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What Bacteria Commonly Cause TPLO Infections?

What Bacteria Commonly Cause TPLO Infections?

Infection

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Owners

Learn which bacteria most commonly cause TPLO infections in dogs, including staph species, how they enter the site, and why identification matters.

By 

Sustainable Vet Group

Updated on

August 3, 2026

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This article is for informational purposes only and is not a substitute for professional veterinary advice. Every case is unique, so always consult your veterinarian for guidance specific to your pet.

This content is intended for veterinary professionals for educational purposes. It does not replace clinical judgment or tailored advice. Always rely on your training, expertise, and the specific context of your patients.

What Bacteria Commonly Cause TPLO Infections?

TPLO surgical site infections are not caused by a single pathogen.

While Staphylococcus pseudintermedius predominates, published culture data from TPLO cases reveals a spectrum of bacteria, including gram-positive cocci, gram-negative rods, and polymicrobial combinations.

Knowing the bacterial landscape informs both prevention strategy and empirical antibiotic decisions pending culture results.

 

Quick answer: S. pseudintermedius is the most common TPLO pathogen, followed by S. aureus. Published data also identify Enterococcus, coagulase-negative staphylococci, Actinomyces, and Corynebacterium. Gram-negative organisms appear more in chronic or polymicrobial infections. MDR strains occur in 20 to 40% of staphylococcal TPLO isolates.

 

Key takeaways

  • S. pseudintermedius is the predominant TPLO pathogen: the most common dog skin commensal; pre-operative MRSP carriage (4.4% of TPLO dogs) increases SSI risk 6.7-fold per PubMed data
  • S. aureus is the second most common isolate: clinically significant and with higher MDR rates (50% in the PMC 769-TPLO study vs 35.1% for S. pseudintermedius)
  • Gram-negative bacteria are less common but clinically important: ResearchGate TPLO implant removal data identified Enterococcus spp. (n=3), coagulase-negative staphylococci (n=5), and other non-staphylococcal organisms
  • Pseudomonas aeruginosa is the most common gram-negative in canine wound infections: inherently resistant to many antibiotic classes, biofilm-forming, and particularly challenging in implant infections
  • MDR strains occur in 20 to 40% of staphylococcal TPLO isolates: empirical antibiotic selection is unreliable; culture-directed therapy is required for all confirmed TPLO infections
  • Polymicrobial infections complicate treatment: multiple species with different susceptibilities may require combination regimens

Gram-positive bacteria in TPLO infections

Staphylococcus pseudintermedius

The dominant pathogen in canine TPLO infections. S. pseudintermedius is a coagulase-positive staphylococcus that colonizes the skin, nares, and perianal area of healthy dogs without causing disease.

When the surgical skin barrier is breached, it is ideally positioned to enter the wound.

PubMed data (549 TPLO dogs) confirms: 4.4% of dogs were MRSP carriers before surgery. MRSP carriage was a risk factor for SSI (OR 6.72; 95% CI 2.12 to 21.4).

MRSP was isolated from 34% of culture-confirmed SSIs in this study.

PMC 769-TPLO study: S. pseudintermedius (n=37) was the most frequent isolate overall. 35.1% of S. pseudintermedius isolates were MDR.

Methicillin-susceptible S. pseudintermedius (MSSP) is generally treatable with cephalosporins (e.g., cephalexin) or amoxicillin-clavulanate. MRSP requires culture-directed selection from a narrow effective range.

Staphylococcus aureus

Less commonly a dog skin commensal than S. pseudintermedius, but the second most frequent TPLO SSI isolate.

S. aureus is more commonly associated with human skin and is often acquired by dogs through close human contact.

PMC 769-TPLO study: S. aureus (n=10) was the second most common isolate. 50% of S. aureus isolates were MDR in this study.

PMC TPLO MRSA case report (Open Veterinary Journal 2021): describes a confirmed MRSA TPLO infection treated with vancomycin and rifampicin combinations.

Coagulase-negative staphylococci

ResearchGate TPLO implant removal study (7.4% of TPLO requiring implant removal): identified hemolytic coagulase-negative staphylococci (n=2) and non-hemolytic coagulase-negative staphylococci (n=3) among confirmed implant infection cases.

Coagulase-negative staphylococci are generally less virulent than S. pseudintermedius and S. aureus but are significant biofilm formers. Biofilm on implant surfaces makes them particularly difficult to eradicate with antibiotics alone.

Enterococcus species

ResearchGate TPLO implant removal study: Enterococcus spp. (n=3) identified among confirmed TPLO implant infections.

Enterococcus faecalis is part of the normal gastrointestinal flora of dogs. It can reach surgical wounds via hematogenous spread (bloodstream seeding from the gut) or from contamination during the perioperative period.

SustainableVet.org confirms: Enterococcus faecalis can infect TPLO plates, providing surfaces where bacteria form biofilms, particularly challenging to treat and potentially necessitating implant removal.

Enterococcus is intrinsically resistant to many cephalosporins and to clindamycin. Treatment typically requires amoxicillin-clavulanate, linezolid, or glycopeptides (vancomycin) depending on susceptibility.

Actinomyces and Corynebacterium species

ResearchGate TPLO implant removal study: Actinomyces spp. (n=1) and Corynebacterium spp. (n=1) identified among TPLO implant infections.

These organisms are uncommon but can cause indolent, chronic wound infections that are frequently missed on short incubation cultures.

Gram-negative bacteria in TPLO infections

Gram-negative bacteria are less common in primary TPLO SSI than gram-positive staphylococci but are disproportionately represented in chronic, treatment-refractory, and polymicrobial infections.

They are also more likely to emerge after prolonged antibiotic courses that select against gram-positive flora.

Pseudomonas aeruginosa

The most clinically significant gram-negative organism in canine wound infections broadly. P. aeruginosa is a gram-negative rod found in soil, water, and the environment.

It is not a normal skin commensal but can colonize wounds and implant surfaces.

PMC (769-TPLO study): Acinetobacter species were among the MDR isolates identified in TPLO SSI cases. P. aeruginosa is similarly represented in broader canine orthopedic SSI literature.

P. aeruginosa forms biofilm, is intrinsically resistant to many antibiotics (penicillins, cephalosporins, clindamycin, chloramphenicol), and requires susceptibility testing to select effective agents.

Effective antibiotics in susceptible strains include antipseudomonal penicillins, some fluoroquinolones, aminoglycosides, and carbapenems.

Acinetobacter species

PMC 769-TPLO study: identified among MDR organisms in TPLO SSI cases.

Acinetobacter baumannii is a gram-negative organism capable of extensive resistance through multiple mechanisms, making it one of the most treatment-resistant pathogens in both human and veterinary medicine.

Escherichia coli

Less commonly implicated in primary TPLO SSI but a recognized cause of polymicrobial wound infections, particularly those with fecal contamination risk or in immunocompromised dogs.

Polymicrobial infections

Polymicrobial infections those involving two or more species simultaneously complicate treatment because each species may have different antibiotic susceptibilities.

PMC 769-TPLO study identified mixed isolate patterns in a proportion of TPLO SSI cases. ResearchGate TPLO implant removal data similarly showed multiple organisms in some confirmed infections.

When polymicrobial infection is confirmed by culture, the antibiotic regimen must cover all identified organisms. This frequently requires combination therapy or broad-spectrum agents increasing the complexity, cost, and side-effect risk of treatment.

For the staph-specific guide, see is staph the most common infection after TPLO surgery?. For the MRSP and MRSA guide, see can MRSP or MRSA occur after TPLO surgery?.

For the antibiotic guide, see what antibiotics are commonly used for TPLO infections. For the infection signs guide, see TPLO plate infection signs and treatment.

Frequently asked questions

Why do gram-negative bacteria cause more problems despite being less common in TPLO?

Gram-negative bacteria like Pseudomonas aeruginosa and Acinetobacter have intrinsic resistance to many antibiotics, form biofilm efficiently, and are often selected by prior antibiotic therapy.

When they appear, they frequently require specialist input and narrow-spectrum agents identified by susceptibility testing.

Does the specific bacteria species affect whether the plate needs to be removed?

Yes, indirectly. Biofilm-forming species (S. pseudintermedius, coagulase-negative staphylococci, P. aeruginosa) are the organisms most likely to colonize the plate surface, making antibiotic-only treatment insufficient and plate removal necessary.

Non-biofilm-forming organisms causing purely soft tissue infections may respond to antibiotics without plate removal.

How quickly should culture be performed when TPLO infection is suspected?

Culture should be performed before antibiotics are started whenever possible. Once antibiotics are started, bacterial numbers fall rapidly, reducing culture sensitivity.

If antibiotics have already been started, consult with your vet about the best timing and sampling method.

Can a TPLO infection be caused by bacteria not on this list?

Yes. The organisms listed represent the most commonly isolated pathogens in published studies, but TPLO infections can be caused by any environmental or commensal organism that gains access to the wound.

This is why culture with species identification is essential empirical antibiotic selection based on probability alone will miss atypical organisms.

What if culture comes back with "no growth" but the wound looks infected?

No-growth cultures can reflect: prior antibiotics suppressing bacterial numbers, fastidious organisms needing extended incubation, biofilm bacteria not detaching into swabs, or inadequate sampling technique.

Discuss repeat culture, deeper tissue sampling, or biopsy with your vet if no-growth results do not match the clinical picture.

Resources

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Step #1

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Ensuring a clean surgical field starts with proper skin preparation. This video demonstrates the best practices for:

  • Shaving the patient – Achieving a close, even shave while minimizing skin irritation
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Following these techniques helps reduce infection risk and improve surgical outcomes. Watch the video to see how it’s done effectively!

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Preventing surgical infections is critical for patient safety and successful outcomes. This course covers:

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