DIFFERENTIAL COUNTING OF MIXED BACTERIAL POPULATIONS

ISOLATION AND IDENTIFICATION OF ENTEROCOCCI FROM THE INTESTINAL TRACT OF THE RAT

Rogers, C. G. (Department of National Health and Welfare, Ottawa, Ontario, Canada), and W. B. Sarles. Isolation and identification of enterococci from the intestinal tract of the rat. J. Bacteriol. 88:965-973. 1964.-Surface inoculation was employed in a comparison of three selective media, M-enterococcus (M) agar, thallium acetate-glucose (TITG) agar, and KF-streptococcus (KF) agar, for enumeration and isolation of enterococci from contents of the digestive tract of the rat. Similar yields of enterococcus colonies were obtained with M, TITG, and KF agar. When cecal contents were examined, species identification of 120 isolates, 40 from each medium, revealed only minor differences in selective activity. Streptococcus faecalis and its variety zymogenes represented 55 to 63% of the isolates from each medium; the remaining strains resembled S. durans or S. faecium. More than 99% of the isolates failed to survive the heat-tellurite tolerance test. Periodic analyses of intestinal contents from young rats indicated that enterococci became established in the gut from 10 to 14 days after birth. The species isolated most frequently on M agar was S. faecalis var. zymogenes. When rats were fed a purified diet with casein as the source of nitrogen, S. faecalis var. zymogenes predominated among isolates from contents of the small intestine plated on M agar. This species was largely replaced by others resembling S. durans or S. faecium when mixtures of l-amino acids provided the dietary nitrogen. Nineteen enterococcus isolates, representing all that met the Sherman criteria, required arginine, glutamic acid, histidine, isoleucine, leucine, methionine, tryptophan, and valine; of these, two strains required in addition threonine, glycine, and lysine; four required threonine and glycine; two, threonine and lysine; and one, threonine.

ECOLOGICAL FACTORS INFLUENCING THE RELATIONSHIPS BETWEEN KLEBSIELLA AND SHIGELLA IN MIXED CULTURE

Hentges, David J. (Loyola University, Chicago, Ill.), and MacDonald Fulton. Ecological factors influencing the relationships between Klebsiella and Shigella in mixed cultures. J. Bacteriol. 87:527-535. 1964.-Viable-cell counts of Shigella flexneri and Klebsiella (Aerobacter aerogenes) in pure and mixed culture were made during growth under predetermined conditions of temperature, pH, oxygen supply, and nutrient supply. In pure culture, environmental changes had marked effects on the Shigella populations. Klebsiella populations were not affected except at 44 C or when aerated; under these conditions, the populations were smaller. In nonaerated mixed culture, under different conditions of temperature, pH, and nutrient supply, Klebsiella interfered with the multiplication of Shigella. Exponential growth of Shigella was interrupted at about the time Klebsiella populations attained a maximal size. In contrast, the presence of Klebsiella in an aerated mixture had little or no effect on Shigella multiplication because Klebsiella failed to attain a maximal population. Different environmental conditions resulted in different Klebsiella to Shigella ratios in mixed cultures. When conditions were favorable for Shigella multiplication, as shown by pure culture controls, the proportion of Shigella in the mixture was generally greater than when conditions were unfavorable.

Interaction between Escherichia coli and Pseudomonas aeruginosa in mixed cultures

Both continuous and stationary cultures were used to detect interactions between Escherichia coli and Pseudomonas aeruginosa in mixed cultures, with pure cultures included as controls. The interactions observed were both pH and substrate dependent. Stimulation of P. aeruginosa in mixture was the most marked interaction, and was, in part, due to changes in carbohydrate metabolism.