Bacteria are unique in that their sole mission is focused on survival. In order to accomplish this, they have continually developed mechanisms to avoid physical and chemical treatments which may affect their survival. Antimicrobial agents are used to treat a wide number of bacterial infections in humans, animals and plants and the development of antimicrobial resistance has emerged as a global problem. Given that antimicrobial resistance originated in the environment, was likely disseminated and dispersed locally, then globally as a result of trade, travel, knowledge and the economies of countries developed, it should be no surprise that we now see antimicrobial resistant clones identified globally.
Salmonella is a global zoonotic foodborne pathogen with over 2600 serotypes/antigenic formulas. Multiple strain diversity has been observed within many of the most common human and animal associated serotypes; analysis of some serotypes from food producing animals suggests a host ‘preference’. Use of serotyping, pulsed field gel electrophoresis, replicon typing, PCR, whole genome sequencing and other tools have enabled investigators to study the mechanisms and transmission of antimicrobial resistance. Interestingly, not only can antimicrobial resistance within a serotype vary, it can also vary by strain within a serotype. Multi-drug resistance is often associated with IncA/C plasmids which likely have an early origin. Extended spectrum β-lactamase (ESBL) producing bacteria mediate resistance to extended-spectrum cephalosporins and ESBL producing salmonellae are recovered globally. The emergence of Salmonella serotypes resistant to fluroquinolones, extended-spectrum cephalosporins, and now carbapenems (the last line antimicrobial available for treatment) poses both a medical and veterinary crisis. Control of antimicrobial resistance is a shared responsibility between the two major users of antimicrobials, the medical and veterinary community which includes food animal production. However, the ecological, human/animal, trade/travel dynamic must be acknowledged and included in discussions.