Improved Culture Methods for the Detection of Ps. pyocyanea.

Williams, Clayton-Cooper, Faulkner, and Thomas (1944) drew attention to the fact that Pseudomonas pyocyanea may survive and even multiply in solutions of cetrimide (cetyl-trimethyl-ammonium-bromide). The use of this compound in selective media for the identification of Ps. pyocyanea was suggested by Harper and Cawston (1945), who recommended a concentration of 1 % in nutrient agar. This medium, however, was shown by Hood (1948) to inhibit the growth of small inocula of Ps. pyocyanea. Concentrations of cetrimide small enough to be without this inhibitory action allowed the growth ofcertain strains ofProteus vulgaris and Bacterium coli. The value of enriching I % cetrimide agar with serum or blood was therefore tested, and a medium containing 10% defibrinated horse blood was found satisfactory for dilute inocula of pure cultures and for the examination of swabs from infected burns (Hood, 1948, 1949). A disadvantage of cetrimide blood agar is its dark-brown colour, which makes it necessary to subculture colonies to a medium (e.g., nutrient agar, or preferably 1% cetrimide agar) on which Ps. pyocyanea can be identified by its pigments. In search of a simpler technique we have studied (1) the use of plasma for enrichment; (2) the use of an ultra-violet lamp for the detection of fluorescence on solid media; and (3) the practical value of lower concentrations of cetrimide without enrichment.