First report of blaOXA and mcr-2 genes co-existing in a multidrug-resistant Pseudomonas aeruginosa isolate recovered from a layer chicken flock in Türkiye

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic and versatile pathogen that causes infections in both humans and animals. It is one of the ESKAPE pathogens, characterized by the ability to rapidly acquire resistance to antimicrobials. In recent years, multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR) P. aeruginosa have been reported worldwide in humans and chickens. In poultry, P. aeruginosa is frequently isolated and spreads easily due to its multiple transmission routes and its ability to infect birds of all ages. As a zoonotic pathogen, it poses a risk to humans via the consumption of contaminated poultry products. This study aimed to isolate P. aeruginosa from a layer chicken flock in Türkiye and investigate its antimicrobial resistance (AMR) and biofilm formation ability. Isolation and identification were performed by conventional bacteriological analysis and sequence analysis of the 16S rRNA gene. Following phenotypic AMR testing, biofilm formation was quantitatively analyzed, and eleven AMR genes were screened by PCR. The recovered P. aeruginosa isolate exhibited resistance to aztreonam, colistin, and meropenem, thereby meeting the criteria for MDR. It also tested positive for blaOXA and mcr-2 resistance genes and was defined as a weak biofilm producer. To the best of our knowledge, this is the first report of blaOXA and mcr-2 genes co-existing in an MDR P. aeruginosa isolate recovered from a layer chicken flock in Türkiye. These findings highlight the potential risk posed by MDR and biofilm forming P. aeruginosa in poultry environments to both human and animal health.