Mixed mycobacterial cultures--occurrence in the clinical laboratory

During a 2-year period we observed at our institution 22 mixed mycobacterial cultures among a total of 991, representing 20 patients. We found no evidence of double infection. Mixed cultures frequently contained saprophytic organisms. Our experiments have shown that subculturing, especially into liquid media, can significantly change the relative quantities of CFU's present in mixed cultures. We believe that the use of agar media is useful for the recognition of mixed cultures.