Pseudomonas aeruginosa from river water: antimicrobial resistance, virulence and molecular typing.

P. aeruginosa isolates were recovered from surface river water samples in La Rioja region (Spain) to characterise their antibiotic resistance, molecular typing and virulence mechanisms. Fifty-two P. aeruginosa isolates were isolated from 15 different water samples (45.4%) and belonged to 23 different PFGE patterns. All isolates were susceptible to all antibiotics tested, except one carbapenem-resistant P. aeruginosa that showed a premature stop codon in OprD porin. Twenty-two sequence types (STs) (six new ones) were detected among 29 selected P. aeruginosa (one strain with different PFGE pattern per sample), being ST274 (14%) the most frequent one. The O:6 and O:3 were the predominant serotypes (31%). Seven virulotypes were detected, being 59% exoS-exoY-exoT-exoA-lasA-lasB-lasI-lasR-rhlAB-rhlI-rhlR-aprA-positive P. aeruginosa. It is noteworthy that the exlA gene was identified in three strains (10.3%), and the exoU gene in 7 (24.1%), exoS in 18 (62.1%), and both exoS and exoU genes in one strain. High motility ranges was found in these strains. Twenty-seven percent of strains produced more biofilm biomass, 90% more pyorubin, 83% more pyocyanin, and 65.5% more than twice of elastase activity compared to PAO1 strain. These results highlight the importance of rivers as temporary reservoirs and sources of P. aeruginosa transmission, and alert to the importance of their epidemiological surveillance in the environment.