One handred and twenty three strains of Pseudomonas aeruginosa (Ps. aerug.) isolated from clinical materials in the Hokkaido University Hospital in 1967 were typed serologically by means of Homma's agglutination method, utilizing a routine set of 12 standard sera. One handred and one strains (82.1%) were typable with an occurrence of type T5 in 36 strains (29.3%), type T8 in 23 (18.7%), type T3 in 9 (7.3%), and Type T1 and T4 each in 7 (5.7%).
Strains of Ps. aerug. were highly resistant to usual antibiotics such as tetracycline, chloramphenicol, streptomycin, kanamycin and carbenicillin with minimum growth inhibitory concentrations (MIC) of more than 50 mcg/ml. The mode of MIC of gentamicin, colistin and polymyxin B were 3.2, 6.3 and 3.2 mcg/ml respectively, which appeared to be within levels of therapeutic efficacy.
The type T5 strains were generally more resistant to the above mentioned eight antibiotics tested, and the type T8 strains were less resistant than all other strains. On the other hand, strains derived from urine samples were more resistant than those from any other sources. The incidence of urine derived strains in type T5 was higher (50%) than that in type T8 (17%). This may be one of the reasons for the higher antibiotic resistance of type T5 strains.
