Simultaneous colonization of Campylobacter jejuni and Salmonella typhimurium in day-old chicks

Day-old chicks were challenged with Campylobacter jejuni or Salmonella typhimurium or both to assess the influence of these two bacteria upon the colonization of one another. Median colonization dose (CD50), a measure indicating the number of organisms required to colonize one-half of the challenged chickens, was used to assess the influence of these organisms upon the colonization of one another. Chicks were gavaged with serial dilutions of 1) C. jejuni, 2) S. typhimurium, 3) dilutions of C. jejuni and a fixed level of S. typhimurium, or 4) dilutions of S. typhimurium and a fixed level of C. jejuni. Six days postchallenge, cecal contents were quantitatively assayed for the challenge organisms. Birds challenged with only C. jejuni or birds challenged with both C. jejuni and S. typhimurium had a CD50 of 120 C. jejuni cells. The CD50 values for S. typhimurium alone (48 cells) and S. typhimurium simultaneously colonized with C. jejuni (180 cells) were not significantly different (P less than .05). The colonization levels of either organism were generally correlated with the challenge dose and ranged up to 63 million cells per gram. It was concluded that the CD50 for both C. jejuni and S. typhimurium in 24-h-old chicks were similar, and the presence of one of these particular co-colonizers does not influence the CD50 of the other.