Selective medium for isolation of Klebsiella pneumoniae

Abstract

Selective media for Klebsiella pneumoniae have been important in studies of hospital-acquired infections. On an agar medium which included ornithine, raffinose, and Koser citrate, K. pneumoniae strains grew as yellow mucoid colonies at 24 h and there was some increase in colony size at 48 h. Other members of Enterobacteriaceae were inhibited or produced small pink colonies on this same medium. Pseudomonas, Providencia, Acinetobacter, and Proteus species did not grow or showed very poor growth. The growth and appearance of these bacteria were not influenced by pH changes over a pH range of 5.2 to 6.4. Of 368 swabs of body sites cultured on MacConkey agar and on the test medium, 121 K. pneumoniae isolates on MacConkey agar and the same number on the test medium resulted. There were no discrepancies between the two media. Upon direct plating of stool, however, more K. pneumoniae colonies were isolated on the test medium than on MacConkey agar. Colonies on the test medium were more readily selected and identified than the colonies on MacConkey agar. There was also no inhibition of K. pneumoniae growth on the test medium compared with blood agar medium. This medium may be useful for the selective isolation of K. pneumoniae.