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

Isothermal microcalorimetry versus checkerboard assay to evaluate in vitro synergism of meropenem-amikacin and meropenem-colistin combinations against multidrug-resistant Gram-negative pathogens

OBJECTIVES

To evaluate the activity of meropenem-amikacin and meropenem-colistin combinations with checkerboard broth microdilution (CKBM) compared to isothermal microcalorimetry (ITMC) assays against a multicentric collection of multidrug-resistant Gram-negative (MDR-GN) clinical isolates, to compare the Fractional inhibitory concentration index (FICI) and time to results of CKBM and ITMC assays.

METHODS

A collection of 333 MDR-GNs showing reduced susceptibility to meropenem (121 Klebsiella pneumoniae, 14 Escherichia coli, 130 Pseudomonas aeruginosa and 68 Acinetobacter baumannii) isolated from different centres (Florence, Madrid, Rotterdam, and Stockholm) was included in the study. The antimicrobial activity of selected combinations was evaluated with CKBM and ITMC. FICI results were interpreted as synergistic/additive and indifferent for values ≤0.5/0.5<x≤1 and >1, respectively. WGS data in a subset of strains was used to evaluate their clonality.

RESULTS

A total of 254 and 286 strains were tested with meropenem-colistin and meropenem-amikacin combinations with ITMC and CKBM, respectively. Synergism/additive effects were observed with 46 strains (20 K. pneumoniae, 4 E. coli, 22 P. aeruginosa) and 20 strains (3 K. pneumoniae, 11 P. aeruginosa and 6 A. baumannii) with meropenem-amikacin and meropenem-colistin combination, respectively, with CKBM. ITMC showed a good concordance with CKBM with 89.5% and 92.2% of cases interpreted within the same FICI category for meropenem-amikacin and meropenem-colistin combinations, respectively. Most of the synergism/additivity effects were detected within 6 hours by ITMC.

CONCLUSIONS

ITMC showed a very good concordance with CKBM against a large collection of MDR-GN and could be implemented for the rapid evaluation of in vitro activity of antimicrobial combinations.

Mycobacterium ulcerans Experimental Dormancy

Whether Mycobacterium ulcerans, the etiological agent of Buruli ulcer in numerous tropical countries, would exist in a dormant state as reported for closely related Mycobacterium species, has not been established. Six M. ulcerans strains were exposed to a progressive depletion in oxygen for 2 months, using the Wayne model of dormancy previously described for M. tuberculosis, and further examined by microscopy after staining of dynamic, dormant, and dead mycobacteria (DDD staining), microcalorimetry and subculture in the presence of dead and replicative M. ulcerans as controls. Mycobacterium ulcerans CU001 strain died during the progressive oxygen depletion and four of five remaining strains exhibited Nile red-stained intracellular lipid droplets and a 14- to 20-day regrowth when exposed to ambient air, consistent with dormancy. A fifth M. ulcerans 19423 strain stained negative in DDD staining and slowly regrew in 27 days. Three tested M. ulcerans strains yielded microcalorimetric pattern similar to that of the negative (dead) homologous controls, differing from that of the homologous positive (replicative) controls. The relevance of these experimental observations, suggesting a previously unreported dormancy state of M. ulcerans, warrants further investigations in the natural ecological niches where M. ulcerans thrive as well as in Buruli ulcer lesions.

Evolution of Antibacterial Drug Screening Methods: Current Prospects for Mycobacteria

The increasing resistance of infectious agents to available drugs urges the continuous and rapid development of new and more efficient treatment options. This process, in turn, requires accurate and high-throughput techniques for antimicrobials’ testing. Conventional methods of drug susceptibility testing (DST) are reliable and standardized by competent entities and have been thoroughly applied to a wide range of microorganisms. However, they require much manual work and time, especially in the case of slow-growing organisms, such as mycobacteria. Aiming at a better prediction of the clinical efficacy of new drugs, in vitro infection models have evolved to closely mimic the environment that microorganisms experience inside the host. Automated methods allow in vitro DST on a big scale, and they can integrate models that recreate the interactions that the bacteria establish with host cells in vivo. Nonetheless, they are expensive and require a high level of expertise, which makes them still not applicable to routine laboratory work. In this review, we discuss conventional DST methods and how they should be used as a first screen to select active compounds. We also highlight their limitations and how they can be overcome by more complex and sophisticated in vitro models that reflect the dynamics present in the host during infection. Special attention is given to mycobacteria, which are simultaneously difficult to treat and especially challenging to study in the context of DST.

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.

Advances in Antimicrobial Resistance Monitoring Using Sensors and Biosensors: A Review

The indiscriminate use and mismanagement of antibiotics over the last eight decades have led to one of the main challenges humanity will have to face in the next twenty years in terms of public health and economy, i.e., antimicrobial resistance. One of the key approaches to tackling antimicrobial resistance is clinical, livestock, and environmental surveillance applying methods capable of effectively identifying antimicrobial non-susceptibility as well as genes that promote resistance. Current clinical laboratory practices involve conventional culture-based antibiotic susceptibility testing (AST) methods, taking over 24 h to find out which medication should be prescribed to treat the infection. Although there are techniques that provide rapid resistance detection, it is necessary to have new tools that are easy to operate, are robust, sensitive, specific, and inexpensive. Chemical sensors and biosensors are devices that could have the necessary characteristics for the rapid diagnosis of resistant microorganisms and could provide crucial information on the choice of antibiotic (or other antimicrobial medicines) to be administered. This review provides an overview on novel biosensing strategies for the phenotypic and genotypic determination of antimicrobial resistance and a perspective on the use of these tools in modern health-care and environmental surveillance.

Rapid detection of extended-spectrum β-Lactamases producers in Enterobacteriaceae using a calorimetry approach

AIM

To design and assess a novel protocol that employs isothermal titration calorimetry (ITC) for rapid detection of extended-spectrum β-lactamase (ESBL)-producers in clinical pathogens.

METHODS AND RESULTS

A total of 69 clinical Enterobacteriaceae isolates were examined in the new ESBL-ITC test by examining the heat profiles associated with enzyme hydrolysis of different substrates (imipenem, cefotaxime and clavulanic acid). The presence of β-lactamase genes in the bacteria tested was confirmed by PCR and DNA sequencing. Comparative analysis between ESBL-ITC and conventional minimum inhibitory concentrations (MIC)/combined disk method (CDM) showed high agreement between the two assays. However, the ESBL-ITC test had a remarkable advantage of providing testing result within 1 h, in comparison to the 32-48 h required by MIC/CDM.

CONCLUSIONS

The ESBL-ITC test developed in this work offers a new option for rapid and accurate detection of ESBL-producers.

SIGNIFICANCE AND IMPACT OF THE STUDY

Timely detection of ESBL-producers is vital to guide the decision-making process in clinical treatment as well as in hospital-infection control. The new ESBL-ITC test provides a rapid phenotypic assay that can be further adapted for clinical diagnosis of ESBL-producing pathogens.

Preclinical Models of Nontuberculous Mycobacteria Infection for Early Drug Discovery and Vaccine Research

Nontuberculous mycobacteria (NTM) represent an increasingly prevalent etiology of soft tissue infections in animals and humans. NTM are widely distributed in the environment and while, for the most part, they behave as saprophytic organisms, in certain situations, they can be pathogenic, so much so that the incidence of NTM infections has surpassed that of Mycobacterium tuberculosis in developed countries. As a result, a growing body of the literature has focused attention on the critical role that drug susceptibility tests and infection models play in the design of appropriate therapeutic strategies against NTM diseases. This paper is an overview of the in vitro and in vivo models of NTM infection employed in the preclinical phase for early drug discovery and vaccine development. It summarizes alternative methods, not fully explored, for the characterization of anti-mycobacterial compounds.

Modern Tools for Rapid Diagnostics of Antimicrobial Resistance

Fast, robust, and affordable antimicrobial susceptibility testing (AST) is required, as roughly 50% of antibiotic treatments are started with wrong antibiotics and without a proper diagnosis of the pathogen. Validated growth-based AST according to EUCAST or CLSI (European Committee on Antimicrobial Susceptibility Testing, Clinical Laboratory Standards Institute) recommendations is currently suggested to guide the antimicrobial therapy. Any new AST should be validated against these standard methods. Many rapid diagnostic techniques can already provide pathogen identification. Some of them can additionally detect the presence of resistance genes or resistance proteins, but usually isolated pure cultures are needed for AST. We discuss the value of the technologies applying nucleic acid amplification, whole genome sequencing, and hybridization as well as immunodiagnostic and mass spectrometry-based methods and biosensor-based AST. Additionally, we evaluate the potential of integrated systems applying microfluidics to integrate cultivation, lysis, purification, and signal reading steps. We discuss technologies and commercial products with potential for Point-of-Care Testing (POCT) and their capability to analyze polymicrobial samples without pre-purification steps. The purpose of this critical review is to present the needs and drivers for AST development, to show the benefits and limitations of AST methods, to introduce promising new POCT-compatible technologies, and to discuss AST technologies that are likely to thrive in the future.

Antimicrobial activity of bioactive glass S53P4 against representative microorganisms causing osteomyelitis - Real-time assessment by isothermal microcalorimetry

Bioactive glass (BAG) is a synthetic bone substitute with intrinsic antimicrobial properties, used for bone defect filling. We evaluated the antimicrobial activity of two formulations of BAG S53P4 against representative pathogens of osteomyelitis: Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Escherichia coli and Candida albicans. Antimicrobial activity of BAG S53P4 was assessed by isothermal microcalorimetry, a highly sensitive assay measuring metabolic-related microbial heat production in real-time. Standard CFUs-counting was performed in parallel. BAG granules (diameter 500-800 μm) and powder (<45 μm) were evaluated in two concentrations (400 and 800 mg/ml). Isothermal microcalorimetry was performed in glass ampoules containing growth medium, BAG and test microorganism, heat production was measured for 24 h. BAG S53P4 inhibited heat production of most-tested microorganisms with heat reduction of 60%-98% compared to positive control after 24 h of exposure to the highest-tested concentration (800 mg/ml). BAG S53P4 in powder formulation (<45 μm) inhibited more microbial growth than in granule formulation (500-800 μm), with the exception of C. albicans for which both formulations presented similar inhibition rates ranging between 87 % and 97 %. The BAG inhibitory ratios estimated from the variation in the growth rate constants of each microorganism compared to the growth control ranged between 2.55 % and 100 %. Comparable results were obtained by CFUs-counting, with complete reduction in cell viability of most microorganisms after ≤ 24 h of microbial exposure to BAG S53P4 powder. In summary, BAG S53P4 demonstrated efficient inhibition of microbial growth, especially in powder formulation.

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.

Thermogenic Characterization and Antifungal Susceptibility of Candida auris by Microcalorimetry

Candida auris has emerged globally as a multidrug-resistant fungal pathogen. Isolates of C. auris are reported to be misidentified as Candida haemulonii. The aim of the study was to compare the heat production profiles of C. auris strains and other Candida spp. and evaluate their antifungal susceptibility using isothermal microcalorimetry. The minimum heat inhibitory concentrations (MHIC) and the minimum biofilm fungicidal concentration (MBFC) were defined as the lowest antimicrobial concentration leading to the lack of heat flow production after 24 h for planktonic cells and 48 h for biofilm-embedded cells. C. auris exhibited a peculiar heat production profile. Thermogenic parameters of C. auris suggested a slower growth rate compared to Candida lusitaniae and a different distinct heat profile compared to that of C. haemulonii species complex strains, although they all belong to the Metschnikowiaceae clade. Amphotericin B MHIC and MBFC were 0.5 µg/mL and ≥8 µg/mL, respectively. C. auris strains were non-susceptible to fluconazole at tested concentrations (MHIC > 128 µg/mL, MBFC > 256 µg/mL). The heat curve represents a fingerprint of C. auris, which distinguished it from other species. Treatment based on amphotericin B represents a potential therapeutic option for C. auris infection.

Emerging technologies for antibiotic susceptibility testing

Superbugs such as infectious bacteria pose a great threat to humanity due to an increase in bacterial mortality leading to clinical treatment failure, lengthy hospital stay, intravenous therapy and accretion of bacteraemia. These disease-causing bacteria gain resistance to drugs over time which further complicates the treatment. Monitoring of antibiotic resistance is therefore necessary so that bacterial infectious diseases can be diagnosed rapidly. Antimicrobial susceptibility testing (AST) provides valuable information on the efficacy of antibiotic agents and their dosages for treatment against bacterial infections. In clinical laboratories, most widely used AST methods are disk diffusion, gradient diffusion, broth dilution, or commercially available semi-automated systems. Though these methods are cost-effective and accurate, they are time-consuming, labour-intensive, and require skilled manpower. Recently much attention has been on developing rapid AST techniques to avoid misuse of antibiotics and provide effective treatment. In this review, we have discussed emerging engineering AST techniques with special emphasis on phenotypic AST. These techniques include fluorescence imaging along with computational image processing, surface plasmon resonance, Raman spectra, and laser tweezer as well as micro/nanotechnology-based device such as microfluidics, microdroplets, and microchamber. The mechanical and electrical behaviour of single bacterial cell and bacterial suspension for the study of AST is also discussed.

Isothermal Microcalorimetry Detects the Presence of Persister Cells in a Staphylococcus aureus Biofilm After Vancomycin Treatment

Staphylococcus aureus biofilm plays a major role in implant-associated infections. Here, the susceptibility of biofilm S. aureus to daptomycin, fosfomycin, vancomycin, trimethoprim/sulfamethoxazole, linezolid, and rifampicin was investigated by isothermal microcalorimetry (IMC). Moreover, the persister status of cells isolated from S. aureus biofilm after treatment with vancomycin was also analyzed. S. aureus biofilm was tolerant to all the antibiotics tested [minimum biofilm bactericidal concentration (MBBC) > 256 μg/ml], except to daptomycin [MBBC and minimum biofilm eradicating concentration (MBEC) = 32 μg/ml] and rifampin (MBBC and MBEC = 128 μg/ml). After the treatment of MRSA biofilm with 1024 μg/ml vancomycin, ∼5% cells survived, although metabolically inactive (persisters). Interestingly, IMC revealed that persister bacteria reverted to a normal-growing phenotype when inoculated into fresh medium without antibiotics. A staggered treatment of MRSA biofilm with vancomycin to kill all the metabolically active cells and daptomycin to kill persister cells eradicated the whole bacterial population. These results support the use in the clinical practice of a therapeutic regimen based on the use of two antibiotics to kill persister cells and eradicate MRSA biofilms. IMC represents a suitable technique to characterize in real-time the reversion from persister to metabolically-active cells.

Interference Disturbance Analysis Enables Single-Cell Level Growth and Mobility Characterization for Rapid Antimicrobial Susceptibility Testing

To support the emerging battle against antimicrobial resistance (AMR), detection methods that allow fast and accurate antimicrobial susceptibility testing (AST) are urgently needed. The early identification and application of an appropriate antibiotic treatment leads to lower mortality rates and substantial cost savings and prevents the development of resistant pathogens. In this work, we present a diffraction-based method, which is capable of quantitative bacterial growth, mobility, and susceptibility measurements. The method is based on the temporal analysis of the intensity of a light diffraction peak, which arises due to interference at a periodic pattern of gold nanostructures. The presence of bacteria disturbs the constructive interference, leading to an intensity decrease and thus allows the monitoring of bacterial growth in very low volumes. We demonstrate the direct correlation of the decrease in diffraction peak intensity with bacterial cell number starting from single cells and show the capability for rapid high-throughput AST measurements by determining the minimum inhibitory concentration for three different antimicrobials in less than 2-3 h as well as the susceptibility in less than 30-40 min. Furthermore, bacterial mobility is obtained from short-term fluctuations of the diffraction peak intensity and is shown to decrease by a factor of 3 during bacterial attachment to a surface. This multiparameter detection method allows for rapid AST of planktonic and of biofilm-forming bacterial strains in low volumes and in real-time without the need of high initial cell numbers.

Collagen VI Contains Multiple Host Defense Peptides with Potent In Vivo Activity

Collagen VI is a ubiquitous extracellular matrix component that forms extensive microfibrillar networks in most connective tissues. In this study, we describe for the first time, to our knowledge, that the collagen VI von Willebrand factor type A-like domains exhibit a broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria in human skin infections in vivo. In silico sequence and structural analysis of VWA domains revealed that they contain cationic and amphipathic peptide sequence motifs, which might explain the antimicrobial nature of collagen VI. In vitro and in vivo studies show that these peptides exhibited significant antibacterial activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa through membrane disruption. Our findings shed new light on the role of collagen VI-derived peptides in innate host defense and provide templates for development of peptide-based antibacterial therapies.

Current and emerging techniques for antibiotic susceptibility tests

Infectious diseases caused by bacterial pathogens are a worldwide burden. Serious bacterial infection-related complications, such as sepsis, affect over a million people every year with mortality rates ranging from 30% to 50%. Crucial clinical microbiology laboratory responsibilities associated with patient management and treatment include isolating and identifying the causative bacterium and performing antibiotic susceptibility tests (ASTs), which are labor-intensive, complex, imprecise, and slow (taking days, depending on the growth rate of the pathogen). Considering the life-threatening condition of a septic patient and the increasing prevalence of antibiotic-resistant bacteria in hospitals, rapid and automated diagnostic tools are needed. This review summarizes the existing commercial AST methods and discusses some of the promising emerging AST tools that will empower humans to win the evolutionary war between microbial genes and human wits.

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.

Activities of fluconazole, caspofungin, anidulafungin, and amphotericin B on planktonic and biofilm Candida species determined by microcalorimetry

We investigated the activities of fluconazole, caspofungin, anidulafungin, and amphotericin B against Candida species in planktonic form and biofilms using a highly sensitive assay measuring growth-related heat production (microcalorimetry). C. albicans, C. glabrata, C. krusei, and C. parapsilosis were tested, and MICs were determined by the broth microdilution method. The antifungal activities were determined by isothermal microcalorimetry at 37°C in RPMI 1640. For planktonic Candida, heat flow was measured in the presence of antifungal dilutions for 24 h. Candida biofilm was formed on porous glass beads for 24 h and exposed to serial dilutions of antifungals for 24 h, and heat flow was measured for 48 h. The minimum heat inhibitory concentration (MHIC) was defined as the lowest antifungal concentration reducing the heat flow peak by ≥50% (≥90% for amphotericin B) at 24 h for planktonic Candida and at 48 h for Candida biofilms (measured also at 24 h). Fluconazole (planktonic MHICs, 0.25 to >512 μg/ml) and amphotericin B (planktonic MHICs, 0.25 to 1 μg/ml) showed higher MHICs than anidulafungin (planktonic MHICs, 0.015 to 0.5 μg/ml) and caspofungin (planktonic MHICs, 0.125 to 0.5 μg/ml). Against Candida species in biofilms, fluconazole's activity was reduced by >1,000-fold compared to its activity against the planktonic counterparts, whereas echinocandins and amphotericin B mainly preserved their activities. Fluconazole induced growth of planktonic C. krusei at sub-MICs. At high concentrations of caspofungin (>4 μg/ml), paradoxical growth of planktonic C. albicans and C. glabrata was observed. Microcalorimetry enabled real-time evaluation of antifungal activities against planktonic and biofilm Candida organisms. It can be used in the future to evaluate new antifungals and antifungal combinations and to study resistant strains.

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

Proper and rapid diagnosis of orthopedic device-related infection is important for successful treatment. Sonication has been shown to improve the diagnostic performance. We hypothesized that the combination of sonication with a novel method called microcalorimetry will further improve and accelerate the diagnosis of implant infection. We prospectively included 39 consecutive patients (mean age 59 years, 62% males) at our institution from whom 29 orthopedic prostheses and 10 osteosynthesis material were explanted. The explanted device was sonicated. The resulting sonication fluid was analyzed using microcalorimetry. Using standardized criteria to define orthopedic device-related infection, 12 cases (31%) were defined as infected. In all, positive periprosthetic tissue cultures were found. The sensitivity and specificity of microcalorimetry of sonication fluid were 100% and 97%, respectively. Mean time to detection, defined as time to reach a rising heat flow signal of 20 µW measured after equilibiration needed to get accurate measurement, was 10.9 h. In summary, microcalorimetry of sonication fluid is a reliable and a fast method in detecting the presence of microorganisms in orthopedic device-related infection.

Comparative analysis of Staphylococcus aureus and Escherichia coli microcalorimetric growth

BACKGROUND

Microcalorimetric bacterial growth studies have illustrated that thermograms differ significantly with both culture media and strain. The present contribution examines the possibility of discriminating between certain bacterial strains by microcalorimetry and the qualitative and quantitative contribution of the sample volume to the observed thermograms. Growth patterns of samples of Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) were analyzed. Certain features of the thermograms that may serve to distinguish between these bacterial strains were identified.

RESULTS

The thermograms of the two bacterial strains with sample volumes ranging from 0.3 to 0.7 ml and same initial bacterial concentration were analyzed. Both strains exhibit a roughly 2-peak shape that differs by peak amplitude and position along the time scale. Seven parameters corresponding to the thermogram key points related to time and heat flow values were proposed and statistically analyzed. The most relevant parameters appear to be the time to reach a heat flow of 0.05 mW (1.67 ± 0.46 h in E. coli vs. 2.99 ± 0.53 h in S. aureus, p < 0.0001), the time to reach the first peak (3.84 ± 0.5 h vs. 5.17 ± 0.49 h, p < 0.0001) and the first peak value (0.19 ± 0.02 mW vs. 0.086 ± 0.012 mW, p < 0.0001). The statistical analysis on 4 parameters of volume-normalized heat flow thermograms showed that the time to reach a volume-normalized heat flow of 0.1 mW/ml (1.75 ± 0.37 h in E. coli vs. 2.87 ± 0.65 h in S. aureus, p < 0.005), the time to reach the first volume-normalized peak (3.78 ± 0.47 h vs. 5.12 ± 0.52 h, p < 0.0001) and the first volume-normalized peak value (0.35 ± 0.05 mW/ml vs. 0.181 ± 0.040 mW/ml, p < 0.0001) seem to be the most relevant. Peakfit® decomposition and analysis of the observed thermograms complements the statistical analysis via quantitative arguments, indicating that: (1) the first peak pertains to a faster, "dissolved oxygen" bacterial growth (where the dissolved oxygen in the initial suspension acts as a limiting factor); (2) the second peak indicates a slower "diffused oxygen" growth that involves transport of oxygen contained in the unfilled part of the microcalorimetric cell; (3) a strictly fermentative growth component may slightly contribute to the observed complex thermal signal.

CONCLUSION

The investigated strains of Staphylococcus aureus and Escherichia coli display, under similar experimental conditions, distinct thermal growth patterns. The two strains can be easily differentiated using a selection of the proposed parameters. The presented Peakfit analysis of the complex thermal signal provides the necessary means for establishing the optimal growth conditions of various bacterial strains. These conditions are needed for the standardization of the isothermal microcalorimetry method in view of its further use in qualitative and quantitative estimation of bacterial growth.

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.

Next-generation antimicrobial susceptibility testing

Antimicrobial resistance has emerged as one of the most-significant health care problems of the new millennium, and the clinical microbiology laboratory plays a central role in optimizing the therapeutic management of patients with infection. This minireview explores the potential value of innovative methods for antimicrobial susceptibility testing of microorganisms that could provide valuable alternatives to existing methodologies in the very near future.

Chip-calorimetric monitoring of biofilm eradication with antibiotics provides mechanistic information

Increased antibiotic resistance of pathogenic bacteria dwelling in biofilm structures has motivated the development of various monitoring tools specifically designed for biofilm investigations. In this study, the potential of the recently emerging chip calorimetry for this purpose was analysed. The activity of biofilms of Pseudomonas putida PaW340 was monitored chip-calorimetrically and compared with counts of colony forming units (CFU), bioluminescence-based ATP measurements, and quantitative confocal laser scanning microscopy (CLSM). The biofilms were treated with antibiotics differing in their mechanisms of action (bactericidal kanamycin vs. bacteriostatic tetracycline) and referenced to untreated biofilms. For untreated biofilms, all methods gave comparable results. Calorimetric killing curves, however, reflecting metabolic responses to biofilm eradication non-invasively in real time, differed from those obtained with the established methods. For instance, heat signals increased right after addition of the antibiotics. This transient increase of activity was not detected by the other methods, since only calorimetry delivers specific information about the catabolic part of the metabolism. In case of the bactericidal antibiotic, CFU misleadingly indicated successful biofilm eradication, whereas calorimetry revealed enduring activity. Our results show that calorimetry holds promise to provide valuable mechanistic information, thereby complementing other methods of biofilm analysis.

Rapid clinical bacteriology and its future impact

Clinical microbiology has always been a slowly evolving and conservative science. The sub-field of bacteriology has been and still is dominated for over a century by culture-based technologies. The integration of serological and molecular methodologies during the seventies and eighties of the previous century took place relatively slowly and in a cumbersome fashion. When nucleic acid amplification technologies became available in the early nineties, the predicted "revolution" was again slow but in the end a real paradigm shift did take place. Several of the culture-based technologies were successfully replaced by tests aimed at nucleic acid detection. More recently a second revolution occurred. Mass spectrometry was introduced and broadly accepted as a new diagnostic gold standard for microbial species identification. Apparently, the diagnostic landscape is changing, albeit slowly, and the combination of newly identified infectious etiologies and the availability of innovative technologies has now opened new avenues for modernizing clinical microbiology. However, the improvement of microbial antibiotic susceptibility testing is still lagging behind. In this review we aim to sketch the most recent developments in laboratory-based clinical bacteriology and to provide an overview of emerging novel diagnostic approaches.

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.