Comparison of three methods for susceptibility testing of Mycobacterium avium subsp. paratuberculosis to 11 antimicrobial drugs

Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI 53706-110, USA.
Journal of Antimicrobial Chemotherapy (Impact Factor: 5.31). 06/2009; 64(2):310-6. DOI: 10.1093/jac/dkp184
Source: PubMed


To evaluate the BACTEC(TM) MGIT(TM) 960/MGIT Para TB (MGIT) system for drug susceptibility testing of Mycobacterium avium subsp. paratuberculosis (MAP), a pathogen implicated in some forms of Crohn's disease.
MICs of 11 drugs for 10 MAP strains were determined using the MGIT system, the BACTEC(TM)460TB system (BACTEC) and conventional agar dilution methods.
MICs determined by MGIT methods showed 80%-100% agreement (+/-1 log(2) dilution) with those determined by the BACTEC and agar dilution methods for ciprofloxacin, levofloxacin, azithromycin and clofazimine. The MGIT and BACTEC methods showed 70%, 80% and 90% agreement (+/-1 log(2) dilution) for MICs of ethambutol, rifabutin and rifampicin; agreement for all drugs increased to 100% at 2 log(2) dilution differences. For clarithromycin, the MGIT method had greater agreement with the agar dilution method (70% at the same dilution) than the BACTEC method (60% at +/-1 log(2) dilution); agreement increased to 100% at +/-2 log(2) dilutions in both cases. The MGIT and agar dilution methods agreed 60% and 100% for amikacin MICs at +/-1 log(2) dilution and +/-2 log(2) dilutions, respectively. By all methods MICs were higher than achievable serum concentrations for isoniazid and dapsone. There was 100% agreement between all three methods for azithromycin, clarithromycin and ciprofloxacin, and 80% agreement for rifampicin using published MIC thresholds available for M. avium complex strains.
This study shows that the MGIT system can be used for rapid and reliable drug susceptibility testing of MAP.

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    • "The economic losses due to reduced production in cattle and sheep as a result of chronic wasting are not just limited to developing nations but also impact developed economies (Bush et al., 2008; Gonda et al., 2007; Sohal et al., 2009; Windsor, 2006). This, coupled with reports of a potential threat to public health due to the association of MAP with Crohn's disease, has resulted in an invigorated interest in understanding its pathogenesis (Greenstein and Collins, 2004; Krishnan et al., 2009; Vankruiningen et al., 1991). "
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    ABSTRACT: Johne's disease (JD) is a chronic disease affecting ruminants and other species caused by the pathogenic mycobacterium, Mycobacterium avium subsp. paratuberculosis (MAP). MAP has developed a multitude of mechanisms to persist within the host, and these in turn are counteracted by the host through various immune pathways. Identifying and characterising the different strategies employed by MAP to alter the host immune system in its favour, and thereby persist intracellularly, could hold the key to developing strategies to fight this disease. In this study we analysed a subset of bovine microarray data derived from early time points after experimental infection with MAP. A specifically developed integrated approach was used to identify and validate host genes involved in cholesterol homeostasis (24DHCR, LDLR, SCD-1), calcium homeostasis and anti-bacterial defence mechanisms, (CD38, GIMAP6) which were downregulated in response to MAP exposure. A trend for upregulation of granulysin gene expression in MAP-exposed cattle in comparison to unexposed cattle was also observed. From these analyses, a model of potential pathogen-host interactions involving these novel pathways was developed which indicates an important role for host lipids in mycobacterial survival and persistence.
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    ABSTRACT: Mycobacterium avium subspecies paratuberculosis (MAP) has been targeted for treatment with clarithromycin and rifamycin derivatives in numerous cases of Crohn's disease (CD). 6-Mercaptopurine and its pro-drug azathioprine are widely used as immunomodulators in the treatment of CD and have recently been shown to have anti-MAP activity in vitro. The objectives of the study were to evaluate the in vitro effects on MAP of (i) 6-mercaptopurine when combined with each of eight conventional antibacterial agents with in vitro anti-MAP activity and (ii) antibacterial combinations consisting of two drugs (clarithromycin combined with amikacin, rifampicin, ciprofloxacin or ethambutol) and three drugs (clarithromycin, rifabutin and clofazimine). The drug interaction effects on nine human isolates of MAP were determined by the chequerboard method adapted for the BACTECMGIT960 culture system and by calculation of the fractional inhibitory concentration index (FICI) for drug combinations. Synergism (FICI < or = 0.5) was observed between 6-mercaptopurine and azithromycin (seven isolates), clarithromycin, rifampicin, rifabutin (four isolates each) and ethambutol (two isolates). 6-Mercaptopurine was not antagonistic with any of the antibacterial agents tested. Among the combinations of two and three antibacterials tested, the clarithromycin/rifampicin combination was synergistic against four isolates, while all other combinations showed no interaction. This in vitro study suggests that 6-mercaptopurine may be synergistic with macrolides and rifamycin derivatives against MAP. The activity of clarithromycin against MAP seems to be enhanced by rifampicin.
    Preview · Article · Sep 2009 · Journal of Antimicrobial Chemotherapy
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