抄録
The influence of antibiotics, bile acid and Escherichia coli on the growth of Salmonella typhi was studied by the following method.
In the presence of several antibiotics diluted to the minimum inhibitory concentration (MIC) against S. typhi and sodium desoxycholate (DC), S. typhi was mixed with two strains of E. coli which were different from each other in sensitivity to antibiotics. The numbers of each viable bacterial cell were then detected.
The results obtained were as follows:
1) DC inhibited S. typhi when the concentration of DC added to the medium was over 2 mg/ml. DC inhibited also the sensitive strain of E. coli when the concentration of DC added to the medium was over 6 mg/ml. But DC did not inhibit the resistant strain of E. coli when the concentration of DC added to the medium was under 10 mg/ml.
2) E. coli inhibited S. typhi. The inhibitory effect of each E. coli strain on the S. typhi growth was proportional to the respective sensitivity to antibiotics.
3) DC enhanced the antibacterial activity of Ampicillin (ABPC) and Cephalothin (CET) against S. typhi. DC enhanced the antibacterial activity of Tetracycline, ABPC and CET against the sensitive strain of E. coli. But DC had no influence on all antibiotics against the resistant strain of E. coll.
4) In the mixed culture of S. typhi and E. coli the antibacterial activity of ABPC and CET against S. typhi decreased as compared with that in a single culture. DC partially restored this antibacterial activity.
5) The resistance to ABPC was transfered from the ABPC-resistant strain of E. coli to S. typhi. DC inhibited the transfer of ABPC resistance when DC concentration was increased.
