High Antimicrobial Susceptibility of Cloacal Enterococci and from Free-Living Dalmatian and Great White Pelicans with Detection of Cefotaximase CTX-M-15 Producing ST69.

In 2022, an outbreak of H5N1 highly pathogenic avian influenza (HPAI) killed 60% of the largest breeding colony of Dalmatian pelicans (DPs) in the world at Mikri Prespa Lake (Greece), prompting a multidisciplinary study on HPAI and other pathogens. This study determines the antimicrobial resistance rates of cloacal enterococci and in DPs. Fifty-two blood and cloacal swab samples were collected from 31 nestlings (20 DP/11 great white pelicans) hatched after the H5N1 outbreak at the Prespa colony and 21 subadult/adult DPs captured at a spring migration stopover. The swabs were inoculated in non-selective and chromogenic-selective media. Identification was performed using MALDI-TOF, and antimicrobial susceptibility was tested. The genetic content was characterized using PCR and sequencing, and the clonality of extended-spectrum beta-lactamase (ESBL)-producing isolates was characterized using Multilocus Sequence Typing. Twenty-eight non-repetitive and 45 enterococci isolates were recovered in non-selective media; most of them were susceptible to all antibiotics tested (85.7% /91.1% enterococci). Three of the fifty-two samples (6%, all adults) contained ESBL- isolates (detected in chromogenic ESBL plates), all carrying the gene and belonging to the lineage ST69. Despite the susceptibility of most fecal and enterococci isolates to all antibiotics tested, the finding that of lineage ST69 carry is of concern. This high-risk clone needs further investigation to elucidate its primary sources and address the growing threat of antimicrobial resistance from an integrated "One Health" perspective. Furthermore, it is imperative to study the potential impacts of ESBL- on the endangered DP further.