Engineers Show Bird Droppings Harbor Abundant Resistant Bacteria May Pose More Health Risks

Environmental engineers from Rice University said that bird droppings may pose more health risks to people than they realize. According to their study, high levels of antibiotic-resistant genes are encoded in the droppings of urban birds, which could carry pathogens.

The study was led by Pingfeng Yu of the Brown School of Engineering at Rice University and published in the Elsevier journal Environmental Pollution.

Earlier studies revealed that bird-carried antibiotic-resistant genes (ARGs) and bacteria (ARBs) could be transmitted to humans when they have contact with feces like swimming or through impacted soil or inhalation of aerosolized fecal particles.

Moreover, studies analyzed the bird feces found near ARG hotspots like the wastewater treatment plants and drainage in the poultry farms. In the study by Rice engineers, they try to dig deeper to quantify the abundance of ARGs, diversity, and seasonal persistence.

High Abundance of Antibiotic-Resistant Pathogens Found in Bird Droppings

Study co-author Pedro Alvarez said they still do not fully understand the factors that exert selective pressure for ARGs in the gastrointestinal system of wild urban birds, which include gulls, ducks, and crows.

"Residual antibiotics that are incidentally assimilated during foraging is likely one of these factors, but further research is needed to discern the importance of other potential etiological factors, such as bird diet, age, gut microbiome structure and other stressors," Alvarez said.

The team compared the 'freshly deposited' samples from each species found around Houston during the winter and summer seasons to those found in the poultry and livestock known to have some mutations.

Their findings suggest that ARGs in all species had significant resistance to tetracycline, beta-lactam, and sulfonamide antibiotics regardless of the season. They were surprised to see the high abundance of ARGs were comparable to those in the fresh feces of birds occasionally fed with antibiotics.

Moreover, the researchers also found that intl1 was more abundant in birds than in farm animals. It is a predominant integron that facilitates the rapid bacterial acquisition of antibiotic resistance.

"Our results indicate that urban wild birds are an overlooked but potentially important reservoir of antimicrobial resistance genes, although their significance as vectors for direct transmission of resistant infections is possible but improbable due to low frequency of human contact," Alvarez said.

Health Risks From Bird Droppings

The researchers also checked ARGs in the soil up to 1 inch deep around bird droppings and found that they are "moderately persistent" in the environment. The researchers noted that the ARGs they found had a half-life of up to 11.1 days.

Furthermore, they reported that among the three urban bird species, crows have the lowest level of ARGs during the summer compared to ducks and gulls. The team thinks that it is probably due to their ecological niches differences.

Compared to ducks and gulls, crows are omnivores and tend to feed on abundant natural food with less anthropogenic contaminations during summer. Additionally, the composition of the gut microbiome in the three species impacts ARG dissemination and enrichment in vivo, which influences ARG levels in bird deposits.

Yu said that their study aims to raise awareness to avoid contact with bird droppings. They found that bacteria from those can cause urinary tract infections and sepsis, respiratory infections, and food poisoning. Especially in winter, bacteria may harbor ARG due to inactivation and differences in moisture levels and temperature.