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is often harmless in the environment, it is an important cause of disease in both human and veterinary medicine. The bacterium is particularly concerning because it possesses a high level of intrinsic resistance to many antibiotics, has a remarkable ability to adapt genetically, and can form resilient biofilms that protect it from both the host immune system and antimicrobial treatments.
The World Health Organisation (WHO) has designated P. aeruginosa as a "Priority Pathogen" due to its role in antimicrobial resistance. It is also one of the six bacterial species that make up the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). These bacteria are responsible for many hospital-acquired infections worldwide and are notorious for their ability to evade antibiotic treatment.
In horses, P. aeruginosa is associated with several important diseases, including genital tract infections, respiratory disease and ocular infections. In mares, infection can contribute to infertility and pregnancy-related problems, making it a significant pathogen in equine breeding operations.
To better understand the occurrence of P. aeruginosa in animal populations, Kellie Strickland and colleagues at the University of the Sunshine Coast, Australia, conducted a large-scale epidemiological study. The researchers analysed 1,669 DNA samples collected between 2010 and 2023 from a variety of healthy and diseased animals in South-East Queensland. The study included samples from wild birds, domestic animals, livestock, kangaroos and koalas.
Overall, the prevalence of P. aeruginosa was relatively low, with only 1.8% of all samples testing positive. However, livestock had the highest prevalence (4.5%), largely driven by horses, which showed a prevalence of 7.4%. This was considerably higher than the rates observed in wild birds (1.5%), koalas (1.6%) and other domestic animals (1.9%). No positive samples were detected in cattle or kangaroos.
Of particular concern was the detection of a genetic mutation known as GyrA Thr83Ile in two horse-derived P. aeruginosa samples. This mutation has previously been associated with resistance to fluoroquinolones, a class of antibiotics commonly used to treat P. aeruginosa infections in both humans and horses. Although the researchers were unable to confirm antibiotic resistance through laboratory culture and susceptibility testing, the presence of this mutation suggests that a resistant subpopulation may be emerging within the equine population.
The findings highlight the importance of ongoing surveillance of antimicrobial resistance in horses. While the overall prevalence of P. aeruginosa was low, the relatively high carriage rate in horses and the detection of a clinically important resistance-associated mutation warrant further investigation.
For more details, see:
Prevalence of Pseudomonas aeruginosa in Australian wild birds, native wildlife, livestock and domestic animals
Kellie R. Strickland, Martina Jelocnik, Erin P. Price & Derek S. Sarovich
Scientific Reports (2026) vol 16, Article number: 15423 (2026)
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