Discriminant analysis of microcalorimetric data of bacterial growth

A standardized method for genus Colletotrichum characterization by isothermal microcalorimetry using thermokinetic parameters

A new standardized method, using isothermal microcalorimetry (IMC), was established to determine thermokinetic parameters from heat flow curves and to demonstrate the reproducibility and repeatability of the parameters of five Colletotrichum species on different days. Measurements on IMC were made at different periods and by two operators. Repeatability and reproducibility (R&R) measurement system analysis was performed on the technique used to measure the heat flow of Colletotrichum strains. The results showed that the %GageR&R was found to be within the acceptable ranges of a measurement system. Also, the parameters obtained from the curves were subjected to a combination of Principal Component Analysis (PCA) and Clustering, the data showed that the total heat (H_t) and maximum growth rate (μ_max) are probably the most specific distinguishing characteristic of the strains evaluated in this study. This study demonstrates, for the first time, the usefulness of IMC in obtaining heat flow curves and thermokinetic parameters, providing repeatable and reproducible measurements over a period and under controlled conditions, for future identifications of phytopathogenic fungi.

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.

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.

Suppression of tricarboxylic acid cycle in Escherichia coli exposed to sub-MICs of aminoglycosides

The metabolic activity of Escherichia coli ATCC 25922 challenged with sub-MICs of aminoglycosides was analyzed with a batch calorimeter. High-performance and gas-liquid chromatographic techniques were utilized to evaluate the concentrations of metabolic reactants, intermediates, and end products. The data reported indicate that aminoglycosides inhibit or delay bacterial catabolism of carboxylic acids, with the following relative degrees of activity: amikacin greater than gentamicin greater than sisomicin greater than netilmicin greater than kanamycin. The decrease in total biomass production was proportional to the degree of tricarboxylic acid cycle inhibition.

Numerical analysis of electrophoretic periplasmic protein patterns, a possible marker system for epidemiologic studies

The whole-cell and periplasmic protein (PP) compositions of 22 Serratia marcescens isolates were examined. Numerical analysis of whole-cell protein patterns was not a useful procedure for measuring relationships between organisms at the subspecific level. However, there was a very good correlation between electrophoretic PP pattern results and those obtained previously from multilocus enzyme electrophoresis (electrophoretic type) and biotype (D. Gargallo-Viola, J. Clin. Microbiol. 27:860-868, 1989). Clustering of isolates by using PP patterns compared by coefficients based on peak position (Dice coefficient) gave more precise information than that obtained by correlation coefficients. PP patterns appeared to be a useful tool that may be of value for epidemiologic studies.