Rapid Detection and quantification of Microorganisms.

Preconditions - An important demand in many fields of hygienics, including food and water technology, is to determine contaminations through different kinds of microorganisms (MOs) -such as bacteria or yeast - in a rapid, simple and reliable way. Both production and delivery should be stopped promptly in order to avoid risks of health. Traditional methods, such as the plate count method, suffer from time consuming procedures and from detection times up to several days. As an alternative, modern procedures offer automatic analyses of large sample, numbers, detections of strong contaminations being available within few hours, the detection time being used as an inverse measure for the interesting initial MO concentration. In pre-studies, the applicants have contributed a so-called Impedance Splitting Technique the effectivity of which is demonstrated by the fact that the technique meanwhile is considered by DIN specifications. Project Aims - Also the above mentioned automatic methods lack from the fact that weak contaminations are detected only after long hours of incubation. This disadvantage was the starting point for the present project which was formulated after intensive pre-studies (e.g., electric and magnetic concentration of MOs, as well as their detection by means of several electrical and chemical parameters). The basic strategy of project is to concentrate MOs of weakly or moderately contaminated liquid samples to a very small local region and to detect them after short periods of incubation in a most sensitive way. Special emphasis will be put on (a) minimum manual handling, (b) avoidance of complicated electromechanical apparatus, and (c) low-cost components of sample managing. Methods - Incubation is planned to be performed in cylindric sample tubes as usual for automatic methods. MO concentration will be performed in a cascade way starting out from 3-dimensional distribution and ending with (quasi) 1 -dimensional spotwise concentration at a central electrode of the tube bottom. For pre-concentration, a sink-mass will be placed on the surface of the sample liquid. The mass will exhibit a central bore including a membrane filter (of less than 1 micro-m pore size) which during the sink process should guide MOs to the bottom. Here MOs will pass into the capture region of a strongly inhomogeneous electrical HF field generated by a plane electrode system. According to dielectrophoresis, the polarized MOs will be guided to the central point electrode. As a possible version, the latter will be used also for MO detection by means of simultaneous evaluations of several electric characteristics (impedance of cell suspension, electrode impedance, electrode contact voltage). Outlook - The new procedure promises to yield strong reductions of the detection time. This advantage should be attained with acceptable additional expenditure, i.e. the sink filter as used for pre-concentration. At its end, the project will yield the following deliverables: (i) Guidelines for optimum procedures for all four pre-concentration, post-concentration, detection and multiparametrical evaluation, (ii) prototypes of complete sample tubes and of an apparatus for simultaneous incubation and analysis of several samples, and (iii) data and experience concerning the practical performance of the new system for analyses of hygienically relevant samples.