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Strains of Pasteurella pestis, grown on Fildes" or sulphite agar, or on a selective medium, at 30 °C formed microcolonies containing from 20 to 50 bacilli in 5 to 6 hours. These microcolonies were treated with a P. pestis bacteriophage and subsequently incubated at 18 °C. Lytic changes in the microcolonies began about 3 hours after application of the phage and the microcolonies were largely destroyed 2 hours later. The phage lysed microcolonies of several strains of Pasteurella pseudotuberculosis, two of Escherichia coli, and one of Shigella dysenteriae at 30 °C but at 18 °C it was active only on E. coli K12 C600 besides P. pestis. The susceptible E. coli strain did not grow on the selective medium, which could therefore be used to increase the specificity of the test. Methods for performing this test in practice are discussed. The technique would allow P. pestis to be identified about 10 hours after inoculation of an agar plate with infected material. Although slower than a fluorescent antibody reaction performed on a direct smear of infected material, this phage-lysis procedure may find a place as a semirapid confirmatory test for P. pestis.

Two coliphage repressers were originally isolated as monomeric proteins. Here it is shown that these repressers attach to DNA in the form of oligomers, possibly as tetramers, and that these oligomers are in rapid equilibrium with the monomers.

Sequential isolates of Pseudomonas aeruginosa from 57 infected sites in 54 patients were pyocine-typed on agar plates containing mitomycin C, by a method depending on inhibition of indicator strains by pyocines produced by the test strains. The inhibition pattern remained constant for cultures from 28 infected sites. In the remaining 29, both predominant and variant patterns could be identified. Many variant patterns differed from the predominant one only to the extent of one indicator strain. Each of two commonly occurring predominating patterns varied characteristically from the other pattern. It was suggested that minor variations in inhibition pattern reflect instability of either pyocine production or pyocine susceptibility of the indicator strains, whereas major variations in pattern signify independent infections.