First nationwide survey on Pseudomonas aeruginosa in Bolivia: susceptibility profiles, resistome analysis and genomic epidemiology

Information on the molecular epidemiology of Pseudomonas aeruginosa and antimicrobial resistance mechanisms remain limited in some South American countries. Therefore, this study aims to decipher the population structure of 111 XDR P. aeruginosa isolates obtained from a national study conducted in Bolivia during 2023-2024. For this purpose, antibiotic susceptibility profiles were determined for 14 antipseudomonal agents. Moreover, all isolates were subjected to whole-genome sequencing (WGS), and through variant calling analysis, sequence types (ST), clonal relatedness, and acquired mutation-driven and transferable resistance mechanisms were elucidated. The most active antipseudomonal agent was colistin (97% susceptible, MIC50/90 = 1/2 mg/L), followed by cefiderocol (93% susceptible, MIC50/90 = 0.25/4 mg/L), according to CLSI. High resistance rates to ceftazidime/avibactam (79.3%) and ceftolozane/tazobactam (82.9%) were documented. Carbapenemases were found in 60.3%, including metallo-ß-lactamases (MBL) such as SPM-1 (35%), VIM-2 (10%), the co-production of NDM-1 and DIM-1 (5%), as well as new IMP variant and the class A enzyme GES-20 (5%). Additionally, ESBLs were detected in 12%, including OXA-17 (6%), PER-1 (2%), and some GES variants. The most commonly detected clone was ST277 (35%), associated with SPM-1, followed by ST309 (25%) which produced OXA-2 and GES variants, and ST235 (20%), which produced OXA-17 and the new IMP-111. In addition, acquired resistance genes, such as aadA1, aadA6, and aadA7, were detected, among others. The high resistance rates for the new combinations ceftolozane/tazobactam and ceftazidime/avibactam, and emerging resistance to last-resort cefiderocol, linked to an alarming spread of high-risk clones such ST277 and ST235 and the very high prevalence of MBLs and ESBLs raises significant concern and underscores the urgent need for establishing epidemiological surveillance and infection control strategies.