Microbiological assays advantages

There are various analytical platforms used to measure folate concentrations in food, each with its advantages and drawbacks. Microbiological assay makes use of bacteria (e.g. Lactobacillus easel) that are very dependent on folate availability for their growth. This assay is commonly used to determine the total folate contents in food, which is expressed in terms of folic acid equivalents. The most important limitation of microbiological assay is that the various vitamers are not distinguishable... 

HPLC techniques present several potential advantages over earlier spectro-photometric, fluorometric, and official microbiological assay methods, which are very tedious and often difficult to perform. These advantages include simple sample preparation, direct analysis of compounds without any derivatization, and potential simultaneous determination of several compounds in a single run, in addition to a reduction of analysis time, excellent precision, and relatively good sensitivity. 

It has been suggested by Wood (53) that, for those microbiological assays which show a strictly linear portion to the standard curve, the so-called slope-ratio method diould be used for calculating the results. This method, of course, has the merit of being statistically sound, and it also has the valuable advantage that it is possible to calculate the fiducial limits of an assay. 

Any transformation that could be affected for such curves so that they would yield linear graphs would have manifest advantages, because it would afford a sound mathematical basis for computation, which is a desirable consideration for any analytical method. In any type of microbiological assay of vitamin Bu the results should be plotted to test whether a dose-response, a log dose-response, or a log dose-log response curve is sufficiently linear to make possible the use of statistical methods. In the assay of vitamin B12 activity in crude materials, however, the most pertinent problem at present is to relate this activity to certain defined substances rather than to obtain the highest accuracy in measuring the Bu activity. 

Microbiological assays have the advantage of specificity and sensitivity, but they are highly time consuming if compared with the physicochemical methods and the analytical protocol must be strictly followed due to the variability in microbiological techniques. 

Dilution assays are generally utilized as early microbiological methods before well defined standards are available. They have the advantage that one can compare the activity of one preparation to another without having a standard. 

Microbiological or immunochemical detection systems offer the advantage to screen, rapidly and at low cost, a large number of food samples for potential residues, but cannot provide definitive information on the identity of violative residues found in suspected samples. For samples found positive by the screening assays, residues can be tentatively identified and quantified by means of the combined force of an efficient liquid chromatographic (LC) separation and a selective physicochemical detection system such as UV, fluorescence, or electrochemical detection. The potential of pre- or postcolumn derivatiza-tion can further enhance the selectivity and sensitivity of the analysis. Nevertheless, unequivocal identification by these methods is not possible unless a more efficient detection system is applied. 

Direct detection of p-lactamase activity has been established as a routine method in mai microbiological diagnostic laboratories (Hrabak et al. 2014). Especially in the case of a direct detection of caibapenemase activity, the MALDI-TOF MS hydrolysis assay should soon be accepted as a gold standard method and may serve as a reference technique together with spectrophotometric assays. The main advantage of MS tools is the ability to detect rapidly both antibiotic hydrolytic products and intact lactamases. 

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