Studies on the Antibiotic-susceptibility of the Isolates from Staphylococcal Infections

The antibiotic susceptibility of 500 strains of staphylococcus aureus isolated from the patients with surgical suppurative diseases from December, 1957 to March, 1961 was studied. The results obtained will be summarized as follows: 1) Only a few strains were inhibited by a low concentration of penicillin. On the contrary, the majority of the strains were inhibited by a low concentration of erythromycin. Distribution curves of susceptibility to streptomycin, chloramphenicol and tetracycline lay between those of penicillin and erythromycin. The incidence of the resistant strains to five antibiotics was, in the order of frequency, 58.2 per cent to penicillin, 37.2 per cent to streptomycin, 18.8 per cent to tetracycline, 6.8 per cent to chloramphenicol and none to erythromycin. Multiple resistant strains numbered 165, the majority of them being resistant to both penicillin and streptomycin. 2) Environmental and geographical influence on staphylococcal susceptibility was studied with three different groups of strains. With streptomycin and tetracyclin, there was a distinct difference between the strains isolated from hospitalized patients of our clinic and the strains isolated from the out-patients of suburban hospitals, the incidence of resistant strains being remarkably high in the former. With chloramphenicol, a considerable number of the strains isolated from hospitalized patients of our clinic required a high concentration for inhibition, although not so remarkable as with streptomycin and tetracycline. With penicillin and erythromycin, there was no remarkable difference in the susceptibility of staphylococci among the three groups. 3) Of the 133 strains isolated from the hospitalized patients of our clinic, the susceptibility of 50 strainss isolated between May, 1958 and January, 1959 and of 50 strains isolated between July, 1959 and March, 1961 were compared. The penicillin resistant strains moderately increased, whereas with strep-tomycin and erythromycin, no significant changes were seen between the two groups. With chloramphenicol and tetracycline, no increase in the incidence of resistant strains was seen, but a decrease of sensitive strains and an increase of moderately resistant strains were seen in the lately isolated group. 4) As for the changes of the susceptibility of staphylococci after administration of a large amount of antibiotics, a decrease of sensitive strains and an increase of resistant strains were seen with every one of five antibiotics, the tendency being most remarkable with streptomycin.