Unveiling a Hidden Threat: Whole Genome Sequencing Exposes the Cross-Hospital Spread of Extensively Drug-Resistant Pseudomonas aeruginosa

Edwin Kamau^1*Brendan Jones²Tatdanai Kitjawat¹Han Ha Youn¹Michael Schweikert¹Angela Caldwell¹Christopher Harens¹Patrick Kiernan³John Mark Velasco⁴Francois Lebreton²Nathanial Copeland¹

• ¹Tripler Army Medical Center, Honolulu, United States
• ²Walter Reed Army Institute of Research, Silver Spring, United States
• ³Naval Medical Center San Diego, San Diego, United States
• ⁴University of the Philippines Manila National Institutes of Health, Manila, Philippines

Whole genome sequencing (WGS) was performed on 10 extensively drug-resistant (XDR) Pseudomonas aeruginosa ST235 isolates to investigate potential healthcare-associated transmission of XDR P. aeruginosa ST235 within a U.S. military treatment facility (MTF), assess its environmental persistence, and determine its genomic relatedness to global strains. Two isolates were from an index patient with prior hospitalization in the Philippines, 4 from a secondary patient in the same ICU, and 4 environmental isolates from the index patient's room sink, collected 9 months later. Core genome multilocus sequence typing (cgMLST) and single nucleotide polymorphism (SNP) analyses were used to assess genetic relatedness. Antimicrobial resistance genes were identified using AMRFinderPlus. Global phylogenetic comparisons were made using publicly available genomes from NCBI and the MRSN database. The 6 clinical isolates differed by only 0–4 SNPs, indicating high genetic relatedness. The 4 environmental isolates differed from the clinical isolates by just 1 allele in cgMLST and 0–4 SNPs. Global phylogenetic analysis showed close clustering with ST235 strains from the Philippines, with the closest match being a 2018 Manila isolate (1–12 allele differences). The isolates carried the blaVIM-2 carbapenemase gene and exhibited resistance to all tested antibiotics. WGS surveillance revealed an undetected intra-hospital transmission of XDR P. aeruginosa ST235 and its persistence in the environment for at least 9 months. The findings underscore the importance of genomic surveillance in identifying AMR outbreaks, especially among patients returning from high-risk regions, and proactive infection control measures to prevent the spread of high-risk AMR clones in healthcare settings.