Abstract
Despite being the target of control efforts for many decades, Salmonella enterica continues to be linked with a large amount of foodborne illnesses and outbreaks worldwide. Over the years, Salmonella isolated from meat products have exhibited a high level of antibiotic resistance. In this study, a total of 351 Salmonella isolates, recovered from cattle fecal samples (n = 31), hides (n = 105), and beef carcasses (n = 215) from 3 abattoirs in Mexico were analyzed for antimicrobial susceptibility. Resistance to at least one antimicrobial drug was found in 205 (58.4%) isolates and 20 different resistance phenotypes were observed among this Salmonella isolates set. Resistance to tetracycline (40.2%) and nalidixic acid (21.1%) was most commonly observed. Additionally, the most common multidrug-resistant (MDR) phenotypes shared resistance to chloramphenicol, streptomycin, tetracycline, and trimethopin/sulfamethoxazole (11.3%), resistance to ampicillin, tetracycline, and trimethopin/sulfamethoxazole (3.4%), and resistance to ampicillin, streptomycin, and tetracycline (2.5%). When it came to antimicrobial resistance phenotypes in each abattoir, we determined there was no statistical difference in the frequency of resistant vs. susceptible Salmonella isolates among the three abattoirs (P > 0.05). These data indicate that Salmonella isolates recovered from beef cattle in Mexico are commonly resistant to antimicrobials and often multiple antimicrobials. In Mexico, antimicrobial resistance, and in particular, multidrug-resistance, maybe of particular concern due to the much higher prevalence of Salmonella in retail beef. This may lead to the spread of resistance and to the reduction of antibiotic efficacy for the control of animal and human infections. Promoting control measures and inspection standards on imported animals and food products should be applied to avoid the spread of antibiotic resistance in various populations and among countries.
Highlights
Salmonella is a foodborne pathogen that is commonly found in beef cattle
Mexico exported about 9% in livestock and animal products to the U.S in 2012 [103]
The data presented in this study strongly suggested that CC398 acquired resistance to methicillin and tetracycline after the introduction to livestock from humans, and later reintroduced to humans [83]
Summary
Salmonella is a foodborne pathogen that is commonly found in beef cattle. Salmonella prevalence on cattle hides ranges from 30- 90% and from 20-60% on preevisceration carcasses depending on geographical location and season (Bosilevac et al, 2009; Brichta-Harhay et al, 2008; Fluckey et al, 2007; Kunze et al, 2008). There is a growing public health concern of the potential of antimicrobial drug resistance in bacterial pathogens, such as Salmonella, entering our food supply (Hur et al, 2012, WHO 2014) When it comes to Salmonella, there is evidence that clonal dissemination plays a critical role for both human and animal infections, and that this is not driven only by, or even primarily by, antimicrobial selection pressure (Butaye et al, 2006, Lucarelli et al, 2010, Hauser et al, 2012). Many of the currently known resistance genes in Salmonella are located on mobile genetic elements such as plasmids, transposons, gene cassettes and genomic islands (Alcaine et al, 2007, Lindsey et al, 2009, Brichta-Harhay et al, 2011, Frye and Jackson et al, 2013) As a consequence such resistance genes are exchanged between bacteria living in the same habitat, e.g. the Enterobacteriaceae in the gastrointestinal tract of humans and animals. These antimicrobial resistance genes can be co-transferred or co-selected even in the absence of a direct selective pressure (Michael et al, 2006, Alcaine et al, 2007, Brichta-Harhay et al, 2011)
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