Pyrazinamide (PZA) is an important first-line tuberculosis drug that is part of the currently used shortcourse tuberculosis chemotherapy. PZA is a prodrug that has to be converted to the active form pyrazinoic acid by pyrazinamidase (PZase) activity, encoded by the pncA gene of Mycobacterium tuberculosis, and loss of PZase activity is associated with PZA resistance. To further define the genetic basis of PZA resistance and determine the frequency of PZA-resistant strains having pncA mutations, we sequenced the pncA gene from a panel of 59 PZA-resistant clinical isolates from Canada, the United States, and Korea. Two strains that did not contain pncA mutations and had positive PZase turned out to be falsely resistant. Three PZase-negative strains (MIC, >900 g of PZA per ml) and one PZase-positive strain (strain 9739) (MIC, >300 g of PZA per ml) did not have pncA mutations. The remaining 53 of the 57 PZA-resistant isolates had pncA mutations, confirming that pncA mutation is the major mechanism of PZA resistance. Various new and diverse mutations were found in the pncA gene. Interestingly, 20 PZA-monoresistant strains and 1 multidrug-resistant isolate from Quebec, Canada, all had the same pncA mutation profile, consisting of an 8-nucleotide deletion and an amino acid substitution of Arg1403Ser. Strain typing indicated that these strains are highly related and share almost identical IS6110 patterns. These data strongly suggest the spread of a PZA-monoresistant strain, which has not previously been described.

This paper reports the results of an efficacy study of a stuttering treatment program known as Modifying Phonation Intervals (MPI), which trains stuttering speakers to reduce the frequency of relatively short phonation intervals (PIs) during connected speech across speaking tasks and situations. Five young adult male stuttering speakers were treated in this computer-based program that systematically trains speakers to reduce selected short PIs found to functionally control stuttering. The treatment process was evaluated using multiple-baseline designs. Treatment was largely self-managed and based on a performance-contingent schedule of within-clinic speaking tasks (Establishment), beyond-clinic speaking tasks (Transfer), and systematic decreases in assessment occasions (Maintenance). Assessments were made at regular intervals before, during, and after treatment. All speakers achieved stutter-free and natural-sounding speech during within- and beyond-clinic speaking tasks at the completion of Maintenance. All were tested 12 months after completion of Maintenance, and all maintained the results. The findings from this study suggest that this procedure may make a significant contribution to stuttering treatment practice.

Two manual liquid medium systems, the Mycobacteria Growth Indicator Tube (MGIT) and MB Redox tube systems, were evaluated in comparison to the radiometric BACTEC-460 semiautomated system for recovery ofMycobacterium tuberculosis from sputum specimens. The highest level of recovery, from a total of 77 culture-positive specimens, occurred with the BACTEC-460 system (92.2%), followed by the MB Redox tube (80.5%) and the MGIT (63.6%) systems. The shortest time to detection was observed also among the cultures in BACTEC-460: a mean of 12 days to a growth index (GI) of 10 and 15 days to a GI of 500. The mean times for the other systems were 16 days for the MB Redox tube system and 17.4 days for the MGIT system. The proportion of cultures grown after more than 3 weeks of incubation was only 2.8 or 8.4% in BACTEC-460 (for a GI of 10 or 500) but 17.7% in MB Redox and 22.5% in MGIT. Despite these differences in comparison to the BACTEC-460 system and some differences between the MGIT and MB Redox tube systems, either of the two manual liquid medium systems presents a reasonable alternative to the BACTEC-460 system, especially for laboratories with a limited workload, and a valuable element in the laboratory protocol, in conjunction with solid media, for obtaining rapid detection of growth from about 80% of culture-positive specimens and for better overall recovery of M. tuberculosis.

A new agar medium to perform pyrazinamide (PZA) susceptibility testing with Mycobacterium tuberculosis has been developed. This medium has an acidic pH of 6.0 instead of the usual for agar media, pH 6.8, to provide optimal conditions for PZA activity, and it also differs from conventional Middlebrook 7H10/7H11 agar in that animal serum (fetal or calf bovine or fetal equine serum) is used instead of oleic acid-albumin-dextrose-catalase to support good growth of M. tuberculosis at the low pH of 6.0. A critical concentration of 900 or 1,200 μg of PZA/ml in this medium made it possible to differentiate between PZA-susceptible and PZA-resistant clinical isolates. This agar medium has the following advantages compared to a liquid medium: it allows determination of the actual proportion of PZA-resistant bacteria in the isolate and it is simple and inexpensive. In addition, it has the potential of being used for a direct susceptibility test with PZA, but this approach will require further confirmation. Further studies to develop critical concentrations of other drugs for this low-pH medium, as well as to investigate the possibility of cultivation in regular (non-CO2) incubators, are in progress.

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