Prevalence and characterization of Listeria monocytogenes in the feces of healthy Austrians

Abstract

The aims of the study were to determine the prevalence of Listeria monocytogenes in the feces of healthy Austrians and to characterize the isolates by various typing methods. Stool specimens from 505 healthy volunteers from the Tyrol were tested for the presence of L. monocytogenes using cold enrichment for 6 months and five different detection methods: conventional plating onto Palcam and Rapid'L.MONO agar, immunomagnetic separation (IMS) followed by conventional plating, enzyme-linked fluorescent immunoassay (ELFA), ELISA, and PCR. L. monocytogenes was isolated by conventional plating from one specimen (0.2%), and a further three were positive on immunomagnetic separation (0.8%). Only one specimen tested positive with ELFA and EIA, although it tested negative by conventional culture, IMS, and PCR. Eighteen of 505 samples were positive by PCR (3.6%), and this included three of the four culture-confirmed specimens. Serotyping, phage-typing, arsenic cadmium, antimicrobial-resistance typing and pulsed-field gel electrophoresis showed that multiple L. monocytogenes isolates from three of the four carriers were indistinguishable. Our data indicate that the Austrian fecal carriage rate is at least 0.8%. In view of a listeriosis incidence of 0.16/100,000 per year, the chances of fecal carriage developing into listeriosis appear to be very low.