Concluding Remarks
Since the 2010 iteration of this book, only 250 studies have been published with ‘Mycobacterium paratuberculosis drug susceptibility testing' included in the PubMed Central search terms; in contrast, ‘Mycobacterium tuberculosis drug susceptibility testing' returned 8296 hits at the time of writing.
It is therefore not surprising that we have yet to establish anti- MAP regimens either from pre-existing TB drugs or novel drug discovery efforts. Fortunately, progress has been made since the publication of the landmark article by Crohn, Ginzburg and Oppenheimer in 1932 (Crohn et al., 1932). Modified media for culturing MAP has been validated by Sung and Collins in 2007, improving TTD. Consequently, RedHill Biopharma formulated a triple antibiotic regimen with CLA, CLO and RIF, and evaluated its potency in vitro against MAP while taking advantage of the BD BACTEC™ MGIT™ Para-TB system previously validated. Preliminary results that have been released by RedHill Biopharma suggest that RHB-104 is the first therapy to provide long-term benefit to patients with Crohn's disease. Previous clinical trial data only supported short-term benefit from antimycobac- terial therapy and lacked microbial specificity (Behr and Kapur, 2008). It is known from metaanalyses that Crohn's disease patients given antibiotics improved their condition better than placebo control groups (Rahimi et al., 2006; Feller et al., 2007; Khan et al., 2011; Davis et al., 2017). Regrettably, most clinical trials examined Crohn's disease therapy outcomes on patients unconfirmed for MAP and, therefore, efficacy of the therapy towards MAP infection could not be concluded. In an Expert Review in Gastroenterology and Hepatology article by Davis et al. in 2017, the importance of evaluating the efficacy of all current and experimental antimy- cobacterial agents against MAP in vitro before designing future trials to supplement previous clinical trial findings was emphasized.Other groups have taken an interest in developing anti-MAP therapies by expanding the search through non-specific mycobacterial chemical space. In other words, targeting MAP with general antimicrobial compounds. Some approaches have yet to produce promising results, while others are gaining traction. For example, disrupting iron homeostasis with metal ion mimic gallium proved to be unsuccessful according to Fecteau and colleagues. In addition, the piperazine backbone, recognized in antihelminth medication, failed to elicit strong anti-MAP activity as demonstrated by Gonec et al. (2017). The most recent drug discovery effort towards MAP came from Pavic et al. (2018) when they repurposed the antimalarial drug primaquine for MAP. Not only did the primaquine series display activity against MAP in their study, but select compounds in the urea and bis-urea primaquine series were also active against M. tuberculosis and clinical isolates of M. avium complex. Nevertheless, novel antimicrobials must pass the rigorous trials of therapy development. First, development must begin with in vitro DST and progress to ex vivo and∕or animal model studies. Lastly, candidate therapies must demonstrate benefit in human clinical trials.
Perhaps the most direct route to establishing DST and discovering antimicrobials for MAP is through the approaches used for the study of M. avium. While working with MAP may be more challenging than M. avium, due to its slow and fastidious growth, the CLSI has provided recommendations for DST methods of other fastidious NTM, such as M. haemophilum (CLSI, 2011). An agar disc elution protocol is available through the CLSI manual.3 One could envision repurposing antibiotics commonly used for M. avium infections for MAP. Moreover, success with repurposed antibiotics against MAP may indicate the necessity for multi-drug regimens in the future.
The fields of veterinary and human medicine have made substantial contributions towards in vitro DST and antimicrobial development for MAP.
One of the critical factors in establishing DST is method validation and laboratory accreditation. A key contribution to MAP DST could be defined MAP mutants with known resistance phenotypes for distribution to clinical microbiology labs and reference centres. Such strains could provide a reference point for labs and assays to determine susceptibility vs resistance. Without appropriate controls, DST results are of uncertain significance and, by extension, have unknown capacity to predict clinical outcomes in veterinary and human medicine. Absence of reliable DST methods is expected to hinder efforts to identify new compounds with anti- MAP activity, further reinforcing the notion that there is a limited role for antimicrobials in the management of MAP infections.Notes
1 N.B. There are no macrophage or pre-clinical model data to substantiate the in vitro efficacy as RHB- 104 is three pre-existing tuberculosis drugs repurposed for MAP infection.
2 Trial is stated to finish October 2019.
3 N.B. This is a non-standardized method recommended by the CLSI.
References
Alcedo, K.P., Thanigachalam, S. and Naser, S.A. (2016) RHB-104 triple antibiotics combination in culture is bactericidal and should be effective for treatment of Crohn's disease associated with Mycobacterium paratuberculosis. Gut Pathogens 8(1). DOI: 10.1186/s13099-016-0115-3.
Andriole, V.T. (2005) The quinolones: past, present, and future. Clinical Infectious Diseases 41(Suppl. 2), S113-S119. DOI: 10.1086/428051.
Automated Blood Culture System (2014) NEWSLETTER Best Practices in Blood Culture Collection Fluorescent Technology in the BD BACTEC™. Available at: www.bmsd.com.my (accessed 9 July 2019).
Beckler, D.R., Elwasila, S., Ghobrial, G., Valentine, J.F. and Naser, S.A. (2008) Correlation between rpoB gene mutation in Mycobacterium avium subspecies paratuberculosis and clinical rifabutin and rifampicin resistance for treatment of Crohn's disease.
World Journal of Gastroenterology 14(17), 2723-2730. DOI: 10.3748∕wjg.14.2723.Behr, M.A. and Kapur, V. (2008) The evidence for Mycobacterium paratuberculosis in Crohn’s disease. Current Opinion in Gastroenterology 24(1), 17-21. DOI: 10.1097∕MOG.0b013e3282f1dcc4.
Borody, T.J., Leis, S., Warren, E.F. and Surace, R. (2002) Treatment of severe Crohn's disease using anti- mycobacterial triple therapy — approaching a cure? Digestive and Liver Disease 34(1), 29-38. DOI: 10.1016∕S1590-8658(02)80056-1.
Chamberlin, W., Borody, T. and Naser, S. (2007a) MAP-associated Crohn's disease map, Koch's postulates, causality and Crohn's disease. Digestive and Liver Disease 39(8), 792-794. DOI: 10.1016/j. dld.2007.05.012.
Chamberlin, W., Ghobrial, G., Chehtane, M. and Naser, S.A. (2007b) Successful treatment of a Crohn's disease patient infected with bacteremic Mycobacterium paratuberculosis. The American Journal of Gastroenterology 102(3), 689-691. DOI: 10.1111/j.1572-0241.2007.01040_7.x.
CLSI (2011) Appendix J. agar disk elution method for Mycobacterium haemophilum: susceptibility testing of mycobacteria, Nocardia spp., and other aerobic actinomycetes. Available at: www.clsi.org (accessed 27 November 2019).
Crohn, B.B., Ginzburg, L., Oppenheimer, G.D. and Ilietis, R. (1932) Regional ileitis. Journal of the American Medical Association 99(16), 1323. DOI: 10.1001∕jama.1932.02740680019005.
Davis, W.C., Kuenstner, J.T. and Singh, S.V. (2017) Resolution of Crohn's (Johne's) disease with antibiotics: what are the next steps? Expert Review of Gastroenterology & Hepatology 11(5), 393-396. DOI: 10.1080/17474124.2017.1300529.
Desmond, E., Woods, G.L., Brown-Elliott, B.A., Hall, G.S. and Conville, P.S. (2011) Susceptibility testing of mycobacteria, nocardiae and other aerobic actinomycetes. In: Susceptibility Testing of Mycobacteria, Nocardiae, and Other Aerobic Actinomycetes, Nocardiae and other aerobic actinomycetes, 2. Clinical and Laboratory Standards Institute, Wayne, Pennsylvania.
Fecteau, M.-E., Fyock, T.L., McAdams, S.C., Boston, R.C., Whitlock, R.H. et al. (2011a) Evaluation of the in vitro activity of gallium nitrate against Mycobacterium avium subsp paratuberculosis. American Journal of Veterinary Research 72(9), 1243-1246. DOI: 10.2460∕ajvr.72.9.1243.
Fecteau, M.-E., Whitlock, R.H., Fyock, T.L., McAdams, S.C., Boston, R.C. et al. (2011b) Antimicrobial activity of gallium nitrate against Mycobacterium avium subsp. paratuberculosis in neonatal calves. Journal of Veterinary Internal Medicine 25(5), 1152-1155. DOI: 10.1111∕j.1939-1676.2011.0768.x.
Fecteau, M.-E., Aceto, H.W., Bernstein, L.R. and Sweeney, R.W. (2014) Comparison of the antimicrobial activities of gallium nitrate and gallium maltolate against Mycobacterium avium subsp. paratuberculosis in vitro. The Veterinary Journal 202(1), 195-197. DOI: 10.1016∕j.tvjl.2014.06.023.
Feller, M., Huwiler, K., Stephan, R., Altpeter, E., Shang, A. et al. (2007) Mycobacterium avium subspecies paratuberculosis and Crohn's disease: a systematic review and meta-analysis. The Lancet Infectious Diseases 7(9), 607-613. DOI: 10.1016∕S1473-3099(07)70211-6.
Fredricks, D.N. and Relman, D.A. (1996) Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates. Clinical Microbiology Reviews 9(1), 18-33. DOI: 10.1128/ CMR.9.1.18.
Gisbert, J.P. and Panes, J. (2009) Loss of response and requirement of infliximab dose intensification in Crohn's disease: a review. The American Journal of Gastroenterology 104(3), 760-767. DOI: 10.1038/ ajg.2008.88.
Gonec, T., Malik, I., Csollei, J., Jampilek, J., Stolarikova, J. et al. (2017) Synthesis and in vitro anti- mycobacterial activity of novel N-Arylpiperazines containing an Ethane-1,2-diyl connecting chain. Molecules 22(12), 2100. DOI: 10.3390∕molecules22122100.
Kahlmeter, G. (2019) Gunnar Kahlmeter and the EUCAST Steering Committee. Redefining susceptibility testing categories S, I and R.
Available at: www.eucast.org (accessed 9 August 2019).Khan, K.J., Ullman, T.A., Ford, A.C., Abreu, M.T., Abadir, A. et al. (2011) Antibiotic therapy in inflammatory bowel disease: a systematic review and meta-analysis. American Journal of Gastroenterology 106(4), 661-673. DOI: 10.1038∕ajg.2011.72.
Kim, S.J. (2005) Drug-susceptibility testing in tuberculosis: methods and reliability of results. European Respiratory Journal 25(3), 564-569. DOI: 10.1183∕09031936.05.00111304.
Kuenstner, J.T., Naser, S., Chamberlin, W., Borody, T., Graham, D.Y. et al. (2017) The consensus from the Mycobacterium avium ssp. paratuberculosis (MAP) conference 2017. Frontiers in Public Health 5(208). DOI: 10.3389∕fpubh.2017.00208.
Lew, W., Pai, M., Oxlade, O., Martin, D. and Menzies, D. (2008) Initial drug resistance and tuberculosis treatment outcomes: systematic review and meta-analysis. Annals of Internal Medicine 149(2), 123134. Available at: http√∕www.embase.com∕search∕results7subaction=viewrecordSfrom=exportSid= L352008599 DOI: 10.7326∕0003-4819-149-2-200807150-00008.
Lin, W., Mandal, S., Degen, D., Liu, Y., Ebright, Y.W. et al. (2017) Structural basis of Mycobacterium tuberculosis transcription and transcription inhibition. Molecular Cell 66(2), 169-179. DOI: 10.1016∕j. molcel.2017.03.001.
Lougheed, K.E.A., Taylor, D.L., Osborne, S.A., Bryans, J.S. and Buxton, R.S. (2009) New anti-tuberculosis agents amongst known drugs. Tuberculosis 89(5), 364-370. DOI: 10.1016∕j.tube.2009.07.002.
Monif, G.R.G. (2018) Understanding therapeutic concepts in Crohn's disease. Clinical Medicine Insights: Gastroenterology 11, 117955221881516. DOI: 10.1177∕1179552218815169.
Necchi, F., Saul, A. and Rondini, S. (2018) Setup of luminescence-based serum bactericidal assay against Salmonella paratyphi a. Journal of Immunological Methods 461, 117-121. DOI: 10.1016∕j. jim.2018.06.025.
Niles, A.L., Moravec, R.A. and Riss, T.L. (2008) Update on in vitro cytotoxicity assays for drug development. Expert Opinion on Drug Discovery 3(6), 655-669. DOI: 10.1517∕17460441.3.6.655.
Oken, H.A., Saleeb, P.G., Redfield, R.R. and Schimpff, S.C. (2017) Is Mycobacterium avium paratuberculosis the trigger in the Crohn's disease spectrum? Open Forum Infectious Diseases 4(3), 1-3. DOI: 10.1093∕ofid∕ofx104.
Pavic, K., Perkovic, I., Pospisilova, Sarka., Machado, M., Fontinha, D. et al. (2018) Primaquine hybrids as promising antimycobacterial and antimalarial agents. European Journal of Medicinal Chemistry 143, 769-779. DOI: 10.1016∕j.ejmech.2017.11.083.
Rahimi, R., Nikfar, S., Rezaie, A. and Abdollahi, M. (2006) A meta-analysis of broad-spectrum antibiotic therapy in patients with active Crohn's disease. Clinical Therapeutics 28(12), 1983-1988. DOI: 10.1016∕j.clinthera.2006.12.012.
Savarino, E., Bertani, L., Ceccarelli, L., Bodini, G., Zingone, F. et al. (2019) Antimicrobial treatment with the fixed-dose antibiotic combination RHB-104 for Mycobacterium avium subspecies paratuberculosis in Crohn's disease: pharmacological and clinical implications. Expert Opinion on Biological Therapy 19(2), 79-88. DOI: 10.1080/14712598.2019.1561852.
Selby, W., Pavli, P., Crotty, B., Florin, T., Radford-Smith, G. et al. (2007) Two-year combination antibiotic therapy with clarithromycin, rifabutin, and clofazimine for Crohn's disease. Gastroenterology 132(7), 2313-2319. DOI: 10.1053∕j.gastro.2007.03.031.
Sung, J.S., Jun, H.H., Manning, E.J.B. and Collins, M.T. (2007) Rapid and reliable method for quantification of Mycobacterium paratuberculosis by use of the BACTEC MGIT 960 system. Journal of Clinical Microbiology 45(6), 1941-1948.
Tallarida, R.J. (2011) Quantitative methods for assessing drug synergism. Genes & Cancer 2(11), 10031008. DOI: 10.1177/1947601912440575.
Zarei-Kordshouli, F., Geramizadeh, B. and Khodakaram-Tafti, A. (2019) Prevalence of Mycobacterium avium subspecies paratuberculosis IS 900 DNA in biopsy tissues from patients with Crohn's disease: histopathological and molecular comparison with Johne's disease in Fars province of Iran. BMC Infectious Diseases 19(1). DOI: 10.1186∕s12879-018-3619-2.
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