title: Intra- and interlaboratory performance of antibiotic disk-diffusion-susceptibility testing of bacterial control strains of relevance for monitoring aquaculture environments.
abstract: In the course of an international research project on hazard analysis of antimicrobial resistance in SE Asian aquaculture environments, 2 European Union and 3 SE Asian laboratories attempted to harmonize a procedure for antimicrobial agent susceptibility testing based on disk diffusion (DD). For this purpose, a selected panel of 10 bacterial control strains of relevance for monitoring warm-water aquaculture environments was sent by the central laboratory to the other participating laboratories. In each laboratory, 10 independently replicated DD determinations of each control strain to 6 antibiotics were performed using Iso-Sensitest Agar (ISA) according to a standard operating procedure (SOP); in total, this study thus yielded 300 data sets for all 5 laboratories. At the end of the study, strain authenticity of subcultures of the control strains used by the respective participating laboratories was verified by the central laboratory. Based on the arithmetic mean of 10 inhibition-zone diameter measurements and standard deviation (SD), intralaboratory SD variations ranged from 0 to 2 mm when 79% of the recorded data sets were considered. In 8% of the data sets, the SD value exceeded 4 mm, which in most cases could be attributed to the fact that the data points for a given strain-disk combination were not normally distributed in one of the laboratories. At the interlaboratory level, 81% of the SD values based on global averaging of 50 data points per strain-disk combination were situated in the 0 to 5 mm range. Comparison with a minimal data set from literature of DD testing performed with Mueller-Hinton (MH) medium indicated that the use of either ISA or MH medium in DD testing has a limited impact on the method's precision among different laboratories. In conclusion, the current study has provided a validated SOP to promote the coordination and harmonization of DD-susceptibility methodologies for aquaculture-associated organisms at an international level. As one of the main action items for the future, new interpretive breakpoints should be specifically designed and validated for aquaculture drugs and organisms.
authors.affiliation: Laboratory of Microbiology, Ghent University, Belgium. geert.huys@ugent.be
authors.forename: Geert
authors.initials: G
authors.lastname: Huys
authors.forename: Margo
authors.initials: M
authors.lastname: Cnockaert
authors.forename: Kerry
authors.initials: K
authors.lastname: Bartie
authors.forename: Dang Thi Hoang
authors.initials: DT
authors.lastname: Oanh
authors.forename: Nguyen Thanh
authors.initials: NT
authors.lastname: Phuong
authors.forename: Temdoung
authors.initials: T
authors.lastname: Somsiri
authors.forename: Supranee
authors.initials: S
authors.lastname: Chinabut
authors.forename: Fatimah Md
authors.initials: FM
authors.lastname: Yussoff
authors.forename: Mohamed
authors.initials: M
authors.lastname: Shariff
authors.forename: Mauro
authors.initials: M
authors.lastname: Giacomini
authors.forename: Stefania
authors.initials: S
authors.lastname: Bertone
authors.forename: Jean
authors.initials: J
authors.lastname: Swings
authors.forename: Alan
authors.initials: A
authors.lastname: Teale
mesh_terms: D000900:Anti-Bacterial Agents / Q000633:toxicity*; D017756:Aquaculture / Q000379:methods*; D001419:Bacteria / Q000187:drug effects* / Q000254:growth & development; D003470:Culture Media; D004058:Diffusion; D024881:Drug Resistance, Bacterial / Q000502:physiology*; D005069:Evaluation Studies as Topic; D008826:Microbial Sensitivity Tests / Q000379:methods*; D012015:Reference Standards
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media