Screening of microorganisms for nitrosation catalysis at pH 7 and kinetic studies on nitrosamine formation from secondary amines by E. coli strains

Abstract

Thirty-eight strains of microorganisms isolated from infected human trachea, urine, blood and faeces were examined for their ability to form N-nitrosomorpholine from morpholine and nitrite at pH 7.25. Twenty-five bacterial strains exhibited nitrosation activity, including 18 out of 19 strains of Escher-ichia coli and three out of nine Pseudomonas aeruginosa, Proteus morganii, Proteus mirabilis, Klebsiella pneumoniae and Neisseria strains; E. coli A10 strain showed the highest activity. Formation of N-nitrosomorpholine was proportional to the incubation time up to 2 h and to the number of resting E. coli A10 cells; the reaction followed Michaelis-Menten kinetics. Nitrosation rate appeared to be dependent on the pKa value of several amines studied. As the nitrosation catalysis was heat-labile, our data suggest that N-nitrosation is catalysed by a bacterial enzyme(s). This reaction may lead to enhanced endogenous nitrosation in subjects suffering from an achlorhydric stomach or from chronk urinary tract infections.