Genotypic diversity and antibiotic resistance in Sphingomonadaceae isolated from hospital tap water

The aim of this study was to infer about the modes and extent of dispersion of Sphingomonadaceae via tap water. Sphingomonadaceae isolated from tap water samples in different places of a hospital were compared, based on intra-species genetic variability and antibiotic resistance phenotypes. These isolates were also compared with others isolated before from houses and dental chairs, served by the same municipal water supply system. Sphingomonadaceae from hospital tap water comprised members of the genera Sphingomonas, Sphingobium, Novosphingobium and Blastomonas. In general, distinct genotypes of Sphingomonadaceae were detected in different hospital areas and in tap water outside the hospital, suggesting these bacteria are not persistent or widespread in the urban water distribution system. Possible intrinsic antibiotic resistance, observed in most or all members of the family or of a genus, was observed for colistin in Sphingomonadaceae, aminoglycosides in the genus Blastomonas and beta-lactams in the genus Sphingobium. Possible acquired resistance phenotypes, not common to all members of a given species, comprised fluoroquinolones, cephalosporins and sulphonamides. Although the potential of Sphingomonadaceae as opportunistic pathogens may be low, the capacity of these bacteria to thrive in water supply systems, combined with the intrinsic or acquired antibiotic resistance, may raise the risk associated with their occurrence in hospital tap water.