摘要：One week after administration of streptomycin to Swiss white mice, caecal flora composition was altered but total populations of cultivable aerobes and anaerobes were unchanged. However, microscopic estimation of numbers demonstrated a 100-fold decrease in caecal fusiform populations. Streptomycin administration also caused an increase in pH of caecal contents and a decrease in caecal volatile fatty acid (VFA) concentrations. Multiplication rates and populations of Shigella sonnei and enterotoxigenic Escherichia coli were greater after culture in caecal contents obtained from streptomycin-treated mice than in contents obtained from untreated mice. When contents from streptomycintreated mice were adjusted to simulate conditions of VFA concentration and pH of contents of untreated mice, multiplication of the pathogens was retarded and growth curves resembled those obtained with contents from untreated mice. Conversely, when the pH of contents from untreated mice was increased to 7.50 to convert VFA to the dissociated form, growth curves of the pathogens were similar to those obtained with contents from streptomycintreated mice. In vivo, s. sonnei and E. coli associated in significantly greater numbers with the caecal mucosa of streptomycin-treated than untreated mice. This was confirmed in vitro with excised mouse caecal tissue suspended in washed cells of the pathogens. Streptomycin administration enhances susceptibility of mice to colonisation with enteric pathogens apparently by increasing the pH and decreasing VFA concentrations of intestinal contents and by facilitating association of pathogens with intestinal mucosa. This may be a reflection of diminished mucosal fusiform populations resulting from the activity of the antibiotic.Keywords: Streptomycin; Colonisation resistance; Mice.
