Omadacycline drug susceptibility testing for non-tuberculous mycobacteria using oxyrase to overcome challenges with drug degradation.

BACKGROUND: Drug susceptibility testing (DST) protocol of omadacycline against non-tuberculous mycobacteria has not yet been established. We developed a method to accurately determine MIC omadacycline MIC against Mycobacterium abscessus (Mab), Mycobacterium avium-complex (MAC), and Mycobacterium kansasii (Mkn). METHODS: First, we identified the oxyrase concentration not affecting Mab, MAC, and Mkn growth followed by omadacycline MIC experiments with and without oxyrase using reference and clinical strains. RESULTS: Oxyrase 0.5 % (v/v) stabilized omadacycline in the culture medium. The median omadacycline MIC was 1 mg/L for Mab and 8 mg/L for Mkn. For MAC, the median omadacycline MIC was 2 mg/L for M. avium, 256 mg/L for M. intracellulare, and 4 mg/L for M. chimaera (p < 0.0001). Wilcoxon matched-pairs signed rank test revealed statistically lower MICs with oxyrase for all MAC subspecies (p < 0.0001), all Mab subspecies (p < 0.0001), and Mkn (p = 0.0002). The decrease in MICs with oxyrase was 17/18 of Mab, 14/19 of Mkn, 8/8 of M. avium, 4/5 M. chimera, but only 11/18 of M. intracellulare (p < 0.013). CONCLUSION: Use of 0.5 % oxyrase could be a potential solution to reliable and reproducible omadacycline MIC of Mab. However, oxyrase demonstrated a variable effect in reducing MICs against MAC and Mkn.

The hemerythrin-like diiron protein from Mycobacterium kansasii is a nitric oxide peroxidase.

The hemerythrin-like protein from Mycobacterium kansasii (Mka HLP) is a member of a distinct class of oxo-bridged diiron proteins that are found only in mycobacterial species that cause respiratory disorders in humans. Because it had been shown to exhibit weak catalase activity and a change in absorbance on exposure to nitric oxide (NO), the reactivity of Mka HLP toward NO was examined under a variety of conditions. Under anaerobic conditions, we found that NO was converted to nitrite (NO2-) via an intermediate, which absorbed light at 520 nm. Under aerobic conditions NO was converted to nitrate (NO3-). In each of these two cases, the maximum amount of nitrite or nitrate formed was at best stoichiometric with the concentration of Mka HLP. When incubated with NO and H2O2, we observed NO peroxidase activity yielding nitrite and water as reaction products. Steady-state kinetic analysis of NO consumption during this reaction yielded a Km for NO of 0.44 µM and a kcat/Km of 2.3 × 105 M-1s-1. This high affinity for NO is consistent with a physiological role for Mka HLP in deterring nitrosative stress. This is the first example of a peroxidase that uses an oxo-bridged diiron center and a rare example of a peroxidase utilizing NO as an electron donor and cosubstrate. This activity provides a mechanism by which the infectious Mycobacterium may combat against the cocktail of NO and superoxide (O2•-) generated by macrophages to defend against bacteria, as well as to produce NO2- to adapt to hypoxic conditions.

MKAN27435 is required for the biosynthesis of higher subclasses of lipooligosaccharides in Mycobacterium kansasii.

Lipooligosaccharides are glycolipids found in the cell wall of many mycobacterial species including the opportunistic pathogen Mycobacterium kansasii. The genome of M. kansasii ATCC12478 contains a cluster with genes orthologous to Mycobacterium marinum LOS biosynthesis genes. To initiate a genetic dissection of this cluster and demonstrate its role in LOS biosynthesis in M. kansasii, we chose MKAN27435, a gene encoding a putative glycosyltransferase. Using Specialized Transduction, a phage-based gene knockout tool previously used to generate null mutants in other mycobacteria, we generated a MKAN27435 null mutant. The mutant strain was found to be defective in the biosynthesis of higher LOS subspecies, viz LOS-IV, LOS-V, LOS-VI and LOS-VII. Additionally, a range of low abundance species were detected in the mutant strain and mass spectroscopic analysis indicated that these were shunt products generated from LOS-III by the addition of up to six molecules of a pentose.

N-substituted 2-isonicotinoylhydrazinecarboxamides--new antimycobacterial active molecules.

This report presents a new modification of the isoniazid (INH) structure linked with different anilines via a carbonyl group obtained by two synthetic procedures and with N-substituted 5-(pyridine-4-yl)-1,3,4-oxadiazole-2-amines prepared by their cyclisation. All synthesised derivatives were characterised by IR, NMR, MS and elemental analyses and were evaluated in vitro for their antimycobacterial activity against Mycobacterium tuberculosis H37Rv, Mycobacterium avium 330/88, Mycobacterium kansasii 235/80 and one clinical isolated strain of M. kansasii 6509/96. 2-Isonicotinoyl-N-(4-octylphenyl)hydrazinecarboxamide displayed an in vitro efficacy comparable to that of INH for M. tuberculosis with minimum inhibitory concentrations (MICs) of 1-2 µM. Among the halogenated derivatives, the best anti-tuberculosis activity was found for 2-isonicotinoyl-N-(2,4,6-trichlorophenyl)hydrazinecarboxamide (MIC=4 µM). In silico modelling on the enoyl-acyl carrier protein reductase InhA confirmed that longer alkyl substituents are advantageous for the interactions and affinity to InhA. Most of the hydrazinecarboxamides, especially those derived from 4-alkylanilines, exhibited significant activity against INH-resistant nontuberculous mycobacteria.

Mutations in the essential FAS II ß-hydroxyacyl ACP dehydratase complex confer resistance to thiacetazone in Mycobacterium tuberculosis and Mycobacterium kansasii.

It has recently been shown that the anti-mycobacterial pro-drug thiacetazone (TAC) inhibits the conversion of double bonds of mycolic acid precursors into cyclopropyl rings in Mycobacterium bovis var BCG, M. marimum and M. chelonae by affecting the cyclopropyl mycolic acid synthases (CMASs) as judged by the build-up of unsaturated mycolate precursors. In our hands, TAC inhibits mycolic acid biosynthesis in Mycobacterium tuberculosis and M. kansasii with almost negligible accumulation of those precursors. Our observations that 'de novo' biosynthesis of all the mycolic acid families decreased upon TAC treatment prompted us to analyse the role of each one of the Type II Fatty Acid Synthase (FASII) enzymes. Overexpression of the hadABC operon, encoding the essential FASII dehydratase complex, but not of any of the remaining FASII genes acting on the elongation of fatty acyl chains leading to the synthesis of meromycolic acids, resulted in high level of resistance to TAC in M. tuberculosis. Spontaneous M. tuberculosis and M. kansasii TAC-resistant mutants isolated during this work revealed mutations in the hadABC genes strongly supporting our proposal that these enzymes are new players in the resistance to this anti-mycobacterial compound.

Reduced pyrazinamidase activity and the natural resistance of Mycobacterium kansasii to the antituberculosis drug pyrazinamide.

Pyrazinamide (PZA), an analog of nicotinamide, is a prodrug that requires conversion to the bactericidal compound pyrazinoic acid (POA) by the bacterial pyrazinamidase (PZase) activity of nicotinamidase to show activity against Mycobacterium tuberculosis. Mutations leading to a loss of PZase activity cause PZA resistance in M. tuberculosis. M. kansasii is naturally resistant to PZA and has reduced PZase activity along with an apparently detectable nicotinamidase activity. The role of the reduction in PZase activity in the natural PZA resistance of M. kansasii is unknown. The MICs of PZA and POA for M. kansasii were determined to be 500 and 125 micrograms/ml, respectively. Using [14C]PZA and [14C]nicotinamide, we found that M. kansasii had about 5-fold-less PZase activity and about 25-fold-less nicotinamidase activity than M. tuberculosis. The M. kansasii pncA gene was cloned on a 1.8-kb BamHI DNA fragment, using M. avium pncA probe. Sequence analysis showed that the M. kansasii pncA gene encoded a protein with homology to its counterparts from M. tuberculosis (69.9%), M. avium (65.6%), and Escherichia coli (28.5%). Transformation of naturally PZA-resistant M. bovis BCG with M. kansasii pncA conferred partial PZA susceptibility. Transformation of M. kansasii with M. avium pncA caused functional expression of PZase and high-level susceptibility to PZA, indicating that the natural PZA resistance in M. kansasii results from a reduced PZase activity. Like M. tuberculosis, M. kansasii accumulated POA in the cells at an acidic pH; however, due to its highly active POA efflux pump, the naturally PZA-resistant species M. smegmatis did not. These findings suggest the existence of a weak POA efflux mechanism in M. kansasii.

Beta-lactamases of Mycobacterium tuberculosis and Mycobacterium kansasii.

Re-emergence of infectious diseases caused by mycobacteria as well as the emergence of multiresistant strains of Mycobacterium has promoted the research on the use of beta-lactames in the treatment of such diseases. Mycobacteria produce beta-lactamases: M. tuberculosis produces a wide-spectrum beta-lactamase whose behaviour mimicks those of Gram-negative bacteria. M. kansasii produces also beta-lactamase which can be inhibited by clavulanic acid. An overview on beta-lactamases from both species is reported.