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M. Siak1
1Western Australian Veterinary Emergency and Specialty WAVES, Veterinary Dermatology, Western Australia, Australia
Pyoderma is a pyogenic skin bacterial infection and the most common skin disease seen in dogs. Staphylococcus pseudintermediusis a commensal as well as the most frequent bacterial pathogen causing bacterial pyoderma in the dog
Underlying causes for bacterial pyoderma
Methicillin resistant Staphylococcus pseudintermedi- us(MRSP)
MRSP infections are a major concern worldwide. MRSP infections are resistant to the antibiotic methicillin,
which is used to deal with B lactamase producing staphylococci. Oxacillin is a replacement for methicillin in laboratories due to availability and stability. Cefoxitin is used to test for methicillin resistance in Staphylococcus aureusbut is not reliable in diagnosis of MRSP.
Methicillin resistance is due to the mecA gene, which encodes for modified penicillin binding protein (pbp2a) that has low affinity for all B lactam antibiotics. The mecA gene is contained within a mobile genetic element called the Staphylococcal Cassette Chromosome mec (SCCmec), which can be transferred between and
within staphylococci species. Horizontal gene transfer is frequent in S. pseudintermediusand multidrug resistant MRSP evolved rapidly through acquisition of a very limited number of mobile gene elements and mutations.
MRSP clones
Molecular testing using multilocus sequence typing (MLST) has allowed differentiation of MRSP into clones, which enables researchers to monitor the spread of MRSP worldwide. The major clones worldwide are the ST 71 in Europe, ST 68 in USA and ST45 in South East Asia.
The prevalence of MRSP in dogs varies geographically and on the studied populations. Published studies in Asia reported frequencies as high as 28% in Thailand and 66.5% in Japan. The prevalence of MRSP in healthy dogs is generally low.
The suggested routes of transmission of S. pseudintermediusbetween dogs include vertical transmission from bitches to puppies (including milk) and horizontal transmission between dogs.
Risk factors for developing MRSP infections
responsive dermatosis) · Malignancies
Diagnosis of bacterial pyoderma
Clinical lesions
· Pustules
· Crusts
· Epidermal collarettes
· Papules
· Focal to multifocal alopecia
· Erosions, ulcers
· Nodules and draining tracts
Infections due to methicillin resistant Staphylococcus pseudintermedius(MRSP) and methicillin
susceptible Staphylococcus pseudintermedius(MSSP) look the same except MRSP infections do not respond to appropriately selected empirical antibiotic.
A clinical diagnosis is made using a combination of consistent clinical lesions and cytological evidence of bacteria with suppurative inflammation i.e. degenerate neutrophils with intracellular cocci. Sampling techniques include direct and indirect (e.g. cotton buds) impression smears and adhesive tape cytology. The slides are stained with a Romanosky stain such as Diff-Quik, and examined under the microscope using the 100X oil immersion field.
· Increased number of antibacterial drug prescriptions · Exposure to multiple drug classes (especially be-
Your Singapore, the Tropical Garden City
  Bacterial pyoderma is always secondary to an underlying cutaneous or systemic disease that disrupts the skin’s defence mechanisms.
· Hypersensitivity dermatitis (adverse food reactions,
· Demodex spp, Sarcoptes scabiei,fleas)
· Endocrinopathies: hypothyroidism, hyperadrenocorti- cism, diabetes mellitus
atopic dermatitis, flea bite hypersensitivity)
· Follicular dysplasia
· Keratinisation disorders (sebaceous adenitis, zinc
· Recent (30 days) antibiotic usage
· Misuse/excessive use of antibiotics
· Breeding dogs
· Hospitalisation/veterinary visits
· Concurrent immunomodulatory therapy · Male? (Finland)

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