title: Association of disease with isolation and virulence of Rhodococcus equi from farm soil and foals with pneumonia.
abstract: OBJECTIVE
  To determine whether isolation and virulence of Rhodococcus equi from soil and infected foals are associated with clinical disease.
  
  
  METHODS
  Cross-sectional and case-control study.
  
  
  METHODS
  R equi isolates from 50 foals with pneumonia and soil samples from 33 farms with and 33 farms without a history of R equi infection (affected and control, respectively).
  
  
  METHODS
  R equi was selectively isolated from soil samples. Soil and clinical isolates were evaluated for virulence-associated protein antigen plasmids (VapA-P) and resistance to the beta-lactam antibiotics penicillin G and cephalothin. Microbiologic cultures and VapA-P assays were performed at 2 independent laboratories.
  
  
  RESULTS
  VapA-P was detected in 49 of 50 (98%) clinical isolates; there was complete agreement between laboratories. Rhodococcus equi was isolated from soil on 28 of 33 (84.8%) affected farms and 24 of 33 (72.7%) control farms, but there was poor agreement between laboratories. Virulence-associated protein antigen plasmids were detected on 14 of 66 (21.2%) farms by either laboratory, but results agreed for only 1 of the 14 VapA-P-positive farms. We did not detect significant associations between disease status and isolation of R equi from soil, detection of VapA-P in soil isolates, or resistance of soil isolates to beta-lactam antibiotics. No association between beta-lactam antibiotic resistance and presence of VapA-P was detected.
  
  
  CONCLUSIONS
  On the basis of soil microbiologic culture and VapA-P assay results, it is not possible to determine whether foals on a given farm are at increased risk of developing disease caused by R equi.
authors.affiliation: Department of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station 77843, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Martens
authors.forename: S
authors.initials: S
authors.lastname: Takai
authors.forename: N D
authors.initials: ND
authors.lastname: Cohen
authors.forename: M K
authors.initials: MK
authors.lastname: Chaffin
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.forename: K
authors.initials: K
authors.lastname: Sakurai
authors.forename: H
authors.initials: H
authors.lastname: Sugimoto
authors.forename: S W
authors.initials: SW
authors.lastname: Lingsweiler
mesh_terms: D000193:Actinomycetales Infections / Q000382:microbiology / Q000662:veterinary*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000942:Antigens, Bacterial / Q000235:genetics; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D004352:Drug Resistance, Microbial; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses; D007769:Lactams; D010957:Plasmids; D018410:Pneumonia, Bacterial / Q000382:microbiology / Q000662:veterinary*; D016929:Rhodococcus equi / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity*; D012988:Soil Microbiology
chemical_list: D000900:Anti-Bacterial Agents; D000942:Antigens, Bacterial; D007769:Lactams