RESUMEN
A rapid method of performing the Limulus amoebocyte lysate (LAL) test in milk is proposed using the Toxinometer ET-201. This instrument measured the increase in turbidity due to the interaction between the endotoxins of the Gram-negative bacteria and the LAL reagent, monitored the ratio Rt of the sequential to the initial transmission at 12 s intervals and quantified endotoxins by determination of the reaction time Tr required to obtain a 5% decrease in Rt. There was a good correlation between the toxinometrically determined endotoxin concentrations and the number of Gram-negative bacteria (SD, 0.18 log(plate count units)), and the repeatability (CV, 6-10%) was high. The assay may be useful for screening raw materials for UHT milk production, as the endotoxin content of the raw material is related to the rest proteinase activity in the UHT milk.
Asunto(s)
Endotoxinas/análisis , Bacterias Gramnegativas/aislamiento & purificación , Prueba de Limulus , Leche/microbiología , Nefelometría y Turbidimetría/instrumentación , Animales , Leche/químicaRESUMEN
Shifts were induced into the microbial community of activated sludge by the pulse addition of soluble starch. The subsequent changes of amylolytic and proteolytic microbial populations were recorded. Four amylolytic strains were isolated and characterized with regard to carrying capacity, specific surface and growth kinetics. The competitive ability of these strains was studied by means of two-member competition experiments. These experiments were analysed according to the Lotka-Volterra model and the de Wit method. The different results obtained suggest that the dominance of the amylolytic Pseudomonas sp. (code 01) is based on a combined occurrence of high amylolytic activity, large relative cell surface, high maximum specific growth rate and reduced sensitivity towards associated proteolytic populations.