FactSentinel

Antibiotic resistance is not confined to the bacterial species in which it originally arises. Bacteria possess several mechanisms for transferring genetic material horizontally, meaning between unrelated species, rather than only vertically from parent to offspring. The most significant of these mechanisms is conjugation, in which bacteria physically connect and transfer small circular pieces of DNA called plasmids. These plasmids often carry resistance genes and can move between different genera entirely, such as from Escherichia coli to Salmonella or Klebsiella. Other mechanisms, including transformation, where bacteria absorb free DNA from their environment, and transduction, where viruses called bacteriophages inadvertently carry genetic material between bacterial cells, further enable this spread.

Scientific consensus, supported by decades of microbiology and genomic research, confirms that mobile genetic elements like plasmids, transposons, and integrons serve as vehicles for resistance genes to jump between species. This has been documented extensively in clinical and environmental settings, including in hospitals, agricultural systems, and wastewater, where diverse bacterial populations coexist and exchange genetic material. The emergence of resistance genes like NDM-1 and mcr-1, found across multiple bacterial species worldwide, provides concrete evidence of this cross-species transfer.

A common misconception is that resistance only develops through mutation within a single bacterial lineage and stays there. While spontaneous mutation does contribute to resistance, horizontal gene transfer is often the more rapid and widespread mechanism, allowing resistance to spread across bacterial communities far faster than mutation alone would permit. This underscores why antibiotic stewardship must address entire microbial ecosystems, not just individual pathogens.