Evaluation of a low-cost calorimetric approach for rapid detection of tuberculosis and other mycobacteria in culture

Detection and Drug Susceptibility Testing of Neisseria gonorrhoeae Using Isothermal Microcalorimetry

Background: Gonorrhea is a frequently encountered sexually transmitted disease that results in urethritis and can further lead to pelvic inflammatory disease, infertility, and possibly disseminated gonococcal infections. Thus, it must be diagnosed promptly and accurately. In addition, drug susceptibility testing should be performed rapidly as well. Unfortunately, Neisseria gonorrhoea is a fastidious microorganism that is difficult to grow and requires culturing in an opaque medium. Methods: Here, we used isothermal microcalorimetry (IMC) to monitor the growth and the antimicrobial susceptibility of N. gonorrhoea. Results: Using IMC, concentrations of N. gonorrhoea between 2000 and 1 CFU·mL⁻¹ were detected within 12 to 33 h. In addition, drug susceptibility could be monitored easily. Conclusions: The use of isothermal microcalorimetry provides an interesting and useful tool to detect and characterize fastidious microbes such as N. gonorrhoea that require media incompatible with optical detection conventionally used in many commercial systems.

A Review of Methods to Determine Viability, Vitality, and Metabolic Rates in Microbiology

Viability and metabolic assays are commonly used as proxies to assess the overall metabolism of microorganisms. The variety of these assays combined with little information provided by some assay kits or online protocols often leads to mistakes or poor interpretation of the results. In addition, the use of some of these assays is restricted to simple systems (mostly pure cultures), and care must be taken in their application to environmental samples. In this review, the necessary data are compiled to understand the reactions or measurements performed in many of the assays commonly used in various aspects of microbiology. Also, their relationships to each other, as metabolism links many of these assays, resulting in correlations between measured values and parameters, are discussed. Finally, the limitations of these assays are discussed.

Crohn's disease: failure of a proprietary fluorescent in situ hybridization assay to detect M. avium subspecies paratuberculosis in archived frozen intestine from patients with Crohn's disease

Objectives

Although controversial, there is increasing concern that Crohn’s disease may be a zoonotic infectious disease consequent to a mycobacterial infection. The most plausible candidate is M. avium subspecies paratuberculosis (MAP) that is unequivocally responsible for Johne’s disease in ruminants. The purpose of this study was to evaluate a proprietary (Affymetrix™ RNA view^®) fluorescent in situ hybridization (FISH) assay for MAP RNA. Non-identifiable intestine from patients with documented Crohn’s disease was assayed according to the manufacturer’s instructions and with suggested modifications. Probes were custom designed for MAP and human β-actin (as the eukaryotic housekeeping gene) from published genomes.

Results

Repetitively, false positive signal was observed in our “No-Probe” negative control. Attempts were made to correct this according to the manufacturer’s suggestions (by modifying wash solutions, using recommended hydrochloric acid titration and different fluorescent filters). None prevented false positive signal in the “No-Probe” control. It is concluded that when performed according to manufactures instruction and with multiple variations on the manufactures recommended suggestions to correct for false positive signal, that the Affymetrix™ RNA view^® cannot be used to detect MAP in pre-frozen resected intestine of humans with Crohn’s disease.

Comparison of isothermal microcalorimetry and BACTEC MGIT960 for the detection of the metabolic activity of Mycobacterium tuberculosis in sputum samples

INTRODUCTION

This study explores the uses of microcalorimetry to detect Mycobacterium tuberculosis (TB) in sputum. Microcalorimetry measures metabolic heat evolution during cellular proliferation of tuberculosis (TB) and is considered as a possible alternative to conventional diagnostic tools.

OBJECTIVES

To compare the time to detection (TTD) from the BACTEC™ MGIT™ 960 and the calScreener™ calorimetric system.

METHODS

Sixty-four sputa samples were selected from patients with confirmed pulmonary tuberculosis. Those sample were then decontaminated and analysed using calorimetry and BACTEC MGIT 960 system.

RESULTS

The incubation period until detection of M. tuberculosis in the sample was 8·5 ± 3·7 days for the MGIT system and 10·1 ± 4·1 days (mean ± SD) for calorimetry.

CONCLUSIONS

The microincubations in the 48-well format calScreener offers potential for rapid and accurate diagnostic of TB in different samples. Although TTD from calorimetry is still longer than with the MGIT, our findings suggest that several improvements are possible. Still, the instrument is ideal for continuous, real-time analysis of net metabolic heat release of limited sample numbers.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our result emphasizes that with further optimization, calorimetry can become an alternative detection method for tuberculosis.

Failure to detect M. avium subspecies paratuberculosis in Johne's disease using a proprietary fluorescent in situ hybridization assay

Objectives

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne’s disease in ruminants. The “gold standard” of MAP detection is by culture, DNA sequencing possibly supplemented by identification of Ziehl–Neelsen positive mycobacteria. The purpose of this study was to evaluate a proprietary (Affymetrix™ RNA view^®) fluorescent in situ hybridization (FISH) assay for MAP RNA. Intestine from a steer with documented Johne’s disease was assayed according to the manufacturer’s instructions. Probes were custom designed for MAP and bovine β-actin (as the eukaryotic housekeeping gene) from published genomes. We attempt to prevent false positive signal in the “no-probe” control, by modifying wash solutions, using recommended hydrochloric acid titration and different fluorescent filters (TritC for Texas Red and “Hope” for Cy-5).

Results

Repetitively, false positive signal was observed in our “no probe” negative control. Attempts to correct this according to the manufacturers suggestions, and with multiple derivative techniques have been unsuccessful. It is concluded that when performed according to manufactures instruction and with multiple variations on the manufactures recommended suggestions to correct for false positive signal, that the Affymetrix™ RNA view^® cannot be used to detect MAP in pre-frozen intestine of cattle with Johne’s disease.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3601-5) contains supplementary material, which is available to authorized users.

Metabolic activity of mature biofilms of Mycobacterium tuberculosis and other non-tuberculous mycobacteria

Mycobacteria are classified into two groups, fast- and slow-growing. Often, fast-growing mycobacteria are assumed to have a higher metabolic activity than their slower counterparts, but in mature biofilms this assumption might not be correct. Indeed, when measuring the metabolic activity of mycobacterial biofilms with two independent non-invasive techniques (isothermal microcalorimetry and tunable diode laser absorption spectrometry), mature biofilms of slow- and fast-growing species appeared more alike than expected. Metabolic heat production rate was 2298 ± 181 µW for M. smegmatis and 792 ± 81 µW for M. phlei, while M. tuberculosis and M. bovis metabolic heat production rates were between these values. These small differences were further confirmed by similar oxygen consumption rates (3.3 ± 0.2 nMole/s and 1.7 ± 0.3 nMole/s for M. smegmatis and M. tuberculosis, respectively). These data suggest that the metabolic potential of slow-growing mycobacterial biofilms has been underestimated, particularly for pathogenic species.

Susceptibility testing of Mycobacterium abscessus by isothermal microcalorimetry

We evaluated a new method for susceptibility testing of a rapidly growing mycobacterium using real-time measurement of heat (microcalorimetry). MICs of 2 clinical Mycobacterium abscessus isolates were determined by microbroth dilution and E-test. For microcalorimetry, Middlebrook-7H10 agar+10% oleic acid-albumin-dextrose-catalase, containing amikacin, clarithromycin, linezolid, and ciprofloxacin was inoculated with ~10(5)CFU/mL. Heat production was measured at 37°C for 72h. Minimal heat inhibition concentration (MHIC) was defined as the lowest antibiotic concentration inhibiting growth-related heat production. Growth of M. abscessus was detected after a median of 16.5h (range, 8.5-26.9h). Heat detection was proportionally delayed with increasing concentration of antibiotics. MHICs for the tested strains were 16 to >16mg/L for amikacin, >8mg/L for clarithromycin, 4 to >16mg/L for ciprofloxacin, 24 to >32mg/L for linezolid. MHICs were in agreement within two 2-fold dilutions with conventional MICs. Microcalorimetry may accelerate antimicrobial susceptibility testing in mycobacteria and provide additional real-time information on the drug effect.

Assessment of diagnostic techniques of urinary tuberculosis

Early diagnosis of active tuberculosis remains an elusive challenge. In addition, one third of the world's population is latently infected with Mycobacterium tuberculosis (Mtb) and up to 10% of infected individuals develop tuberculosis (TB) in their lifetime. In this investigation, the incidence of urinary tuberculosis among renal patients was studied. Three hundreds urine samples were processed for detection of Mtb by Ziehl-Neelsen (ZN) smear examination, Lowenstein Jensen (LJ) medium, radiometric BACTEC460 system as well as polymerase chain reaction (PCR) followed by DNA Enzyme Immunoassay (DEIA) test. Out of 300 urine samples, 2 were positive by both ZN smears and LJ medium with incidence rate of 0.66 %, 3 positive samples by BACTEC460 culture system with incidence of 1%. PCR assay gave more positive results than smear and culture examination (i.e. 8 positive samples with incidence rate of 2.6%). The specificities were 25% for both ZN smears and LJ medium, 37.5% for BACTEC460 culture system, and 100% for PCR test, while sensitivities of all assays were 100%. Thus PCR is a rapid and sensitive method for the early diagnosis of urinary tuberculosis.

Growth of mycobacteria in urine determined by isothermal microcalorimetry: implications for urogenital tuberculosis and other mycobacterial infections

OBJECTIVE

To overcome the limitations of current urine-based diagnostic assays of urogenital tuberculosis, we used isothermal microcalorimetry to detect the metabolic activity of Mycobacterium tuberculosis and other commonly neglected pathogenic mycobacteria in urine and accurately determine their growth parameters.

METHODS

A microcalorimeter equipped with 48 channels was used. Detection was accomplished, and growth was monitored for 4 different Mycobacterium species in sterilized and modified urine at 37 °C by measuring metabolic heat flow (μW = μJ/s) as a function of time. These strains were M. smegmatis, M. phlei, M. kansasii, and M. tuberculosis. The data were integrated to perform curve fitting and extract the growth parameter from the raw data.

RESULTS

In sterilized urine, M. smegmatis showed the fastest growth rate (0.089 ± 0.017 [h(-1)]), followed by M. phlei (0.072 ± 0.016 [h(-1)]) and M. kansasii (0.007 ± 0.001 [h(-1)]). No growth of M. tuberculosis was detected in sterilized urine. However, in serum-supplemented urine, growth of M. tuberculosis was observed within 3 weeks at a growth rate of 0.008 ± 0.001 [h(-1)]. Biofilm formation was enhanced in the serum supplemented urine.

CONCLUSION

Isothermal microcalorimetry allows rapid and accurate detection of mycobacterial growth in urine. Given the absence of data on the mycobacterial growth in urine, isothermal microcalorimetry could be used to unravel key aspects of Mycobacterium physiology in the urinary tract and potentially contribute to improvement in the diagnosis and treatment of urogenital tuberculosis.

Application of a microcalorimetric method for determining drug susceptibility in mycobacterium species

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 μg/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.