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Reports developments related to hygiene, quality and product traceability of poultry as of December 2001. Analysis on antimicrobial resistance in Campylobacter from broilers; Depletion of amoxicillin in tissues of broilers after administering oral soluble powder in drinking water; Important factors affecting the consumer selection of fresh eggs.

Abstract Antimicrobial resistance is of primary importance regarding public and animal health issues. Persistence and spread of resistant strains within a population contribute to the maintenance of a reservoir and lead to treatment failure. An experimental trial was carried out to study the horizontal transmission of a fluoroquinolone-resistant Escherichia coli strain from inoculated to naïve pigs. All naïve contact pigs had positive counts of fluoroquinolone-resistant E. coli after only two days of contact. Moreover, re-infections of inoculated pigs caused by newly contaminated animals were suspected. A maximum likelihood method, based on a susceptible-infectious-susceptible (SIS) model, was used to determine the transmission parameters. Two transmission levels were identified depending on the quantity of bacteria shed by infected individuals: (i) low-shedders with bacterial counts of resistant E. coli in the faeces between 5*103 and 106 CFU/g (βL = 0.41 [0.27; 0.62]), (ii) high shedders with bacterial counts above 106 CFU/g (βH = 0.98 [0.59; 1.62]). Hence, transmission between animals could be pivotal in explaining the persistence of resistant bacteria within pig herds.

Abstract Background The project "Antibiotic resistance in bacteria of animal origin – II" (ARBAO-II) was funded by the European Union (FAIR5-QLK2-2002-01146) for the period 2003–05. The aim of this project was to establish a program for the continuous monitoring of antimicrobial susceptibility of pathogenic and indicator bacteria from food animals using validated and harmonised methodologies. In this report the first data on the occurrence of antimicrobial resistance among bacteria causing infections in pigs are reported. Methods Susceptibility data from 17,642 isolates of pathogens and indicator bacteria including Actinobacillus pleuropneumoniae, Streptococcus suis and Escherichia coli isolated from pigs were collected from fifteen European countries in 2002–2004. Results Data for A. pleuropneumoniae from infected pigs were submitted from five countries. Most of the isolates from Denmark were susceptible to all drugs tested with the exceptions of a low frequency of resistance to tetracycline and trimethoprim – sulphonamide. Data for S. suis were obtained from six countries. In general, a high level of resistance to tetracycline (48.0 – 92.0%) and erythromycin (29.1 – 75.0%) was observed in all countries whereas the level of resistance to ciprofloxacin and penicillin differed between the reporting countries. Isolates from England (and Wales), France and The Netherlands were all susceptible to penicillin. In contrast the proportion of strains resistant to ciprofloxacin ranged from 12.6 to 79.0% (2004) and to penicillin from 8.1 – 13.0% (2004) in Poland and Portugal. Data for E. coli from infected and healthy pigs were obtained from eleven countries. The data reveal a high level of resistance to tetracyclines, streptomycin and ampicillin among infected pigs whereas in healthy pigs the frequency of resistance was lower. Conclusion Bacterial resistance to some antimicrobials was frequent with different levels of resistance being observed to several antimicrobial agents in different countries. The occurrence of resistance varied distinctly between isolates from healthy and diseased pigs, with the isolates from healthy pigs generally showing a lower level of resistance than those from diseased pigs. The study suggests that the choice of antimicrobials used for the treatment of diseased animals should preferably be based on knowledge of the local pattern of resistance.

This work generates the data needed to set epidemiological cut-off values for disc-diffusion zone measurements of Vibrio cholerae. The susceptibility of 147 European isolates of non-O1/non-O139 V. cholerae to 19 antibiotics was established using a standardised disc diffusion method which specified incubation of Mueller Hinton agar plates at 35°C. Epidemiological cut-off values were calculated by analysis of the zone size data with the statistically based normalised resistance interpretation method. Cut-off values for 17 agents were calculated by analysis of the aggregated data from all 4 laboratories participating in this study. The cut-off values calculated were ≥18 mm for amoxicillin/clavulanate, ≥18 mm for amikacin, ≥19 mm for ampicillin, ≥27 mm for cefepime, ≥31 mm for cefotaxime, ≥24 mm for ceftazidime, ≥24 mm for chloramphenicol, ≥31 mm for ciprofloxacin, ≥16 mm for erythromycin, ≥ 27 mm for florfenicol, ≥16 mm for gentamicin, ≥23 mm for imipenem, ≥25 mm for meropenem, ≥29 mm for nalidixic acid, ≥28 mm for norfloxacin, ≥13 mm for streptomycin and ≥23 mm for tetracycline. For the other 2 agents the data from 1 laboratory was excluded from the censored aggregation because the data from that laboratory was considered excessively imprecise. The cut-off values for these 2 agents calculated for the aggregation of the data from 3 laboratories were ≥23 mm for trimethoprim and ≥24 mm for trimethoprim/sulfamethoxazole. These zone size data will be submitted to the Clinical Laboratory Standards Institute (CLSI) and European Committee for Antimicrobial Susceptibility Testing (EUCAST) for their consideration in setting international consensus epidemiological cut-off values for non O1/non-O139 V. cholerae.

Streptococcus suis, an emerging zoonotic pathogen, causes invasive infections and substantial economic losses in the pig industry worldwide. Antimicrobial resistance against 22 antibiotics was studied for 200 S . suis strains collected in different geographical regions of France. Most of the strains (86%) showed resistance to at least one antibiotic with a low rate of resistance to fluoroquinolones, penicillins, pleuromutilin, and diaminopyrimidine-sulfonamides, and a higher rate to macrolides-lincosamides and tetracycline. Multi-resistance patterns were observed in 138 strains; three of them being resistant to six antibiotic families. Statistical analyses highlighted a decrease in the resistance to trimethoprim-sulfamethoxazole, in our collection, between the two periods studied-before 2010 and after 2015-as well as an impact of the geographical origin with a higher rate of resistance to macrolides-lincosamides and penicillin in Brittany than in the other French regions. Furthermore, macrolides-lincosamides and tetracycline resistance patterns were more likely to be found in pig isolates than in human and wild boar isolates. A difference in resistance was also observed between serotypes. Most of the penicillin-resistant strains belong to serotypes 1, 5, 9, 11, 12, 15, 27, and 29. Finally, penicillin and pleuromutilin resistances were mostly found in "non-clinical" isolates. The empirical treatment of human and porcine infections due to S. suis in France can therefore still be carried out with beta-lactams. However, this study emphasizes the need to monitor antimicrobial resistance in this zoonotic pathogen., Competing Interests: The authors declare no conflict of interest.

Enterococcus cecorum is a member of the normal poultry gut microbiota and an emerging poultry pathogen. Some strains are resistant to key antibiotics and coccidiostats. We evaluated the impact on chicken excretion and persistence of a multidrug-resistant E. cecorum of administering narasin or antibiotics. E. cecorum CIRMBP-1294 (Ec1294) is non-wild-type to many antimicrobials, including narasin, levofloxacin, oxytetracycline and glycopeptides, it has a low susceptibility to amoxicillin, and carries a chromosomal vanA operon. Six groups of 15 chicks each were orally inoculated with Ec1294 and two groups were left untreated. Amoxicillin, oxytetracycline or narasin were administered orally to one group each, either at the recommended dose for five days (amoxicillin, oxytetracycline) or continuously (narasin). Faecal samples were collected weekly and caecal samples were obtained from sacrificed birds on day 28. Ec1294 titres were evaluated by culture on vancomycin- and levofloxacin-supplemented media in 5 % CO 2 . For inoculated birds given narasin, oxytetracycline or no antimicrobials, vancomycin-resistant enterococci were searched by culture on vancomycin-supplemented media incubated in air, and a PCR was used to detect the vanA gene. Ec1294 persisted in inoculated chicks up to day 28. Compared to the control group, the Ec1294 titre was significantly lower in the amoxicillin- and narasin-receiving groups on days 21 and 28, but was unexpectedly higher in the oxytetracycline-receiving group before and after oxytetracycline administration, preventing a conclusion for this group. No transfer of the vanA gene to other enterococci was detected. Other trials in various experimental conditions should now be conducted to confirm this apparent absence of co-selection of the multi-drug-resistant E. cecorum by narasin or amoxicillin administration., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Introduction: As part of the EU Joint Action on Antimicrobial Resistance (AMR) and Healthcare-Associated Infections, an initiative has been launched to build the European AMR Surveillance network in veterinary medicine (EARS-Vet). So far, activities included mapping national systems for AMR surveillance in animal bacterial pathogens, and defining the EARS-Vet objectives, scope, and standards. Drawing on these milestones, this study aimed to pilot test EARS-Vet surveillance, namely to (i) assess available data, (ii) perform cross-country analyses, and (iii) identify potential challenges and develop recommendations to improve future data collection and analysis., Methods: Eleven partners from nine EU/EEA countries participated and shared available data for the period 2016-2020, representing a total of 140,110 bacterial isolates and 1,302,389 entries (isolate-antibiotic agent combinations)., Results: Collected data were highly diverse and fragmented. Using a standardized approach and interpretation with epidemiological cut-offs, we were able to jointly analyze AMR trends of 53 combinations of animal host-bacteria-antibiotic categories of interest to EARS-Vet. This work demonstrated substantial variations of resistance levels, both among and within countries (e.g., between animal host species)., Discussion: Key issues at this stage include the lack of harmonization of antimicrobial susceptibility testing methods used in European surveillance systems and veterinary diagnostic laboratories, the absence of interpretation criteria for many bacteria-antibiotic combinations of interest, and the lack of data from a lot of EU/EEA countries where little or even surveillance currently exists. Still, this pilot study provides a proof-of-concept of what EARS-Vet can achieve. Results form an important basis to shape future systematic data collection and analysis., Competing Interests: BK and EM work for a commercial veterinary laboratory with EARS-Vet activity not influencing the laboratory work. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Lagrange, Amat, Ballesteros, Damborg, Grönthal, Haenni, Jouy, Kaspar, Kenny, Klein, Lupo, Madec, Salomonsen, Müller, Madero, Nilsson, Norström, Nykäsenoja, Overesch, Pedersen, Pohjanvirta, Slowey, Justo, Urdahl, Zafeiridis, Zini, Cazeau, Jarrige, Collineau and on behalf of the EARS-Vet network.)

Colistin resistance has been the subject of much attention since mcr genes encoding plasmid-mediated colistin resistance description in 2015. To date, surveillance data about resistance levels encountered in food-producing animals are scarce. In France, the Resapath dataset, consisting in a large collection of disk diffusion antibiogram results transmitted by a network of laboratories. It offers a unique opportunity to study the evolution of resistance towards colistin over the past 15 years in Escherichia coli isolated from diseased food-producing animals. This study used a Bayesian hierarchical Gaussian mixture model to estimate the resistant proportions from those data. This non-classical approach deals with the colistin-specific problem of overlapping distributions of diameters measured for susceptible and resistant isolates that makes the definition of epidemiological cut-off very hard. This model also considers the variability observed between the measurements performed by different laboratories. Proportion of resistant isolates has been calculated for several food-producing animals and most encountered diseases. From those estimations, a marked evolution of the proportions of resistant isolates is noticeable, for swine suffering from digestive disorders. In this group, an increase over the 2006-2011 period from 0.1% [ 0.0%, 1.2%] in 2006-28.6% [25.1%, 32.3%] in 2011 was followed by a decrease to reach 3.6% [2.3%;5.3%] in 2018. For isolates related to digestive disorders in calves, percentages increased and reached 7% in 2009 then decreased as for swine. In contrast, for poultry productions, estimated proportions and credibility intervals were constantly very close to zero., Competing Interests: Conflict of interest No conflict of interest to be declared., (Copyright © 2023. Published by Elsevier B.V.)

Enterococcus cecorum, a commensal Gram-positive bacterium of the chicken gut, has emerged as a worldwide cause of lameness in poultry, particularly in fast-growing broilers. It is responsible for osteomyelitis, spondylitis, and femoral head necrosis, causing animal suffering, mortality, and antimicrobial use. Research on the antimicrobial resistance of E. cecorum clinical isolates in France is scarce, and epidemiological cutoff (ECOFF) values are unknown. To determine tentative ECOFF (CO WT ) values for E. cecorum and to investigate the antimicrobial resistance patterns of isolates from mainly French broilers, we tested the susceptibility of a collection of commensal and clinical isolates ( n  = 208) to 29 antimicrobials by the disc diffusion (DD) method. We also determined the MICs of 23 antimicrobials by the broth microdilution method. To detect chromosomal mutations conferring antimicrobial resistance, we investigated the genomes of 118 E. cecorum isolates obtained mainly from infectious sites and described previously in the literature. We determined the CO WT values for more than 20 antimicrobials and identified two chromosomal mutations explaining fluoroquinolone resistance. The DD method appears better suited for detecting E. cecorum antimicrobial resistance. Although tetracycline and erythromycin resistances were persistent in clinical and nonclinical isolates, we found little or no resistance to medically important antimicrobials.

Streptococcus suis is a zoonotic pathogen causing important economic losses in swine production. The most commonly used antibiotics in swine industry are tetracyclines, beta-lactams, and macrolides. Resistance to these antibiotics has already been observed worldwide (reaching high rates for macrolides and tetracyclines) as well as resistance to aminoglycosides, fluoroquinolones, amphenicols, and glycopeptides. Most of the resistance mechanisms are encoded by antibiotic resistance genes, and a large part are carried by mobile genetic elements (MGEs) that can be transferred through horizontal gene transfer. This review provides an update of the resistance genes, their combination in multidrug isolates, and their localization on MGEs in S. suis. It also includes an overview of the contribution of biofilm to antimicrobial resistance in this bacterial species. The identification of resistance genes and study of their localization in S. suis as well as the environmental factors that can modulate their dissemination appear essential in order to decipher the role of this bacterium as a reservoir of antibiotic genes for other species.

Standard disc diffusion and MIC test procedure were used to investigate the susceptibility of two hundred and fifty-one isolates collected from infected fish in France to florfenicol, oxolinic acid and tetracycline. The tests were performed at 22 ± 2℃ and for the 177 Yersinia ruckeri they were read after 24-28 hr incubation and for the 74 Aeromonas salmonicida isolates they were read after 44-48 hr. Applying epidemiological cut-off values to the susceptibility data generated in these tests, the isolates were categorized as wild-type or non-wild-type. The agent-specific categories into each isolate were placed on the basis of the data generated by the two methods were in agreement in 98% of the determinations made. It is argued that, with respect to categorising isolates, disc diffusion and MIC methods can be considered as equally valid at this temperature and after both periods of incubation., (© 2021 The Authors. Journal of Fish Diseases published by John Wiley & Sons Ltd.)

Livestock data on antimicrobial resistance (AMR) are commonly collected from bacterial populations of clinical and non-clinical isolates. In contrast to data on non-clinical isolates from livestock, data on clinical isolates are not harmonized in Europe. The Normalized Resistance Interpretation (NRI) method was applied to overcome the lack of harmonization of laboratory methods and interpretation rules between monitoring systems. Statistical analyses were performed to identify associations between the isolate type (clinical vs. non-clinical) and resistance to four antimicrobials (ampicillin, tetracycline, gentamicin, and nalidixic acid) per animal category in Germany and France. Additional statistical analyses comparing clinical and non-clinical isolates were performed with the available data on the same antimicrobial panel and animal categories from the UK and Norway. Higher resistance prevalence was found in clinical isolates compared to non-clinical isolates from calves to all antimicrobials included in Germany and France. It was also found for gentamicin in broilers from France. In contrast, in broilers and turkeys from Germany and France and in broilers from the UK, a higher resistance level to ampicillin and tetracycline in non-clinical isolates was encountered. This was also found in resistance to gentamicin in isolates from turkeys in Germany. Resistance differed within countries and across years, which was partially in line with differences in antimicrobial use patterns. Differences in AMR between clinical and non-clinical isolates of Escherichia coli are associated with animal category (broiler, calf, and turkey) and specific antimicrobials. The NRI method allowed comparing results of non-harmonized AMR systems and might be useful until international harmonization is achieved.

By 2010, systems set up to monitor the antimicrobial resistance of pathogenic bacteria and antimicrobial usage identified a sustained increase regarding third- and fourth-generation cephalosporin resistance in French pig production. This sector mobilised and collectively committed to responsible action in the following months. This led to a multi-professional voluntary stewardship programme that was started in 2011. A consensus of veterinary opinion led to the definition of restrictive rules on the prescription of the third- and fourth-generation cephalosporins targeted by the antimicrobial stewardship programme (ASP). All pig sector professionals, including farmers, were informed. Existing monitoring systems for usage and resistance were supplemented by data from the records of veterinarians' cephalosporin deliveries and from individual pig farm surveys investigating antimicrobial usage. The second step, from 2014, entailed regulatory measures that consolidated the programme by setting quantitative reduction objectives and specifying the terms and conditions for prescribing and dispensing a list of critical antimicrobial molecules including cephalosporins. All the data sources confirmed a significant fall of more than 90% in cephalosporin usage in the French pig production sector between 2010 and 2016. Monitoring systems recorded that the resistance of commensal and pathogenic Escherichia coli isolates also tended to decrease over the same period. The stewardship programme proved highly effective in reducing usage and containing resistance, illustrating the efficiency of a well-defined multi-professional strategy., (© 2020 The Authors Veterinary Medicine and Science Published by John Wiley & Sons Ltd.)

Objectives: To characterize and compare resistance trends in clinical Escherichia coli isolates from humans, food-producing animals (poultry, cattle and swine) and pets (dogs and cats)., Methods: Antibiogram results collected between January 2014 and December 2017 by MedQual [the French surveillance network for antimicrobial resistance (AMR) in bacteria isolated from the community] and RESAPATH (the French surveillance network for AMR in bacteria from diseased animals) were analysed, focusing on resistance to antibiotics of common interest to human and veterinary medicine. Resistance dynamics were investigated using generalized additive models., Results: In total, 743 637 antibiograms from humans, 48 170 from food-producing animals and 7750 from pets were analysed. For each antibiotic investigated, the resistance proportions of isolates collected from humans were of the same order of magnitude as those from food-producing animals or pets. However, resistance trends in humans differed from those observed in pets and food-producing animals over the period studied. For example, resistance to third-generation cephalosporins and fluoroquinolones was almost always below 10% for both humans and animals. However, in contrast to the notable decreases in resistance observed in both food-producing animals and pets, resistance in humans decreased only slightly., Conclusions: Despite several potential biases in the data, the resistance trends remain meaningful. The strength of the parallel is based on similar data collection in humans and animals and on a similar statistical methodology. Resistance dynamics seemed specific to each species, reflecting different antibiotic-use practices. These results advocate applying the efforts already being made to reduce antibiotic use to all sectors and all species, both in human and veterinary medicine., (© The Author(s) 2020. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

This paper presents the impact on antimicrobial resistance (AMR) in poultry and pig bacteria of the French EcoAntibio plan, a public policy to reduce antimicrobial use in animals. The analysis was performed using sales data of veterinary antimicrobials and AMR data from bacteria obtained at slaughterhouse and from diseased animals. From 2011-2018, fluoroquinolones exposure decreased by 71.5 % for poultry and 89.7 % for pigs. For Campylobacter jejuni isolated from broilers at slaughterhouses, ciprofloxacin resistance increased from 51 % in 2010 to 63 % in 2018, whereas for turkeys the percentages varied from 56 % in 2014 to 63 % in 2018. For commensal E. coli isolated from the caecal content of broilers at slaughterhouses, the resistance to ciprofloxacin - assessed using an epidemiological cut-off value - increased in broiler isolates from 30.7 % in 2010 to 38.1 % in 2018. In turkeys, the percentage of resistant E. coli isolates decreased from 21.3 % in 2014 to 15.2 % in 2018, whereas in pigs, it increased from 1.9 % in 2009 to 5.5 % in 2017. However, for E. coli isolated from diseased animals, when the breakpoints of 2018 were applied, resistance to fluoroquinolones significantly decreased between 2010 and 2018 from 9.0%-5.4% for broilers/hens, from 7.4 % to 3.4 % for turkeys and from 9.4 % to 3.6 % for pigs. These data show that the major, rapid decrease in the exposition to fluoroquinolones had contrasting effects on resistance in the diverse bacterial collections. Co-selection or fitness of resistant strains may explain why changes in AMR do not always closely mirror changes in use., Competing Interests: Declaration of Competing Interest None., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Objectives: To examine the relevance of co-resistance to amoxicillin and tetracycline as an indicator of multidrug resistance (MDR) in animal health., Methods: Escherichia coli isolates collected between 2012 and 2016 by the French surveillance network for antimicrobial resistance in diseased animals (RESAPATH) were analyzed. The proportions of MDR isolates and the proportions of isolates presenting co-resistance to amoxicillin and tetracycline were calculated for seven animal species (cattle, horse, dog, swine, poultry, duck, and turkey). The degree of agreement between these two proportions was estimated by calculating the kappa value., Results: In total, 55,904 isolates were analyzed. MDR proportions were variable among animal species, ranging from 21.9% [20.2; 23.7] in horses to 56.0% [55.4; 56.7] in cattle. A similar situation was observed for proportions of isolates with co-resistance to amoxicillin and tetracycline, with the highest value for cattle 65.0% [64.3; 65.6]. This co-resistance was also most often associated with resistance to other antibiotics, regardless of the animal species considered. Comparative analysis showed substantial agreement between MDR and this co-resistance, with a kappa value of 0.75, all animal species considered., Conclusion: Given the widespread use of penicillins and tetracyclines in animal health, co-resistance to amoxicillin and tetracycline could be an efficient indicator of MDR in E. coli isolates. Based on a specific resistance profile and not an arbitrary number of resistances compared with MDR, this potential indicator is also precise, convenient and suitable for routine use., (Copyright © 2019 Bourély, Cazeau, Jarrige, Jouy, Haenni, Lupo, Madec, Leblond and Gay.)

Surveillance of Pasteurella multocida resistance in food-producing animals is essential to guide the first-line treatment of respiratory diseases and to limit economic losses. Since Pasteurella are the most common bacteria isolated from dog and cat bites, this surveillance is also needed to guide treatment in humans in case of bites. The aim of this study was to characterize the phenotypic resistance of P. multocida strains isolated from respiratory infections in animals, including both food-producing animals and pets. Data collected between 2012 and 2017 by the French national surveillance network for antimicrobial resistance referred to as RESAPATH were analyzed. The proportions of resistance to antimicrobials of relevance in veterinary and human medicines were estimated for each animal species. For cattle, resistance trends over the period were investigated using non-linear analysis applied to time-series. In total, 5356 P. multocida isolates were analyzed. Proportions of resistance of P. multocida were almost all below 20% over the period, and, more precisely, all resistance proportions were below 10% for rabbits, sheep and dogs. The highest resistance proportions to enrofloxacin were identified for cattle (4.5%) and dogs (5.2%). Despite its frequent use in livestock, resistance to florfenicol was less than 1% in P. multocida strains, regardless of the animal species considered. Time series analyses revealed continuous increases in resistance to tetracycline, tilmicosin, flumequine and fluoroquinolones in P. multocida strains isolated from cattle. These trends contrast with the decrease in use of antibiotics in cattle in France and with the decrease in resistance observed in E. coli isolated from diseased cattle., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Colistin resistance associated with plasmidic resistance genes is a serious public health issue. We aimed at studying the transmission of an mcr-1 colistin- and rifampicin-resistant Escherichia coli strain between inoculated pigs and sentinels in different controlled conditions. Three groups of four pigs were bred in separated animal rooms and inoculated on Day 0 (D0). In each inoculated group, six contact pigs were introduced on D2. The first inoculated-and-contact group was left untreated. The ten pigs in the second inoculated-and-contact group received colistin (100 000 IU/kg) before inoculation or contact (D-7 to D-5), simulating prophylactic administration. Pigs in the third inoculated-and-contact group were treated just after inoculation or before transfer (D0 to D2), simulating metaphylactic administration. Faecal samples were regularly collected and segments of intestinal tracts were obtained at necropsy, on D20-D22. Samples were cultured on rifampicin-supplemented media, and PCR was used to detect the mcr-1 gene. The kinetics of infection, based on culture results, were analysed using an SIR model. The inoculated strain was detected in all inoculated and contact pigs. The SIR model showed that one infected pig could transmit the resistant bacteria to one susceptible individual in less than 3 h on average. Prophylactic administration significantly enhanced the transmission rate and resulted in more samples containing the mcr-1 resistance gene at necropsy. No effect of metaphylactic administration could be detected on the transmission rate, nor on the carriage of the resistant strain. Our study confirms that colistin should not be used in a prophylactic manner., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Colistin-resistant Escherichia coli are isolated from pigs suffering from post-weaning diarrhea (PWD). This study was designed to develop an experimental model of PWD using mcr-1-carrying shiga toxin-producing E. coli (STEC) or enterotoxigenic E. coli (ETEC), for the future evaluation of control measures. Three groups of eight piglets, kept in high biosecurity units, were orally inoculated with mcr-1-positive STEC or ETEC, and one unchallenged group was used as a control. Clinical signs were recorded. Regularly-collected fecal samples and samples obtained from the digestive tract of animals sacrificed one month after inoculation were cultured in selective media and isolates were characterized. Blood samples were used to genotype the polymorphisms of the pigs' intestinal receptors for F4 and F18 E. coli adhesins. Diarrhea was more frequent and more fecal samples contained the inoculated strain in the group inoculated with the O149-F4 ETEC strain than with the O141-F18 or O139-F18 STEC strains. However, fewer positive samples were obtained from the two pigs with the F4 resistant genotype. The three inoculated strains could be re-isolated up to the end of the experiment. Excretion peaked on the first week after inoculation with the O149-F4 ETEC strain, and later for the other two. An mcr-1 gene transfer to other commensal isolates was observed only for O139-F18 STEC, while the loss of mcr-1 from the inoculated strain occurred in all groups. The O149-F4 ETEC challenge may be used to evaluate alternative solutions to combat PWD caused by colistin-resistant E. coli in pigs., (Copyright © 2018 Elsevier B.V. All rights reserved.)