THE EMERGENCE OF ANTIMICROBIAL RESISTANCE

The ability of bacteria to resist antibiotics is embedded in their evolutionary history (Gillings et al. 2008). In soil and other environments, antibiotic-producing bacteria and the bacterial species to which the antibiotics are being directed, have co-evolved (Perry and Wright 2013).

Bacteria primarily resist antibiotics via three modes: inactivation or modification of the antibiotic; reduced uptake by efflux or alteration of cell permeability; and modification of proteins targeted by antibiotics (Tenover 2006). Despite the three broad mechanisms that facilitate resistance, the genetic basis of these mechanisms is extremely diverse (Blair et al. 2015). For example, irre­spective of mode of resistance, the genes that confer resistance can be intrinsic or extrinsic. Intrinsic resist­ance arises from endogenous genes of the bacterial spe­cies (Hollenbeck and Rice 2012). Extrinsic resistance is acquired through horizontal gene transfer whereby resistance genes are associated with mobile genetic ele­ments such as plasmids, transposons and integrons (Gill­ings 2014; Blair et al. 2015). These genetic mechanisms can be mobilised and transferred to bacteria within the same species and to different bacterial species (Gillings et al. 2008). The genetic machinery that enables resist­ance has been and continues to be an important mecha­nism for the evolution of bacteria (Gillings 2014).

Factors typically recognised as drivers of disease emergence, including urbanisation, agricultural intensi­fication and increased global travel/wildlife tourism and trade (Jones et al. 2008), can also facilitate the spread of antibiotic resistant bacteria. Wildlife conservation man­agement and wildlife research further provide avenues for pathogen exchange, inclusive of resistant bacteria, across species boundaries. All drivers result in increased opportunity for pathogen transmission across species boundaries by increasing the proximity of humans and domesticated animals to wildlife and connecting the microorganisms that each host carries. The processes that facilitate pathogen transmission across species boundaries and through the environment is represented within the One Health framework (WHO 2024).

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