Inhibition of in vitro Salmonella typhimurium colonization in porcine cecal bacteria continuous-flow competitive exclusion cultures

Continuous-flow (CF) chemostate cultures were used as models to determine t he potential usefulness of undefined porcine cecal bacteria as competitive exclusion (CE) cultures against colonization by Salmonella Typhimurium. One culture, pCF1, was derived from cecal bacteria of an animal maintained on antibiotic-free feed, while the other culture, pCF4, was derived from cecal bacteria of an animal maintained on feed containing chlortetracycline. The effectiveness against a chlortetracycline-resistant Salmonella Typhimurium was examined in CF cultures maintained in the absence (pCF1 and pCF4) and presence (cpCF1 and cpCF4) of chlortetracycline. CF cultures were inoculate d with each of 10(2), 10(4), and 10(6) Salmonella Typhimurium CFU/mL. Chemo stat inocula of 10(2) Salmonella CFU/ml resulted in no Salmonella Typhimuri um being detected at 2 and 3 days postinoculation in pCF1 and pCF4, respect ively, and after 2 days in both cpCF1 and cpCF4. Inoculations of 104 Salmon ella Typhimurium CFU/ml resulted in clearance from pCF1 and pCF4 within 4 d ays and within 3 days from cpCF1 and cpCF4. Following inoculation with 106 CFU/ml, no Salmonella Typhimurium were detected in all CF cultures by 6 day s postinoculation. The results indicated that in vitro CF cultures of porci ne cecal bacteria were able to inhibit the growth of Salmonella Typhimurium . The ability to Limit Salmonella Typhimurium growth was not restricted by prior exposure of the cecal bacteria to the feed additive chlortetracycline . The present study demonstrates the potential application of CF cultures a s models to aid in the identification of CE cultures against salmonellosis in pigs.