Surveillance of carbapenem-resistant Pseudomonas aeruginosa isolates obtained from patients treated in a paediatric hospital in Mexico

Pseudomonas aeruginosa is an important cause of infections in hospitalized paediatric patients, which can prolong hospital stays, increase medical care costs, and increase morbidity and mortality. The aim of this study was to describe the molecular characteristics of carbapenem-resistant P. aeruginosa (CR-PA) isolates obtained from paediatric patients, along with their clinical data, infection type, treatment, and outcome. From January 2018 to March 2020, 65 P. aeruginosa isolates were prospectively collected, and carbapenemases were detected. The genes mexR, nalC, nalD, and oprD were amplified, sequenced, and analysed. The sequence types (STs) were determined by Multilocus sequence typing. Clinical information on the origin, evolution, treatment, and outcome of the infections was collected. Most isolates (81.6%, n = 53) were carbapenemase-negative; 18.4% (n = 12) were carbapenemase producers, with IMP being the most common (7/12). In the sequences of the mexR, nalC and nalD genes, 25% (n = 16), 8.5%(n = 6), and 10.6%(n = 7), respectively, presented modifications in the open reading frame, and stop codons were observed in 17.3% of mexR and 2.1% of nalD sequences. Premature stop codons were present in 70.6% of the oprD sequences, and frameshift mutations were observed in 75.5%. The isolates were distributed among 35 ST; ST348 (16.9%, n = 11), ST309 (12.3%, n = 8), and ST389 (10.8%, n = 7) were the most frequent. High-risk clones (HRC) including ST358, ST309, ST389, ST395, ST234 and ST11 were detected. A total of 92% (n = 60) of patients with CR-PA had underlying health conditions, the most frequent being congenital disorders. The most common empirical therapy was a combination of meropenem and an aminoglycoside or colistin (52.6%, n = 34), while among definitive treatments, monotherapy was used in 67.7% of patients, and 29.2% received a two-drug combination. The complications were associated with mortality (RR = 2.5, p < 0.0001). A total of 89.2% of infections were hospital-acquired. Modification of the porin OprD was the main mechanism of carbapenem resistance among P. aeruginosa isolates; however, carbapenemase-producing strains were observed, mainly from the imipenemase (IMP) family. 60% of the isolates belonged to STs, considered HRC. Of the clinical variables analysed, only the presentation of complications was associated with mortality.