HARMONIC SIGNATURES OF MICROORGANISMS

The frequency/amplitude effect of various microorganisms exposed to pe riodic (time varying) electric fields, when proximate to immersed elec trodes, has been studied using a novel analytical instrument. The harm onic distribution, in complex signals caused by cells exposed to harmo nic free waveforms and occupying part of the electrode/suspension inte rface volume, was shown to be almost entirely due to the change in the standing interfacial transfer function by the (dielectrically nonline ar) presence of cells. Thus, the characteristic interfacial non-linear ity is viewed as variable, being uniquely modulated by the presence of particular cells in the interfacial region. Little can be attributed to bulk (far field) effects. The tendency for subtle (characteristic) signal distortion to occur as a function of particulate (cell or molec ular) occupancy of the near electrode interfacial region under control led current conditions leads to the method of sample characterisation by harmonic (Fourier) analysis. We report here, as a sequel to our ori ginal studies (Hutchings et al., 1993; Hutchings and Blake-Coleman, 19 93), preliminary results of the harmonic analysis of microbial suspens ions under controlled signal conditions using a three-electrode config uration. These data provide three-dimensional graphical representation s producing harmonic 'surfaces' for various microorganisms. Thus, cell type differences are characterised by their 'harmonic signature'. The visual distinction provided by these 'surface' forming three-dimensio nal plots is striking and gives a convincing impression of the ability to identify and enumerate specific microorganisms by acquisition of c ell-modulated electrode interfacial Fourier spectra.