title: Evaluation of direct Etest for antimicrobial susceptibility testing of bacteria isolated from synovial fluid of horses using enrichment bottles.
abstract: This study evaluated the Etest for direct antimicrobial susceptibility testing (AST) of bacteria from equine synovial specimens, incubated in BACTEC enrichment bottles. Ninety-four culture-positive broths were inoculated onto agar to directly determine the minimum inhibitory concentrations (MICs) of 13 antimicrobials, using the Etest (direct Etest). Results were compared with those obtained with the agar dilution reference method, the standard Etest, and the disc diffusion method, after subculture and standardisation of the inoculum. For categorical comparison of AST results, MICs were translated into susceptibility categories, using clinical breakpoints. The direct Etest predicted categorical susceptibility/resistance of bacteria from equine synovial fluid with acceptable accuracy (overall categorical agreement, 91%) and was more reliable than the disc diffusion test. The direct Etest was less accurate than the standard Etest for generating MICs ± 1 log dilution relative to the reference method (overall essential agreement, 69% vs. 89%). As the Etest generated a high percentage of inaccuracies with trimethoprim and sulfadiazine, these were less suitable antimicrobial agents for inclusion. In conclusion, the direct Etest reliably predicted the susceptibility of isolates from equine synovial fluid for the tested antimicrobials, except for trimethoprim and sulfadiazine. Since it did not require subculture and preparation of a standardised inoculum, direct Etest results were available at least 24 h earlier than with other methods, which could facilitate the diagnosis of synovial infections. However, when accuracy is prioritised over speed for MIC determination, the standard Etest is preferred over the direct Etest.
authors.affiliation: Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B9820 Merelbeke, Belgium. Electronic address: michele.dumoulin@ugent.be.
authors.forename: M
authors.initials: M
authors.lastname: Dumoulin
authors.affiliation: Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B9820 Merelbeke, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Martens
authors.affiliation: Microbiology Laboratorium, AZ Sint-Lucas, Groenebriel 1, B-9000 Ghent, Belgium.
authors.forename: A-M
authors.initials: AM
authors.lastname: Van den Abeele
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Boyen
authors.affiliation: Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B9820 Merelbeke, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Oosterlinck
authors.affiliation: Dierenkliniek De Bosdreef, Spelonckvaart 46, B-9180 Moerbeke-Waas, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Wilderjans
authors.affiliation: Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B9820 Merelbeke, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Gasthuys
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Haesebrouck
authors.affiliation: Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B9820 Merelbeke, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Pille
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D001424:Bacterial Infections / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary*; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods / Q000662:veterinary*; D006734:Horse Diseases / Q000175:diagnosis* / Q000382:microbiology; D006736:Horses; D008826:Microbial Sensitivity Tests / Q000379:methods / Q000662:veterinary*; D013582:Synovial Fluid / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents
keywords: Bactec blood culture medium enrichment; Direct susceptibility testing; Etest; Horse; Synovial infection