AN INTERLABORATORY COMPARISON OF PHYSICOCHEMICAL METHODS FOR STUDYING THE SURFACE-PROPERTIES OF MICROORGANISMS - APPLICATION TO STREPTOCOCCUS-THERMOPHILUS AND LEUCONOSTOC-MESENTEROIDES

The overall properties of the cell surface of Streptococcus thermophilus and Leuconostoc mesenteroides, two fouling microorganisms from dairy industry, were determined by a variety of physico-chemical methods. The study was carried out as an interlaboratory comparison to identify seemingly unimportant but yet critical steps in the experimental methods, i.e., contact-angle measurements, electrophoresis, X-ray photoelectron spectroscopy (XPS) and transmission Fourier-transform IR spectroscopy (FTIR). Particularly with regard to the contact-angle measurements, it turned out that the original papers, in which the technique was explained, did not contain enough detail. On the basis of the present experience, more emphasis is put on a slow preparation of bacterial samples and monitoring of the drying process by contact-angle measurements. Furthermore, the known importance of the suspending buffer in zeta potentials becomes extremely obvious since one of the strains employed preferentially adsorbed K+ from the buffer. Artefacts created during freeze-drying for XPS and FTIR analyses are mentioned. It is pointed out that the above four methods form a unique set of techniques for studying microbial cell surfaces, in the sense that the results of the various methods allow an interpretation of the physico-chemical properties of the cells in terms of their chemical composition. © 1990.