title: Antimicrobial susceptibility and molecular characterization of avian pathogenic Escherichia coli isolates.
abstract: Ninety-five avian pathogenic Escherichia coli (APEC) isolates recovered from diagnosed cases of avian colibacillosis from North Georgia between 1996 and 2000 were serotyped and examined for typical virulence-factors, susceptibility to antimicrobials of human and veterinary significance, and genetic relatedness. Twenty different serotypes were identified, with O78 being the most common (12%). The majority of the avian E. coli isolates (60%), however, were non-typeable with standard O antisera. Eighty-four percent of isolates were PCR positive for the temperature-sensitive hemagglutinin (tsh) gene and 86% positive for the increased serum survival (iss) gene. Multiple antimicrobial-resistant phenotypes (> or =3 antimicrobials) were observed in 92% of E. coli isolates, with the majority of isolates displaying resistance to sulfamethoxazole (93%), tetracycline (87%), streptomycin (86%), gentamicin (69%), and nalidixic acid (59%). Fifty-six E. coli isolates displaying resistance to nalidixic acid were co-resistant to difloxacin (57%), enrofloxacin (16%), gatifloxacin (2%), and levofloxacin (2%). DNA sequencing revealed point mutations in gyrA (Ser83-Leu, Asp87-Tyr, Asp87-Gly, Asp87-Ala), gyrB (Glu466-Asp, Asp426-Thr), and parC (Ser80-Ile, Ser80-Arg). No mutations were observed in parE. Twelve of the quinolone-resistant E. coli isolates were tolerant to cyclohexane, a marker for upregulation of the acrAB multi-drug resistance efflux pump. Quinolone-resistant isolates were further genetically characterized via ribotyping. Twenty-two distinct ribogroups were identified, with 61% of isolates clustering into four major ribogroups, indicating that quinolone resistance has emerged among multiple avian pathogenic E. coli serogroups and chromosomal backgrounds.
authors.affiliation: Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, 8401 Muirkirk Road, Laurel, MD 20708, USA.
authors.forename: Shaohua
authors.initials: S
authors.lastname: Zhao
authors.forename: John J
authors.initials: JJ
authors.lastname: Maurer
authors.forename: Susannah
authors.initials: S
authors.lastname: Hubert
authors.forename: Juan F
authors.initials: JF
authors.lastname: De Villena
authors.forename: Patrick F
authors.initials: PF
authors.lastname: McDermott
authors.forename: Jianghong
authors.initials: J
authors.lastname: Meng
authors.forename: Sherry
authors.initials: S
authors.lastname: Ayers
authors.forename: Linda
authors.initials: L
authors.lastname: English
authors.forename: David G
authors.initials: DG
authors.lastname: White
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D002645:Chickens; D016000:Cluster Analysis; D027081:DNA Gyrase / Q000737:chemistry / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000737:chemistry / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000145:classification* / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000662:veterinary; D011201:Poultry Diseases / Q000382:microbiology*; D021521:Ribotyping / Q000662:veterinary; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014774:Virulence
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase