[Setsunan University] Migratory Gulls May Also Carry Antibiotic-Resistant Bacteria

A research group led by Professor Takehiko Misaka and undergraduate students Ren Fujita (currently a graduate student at Setsunan University) and Riko Oshima (currently a graduate student at Osaka Institute of Technology) from the Laboratory of Molecular Ecology, Department of Life Sciences at Setsunan University (President: Yasuyuki Kubo), along with Associate Professor Masayoshi Kawai from Gyohoku University, conducted a detailed analysis of the gut microbiota and antibiotic-resistant bacteria in Slaty-backed Gulls breeding in Hokkaido. Their findings revealed that Stenotrophomonas maltophilia*, a bacterium known to cause hospital-acquired infections, is present in high proportions in their feces. Many of the isolated strains exhibited strong biofilm formation ability and high motility. Furthermore, approximately 18% of the strains were resistant to two types of antibiotics used to treat infections caused by this bacterium. These results suggest that migratory gulls can carry antibiotic-resistant bacteria in their intestines and potentially spread them into the natural environment through their feces. From a One Health perspective, which views humans, animals, and the environment as interconnected, this study highlights the importance of continuous monitoring of antibiotic-resistant bacteria, including in wild birds.

This research was published on July 6, 2026, in the academic journal "Microbiology Spectrum" by the American Society for Microbiology.

URL: https://doi.org/10.1128/spectrum.00947-26

Key Points of This Research:

● Stenotrophomonas maltophilia, a bacterium known to cause hospital-acquired infections, was frequently detected in the feces of Slaty-backed Gulls.

● This suggests the necessity of measures against the environmental spread of antibiotic-resistant bacteria by migratory birds in medical facilities and elderly care homes.

Background of the Research

Antibiotic-resistant bacteria are a significant global public health concern. In recent years, the potential for migratory birds to transport antibiotic-resistant bacteria across national borders has garnered attention. While birds themselves are not typically administered antibiotics, water birds like gulls may forage in areas such as sewage treatment plants, waste disposal sites, rivers, and farmlands where livestock waste flows. These environments can contain antibiotics and antibiotic-resistant bacteria originating from humans and livestock, which birds may ingest. Gulls not only travel tens of kilometers daily for foraging but also migrate over a thousand kilometers during migration seasons. Therefore, there is concern that they may carry acquired antibiotic-resistant bacteria in their intestines to different regions and spread them into the environment through their feces.

The Slaty-backed Gull, the subject of this study, breeds around Hokkaido in the summer and migrates to regions from western Japan to Southeast Asia in the winter. Colistin-resistant E. coli has previously been detected in this species, indicating its potential as a host and carrier of antibiotic-resistant bacteria. This study aimed to clarify the types of antibiotic-resistant bacteria carried by Slaty-backed Gulls and their genetic and biological characteristics.

Research Content

In this study, fresh feces collected from Slaty-backed Gulls at their breeding grounds in eastern Hokkaido in 2024 were analyzed. The results showed that the total number of bacteria in the feces was approximately 10 million to 100 million per gram, with Stenotrophomonas maltophilia accounting for 14% to 47% of this total. Furthermore, resistant bacteria that grew on media containing the antibiotics meropenem, ciprofloxacin, and colistin were all Stenotrophomonas maltophilia. These resistant bacteria were detected in 53% of the samples, with approximately 100 to 10,000 viable cells per gram of feces confirmed.

Antibiotic susceptibility testing was performed on 60 isolated strains. Approximately 18% of the strains showed resistance to both sulfamethoxazole-trimethoprim combination (ST combination) and levofloxacin, which are used to treat infections caused by this bacterium. On the other hand, 95% of the strains were susceptible to minocycline, another potential therapeutic agent. Additionally, almost all isolated strains exhibited strong biofilm formation ability and high motility. Furthermore, genes related to pathogenicity and host attachment were also identified.

Significance of This Research

Stenotrophomonas maltophilia is an opportunistic pathogen that is problematic in hospital-acquired infections. It can cause infections, particularly in patients in ICUs, immunocompromised patients, and those undergoing long-term antibiotic treatment. This bacterium is inherently less susceptible to many antibiotics widely used for Gram-negative bacillus infections, such as carbapenems and aminoglycosides. It is also known to easily develop resistance to quinolone antibiotics and others.

The first-line treatment for infections caused by this bacterium is generally the ST combination, with levofloxacin or minocycline used as alternative drugs. Some of the strains isolated in this study showed resistance to both the ST combination and levofloxacin, possessing characteristics that warrant clinical attention. On the other hand, the susceptibility of many strains to minocycline confirmed that there is still room for therapeutic drug selection.

These findings suggest that Slaty-backed Gulls carry drug-resistant Stenotrophomonas maltophilia in their intestines and may spread it to aquatic environments, ports, and urban areas through their feces. Particular caution may be needed in the surrounding environments of places with a high risk of infection by antibiotic-resistant bacteria, such as medical facilities and elderly care homes.

This knowledge demonstrates that migratory birds can serve as hosts for antibiotic-resistant bacteria in the environment and, furthermore, as carriers connecting different regions. From a One Health perspective, which views humans, animals, and the environment as interconnected, the importance of strengthening surveillance systems for antibiotic-resistant bacteria, including those in wild birds, has been highlighted.

Glossary:

*Stenotrophomonas maltophilia

A bacterium widely found in natural environments such as water and soil. While generally of low pathogenicity, it can cause pneumonia and bloodstream infections in immunocompromised patients. Cases have been reported where it develops as a secondary infection during the treatment process for COVID-19, contributing to severe illness. Due to its resistance to many antibiotics, it is an opportunistic pathogen problematic in hospital-acquired infections.

Publication Information:

Paper Title: High abundance of Stenotrophomonas maltophilia in slaty-backed gull breeding in Northern Japan

Authors: Masayoshi Kawai, Ren Fujita, Riko Oshima, Takehiko Misaka

Journal: Microbiology Spectrum

DOI: https://doi.org/10.1128/spectrum.00947-26

Publication Date: July 6, 2026

This research was supported by JSPS KAKENHI grants 25K03284 and 25K22352.