It was already reported in the previous study that in the sensitivity tests on ampicillin, cephalexin and cyclacillin, the MICs were fluctuated by the size of inocula and that those fluctuations were classified into three types of sensitivities,
i. e., Se-Se type, Re-Re type and Re-Se type.
In this investigation, the correlation between those types of sensitivities and protecting effects was studied in mice infections with
S. aureus or
E. coli through intraperitoneal challenge by varying challenge doses.
The organisms were proved to have shown three types of sensitivities to three antibiotics respectively. Single oral dose of the above antibiotics was given to infected mice at certain intervals after the challenge.
It was noted that the protecting effects were fluctuated by the challenge dose. The protecting effects correlated with the type of sensitivities were recognized only when 10
7 viable cell per mouse was challenged to mice.
No protecting effects were noted, however, when the challenge dose more than 10
8 viable cell per mouse was injected, irrespective of the type of sensitivities.
The protecting effects were shown in all types of sensitivities when both challenge doses 10
5 and 10
6 viable cell per mouse were injected in experimental
E. coli infection, and no significant difference was noted in the protecting effects between two different challenge doses.
Both cephalexin and cyclacillin had shown higher protecting effects when they were given to mice one hour after the challenge than when given immediately thereafter. In ampicillin, no difference was noted, however, between the two different intervals for administration.
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