title: Effect of Tetracycline Dose and Treatment Mode on Selection of Resistant Coliform Bacteria in Nursery Pigs.
abstract: This study describes the results of a randomized clinical trial investigating the effect of oxytetracycline treatment dose and mode of administration on the selection of antibiotic-resistant coliform bacteria in fecal samples from nursery pigs. Nursery pigs (pigs of 4 to 7 weeks of age) in five pig herds were treated with oxytetracycline forLawsonia intracellularis-induced diarrhea. Each group was randomly allocated to one of five treatment groups: oral flock treatment with a (i) high (20 mg/kg of body weight), (ii) medium (10 mg/kg), or (iii) low (5 mg/kg) dose, (iv) oral pen-wise (small-group) treatment (10 mg/kg), and (v) individual intramuscular injection treatment (10 mg/kg). All groups were treated once a day for 5 days. In all groups, treatment caused a rise in the numbers and proportions of tetracycline-resistant coliform bacteria right after treatment, followed by a significant drop by the time that the pigs left the nursery unit. The counts and proportions of tetracycline-resistant coliforms did not vary significantly between treatment groups, except immediately after treatment, when the highest treatment dose resulted in the highest number of resistant coliforms. A control group treated with tiamulin did not show significant changes in the numbers or proportions of tetracycline-resistant coliforms. Selection for tetracycline-resistant coliforms was significantly correlated to selection for ampicillin- and sulfonamide-resistant strains but not to selection for cefotaxime-resistant strains. In conclusion, the difference in the dose of oxytetracycline and the way in which the drug was applied did not cause significantly different levels of selection of tetracycline-resistant coliform bacteria under the conditions tested.IMPORTANCEAntimicrobial resistance is a global threat to human health. Treatment of livestock with antimicrobials has a direct impact on this problem, and there is a need to improve the ways that we use antimicrobials in livestock production. We hypothesized that antibiotic resistance development following treatment of diarrhea in nursery pigs could be reduced either by lowering the dose of oxytetracycline or by replacing the commonly used practice of flock treatment with individual or small-group treatments, since this would reduce the number of pigs treated. However, the study showed no significant difference between treatment groups with respect to the number or proportion of tetracycline-resistant coliforms selected. The most important conclusion is that under practical field conditions, there will be no added value, in terms of lowering resistance development, by exchanging flock treatment for individual or small-group treatment of nursery pigs. The reason for the lack of an effect of single-animal treatment is probably that such animals share the environment with treated animals and take up resistant bacteria from the environment.
authors.affiliation: Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Kaare
authors.initials: K
authors.lastname: Græsbøll
authors.affiliation: Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Damborg
authors.affiliation: Section for Bacteriology, Pathology and Parasitology, National Veterinary Institute, Danish Technical University, Frederiksberg, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Mellerup
authors.affiliation: Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Ana
authors.initials: A
authors.lastname: Herrero-Fresno
authors.affiliation: Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Inge
authors.initials: I
authors.lastname: Larsen
authors.affiliation: Odder Veterinary Practice, Odder, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Holm
authors.affiliation: Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Nielsen
authors.affiliation: Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: Lasse Engbo
authors.initials: LE
authors.lastname: Christiansen
authors.affiliation: Section for Bacteriology, Pathology and Parasitology, National Veterinary Institute, Danish Technical University, Frederiksberg, Denmark.
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Angen
authors.affiliation: Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Shahana
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: Section for Bacteriology, Pathology and Parasitology, National Veterinary Institute, Danish Technical University, Frederiksberg, Denmark.
authors.forename: Anders
authors.identifier: http://orcid.org/0000-0002-2175-830X
authors.initials: A
authors.lastname: Folkesson
authors.affiliation: Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark jeo@sund.ku.dk.
authors.forename: John Elmerdahl
authors.identifier: http://orcid.org/0000-0001-6225-6587
authors.initials: JE
authors.lastname: Olsen
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D001419:Bacteria / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D045824:Desulfovibrionaceae Infections / Q000188:drug therapy / Q000382:microbiology / Q000503:physiopathology / Q000662:veterinary*; D003967:Diarrhea / Q000188:drug therapy / Q000382:microbiology / Q000503:physiopathology / Q000662:veterinary*; D024881:Drug Resistance, Bacterial; D005243:Feces / Q000382:microbiology; D020639:Lawsonia Bacteria / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology; D010118:Oxytetracycline / Q000008:administration & dosage*; D013552:Swine / Q000254:growth & development / Q000382:microbiology; D013553:Swine Diseases / Q000188:drug therapy* / Q000382:microbiology / Q000503:physiopathology
chemical_list: D000900:Anti-Bacterial Agents; D010118:Oxytetracycline
keywords: dose; flock treatment; nursery pigs; tetracyclines