Use of a laboratory model hospital sink system to investigate fluctuation of Gram-negative bacteria in sink waste traps

Hospital sinks in the UK have recently been under scrutiny as possible reservoirs for Gram-negative bacteria, especially carbapenem resistant Enterobacterales (CRE). These strains have been found in intensive care wards across the country and can re-enter the clinical environment, representing a risk to vulnerable patients. Two sink waste traps known to be colonized with CRE were collected from a hospital and fitted to a vertical-draining and rear-draining handwash sink installed within a laboratory model sink system. Sinks were automatically flushed four times a day and, as per usual in the model, TSB was provided once daily to maintain microbial populations. Gram-negative bacteria were regularly monitored using selective culture, MALDI-TOF and antibiotic disk diffusion. The short-term effect of adding simulated IV fluids (5% glucose or 0.9% NaCl) and the impact of sink design on Gram-negative proliferation were investigated.Communities included Enterobacter asburiae ; Klebsiella oxytoca ; Pseudomonas aeruginosa and Citrobacter freundii , among others, including CRE. The addition of simulated IV fluids did not induce Gram-negative bacterial proliferation in the time frame of the experiment. Differences were observed in the fluctuation of Gram-negative levels after flushing between the different sink designs. Gram-negative numbers in vertical-draining sinks decreased immediately after the tap was flushed and subsequently increased between flushes. However, in rear-draining sinks, little fluctuation was observed.Hospital sink waste traps can harbour Gram-negative bacteria resistant to antibiotics. In our experimental conditions, the type of sink was the determining factor in the magnitude of fluctuation in Gram-negative populations while simulated IV fluids had little effect.