Evaluation of IS1245-based PCR for detection of mycobacterium avium bacteraemia in AIDS patients

A PCR method based on the repetitive IS1245 sequence was evaluated for the detection of Mycobacterium avium bacteraemia in AIDS patients. Two blood preparation methods were applied: lysis of erythrocytes using a hypotonic buffer and Ficoll density centrifugation. Results were compared with culture and PCR amplification of the non-repetitive pMav22 sequence. Fifty-one of 251 tested samples grew M. avium. Bacterial densities lower than 10 cfu/ml blood were frequent, they occurred in 59% of blood samples from patients with mycobacteraemia. Inhibitory substances were detected more frequently with the lysis method (36%) than the Ficoll processed samples (19%). While specificity of PCR was high, sensitivities varied according to the methods used and the load of infection in the bloodstream. False-negative PCR results were attributable to low level bacteraemia and inhibition of PCR. Moreover, 1 of 186 and 9 of 51 M. avium strains investigated lacked the IS1245 and the pMav22 sequence, respectively. Sensitivities of culture, IS1245- and pMav22-based PCR were 88, 64 and 58%, within the lysis processed samples and 95, 86 and 50% using Ficoll prepared samples, respectively. Thus, we conclude that IS1245-based PCR is a rapid and specific method for diagnosing M. avium bacteraemia and shows a higher sensitivity than single copy gene targets, but that the sensitivity is inferior to culture.