Experimental infection of neonatal pigs with CNF toxin-producing strains of Escherichia coli.

To examine and compare the pathogenicity of cytotoxic necrotising factor (CNF)-producing Escherichia coli, two litters of piglets were infected orally with 10(10) E coli O88 or 10(10) E coli O32 strains. Of the six piglets infected with E coli O88, two died within 24 hours and three developed blood-stained diarrhoea. The other piglets were killed one, five, six and eight days after infection, when bacterial cultures indicated an overwhelming bacteraemic infection with E coli O88 in the early stages followed by clearance through the large intestine. The pathological changes consisted of an early enteritis, progressing to enterocolitis and a bacteraemic spread to the lungs. The histopathological changes were characteristic of toxaemic effects in brain, heart, liver and kidney, and characterised by congestion, oedema and exudation. Infection with E coli O32 produced a milder but similar enterocolitis, also with bacterial colonisation in the lungs. The histopathological findings again reflected a toxaemia. The enteritis was more persistent after E coli O32 infection and the strain persisted in large numbers in the intestine. No evidence of bacterial adherence to the intestinal mucosa was found with either strain. Enteroinvasion was only evident in one E coli O88-infected piglet, but the consistent occurrence of interstitial pneumonia showed the predilection of these organisms for the lung. The results confirm the toxigenic properties of CNF+ E coli and suggest an important role for this organism in enteric infection of young pigs.

Evaluation of a mixture of trimethoprim and sulphaquinoxaline for the treatment of poultry: safety and palatability studies.

The safety of a 1:3 mixture of trimethoprim (TMP) and sulphaquinoxaline (SQX) for administration in food or water was assessed in broiler chickens, chicks of an egg laying strain and breeding fowl. The only effects recorded in six-week-old broilers medicated for seven days at levels ranging from 16 to 133 mg TMP plus SQX per kg bodyweight were decreases in water or food consumption, probably caused by unpalatability at overdosage levels, and associated decreases in weight gain and packed cell volume at an achieved overdose level of 4.4 times the recommended use concentration (RUC). Breeding fowl medicated at levels of 1 X or 3 X RUC for 14 days showed slightly reduced reproductive performance reflected by lowered egg production, egg weight and hatchability. These effects were temporary and performance equal to that of unmedicated birds was re-established by 14 days after medication ceased. Week-old chicks medicated for five days at levels from 0.7 to 4.7 X RUC showed normal growth rate over 12 days. Eleven-day-old chicks could not distinguish medicated from unmedicated water.

Appraisal of the suitability of a disease model of acute salmonellosis in calves for chemotherapeutic studies.

When young calves were dosed orally with 10(10) organisms of a culture of Salmonella dublin, typical symptoms of acute salmonellosis followed with a death rate of 86 per cent. Peak mortality occurred six days after infection. As a result of a statistical appraisal of the consistency of mortality in groups of untreated calves a model is proposed for the therapeutic evaluation of antibacterial compounds, which compares the number of survivors in groups of seven or eight calves with a minimum of four needed for significant indication of efficacy. Bacteriological and pathological investigations showed that the experimental disease was initially an acute systemic infection followed by severe enteritis. Measurements of plasma concentrations of enzymes and other constituents did not achieve the desired objective of establishing a method of quantitative evaluation of the clinical status of individual animals, although some changes occurred which were consistent with the pathology of the disease and suggested possible mechanisms by which jaundice occurred.

Distribution of trimethoprim/sulphadiazine in plasma, tissue and synovial fluids.

The subcutaneous implantation of tissue cages was used to study the distribution of trimethorprim and sulphadiazine into tissue (interstitial) fluid in calves, sheep and dogs over a 24-hour period. After oral dosing there was good gastrointestinal absorption of both antibacterial agents in dogs but only of the sulphonamide in sheep. The concentration of trimethoprim in tissue fluid peaked at five to seven hours after administration when it exceeded the plasma concentration. Sulphadiazine persisted in the plasma for longer than trimethoprim, but distribution into tissue fluid was slower. The findings show that reliance on plasma concentration curves alone in determinations of bioavailability of chemotherapeutic agents may lead to false interpretations.