# A Two-Year Study on Swifts (Apus spp.) as Bioindicators of Environmental Antimicrobial Resistance Within a One Health Framework

## TL;DR

This study explores how swift birds can indicate environmental antimicrobial resistance, showing they carry resistant bacteria despite not being treated with antibiotics.

## Contribution

The study introduces swifts as potential bioindicators of environmental antimicrobial resistance within a One Health framework.

## Key findings

- 30.36% of bacterial isolates from swifts showed non-wild type antimicrobial resistance.
- Bacillales isolates had significantly higher resistance rates compared to other bacterial groups.
- Swifts carried methicillin-resistant staphylococci and carbapenem-resistant isolates, indicating environmental exposure to resistant bacteria.

## Abstract

Antimicrobial resistance (AMR) is a global threat to human, animal and environmental health, underscoring the need for integrated surveillance to understand its dynamics and ecosystem interactions. This study investigated the potential of swifts (Apus spp.), long-distance migratory birds, as valuable bioindicators of environmental AMR dissemination. Four sampling sessions were conducted over two years (2023–2024) at a wildlife rehabilitation center in Trieste, Italy. Buccal and cloacal swabs were collected from 47 swifts: 10 sampled at arrival and 37 before autumn migration. Swabs were streaked on selective media for targeted isolation of Enterobacterales, Bacillales and Lactobacillales, yielding 168 bacterial isolates. Bacteria were identified using MALDI-TOF and antimicrobial susceptibility was assessed through disk diffusion method, using ECOFFs values or “no inhibition zone” criterion. Of the 168 bacterial isolates, 51 (30.36%) were non-wild type (NWT), with highest percentages of NWT isolates for clarithromycin (33.33%), erythromycin (31.50%), clindamycin (21.88%) and tetracycline (14.29%). Methicillin-resistant staphylococci (45.83%) and carbapenem NWT isolates (9.38%) were also detected. Bacillales isolates showed significantly higher NWT proportion (58.33%; p < 0.0001) compared to Enterobacterales and Lactobacillales. These findings, in clinically healthy non-antimicrobial treated swifts, suggest environmental exposure to resistant bacteria, and support a possible role of swifts as bioindicators of environmental AMR contamination, highlighting the need to strengthen environmental AMR surveillance within a One Health perspective.