Study on Resistivity of Shigella against Antibiotics

Abstract

The research was made for the 1, 663 Shigella strains, which were prevailing in 1958, to grasp the state of resistivity of those strains against antibiotics. The degrees of resistibility against Chloramphenicol, Streptomycin and Tetracycline were examined for that purpose.The finding are as follows:(1) The distribution of bacterial types:No remarkable difference in the distribution is found between the patients and the carriers. The main types of bacteria are Shigella flexner 2a, Shigella sonnei, Shigella flexner 3a, Shigella flexner 2b and Shigella flexner 1b.(2) The resistibility against eacn antibiotics:As has been reported so far, the degree of the resistibility of Shigella sonnei is lower than that of Shigella flexner. There is little difference in the resistibility between the patients and the carriers.(3) The frequency of appearance of the resistant strains:Little difference in the frequency of appearance of shigella flexner is found between the patients and the carriers, but that of Shigella sonnei shows the high rate only for the patients. Observing the frequency by age, those for the 0-9 and 20-49 age groups show the high rates. Observing it by the group of the patients or the carriers, only that for the group of the 0-9 years old patients shows the high rate.(4) Examination of the resistant strains:Examining the resistant strains by the group of the patients or the carriers, both groups have many of the resistant strains against three antibiotics-Chloramphenicol, Streptomycin and Tetracycline. It is noted, however, that particularly the patients have many of the same, while the carriers havitng the resistant strains against one antibiotics, Streptomycin, amount to 30 per cent of them.(5) Peculiarity of Shigella sonnei:Comparing Shigella sonnei with other types of bacteria, the degree of resistibility of the former is lower than the latters, but the frequency of appearance of the resistant strains to the former shows the highest rate of all, and such trend is remakable only for the patients and not for the carriers. Those findings are noticed as well as the fact that Shigella sonnei is recently increasing year by year.(6) Consideration on the mechanism of resistivity forming:There are many, at present, who support the salutation theory for the explanation of the mechanism. However, it is difficult to explain the whole only by that theory. Accordingly. the medium resistant strains were taken up to examine about the adaptation theory, and it was tried to make clear the difficult points from that angle.As the results, the followings were found:The frequency of appearance of the medium resistant strains decreases or increases almost in parallel with that of the resistant strains. The bacterial types were divided into three groups having resistivity, medium resistivity and resistibility each, and the frequencies of appearance of the resistant strains against the said three antibiotics were examined for each group. Comparing that against one of three antibiotics with those against the other two antibiotics each other, it was found that the frequencies of appearance for those groups were high in the order of one with resistivity, with medium resistivity and with resistibility. It suggests that the group with medium resistivity exists as a process to the group with resistivity. Thus, the main part of the mechanism of resistivity forming can be explained by the salutation theory, but the adaptation theory can not be disregarded.