[The growth and lipopolysaccharide production of Escherichia coli and Pseudomonas aeruginosa].

The course of growth and LPS production of two strains of type cultures of Escherichia coli (ATCC 11229, ATCC 25922), one E. coli mutant strain P400 and one type strain of Pseudomonas aeruginosa (ATCC 15442), grown partly by repeated cultures in BHI and partly also in minimal medium or in 1:10 diluted PC broth in a gyratory shaker (60 rpm) at 30 degrees C, was monitored respectively by counting the cfu and by simultaneous determination of LPS by means of the three miniaturized LAL-tests, i.e. the capillary test, the "Mini" endotoxin test and the Coatest endotoxin method. All three tests yielded generally comparable and reproducible results. The LPS content for a defined number of cfu was virtually in the same order of magnitude in all cases, regardless of the nutrient content of the culture medium. The quantity of LPS was relatively high in the initial phases of growth but then decreased significantly to constant levels in the stationary phase. There was a remarkable increase in the yield of LPS in the mid- and late stages of the exponential phase in the three strains, in contrast to the mutant in which the LPS content declined continuously. A possible explanation for this variation could be due to the fact that specific cell membrane proteins, which are lacking in the mutant, react differently with the LPS and thus with the Limulus Amoebocyte lysate. When the LAL tests are used for the rapid determination of the gram negative bacterial load of in particular perishable fresh foods, in which generally bacterial cells are at different stages of the exponential growth phase, then it is necessary to standardize each method specifically both for the product and for the storage conditions.