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A radioimmunoassay for detection of C1q-binding IgG aggregates and antigen-IgG antibody complexes is described. The assay makes use of solid-phase C1q and 32p-labelled protein A-rich Staphylococcus aureus as an indicator system. Both 19S and heavier IgG aggregates that fixed C1q were detected. The sensitivity of the assay permitted detection of heavy (19-25S) IgG aggregates at a concentration of 8 mug/ml or less. The results indicated that detection of IgG in this assay is dependent on the degree of IgG polymerization and the molar ratio between the solid-phase C1q and the IgG polymers. Albumin-anti-albumin complexes, preformed at equilibrium with antibody to antigen molar ratios of 2:1 to 3:1 and at antigen concentrations of 25 to 40 mug/ml, were also detectable using the described radioimmunoassay.

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The potential of microcalorimetry as a rapid method for the estimation of bacterial levels in ground meat was studied. The exothermic heat production rates (HPRs) of Escherichia coli and meat suspensions were measured in a BioActivity Monitor and correlated to log10 CFU/ml or g. Comparative experiments using 0.1% peptone saline (PS) or nutrient broth (NB) as the suspending medium showed that maximum HPRs (peak times) were obtained faster with NB than with PS, and that HPR peaks were more distinct when using NB. Two series of 11 meat samples suspended 1:10 in NB were examined at instrument operating temperatures of 21 and 30°C, respectively, and HPRs were compared to mesophilic colony counts (30°C/3 d) and to psychrotrophic counts (17°C/17 h then 7°C/72 h). Peak times at 30°C were considerably shorter than those at 21°C. The correlation between both plate count methods and the peak times were better when measuring at 21°C than at 30°C. Significant correlations between HPRs and colony counts were obtained with all experimental conditions. Results indicate that micro-calorimetric measurements of 10−1 NB suspensions of ground meat provide a promising analytical tool for estimation of the bacterial levels in less than 24 h in the range of 105 to 108 CFU/g.

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