Abstract
Antimicrobial resistance has become a major challenge in veterinary medicine, particularly in the context of bacterial pathogens that play a role in both humans and animals. This review serves as an update on acquired resistance mechanisms in bacterial pathogens of human and animal origin, including examples of transfer of resistant pathogens between hosts and of resistance genes between bacteria. Acquired resistance is based on resistance-mediating mutations or on mobile resistance genes. Although mutations are transferred vertically, mobile resistance genes are also transferred horizontally (by transformation, transduction or conjugation/mobilization), contributing to the dissemination of resistance. Mobile genes specifying any of the three major resistance mechanisms - enzymatic inactivation, reduced intracellular accumulation or modification of the cellular target sites - have been found in a variety of bacteria that may be isolated from animals. Such resistance genes are associated with plasmids, transposons, gene cassettes, integrative and conjugative elements or other mobile elements. Bacteria, including zoonotic pathogens, can be exchanged between animals and humans mainly via direct contact, but also via dust, aerosols or foods. Proof of the direction of transfer of resistant bacteria can be difficult and depends on the location of resistance genes or mutations in the chromosomal DNA or on a mobile element. The wide variety in resistance and resistance transfer mechanisms will continue to ensure the success of bacterial pathogens in the future. Our strategies to counteract resistance and preserve the efficacy of antimicrobial agents need to be equally diverse and resourceful.
Highlights
Antimicrobial agents are used extensively in aquaculture, horticulture, and to treat bacterial infections in humans and animals
Whenever antimicrobial agents are applied to either humans or animals, a selective pressure is set under which susceptible bacteria are inhibited in their growth or killed, whereas resistant bacteria can propagate at the expense of the susceptible bacteria.[64, 65]
If a multidrug-resistance mobile genetic elements (MGEs) is transferred to new bacterial host and this host cell gains all the resistance genes associated with the MGE, the selective pressure imposed by the use of a single antimicrobial agent will ensure that the new host cell does not lose the multidrug-resistance MGE.[64, 65]
Summary
Antimicrobial agents are used extensively in aquaculture, horticulture, and to treat bacterial infections in humans and animals. Bacteria have developed and refined various ways and means to resist or escape the inhibitory effects of the antimicrobial agents.[1, 2] In addition, certain bacterial pathogens have managed to accumulate or develop resistances to multiple classes of antimicrobial agents at the same time Such multidrug-resistant, extensively resistant or even pan-drug resistant pathogens[4] typically succeed in human and veterinary healthcare establishments or in patients repeatedly requiring antibacterial therapy. For the first time in decades, the prognosis for patients with infections caused by multidrug-resistant bacteria has been seriously compromised by the lack of effective antimicrobial agents This development has threatened the advancement of modern medicine.[5]
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