Molecular evidence for heterogeneity of the multiple-drug-resistant Mycobacterium tuberculosis population in Scotland (1990 to 1997)

Multiple-drug-resistant Mycobacterium tuberculosis (MDR-MTB) has been well studied in hospitals or health care institutions and in human immunodeficie ncy virus-infected populations. However, the characteristics of MDR-MTB in the community have not been well investigated, An understanding of its prev alence and circulation within the community will help to estimate the probl em and optimize the strategies for control and prevention of its developmen t and transmission. In this study, MDR-MTB isolates from Scotland collected between 1990 and 1997 were characterized, along with non-drug-resistant is olates. The results showed that they were genetically diverse, suggesting t hey were unrelated to each other and had probably evolved independently. Se veral new alleles of rpoB, katG, and ahpC were identified: rpoB codon 525 ( ACC-->AAC; Thr525Asn); katG codon 128 (CGG-->CAG; Arg128Gln) and codon 291 (GCT-->CCT; Ala291Pro); and the ahpC synonymous substitution at codon G (AT T-->ATC). One of the MDR-MTB isolates from an Asian patient had an IS6110 r estriction fragment length polymorphism pattern very similar to that of the MDR-MTR W strain and had the same drug resistance-related alleles but did not have any epidemiological connection with the W strains. Additionally, a cluster of M. tuberculosis isolates was identified in our collection of 71 5 clinical isolates; the isolates in this cluster had genetic backgrounds v ery similar to those of the W strains, one of which had already developed m ultiple drug resistances, The diverse population of MDR-MTB in Scotland, al ong with a low incidence of drug-resistant M. tuberculosis, has implication s fur the control of the organism and prevention of its spread.