Effects of interactions of antibacterial drugs with each other and with 6-mercaptopurine on in vitro growth of Mycobacterium avium subspecies paratuberculosis

Abstract

Objectives: 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). Methods:The drug interaction effects on nine human isolates of MAP were determined by the chequerboard method adapted for the BACTEC TM MGIT TM 960 culture system and by calculation of the fractional inhibitory concentration index (FICI) for drug combinations.Results: Synergism (FICI 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.Conclusions: 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.

Vitamins A & D Inhibit the Growth of Mycobacteria in Radiometric Culture

“…For example, we [17], [18], [20]–[22], [30], [31], and others [34], [35], have shown inhibition of MAP growth with medications used to treat “autoimmune” and “inflammatory” diseases. In the present study we show direct inhibition of mycobacterial growth by vitamins A and D in culture.…”

Profound remission in Crohn’s disease requiring no further treatment for 3–23 years: a case series

“…However, one difference between MAP and the MTB complex is that MAP doesn't lead to deterioration when immunosuppressives are given, just one of the different characteristics between atypical (avium) mycobacteria and MTB complex. A proposition, based on multiple studies, is that immunosuppressives actually work in CD by their secondary antibiotic action on MAP [36][37][38]. Interestingly, anti-TNF α agents have been shown to reduce Mycobacterial survivability and may be a key reason why they work well with AMAT to accelerate healing [39], especially that of Crohn's fistulae [26].…”

Anaerobic adaptation of Mycobacterium avium subspecies paratuberculosis in vitro: similarities to M. tuberculosis and differential susceptibility to antibiotics

“…Unfortunately, the most sensitive of the methods used for MAP susceptibility testing, the BACTEC 460 system, is no longer commercially supported nor are consumables available, which in particular negatively impacts assessment of bacteriostatic drugs. Secondly, a number of investigators have demonstrated dose-dependent inhibition of MAP in culture by a number of anti-inflammatory drugs including methotrexate and 6-mercaptopurine [37–44]. As a result, Greenstein et al postulated that treatment of patients with inflammatory bowel disease with methotrexate and 6-mercaptopurine may result in inhibition of MAP and secondarily a decrease in pro-inflammatory cytokines [42].…”