[Characterization of oligonucleotides with LNA-monomers for PCR detection of point mutations in mycobacteria...

Point mutations associated with isoniazid resistance in Mycobacterium tuberculosis (MTB) have been analyzed in codon 315 of the katG gene by conventional polymerase chain reaction (PCR) using primers containing locked nucleic acid (LNA) modified nucleotides. Purity and structure of primers containing 5 LNA monomers of 17 nucleotides in length were characterized by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) and a 17-mer duplex formed by two complementary oligonucleotides was characterized by the method of thermal denaturation. The duplex containing five LNA monomers per each strand was characterized by a higher melting temperature than it was expected using extrapolation of theoretical calculation for nucleotide modification of one strand of the duplex. Detection of any of six possible mutations in katG codon 315 (i.e. discrimination between sensitive and resistant MTB) requires just one PCR employing a set of two primers with one LNA-modified primer; this is an important advantage of oligonucleotides containing LNA over unmodified nucleotides: employment of multiplex PCR would require up to 12 primers. Problems of control of oligonucleotide modification by LNA monomers are discussed.