Pseudomonas is a bacterium involved in food spoilage, plant disease and opportunistic infections in humans. It is one the most common bacteria found on food, but it is unknown if the Pseudomonas on food pose a health threat.

We set out to explore if Pseudomonas on food is a risk to our health. We cultured food, including meats of animal origin, seafood and leafy greens, for all Pseudomonas species and characterised the genomes of the Pseudomonas found.

We wanted to know if Pseudomonas poses a risk to human health either as a disease-causing microbe, or as a carrier of antimicrobial resistance (AMR) genes. Antimicrobial resistance is a threat to human health because it hinders the treatment of infections.

We found Pseudomonas on 88% of food samples and most samples contained multiple Pseudomonas species. One of these species, Pseudomonas koreensis, was isolated from seafood for the first time.

The Pseudomonas species found had never caused an infection or rarely caused infections in immunocompromised patients, and contained no AMR genes. Instead, these bacteria were most likely associated with food spoilage.

One species of Pseudomonas we specifically looked for is Pseudomonas aeruginosa. We were particularly interest in this species because it is involved in opportunistic infections, such as swimmer’s ear, burn wound infections and pneumonia in cystic fibrosis patients. We were concerned that we may be missing this bacterium as it may be found on food at a lower concentration to other Pseudomonas species, so we used a different laboratory approach to specifically look for it.

Using enrichment and culturing on cetrimide agar we found P. aeruginosa on 11% of food samples. The P. aeruginosa found on food contained multiple AMR genes and a quarter of the strains isolated from food were similar to those that have been isolated from human infections.

Most of the Pseudomonas on food do not cause infections in humans nor are they resistant to antimicrobial drugs. A small proportion of foods do contain the antimicrobial resistant P. aeruginosa, and as we continuously consume food and are exposed to the bacteria on them, the contribution of food to infections caused by this bacterial species needs to be investigated further.

Further research should also focus on identifying foods that frequently contain P. aeruginosa, how food becomes contaminated with this bacterium, and which food processing techniques can remove them. This should help prevent infections associated with P. aeruginosa.