petek, 2. januar 2015

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) infections

Clinical signs

There are no clinical markers to distinguish between MRSP and MSSP. The clinical presentation is the same as for other pyodermas. We distinguish between:
- Surface (intertrigo, ‘hot spots’)
- Superficial (bacterial folliculitis, impetigo, muco-cutaneous pyoderma, superficial-spreading pyoderma)
- Deep pyoderma (furunculosis, pododermatitis with granulomas, lick granuloma, callus pyoderma)
Lesions include: papules, pustules, erythema, hyperpigmentation, alopecia, scaling and collarets for superficial lesions and fistulas, nodules and bullae for deep infections. Additionally, MRSP can be found in otitis cases.

A resistant bacteria is usually suspected if:
  • The lesions improved less then 50% within 2 weeks of antibiotic treatment
  • If new lesions develop during antibiotic treatment
  • If despite 6 weeks of antibiotic treatment, lesions are still present
  • If intracellular rods are found on cytology
  • Prior history of drug resistant infection in the household pets


A correct early diagnosis of a MRSP infection is essential, as one can then start implementing measures to prevent bacterial transmission to other beings and to the environment (MRSP can persist in the environment for months) and select the proper therapeutic regime. Before performing a culture, a cytological examination should be always performed to visualize the bacteria (rods, cocci) or other infectious agents (fungi). If the culture comes back negative, but we have seen bacteria in the cytology one has to repeat the cultures (if still clinical signs).
The material for the culture can be obtained with swabs (erosions, pustules) and skin biopsies if the lesions are deep (in this case the overlying surface should be disinfected and a 4-6mm punch taken, before putting the material in the culture medium, the intact epidermis should be eliminated to avoid surface contaminants).
The material should be sent to the lab, which then performs cultures and susceptibility tests (Kirby Bauer disc diffusion test and/or minimum inhibitory concentrations). To further characterize the bacteria and their resistance pattern, the following tests can be performed: PBP2a latex bead agglutination test, mecA PCR, SCCmec typing, D-test (for inducible clindamycin resistance), … If the animals were or are currently on antibiotics the lab should be informed about this situation and the used antibiotic, to implement measures to prevent false negative results (the lab can then enrich and/or prolong the cultures as the bacteria may be less ‘vital’ due to used antibiotics).


The treatment follows the same principles as for susceptible infections. Its success depends on the bacteria (susceptibility), severity of lesions, pet and owner compliance and on the underlying primary disease.
It is important to eliminate the bacteria and prevent their spread as soon as possible, therefore a combination therapy consisting of shampoos (chlorhexidin, benzoyl peroxide, ethyl lactate) and systemic treatment should be combined whenever possible for generalized disease. For focal lesions antibacterial shampoos or creams (mupirocin, fucidic acid) can be used. Problems with topical therapy include poor owner compliance, poor penetrations in deeper tissues, biofilm formation and resistance.
The antibiotic use should depend on the sensitivity results, some MRSP are multi-drug resistant as they can acquire or express more then one resistance gene. Often MRSP maybe be susceptible to the following antibiotics: chloramphenicol, trimethoprim/sulfamethoxazole, amikacin, fucidic acid, doxycycline.
Antibiotics such as vancomycin, teicoplanin, linezolid are exclusively reserved for treatment of humans infected with multi-resistant MRSA.


Each practice should utilize special prevention measures for cases of resistant infection (appropriate owner education, hygiene measures, restricted antibiotics use).

Zoonotic potential

There are reports of MRSP carriage in owners of dogs which were infected with MRSP (same strain) or in veterinarians and veterinary personnel. Human infections are very rare, but possible (attention to immune-suppressed animal owners and care-takers).

  1. Linek M. Proceedings of the 27th Annual congress of the ESVD-ECVD 2014, p114-118.
  2. Hillier A et al.  Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis (Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases). Vet Dermatol. 2014 Jun;25(3):163-75
  3. Beco L et al. Suggested guidelines for using systemic antimicrobials in bacterial skin infections (1): diagnosis based on clinical presentation, cytology and culture. Vet Rec. 2013 Jan 19;172(3):72-8.
  4. Beco L et al. Suggested guidelines for using systemic antimicrobials in bacterial skin infections: part 2 antimicrobial choice, treatment regimens and compliance. Vet Rec. 2013 Feb 9;172(6):156-60
  5. Bannoehr J, Guardabassi L. Staphylococcus pseudintermedius in the dog: taxonomy, diagnostics, ecology, epidemiology and pathogenicity. Vet dermatol 2012 Aug;23(4):253-66

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