La resistenza agli antibiotici in Pseudomonas aeruginosa: studio molecolare ed epidemiologico in un nosocomio marchigiano

Antibiotic resistance in Pseudomonas aeruginosa: molecular and epidemiological study in a hospital in the Marche region Background: In the last years P.aeruginosa has became one of most drug resistant microorganism. Despite introduction of new antibiotics such as Ceftolozane/tazobactam (C/T), a novel cephalosporin/β-lactamase inhibitor combination with a potent activity against Pseudomonas aeruginosa isolates, several resistant P. aeruginosa isolates have been reported. From November 2016 to April 2019 we performed both a retrospective study on C/T prescriptions and activity both a survey on clinical strains of P. aeruginosa isolated at “Ospedali Riuniti” of Ancona, Italy, characterising the resistant isolates. Materials/methods: From November 2016 to April 2019 we have collected data about C/T activity and efficacy against all multidrug resistant gram negative isolated at Ospedali Riuniti of Ancona. Particularly we have studied activity of C/T against P.aeruginosa, and microbiological and genetic charateristics of this microorganism. MICs to C/T were determined with gradient test for all P. aeruginosa recovered at the clinical laboratory of “Ospedali Riuniti” from October 2018 to March 2019. Resistant strains were characterized and typed by SpeI-PFGE. We have determined also AmpC production, we have performed DNA extraction and PCR exam. NGS with an Illumina Miseq platform was performed on representative strains to identify the mechanisms of C/T resistance. Results: Over 34 pt, who have received C/T as therapy against multidrug resistant gram negative infections, 53% had CCI >3, 21% underwent to surgery in the previous three months, 32% had pneumonia as acute comorbidities, 18%has died, 26% have experienced a therapeutic failure. CCI>3, pneumonia, P.aeruginosa infection and a previous corticosteroid therapy were a negative prognostic factors. P.aeruginosa resulted resistant to carbapenem, cephalosporin, piperacillina/tazobactam and fluorochinolons, but not to colistin. Over 317 isolated and screened isolates, 15 were resistant to C/T (MIC > 8 mg/L; 4.73%). PFGE showed that 8/15 were strictly related. NGS revealed 6 different STs. The resistance mechanisms to C/T included the metallo β-lactamase (MBL)-econding genes blaVIM-2 in 8 isolates belonging to ST111, and blaIMP in 2 isolates (blaIMP-19 in ST175 and blaIMP-13 in ST621). Additionally, blaPER-1 β-lactamase gene was detected in 2 isolates (ST235) and the blaGES β-lactamase gene in 1 isolate (ST175). Notably, in 2 strains (ST70 and ST3354) no acquired β-lactamase genes involved in C/T resistance has been detected but they showed alterations in ampC. Modifications in these genes and in ampC promoter (ampR) were also detected in all resistant strains except in ST175 isolates (possessing a wild type ampC and ampR). Conclusions: C/T has confirmed its high activity and efficacy against multidrug gram negative infections. There was a low rate of resistance to C/T, but several resistance mechanisms were identified, among which production of MBLs was the most common. Moreover, we found a possible mini-outbreak of blaVIM positive strains. Despite what has been pointed out, we must recognize that this study is limited by the low number of enrolled patients, by the retrospectivity and by being monocentric, but it can be considered an initial approach for further prospective future studies, involving other hospitals in the Region, to better to define both the therapeutic efficacy of C / T and the epidemiology of P. aeruginosa

Antibiotico-resistenza a Pseudomonas aeruginosa: studio molecolare ed epidemiologico in un ospedale marchigiano. Negli ultimi anni P.aeruginosa è diventato uno dei microrganismi più resistenti ai farmaci. Nonostante l'introduzione di nuovi antibiotici come Ceftolozane/tazobactam (C/T), una nuova combinazione di inibitori della cefalosporina/β-lattamasi con una potente attività contro gli isolati di Pseudomonas aeruginosa, sono stati riportati diversi isolati di P. aeruginosa resistenti.