[Colony count and LPS content of gram-negative bacteria in cold storage foods and water]

In storage trials, the multiplication of gram negative bacteria was monitored by means of both colony counts and LPS-formation as determined by the three LAL tests methods (the Capillary test, the "Mini" Endotoxin test and the Coatest endotoxin method). The detection limits of the colony forming units which could be determined by the three LAL tests were initially set in model experiments in which beef (M. cleidooccipitalis) was variously inoculated with stationary-phase cells of Pseudomonas sp. previously grown at 30 degrees C. In all three methods, measurable amounts of LPS were possible only at colony counts above 10(3)/ml, g or cm2. The detection limits for colony counts of vacuum packed, aerobically stored beef muscle (Caput long. of M. triceps brachii) were found to lie between 1.0 x 10(3) and 1.0 x 10(4)/g for the Capillary test and the Coatest endotoxin method, and 5.0 x 10(4)/g for the "Mini" Endotoxin test. In the case of poultry carcasses the detection limits lay between 2.0 x 10(1) and 7.0 x 10(2)/cm2 and were thus considerably lower than for beef. With very low levels of bacterial loads, substrate interference in the LPS-LAL reaction must be taken into account. Linear regression analysis gave satisfactory correlation between the concentration of LPS and colony forming units for beef, poultry carcasses, ground beef and mixed salad. An acceptable proportionality was established only for beef and poultry carcasses. Potable water, stagnant for a fortnight in an experimental piping system and sampled at five different points, showed significant regrowth of oligocarbotolerant aquatic bacteria. However, only very low levels of LPS could be determined. All three LAL test methods can be recommended for rapid determination of the load of gram negative bacteria in meat and meat products.