Widespread Pyrazinamide-Resistant Mycobacterium tuberculosis Family in a Low-Incidence Setting

Abstract

An unusually high prevalence of pyrazinamide (PZA) monoresistance in Mycobacterium tuberculosis has been observed in Quebec. In the absence of a recognized outbreak, we hypothesized that these isolates most likely represented reactivation of an old endemic strain in this low-incidence area. A case-control study of 77 PZAresistant isolates with a specific Quebec mutation and 253 PZA-susceptible control M. tuberculosis isolates was undertaken. By molecular analysis, all 77 case isolates shared a unique mutation profile in the pncA gene which was not present in control isolates. While control isolates manifested diverse IS6110 restriction fragment length polymorphism (RFLP) patterns, spoligotypes, and major genetic groups, case isolates had similar but nonidentical IS6110 RFLP patterns, had common spoligotypes, and were confined to one major genetic group, suggesting a common clonal ancestor. By epidemiologic and geographic analyses, however, there were no significant differences between the cases and the controls. We conclude that a clonally related family of PZAmonoresistant M. tuberculosis isolates in Quebec represents historic rather than recent transmission.

Pharmacokinetics-Pharmacodynamics of Pyrazinamide in a Novel In Vitro Model of Tuberculosis for Sterilizing Effect: a Paradigm for Faster Assessment of New Antituberculosis Drugs

“…Daily doses higher than 60 mg/kg in children and 4 g in adults were more successful in achieving the exposures associated with optimal sterilization in larger proportions of patients. The higher doses have the extra advantage in that with a daily dose schedule, they are also optimized to minimize the emergence of drug resistance, given that pyrazinamide monoresistance is being reported in diverse parts of the world (11,42,51). Unfortunately, pyrazinamide doses of Ͼ40 mg/kg have been associated with higher rates of toxicity when they were used in the past.…”

Genomic Characterization of an EndemicMycobacterium tuberculosisStrain: Evolutionary and Epidemiologic Implications

“…Conversely, matched IS6110 RFLP patterns have been inferred to occur due to reactivation in certain low incidence settings, although it has often been difficult to confidently exclude some degree of ongoing transmission (6,10,46). On the basis of our previous data showing no more evidence of transmission with our strain than with random controls, we now have a setting that permits a more thorough investigation of the impact of established endemic strains in molecular epidemiologic studies (28).…”

“…In Quebec, Canada, we have characterized a prevalent pyrazinamide (PZA) monoresistant M. tuberculosis family based on a distinct mutation profile in the pncA gene (28). The epidemiologic profile of pncA mutant cases and randomly sampled Canadian-born controls was reported previously and provided strong evidence against recent epidemic spread.…”

“…M. tuberculosis DNA was extracted from clinical isolates by standardized methods, and all study isolates were characterized by the following tests. The "Quebec" mutation profile in the pncA gene-an 8-bp deletion (ATGGCTTG at position 446) and point mutation (C to A) at position 418-was identified by PCR-restriction fragment length polymorphism (RFLP) as described previously (28). IS6110 RFLP by Southern blot was performed by standardized methods (41).…”

“…PZA resistance was defined as an MIC of Ͼ100 mg/liter and was confirmed with the pyrazinamidase activity assay (45). Additional biochemical and genetic tests were performed to exclude M. bovis as previously described (28).…”