Resistance determinants and their genetic context in enterobacteria from a longitudinal study of pigs reared under various husbandry conditions

Pigs are major reservoirs of resistant Enterobacteriaceae that can reach humans through consumption of contaminated meat or vegetables grown in manure-fertilized soil. Samples were collected from sows during lactation and their piglets at five time points spanning the production cycle. Cefotaxime-resistant bacteria were quantified and isolated from feed, feces, manures and carcasses of pigs reared with penicillin-using or antibiotic-free husbandries. The isolates were characterized by antibiotic susceptibility testing, whole genome sequencing and conjugation assays. The extended spectrum β-lactamase (ESBL) phenotype was more frequent in isolates originating from antibiotic-free animals, while the bacteria isolated from penicillin-using animals were on average resistant to a greater number of antibiotics. The ESBL-encoding genes identified were blaCTX-M-1, blaCTX-M-15 and blaCMY-2 and they co-localised on plasmids with various genes encoding resistance to ß-lactams, co-trimoxazole, phenicols and tetracycline, all antibiotics used in pig production. Groups of genes conferring the observed resistance and the mobile elements disseminating multidrug resistance were determined. The observed resistance to ß-lactams was mainly due to the complementary actions of penicillin-binding proteins, an efflux pump and ß-lactamases. Most resistance determinants were shared by animals raised with or without antimicrobials. This suggests a key contribution of indigenous enterobacteria maternally transmitted along the sow lineage, regardless of antimicrobial use. It is unclear if the antimicrobial resistance observed in the enterobacteria populations of the commercial pig herds studied were present before the use of antibiotics, or the extent to which historical antimicrobial use exerted a selective pressure defining the resistant bacterial populations in farms using penicillin prophylaxis. Importance: Antimicrobial resistance is a global threat that needs to be fought on numerous fronts along the One Health continuum. Vast quantities of antimicrobials are used in agriculture to ensure animal welfare and productivity, and are arguably a driving force for the persistence of environmental and food-borne resistant bacteria. This study evaluated the impact of conventional, organic and other antibiotic-free husbandry practices on the frequency and nature of antimicrobial resistance genes and multidrug resistant enterobacteria. It provides knowledge about the relative contribution of specific resistance determinants to observed antibiotic resistance. It also showed the clear co-selection of genes coding for extended-spectrum beta-lactamases and genes coding for the resistance to antibiotics commonly used for prophylaxis or in curative treatments in pig operations.

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Antimicrobial resistance in United States retail ground beef with and without label claims regarding antibiotic use

Journal of Food Protection ◽

10.4315/jfp-20-376 ◽

2020 ◽

Author(s):

John W. Schmidt ◽

Amit Vikram ◽

Enrique Doster ◽

Kevin Thomas ◽

Margaret D Weinroth ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Production System ◽

Ground Beef ◽

Antibiotic Use ◽

Resistant Bacteria ◽

Antimicrobial Use ◽

Food Animal ◽

Antimicrobial Resistance Genes ◽

Human Health Impacts ◽

Beef Products

Antibiotics used during food-animal production account for approximately 77% of U.S. antimicrobial consumption by mass. Ground beef products labeled as raised without antibiotics (RWA) are perceived to harbor lower antimicrobial resistance (AMR) levels than conventional (CONV) products with no label claims regarding antimicrobial use. Retail ground beef samples were obtained from 6 U. S. cities. Samples with a RWA or USDA Organic claim ( N = 299) were assigned to the RWA production system. Samples lacking these claims ( N = 300) were assigned to the CONV production system. Each sample was cultured for the detection of five antimicrobial resistant bacteria. Genomic DNA was isolated from each sample and qPCR was used to determine the abundance of ten antimicrobial resistance genes (ARGs). Tetracycline-resistant Escherichia coli (CONV = 46.3%; RWA = 34.4%, P < 0.01) and erythromycin-resistant Enterococcus (CONV = 48.0%; RWA = 37.5%, P = 0.01) were more frequently detected in CONV. Salmonella were detected in 1.2% of samples. The ARG bla CTX-M (CONV = 4.1 log 10 normalized abundance, RWA = 3.8 log 10 normalized abundance, P < 0.01) was more abundant in CONV ground beef. The ARGs mecA (CONV = 4.4 log 10 normalized abundance, RWA = 4.9 log 10 normalized abundance, P = 0.05), tet (A) (CONV = 3.9 log 10 normalized abundance, RWA = 4.5 log 10 normalized abundance, P < 0.01), tet (B) (CONV = 3.9 log 10 normalized abundance, RWA = 4.5 log 10 normalized abundance, P < 0.01), and tet (M) (CONV = 5.4 log 10 normalized abundance, RWA = 5.8 log 10 normalized abundance, P < 0.01) were more abundant in RWA ground beef. Although these results suggest that antimicrobial use during U. S. cattle production does not increase human exposure to AMR via ground beef quantitative microbiological risk assessments are required for authoritative assessments regarding the human health impacts of antimicrobial uses during beef production.

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Characterization and Horizontal Transfer of Antimicrobial Resistance Genes and Integrons in Bacteria Isolated from Cooked Meat Products in China

Journal of Food Protection ◽

10.4315/0362-028x.jfp-17-119 ◽

2017 ◽

Vol 80 (12) ◽

pp. 2048-2055 ◽

Cited By ~ 2

Author(s):

Tao Yu ◽

Xiaobing Jiang ◽

Yu Liang ◽

Yanping Zhu ◽

Jinhe Tian ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Resistance Genes ◽

Meat Products ◽

Multidrug Resistant ◽

Resistant Bacteria ◽

Integrase Gene ◽

Antimicrobial Resistance Genes ◽

Class 1 ◽

Cooked Meat ◽

Cooked Meat Products

ABSTRACT The aim of this study was to investigate antimicrobial resistance and the presence and transferability of corresponding resistance genes and integrons in bacteria isolated from cooked meat samples in the People's Republic of China. A total of 150 isolates (22 species belonging to 15 genera) were isolated from 49 samples. Resistance of these isolates to antimicrobials was commonly observed; 42.7, 36.0, and 25.3% of the isolates were resistant to tetracycline, streptomycin, and ampicillin, respectively. Multidrug resistance was observed in 41 (27.3%) of the isolates. Sixteen resistance genes, i.e., blaTEM-1 and blaCTX-M-14 (β-lactams), aac(3)-IIa (gentamicin), strA and strB (streptomycin), qnrB and qnrS (fluoroquinolone), sul1, sul2, and sul3 (sulfamethoxazole), cat1 and cat2 (chloramphenicol), and tetM, tetA, tetS, and tetB (tetracycline), were found in 54 isolates. One isolate of Pseudomonas putida carried qnrB, and sequence analysis of the PCR product revealed 96% identity to qnrB2. The qnr genes were found coresiding and were cotransferred with bla genes in two isolates. Twelve isolates were positive for the class 1 integrase gene, and four isolates carried the class 2 integrase gene. However, no class 3 integrase gene was detected. One isolate of Proteus mirabilis carried dfrA32-ereA-aadA2, and this unusual array could be transferred to Escherichia coli. Nonclassic class 1 integrons lacking qacEΔ1 and sul1 genes were found in 2 of the 12 intI1-positive isolates. Our results revealed the presence of multidrug-resistant bacteria in cooked meats and the presence and transferability of resistance genes in some isolates, suggesting that cooked meat products may act as reservoirs of drug-resistant bacteria and may facilitate the spread of resistance genes.

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Antimicrobial resistance in Campylobacter coli and Campylobacter jejuni from human campylobacteriosis in Taiwan, 2016–2019

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01736-21 ◽

2021 ◽

Author(s):

Ying-Shu Liao ◽

Bo-Han Chen ◽

Ru-Hsiou Teng ◽

You-Wun Wang ◽

Jui-Hsien Chang ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Efflux Pump ◽

Genetic Resistance ◽

Multidrug Resistant ◽

23S Rrna ◽

Campylobacter Coli ◽

Rapid Diagnostics ◽

Phenotypic Resistance ◽

Resistance Determinants ◽

Level Resistance

Campylobacter coli and C. jejuni are highly resistant to most therapeutic antimicrobials in Taiwan, rapid diagnostics of resistance in bacterial isolates is crucial for the treatment of campylobacteriosis. We characterized 219 (40 C. coli and 179 C. jejuni ) isolates recovered from humans between 2016 and 2019 using whole-genome sequencing to investigate the genetic diversity among isolates and the genetic resistance determinants associated with antimicrobial resistance. Susceptibility testing with 8 antimicrobials was conducted to assess the concordance between phenotypic resistance and genetic determinants. The conventional and core genome multilocus sequence typing analysis revealed diverse clonality among the isolates. Mutations in gyrA (T86I, D90N), rpsL (K43R, K88R), and 23S rRNA (A2075G) were found in 91.8%, 3.2%, and 6.4% of the isolates, respectively. Horizontally transferable resistance genes ant( 6 )-I , aad9 , aph(3’)-IIIa , aph(2”) , blaOXA , catA / fexA , cfr(C) , erm(B) , lnu , sat4 , and tet were identified in 24.2%, 21.5%, 33.3%, 11.9%, 96.3%, 10.0%, 0.9%, 6.8%, 3.2%, 13.2%, and 96.3%, respectively. High-level resistance to 8 antimicrobials in isolates was 100% predictable by the known resistance determinants, whereas low-level resistance to azithromycin, clindamycin, nalidixic acid, ciprofloxacin, and florfenicol in isolates was associated with sequence variations in CmeA and CmeB of the CmeABC efflux pump. Resistance-enhancing CmeB variants were identified in 62.1% (136/219) of isolates. In conclusion, an extremely high proportion of C. coli (100%) and C. jejuni (88.3%) were multidrug-resistant and a high proportion (62.5%) of C. coli isolates had been resistant to azithromycin, erythromycin, and clindamycin that would complicate the treatment of invasive campylobacteriosis in this country.

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De-escalation of antimicrobial therapy in ICU settings with high prevalence of multidrug-resistant bacteria: a multicentre prospective observational cohort study in patients with sepsis or septic shock

Journal of Antimicrobial Chemotherapy ◽

10.1093/jac/dkaa375 ◽

2020 ◽

Vol 75 (12) ◽

pp. 3665-3674 ◽

Cited By ~ 3

Author(s):

Christina Routsi ◽

Aikaterini Gkoufa ◽

Kostoula Arvaniti ◽

Stelios Kokkoris ◽

Alexandros Tourtoglou ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Antimicrobial Therapy ◽

Sofa Score ◽

Multivariate Regression Analysis ◽

Multidrug Resistant ◽

Resistant Bacteria ◽

Antibiotic Resistant ◽

Number Of Patients ◽

Observational Cohort ◽

The Impact

Abstract Background De-escalation of empirical antimicrobial therapy, a key component of antibiotic stewardship, is considered difficult in ICUs with high rates of antimicrobial resistance. Objectives To assess the feasibility and the impact of antimicrobial de-escalation in ICUs with high rates of antimicrobial resistance. Methods Multicentre, prospective, observational study in septic patients with documented infections. Patients in whom de-escalation was applied were compared with patients without de-escalation by the use of a propensity score matching by SOFA score on the day of de-escalation initiation. Results A total of 262 patients (mean age 62.2 ± 15.1 years) were included. Antibiotic-resistant pathogens comprised 62.9%, classified as MDR (12.5%), extensively drug-resistant (49%) and pandrug-resistant (1.2%). In 97 (37%) patients de-escalation was judged not feasible in view of the antibiotic susceptibility results. Of the remaining 165 patients, judged as patients with de-escalation possibility, de-escalation was applied in 60 (22.9%). These were matched to an equal number of patients without de-escalation. In this subset of 120 patients, de-escalation compared with no de-escalation was associated with lower all-cause 28 day mortality (13.3% versus 36.7%, OR 0.27, 95% CI 0.11–0.66, P = 0.006); ICU and hospital mortality were also lower. De-escalation was associated with a subsequent collateral decrease in the SOFA score. Cox multivariate regression analysis revealed de-escalation as a significant factor for 28 day survival (HR 0.31, 95% CI 0.14–0.70, P = 0.005). Conclusions In ICUs with high levels of antimicrobial resistance, feasibility of antimicrobial de-escalation was limited because of the multi-resistant pathogens isolated. However, when de-escalation was feasible and applied, it was associated with lower mortality.

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Antimicrobial use in swine production and its effect on the swine gut microbiota and antimicrobial resistance

Canadian Journal of Microbiology ◽

10.1139/cjm-2015-0239 ◽

2015 ◽

Vol 61 (11) ◽

pp. 785-798 ◽

Cited By ~ 30

Author(s):

Devin B. Holman ◽

Martin R. Chénier

Keyword(s):

Antimicrobial Resistance ◽

Gut Microbiota ◽

Resistant Bacteria ◽

Antimicrobial Use ◽

Swine Production ◽

Duration Of Treatment ◽

Continuous Administration ◽

Resistance Determinants ◽

The North ◽

Culture Independent

Antimicrobials have been used in swine production at subtherapeutic levels since the early 1950s to increase feed efficiency and promote growth. In North America, a number of antimicrobials are available for use in swine. However, the continuous administration of subtherapeutic, low concentrations of antimicrobials to pigs also provides selective pressure for antimicrobial-resistant bacteria and resistance determinants. For this reason, subtherapeutic antimicrobial use in livestock remains a source of controversy and concern. The swine gut microbiota demonstrates a number of changes in response to antimicrobial administration depending on the dosage, duration of treatment, age of the pigs, and gut location that is sampled. Both culture-independent and -dependent studies have also shown that the swine gut microbiota contains a large number of antimicrobial resistance determinants even in the absence of antimicrobial exposure. Heavy metals, such as zinc and copper, which are often added at relatively high doses to swine feed, may also play a role in maintaining antimicrobial resistance and in the stability of the swine gut microbiota. This review focuses on the use of antimicrobials in swine production, with an emphasis on the North American regulatory context, and their effect on the swine gut microbiota and on antimicrobial resistance determinants in the gut microbiota.

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A Model to Investigate the Impact of Farm Practice on Antimicrobial Resistance in UK Dairy Farms

Bulletin of Mathematical Biology ◽

10.1007/s11538-021-00865-9 ◽

2021 ◽

Vol 83 (4) ◽

Author(s):

Christopher W. Lanyon ◽

John R. King ◽

Dov J. Stekel ◽

Rachel L. Gomes

Keyword(s):

Antimicrobial Resistance ◽

Management Practices ◽

Animal Husbandry ◽

Antibiotic Use ◽

Health Impact ◽

Multidrug Resistant ◽

Equation Model ◽

Resistant Bacteria ◽

Waste Management Practices ◽

The Impact

AbstractThe ecological and human health impact of antibiotic use and the related antimicrobial resistance (AMR) in animal husbandry is poorly understood. In many countries, there has been considerable pressure to reduce overall antibiotic use in agriculture or to cease or minimise use of human critical antibiotics. However, a more nuanced approach would consider the differential impact of use of different antibiotic classes; for example, it is not known whether reduced use of bacteriostatic or bacteriolytic classes of antibiotics would be of greater value. We have developed an ordinary differential equation model to investigate the effects of farm practice on the spread and persistence of AMR in the dairy slurry tank environment. We model the chemical fate of bacteriolytic and bacteriostatic antibiotics within the slurry and their effect on a population of bacteria, which are capable of resistance to both types of antibiotic. Through our analysis, we find that changing the rate at which a slurry tank is emptied may delay the proliferation of multidrug-resistant bacteria by up to five years depending on conditions. This finding has implications for farming practice and the policies that influence waste management practices. We also find that, within our model, the development of multidrug resistance is particularly sensitive to the use of bacteriolytic antibiotics, rather than bacteriostatic antibiotics, and this may be cause for controlling the usage of bacteriolytic antibiotics in agriculture.

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Molecular Analysis of Antimicrobial Resistance among Enterobacteriaceae Isolated from Diarrhoeic Calves in Egypt

Animals ◽

10.3390/ani11061712 ◽

2021 ◽

Vol 11 (6) ◽

pp. 1712

Author(s):

Abdel-Moamen E. Meshref ◽

Ibrahim E. Eldesoukey ◽

Abdulaziz S. Alouffi ◽

Saleh A. Alrashedi ◽

Salama A. Osman ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Klebsiella Oxytoca ◽

Conventional Polymerase Chain Reaction ◽

Multidrug Resistant ◽

Resistant Bacteria ◽

M Gene ◽

Resistant Species ◽

Antimicrobial Resistance Genes ◽

Class 1 ◽

Shigella Spp

The present study was designed to investigate the presence of genes that conferred resistance to antimicrobials among Enterobacteriaceae that were isolated from diarrhoeic calves. A total of 120 faecal samples were collected from diarrhoeic calves that were raised in Kafr El-Sheikh governorate, Egypt. The samples were screened for Enterobacteriaceae. A total of 149 isolates of bacteria were recovered and identified; Escherichia coli was found to be the most overwhelming species, followed by Citrobacter diversus, Shigella spp., Serratia spp., Providencia spp., Enterobacter spp., Klebsiella pneumoniae, Proteus spp., Klebsiella oxytoca, and Morganella morganii. All isolates were tested for susceptibility to 12 antimicrobials; resistant and intermediately resistant strains were screened by conventional polymerase chain reaction for the presence of antimicrobial resistance genes. Of the 149 isolates, 37 (24.8%) exhibited multidrug resistant phenotypes. The most prevalent multidrug resistant species were E. coli, C. diversus, Serratia spp., K. pneumoniae, Shigella spp., Providencia spp., and K. oxytoca. Class 1 integrons were detected in 28 (18.8%) isolates. All isolates were negative for class 2 integrons. The blaTEM gene was identified in 37 (24.8%) isolates, whereas no isolates carried the blaCTX-M gene. The florfenicol gene (floR) was detected in two bacterial isolates (1.3%). The findings of this study reveal that calves may act as potential reservoirs of multidrug resistant bacteria that can be easily transmitted to humans.

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Antibiotic Resistance Profile and Resistance Determination of Bacteria Isolated from Water in Southern Benin

Journal of Advances in Microbiology ◽

10.9734/jamb/2021/v21i430345 ◽

2021 ◽

pp. 91-105

Author(s):

Hornel Koudokpon ◽

Victorien Dougnon ◽

Christelle Lougbegnon ◽

Esther Deguenon ◽

Wassiyath Mousse ◽

...

Keyword(s):

Drinking Water ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Water Samples ◽

Meca Gene ◽

Multidrug Resistant ◽

Resistant Bacteria ◽

Gram Negative ◽

Antimicrobial Resistance Genes ◽

Southern Benin

Background: The environment plays an important role in the dissemination of multidrug resistant bacteria, especially through the aquatic ecosystem, including hospital effluents, rivers, but also spring water and drinking water. This study aims to determine selected antimicrobial resistance genes in some aquatic matrices in southern Benin. Methods: Collected water samples were filtered through a membrane 0.22 µm thick. After filtration, the membrane was deposited on Muëller Hinton agar. Then the colonies resulting from this subculture were subjected to a microbiological examination by the conventional method. The antibiotic sensitivity test was carried out by the Kirby Bauer method according to the recommendations of the French Society of Microbiology. Resistance genes were looked for by PCR. Results: Of the 222 water samples collected, 265 bacterial strains were isolated, the majority of which were strains of Coagulase Negative Staphylococcus (CNS) with 37.74% (n = 100), followed by strains of Klebsiella pneumoniae (21.89%; n = 58), Escherichia coli (10.57%; n = 28). All isolated gram-negative bacilli strains are multidrug resistant with resistance of all strains to amoxicillin, ampicillin and amoxicillin + clavulanic acid. Of the 15 resistance genes searched in the genome of Gram-negative bacilli strains, 8 were detected, namely the TEM, SHV, CTX-M15, VIM, NDM, SUL1, SUL2 and AADA genes. Resistance of CNS strains to amoxicillin, oxacillin and cefoxitin was observed. The meca gene was detected in all CNS strains. The vanA and VanB genes were only detected in strains isolated from drinking water in sachets collected from producers and street sellers. Conclusion: These results show the dissemination of resistance genes in Benin and once again confirms the urgency of a global fight against antimicrobial resistance.

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Withdraw of prophylactic antimicrobials does not change resistome in pigs

10.21203/rs.2.18011/v1 ◽

2019 ◽

Author(s):

Maria Fernanda Loayza Villa ◽

Alejandro Torres ◽

Lixin Zhang ◽

Gabriel Trueba

Keyword(s):

Antibiotic Resistance ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Resistant Bacteria ◽

Productive Performance ◽

Fitness Costs ◽

Antibiotic Resistant ◽

Human Microbiota ◽

Antimicrobial Resistance Genes ◽

The Impact

Abstract Background: The use of antimicrobials in the animal industry has increased the prevalence of antibiotic resistant bacteria and antimicrobial-resistance genes which can be transferred to human microbiota through the food chain or the environment. To reduce the influx of antibiotic-resistance to the human microbiota, restrictions on antimicrobials (in food animals) have been implemented in different countries. We investigated the impact of an antimicrobial restriction on the frequency of antimicrobial-resistant bacteria in pigs (PCI 1050) from an Ecuadorian farm. Results: No differences in antimicrobial resistant coliforms or antimicrobial resistance genes (richness and abundance) were found when we compared animals fed with or without antibiotics. Nevertheless, the absence of antimicrobials in pigs didn’t impact the productive performance of animals. Conclusion: Fitness costs of antimicrobial resistance in bacteria within intestinal microbiota of animals seems to be overestimated. Avoiding antimicrobials as prophylactics in pigs fed is not enough to control maintenance and spread of antimicrobial resistance.

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Antimicrobial Resistance in Retail Ground Beef with and Without a “Raised Without Antibiotics” Claim

Meat and Muscle Biology ◽

10.22175/mmb.10781 ◽

2019 ◽

Vol 3 (2) ◽

Author(s):

J. W. Schmidt ◽

A. Vikram ◽

K. Thomas ◽

T. M. Arthur ◽

M. Weinroth ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Production System ◽

Bacterial Infections ◽

Meat Products ◽

Ground Beef ◽

Animal Production ◽

Resistant Bacteria ◽

Antimicrobial Use ◽

Food Animal ◽

Antimicrobial Resistance Genes

ObjectivesThe occurrences of human bacterial infections complicated by antimicrobial resistance (AMR) have increased in recent decades. Concerns have been raised that food-animal production practices that incorporate antimicrobials contribute significantly to human AMR exposures since food-animal production accounts for approximately 81% of U.S. antimicrobial consumption by mass. Although empirical studies comparing AMR levels in meat products, including ground beef, are scant ground beef products with Raised without Antibiotics (RWA) label claims are perceived to harbor less AMR than “conventional” (CONV) products with no label claims regarding antimicrobial use. The objective of this research was to determine AMR levels in retail ground beef with and without an RWA label claims.Materials and MethodsRetail ground beef samples were obtained from 6 U.S. cities. Samples were obtained on the following dates: 9/18/2017, 10/30/2017, 11/27/2017. 1/29/2018. 3/5/2018, and 6/11/2018. A total of 599 samples were obtained. Samples with a “Raised without Antibiotics” or USDA Organic claim (N = 299) were assigned to the RWA production system. Samples lacking a “Raised without Antibiotics” claim (N = 300) were assigned to the CONV production system. Each sample was cultured for the detection of five antimicrobial resistant bacteria (ARB). Genomic DNA was isolated from each sample and qPCR was used to determine the abundance of ten antimicrobial resistance genes (ARGs). The impacts of production system and city on ARB detection were assessed by the Likelihood-ratio chi-squared test. The impacts of production system and city on ARG abundance was assessed by two-way ANOVA.ResultsTetracycline-resistant Escherichia coli (CONV = 46.3%; RWA = 34.4%) and erythromycin-resistant Enterococcus (CONV = 48.0%; RWA = 37.5%) were more frequently (P < 0.01) detected in CONV. Detection of third generation cephalosporin-resistant E. coli (CONV = 5.7%; RWA = 1.0%), vancomycin-resistant Enterococcus (CONV = 0.0%; RWA = 0.0%) and methicillin-resistant Staphylococcus aureus (CONV = 1.3%; RWA = 0.7%) did not differ (P = 1.00). The blaCTX-M ARG was more abundant in CONV (2.4 vs. 2.1 log copies/gram, P = 0.01) but the tet(A) (2.4 vs. 2.5 log copies/gram, P = 0.02) and tet(M) (3.6 vs. 3.9 log copies/gram, P < 0.01) ARGs were more abundant in RWA. aadA1, blaCMY-2, mecA, erm(B), and tet(B) abundances did not differ significantly (Fig. 5) (P > 0.05). Abundances of aac (6’)-Ie-aph (2”)-Ia and blaKPC-2 were not analyzed since they were quantified in less than 5% of the samples.ConclusionU.S. retail CONV and RWA ground beef harbor generally similar levels of AMR since only 5 of 15 AMR measurements were statistically different between production systems. Three AMR measurements were higher in CONV, while 2 AMR measurements were higher in RWA. These results are in general agreement with a recently published study authored by our group that examined antimicrobial resistance in CONV and RWA ground beef obtained from U.S. foodservice suppliers (Vikram et al., J. Food Prot. 81:2007–2018. 2018.). Together these studies suggest that antimicrobial use during U.S. cattle production has minimal to no impact on human exposure to AMR via ground beef.Figure 5.

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