Nutritional and metabolic features of Eubacterium suis

Abstract

We studied the nutritional and metabolic features of Eubacterium suis, an anaerobic animal pathogen that causes cystitis and pyelonephritis in pigs. Peptone-yeast extract-starch (PYS) medium, which contained Trypticase (BBL Microbiology Systems), yeast extract, starch, minerals, cysteine, and sodium carbonate, was shown to support excellent growth of this organism (absorbance at 600 nm = 1.8). Growth was considerably less (absorbance at 600 nm = 0.6) when the starch in the medium was replaced by maltose. Formate, acetate, and ethanol were the major products of fermentation of starch or maltose. The organism appears to require a fermentable carbohydrate for growth since the deletion of starch from PYS resulted in a negligible amount of growth. Growth decreased by ~20% when CO2 was rigorously excluded from PYS minus Na2CO3. The deletion of only yeast extract from PYS resulted in a decrease in growth of about 75%, and the simultaneous deletion of both yeast extract and Trypticase resulted in negligible growth. When the yeast extract in PYS was replaced by a defined mixture of purine and pyrimidine bases, vitamins, and amino acids, growth was ≥80% that observed in PYS. The deletion of Trypticase from this medium resulted in no detectable growth, suggesting a possible peptide requirement for E. suis growth. Good growth (absorbance at 600 nm = 1.4) was obtained when adenine and uracil were substituted for the mixture of purine and pyrimidine bases in modified PYS; the substitution of pyridoxal, riboflavin, and nicotinic acid for the vitamin mixture gave comparable growth. The nutritional requirements of E. suis apparently reflect the fact that the organism adapts to its natural niche by doing away with certain biosynthetic capabilities which it does not seem to require.