Where Should We Sample? Identifying Representative Sampling Sites for Surveillance of Hospital Sink Reservoirs

<title>Abstract</title> <p> Objectives Hospital sink systems are increasingly recognized as reservoirs of clinically relevant bacteria, including multidrug-resistant organisms. However, evidence guiding the selection of representative sampling locations within sink systems remains limited. We compared culture-based bacterial diversity, temporal detection patterns, and antimicrobial resistance gene profiles across different sink components to identify practical and representative locations for routine environmental surveillance. Methods Environmental sampling was conducted over a four-week period in four sinks in a surgical intensive care unit of a tertiary-care university hospital. Four sink components were sampled: splash area, wash basin, sink strainer, and siphon. Culture-based species diversity was evaluated using the Shannon diversity index. Selected Gram-negative isolates were screened for antimicrobial resistance genes using a DNA microarray assay. Results Sampling location markedly influenced bacterial community composition. The proportion of Gram-negative isolates increased from 37% in the splash area and 61% in the wash basin to 88% in the strainer and 92% in the siphon. Clinically relevant Gram-negative species, including <italic>C. freundii, E. cloacae, K. pneumoniae, P. aeruginosa</italic> , and antimicrobial resistance genes (carbapenemase and extended-spectrum β-lactamase-associated determinants) were predominantly detected from drainage-associated components. The strainer showed the highest species diversity and a higher Shannon index than the siphon (2.146 vs. 1.985). Conclusions Sampling location strongly influenced detection of wastewater-associated bacteria and resistance genes. Targeting drainage-associated sites, particularly the sink strainer, improves the detection of clinically relevant bacteria and enhances inter-institutional comparability. Surveillance of resistant and susceptible bacteria is essential for characterizing sink reservoirs, assessing controls, and prioritizing interventions. </p>