A New Method For Microbiological Analysis That Could Be Used For Point-Of-Care Testing (POCT)

Abstract

Standardized microbiological methods used in clinical analysis are based on traditional microbial enrichment on selective media, possibly followed by characterization of bacteria with molecular methods. These techniques present several difficulties, such as the subjectivity in the interpretation of genetic, biochemical or morphological tests and the possible interference of biological matrices, specially when low levels of contamination are present. In addition, standardized microbiological analyses are characterised by the high cost of the method, both in terms of labor and supplies, and above all, by the long time needed to obtain definitive results (from 3 to 7 days). These reasons have led to the development and refinement of microbiological POCTs which are now available for several microorganisms, even thought no microbiological POCT was up to now developed for the count of total viable bacteria (TVC) in serum, urine or other biological fluids.MBS srl (a spin-off of Roma Tre University, Rome, Italy) has developed and patented an alternative method for selective counting of bacteria, called Micro Biological Survey (MBS) method. The MBS method is based on colorimetric survey performed in mono-use disposable reaction vials in which samples can be inoculated without any preliminary treatment. The analyses can be carried out by untrained personnel and anywhere they are necessary, without the need for any other instrumentation than a thermostated optical reader that can automatically detect the colour change providing the number of bacteria present into the sample. The MBS method measures the catalytic activity of redox enzymes in the main metabolic pathways of bacteria, allowing an unequivocal correlation between the observed enzymatic activity and the number of viable cells present in the samples. The time required for a color change is inversely related to the log of bacterial concentration; like an enzymatic reaction, the greater the number of bacteria, the faster the color change.The objective of this study was the primary validation, in accord with ISO 13843:2003 (Guidance on validation of microbiological methods), of the quantitative Micro Biological Survey (MBS) method for Total Viable Count (TVC). Validation aims to compare the results obtained with an alternative method, in this case the MBS method, with the results obtained with the reference method. To verify the equivalence between the two methods different parameters were analyzed: selectivity, linearity and accuracy. The validation has shown that the MBS method gives similar results and is in agreement with the reference methods. The MBS method could therefore represent a worthy aid in microbiological analysis as POCT device without replacing the analysis carried out with traditional methods which are very precise though often long and complex.

Management of Urinary Tract Infections: Problems and Possible Solutions

“…The MBS method allows rapid and accurate bacterial quantification through an automated colorimetric culture-based test; urine samples are inoculated into disposable ready-to-use reaction vials, which color will change thanks to redox indicators following bacterial growth after incubation (see Figure 1). Results of preliminary in vitro validation studies [62,63] showed that the results obtained with this method are comparable to the reference culture-based methods.…”

A new point-of-care test for the rapid detection of urinary tract infections

“…Bacteriuria is automatically detected upon blue to yellow color change of the medium in the reaction vial during time. Criteria for definition of positive and negative results followed results of previous in vitro studies on artificially contaminated urine samples [19], later confirmed by results from the first clinical trial [21], meaning color change within 5.24 h indicated positivity while slower color change or no color change within analytical timeframe (24 h) indicated negativity. Vials were incubated in the MBS Multireader, which automatically detects the time for color change, at 37°C.…”

“…The Micro Biological Survey (MBS) POCT is a simple test developed by MBS Diagnostics Ltd. (London, UK) for the management of UTIs [19,20] (Fig. S1 in Supplementary material).…”

A new device for the prompt diagnosis of urinary tract infections

“…The colorimetric MBS method was used according to the previously described procedure [10]: 1 mL of artificially contaminated urine samples was analyzed with four different MBS vials (UBC, without antibiotics, UBC+BAN, UBC+CIP, and UBC+TMP-SMZ). The vials were then inserted into the MBS thermostatic optical reader at 37 °C which automatically detected the color change due to the growth of bacteria.…”

“…In a previous study [10] a preliminary validation of the quantitative MBS method was carried out, in accordance with ISO Standards, in order to explore the possibility to use it as a microbiological POCT in UTIs. Precision, variance, uncertainty, linearity and accuracy were determined for all bacterial species tested with the MBS method, demonstrating that the MBS results were in good agreement with the ones obtained with the reference method of colony count on plate count agar for the bacterial species most commonly isolated in UTIs.…”