First documentation of isoniazid reversion in Mycobacterium tuberculosis.

BACKGROUND: Drug-resistant strains of Mycobacterium tuberculosis are increasing worldwide and pose a major threat to global health. However, it remains unsettled whether drug-resistant mutants are fixed in the bacterial population or if they would revert in the absence of drug pressure. OBJECTIVE: To document the occurrence of isoniazid (INH) reversion in a patient with multidrug-resistant tuberculosis (TB) and investigate its association with fitness cost. DESIGN: Genotypic and phenotypic assays were used to characterize the reversion of INH resistance in isolates from a patient with pulmonary TB. The pre-reversion katG mutation was reconstructed in a pan-susceptible laboratory strain (H37Rv DeltakatG::katG W300G) and tested for susceptibility to INH and oxidative stress. RESULTS: Genotyping and drug susceptibility testing showed that an isogenic strain of M. tuberculosis reverted from an INH-resistant to a susceptible phenotype in the absence of INH therapy. The genotypic basis of this reversion was mapped to the katG codon 300 which reverted from GGG (glycine, G) to a wild-type codon, TGG (tryptophan, W). The H37Rv DeltakatG::katG W300G mutant was resistant to INH, but also showed a deficiency in coping with oxidative stress. CONCLUSION: This study confirms that, in the absence of INH pressure, some INH-resistant mutants will revert to a drug-susceptible phenotype. This finding may have broader implications for INH-resistant strains and for the clinically useful lifespan of INH.

Rapid Identification of Mycobacterium tuberculosis and nontuberculous mycobacteria by multiplex, real-time PCR.

The rapid identification of mycobacteria from culture is of primary importance for the administration of empirical antibiotic therapy and for the implementation of public health measures, yet there are few commercially available assays that can easily and accurately identify the mycobacteria in culture in a timely manner. Here we report on the development of a multiplex, real-time PCR assay that can identify 93% of the pathogenic mycobacteria in our laboratory in two parallel reactions. The mycobacteria identified by this assay include the Mycobacterium tuberculosis complex (MTC), the M. avium complex (MAC), the M. chelonae-M. abscessus group (MCAG), the M. fortuitum group (MFG), and M. mucogenicum. The primer targets included the 16S rRNA gene and the internal transcribed spacer. The assay was initially validated with a repository of reference strains and was subsequently tested with 314 clinical cultures identified by the AccuProbe assay or high-performance liquid chromatography. Of the 314 cultures tested, multiplex, real-time PCR produced congruent results for 99.8% of the 1,559 targets evaluated. The sensitivity and the specificity were each 99% or greater for MTC (n = 96), MAC (n = 97), MCAG (n = 68), and M. mucogenicum (n = 9) and 95% and 100%, respectively, for MFG (n = 19). We conclude that this multiplex, real-time PCR assay is a useful diagnostic tool for the rapid and accurate identification of MTC and clinically relevant nontuberculous mycobacteria.

Substance use among adolescents: fulfilling a need state.

A factor that has received little investigation concerns the feeling state of need fulfillment and how this may relate to the significant public health problem of adolescent substance use. A survey of 823 students was conducted at a suburban public high school in the Southeastern United States. The questionnaire contained a scale focusing on fulfillment of adolescent needs, the Children's Depression Inventory, and items on current substance use. The results of t-tests indicated that the higher the adolescent is on the Need scale, the greater the likelihood of engaging in substance use (p < .05). Further, results indicated that cigarette smoking, drinking alcohol, and smoking marijuana are associated with significantly higher scores on the Need scale for both males and females. Although the Need scale was significantly positively correlated with the Children's Depression Inventory (r = .45, p = .0001), the two feeling states were not collinear. However, the Need scale was not significantly correlated with age, indicating that the need state is not simply a developmental process (r = .04, p = .11). The results suggest that a feeling state of unfulfilled needs may propel adolescents into the destructive behavior of substance use. A state of high wants and needs that cannot be gratified simply in a complex society may be a precursor of substance use.

Effects of classically differentiated supplementary feedback cues on tracking skill.

Although previous studies had shown that classical predifferentiation of green (CS-j and red (CS+) cues enabled them to facilitate tracking performance when used as supplementary indicators of correct and incorrect responses respectively, the studies were inconclusive concerning specific conditional properties versus nonspecific arousal consequences of the cues. A sample of 108 Ss was exposed to the same predifferentiation procedure, but then were subgrouped in terms of the kind of feedback signal received in tracking (no signal, red only, green only, both signals). A nonspecificity theory predicts subgroup equality of tracking performances while specificity theory predicts the dependence of performance level on the kind of signal received. Results corroborated previous findings and the view that tracking effects were reasonably attributable to the transfer of specific stimulus functions generated in the differentiation trials.