Pseudomonas is a ubiquitous genus that also causes human, animal and plant diseases. Most studies have focused on clinical P. aeruginosa strains from humans, but they are scarce on animal strains. this study was aimed to determine the occurrence of Pseudomonas spp. among faecal samples of healthy animals, and to analyse their antimicrobial resistance, and pathogenicity. Among 704 animal faecal samples analysed, 133 Pseudomonas spp. isolates (23 species) were recovered from 46 samples (6.5%), and classified in 75 different PFGE patterns. Low antimicrobial resistance levels were found, being the highest to aztreonam (50.3%). Five sequence-types (ST1648, ST1711, ST2096, ST2194, ST2252), two serotypes (O:3, O:6), and three virulotypes (analysing 15 virulence and quorum-sensing genes) were observed among the 9 P. aeruginosa strains. Type-3-Secretion System genes were absent in the six O:3-serotype strains that additionally showed high cytotoxicity and produced higher biofilm biomass, phenazine pigments and motility than PAO1 control strain. In these six strains, the exlAB locus, and other virulence genotypes (e.g. RGP69 pathogenicity island) exclusive of PA7 outliers were detected by whole genome sequencing. This is the first description of the presence of the ExlA exolysin in P. aeruginosa from healthy animals, highlighting their pathological importance. Pseudomonas is a non-fermenting Gram-negative bacterium that colonizes different terrestrial and aquatic niches. Members of this genus inhabit in a wide variety of environments, due to their metabolic capacity and broad potential for adaptation to different conditions 1. Moreover, various animals, such as birds or micromammals, have the ability to act as reservoirs of bacterial pathogens able to cause disease in humans, or environmental contaminations 2. There is great interest in Pseudomonas because of its involvement in plant and human diseases, but also by their potential in biotechnological applications 3. This genus comprises a wide variety of species, including the opportunistic pathogen P. aeruginosa which is of increasing medical and veterinary importance, causing infections mostly in patients with compromised immune systems, or in people suffering from cystic fibrosis 1. It is also a cause of diseases in livestock and companion animals, including urinary tract infections in dogs, mastitis in dairy cows, and endometritis in horses 4,5. P. aeruginosa has intrinsic resistance to several antibiotics and capacity to acquire new resistance mechanisms. Acquired resistance in P. aeruginosa is multifactorial and attributable to chromosomal mutations and to the acquisition of genes by horizontal transfer 6. Integrons are genetic elements that play an important role in antimicrobial resistance transfer. These elements are able to capture, integrate, and express gene cassettes
