Application of a Microcalorimetric Method for Determining Drug Susceptibility in Mycobacterium Species

Abstract

Mycobacterium tuberculosis is a global public health concern, particularly with the emergence of drug-resistant strains. Immediate identification of drug-resistant strains is crucial to administering appropriate treatment before the bacteria are allowed to spread. However, developing countries, which are most affected by drug resistance, are struggling to combat the disease without the facilities or funds for expensive diagnostics. Recent studies have emphasized the suitability of isothermal microcalorimetry (IMC) for the rapid detection of mycobacteria. In this study, we investigate its suitability for rapid and reliable M. tuberculosis drug susceptibility testing. Specifically, IMC was used to determine the MICs of three drugs, namely, isoniazid, ethambutol, and moxifloxacin, against three mycobacteria, namely, Mycobacterium smegmatis, Mycobacterium avium, and Mycobacterium tuberculosis. The Richards growth model was used to calculate growth parameters, namely, the maximum bacterial growth rate and the lag phase duration from integrated heat flow-versus-time results. For example, MICs of isoniazid, ethambutol, and moxifloxacin were determined to be 1.00, 8.00, and 0.25 g/ml, respectively. IMC, as described here, could be used not just in industrialized countries but also in developing countries because inexpensive and sensitive microcalorimeters are now available. Drug-resistant strains of Mycobacterium tuberculosis are becoming increasingly widespread, creating a global health concern and making the treatment of tuberculosis even more difficult. Most of the cases reported in 2009 were in European countries and South Africa. However, it is likely that the occurrence of multidrug-resistant M. tuberculosis (MDR-TB), which is defined as a strain of M. tuberculosis that is resistant to both isoniazid and rifampin, is greatly underestimated in developing countries because the diagnosis is difficult and expensive (28). Direct identification of MDR-TB requires exposing an M. tuberculosis specimen to antibiotics to which it might be resistant at a series of concentrations and assessing the effects on growth-i.e., determining whether the MIC is abnormally high. In addition to M. tuberculosis, the incidence of infections caused by mycobacteria other than M. tuberculosis (MOTT) is continuously increasing, with Mycobacterium abscessus being the most pathogenic fast-growing mycobacterium (17,18,26). However, most MOTT infections have been overlooked, drug susceptibility test results are inconsistent, and some MOTT still need study to determine effective treatment (27). The determination of MICs for M. tuberculosis and MOTT by standard means is labor-intensive and/or expensive and can produce ambiguous results (11,24). Using the proportion method to determine drug susceptibility of an M. tuberculosis specimen (potentially MDR-TB) entails inoculating plates with various concentrations of each antibiotic and waiting up to 6 weeks for visible colonies to be formed. Results of tetrazolium salt assays can fluctuate depending on ...

Accurate and early diagnosis of orthopedic device‐related infection by microbial heat production and sonication

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Novel microcalorimetric assay for antibacterial activity of implant coatings: The cases of silver‐doped hydroxyapatite and calcium hydroxide

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Activities of Fluconazole, Caspofungin, Anidulafungin, and Amphotericin B on Planktonic and Biofilm Candida Species Determined by Microcalorimetry

“…Isothermal microcalorimetry refers to heat measurement under a constant temperature, which has high sensitivity (in the microwatt range) and allows real-time monitoring of heat production (24). In several studies, microcalorimetry was used to study the metabolic activities and drug susceptibilities of bacteria, mycobacteria, pro-tozoa, schistosomas, and fungi (yeasts and molds) (25)(26)(27)(28)(29)(30)(31)(32).…”