Tylosin and chlorotetracycline decrease the duration of fecal shedding of E. coli O157:H7 by swine

Previously we have shown that experimentally infected swine, fed an antibiotic-free diet, can become colonized and shed Escherichia coli O157:H7 for at least 2 months. However, in epidemiological studies this organism is only rarely recovered from domestic swine and the basis for this discrepancy is not clear. In this report we demonstrate that significantly fewer pigs fed diets containing subtherapeutic levels of either tylosin or chlorotetracycline shed E. coli O157:H7 for longer than 2 weeks compared to those fed an antibiotic-free diet. In contrast to tylosin and chlorotetracycline, the addition of bacitracin methylene disalicylate to the diet did not influence the recovery of E. coli O157:H7. These results suggest that some antibiotics may alter the gastrointestinal tract flora in ways that create a less favorable environment for E. coli O157:H7 in swine.