An enzyme immunoassay was developed to detect Salmonella in foods. Indirect test protocols were developed for use with microtitration plates or Gilford microcuvettes. Samples from enrichment cultures were mixed with H-specific immunoglobulin G and allowed to react; unbound antibody was removed by three 5-min centrifugation washes; goat anti-rabbit antibody conjugated to alkaline phosphatase was added and allowed to react; and unbound conjugate was removed by centrifugation washing as before. Salmonella-positive samples were indicated by the production of a chromogenic reaction product after the addition of alkaline phosphatase substrate. The color could be read visually or quantified by absorbance. Ninety-eight food samples were examined to compare the enzyme immunoassay with enrichment serology, immunofluorescence, and the Food and Drug Administration pure culture technique. The enzyme immunoassay was sensitive and specific, and it possessed advantages over methods currently in use. Furthermore, when the enzyme immunoassay was used to screen preenrichment media, the results indicated that it might be decidedly more sensitive than the conventional pure culture technique. The detection of salmonellae in foods and foodstuff involves a series of enrichment steps because these pathogens, when present in foods, are generally found in low numbers and are often sublethally injured. Therefore, detection methodologies for salmonellae must be sensitive and allow for the resuscitation and growth initiation of injured cells. Two methods of Salmonella detection are currently recommended by the Food and Drug Administration (3): (i) a pure culture technique (PCT) involving preenrichment, selective enrichment, and selective plating; and (ii) immunofluorescence (IF) after selective enrichment. The PCT is an expensive and time-consuming process that requires 4 or 5 days for analysis (3). In contrast, IF is more rapid; it is sensitive, but many false-positives are obtained because polyvalent OH antisera are used and anti-O antibodies cross-react with a wide spectrum of related enteric bacteria (16, 17). Enrichment serology (ES; 13), a third method used by some laboratories, is more specific than IF, but ES is more cumbersome and has not met with widespread acceptance. The list of additional techniques for the detection of salmonellae is lengthy; however, the acceptance of a new procedure requires that it demonstrate det Journal paper no.

An indirect enzyme-labeled antibody technique (ELAT), in which Salmonella typhimurium was used as a model, was developed as a method to detect Salmonella in food samples. A cellulose-acetate membrane filter, the matrix for detection, was placed on a membrane-filter base and overlaid with a multiwelled lucite template. Mixed broth enrichment cultures were dispensed in the template wells, and cells were spotted onto the membrane via suction. After fixation, the membranes were immersed in rabbit anti-S. typhimurium flagella antibody, washed, immersed in goat anti-rabbit antibody conjugated to peroxidase, and washed. Exposure of membranes to the substrates 3,3'-diaminobenzidine or benzidine resulted in development of brown or blue macroscopic reaction products, respectively, on spots containing S. typhimurium. ELAT results agreed with those of enrichment serology and cultural procedures on three food products containing known levels ofS. typhimurium. Because of the magnification effect of the enzyme-substrate reaction, fewer cells were needed for detection than with enrichment serology, thereby reducing the total analysis time. The ability to test 14 or more samples simultaneously on a 47-mm membrane filter would facilitate screening large numbers of samples. Pending the development of a pure H antisera pool for the common Salmonella serotypes free from 0 antibodies, the ELAT demonstrated potential as a Salmonella detection methodology.

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A mutant of Saccharomyces cerevisiae, which forms large, multicellular flocs in liquid culture, rapidly fermented media containing high concentrations of glucose (100-180 g/L) in a continuous nonaerated tower fermentor at 30 degrees C. The fermentor operated continuously for seven months. Batch and tower fermentor data were fitted to a kinetic model incorporating linear ethanol inhibition and Monod dependence on glucose. Conversion, ethanol yield, and ethanol productivity were related to the apparent fermentation time for initial glucose concentrations of 130 and 180 g/L. Productivities of 8-12 g ethanol/L h were achieved through the yeast bed giving conversions exceeding 90% of the theoretical yield.

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