Multidrug-resistant Gram-negative clinical isolates with reduced susceptibility/resistance to cefiderocol: which are the best present and future therapeutic alternatives?

PURPOSE: To evaluate the different present and future therapeutic ß-lactam/ß-lactamase inhibitor (BL/BLI) alternatives, namely aztreonam-avibactam, imipenem-relebactam, meropenem-vaborbactam, cefepime-zidebactam, cefepime-taniborbactam, meropenem-nacubactam, and sulbactam-durlobactam against clinical isolates showing reduced susceptibility or resistance to cefiderocol in Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa. METHODS: MIC values of aztreonam, aztreonam-avibactam, cefepime, cefepime-taniborbactam, cefepime-zidebactam, imipenem, imipenem-relebactam, meropenem, meropenem-vaborbactam, meropenem-nacubactam, sulbactam-durlobactam, and cefiderocol combined with a BLI were determined for 67, 9, and 11 clinical Enterobacterales, P. aeruginosa or A. baumannii isolates, respectively, showing MIC values of cefiderocol being ≥1 mg/L. If unavailable, the respective ß-lactam breakpoints according to EUCAST were used for BL/BLI combinations. RESULTS: For Enterobacterales, the susceptibility rates for aztreonam, cefepime, imipenem, and meropenem were 7.5%, 0%, 10.4%, and 10.4%, respectively, while they were much higher for cefepime-zidebactam (91%), cefiderocol-zidebactam (91%), meropenem-nacubactam (71.6%), cefiderocol-nacubactam (74.6%), and cefiderocol-taniborbactam (76.1%), as expected. For P. aeruginosa isolates, the higher susceptibility rates were observed for imipenem-relebactam, cefiderocol-zidebactam, and meropenem-vaborbactam (56% for all combinations). For A. baumannii isolates, lower susceptibility rates were observed with commercially or under development BL/BLI combos; however, a high susceptibility rate (70%) was found for sulbactam-durlobactam and when cefiderocol was associated to some BLIs. CONCLUSIONS: Zidebactam- and nacubactam-containing combinations showed a significant in vitro activity against multidrug-resistant Enterobacterales clinical isolates with reduced susceptibility to cefiderocol. On the other hand, imipenem-relebactam and meropenem-vaborbactam showed the highest susceptibility rates against P. aeruginosa isolates. Finally, sulbactam-durlobactam and cefiderocol combined with a BLI were the only effective options against A. baumannii tested isolates.

Impact of veterinary antibiotics on plasmid-encoded antibiotic resistance transfer.

OBJECTIVES: Resistance genes can be genetically transmitted and exchanged between commensal and pathogenic bacterial species, and in different compartments including the environment, or human and animal guts (One Health concept). The aim of our study was to evaluate whether subdosages of antibiotics administered in veterinary medicine could enhance plasmid transfer and, consequently, resistance gene exchange in gut microbiota. METHODS: Conjugation frequencies were determined with Escherichia coli strains carrying IncL- (blaOXA-48) or IncI1-type (blaCTX-M-1) plasmids subjected to a series of subinhibitory concentrations of antibiotics used in veterinary medicine, namely amoxicillin, ceftiofur, apramycin, neomycin, enrofloxacin, colistin, erythromycin, florfenicol, lincomycin, oxytetracycline, sulfamethazine, tiamulin and the ionophore narasin. Treatments with subinhibitory dosages were performed with and without supplementation with the antioxidant edaravone, known as a mitigator of the inducibility effect of several antibiotics on plasmid conjugation frequency (PCF). Expression of SOS-response associated genes and fluorescence-based reactive oxygen species (ROS) detection assays were performed to evaluate the stress oxidative response. RESULTS: Increased PCFs were observed for both strains when treating with florfenicol and oxytetracycline. Increased expression of the SOS-associated recA gene also occurred concomitantly, as well as increased ROS production. Addition of edaravone to the treatments reduced their PCF and also showed a decreasing effect on SOS and ROS responses for both plasmid scaffolds. CONCLUSIONS: We showed here that some antibiotics used in veterinary medicine may induce transfer of plasmid-encoded resistance and therefore may contribute to the worldwide spread of antibiotic resistance genes.

A Selective Culture Medium for Screening Cefiderocol Resistance in Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii.

Cefiderocol (FDC) is a siderophore cephalosporin with a broad spectrum of activity against many multidrug-resistant Gram-negative bacteria. Acquired resistance to FDC has been already reported among Gram-negative isolates, thus highlighting the need for rapid and accurate identification of such resistant pathogens, in order to control their spread. Therefore, the SuperFDC medium was developed to screen FDC-resistant Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii. After testing several culture conditions, a selective medium was set up by supplementing an iron-depleted agar medium with 8 µg/mL of FDC and evaluated with a collection of 68 FDC-susceptible and 33 FDC-resistant Gram-negative isolates exhibiting a variety of ß-lactam resistance mechanisms. The sensitivity and specificity of detection of this medium were evaluated at 97% and 100%, respectively. In comparison with the reference broth microdilution method, only 3% very major errors were found. In addition, excellent detection performances were obtained by testing spiked stools with a lower limit of detection ranging between 100 and 103 CFU/mL. The SuperFDC medium allows detection of FDC-resistant Gram-negative isolates regardless of their corresponding resistance mechanisms.

Characterization of OXA-204, a carbapenem-hydrolyzing class D ß-lactamase from Klebsiella pneumoniae.

A Klebsiella pneumoniae clinical isolate recovered in Tunisia showed resistance to all ß-lactams and decreased susceptibility to carbapenems. K. pneumoniae 204 expressed the carbapenem-hydrolyzing ß-lactamase OXA-204, differing from OXA-48 by two amino acid substitutions (Gln98His and Thr99Arg) (class D ß-lactamase [DBL] numbering). OXA-48 and OXA-204 shared similar resistance profiles, hydrolyzing carbapenems but sparing broad-spectrum cephalosporins. The bla(OXA-204) gene was located on a ca. 150-kb IncA/C-type plasmid, which also carried the bla(CMY-4) gene. The bla(OXA-204) gene was associated with an ISEcp1 element, whereas the bla(OXA-48) genes are usually associated with IS1999.

Efficacies of colistin and tigecycline in mice with experimental pneumonia due to NDM-1-producing strains of Klebsiella pneumoniae and Escherichia coli.

New Delhi metallo-ß-lactamase-1 (NDM-1)-producing Enterobacteriaceae have emerged as a global threat. The aim of this study was to assess the efficacies of colistin and tigecycline in an experimental model of pneumonia caused by NDM-1-producing Escherichia coli and Klebsiella pneumoniae. The susceptibilities of K. pneumoniae NDM, E. coli NDM and K. pneumoniae ATCC 29665 were determined using the broth microdilution technique. The pharmacokinetics of colistin and tigecycline in an experimental model of pneumonia were performed using immunocompetent C57BL/6 mice. Mice were treated with colistin (60 mg/kg/day) or tigecycline (10 mg/kg/day). Mortality, bacteraemia and lung bacterial concentrations were recorded. The strains were susceptible to colistin and tigecycline. The ratio of area under the concentration-time curve/minimum inhibitory concentration (AUC/MIC) for colistin was 158.5 (all three strains) and that for tigecycline was 18.5 (K. pneumoniae NDM) and 37 (K. pneumoniae ATCC 29665 and E. coli NDM). In vivo, colistin decreased bacterial lung concentrations of K. pneumoniae NDM and K. pneumoniae ATCC 29665 by 1.16 log colony-forming units (CFU)/g and 2.23 logCFU/g, respectively, compared with controls (not significant). Tigecycline reduced K. pneumoniae NDM and K. pneumoniae ATCC 29665 load by 2.67 logCFU/g and 4.62 logCFU/g (P<0.05). Colistin and tigecycline decreased lung concentrations of E. coli NDM by 2.27 logCFU/g and 4.15 logCFU/g (P<0.05), respectively, compared with controls, and was more active than colistin (P<0.05). In conclusion, these results suggest that colistin is inappropriate for treating pneumonia due to NDM-1-producing K. pneumoniae and its efficacy was suboptimal against NDM-1-producing E. coli. A high tigecycline dose was efficacious for treating experimental pneumonia due to NDM-1-producing E. coli and K. pneumoniae.

Broad-spectrum beta-lactams for treating experimental peritonitis in mice due to Escherichia coli producing plasmid-encoded cephalosporinases.

OBJECTIVES: To investigate the correlation between in vitro activity and in vivo efficacy of broad-spectrum beta-lactams for treating experimental infections due to Escherichia coli expressing two types of plasmid-mediated AmpC-type beta-lactamases, LAT-1 and FOX-1. METHODS: Susceptibility testing and time-kill curves were determined for piperacillin/tazobactam, ceftazidime, cefepime and imipenem. A mouse model of peritonitis was developed to determine 50% effective doses (ED(50)s) of beta-lactams against E. coli clinical strains producing recombinant plasmids pLAT-1 and pFOX-1. RESULTS: MIC and MBC values correlated with the ED(50)s for ceftazidime, cefepime and imipenem. Among the beta-lactams tested, both cefepime and imipenem were effective for treating peritonitis caused by E. coli strains harbouring pLAT-1 or pFOX-1, whereas ceftazidime was effective only against E. coli (pLAT-1). Piperacillin/tazobactam was not effective for treating infections with either of these two strains. CONCLUSIONS: Piperacillin/tazobactam was not efficacious for treating infections due to E. coli producing plasmid-mediated AmpC-type beta-lactamases, whereas cefepime and imipenem were efficacious.

Multiplex PCR for detection of plasmid-mediated quinolone resistance qnr genes in ESBL-producing enterobacterial isolates.

OBJECTIVES: To develop a rapid and reliable single-tube-based PCR technique for detecting simultaneously the plasmid-mediated quinolone resistance qnrA, qnrB and qnrS genes. METHODS: After multiple alignments, primers were designed to detect known qnr variants (six for qnrA-, six for qnrB- and two for qnrS-like genes). They were used for screening a collection of 64 expanded-spectrum beta-lactamase (ESBL)-producing enterobacterial isolates from Kuwait, collected from 2002 to 2004, as ESBL genes have been often associated with qnr genes. Sequencing was performed to identify qnr and associated ESBL genes. RESULTS: In optimized conditions, all positive controls (used separately or mixed) confirmed the specificity of the PCR primers. Out of 64 isolates, only 3 isolates were positive for a qnrB-like gene (4.7%), whereas no qnrA-like and qnrS-like gene was detected. A qnrB2 gene was detected in an Enterobacter cloacae K34 (SHV-12+) isolate, whereas qnrB1-like (termed qnrB7) and qnrB6-like (termed qnrB8) genes were identified from E. cloacae K37 (SHV-12+) and Citrobacter freundii K70 (VEB-1b+) isolates, respectively. CONCLUSIONS: We report here a fast and reliable technique for rapid screening of qnr-positive strains to be used for epidemiological surveys. A low prevalence of Qnr determinants among ESBL-producing Enterobacteriaceae was identified in the study with Kuwaiti isolates.