Membrane processes such as, reverse osmosis (RO), is one option for drinking water treatment where a high
product quality is desired. RO membranes are able to effectively remove organic and inorganic compounds
and microorganisms from water. One of the most serious problems in this system is membrane fouling caused
by the microbial biofilm formation. Biofilms contributes to RO membrane deterioration, but it also were associated with human health risks, since they can be reservoirs of human opportunistic pathogens and/or antibiotic
resistant bacteria. In the present study, samples from a drinking-water RO system were analyzed to determine
the bacterial composition of the different frames of RO system: feed water, rejection water and permeate
water. A total of 215 strains were identified using two methodologies, one genomic (16S rRNA gene) and
other proteomic (MALDI-TOF MS). The majority bacterial groups identified were Gammaproteobacteria,
Firmicutes and Betaproteobacteria, whereas Alfaproteobacteria, Bacteroidetes, and Actinomycetales were the minority bacterial identified groups. Antibiotic resistance analysis of the bacterial strains to 14 antibiotics tested revealed that resistance to three or more classes of antibiotics was observed in 37.2% of the isolates, being the
occurrence of multiple antibiotic resistance phenotypes mainly related to the taxonomic affiliation of the microorganisms. Regarding of the bacterial groups, the antibiotic resistance percentages among the strains were 68.2%
to β-lactams, 56.8% to macrolides, 36.4% to quinolones, 34.1% to cephalosporins, 22.7% to aminoglycosides and
9.1% to tetracyclines. On the other hand, >60% of the bacterial strains produced biofilms in vitro; from them,
Aeromonas caviae, Pseudomonas aeruginosa and Sphingopyxis terrae were strong biofilm formers
