THE ANAEROBICALLY CULTURED CECAL FLORA OF ADULT FOWLS THAT PROTECTS CHICKENS FROM SALMONELLA INFECTIONS

In this work we have analyzed the bacterial composition of anaerobically cultured cecal contents (mixed broth culture) of adult fowls previously shown able to protect 1 day old chickens from oral Salmonella infections. All four cultures studied in this paper gave complete protection against Salmonella infantis when used undiluted or in the 10-2 dilution and at least some protection in the 10-4 dilution. The total aerobic as well as anaerobic counts on the nonselective medium used (VLMH) were of the order of 108 viable organisms/ml indicating that the mixed broth culture consisted predominantly of facultative organisms. From a total of 239 colonies isolated on the basis of colony morphology 66 were obligate anaerobes and 173 facultative anaerobic or microaerophilic species. Isolates were selected from each medium. They were grouped and tentatively classified on the basis of their ability to grow on selective media, their colony and cell morphology, Gram stain and products formed from glucose fermentation (obligate anaerobes). Further characterization was performed using conventional carbohydrate fermentation and biochemical tests. However only a minor fraction of the anaerobic isolates could be identified as being identical to known species. The most numerous species were E. coli and various Lactobacilli which were still found in the highest dilution (10-8) of the broths. Fecal streptococci were the next most frequent, isolated at the 10-7 dilution. The obligate anaerobes isolated included Gram-positive cocci and Gram-positive and -negative rods tentatively classified as Eubacteria, Propionibacteria, Clostridia, Fusobacteria and Bacteroides. A large number of them were isolated from the 10-6 dilution and some species of Eubacteria and Clostridia could only be recovered from the 10-3 or 10-4 dilutions.