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Study helps veterinarians understand persistent infections

Many pet owners and veterinarians struggle to help pets that just can’t shake an infection. Itchy ears that don’t get better, recurrent urinary tract infections, wounds that never completely heal – all persistent infections that can frustrate even the most caring owner and diligent veterinarian.

The causes of persistent infections, despite appropriate therapy, are not completely understood, but a recent publication from a Morris Animal Foundation Veterinary Student Scholar might shed some light.

Meagan Walker, a third-year student at the University of Guelph’s Ontario Veterinary College, looked at the difference in antibiotic susceptibility between methicillin-sensitive and methicillin-resistant planktonic and biofilm Staphylococcus pseudointermedius. Methicillin-resistant Staphylococcus pseudointermedius is a skin bacteria predominantly found in animals that is similar to methicillin-resistant Staphyclocoous aureus in people. Walker suspected that S. pseudointermedius embedded in biofilm would be more resistant to antibiotics, and that current antibiotic-sensitivity testing methods would underestimate the concentration of antibiotics required to effectively treat biofilm S. pseudointermedius.

Biofilms are “mats” of bacteria and other substances, such as fungi and algae. Most bacteria tend to grow as free-floating, or planktonic, organisms. However, under the right conditions, some bacteria aggregate together. This community of organisms can produce a special, slimy glue-like substance that binds the group together, forming a biofilm. This “glue” helps the bacteria adhere to all kinds of materials, such as body tissues, metal (including exam tables), and medical implants.

Walker demonstrated that biofilm-embedded S. pseudointermedius were more resistant to antibiotics (667-4,000 times) than non-biofilm embedded S. pseudointermedius. She also demonstrated that normally methicillin-sensitive S. pseudointermedius behaved more like methicillin-resistant S. pseudointermedius when they were in biofilms. Walker showed that using conventional methods of determining antibiotic sensitivity markedly underestimated the concentration needed to treat these bacteria. Her results demonstrate that veterinarians need to re-think treatment strategies if biofilms are suspected to be present.

“I think the results of this study are very significant,” said Walker. “They illustrate a flaw in the way we diagnose and treat biofilm-associated infections. By culturing and testing the sensitivity of only the planktonic bacteria, we greatly overestimate the bacteria’s sensitivity to antimicrobials, leading to the failure of treatment plans.”

In addition to publishing her results, Walker also presented her data to Morris Animal Foundation staff, trustees and board members in June 2016. She was one of five student scholars selected to attend the Foundation’s annual board meeting based on evaluation of the scientific merit and quality of their studies. The five finalists competed for prizes, and Walker received the $500 top award for overall presentation.

Morris Animal Foundation has been supporting veterinary student scholars for more than 10 years. Training the next generation of veterinary scientists is an important part of the Foundation’s mission.

Walker’s study, “Evaluation of the Impact of Methicillin-Resistant Staphylococcus pseudointermedius Biofilm Formation on Antimicrobial Susceptibility” was published in the August 2016 issue of Veterinary Surgery.

September 20, 2016