Adaptation of Autocatalytic Fluctuations to Diffusive Noise

Evolution of a system of diffusing and proliferating mortal reactants is analyzed in the presence of randomly moving catalysts. While the continuum description of the problem predicts reactant extinction as the average growth rate becomes negative, growth rate fluctuations induced by the discrete nature of the agents are shown to allow for an active phase, where reactants proliferate as their spatial configuration adapts to the fluctuations of the catalysts density. The model is explored by employing field theoretical techniques, numerical simulations and strong coupling analysis. For d<=2, the system is shown to exhibits an active phase at any growth rate, while for d>2 a kinetic phase transition is predicted. The applicability of this model as a prototype for a host of phenomena which exhibit self organization is discussed.Comment: 6 pages 6 figur

A comparison of serotyping, BRENDA-typing and incompatibility grouping, and toxin testing of haemolytic Escherichia coli isolated from piglets before and after weaning

Before weaning, some young pigs in a research piggery excreted in their faeces a weakly haemolytic non-enterotoxigenic serotype of Escherichia coli. After weaning, all of the pigs excreted strongly haemolytic Escherichia coli of known enteropathogenic serotypes (0-138 and 0-139). The 0-138 serotype produced vero cell toxin, whilst the 0-139 serotype elaborated heat labile enterotoxin. Haemolytic enterotoxigenic E. coli were also recovered from three-week-old unweaned piglets with so-called ‘milk scours’ and from pigs with post-weaning diarrhoea on two local commercial piggeries. Selected haemolytic isolates were compared using serotyping, bacterial restriction endonuclease DNA analysis (BRENDA) and incompatibility grouping. The three typing methods divided most of the isolates into the same groupings; the exceptions were two isolates with the same BRENDA pattern and incompatibility group, but with different H-serotypes, and eleven isolates with the same serotype and BRENDA pattern but which showed differences in colony compatibility such that they were divided into five subgroups of a single incompatibility type