The sensitivity to 8 antibiotics, PC, SM, CM, TM, AM, EM, CBM and LM, of the pathogenic staphylococci isolated from the surgical infections and otorhi-nological diseases and from the aerial dusts in the hospital and the nasal vestibules of the hospital workers during the 2 years from January, 1953 to December, 1954 was investigated and the bacteriological characteristics were comparatively studied between the PC-resistant and the PC-sensitive strains. The results obtained are as follows.
1) Sixty strains (45.4%) out of the 132 staphylococcal strains isolated from the surgical infections were found to be resistant to more than 1.0 μ/m1 of PC and the PC-resistant strains were confirmed to have increased since 1950 and furthermore the tendency of the increase of the highly resistant strains was noticed. Ten (50%) out of the 20 strains of staphylococcus isolated from the otorhinological diseases were PC-resistant as well.
2) Most of the PC-resistant strains were found in the cases to which more than 610, 000 units of PC had been administered, which fact suggests that the PC treatment in the past considerably influences the emergence of the PC-resistant strains.
3) The PC-resistant strains were more frequently found in the suppurative operation wounds and were more often found in the open lesions than in the closed foci.
4) Around 70% of the infections of the hospital workers and in-patients were found to be due to the PC-resistant strains, this figure being higher than 37.6% of the out-patients. However, it was found that also the out-patients were fairly influenced by the PC-resistant strains.
5) Twenty-eight (75.7%) out of the 37 strains of pathogenic staphylo-coccus isolated from the aerial dusts in the hospital and from the nasal vestibules of the hospital workers were found to be PC-resistant and the significance of the cross-infection in the hospital with the PC-resistant staphylococci was recognized.
6) Among the 155 strains of staphylococci, SM-resistant strains were 23.2%, TM- and AM-resistants 3.8% and CBM-resistants 1.9%, while no strains were found to be resistant to any of CM, EM and LM.
7) Between the PC-resistant and the sensitive strains no significant difference could be found in the production of pigment, coagulase and hyaluroni-dase, the liquefaction of gelatine, the sugar fermentation and the pathogenicity to the rabbit skin except the production of penicillinase and so the clinically important PC-resistant staphylococci are considered to retain their full pathogenicity.
8) From the view-point of drug-sensitivity PC should not be abused to the staphylococcal infections but the antibiotics of the tetracycline series such as TM, AM etc. or CM, EM, LM etc. should be employed. But, around 35% of them are the cases due to the staphylococcus strains which are the most sensitive to PC, in which PC should be a first choice.
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