Comparison of sludge and clinical isolates of Listeria monocytogenes

Aims: Listeria monocytogenes strains isolated in the same geographical area from sewage sludge and from patients presenting with listeriosis were comp ared. Methods stud Results: Al isolates were typed by serotyping, phage typing an d SmaI/ApaI pulsed-field gel electrophoresis (PFGE). Among the sludge isola tes (n = 32), 22 subtypes could be distinguished by the combination of all typing methods. The human isolates (n = 11) were distributed into 10 subtyp es which clearly differed from those observed among sludge isolates, except for one cluster formed by two related. human isolates which showed high si milarity in PEGE pattern (SmaI: 92%; ApaI: 89.5%) with one sludge isolate. Conclusions: These results suggest the existence of an epidemiological link between sludge and human isolates, but they may also be reflecting the dis tribution of L. monocytogenes types within the environment. Significance and Impact of the Study: Sludge and human L. monocytogenes may be related but further epidemiological studies are necessary to elucidate this point.