• Dog and Cat Resistant Staphylococci

    22 September at 16:36 from atlas

    Dr Robert Hilton BVSc (Hons) MANZCVS  MRCVS

    RCVS (UK)  Certificate Holder in Veterinary Dermatology

    PO Box 42 Yarrambat 3091

    Telephone 0433-853560

    Website www.skinvet.org

    Email rob@skinvet.org

    Staphylococcal resistance in dogs and cats. An emerging crisis

    Incidence. Rising rapidly.

    Staphylococcus pseudintermedius. Coagulase positive. Coagulase negative in heavy growth pathogenic. Occasional S. aureus. Biochemical vs genetic ID

    Mechanisms of resistance

    • Penicillinase breaking beta lactam ring. Since 50s . Amoxicillin no better than penicillin with respect to staph
    • MEC-a coded chromosomal cassette and other genetic transfers . Penicillin binding protein
    • Point mutations. Less important with beta lactams but most important with lincosamides (clindamycin, lincomycin) fluoroquinolone and rifampicin.

    Concept of MIC  vs  MUP . What does sensitivity mean?

    Heterogeneity of resistance

    First line antibiotics

    • Cephalexin  25-35,mg/kg bid
    • clindamycin 10mg/kg bid
    • Amoxiclav? 15-20mg/kg bid
    • Convenia (cefovecin) ???? Gen 3

    Second line antibiotics. Not to be used without culture

    • Doxycycline 5mg/kg bid
    • Sulfa trimethoprim 480 tab 1/20kg
    • Fluoroquinolones . Empty stomach concentration dependent

    Third line antibiotics. Never to be used unless first line and second line exhausted

    • Pradofloxacin
    • Rifampicin. Liver and bone marrow 5mg/kg bid
    • Systemic fusidic acid 25-30mg/kg bid point mutations

    Duration of treatment


    • Superficial pyoderma minimum of 3 weeks or 7-10 days visible cure. Evidence?
    • Deep pyoderma minimum of 3 weeks after visible cure. Maybe months

    Causes of antibiotic failure

    • Inadequate duration
    • Inadequate dose
    • Resistance
    • Failure to use topical treatment
    • Compliance
    • Was not an infection in the first place. Pemphigus or drug reactions

    Topical treatment . Absolute essential. No animal repeat no animal should have antibiotics dispensed for a skin infection unless it is accompanied by topical treatment.

    Sometimes topical is enough. Surface pyoderma hotspots. Some cases of superficial pyoderma. Allowing client pick up after 3 to 5 days.

    First line topical treatment

    • Chlorhexidine. Pyohex shampoo and lotion. Think do you need a shampoo? Malaseb completely inappropriate for bacterial pyoderma due to strong surfactants
    • 2.5 % SOLUTION chlorhexidine dab on . Stability of made up?????
    • BLEACH  RCH protocol


    • Silver sulphadiazine FLAMAZINE. Potential chlorhexidine synergy

    Second line topical therapy

    • Topical fucidic acid (Fucidin human)
    • Mupirocin topical bid point mutations
    • Topical gentamycin


    Reduced susceptibility to chlorhexidine in staphylococci: is it increasing and does it matter?

    Carolyne Horner, Damien Mawer, Mark Wilcox

    Journal of Antimicrobial Chemotherapy, Volume 67, Issue 11, November 2012, Pages 2547-2559, https://doi.org/10.1093/jac/dks284


    As well as a broad range of activity, a key potential advantage of chlorhexidine, especially when used as a skin disinfectant, is its 'residual activity


    In staphylococci, chlorhexidine resistance is often defined as an MIC ≥4 mg/L,

    The presence of organic matter, biofilms and biocide residues at sublethal concentrations are additional factors that need to be taken into account when comparing the in vitro and in vivo susceptibility of biocides.


    The concept of heterogeneous resistance to chlorhexidine, defined as the presence of subpopulations of staphylococci that can survive at in-use concentrations of the agent, is a plausible one

    Staphylococci have the capacity to efflux lipophilic cations, such as quaternary ammonium compounds, intercalating dyes, diamidines and biguanidine compounds, including chlorhexidine.


    Genetic linkage between the qacA/B genes and β-lactamase resistance  has been reported; an association that has been noted in both S. aureus and coagulase-negative staphylococci


    Specific incidence in humans still not clear because of clonal variations, geographic differences and testing method variations. Incidence is rising

    How to culture

    • Superficial pyoderma. Pustules or multiple collarettes with a dry swab then put in the transport medium
    • Deep pyoderma. Draining sinuses or needle aspiration

    Must go to a laboratory that is prepared to test for third line antibiotics.

    When to culture?

    • More a question of when not to culture rather than when to culture
    • History of previous antibiotic use
    • Generalized superficial pyoderma
    • Failure of first-line antibiotic


    • Generally like a fish needs a bicycle
    • Topical steroids make no sense in superficial or deep pyoderma. Helps surface hotspots
    • Most patients are immunosuppressed enough already
    • Lokivetmab (Cytopoint) to deal with itch if needed but unlikely to work in the face of active infection. Neither will anything else

    Policies that need to be developed

    Decontamination of clippers and Rooms. Hand washing and protocols

    Decontamination after clinical cure? ... value?

    • Whole body topical therapy
    • Combined culture of nasal and perianal