phaidra.vetmeduni.ac.at o:1926 DOI 10.3390/antibiotics11040467 Escherichia coli Isolated from Organic Laying Hens Reveal a High Level of Antimicrobial Resistance despite No Antimicrobial Treatments The present study investigated the resistance characteristics of E. coli isolates originating from 18 organic laying hen flocks. E. coli was isolated from different organs at three different time points, resulting in 209 E. coli isolates. The antibiotic susceptibility was determined by applying a microdilution assay. General, a high resistance rate was found. The antibiotic susceptibility was independent from the presence of pathological lesions, the isolation site, or the affiliation to a pathogenic serogroup. The majority of the isolates proved to be multi-drug-resistant (95.70%), of which 36.84% could be categorized as extensively drug-resistant. All isolates were resistant to oxacillin and tylosin. Resistance rates to amoxicillin (67.94%), cefoxitin (55.98%), ceftazidime (82.30%), colistin (73.68%), nalidixic acid (91.87%), streptomycin (42.58%), tetracycline (53.59%), and sulfamethoxazole (95.22%) were high. None of the isolates revealed pan-drug-resistance. A great heterogeneity of resistance profiles was found between isolates within a flock or from different organs of the same bird, even when isolates originated from the same organ. An increase in antimicrobial resistance was found to be correlated with the age of the birds. The fact, that no antibiotic treatment was applied except in two flocks, indicates that resistant bacteria circulating in the environment pose a threat to organic systems. eng Antibiotic-Resistance; E.-Coli; Humans; Susceptibility; Chicken; Genes; Bacteria; Animals; Poultry; Meat 2023-08-01T09:36:47.680Z LOMv1.0 Author BEGIN:VCARD VERSION:3.0 N:Hess;Claudia; FN:Claudia Hess X-ORCID:https://orcid.org/0000-0002-3535-5157 END:VCARD BEGIN:VCARD VERSION:3.0 N:Hess;Michael; FN:Michael Hess X-ORCID:https://orcid.org/0000-0002-6991-0120 END:VCARD BEGIN:VCARD VERSION:3.0 N:Zloch;Angelika; FN:Angelika Zloch END:VCARD BEGIN:VCARD VERSION:3.0 N:Troxler;Salome; FN:Salome Troxler X-ORCID:https://orcid.org/0000-0001-9954-809X END:VCARD BEGIN:VCARD VERSION:3.0 N:Jandreski-Cvetkovic;Delfina; FN:Delfina Jandreski-Cvetkovic END:VCARD https://w3id.org/kim/hcrt/scheme https://w3id.org/kim/hcrt/text Textdokument Text LOMv1.0 yes https://creativecommons.org/licenses/by/4.0 application/pdf 887286 https://phaidra.vetmeduni.ac.at/o:1926 https://phaidra.vetmeduni.ac.at/api/object/o:1926/thumbnail LOMv1.0 discipline