Objective: To examine the microbial diversity, colonization process and possible transmission routes of HAI-causative agents in two step-down care unit (SDCU) at a tertiary care hospital. 

Methodology: Patients admitted to SDCU within 48 hours of admission with no evidence of infection present, relatives of infected patients, and nurses were included. Samples form skin surfaces and creases were collected from participants for microbial culture. Environmental surfaces near patients and medical devices were also sampled. Infected patients were monitored over 45 days. All isolates recovered were identified by MALDI-TOF. Clonal relatedness and antimicrobial susceptibility were determined in selected HAI-causative agents, environmental, nurses, and clinical isolates. 

Results: A total of 2,762 isolates corresponding to 126 species were identified. Eight out of eleven patients developed 1-3 HAIs, from which 14 isolates were recovered as causative agents. Acinetobacter baumannii (36%) was distributed in clone A (n = 1), B (n = 3), and F (n = 1); Klebsiella pneumoniae (29%) in clones A (n = 2) and B (n = 1) and Enterobacter cloacae (7%) in one clone A. Causative agents were progressively recovered from environmental surfaces and medical devices before and after HAI onset. From overall samples sites, coagulase negative staphylococci represented 44.64% (1233/2762), A. baumannii 7.53% (208/2762 isolates) and E. faecium/Enterococcus faecalis 5.18% (143/2762) of the isolates. A. baumannii was detected more frequently on diverse surfaces and persisted in patients’ nostrils during the hospital stay. 

Conclusion: High contact surfaces in hospitals are reservoirs for pathogens. Highly related strains were recovered from environmental surfaces, patients, and nurses before and after HAI outcome.