MRSA, biosecurity and more (Proceedings)


MRSA, biosecurity and more (Proceedings)

Apr 01, 2008

Basic comments about AB resistance

  • All antibiotics select for look for it- you find it....
  • Antibiotics used in animal health just like all AB's
  • AB resistance poses threat to human health
  • Many factors that contribute to emergence and dissemination of antibiotic resistance
  • Not possible to quantify 'attributable risk' for any of the complex factors that contribute to resistance

Microbes of resistance concern in horses

  • Salmonella [3rd generation cephalosporins, fluoroquinolones]
  • E. coli [same as above]
  • Enterococci [ fluoroquinolones, gentamicin, vancomycin, macrolides]
  • MRSA [3rd generation cephlosporins, fluoroquinolones, macrolides]

Patient file
Factors that increase resistance
  • Inadequate dosing
  • Indiscriminate use of antibiotics
  • Inadequate duration of therapy
  • Noncompliant owners
  • Close physical contact between horses & owners
  • Public awareness- increasing attention in literature
  • Evidence of bidirectional transfer
  • Strong evidence of carrier states for both pets and humans
  • MRSAs documented to arise from both human and veterinary hospitals

Veterinary Microbiology


Gram-negative, flagellated facultatively anaerobic bacilli

Possessing 3 major antigens:

* H (flagellar): phase 1/phase 2

* O (somatic): surface of outer membrane, determined by specific sugar sequences on cell surface

* Vi : superficial antigen overlying the O antigen, present in only a few serovars (S typhi)

  • Cell envelope contains complex LPS
  • 2449 serotypes



1) ability to invade cells

2) complete LPS coat

3) ability to replicate intracellularly

4) elaboration of toxin(s)

Methicillin-Resistant Staphylococcus aureus (MRSA) in Horses

Equine Salmonellosis
  • Most important hospital associated pathogen in human medicine
  • Increasingly reported in animals
  • MRSA infection of horses + horse personnel is emerging problem
  • Disease can occur in either species and interspecies transmission propagates MRSA