Infections caused by ceftolozane/tazobactam and ceftazidime/avibactam-resistant P. aeruginosa infections are an emerging concern. We aimed to analyze the underlying ceftolozane/tazobactam and ceftazidime/avibactam resistance mechanisms in all MDR/XDR P. aeruginosa isolates recovered during one year (2020) from patients with a documented P. aeruginosa infection. Fifteen isolates showing ceftolozane/tazobactam and ceftazidime/avibactam resistance were evaluated. Clinical conditions, previous positive cultures and β-lactams received in the previous month were reviewed for each patient. MICs were determined by broth microdilution. MLSTs and resistance mechanisms were determined using short- and long-read WGS. The impact of PDCs on β-lactam resistance was demonstrated by cloning into an ampC -deficient PAO1 derivative (PAOΔC) and construction of 3D models. Genetic support of acquired β-lactamases was determined in silico from high-quality hybrid assemblies. In most cases, the isolates were recovered after treatment with ceftolozane/tazobactam or ceftazidime/avibactam. Seven isolates from different STs owed their β-lactam resistance to chromosomal mutations and all displayed specific substitutions in PDC: Phe121Leu and Gly222Ser, Pro154Leu, Ala201Thr, Gly214Arg, ΔGly203-Glu219 and Glu219Lys. In the other eight isolates, the ST175 clone was overrepresented (6 isolates) and associated with IMP-28 and IMP-13, whereas two ST1284 isolates produced VIM-2. The cloned PDCs conferred enhanced cephalosporin resistance. 3D PDC models revealed rearrangements affecting residues involved in cephalosporin hydrolysis. Carbapenemases were chromosomal (VIM-2) or plasmid-borne (IMP-28, IMP-13), and associated with class-1 integrons located in Tn402-like transposition modules. Our findings highlight that cephalosporin/ß-lactamase inhibitors are potential selectors of MDR/XDR P. aeruginosa strains producing PDC variants or metallo-ß-lactamases. Judicious use of these agents is encouraged.

Outpatient parenteral antimicrobial therapy (OPAThttp) programs have become an important healthcare tool around the world. Portable elastomeric infusion pumps are functional devices for ambulatory delivery of antimicrobial drugs, and their stability is an essential point to guarantee an appropriate infusion administration. We conducted a systematic review to provide a synthesis and a critical evaluation of the current evidence regarding antimicrobial stability in elastomeric pumps. Data sources were PubMed, EMBASE, and Web of Sciences. The review protocol was registered on the Center for Open Science, and it was carried out following the PRISMA guidelines. Studies were eligible if the aim was the evaluation of the physicochemical stability of an antimicrobial agent stored in an elastomeric device. Of the 613 papers identified, 33 met the inclusion criteria. The most studied group of antimicrobials was penicillins, followed by cephalosporins and carbapenems. In general, the stability results of the antimicrobials that have been studied in more than one article agree with each other, with the exception of ampicillin, flucloxacillin, and ceftazidime. The antibiotics that displayed a longer stability were glycopeptides and clindamycin. Regarding the stability of antifungals and antivirals, only caspofungin, voriconazole, and ganciclovir have been investigated. The information provided in this article should be considered in patient treatments within the OPAT setting. Further stability studies are needed to confirm the appropriate use of the antimicrobials included in this program to ensure optimal patient outcomes.

Currently, ampicillin plus ceftriaxone (AC) is one of the preferred treatments for Enterococcus faecalis infective endocarditis. However, there is a lack of stability data for the combination of both drugs in elastomeric devices, so the inclusion of AC in Outpatient Parenteral Antimicrobial Therapy (OPAT) programs is challenging. The objective of the study was to determine the stability of AC in elastomeric pumps when stored at 8 ± 2 °C, 25 ± 2 °C, 30 ± 2 °C and 37 ± 2 °C using LC-MS/MS. The combination was diluted in 0.9% sodium chloride and the final concentrations were ampicillin 24 g/L plus ceftriaxone 8 g/L. Physical and chemical stability were evaluated at 12, 20, 24, 36 and 48 h after preparation. Stability was met at each time point if the percentage of intact drug was ≥90% of its respective baseline concentration and color and clearness remained unchanged. The drug combination was stable for 48 h when it was kept at 8 ± 2 °C. At 25 ± 2 °C and 30 ± 2 °C, they were stable for 24 h of storage. At 37 ± 2 °C, the stability criterion was not met at any time point. These results prove that AC could be included in OPAT programs using elastomeric infusion devices for the treatment of E. faecalis infections.

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