title: Characterization of persistent and transient Escherichia coli isolates recovered from clinical mastitis episodes in dairy cows.
abstract: Escherichia coli usually cause transient intramammary infections in dairy cows, but persistent intramammary infections have been observed. The objective of the study was to compare antimicrobial resistance and virulence genes found in persistent and transient E. coli isolated from clinical mastitis cases in a cohort of 91 Canadian dairy herds monitored over a 2-year period. Antimicrobial susceptibility was determined by broth microdilution and the presence of 27 virulence genes associated with extra-intestinal E. coli infections was determined by colony hybridization. Proportion of resistance in persistent E. coli ranged from 0.0% (enrofloxacin) to 27.8% (ampicillin and tetracycline). Proportion of resistance in transient E. coli ranged from 0.0% (enrofloxacin) to 16.8% (tetracycline). Odds of being classified as a persistent isolate increased by a factor of 1.6 (95% CI: 1.1, 2.4) for each aditional resistance observed (e.g. isolates resistant to four antimicrobial agents had 1.6 times higher odds of belonging to the persistent groups compared to isolates demonstrating resistance to three agents). Persistency was associated with higher odds of resistance to ampicillin (OR: 9.8, P<0.01) or cephalothin (OR: 7.6, P=0.02). Persistent isolates had 5.4 times higher odds (95% CI: 1.2, 24.0) of harboring virulence gene iroN. Similarly, persistent isolates had 8.6 times higher odds (95% CI: 2.8, 27.1) of possessing the virulence gene sitA. In conclusion, this study confirmed that persistency of intramammary E. coli isolates is associated with certain traits. Findings concerning iron-acquisition shed new light on the mechanisms of intramammary survival.
authors: Département de pathologie et microbiologie, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S 7C6.
authors: Julie-Hélène
authors: JH
authors: Fairbrother
authors: Département de pathologie et microbiologie, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S 7C6; Canadian Bovine Mastitis and Milk Quality Research Network, C.P. 5000 Saint-Hyacinthe, Québec, Canada J2S 7C6. Electronic address: simon.dufour@umontreal.ca.
authors: Simon
authors: S
authors: Dufour
authors: Département de pathologie et microbiologie, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S 7C6; OIE Reference Laboratory for Escherichia coli (EcL), Faculté de médecine vétérinaire, Université de Montréal, 3200 Sicotte, Saint-Hyacinthe, Québec, Canada J2S 7C6.
authors: John Morris
authors: JM
authors: Fairbrother
authors: Département de sciences cliniques, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S 7C6.
authors: David
authors: D
authors: Francoz
authors: OIE Reference Laboratory for Escherichia coli (EcL), Faculté de médecine vétérinaire, Université de Montréal, 3200 Sicotte, Saint-Hyacinthe, Québec, Canada J2S 7C6.
authors: Éric
authors: É
authors: Nadeau
authors: Département de pathologie et microbiologie, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S 7C6; Canadian Bovine Mastitis and Milk Quality Research Network, C.P. 5000 Saint-Hyacinthe, Québec, Canada J2S 7C6.
authors: Serge
authors: S
authors: Messier
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002170:Canada; D002417:Cattle; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005260:Female; D008414:Mastitis, Bovine / Q000188:drug therapy / Q000382:microbiology*; D014774:Virulence
chemical_list: D000900:Anti-Bacterial Agents
keywords: Antimicrobial resistance; Bovine; Escherichia coli; Mastitis; Persistance; Virulence