Tuberculosis due to Mycobacterium bovis in the Australian population: DNA typing of isolates, 1970-1994

SETTING: Bacteriologically confirmed cases of Mycobacterium bovis in the Au stralian population. OBJECTIVE: To evaluate the DNA fingerprinting techniques commonly used for M. bovis on isolates from humans and determine whether they were useful for determining the origin of human infection. DESIGN: M. bovis strains isolated between 1970 and 1994 were obtained from five Australian Reference Laboratories. Four DNA fingerprinting techniques, comprising Southern hybridisation with three different probes (the inserti on sequence [IS]6110, the polymorphic guanine-cytosine-rich sequence [PGRS] and the direct repeat [DR]) and a PCR-based method (spoligotyping) were us ed. RESULTS: The PGRS, DR and IS6110 RFLP methods identified 32, 22 and 14 diff erent types respectively from the 45 isolates available. Spoligotyping iden tified 18 different types. When all methods were combined 41 different stra ins were identified. Clear differences were found between many isolates fro m Australian-born patients and those from patients born overseas. CONCLUSIONS: The PGRS RFLP method was the most effective method for typing the human strains, but a combination of methods is recommended for maximum sensitivity. Most Australian-born patients that had worked in the meat and livestock industries were infected with strains similar to those that are c ommonly found in Australian cattle, confirming the occupational risk in the se industries. Patients born overseas were typically infected with strains genetically different from those of patients born in Australia. This sugges ts that patients born overseas identified with M. bovis were presenting wit h reactivation of infection acquired outside Australia.