It is well established that oral infection in mice with
S. enteritidis is influenced by the status of intestinal microbial flora and the normal flora can provide resistance to the salmonella infection. In this report, changes in the intestinal flora and the susceptibility to
S. enteritidis No. 11 strain in mice after oral administration of several antibiotics were investigated.
There observed significant increase of mortality by oral challenge of
S. enteritidis after the treatment (oral administration) with Erythromycin (EM), lincomycin (LCM), and kanamycin (KM). However, increase of mortality was not observed in mice treated with Streptomycin (SM) or Nalidixic acid (NA). Although failed to increase the mortality of mice, SM, like EM, considerably promoted the growth of
S. enteritidis in the intestinal tract. On the contrary, in the NA-treated mouse intestine the organisms diminished in number.
The significant decrease in number of Enterococci and Anaerobes-especially Gram-positive bacilli-in the intestine was demonstrated in mice treated with EM. On the other hand, in mice treated with NA, coliform bacteria decreased remarkably in number. Furthermore, SM treatment reduced the number of coliform bacteria and Enterococci.
When a strain of Enterococci, BIO-4R, was given to EM- or SM-treated mice the susceptibility to
S. enteritidis was notably suppressed. Whereas, the oral administration of
Clostridium butyricum MB strain to EM-treated mice made them more susceptible against the salmonella infection.
From these data, it is concluded that Enterococci and Gram-positive Anaerobes such as Corynebacterium may be the most important flora as a resistance-inducing factor in mice against salmonella enteritidis infection.
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