Search Results

Abstract

Objective—To determine whether specific strains of Listeria monocytogenes, as determined by genetic characteristics and virulence phenotypes, were associated with distinct clinical manifestations of listeriosis in cattle and thus may potentially have tissue specificity.

Animals—32 cattle.

Procedure—DNA sequence data for the virulence genes actAand inlAwere used to infer the phylogeny of L monocytogenes and to test for positive selection. Isolates were screened for the presence or absence of internalin genes and assigned an internalin profile. Plaquing assays were performed to determine the relative cytopathogenicity of each isolate. Categorical data analyses were performed to describe associations among L monocytogenes genotypes, virulence phenotypes, and clinical manifestations of listeriosis.

Results—Results confirmed that L monocytogenes represents 2 deeply separated evolutionary lineages. Genes actA and inlA contained amino acid sites under positive selection, and specific residues at some sites were associated with lineage and manifestation of listeriosis. Whereas lineage I was clonal and predominantly composed of isolates from cases of encephalitis, lineage II was more genetically diverse and equally represented by isolates from cases of encephalitis versus septicemia and fetal infection. Lineage I isolates also had greater cytopathogenicity in vitro, compared with lineage II isolates.

Conclusions and Clinical Relevance—Results indicated that L monocytogenes virulence genes underwent positive selection that is consistent with the diversification of 2 evolutionary lineages: lineage I is clonal and associated with encephalitis, and lineage II is more genetically diverse and equally likely to cause both major forms of listeriosis in cattle.

Abstract

Objective—To assess seasonal variation in prevalence of Listeria monocytogeneson ruminant farms and identify management practices associated with ruminant listeriosis and fecal shedding of L monocytogenes.

Study Design—Case-control study.

Sample Population—2,056 samples of feces, feed, soil, and water from 24 case farms with listeriosis and 28 control farms without listeriosis.

Procedure—Samples were collected and evaluated via bacterial culture for L monocytogenes. Univariate associations between farm management practices and listeriosis and fecal shedding of L monocytogenes were assessed. Multivariate models were developed to identify farm management practices associated with listeriosis and fecal shedding of L monocytogenes.

Results—The prevalence of L monocytogeneson cattle, goat, and sheep farms was seasonal, especially in fecal samples, with peak prevalence in winter. Although the prevalence of L monocytogenes in feedstuffs from small-ruminant farms also peaked during winter, the bacterium was detected at a constant rate in cattle farm feedstuffs throughout the year. Farm management practices, animal health and hygiene, and feedstuff quality and storage were associated with ruminant listeriosis and fecal shedding of L monocytogenes.

Conclusions and Clinical Relevance—Results suggest that the prevalence of L monocytogenes on ruminant farms is seasonal, management practices are associated with ruminant listeriosis and fecal shedding of L monocytogenes, and the epidemiologic features of listeriosis differ in cattle versus small ruminants. Awareness of risk factors may be used to develop control measures to reduce animal disease and introduction of L monocytogenes into the human food chain. (J Am Vet Med Assoc 2005;227:1808–1814)