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This study evaluated biofilm formation and antimicrobial susceptibility of Pseudomonas aeruginosa isolated to evaluate the microbiological quality of 80 natural mineral water samples sold in 20 L bottles. The quantity of P. aeruginosa and enterococci was assessed, including total coliforms, thermotolerant coliforms and sulfite-reducing clostridia (SRC). Biofilm production from P. aeruginosa was evaluated in brain heart infusion broth (BHI) and sterile natural mineral water at temperatures of 25 and 35°C for 24 and 48 h. Antimicrobial susceptibility tests were performed using the agar diffusion method (Kirby-Bauer). Of the 80 samples analyzed, 40 (50%) presented unsatisfactory microbiological quality according to RDC no. 275/05. Thirty-eight (47.5%) samples presented P. aeruginosa, nine (11.2%) total coliforms, four (5.0%) SRC and one (1.2%) thermotolerant coliform. Sixteen P. aeruginosa strains (51.6%) were classified as non-adherent or weakly adherent, both in BHI as in mineral water. However, five strains (16.1%) were strongly adherent in the two matrices, mainly in BHI at the temperature of 25ºC. The study also isolated resistant or intermediate resistant strains to antibiotics of aminoglycosides and/or β-lactams classes. It was concluded that P. aeruginosa isolates were able to produce biofilm in the studied matrices and presented resistance to antimicrobials. Half of the samples presented unsatisfactory microbiological quality, mostly due to P. aeruginosa contamination.

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