REPRODUCIBILITY OF LYSIS-CENTRIFUGATION CULTURES FOR QUANTIFICATION OF MYCOBACTERIUM-AVIUM COMPLEX BACTEREMIA

While quantitative mycobacterial blood cultures have been accepted as the standard for evaluating response to various Mycobacterium avium co mplex (MAC) treatment regimens, variability in this methodology has no t been evaluated in a rigorous fashion. We thus studied the reproducib ility of quantitative MAC cultures by a lysis-centrifugation culture s ystem within and among five institutions. To measure the intralaborato ry variation in mycobacterial colony counts, colony counts from duplic ate blood specimens collected from 52 AIDS patients with MAC bacteremi a were determined. Colony counts ranged from 0 to 50,000 CFU/ml. Nonpa rametric analyses revealed there was no significant difference in colo ny counts between the 52 duplicate specimens. The agreement between th e intralaboratory paired specimens, as measured by the intraclass corr elation coefficient, was 0.997. To measure the interlaboratory variati on, multiple 10-ml aliquots from 12 patients were distributed to five institutions and processed within 24 to 32 h by lysis-centrifugation. For the 12 specimens distributed to the five laboratories, two-way ana lysis of variance for repeated measures revealed no significant differ ence in an individual patient's colony counts between laboratories (P > 0.2). We conclude that quantitation of mycobacterial colony counts b y the lysis-centrifugation system is reproducible within and between i nstitutions. Clinical trials evaluating response to therapeutic interv entions for MAC can use multiple laboratories for quantitation of myco bacteremia. Furthermore, a 24- to 32-h delay in processing appeared to have no impact on reproducibility.