Characterization of the susceptibility of mycobacteria in BACTEC 12B media containing PANTA that had been supplemented with ceftazidime, and characterization of the individual components of PANTA in the presence of C18-carboxypropylbetaine.

C(18)-carboxypropylbetaine (CB-18) specimen processing has enhanced the diagnosis of mycobacterioses by smear, culture, and nucleic acid amplification. However, toxic side effects of CB-18 in liquid culture, especially in the presence of antibiotics, have been reported. The interaction of CB-18 at 20-25 microg/ml with the individual components of the antibiotic supplement PANTA that had been fortified with ceftazidime (PANTA-caz) was characterized in BACTEC 12B cultures using four mycobacterial isolates. When the Mycobacterium tuberculosis isolate ATCC 27294 was examined CB-18 plus PANTA-caz did not significantly alter the time-to-positive (i.e., time to a growth index (GI) of 15 (GI(15))), but did significantly increase the time to a GI of 500 (GI(500)) by approximately 8.5 days. This result could be attributed primarily to nalidixic acid, but also to ceftazidime to a lesser degree. Statistically significant increases in GI(15) of 12.5 days and GI(500) of 16.5 days were observed in the presence of CB-18 plus PANTA-caz with the Mycobacterium avium isolate ATCC 25291. These increases were due exclusively to trimethoprim. Statistically significant increases of approximately 2.5 and 9 days in GI(15) and GI(500), respectively, were observed with Mycobacterium kansasii ATCC 12478 in CB-18 plus PANTA-caz. The presence of nalidixic acid and ceftazidime were responsible for these alterations. When the behavior of the Mycobacterium fortuitum isolate ATCC 6841 was investigated in CB-18 plus PANTA-caz, significant increases in GI(15) of 8.5 days and GI(500) of 13 days were observed. The additive effects of nalidixic acid and azlocillin were responsible for these results. No single component of the PANTA-caz formulation was responsible for the interaction between CB-18 and PANTA-caz, although nalidixic acid contributed to these effects most often. These findings are consistent with the previous recommendation that CB-18 specimen processing follow a dilution-based format to ensure that the concentration of CB-18 carried-over into liquid media falls below 5-10 microg/ml.