Proteus Infections in a General Hospital. I. Biochemical Characteristics and Antibiotic Susceptibility of the Organisms

Biochemical characteristics, bacteriophage and bacteriocine typing, Dienes tests, and susceptibility to antibiotics were used to classify strains of Proteus mirabilis from 209 patients at Boston City Hospital, Boston, Mass. Three fourths of the strains could be classified into 10 major proticine types. Strains of proticine types 6 and 9 were the most closely related by Dienes tests and by their antibiotic resistance patterns. Gentamicin was uniformly active against strains of P. mirabilis, but approximately 15% were resistant to kanamycin. Carbenicillin was the most active of the penicillins; 20% of the strains were resistant to ampicillin. There was a marked inoculum effect with most of the antibiotics. Carbenicillin and gentamicin were equally active against P. mirabilis and against indole-positive strains of Proteus.