Submitted to: Rushmore Conference on Mechanisms in Pathogenesis of Enteric Diseases
Publication Type: Abstract Only
Publication Acceptance Date: 10/2/1998
Publication Date: N/A
Technical Abstract: Antibiotics are often administered to swine as feed additives at subtherapeutic concentrations to enhance feed conversion and animal growth and at therapeutic dosages to combat salmonellosis. Competitive exclusion (CE) is the use of beneficial bacteria to inhibit colonization of the digestive tract by enteropathogens. The objective of the present study was to determine the in vitro effect of chlortetracycline (CTC) on the ability of CE bacteria to eliminate Salmonella typhimurium (St) from continuous-flow (CF) chemostat cultures. CF cultures of CE bacteria were derived from cecal microflora collected from swine maintained on unmedicated feed or on feed containing CTC at 200 g/ton. Both CF cultures were grown in vitro in chemostat vessels and in the presence of CTC at 220 or 440 ug/ml. Inocula of 10**4 St (CTC-resistant) cfu/ml in both cultures containing 220 ug/ml of CTC resulted in the clearance of St by 4 days after inoculation. No St were detected at 2, 3, or 4 days after inoculation of cultures at 10**2, 10**4, or 10**6 St (CTC-resistant) cfu/ml, respectively, in chemostats containing CTC at 440 ug/ml. These data suggest that the CF cultures have the potential for use as CE cultures in the presence of CTC to reduce St colonization in the porcine digestive tract.