Genetic mechanisms of antimicrobial resistance identified in Salmonella enterica, Escherichia coli, and Enteroccocus spp. isolated from U.S. food animals

Abstract

The prevalence of antimicrobial resistance (AR) in bacteria isolated from U.S. food animals has increased over the last several decades as have concerns of AR foodborne zoonotic human infections. Resistance mechanisms identified in U.S. animal isolates of Salmonella enterica included resistance to aminoglycosides (e.g., alleles of aacC, aadA, aadB, ant, aphA, and StrAB), β-lactams (e.g., blaCMY−2, TEM−1, PSE−1), chloramphenicol (e.g., floR, cmlA, cat1, cat2), folate pathway inhibitors (e.g., alleles of sul and dfr), and tetracycline [e.g., alleles of tet(A), (B), (C), (D), (G), and tetR]. In the U.S., multi-drug resistance (MDR) mechanisms in Salmonella animal isolates were associated with integrons, or mobile genetic elements (MGEs) such as IncA/C plasmids which can be transferred among bacteria. It is thought that AR Salmonella originates in food animals and is transmitted through food to humans. However, some AR Salmonella isolated from humans in the U.S. have different AR elements than those isolated from food animals, suggesting a different etiology for some AR human infections. The AR mechanisms identified in isolates from outside the U.S. are also predominantly different. For example the extended spectrum β-lactamases (ESBLs) are found in human and animal isolates globally; however, in the U.S., ESBLs thus far have only been found in human and not food animal isolates. Commensal bacteria in animals including Escherichia coli and Enterococcus spp. may be reservoirs for AR mechanisms. Many of the AR genes and MGEs found in E. coli isolated from U.S. animals are similar to those found in Salmonella. Enterococcus spp. isolated from animals frequently carry MGEs with AR genes, including resistances to aminoglycosides (e.g., alleles of aac, ant, and aph), macrolides [e.g., erm(A), erm(B), and msrC], and tetracyclines [e.g., tet(K), (L), (M), (O), (S)]. Continuing investigations are required to help understand and mitigate the impact of AR bacteria on human and animal health.

Antibiotic resistance in Enterobacteriaceae: mechanisms and clinical implications

“…47 The feces of humans and animals contaminate the environment, and drinking and environmental water supplies may harbor highly resistant E coli in both resource poor and rich countries. [48][49][50][51][52][53][54] Antibiotic resistant human pathogens are also common in food and in food chain animals, [55][56][57][58][59][60][61] and household pets may carry similar multi-resistant isolates to humans. 62 63 Wild animals are often affected, 64 particularly scavengers such as seagulls, which are important vectors of antibiotic resistance including in known human pathogens.…”

EVALUACIÓN DE RÍOS DEL VALLE DE CULIACÁN, MÉXICO, COMO RESERVORIOS DE SEROTIPOS DE Salmonella RESISTENTES A ANTIBIÓTICOS

“…Después se sumaron esfuerzos para estudiar y controlar la RA de este serotipo, así como otros serotipos emergentes (Frye y Jackson 2013). En este sentido, se debe prestar especial atención a los serotipos que muestran RMA de origen acuático, incluyendo Salmonella Oranienburg, Salmonella Saintpaul, Salmonella Minnesota y Salmonella Muenchen, ya que son los principales serotipos dispersos en la región noroeste de México (López et al 2009, Jiménez et al 2011 y se relacionan con brotes mundiales de SNT (Behravesh et al 2011, Pui et al 2011, CDC 2013.…”

“…Por último, la aparición de cepas con RMAexhibida por la mayoría de los serotipos de Salmonella-tiene un impacto negativo en la eficacia del tratamiento antimicrobiano; en consecuencia, puede conducir a aumentos en las tasas de morbimortalidad de la salmonelosis (Frye y Jackson 2013). Además, un aumento de la resistencia a la ampicilina entre los serotipos de Salmonella incluidos en este estudio se considera un problema de salud en México, ya que este antibiótico es uno de los más recetados.…”

Salmonella Control in Food Production

“…Various antimicrobial agents have different mechanisms of action by which they are classified. Different aspects of antimicrobial response in Salmonella response to clinical antimicrobials has been extensively covered elsewhere (Angulo et al, 2000;Alcaine et al, 2007;Hur et al, 2012;Frye and Jackson, 2013;Ricke and Rivera Calo, 2015) and so will be only briefly touched on here. Two issues make foodborne Salmonella antibiotic resistance problematic for public health.…”

“…Antimicrobial agents that either inhibit the bacterial cell's ability to maintain the peptidoglycan structure or altogether prevent peptidoglycan synthesis include several classes of beta lactams such as penicillin, modified versions of penicillin, namely oxacillin and methicillin, along with cephalosporins and carbapenems (Frye and Jackson, 2013). Antimicrobial agents that either inhibit the bacterial cell's ability to maintain the peptidoglycan structure or altogether prevent peptidoglycan synthesis include several classes of beta lactams such as penicillin, modified versions of penicillin, namely oxacillin and methicillin, along with cephalosporins and carbapenems (Frye and Jackson, 2013).…”