Experimental ecological studies on H2 plasmids in the intestine and faeces of the calf

Antibiotic resistance: consequences of inaction

Bacterial resistance presents therapeutic dilemmas to clinicians worldwide. The warnings were there long ago, but too few people heeded them. Thus an emerging problem has grown to a crisis. Resistance is an ecological phenomenon stemming from the response of bacteria to the widespread use of antibiotics and their presence in the environment. While determining the consequences of inaction on the present and future public health, we must work to remedy the lack of action in the past. By improving antibiotic use and decreasing resistance gene frequency at the local levels, we can move towards reversing the resistance problem globally.

Diagnostic and public health dilemma of lactose-fermenting Salmonella enterica serotype Typhimurium in cattle in the Northeastern United States

The presence of lactose-fermenting Salmonella strains in clinical case materials presented to microbiology laboratories presents problems in detection and identification. Failure to detect these strains also presents a public health problem. The laboratory methods used in detecting lactose-fermenting Salmonella enterica serotype Typhimurium from six outbreaks of salmonellosis in veal calves are described. Each outbreak was caused by a multiply-resistant and lactose-fermenting strain of S. enterica serotype Typhimurium. The use of Levine eosin-methylene blue agar in combination with screening of suspect colonies for C8 esterase enzyme and inoculation of colonies into sulfide-indole-motility medium for hydrogen sulfide production was particularly effective for their detection. A hypothesis for the creation of lactose-fermenting salmonellae in the environment is presented. It is proposed that the environment and husbandry practices of veal-raising barns provide a unique niche in which lactose-fermenting salmonellae may arise.

Transfer of plasmids between strains of Escherichia coli under rumen conditions

Strains of Escherichia coli originally isolated from the rumen of sheep were shown to be capable of exchanging a 60kb plasmid, conferring resistance to tetracycline and ampicillin, at low frequencies (below 10(-6) per recipient) under anaerobic conditions in the presence of (a) autoclaved and clarified rumen fluid, (b) raw clarified rumen fluid, or (c) whole rumen fluid. Under anaerobic conditions the two rumen strains showed no inhibition of growth rate when 50 mmol l-1 volatile fatty acids were added to LB medium at pH 7, although significant inhibition resulted with 100 mmol l-1 VFA. The two rumen strains, and four strains from the pig gut, showed less inhibition of anaerobic growth by volatile fatty acids than did three laboratory strains examined for comparison. These findings indicate that plasmid transfer between certain E. coli strains can occur under conditions that closely simulate an anaerobic but environment.

IncH plasmids in Escherichia coli strains isolated from broiler chicken carcasses

Plasmids conferring tellurite resistance were transferred at low temperature (27 degrees C) from Escherichia coli strains isolated from chicken carcasses at the time of slaughter and after storage. They belonged to group IncH, as evidenced by their large molecular weight and incompatibility with plasmid pIP233. E. coli strains contaminating chickens meat can thus represent a source of IncH plasmids in the food chain of humans.