Effect of Antimicrobial Dosage Regimen on Salmonella and Escherichia coli Isolates from Feeder Swine

ABSTRACT A body of evidence exists that suggests that antimicrobial use in food animals leads to resistance in both pathogenic and commensal bacteria. This study focused on the impact of three different antimicrobial regimes (low-level continuous, pulse, and no antimicrobial) for two antimicrobials (chlortetracycline and tylosin) on the presence of Salmonella spp. and on the prevalence of antimicrobial resistance of both Salmonella spp. and nonspecific Escherichia coli in fecal samples from feeder swine. The prevalence of fecal samples positive for Salmonella spp. significantly decreased between the samples taken at feeder placement compared to samples taken when the animals were close to market weight. Differences in resistance of Salmonella spp. did not appear to be influenced by dosing treatment including the control. Analysis of antimicrobial resistance examining both susceptibility and resistance, as well as MIC outcomes, demonstrated that only resistance to cephalothin increased in E. coli under the pulse chlortetracycline treatment. These results suggest that the dosing regimes examined in this study did not lead to an increase in either the prevalence of Salmonella spp. or the prevalence of antimicrobial resistance in isolates of Salmonella spp. or E. coli.

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Genomic evolution of antimicrobial resistance in Escherichia coli

Scientific Reports ◽

10.1038/s41598-021-93970-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Pimlapas Leekitcharoenphon ◽

Markus Hans Kristofer Johansson ◽

Patrick Munk ◽

Burkhard Malorny ◽

Magdalena Skarżyńska ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Virulence Genes ◽

Mobile Genetic Elements ◽

Whole Genome ◽

Sequencing Analysis ◽

Metagenomic Sequencing ◽

Fecal Samples ◽

E Coli ◽

Genetic Elements

AbstractThe emergence of antimicrobial resistance (AMR) is one of the biggest health threats globally. In addition, the use of antimicrobial drugs in humans and livestock is considered an important driver of antimicrobial resistance. The commensal microbiota, and especially the intestinal microbiota, has been shown to have an important role in the emergence of AMR. Mobile genetic elements (MGEs) also play a central role in facilitating the acquisition and spread of AMR genes. We isolated Escherichia coli (n = 627) from fecal samples in respectively 25 poultry, 28 swine, and 15 veal calf herds from 6 European countries to investigate the phylogeny of E. coli at country, animal host and farm levels. Furthermore, we examine the evolution of AMR in E. coli genomes including an association with virulence genes, plasmids and MGEs. We compared the abundance metrics retrieved from metagenomic sequencing and whole genome sequenced of E. coli isolates from the same fecal samples and farms. The E. coli isolates in this study indicated no clonality or clustering based on country of origin and genetic markers; AMR, and MGEs. Nonetheless, mobile genetic elements play a role in the acquisition of AMR and virulence genes. Additionally, an abundance of AMR was agreeable between metagenomic and whole genome sequencing analysis for several AMR classes in poultry fecal samples suggesting that metagenomics could be used as an indicator for surveillance of AMR in E. coli isolates and vice versa.

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Genotyping and antimicrobial resistance in Escherichia coli from pig carcasses

Pesquisa Veterinária Brasileira ◽

10.1590/s0100-736x2017001100010 ◽

2017 ◽

Vol 37 (11) ◽

pp. 1253-1260 ◽

Cited By ~ 1

Author(s):

Caroline Pissetti ◽

Gabriela Orosco Werlang ◽

Jalusa Deon Kich ◽

Marisa Cardoso

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Antimicrobial Agents ◽

Commensal Bacteria ◽

Pfge Analysis ◽

Gene Detection ◽

E Coli ◽

Antimicrobial Resistance Profile ◽

Resistant Strains ◽

Pig Carcasses

ABSTRACT: The increasing antimicrobial resistance observed worldwide in bacteria isolated from human and animals is a matter of extreme concern and has led to the monitoring of antimicrobial resistance in pathogenic and commensal bacteria. The aim of this study was to evaluate the antimicrobial resistance profile of Escherichia coli isolated from pig carcasses and to assess the occurrence of relevant resistance genes. A total of 319 E. coli isolates were tested for antimicrobial susceptibility against different antimicrobial agents. Moreover, the presence of extended-spectrum β-lactamase (ESBL) and inducible ampC-β-lactamase producers was investigated. Eighteen multi-resistant strains were chosen for resistance gene detection and PFGE characterization. The study showed that resistance to antimicrobials is widespread in E. coli isolated from pig carcasses, since 86.2% of the strains were resistant to at least one antimicrobial and 71.5% displayed multi-resistance profiles. No ampC-producing isolates were detected and only one ESBL-producing E. coli was identified. Genes strA (n=15), floR (n=14), aac(3)IVa (n=13), tetB (n=13), sul2 (n=12), tetA (n=11), aph(3)Ia (n=8) and sul3 (n=5) were detected by PCR. PFGE analysis of these multi-resistant E. coli strains showed less than 80% similarity among them. We conclude that antimicrobial multi-resistant E. coli strains are common on pig carcasses and present highly diverse genotypes and resistance phenotypes and genotypes.

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Antimicrobial resistance pattern of extended-spectrum β-lactamase-producing Escherichia coli isolated from fecal samples of piglets and pig farm workers of selected organized farms of India

Veterinary World ◽

10.14202/vetworld.2020.360-363 ◽

2020 ◽

Vol 13 (2) ◽

pp. 360-363

Author(s):

Shikha Tamta ◽

Obli Rajendran Vinodh Kumar ◽

Shiv Varan Singh ◽

Bommenahalli Siddaramiah Pruthvishree ◽

Ravichandran Karthikeyan ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Susceptibility Testing ◽

Farm Workers ◽

Resistance Pattern ◽

Antibiotic Susceptibility Testing ◽

M Gene ◽

Fecal Samples ◽

E Coli ◽

Pig Farm

Background and Aim: Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli are gradually increasing worldwide and carry a serious public threat. This study aimed to determine the antimicrobial resistance pattern of ESBL-producing E. coli isolated from fecal samples of piglets and pig farm workers. Materials and Methods: Fecal samples from <3-month-old piglets (n=156) and farm workers (n=21) were processed for the isolation of ESBL-producing E. coli in MacConkey agar added with 1 μg/mL of cefotaxime. E. coli (piglets=124; farm workers=21) were tested for ESBL production by combined disk method and ESBL E-strip test. Each of the ESBL-positive isolate was subjected to antibiotic susceptibility testing. The ESBL-producing E. coli were further processed for genotypic confirmation to CTX-M gene. Results: A total of 55 (44.4%, 55/124) and nine (42.9%, 9/21) ESBL-producing E. coli were isolated from piglets and farm workers, respectively. Antibiotic susceptibility testing of the ESBL-positive E. coli isolates from piglets and farm workers showed 100% resistance to ceftazidime, cefotaxime, cefotaxime/clavulanic acid, ceftazidime/clavulanic acid, and cefpodoxime. A proportion of 100% (55/55) and 88.9% (8/9) ESBL-positive E. coli were multidrug resistance (MDR) in piglets and farm workers, respectively. On genotypic screening of the ESBL E. coli isolated from piglets (n=55), 15 were positive for the blaCTX-M gene and of the nine ESBL E. coli from farm workers, none were positive for the blaCTX-M gene. Conclusion: Although there was no significant difference in isolation of ESBL-producing E. coli between piglets and farm workers, the ESBL-positive E. coli from piglets showed relatively higher MDR than farm workers.

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Impact of UV and Peracetic Acid Disinfection on the Prevalence of Virulence and Antimicrobial Resistance Genes in Uropathogenic Escherichia coli in Wastewater Effluents

Applied and Environmental Microbiology ◽

10.1128/aem.00418-14 ◽

2014 ◽

Vol 80 (12) ◽

pp. 3656-3666 ◽

Cited By ~ 24

Author(s):

Basanta Kumar Biswal ◽

Ramzi Khairallah ◽

Kareem Bibi ◽

Alberto Mazza ◽

Ronald Gehr ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Peracetic Acid ◽

Content Type ◽

E Coli ◽

Antimicrobial Resistance Genes ◽

Antimicrobial Resistance Gene ◽

Municipal Wastewaters ◽

The Impact

ABSTRACTWastewater discharges may increase the populations of pathogens, includingEscherichia coli, and of antimicrobial-resistant strains in receiving waters. This study investigated the impact of UV and peracetic acid (PAA) disinfection on the prevalence of virulence and antimicrobial resistance genes in uropathogenicEscherichia coli(UPEC), the most abundantE. colipathotype in municipal wastewaters. Laboratory disinfection experiments were conducted on wastewater treated by physicochemical, activated sludge, or biofiltration processes; 1,766E. coliisolates were obtained for the evaluation. The target disinfection level was 200 CFU/100 ml, resulting in UV and PAA doses of 7 to 30 mJ/cm2and 0.9 to 2.0 mg/liter, respectively. The proportions of UPECs were reduced in all samples after disinfection, with an average reduction by UV of 55% (range, 22% to 80%) and by PAA of 52% (range, 11% to 100%). Analysis of urovirulence genes revealed that the decline in the UPEC populations was not associated with any particular virulence factor. A positive association was found between the occurrence of urovirulence and antimicrobial resistance genes (ARGs). However, the changes in the prevalence of ARGs in potential UPECs were different following disinfection, i.e., UV appears to have had no effect, while PAA significantly reduced the ARG levels. Thus, this study showed that both UV and PAA disinfections reduced the proportion of UPECs and that PAA disinfection also reduced the proportion of antimicrobial resistance gene-carrying UPEC pathotypes in municipal wastewaters.

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Antimicrobial Resistance in ESBL-Producing Escherichia coli Isolated from Layer and Pig Farms in Thailand

Acta Scientiae Veterinariae ◽

10.22456/1679-9216.81823 ◽

2018 ◽

Vol 46 (1) ◽

pp. 8 ◽

Cited By ~ 1

Author(s):

Aniroot Nuangmek ◽

Suvichai Rojanasthien ◽

Suwit Chotinun ◽

Panuwat Yamsakul ◽

Pakpoom Tadee ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Function Analysis ◽

Commensal Bacteria ◽

Farm Worker ◽

Stagnant Water ◽

E Coli ◽

Pig Farms ◽

Resistance Patterns ◽

Pig Farm

Background: Study of drug resistance of commensal bacteria in both humans and animals can determine the scale of the drug resistance problem. Usage of antimicrobials to treat infections in humans and animals has generated extensive antimicrobial pressure not only on targeted pathogens but also on commensal bacteria. Commensal Escherichia coli appears to be the major reservoir for resistant genes implicated in the transmission of genetic traits from one bacterium to another. Antimicrobial resistance in Enterobacteriaceae has increased dramatically worldwide in the last decade. An increasing number of community-onset extended-spectrum beta-lactamase (ESBL)-producing bacterial infections, especially those caused by ESBL-producing E. coli, have been reported in many countries, including Thailand. Moreover, ESBL-producing E. coli have been widely detected in food-producing animals and the environment. The increased use of ESBLs in food animals is a serious public health problem. The objective of the study was to determine the prevalence and antimicrobial resistance pattern of ESBL-producing E. coli isolated from pigs, layers, farm workers and stagnant water, in order to increase awareness about antimicrobial usage on farms and to minimize the expansion of the antimicrobial resistance phenomenon in farm settings.Materials, Methods & Results: A total of 588 samples were collected from 107 pig farms and 89 layer farms in Chiang Mai–Lamphun and Chon Buri provinces during May 2015-April 2016. Double-disk diffusion method according to EUCAST (European Committee on Antimicrobial Susceptibility Testing) guidelines was used for detection. The results demonstrated that 36.7% (216/588) of samples were ESBL-producing E. coli-positive, including rectal swabs 74.8% (80/107), pig farm worker stool swabs 57.0% (61/107), stagnant water on pig farms 21.5% (23/107), healthy layer rectal swabs 6.7% (6/89) and layer farm worker stool swabs 51.7% (46/89). Most of the isolates were resistant against ampicillin (99.5%), followed by erythromycin (98.6%) and ceftriaxone (96.3%). All of them were classified as multidrug-resistant strains. Moreover, AMP-CRO-E-TE-C-SXT-CN was the most frequent phenotype pattern detected in animals, humans and the environment, followed by AMP-CRO-E-TE-C-SXT-NA-CN.Discussion: The present study offers clear evidence that the prevalence of ESBL-producing E. coli in healthy pigs is higher than in layers. One possible explanation is that a large amount and variety of antimicrobials are used on pig farms, resulting in a common and significant source of drug-resistant ESBL-producing E. coli. The lower incidence of ESBL-producing E. coli in samples from a pig farm environment than in samples of animal origin indicate that pigs are a reservoir of a reservoir for resistant bacteria and a source of environmental contamination. Antimicrobial resistance patterns of ESBLproducing E. coli detected in all sample types and study locations were quite similar. In almost all ESBL-producing E. coli isolates, resistance was shown against ampicillin, erythromycin, ceftriaxone, tetracycline and chloramphenicol. Moreover, multidrug resistance was found in all isolates of ESBL-producing E. coli. The differences in antimicrobial agent resistance patterns can be used to differentiate sources by employing analytical tools such as discriminant function analysis. A molecular typing protocol is recommended for use in a discriminant function analysis for pattern determination of pathogen spreading. However, genetic fingerprinting techniques for microbial source tracking are more expensive, and facilities with appropriate equipment and expertise are required.

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Live yeast and yeast extracts with and without pharmacological levels of zinc on nursery pig growth performance and antimicrobial susceptibilities of fecal Escherichia coli

Journal of Animal Science ◽

10.1093/jas/skab330 ◽

2021 ◽

Author(s):

Jenna A Chance ◽

Joel M DeRouchey ◽

Raghavendra G Amachawadi ◽

Victor Ishengoma ◽

Tiruvoor G Nagaraja ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Growth Performance ◽

Dilution Method ◽

Fecal Samples ◽

Minimal Inhibitory Concentrations ◽

E Coli ◽

Nursery Pig ◽

Dietary Treatments ◽

Live Yeast

Abstract A total of 360 weanling barrows (Line 200 ×400, DNA, Columbus NE; initially 5.6 ± 0.03 kg) were used in a 42-d study to evaluate yeast-based pre- and probiotics (Phileo by Lesaffre, Milwaukee, WI) in diets with or without pharmacological levels of Zn on growth performance and antimicrobial resistance (AMR) patterns of fecal Escherichia coli. Pens were assigned to 1 of 4 dietary treatments with 5 pigs per pen and 18 pens per treatment. Dietary treatments were arranged in a 2 × 2 factorial with main effects of yeast-based pre- and probiotics (none vs. 0.10% ActiSaf Sc 47 HR+, 0.05% SafMannan, and 0.05% NucleoSaf from d 0 to 7, then concentrations were lowered by 50% from d 7 to 21) and pharmacological levels of Zn (110 vs. 3,000 mg/kg from d 0 to 7, and 2,000 mg/kg from d 7 to 21 with added Zn provided by ZnO). All pigs were fed a common diet from d 21 to 42 post-weaning. There were no yeast ×Zn interactions or effects from yeast additives observed on any response criteria. From d 0 to 21, and 0 to 42, pigs fed pharmacological levels of Zn had increased (P < 0.001) ADG and ADFI. Fecal samples were collected on d 4, 21, and 42 from the same three pigs per pen for fecal dry matter (DM) and AMR patterns of E. coli. On d 4, pigs fed pharmacological levels of Zn had greater fecal DM (P = 0.043); however, no differences were observed on d 21 or 42. E. coli was isolated from fecal samples and the microbroth dilution method was used to determine the minimal inhibitory concentrations (MIC) of E. coli isolates to 14 different antimicrobials. Isolates were categorized as either susceptible, intermediate, or resistant based on Clinical and Laboratory Standards Institute (CLSI) guidelines. The addition of pharmacological levels of Zn had a tendency (P = 0.051) to increase the MIC values of ciprofloxacin; however, these MIC values were still well under the CLSI classified resistant breakpoint for Ciprofloxacin. There was no evidence for differences (P > 0.10) for yeast additives or Zn for AMR of fecal E. coli isolates to any of the remaining antibiotics. In conclusion, pharmacological levels of Zn improved ADG, ADFI, and all isolates were classified as susceptible to ciprofloxacin although the MIC of fecal E. coli tended to be increased. Thus, the short-term use of pharmacological levels of Zn did not increase antimicrobial resistance. There was no response observed from live yeast and yeast extracts for any of the growth, fecal DM, or AMR of fecal E. coli criteria.

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Impact of antibiotic usage on extended-spectrum β-lactamase producing Escherichia coli prevalence

Scientific Reports ◽

10.1038/s41598-021-91332-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Jeong Yeon Kim ◽

Yunjin Yum ◽

Hyung Joon Joo ◽

Hyonggin An ◽

Young Kyung Yoon ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Antimicrobial Stewardship ◽

Antibiotic Usage ◽

Transfer Model ◽

Free Text ◽

E Coli ◽

Extended Spectrum ◽

Hospital Acquired ◽

The Impact

AbstractAn increase in antibiotic usage is considered to contribute to the emergence of antimicrobial resistance. Although experts are counting on the antimicrobial stewardship programs to reduce antibiotic usage, their effect remains uncertain. In this study, we aimed to evaluate the impact of antibiotic usage and forecast the prevalence of hospital-acquired extended spectrum β-lactamase (ESBL)—producing Escherichia coli (E. coli) using time-series analysis. Antimicrobial culture information of E. coli was obtained using a text processing technique that helped extract free-text electronic health records from standardized data. The antimicrobial use density (AUD) of antibiotics of interest was used to estimate the quarterly antibiotic usage. Transfer function model was applied to forecast relationship between antibiotic usage and ESBL-producing E. coli. Of the 1938 hospital-acquired isolates, 831 isolates (42.9%) were ESBL-producing E. coli. Both the proportion of ESBL-producing E. coli and AUD increased over time. The transfer model predicted that ciprofloxacin AUD is related to the proportion of ESBL-producing E. coli two quarters later. In conclusion, excessive use of antibiotics was shown to affect the prevalence of resistant organisms in the future. Therefore, the control of antibiotics with antimicrobial stewardship programs should be considered to restrict antimicrobial resistance.

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Antimicrobial resistance prevalence of pathogenic and commensal Escherichia coli in food-producing animals in Belgium

Vlaams Diergeneeskundig Tijdschrift ◽

10.21825/vdt.v83i5.16634 ◽

2014 ◽

Vol 83 (5) ◽

pp. 225-233 ◽

Cited By ~ 2

Author(s):

I. Chantziaras ◽

J. Dewulf ◽

F. Boyen ◽

B. Callens ◽

P. Butaye

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Broiler Chickens ◽

Broiler Chicken ◽

Susceptibility Testing ◽

Commensal Bacteria ◽

The Other ◽

E Coli ◽

Veal Calves ◽

Veal Calf

In this article, detailed studies on antimicrobial resistance to commensal E. coli (in pigs, meatproducing bovines, broiler chickens and veal calves) and pathogenic E. coli (in pigs and bovines) in Belgium are presented for 2011. Broiler chicken and veal calf isolates of commensal E. coli demonstrated higher antimicrobial resistance prevalence than isolates from pigs and bovines. Fifty percent of E. coli isolates from broiler chickens were resistant to at least five antimicrobials, whereas sixty-one percent of bovine E. coli isolates were susceptible to all antimicrobials tested. On the other hand, bovine pathogenic E. coli isolates showed an extended resistance profile with more than half of the isolates being resistant to ten or more antimicrobials. The results are not significantly different from the results from previously published studies on commensal bacteria in pigs in Belgium, although different methodologies of sampling and susceptibility testing were used.

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The impact of therapeutic-dose induced intestinal enrofloxacin concentrations in healthy pigs on fecal Escherichia coli populations

BMC Veterinary Research ◽

10.1186/s12917-020-02608-9 ◽

2020 ◽

Vol 16 (1) ◽

Author(s):

Joren De Smet ◽

Filip Boyen ◽

Siska Croubels ◽

Geertrui Rasschaert ◽

Freddy Haesebrouck ◽

...

Keyword(s):

Escherichia Coli ◽

Intestinal Tract ◽

Intestinal Content ◽

Bolus Administration ◽

Wild Type ◽

Fecal Samples ◽

E Coli ◽

Administration Routes ◽

The Impact

Abstract Background Knowledge of therapy-induced intestinal tract concentrations of antimicrobials allows for interpretation and prediction of antimicrobial resistance selection within the intestinal microbiota. This study describes the impact of three different doses of enrofloxacin (ENR) and two different administration routes on the intestinal concentration of ENR and on the fecal Escherichia coli populations in pigs. Enrofloxacin was administered on three consecutive days to four different treatment groups. The groups either received an oral bolus administration of ENR (conventional or half dose) or an intramuscular administration (conventional or double dose). Results Quantitative analysis of fecal samples showed high ENR concentrations in all groups, ranging from 5.114 ± 1.272 μg/g up to 39.54 ± 10.43 μg/g at the end of the treatment period. In addition, analysis of the luminal intestinal content revealed an increase of ENR concentration from the proximal to the distal intestinal tract segments, with no significant effect of administration route. Fecal samples were also screened for resistance in E. coli isolates against ENR. Wild-type (MIC≤0.125 μg/mL) and non-wild-type (0.125 < MIC≤2 μg/mL) E. coli isolates were found at time 0 h. At the end of treatment (3 days) only non-wild-type isolates (MIC≥32 μg/mL) were found. Conclusions In conclusion, the observed intestinal ENR concentrations in all groups showed to be both theoretically (based on pharmacokinetic and pharmacodynamic principles) and effectively (in vivo measurement) capable of significantly reducing the intestinal E. coli wild-type population.

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Antimicrobial resistance in commensal Escherichia coli and Enterococcus spp. is influenced by production system, antimicrobial use, and biosecurity measures on Spanish pig farms

Porcine Health Management ◽

10.1186/s40813-021-00206-1 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Oscar Mencía-Ares ◽

Héctor Argüello ◽

Héctor Puente ◽

Manuel Gómez-García ◽

Edgar G. Manzanilla ◽

...

Keyword(s):

Escherichia Coli ◽

Antimicrobial Resistance ◽

Production System ◽

Production Systems ◽

Multidrug Resistant ◽

Antimicrobial Use ◽

Global Public Health ◽

E Coli ◽

Pig Farms ◽

Surveillance Programs

Abstract Background Antimicrobial resistance (AMR) is a global public health threat consequence of antimicrobial use (AMU) in human and animal medicine. In food-producing animals factors such as management, husbandry or biosecurity may impact AMU. Organic and extensive Iberian swine productions are based on a more sustainable and eco-friendly management system, providing an excellent opportunity to evaluate how sustained differences in AMU impact the AMR in indicator bacteria. Here, we evaluate the usefulness of commensal Escherichia coli and Enterococcus spp. isolates as AMR bioindicators when comparing 37 Spanish pig farms from both intensive and organic-extensive production systems, considering the effect of AMU and biosecurity measures, the last only on intensive farms. Results The production system was the main factor contributing to explain the AMR differences in E. coli and Enterococcus spp. In both bacteria, the pansusceptible phenotype was more common (p < 0.001) on organic-extensive farms when compared to intensive herds. The microbiological resistance in commensal E. coli was, for most of the antimicrobials evaluated, significantly higher (p < 0.05) on intensive farms. In enterococci, the lincosamides usage revealed the association between AMR and AMU, with an increase in the AMR for erythromycin (p < 0.01), quinupristin-dalfopristin (p < 0.01) and the multidrug-resistant (MDR) phenotype (p < 0.05). The biosecurity measures implemented on intensive farms influenced the AMR of these bioindicators, with a slightly lower resistance to sulfamethoxazole (p < 0.01) and the MDR phenotype (p < 0.05) in E. coli isolated from farms with better cleaning and disinfection protocols. On these intensive farms, we also observed that larger herds had a higher biosecurity when compared to smaller farms (p < 0.01), with no significant associations between AMU and the biosecurity scores. Conclusions Overall, this study evidences that the production system and, to a lesser extent, the biosecurity measures, contribute to the AMR development in commensal E. coli and Enterococcus spp., with antimicrobial usage as the main differential factor, and demonstrates the potential value of these bacteria as bioindicators on pig farms in AMR surveillance programs.

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