Specific killing and resensitization of pathogenic <i>Escherichia coli</i> strains carrying <i>bla</i> CTX-M-15 β-lactamase using targeted-antibacterial-plasmids (TAPs)

Targeted-Antibacterial-Plasmids (TAPs) offer a precise approach to combat multidrug-resistant bacteria by selectively removing resistant strains while preserving commensals. Here, we assess TAPs that deliver CRISPR/Cas systems via conjugation to kill or resensitize extended-spectrum β-lactamase (ESBL)-producing Escherichia coli carrying the blaCTX-M-15 gene. We systematically tested multiple variables in the TAP approach, including two commensal E. coli donors, three distinct helper plasmids encoding the transfer machineries, and six recipient strains harbouring the resistance gene either chromosomally or on a plasmid. Cas9-based TAPs induced double-stranded breaks in chromosomal blaCTX-M-15 genes, resulting in immediate bacterial death. When the target gene was plasmid-borne, Cas9 cleavage triggered plasmid loss and partial toxin-antitoxin-mediated killing. In contrast, dCas9-based TAPs inhibited blaCTX-M-15 expression without affecting cell viability, thereby restoring third-generation cephalosporin susceptibility. In mixed-culture experiments, TAPs specifically eliminated only blaCTX-M-15-carrying E. coli while sparing other non-targeted bacterial species. Conjugation assays in human faeces demonstrated substantial suppression of cefotaxime-resistant (CtxR) E. coli by both Cas9- and dCas9-based TAPs, underscoring their efficacy in complex microbial environments. These findings highlight TAPs' decolonization promise, paving the way for future microbiome-editing interventions against multidrug-resistant carriage or infection.