Downloaded from www.microbiologyresearch.org by

WE have previously reported our method of typing strains of Pseudomonas pyocyanea (Ps. aeruginosa) by their ability to produce pyocines that give characteristic patterns of inhibition on a set of eight indicator strains (Gillies and Govan, 1966). We also noted that unless incubation of the strain to be typed was undertaken with fairly strict limits on the temperature and period of incubation, a significant proportion of strains gave aberrant results. Our method, although employing fewer indicator strains, was more sensitive than that of Darrell and Wahba (1964) and allowed the recognition of a greater number of pyocine types of Ps. pyocyanea. In the present paper we report more fully on the main typing procedure and outline a method of subdividing strains of pyocine type 1, the commonest type in our series. We also present evidence in support of a hypothesis made in our earlier paper, namely that the finding of strains of more than one type in a patient’s lesion is due to infection with strains of different types, and not to instability and variation of type in a single infecting strain