Mutations in mutT genes of Mycobacterium tuberculosis isolates of Beijing genotype Nicoletta Lari, 1 Laura Rindi, 1 Daniela Bonanni, 1 Enrico Tortoli 2 and Carlo Garzelli 1 Correspondence Carlo Garzelli garzelli@biomed.unipi.it 1 Dipartimento di Patologia Sperimentale, Biotecnologie Mediche, Infettivologia ed Epidemiologia, Universita ` di Pisa, I-56127 Pisa, Italy 2 Centro Regionale di Riferimento per i Micobatteri, Laboratorio di Microbiologia e Virologia, Ospedale Careggi, I-50134 Firenze, Italy Received 25 July 2005 Accepted 9 January 2006 Missense alterations in genes mutT4 and mutT2, which encode DNA repair enzymes, were sequenced from 30 clinical isolates of Mycobacterium tuberculosis of Beijing genotype, mostly from patients with primary tuberculosis, to evaluate their contribution to anti-mycobacterial drug resistance. The mutation Arg to Gly at codon position 48 (CGG to GGG) of mutT4 was found in 21 isolates; of these, 16 isolates also harboured the mutation Gly to Arg at position 58 (GGA to CGA) of mutT2. No statistically significant association was found between mutT4 and mutT2 mutations, and drug resistance. Furthermore, no mutations in mutT4 or mutT2 were found in any of 24 isolates resistant to multiple drugs, nor in 28 anti-mycobacterial drug-susceptible isolates of different genotypes. These data confirm that the polymorphism of mutT genes is characteristic and unique to the Beijing phylogenetic lineage. The mutator phenotype does not appear to increase prevalence of drug resistance, but further studies are required to investigate the mutation rates of Beijing isolates in response to drug exposure. INTRODUCTION Molecular typing of Mycobacterium tuberculosis strains isolated in several countries in recent years has revealed that a family of strains known as ‘Beijing’ (or ‘Beijing/W’ or ‘W-Beijing’) is widespread around the world (Bifani et al., 2002; Filliol et al., 2003; Glynn et al., 2002). M. tuberculosis strains of Beijing genotype are mostly prevalent in Asia, but recent data suggest that they have spread to eastern Europe and Indo-China, being significantly more prevalent among younger patients than older patients in Vietnam (Anh et al., 2000). There is concern that the Beijing family may have a predilection for drug resistance, especially multidrug resis- tance (Glynn et al., 2002). In fact, the Beijing genotype of M. tuberculosis, with a higher prevalence of drug-resistance mutations than non-Beijing strains, has been identified in 40–50 % of the clinical isolates studied in Russia during the last decade (Mokrousov et al., 2003). In M. tuberculosis, resistance to anti-mycobacterial drugs is exclusively due to genomic mutations in specific genes (Ramaswamy & Musser, 1998). With other bacteria, mutated phenotypes commonly result from defects in DNA repair (Horst et al., 1999), so it has been suggested that Beijing strains may have defective DNA repair systems, which would confer a mutator phenotype allowing an increased mutation rate, thus leading to a selective advantage during exposure to anti-mycobacterial drugs. An in silico analysis has shown that most mismatch-repair systems commonly found in Escherichia coli (Mizrahi & Andersen, 1998) are missing in M. tuberculosis, and only a number of putative genes encoding DNA repair enzymes, such as mutT, ogt, mutM and mutY, have been detected in the M. tuberculosis genome (Rad et al., 2003). Analysis of strains representing different branches of the Beijing geno- type has shown that the Beijing strains display unique missense alterations in putative mut genes, including two of the mutT type (the ORF Rv3908, designated mutT4 and mutT2) and ogt. These polymorphisms were found to be characteristic and unique to the Beijing phylogenetic lineage (Rad et al., 2003). The aim of this investigation was to study the variation in mutT genes in clinical isolates of Beijing M. tuberculosis to evaluate the contribution, if any, of mutT gene mutations to drug resistance. METHODS Clinical isolates. A total of 30 M. tuberculosis isolates of Beijing genotype, obtained from 2002 to 2004 from separate patients with tuberculosis (TB) hospitalized in Tuscany, Italy, were studied. Nineteen isolates were from patients with primary TB with no records of previous anti-TB therapy, two isolates were from patients Abbreviations: PGG, principal genotypic group; TB, tuberculosis. 46261 G 2006 SGM Printed in Great Britain 599 Journal of Medical Microbiology (2006), 55, 599–603 DOI 10.1099/jmm.0.46261-0