Carbapenem-resistant Klebsiella pneumoniae (CR-Kp) is currently a serious global concern. Antimicrobial stewardship programs (ASPs) are one of the key strategies to overcome this resistance. However, evidence about the long-term clinical and ecological impacts of ASPs is scarce. A multidisciplinary team conducted a multifaceted intervention in a CR-Kp endemic hospital over a 6-year period. We assessed the monthly long-term impacts of ASPs on carbapenem use, incidence density (ID), and crude death rates of hospital-acquired CR-Kp infections. Other variables potentially related to CR-Kp incidence and healthcare activity indicators were monitored. Carbapenem use showed a sustained reduction over the long term, with a difference of −66.19% (95% CI −87.03 to −45.34) between the expected pre-intervention trend consumption value and that obtained six years after starting the program. The ID of CR-Kp also decreased significantly and was maintained over the long term, with a relative reduction of −88.14% (95% CI; −100.4 to −75.85) at the end of the study period. The crude death rate of CR-Kp at 14 and 28 days decreased significantly after the intervention and remained steady after six years. Infection control indicator trends remained stable. This mixed ASP contributed to reducing the high incidence of infections and mortality rates of CR-Kp, achieving a sustained ecological and clinical effect.

Objectives: To generate in vitro ceftazidime-avibactam-resistant mutants derived from Klebsiella pneumoniae producing OXA-48 or OXA-48 derivatives OXA-131 and OXA-232 carbapenemases, to define their antimicrobial susceptibility phenotype and to analyse mutations potentially involved in resistance to ceftazidime-avibactam. Methods: Mutants were obtained by plating overnight bacterial cultures on Mueller-Hinton agar plates containing increasing concentrations of ceftazidime-avibactam (0.5/4–32/4 mg/L). MICs were determined using Sensititre™ DKMNG panels. Whole-genome sequencing of 8 parental strains and 31 mutant derivatives was performed with Illumina. Results: All parental strains were susceptible to ceftazidime-avibactam (MIC ≤ 0.5/4–2/4 mg/L) and either susceptible or resistant to meropenem (MIC 0.5 to >16 mg/L) and imipenem (MIC ≤ 0.5 to >16 mg/L). MICs of ceftazidime-avibactam for the mutants increased up to 4 to >16 mg/L, while MICs of meropenem and imipenem for most mutants either increased up to >16 mg/L or remained unchanged. Whole-genome sequencing of the mutants identified alterations in genes coding for proteins related to AcrAB-TolC (AcrB, AcrR), PBPs (PBP2, PBP3), porins (OmpK36, EnvZ) or the stress or stringent responses (RseB, CpxA, SpoT). No mutations were detected in genes coding for OXA-48-like enzymes or other β-lactamases. Conclusions: Ceftazidime-avibactam can select in vitro mutants of OXA-48-like carbapenemase-producing K. pneumoniae resistant to this combination and, in some cases, also to carbapenems. No mutations related to ceftazidime-avibactam resistance were found in genes coding OXA-48-like enzymes, but they were detected in genes related to active efflux, PBPs, permeability or proteins of the stress and stringent responses.

Background/Objectives: Ceftazidime-avibactam (CAZ/AVI) and cefiderocol (FDC) retain activity against most clinical isolates of KPC-producing Klebsiella pneumoniae (KPC-Kp). Nevertheless, the emergence of cross-resistance between both agents has become an increasing clinical concern. In this study, the development of resistance to both CAZ/AVI and FDC was retrospectively investigated in KPC-Kp isolates recovered from patients treated with CAZ/AVI between 2014 and 2023. Methods: Twenty-two isolates (pre- and post-therapy) obtained from nine patients were included. Demographic and clinical data were collected. FDC susceptibility testing was determined for both clinical isolates and E. coli TOP10 transformants by reference broth microdilution using iron-depleted medium, and MICs were interpreted according to EUCAST breakpoints. Resistance mechanisms were characterized using whole genome sequencing. Results: Cross-resistance to both CAZ/AVI and FDC emerged in six patients (66.7%) during CAZ/AVI therapy, after a median treatment duration of 12.8 ± 7.6 days. The presence of different KPC-3 variants in the CAZ/AVI-FDC resistant isolates was revealed by genomic analysis. Furthermore, the role of KPC-28, KPC-31, KPC-47, KPC-94, KPC-95, and KPC-148 in mediating reduced susceptibility to CAZ/AVI and FDC was confirmed by AST of transformants carrying bla_KPC variants. However, differences in MIC values compared with those obtained for the corresponding clinical isolates supported the relevance of additional mechanisms of co-resistance. The presence of ferric citrate transport (FEC) system was also associated with higher FDC MICs. Mutations in genes coding siderophore-iron transporter, PBPs, sensor histidine kinase or Tol-Pal system were also found in some of the isolates. Conclusions: These findings highlight the ability of KPC-Kp to develop co-resistance to both CAZ/AVI and FDC during CAZ/AVI therapy.

Background/Objectives: The susceptibility of Corynebacterium spp. to antimicrobial agents is species-related, with increasing levels of resistance to fluoroquinolones in several species related to their continued use in clinical practice. The objectives were to determine the in vitro activity of delafloxacin in comparison with other fluoroquinolones against clinical isolates of Corynebacterium spp., to compare MICs of delafloxacin obtained with gradient strips and with reference microdilution, and to investigate the mechanisms related to fluoroquinolone resistance in the tested strains. Methods: Fifty-three clinical isolates, assigned to five species of Corynebacterium spp., were evaluated using reference microdilution for delafloxacin, ciprofloxacin, levofloxacin, and moxifloxacin (with and without reserpine or phenylalanine-arginine β-naphthylamide), and gradient strips for delafloxacin. The QRDR of the gyrA gene was amplified using primers specific to the different species, and mutations were defined after aligning against the corresponding reference sequences. Results: Delafloxacin was the most active compound with MIC₅₀/MIC₉₀ values of 0.5/8 mg/L. Single mutations at the QRDR were observed in isolates, with MICs of delafloxacin ranging from 0.016 to 4 mg/L, while double mutations occurred in isolates, with MICs ranging from 0.125 to 16 mg/L. The delafloxacin gradient strips showed an essential agreement of 88.7%, bias of −5%, and a Kappa index of 0.848. Conclusions: Increased MICs of delafloxacin against Corynebacterium spp. are related to the presence of non-conservative mutations in the QRDR of gyrA. Delafloxacin gradient strips could be a reasonable alternative for use in the clinical routine of the microbiology laboratory. Delafloxacin could represent an alternative for treating infections due to some species of Corynebacterium.