Conjugative Plasmids Rarely Confer Antibiotic Resistance or Virulence

Antimicrobial-resistant bacteria cause over a million deaths annually. This study investigates the role of plasmid mobility types in disseminating antimicrobial resistance genes (ARGs) and virulence genes (VGs). By analyzing 142,492 fully sequenced plasmids from bacterial isolates and metagenomes, we offer a comprehensive representation of plasmid distribution in microbial communities. Our findings reveal that conjugative plasmids (pCONJ) are less common than previously estimated, comprising only 4.14% of the dataset. Mobilizable plasmids (pMOB) are the most prevalent (66.82%), followed by non-transmissible plasmids (pNT) at 29.04%. Although plasmids are recognized as key drivers of ARG dissemination, only 3.8% of plasmids encode ARGs. Among pCONJ plasmids, 6.9% harbor ARGs, and just 0.18% carry VGs. These findings contrast with earlier estimates, which overrepresented clinically associated plasmids. Interestingly, ARGs are more frequently associated with pMOB plasmids, which exhibit higher ARG density. In contrast, VGs are primarily found in pCONJ plasmids. This study highlights the significance of pMOB plasmids in ARG dissemination, emphasizing their role in resistance spread. Our results challenge prevailing assumptions about plasmid-mediated gene transfer and underscore the need to prioritize pMOB plasmids in future epidemiological studies. These insights contribute to a deeper understanding of plasmid dynamics and their implications for public health.