The Separation and Estimation of Microbial Populations Using Biochemical and Biophysical Techniques.
Investigation of the adsorption of micro-organisms to ion exchange resins revealed two types of interaction. In the approximate range pH 1 - 5 adsorption was not related to the ionogenic groups of the resin. At higher pH values (5 - 9) a more specific interaction occurred which was dependent upon the ionogenic groups of the resin and the ionic composition of the suspending medium. The specific adsorption of Staphylococcus aureus and of yeasts to strongly basic anion exchange resin was progressively inhibited by increasing salt concentration. A large proportion of the adsorbed organisms was recovered in a viable condition by elution with salts solutions (0.2 - 0.6M). The specific adsorption of micro-organisms to cation exchange resins did not occur from distilled water but organisms were strongly adsorbed from dilute salt suspensions (0.05M). Adsorbed organisms were eluted in a viable condition by alteration of the pH and ionic composition of the medium. Novel methods were demonstrated for the chromatographic resolution of mixtures of Staph, aureus and E. coli by differential adsorption or elution using small columns (lg) of cation exchange resin. The mechanism by which cells adhere to ion exchange resins was investigated. Two major cell surface components, teichoic acid and lipopolysaccharide, were shown not to be involved in the adsorption of cells to anion exchange resin. Cell surface protein was implicated in the adsorption of Staph, aureus to both types of resin. The blockage of cell surface cationic groups (e.g. amino) inhibited adsorption to cation exchange resin whilst the blockage of anionic groups (e.g. carboxyl) promoted adsorption. The separation of micro-organisms from foods was demonstrated using both anion and cation exchange resins. The recovery of raw meat flora from anion exchange resin (20%) was much lower than that from cation exchange resin (75%). Two rapid methods for the estimation of micro-organisms in foods were investigated. An inverse linear relationship was found between numbers of micro-organisms and impedimetric response which permitted the rapid estimation of micro-organisms in two foodstuffs. The rapid estimation of micro-organisms in meat by the photometric estimation of microbial ATP was achieved only after separation of the microorganisms from the meat.