revealed that the sequence is part of th e mpcA gene, which encodes a phospholipase C, To investigate further t he distribution of the mtp40 sequence, we analyzed strains of the M, t uberculosis complex by PCR and were able to amplify the mtp40 sequence in 90 of 93 strains of M, tuberculosis and in 2 strains of Mycobacter ium microti but not in M, bovis or M, bovis BCG, Based on this, we dev eloped a dot blot assay using genomic DNA which allows M, bovis to be distinguished from the majority of M, tuberculosis strains, We also pr obed Southern blots of 140 clinical isolates of M, tuberculosis to det ermine the frequency of strains lacking mtp40, This revealed an unexpe cted polymorphism in the phospholipase region, Two fragments were dete cted in 57% of samples, The expected fragment of 0.75 kbp corresponds to the region of mpcA containing mtp40. A 2,1-kbp fragment was observe d to belong to a recently discovered second phospholipase gene, mpcB. In addition, some strains appeared to lack both genes, while others sh owed only the presence of mpcA. A few strains had additional bands, su ggesting the existence of other homologs to the two phospholipase gene s, We also detected the insertion of IS6110 in the mpcA coding region of one strain, The absence of these genes in some clinical isolates ra ises questions about their function during infection and in the develo pment of tuberculosis disease in humans.