Antibiotic-resistant bacterial infection has become an endemic health threat in recent decades. These infections are difficult to be cured by conventional antibiotics, leading to prolonged hospital stays and increased mortality. Antibiotic resistance genes are commonly encoded on either the chromosome or plasmids. Bacterial plasmids are extra-chromosomal circular DNA that are able to replicate independently within bacterial hosts. Transfer of plasmids between bacterial cells via conjugation is an effective approach to disseminate antimicrobial resistance. Inhibiting plasmid replication will be an attractive idea to modify antibiotic-resistant bacteria to drug sensitive.

In this project, we aim to suppress the replication of a multidrug resistance plasmid, pNDM-HK, utilizing the counter-transcribed RNA (ctRNA). pNDM-HK is the first plasmid that encodes New Delhi metallo-β-lactamase (NDM-1), a carbapenemase, in Hong Kong. Previously we has sequenced the pNDM-HK encoded small regulatory RNAs (sRNAs) and proposed NDM-sR2 as the ctRNA to regulate plasmid replication. Herein, we confirmed NDM-sR2 could suppress the expression of replication protein in pNDM-HK. This ctRNA was then integrated into a phage to infect bacteria harboring pNDM-HK. Interestingly, resulting transductants got rid of the drug resistance plasmid after infection. Meanwhile, they became susceptible to various antibiotics including extended-spectrum β-lactamases (ESBLs) and carbapenems. In conclusion, this is the first study to remove a clinical multidrug resistance plasmid with the combination of phage and ctRNA. We believe this approach could be further developed as a therapeutic tool to combat antibiotic-resistant bacteria.