Human listeriosis caused by Listeria ivanovii

Abstract

Two species of Listeria are pathogenic; L. monocytogenes infects humans and animals, and L. ivanovii has been considered to infect ruminants only. We report L. ivanovii-associated gastroenteritis and bacteremia in a man. This isolate was indistinguishable from prototypic ruminant strains. L. ivanovii is thus an enteric opportunistic human pathogen.

Figure

Characterization of the Listeria ivanovii subsp. ivanovii isolates from a 55-year-old man with gastroenteritis and bacteremia. A) The 4 isolates, 07/00250, 07/00251, and 07/00252 from blood, and 07/00253 from feces, were analyzed by pulsed-field gel electrophoresis (PFGE) with ApaI and SmaI restriction enzymes (9). The L. ivanovii subsp. ivanovii type strain American Type Culture Collection (ATCC) 19119 was used as control. Profiles were compared according to band positions by using the Dice coefficient and were clustered by using unweighted pair–group method averages. Criterion of dissimilarity = 1 band difference (maximum position tolerance 1.5%). B) L. ivanovii–specific virulence locus LIPI-2 and its phenotypic marker (sphingomyelinase production as shown by a CAMP-like test with an indicator strain of Rhodococcus equi on sheep blood agar). Left, genetic structure of LIPI-2. Arrowheads indicate positions of the oligonucleotide primers used in the 19 intragenic and intergenic PCRs to map the locus in the isolates; arrows represent genes (those belonging to LIPI-2 are gray, the sphingomyelinase gene is black, and flanking genes from the core listerial genome are white) (10). Right, typical shovel-shaped synergistic hemolysis reactions caused by L. ivanovii sphingomyelinase in the presence of R. equi cholesterol oxidase compared with the negative reaction given by L. monocytogenes (Lm). C) Invasion (gentamicin protection) assays in bovine (Madin-Darby bovine kidney) and human (HeLa) epithelial cells. The human isolates were compared with ruminant isolates ATCC 19119, PAM 55, and PAM 19 and with the L. monocytogenes strain P14A. Error bars indicate SEM of at least 2 duplicate experiments.