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, standard- ized 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 develop- ment and refinement of microbiological POCTs which are now available for several microorganisms, even thought no mi- crobiological POCT was up to now developed for the count of total viable bacteria (TVC) in serum, urine or other bio- logical 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 meta- bolic 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 con- centration; 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 micro- biological methods), of the quantitative Micro Biological Survey (MBS) method for Total Viable Count (TVC). Valida- tion aims to compare the results obtained with an alternative method, in this case the MBS method, with the results ob- tained 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 agree- ment 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.