Abstract
Interaction of viable micro-organisms with negatively charged cation exchange resin, Bio-Rex 70 and with hydrophobic Phenyl-sepharose gel was investigated. These chromatographic materials can be used to resolve, to a greater or lesser extent, binary mixtures of some organisms both from broth cultures and from artificially inoculated food suspensions. The mechanism of interaction between micro-organisms and the chromatographic adsorbents, Bio-Rex 70 and Phenyl-sepharose was also investigated. The presence of specific microbial cell surface proteins i.e. K88a antigen of E. coli and protein A of Staph. aureus enhanced adsorption of the organisms to both Bio-Rex 70 and Phenyl-sepharose. The interaction of micro-organisms with negatively charged Bio-Rex 70 may not involve significantly the opposite charges on these bodies. Several lines of evidence strongly suggest that organisms interact with the 'hydrophobic' acrylic matrix of Bio-Rex 70. For instance, the modification of carboxyl groups of Bio-Rex 70 by various treatments did not reduce adsorption of Staph. aureus compared with the non-treated control. The adsorption of micro-organisms to Phenyl-sepharose gel involved hydrophobic interactions e. g. in distilled water ca 40% of Staph. aureus adsorbed to the gel while in presence of 1M (NH[4])[2]SO[4] the adsorption was >99%. Novel immunosorbent chromatographic methods were demonstrated for the enrichment of viable cells of Salm. typhimurium from mixed broth cultures containing other Enterobacteriaceae. There was 11-fold enrichment of Salm. typhimurium from a mixture with E. coli and 5-fold enrichment from a mixture with Cit. freundii using Salmonella antiserum coupled to a magnetic gel, Magnogel AcA 44. However, Salm. typhimurium was not enriched from food preenrichment broths. A method involving separation and concentration of micro-organisms from meats was devised prior to rapid estimation of the organisms by measurement of microbial ATP. A linear relationship was found between log[10] (total viable count) and log[10] (microbial ATP content) for lamb (r = 0.98) and for beef (r = 0.97).