Felis ISSN 2398-2950

Meticillin-resistant Staphylococcus pseudintermedius

Introduction

Classification

Taxonomy

• Genus: Staphylococcus
• Family: Micrococcaceae
• Species: pseudintermedius
• Antimicrobial-resistance: carries additional genetic marker mecA for meticillin-resistance and broad β-lactam resistance.

Etymology

• Gk: staphyle- bunch of grapes; coccus- grain or berry; Gk: pseud- like/similar to; Latin: intermedius:-in-between. S. intermedius was first described in 1976 as the main skin pathogen in dogs with characteristics ‘in between’ S. aureus and S. epidermidis; S. pseudintermedius was formerly named S. intermedius. It was first described as a separate species in 2005 when results from molecular analyses became available.
• Meticillin (INN; international non-proprietory name) or Methicillin (USAN; United States adopted names): semisynthetic penicillin introduced for clinical use in 1959 but no longer manufactured today. Marker for broad beta-lactam antibiotic resistance.

Active Forms

Clinical Effects

Epidemiology

Habitat

• Healthy dogs (and cats):
  • Although MRSP may be carried on skin and mucosae, this is considered rare (its meticillin-susceptible counterpart S. pseudintermedius is part of the microflora of most dogs, less frequent in cats, but MRSP is thought to only succeed as a coloniser (microflora) if there is selection pressure from antimicrobial therapy).
  • Known staphylococcal carriage sites in dogs: nostrils, oropharynx, mucocutaneous junctions such as the perianal skin, external genitalia, skin (including squames and hair shed into the environment).
  • Higher risk of MRSP carriage in animals that have previously suffered from MRSP infection.
  • May also inhabit the gastrointestinal tract.
• Infected pets:
  • In pus, infected body fluids such as urine, other infection sites.
  • MRSP likely carried at skin and mucosal sites during active infection, supported by licking/grooming behavior.
• Environment:
  • Nosocomial pathogen (veterinary clinics and veterinary hospitals).
  • Dry surfaces for many months (including home environment).
  • Adhere to squames and hair shed into the environment.

Lifecycle

• Reproduction by binary fission.

Pathological effects

• Infections involving MRSP show the same pathology as those due to meticillin-susceptible S. pseudintermedius (MSSP). No difference in virulence between MRSP and MSSP.
• Typically skin and ear infections, traumatic and post-surgical wound infections, possibly complicated by implants, suture material and biofilm.
• Any other organs (eg urinary tract, respiratory tract) as for other staphylococci.
• No lasting immunity.

Other Host Effects

• Same as for other Staphylococcus spp. and as for meticillin-susceptible S. pseudintermedius.
• MRSP can colonize skin and mucous membranes of healthy animals and predispose to subsequent MRSP infection.
• Has host-preference (dog) but is not host-specific, ie can contaminate or colonize other host species and cause infection in immune-compromised individuals (opportunistic).

Control

Control via chemotherapies

• All MRSPs are resistant to all beta-lactam antibiotics Resistant bacterial infections, regardless of individual in vitro susceptibilities.
• Topical antibacterial therapy should be used whenever possible Therapeutics: antimicrobial drug Therapeutics: bacterial infection.
• 2-4% chlorhexidine Chlorhexidine preparations and/or fusidic acid Fusidic acid containing creams have good efficacy if owner and pet are compliant.
• When systemic therapy is indicated, antibacterial selection should always be based on susceptibility test results.
• If no susceptibilities identified, extended testing may be discussed with the laboratory.

Vaccination

• None commercially available.

Other countermeasures

• For known MRSP patients: Barrier nursing or isolation:
  • Outpatients should be booked in for last appointment of the day.
  • Waiting and walking in the practice should be minimized.
  • Cleaning and disinfection of used rooms and equipment before next patient.
  • Personal hygiene: protective clothing and hand hygiene.
• Prevent spread of MRSP from unknown carriers or infected patients:
  • As for other multidrug-resistant or contagious pathogens.
  • Frequent and correct hand washing is the single most effective measure to prevent spread within veterinary surgeries.
  • Cleaning will remove 90% of bacterial pathogens.
  • Disinfection will not replace cleaning.
  • MRSP can be killed effectively with biocides recommended for staphylococci if used according to manufacturer’s instructions.
• Inform owner and in-contact people (staff) of zoonotic potential. Immuno-compromised people may want to seek advice from their general practitioner/physician.

Diagnosis