2-pyridone-5-carboxylic acid (also known as 6-hydroxynicotinic acid) is formed from the nicotinic acid under the action of Pseudomonas aeruginosa and Serratia marcescens. The quantity of 6-hydroxynicotinic acid produced correlates well with the viable bacterial count. All others bacteria causing urinary infection, such as Escherichia coli, Klebsiella pneumonia, Enterobacter aerogenes, Enterococcus faecalis, Streptococcus gp B and Staphylococcus aureus do not metabolize nicotinic acid under similar conditions.