Bacteraemia due to extensively drug-resistant Pseudomonas aeruginosa sequence type 235 high-risk clone: Facing the perfect storm.

Predictors of mortality and the impact of multidrug resistance and virulence on patients with Pseudomonas aeruginosa (PA) bacteraemia were evaluated. Patients with PA bacteraemia in a 12-month period were retrospectively analysed. Carbapenemase production, molecular typing and identification of virulence factor ExoU were carried out. The activity of ceftolozane-tazobactam and ceftazidime-avibactam was also investigated. The primary endpoint was 30-day crude mortality. Of 64 patients with bacteraemia, 24 (37.5%) were caused by extensively drug-resistant PA (XDR-PA): 10 (41.7%) cases involved the VIM-2 carbapenemase-producing ST175 clone, 11 (45.8%) the GES-5 carbapenemase-producing ST235 clone, and 3 (12.5%) were non-carbapenemase producers. The exoU genotype was detected in all ST235 strains and in 6 (15%) of the non-XDR isolates. Ceftazidime-avibactam (58.3%) showed greater activity than ceftolozane-tazobactam (12.5%) against XDR-PA isolates, particularly in GES-5 producers (100%). The 30-day crude mortality rate in patients with XDR-PA bacteraemia was higher than in cases caused by susceptible strains (62.5% vs. 30%; P=0.02). Multivariate analysis showed that independent risk factors associated with 30-day crude mortality were Pitt score ≥2 (OR, 42.31; 95% CI, 4.88-366.7; P=0.001) and respiratory source of bacteraemia (OR, 49.13; 95% CI 3.89-620.5; P=0.003). Stratified analysis adjusting for respiratory source revealed a non-significant trend towards higher mortality in patients with bacteraemia caused by the ST235 clone and exoU-producing isolates. These data support the notion that the XDR phenotype associated with the GES-5 carbapenemase-producing ST235 clone and the exoU-positive genotype adversely affects the outcome of patients with PA bacteraemia, particularly those with respiratory tract infections and a severe clinical presentation.