Staph infections and Methicillin Resistance in Companion Animals
August 30, 2012
Staphylococcus (staph) bacteria are all around us in an intimate
way since it normally lives on the skin and mucous membranes of
both people and animals alike. It usually is not of a concern to
the individual if the skin is functioning normally and there is not
a risk for infection (e.g., systemic illness and immune
compromise). When infection is present, usually of the skin, most
staph bacteria are susceptible to commonly prescribed antibiotics.
Although many individuals walk around every day with staph
bacteria, not all staph are alike. Indeed, Staphylococcus
aureus prefers people (as well as pigs and some horses) over dogs
and cats, Staphylococcus pseudintermedius likes the skin of
companion animals over man.
"Methicillin-resistant staph" refers to Staphylococcus
bacteria that have developed a resistance to commonly prescribed
penicillin and penicillin-like antibiotics, making infections
difficult to treat. Again, most staph bacteria are susceptible to a
wide array of antibiotics, but these particular staph have
developed resistance to typical antibiotics, hence they are more
challenging to eliminate.
Dr. Adam Patterson, clinical assistant professor and chief of
dermatology at the Texas A&M College of Veterinary Medicine
& Biomedical Sciences Small Animal Hospital, explained staph
skin infections (pyoderma) in animals present as skin sores
recognized as redness, pimples, scabs, dander, and hair loss. Many
times these infections itch and result from uncontrolled allergic
skin disease. When this type of infection occurs, it usually
responds to correctly prescribed and administered topical and/or
systemic antibacterial treatments.
If the infection is not easily treated by an appropriate course
of antibiotics, then the chance for a "resistant" infection is
heightened. Although subject to debate, as this is an area of
ongoing research, Patterson said risk factors for
methicillin-resistant staph infections in both people and animals
seem to include repeated courses of antibiotics, chronic skin
disease, immune compromise, recurring hospital visits, and
indwelling medical implants such as those used for orthopedic
surgery. When these risk factors are present in animals with
pyoderma, veterinarians perform a culture of the skin sore to
determine if the bacteria are indeed methicillin-resistant.
"A resistant infection doesn't look different than susceptible
infections, the only way to know is to culture the skin," Patterson
Once it is confirmed the pet is infected with
methicillin-resistant staph, the veterinarian can determine the
best course of action. Patterson said the most common treatments
are topical such as antiseptic shampoos and culture-based systemic
"When we can, we try to treat them topically," Patterson said.
"Methicillin resistance doesn't mean that the bacteria are more
pathogenic, they just are not killed by common antibiotics
People with methicillin-resistant staph are said to have MRSA
(methicillin-resistant Staphylococcus Aureus). Since dogs
and cats tend to have a different species of staph on their skin,
resistant bacteria are most often called
methicillin-Resistant Staphylococcus Pseudintermedius (MRSPi
or MRSP). People are normally not infected with MRSPi; likewise,
dogs and cats are normally not infected with MRSA. Common transfer
of MRSPi from pets to people has been fairly rare and isolated to
date, while transfer of MRSA from people to pets is somewhat more
likely. Again, MRSPi is predominantly found in companion pets,
while MRSA is primarily found in people.
"We don't know much about dog-to-dog spread, but it is a large
component of research on the epidemiology of methicillin resistance
as we move forward," Patterson said.
A few simple recommendations to help reduce the chance of
transfer of staph bacteria between household people and pets once
an animal has confirmed MRSPi infection include: administering the
veterinary-prescribed treatment as directed, wearing gloves when
treating the affected pet with topical therapy, keeping young
children and immuno-compromised people (cancer, HIV/AIDS, etc.)
away from the affected pet, keeping personal skin wounds covered
and protected, discouraging the pet from licking the face of
people, and not letting the affected pet share the bed or linens
with household persons. Above all, Patterson emphasized the need to
wash all surfaces of the hands after handling the affected
pet. Additionally, a search into why the pet has a resistant
infection should be undertaken and corrected once identified.
If you develop skin sores or have concerns about your personal
health once a methicillin-resistant staph infection has been
confirmed in your pet, then consult your physician.
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