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  • Author or Editor: Martin Wiedmann x
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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.

Full access
in American Journal of Veterinary Research

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)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To investigate potential sources of an epizootic of listerial encephalitis, using molecular diagnostic and typing methods.

Sample Population

A flock of about 655 sheep.

Procedure

An epizootiologic investigation was performed. Clinical, feed, and environmental samples were tested for Listeria monocytogenes, using polymerase chain reaction and culture methods; recovered isolates were “fingerprinted,” using an automated ribotyping system.

Results

Listeria monocytogenes was recovered from brain specimens of 7 sheep with clinical signs of listerial encephalitis. All clinical isolates had fingerprints identical to those of isolates from farm equipment used to transport silage. Corn silage, which was not fed to the sheep, also contained L monocytogenes of the same pattern type as defined by ribotyping. Listeria monocytogenes was not isolated from the stored haylage designated for feeding the sheep (the cut-off point for isolation being < 102 colony-forming units/g).

Conclusions

Corn silage was implicated as the source of a listeriosis epizootic. It appears to have cross-contaminated the haylage destined for the sheep during handling with a front-end loader. Suspension of silage feeding coincided with cessation of listeriosis cases.

Clinical Relevance

Use of advanced molecular techniques can help to identify the sources and restrict the scope of an epizootic. In epizootics, a single L monocytogenes strain can lead to infection of multiple animals, with rapid progression of the disease. (Am J Vet Res 1997;58:733–737)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the duration of fecal shedding of and serologic response to Salmonella spp after natural infection in dairy calves and characterize Salmonella organisms recovered from these herds.

Design—Longitudinal study.

Animals—Calves from 2 dairy herds (A and B) in the northeast United States that were identified at the beginning of a Salmonella outbreak.

Procedures—Fecal samples were collected twice per week (herd A) or once per week (herd B); blood samples were collected for serologic testing once per week in both herds. Bacteriologic culture of fecal samples was performed, and Salmonella isolates were characterized by serotype, pulsed-field gel electrophoresis (PFGE) pattern, and antimicrobial resistance profile.

Results—All Salmonella isolates from herd A were serovar Typhimurium var Copenhagen, had the same PFGE pattern, and were resistant to at least 9 antimicrobials. All isolates from herd B were Salmonella Typhimurium, represented 2 PFGE patterns, and were susceptible to all antimicrobials evaluated. The estimated duration of fecal shedding was 14 days in herd A and 9 days in herd B. Few calves were seropositive for antibody against Salmonella lipopolysaccharide within the first week after birth (0 of 20 in herd A and 13 of 79 in herd B) or seroconverted (6 in herd A and 4 in herd B). Fecal shedding was more common in calves that seroconverted, but overall, there was not a strong association between seropositivity and fecal shedding of Salmonella organisms.

Conclusions and Clinical Relevance—Although the herds differed in serologic response and Salmonella subtype, the duration of fecal shedding among calves was similar between herds.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objectives

To develop a reference database for characterization of bovine Staphylococcus aureus and Streptococcus agalactiae strains by automated ribotyping and to use it to assess the discriminatory power of this typing procedure and the geographic distribution of Sta aureus and Str agalactiae strains in New York state dairy herds.

Sample Population

22 commercial dairy herds.

Procedure

Isolates of Sta aureus and Str agalactiae from bovine milk were identified by standard bacteriologic procedures, then typed by automated ribotyping. Antimicrobial susceptibility of isolates was tested in vitro. Two indicators made from the data were percentage of farms with multiple ribotypes and percentage of single ribotypes found in several geographic regions. Standard bacteriologic diagnosis, automated ribotyping, and determination of antibiograms (Kirby-Bauer method) also were done.

Results

Of 50 Sta aureus and 44 Str agalactiae isolates from composite milk samples of 12 and 10 herds, respectively, 18 and 14 ribotypes, respectively, were identified. The discriminatory power of automated ribotyping was approximately 0.96 (Hunter-Gaston's formula). A higher percentage of herds with Sta aureus had multiple ribotypes. The most common Sta aureus ribotypes tended to have broader geographic distribution. Some Sta aureus ribotypes were significantly associated with antibiotic resistance profiles.

Conclusions

Automated ribotyping appears to characterize bovine strains of bacteria associated with intramammary infections with a high discriminatory index. Potential applications include identification of strains that appear to have broad geographic distribution suggesting interfarm transfer, discrimination between recurrent versus new intramammary infections (ie, for control of Str agalactiae and Sta aureus), and evaluation of antibiotic therapy. (Am J Vet Res 1997;58:482–487)

Free access
in American Journal of Veterinary Research