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ABSTRACT The distribution of Escherichia coli O157 in bovine feces was examined by testing multiple samples from fecal pats and determining the density of E. coli O157 in immunomagnetic separation (IMS)-positive fecal samples. The density of E. coli O157 in bovine feces was highly variable, differing by as much as 76,800 CFU g −1 between samples from the same fecal pat. The density in most positive samples was <100 CFU g −1 , the limit of reliable detection by IMS. Testing only one 1-g sample of feces per pat with IMS may result in a sensitivity of detection as low as 20 to 50%. It is therefore probable that most surveys have greatly underestimated the prevalence of E. coli O157 shedding in cattle and the proportion of farms with shedding cattle. The sensitivity of the detection of E. coli O157 in bovine feces can be as much as doubled by testing two 1-g samples per pat rather than one 1-g sample.

AIMS:To define a method that describes antimicrobial resistance of meta-populations of bacteria in both a quantitative and biologically meaningful way. METHODS AND RESULTS:Using spiral plating and colony counting technology we obtained, from animal faecal samples, the density of Escherichia coli that grow at different concentrations of antibiotic. A mathematical description of this dose-response curve fitted the data well. The parameters of this model have biological meaning and the model allowed subtle differences between meta-populations to be detected. CONCLUSIONS:This method, termed MPA (meta-population analysis), is practical and provides a useful quantitative description of antimicrobial resistance in a bacterial meta-population. SIGNIFICANCE AND IMPACT OF THE STUDY:This study shows that resistance can be defined quantitatively. The method may be used in many epidemiological and clinical studies of antimicrobial resistance in animals and humans.

A cationic benzoxazole compound used commercially as an optical brightener was found to have a selective bactericidal effect at low concentrations on a wide range of bacterial phytopathogens; many strains of Agrobacterium, Corynebacterium, Erwinia, Pseudomonas and Xanthomonas were tested. Known phytopathogenic species of Corynebacterium, Pseudomonas and Xanthomonas were rapidly killed, whereas saprophytic strains of Corynebacterium and Pseudomonas were resistant to 500 parts/106. The phytopathogenic Erwinia spp. were inhibited only by the higher concentrations of AN, and some saprophytic E. herbicola var. herbicola strains were slightly sensitive. The extent and nature of this selective bactericidal property is examined and discussed. Resistant mutant colonies were very rarely encountered. The results are of significance in that the recognition of such phytopathogens under laboratory conditions is made easier. The resistance of Ps. aeruginosa to the compound and its almost unique ability to utilize it as a sole carbon source offer a means of isolating this organism.

Controlled substrate addition was used to maintain mixed microbial cultures in fermenters at either pH 7.0 or 70% dissolved oxygen saturation. Control of pH permitted a greater volume of substrate to be processed. Ammonium nitrogen concentrations were similar for both fermenters but concentrations of oxidized nitrogen varied. Nitrification/denitrification sequences appeared to be initiated by unscheduled changes in dissolved oxygen concentration. It was possible to maintain a steady state with respect to a controlled parameter and end‐product quality but other parameters fluctuated.