Navigating methicillin resistance in veterinary dermatology

Certain Staphylococcus species have acquired methicillin resistance, a trait that renders them resistant to many commonly used antibiotics, making these cases significantly more difficult to treat. When standard treatments fail or when infections involve deeper tissues, a skin culture becomes an essential diagnostic tool. Dermatologists use these cultures to pinpoint the exact strain of bacteria—an essential step for patients with a history of frequent antibiotic use.

“There's a whole lot about methicillin resistance out there. There's a whole lot of scary things out there, and it's a very important thing," said Darin Dell, DVM, DACVD. "But my feeling is that in day-to-day practice, we often get kind of overwhelmed by...this methicillin resistance. There's antibiotic resistance everywhere. It's almost too big a problem to deal with, right?”

During his lecture, “Fighting the Good Fight: A Complete Approach to Antimicrobial Therapy in Dermatology,” at the 2026 Veterinary Meeting & Expo, Dell shared insights on antimicrobial therapy and current research into resistance patterns.

Understanding methicillin resistance

In a clinical setting, methicillin resistance refers to specific strains of Staphylococcus bacteria. In dogs, the most common culprit is Staphylococcus pseudintermedius (leading to methicillin-resistant S pseudintermedius [MRSP]).

Technically, modern labs use oxacillin rather than methicillin to test for this resistance, but the clinical implication remains the same: These bacteria carry a mecA gene. This gene allows them to produce a modified penicillin-binding protein, which renders an entire class of antibiotics, including penicillins and cephalosporins, completely ineffective.

Patients who have previously undergone antibiotic therapy, those hospitalized in multispecialty facilities, or those taking immunosuppressants for conditions like Addison disease are at a higher risk for contracting methicillin-resistant infections. In these cases, clinical resolution is the primary goal. MRSP can linger on a patient’s skin for up to a year after the visible sores have healed. Therefore, it is not always necessary to entirely clear the bacteria from the skin, but rather to resolve the active infection and halt the inflammatory cycle.

RELATED: Overcoming patient and client barriers in dermatology

“When people ask me, ‘Should I culture this again after I think the skin is clear?’ the answer is no," Dell said. "Clinical resolution is what I want, [and] cytologic resolution is what I want. You can culture all the time. It's not going to change what you're going to do. Because what you're going to do is continue topical antimicrobial therapy. That is how we get out of this drug resistance problem—using more topical antimicrobials, either with or instead of systemic antibiotics, to disrupt the resistance genes and change the preference for what's on the skin.”

Dell’s primary takeaway is to avoid antibiotics when they are not strictly necessary. Increased exposure increases the risk of resistance. He noted that although owners often request antibiotics, they should be withheld unless there is cytologic proof of infection. If cytology shows low bacterial counts, Dell often recommends using a medicated shampoo first and reevaluating in 1 week.

Recent research

In a recent issue of the Journal of the American Veterinary Medical Association, researchers published findings aimed at quantifying the frequency and resistance patterns of methicillin-resistant staphylococci in companion animals, including S aureus (MRSA), S pseudintermedius (MRSP), and S schleiferi (MRSS). The team utilized historical susceptibility data from a national diagnostic laboratory, analyzing samples from dogs and cats across the US between 2019 and 2022.

The study identified 110,423 MRSP, 5618 MRSA, and 20,934 MRSS isolates. MRSP was predominantly found in dogs, with skin and soft tissue being the most common infection sites. Although MRSA and MRSS were also primarily isolated from dogs, the study noted significant regional, species-specific, and yearly differences in susceptibility. MRSP isolates generally showed higher levels of multidrug resistance compared with MRSA and MRSS.

“This study provides insight into the distribution and antimicrobial resistance patterns of MRSA, MRSP, and MRSS in companion animals in the US," the researchers stated. "Resistance rates for enrofloxacin, marbofloxacin, and chloramphenicol may be higher than reported in this analysis due to recent changes in [minimum inhibitory concentration] breakpoints.... The findings underscore significant geographical and temporal variations in resistance, emphasizing the need for tailored antimicrobial stewardship programs.”

Conclusion

Ultimately, managing methicillin-resistant infections in veterinary dermatology requires a shift from aggressive systemic intervention to strategic antimicrobial stewardship.

“The big ones are...don't use a systemic antibiotic unless you're sure that you need it," Dell said. "Do your physical exam, do cytology. If there's no proof that you need it, don't do it. That's the biggest thing we can all do to help prevent antibiotic resistance.”

References

1. Dell D. Fighting the good fight: a complete approach to antimicrobial therapy in dermatology. Presented at: 2026 Veterinary Meeting & Expo; January 17-21, 2026; Orlando, FL.
2. Sobkowich KE, Hui AY, Poljak Z, Szlosek D, Plum A, Weese JS. Nationwide analysis of methicillin-resistant staphylococci in cats and dogs: resistance patterns and geographic distribution. Am J Vet Res. 2025;86(3):ajvr.24.09.0253. doi:10.2460/ajvr.24.09.0253
3. McCafferty C. Q&A with Darin Dell, DVM, DACVD. dvm360. January 26, 2026. Accessed January 26, 2026. https://www.dvm360.com/view/with-darin-dell-dvm-dacvd