Study review: Evaluation of resistance patterns in dogs, before and after antimicrobial use

The impact of systemic antimicrobial therapy on mucosal staphylococci in a population of dogs in Northwest England1

The appropriate use of antimicrobial drugs (AMD) is critical in maintaining the health and welfare of veterinary patients.  However, AMD use is a risk factor for selection of antimicrobial resistant (AMR) staphylococci in dogs,2,3,4,5 which underscores the need for vigilance in the judicious use of AMD. 

Schmidt et al conducted a prospective, longitudinal study to determine risk factors for AMR among mucosal staphylococci in dogs1 enrolled from three centers in the UK.    Nasal and perianal swabs (n=463) were collected from 127 dogs treated systemically with antibiotics, before and immediately after treatment of various infections and again at 1 and 3 months post-treatment. Staphylococcus isolated from the samples were characterized as coagulase positive (CoPS) versus coagulase negative (CoNS), methicillin-resistant (MRS), multidrug-resistant (MDR) and fluoroquinolone-resistant (FQR).    

The most common indication for systemic treatment was pyoderma (N=81, 63.8%).  Treatment durations were < 1 week (N=33), >1 week but < 3 weeks (N=48), or > 3 weeks (N=46) as prescribed by the attending veterinarian.  The antibiotics used and number of treated dogs (percentage) were: cephalexin – 31 (24.4%), clavulanate-amoxicillin – 29 (22.8%), clindamycin – 28 (22.1%); cefovecin – 26 (20.5%); fluoroquinolones (enrofloxacin or marbofloxacin) – 13 (10.2%).   The Staphylococcus species isolated are listed below.

Staphylococcus species

Percentage of 127 dogs

Percentage of 463 samples

S. pseudintermedius



S. aureus



S. schleiferi



Results: There was an increased in AMR for most antibiotics immediately post-treatment, with a significant risk for detection of MRS, MDR and FQR staphylococci identified for fluoroquinolones and for MDR staphylococcus with cephalexin.   The percentage of samples with AMR staphylococci declined from immediately to three months post-treatment and there was no significant difference between resistance prevalence, except for a significant increase in the detection of MDR staphylococcus after fluoroquinolone treatment at one month and after cephalexin at 3 months post-treatment.

Clinical relevance:

  1. The results of the study showed levels of resistance increase in mucosal staphylococci immediately post-treatment and returned to pre-treatment prevalence by one to three months post-treatment for most antibiotics and types of resistance investigated.
  2. AMD use is a risk factor for selection of antimicrobial resistant staphylococci in dogs.2,3,4,5
  3. The increase in AMR staphylococci in the mucosal bacteria can be a concern for immune-compromised patients or patients predisposed to recurrent infections, since the mucosal bacteria can serve as a source for resistant infection.
  4. The study results underscore the need for adherence to hand hygiene and infection control protocols, since AMR staphylococci may be shared between individuals and in the hospital environment.
  5. This study supports the need to assure judicious use of antibiotics.

Written by Sharon l. Campbell, DVM, MS, DACVIM
and Amy Trettien, DVM


1) Schmidt VM, Pinchbeck G, Nuttall T, et al.  Impact of systemic antimicrobial therapy on mucosal staphylococci in a population of dogs in Northwest England. Vet Dermatol (2018) DOI:10.111/vde.12538.
2) Soares Magalhaes RJ, Loeffler A, Linday J, et al.  Risk factors for methicillin-resistant Staphylococcus aureus (MRSA) infections in dog and cats: a case control study. Vet Res. (2010) 41:55.
3) Nienhoff U, Kadiec K, Chaberny IF, et al. Methicillin-resistant Staphylococcus pseudintermedius among dogs admitted to a small animal hospital Vet Micro (2011) 150: 191-197.
4) Weese JS, Faires MC, Frank LA, et al. Factors associated with methicillin-resistant verse methicillin-susceptible Staphylococcus pseudintermedius infection in dogs. JAVMA (2012) 240: 1450-1455.5) Huerta b, Maldonado A, Ginel PJ, et al. Risk factors associated with antimicrobial resistance of staphylococci in canine pyoderma.  Vet Micro (2011) 150: 302-306.


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