Gram-negative bacilli resistant to carbapenems (GNB-CR) are of critical priority, according to the WHO, for research and development of new antibiotics. Most of the new β-lactams with β-lactamase inhibitors are not effective for the treatment of infections caused by NDM-producing GNB-CR, which have emerged in different countries, including Brazil. Polymyxin B (POLB), despite its undeniable toxicity, still remains a therapeutic option, but some bacteria are intrinsically resistant, imposing additional/insurmountable therapeutic difficulties. Our objective was to evaluate the distribution of carbapenemases and susceptibility to ceftazidime-avibactam (CZA) and POLB among GNB resistant (R) or intermediate (I – susceptible, increased exposure) to meropenem (MEM). A retrospective study was conducted with bacteria recovered from blood cultures of patients from a tertiary hospital in southern Brazil (11/2024-05/2025). They were identified by MALDI-TOF; susceptibility to MEM and CZA was assessed by disk diffusion (BrCAST). The MIC of POLB was determined by broth microdilution (BrCAST). The presence of carbapenemase was evaluated by NG-Test® CARBA-5 (NDM, IMP, VIM, OXA-48, KPC) and/or by HRM-qPCR (blaKPC, blaGES, blaNDM-1, blaIMP, blaVIM and blaOXA-48-like). During the study, 514 GNB R or I to MEM were recovered, with 13.2% (68/514) from blood cultures, mostly K. pneumoniae (45.6%, 31/68), P. aeruginosa (17.6%) and A. baumannii (10.3%). E. coli (8.8%), Enterobacter sp. (5.9%), S. marcescens (4.4%), K. oxytoca (2.9%), M. morganii (2.9%) and P. mosselii (1.5%) were also recovered, ensuring diversity. Among Enterobacterales (n = 48), 10 were MEM I and 38 (79.2%) R. All non-fermenters (n = 20) were MEM R. Susceptibility to CZA was assessed for all isolates, except A. baumannii and P. mosselii, with 55% (33/60) R. Of these, 56.5% were K. pneumoniae (n = 13) and P. aeruginosa (n = 10), all NDM producers, except 1 S. marcescens blaKPC. Among CZA R isolates, 24.2% (8/33) were also resistant to POLB, including 1 S. marcescens and 2 M. morganii, intrinsically resistant. Treating severe infections caused by GNB-CR is challenging, especially considering the spread of NDM-producing isolates. Therefore, microbiological surveillance programs, infection control and rational use of antibiotics should be strengthened, in addition to continued investment in therapeutic and diagnostic strategies.
Moreira et al. (Sun,) studied this question.