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The increasing emergence of drug-resistant Mycobacterium tuberculosis poses significant threat to the treatment of tuberculosis. Conventional susceptibility testing for the front-line tuberculosis drug pyrazinamide (PZA) is difficult, because of the requirement for acid pH for the drug to show activity. Resistance to PZA in M. tuberculosis is caused by mutations in the pncA gene, and detection of pncA mutations can be an indicator of PZA resistance. In this study, we examined the feasibility of a microarray-based approach exploiting short overlapping oligonucleotides (sliding-frame array) to rapidly detect pncA mutations (substitutions, deletions, and insertions) in multiple strains of PZA-resistant M. tuberculosis. The genetic mapping of these mutations is necessary to link the gene sequence to the protein function defined by mutant phenotype. Microarray analysis was performed in a blind manner using 57 isolates of M. tuberculosis for which the sequence of the pncA gene was previously determined. Our results showed that all mutations could be unambiguously detected, suggesting that microarray can be a routine and valuable tool for rapid identification of drug-resistant M. tuberculosis isolates. We expect that mutation mapping with a sliding-frame microarray will accelerate the molecular analysis of drug-resistant M. tuberculosis bacteria and the microorganism populations.

Background: Pyrazinamide is a paradoxical frontline tuberculosis drug characterized by high in vivo steril- izing activity but poor in vitro activity. This separation in pyrazinamide activity reflects differences between the in vivo tissue environment and in vitro culture conditions. The well-known acid pH requirement for pyrazin- amide activity was discovered previously based on such reasoning but does not completely explain the discrepancy between in vivo and in vitro activity of pyrazinamide. This study examined the effect of iron, which could potentially be elevated in local inflammatory lesions, on pyrazinamide activity in vitro. Materials and methods: The effect of iron on the activity of pyrazinamide or its active derivative pyrazinoic acid against Mycobacterium tuberculosis was assessed in liquid medium in a drug exposure assay or in solid medium with pyrazinamide plus iron or pyrazinamide alone. The effect of iron on pyrazinamide or pyrazinoic acid was expressed as percentage of growth inhibition. Results: We have shown that iron enhances the activity of pyrazinamide and pyrazinoic acid against M. tuberculosis in both liquid and solid media at acid pH 5.6. Iron enhanced the activity of pyrazinoic acid but not pyrazinamide against the naturally pyrazinamide-resistant Mycobacterium bovis BCG. Other metal ions such as magnesium, calcium and zinc did not enhance the activity of pyrazinamide or pyrazinoic acid. Conclusions: Iron increased the activity of pyrazinamide or pyrazinoic acid against M. tuberculosis in vitro. These findings may have implications for the study of mechanism of action of pyrazinamide and possible iron supplement for improving the activity of pyrazinamide.

Actinobacillus pleuropneumoniae is an important pathogen of swine. Lipopolysaccharide (LPS) has been identified as the major adhesin of A. pleuropneumoniae and it is involved in adherence to porcine respiratory tract cells. We previously generated seven rough LPS mutants of A. pleuropneumoniae serotype 1 by using a mini-Tn 10 transposon mutagenesis system [Rioux S, Galarneau C, Harel J et al. Isolation and characterization of mini-Tn 10 lipopolysaccharide mutants of Actinobacillus pleuropneumoniae serotype 1. Can J Microbiol 1999; 45: 1017—1026]. The purpose of the present study was to characterize these mutants in order to learn more about LPS O-antigen biosynthesis genes and their organization in A. pleuropneumoniae, and to determine the surface properties and virulence in pigs of these isogenic mutants. By mini-Tn 10 insertions in rough mutants, four putative genes (ORF12, ORF16, ORF17, and ORF18) involved in O-antigen biosynthesis in A. pleuropneumoniae serotype 1 were found within a region of 18 ORFs. This region is homologous to the gene cluster of serotype-specific O-polysaccharide biosynthesis from A. actinomycetemcomitans strain Y4 (serotype b). Two mutants showed homology to a protein with identity to glycosyltransferases (ORF12); two others had the mini-Tn 10 insertion localized in genes encoding for two distinct proteins with identity to rhamnosyltransferases (ORF16 and ORF17) and three showed homology to a protein which is known to initiate polysaccharide synthesis (ORF18). These four ORFs were also present in A. pleuropneumoniae serotypes 9 and 11 that express an O-antigen that serologically cross-reacts with serotype 1. Evaluation of some biological properties of rough mutants seems to indicate that the absence of O-chains does not appear to have an influence on the virulence of the bacteria in pigs and on the overall surface hydrophobicity, charge and hemoglobin-binding activity, or on LAL activation. An acapsular mutant was included in the present study in order to compare the influence of O-chains and capsule polysaccharides on different cell surface properties. Our data suggest that capsular polysaccharides and not O-chains polysaccharides have a major influence on surface properties of A. pleuropneumoniae serotype 1 and its virulence in pigs.

Background Pyrazinamide is a paradoxical frontline tuberculosis drug characterized by high sterilizing in vivo activity but poor in vitro activity. Pyrazinamide is thought to act by the entrapment of pyrazinoic acid in the bacterial cell, leading to acidification and membrane damage. Consequently, the effects of weak acids and molecules affecting membranes added to pyrazinamide were studied. Objectives To examine the effects of weak acids, UV, oxidative stress and additional energy inhibitors on pyrazinamide activity in vitro against Mycobacterium tuberculosis as well as the effect of pyrazinamide on Escherichia coli ampicillin persisters. Methods Drug exposure experiments followed by cfu counts were performed to determine the effects of the above various factors on pyrazinamide activity in vitro against M. tuberculosis. Results Some weak acids such as benzoic acid, sorbic acid and propyl hydroxybenzoic acid could enhance the activity of pyrazinamide in vitro against old tubercle bacilli but not young bacilli whereas other weak acids such as salicylic acid and lactic acid did not appear to enhance pyrazinamide activity. While energy inhibitors carbonylcyanide m-chlorophenylhydrazone and dinitrophenol enhanced pyrazinamide activity for old tubercle bacilli but not young bacilli, valinomycin and KCN increased pyrazinamide activity for both young and old bacilli. Oxidative stresses due to H2O2 and menadione did not have a significant effect on pyrazinamide activity. UV, which presumably damages the membrane, enhanced the activity of pyrazinamide. Pyrazinamide, which otherwise has no activity against actively growing E. coli bacteria, could kill non-growing starved E. coli and also ampicillin-tolerant persisters. Conclusions Some weak acids, UV and various energy inhibitors were found to enhance the activity of pyrazinamide in vitro against M. tuberculosis. Pyrazinamide shows preferential activity against both M. tuberculosis and E. coli persisters over the growing forms.

Pyrazinamide is an important sterilizing drug that shortens tuberculosis (TB) therapy. However, the mechanism of action of pyrazinamide is poorly understood because of its unusual properties. Here we show that pyrazinoic acid, the active moiety of pyrazinamide, disrupted membrane energetics and inhibited membrane transport function in Mycobacterium tuberculosis. The preferential activity of pyrazinamide against old non-replicating bacilli correlated with their low membrane potential and the disruption of membrane potential by pyrazinoic acid and acid pH. Inhibitors of membrane energetics increased the antituberculous activity of pyrazinamide. These findings shed new light on the mode of action of pyrazinamide and may help in the design of new drugs that shorten therapy.