Quantifying translocation of Listeria monocytogenes in rats by using urinary nitric oxide-derived metabolites

The urinary nitric oxide metabolites NO2- and NO3- (summed as NOx) are a no ninvasive, quantitative biomarker of translocation of salmonella from the i ntestinal lumen to systemic organs. Listeria monocytogenes is a food-borne gram-positive pathogen that can also cross the intestinal epithelium. In th is study, we tested the efficacy of urinary NOx as a marker of listeria tra nslocation. Rats (eight per group) were orally infected with increasing dos es oft. monocytogenes; control rats received heat-killed listeria. The kine tics of urinary NOx and population levels of Listeria in feces were determi ned for 7 days. Another group of rats was killed 1 day after infection to v erify translocation by culturing viable Listeria from systemic organs. Oral administration of increasing doses oft. monocytogenes resulted in a time- and dose-dependent increase in urinary NOx excretion. Translocation was a p rerequisite for inducing a NOx response, since heat-killed L. monocytogenes did not elevate NOx excretion in urine. Fecal counts of Listeria also show ed dose and time dependency. Moreover, the number of viable L. monocytogene s cells in mesenteric lymph nodes also increased in a dose-dependent manner and correlated with urinary NOx. In conclusion, urinary NOx is a quantitat ive, noninvasive biomarker of listeria translocation.