Pulsed Field Gel Electrophoresis and Genetic Diversity in Mycobacterium tuberculosis

Tuberculosis is a considerable public health problem due to its high risk of person-to-person transmission, morbidity, and mortality especially in developing countries. According to the World Health Organization there is the emergence of multi-drug resistant M. tuberculosis and the association of TB with HIV has led to TB being declared. Molecular genotyping methods are important in detecting the dominance of transmission or reinfection in a population. During one year study genotyping of 100 of M. tuberculosis (M.t.) isolates from patients referred to Pasteur Institute of Iran were accomplished with PFGE method. After identification of M.t. isolates and performing of antibiotic susceptibility test using standard methods, Melted Incert agarose and lysozyme were mixed with bacterial suspension to prepare PFGE plaques. After lyses and washing process the plaques digested with XbaI restriction enzyme. Finally the digested DNA fragments on 1% agarose with PFGE method were stained with ethidium bromide and analyzed with GelcomparII software. Dendrogram of genetic diversity among 100 M.t. isolates were obtained in comparison of molecular weight marker and revealed two common types. Pulsotype A with 71 isolates and just one MDR and pulsotype B included 29 isolates and 3 MDR cases. No correlation between antibiotypes and pulsotypes were observed. It is very important to know about the existence of any clonal expansion of special M.t. genotypes with resistant strains. Our research shows 3 MDR isolates into the low incidence pulsotype B which could be an alarm for more accurate MDR-TB surveillance program. Probably such observed limited polymorphism may be due to conservation of restriction sites of XbaI enzyme. In order to investigate the genetic relatedness of isolates using other restriction enzymes and different molecular typing methods simultaneously were recommended.