Abstract
Handwashing sinks and drains are increasingly identified as reservoirs for antibiotic-resistant pathogens, including carbapenemase-producing members of the Enterobacteriaceae (CPE). Yet their bacterial content is poorly documented, particularly in relation to exposure to potable water supplies of varying mineral content (hardness). Thus, the aim of this study was to characterise the microbiota of handwashing sink drain traps situated in clinical and non-clinical areas of a UK hospital located in a soft water supply area and with a known high prevalence of CPE colonisation.
Culture- and non-culture DNA-based methods were used to determine levels of coliforms, heterotrophs, and CPE, and the diversity and composition of suspended (planktonic) and surface-associated (biofilm) communities, respectively. The propensity of CPE to form biofilms and undergo conjugative plasmid transfer was also assessed in potable water representing ‘soft’ and ‘hard’ water characteristics.
Culture-based data found that levels of heterotrophs and coliforms were relatively consistent, but levels of CPE varied over 6 logs in the different sinks. 16S rRNA data revealed that all sinks were dominated by Proteobacteria, but otherwise those located in clinical and non-clinical areas did not vary markedly in diversity or composition. Some taxa-specific differences were detected though, with those in clinical areas containing significantly higher abundances of Burkholderiaceae and Melainabacteria, and those in non-clinical areas, containing higher abundances of Pseudomonadales, including Moraxellaceae. Exposure of microbial communities to ‘soft’ then ‘hard’ water supplies did not result in measurable changes in population composition and diversity. Multiple species of CPE were found, all harbouring the blaKPC-2 allele within Tn4401a in different IncFIB, IncX3 and IncN plasmids. Somewhat surprisingly, biofilm formation of common CPE species was greater in ‘soft' water, as were rates of conjugation for surface-associated cells.
When taken together, our findings show that handwashing sinks contain diverse bacterial communities including CPE, and changes in potable water quality could impact the spread of resistance.