A rapid PCR-based test for the diagnosis of pulmonary tuberculosis, the Roche AMPLICOR Mycobacterium tuberculosis test (AMPLICOR MTB), was evaluated. Results from AMPLICOR MTB were compared with culture results and the final clinical diagnosis for each patient. A total of 985 specimens from 372 patients were tested. When AMPLICOR MTB results were compared with resolved results, i.e., a specimen grew M. tuberculosis or was obtained from a patient with a clinical diagnosis of tuberculosis, the sensitivity, specificity, positive predictive value, and negative predictive value for the AMPLICOR MTB test were 66.7, 99.6, 91.7, and 97.7%, respectively. These results were comparable to those obtained from culture. Test results were available approximately 6.5 h after specimen receipt in the laboratory. Our data demonstrate that AMPLICOR MTB will provide rapid, valuable information for the diagnosis and control of tuberculosis.

The effect of calcium and magnesium on the susceptibility of 13 species of Pseudomonas to tetracycline, gentamicin, polymyxin B, and carbenicillin was measured. The majority of the minimum inhibitory concentrations (MICs) of these antibiotics was increased if these cations were added to the test media. The increases in MICs caused by calcium or magnesium were similar, but the combination of both -ions generally caused a greater change than either alone. Although the MIC of polymyxin B was most affected by calcium and magnesium, its interpretive susceptibilities (i.e., whether susceptible or resistant) were least changed. Susceptibility tests on Pseudomonas species probably should be done with Muller-Hinton broth supplemented with physiological concentrations of calcium and magnesium to better approximate the in vivo activity of these antibiotics. When the susceptibility tests were performed with Mueller-Hinton agar, the MICs were slightly less than those obtained with Mueller-Hinton broth supplemented with both cations but greater than those obtained with MuellerHinton broth supplemented with individual cations.

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A study to delineate the feasibility of a biphasic-culture approach for detection and isolation of mycobacteria from clinical specimens except blood was conducted in four medical centers. The biphasic system (Septi-Chek AFB, Roche Diagnostic Systems, Nutley, N.J.) was compared with conventional mycobacterial isolation media and the BACTEC system. Septi-Chek AFB showed the highest degree of mycobacterial recovery. In addition, Septi-Chek AFB consistently shortened the time required for recovery of mycobacteria from clinical specimens and supported the growth of small inoculum numbers of stock cultures of 14 mycobacterial species. The study indicates the feasibility and potential advantages of the biphasic approach for detection and isolation of mycobacteria.