Relative contribution of biological variation and technical variables to zone diameter variations of disc diffusion susceptibility testing
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Relative contribution of biological variation and technical variables to zone diameter variations of disc diffusion susceptibility testing. / Hombach, Michael; Ochoa, Carlos; Maurer, Florian P; Pfiffner, Tamara; Böttger, Erik C; Furrer, Reinhard.
In: J ANTIMICROB CHEMOTH, Vol. 71, No. 1, 01.2016, p. 141-51.Research output: SCORING: Contribution to journal › SCORING: Journal article › Research › peer-review
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TY - JOUR
T1 - Relative contribution of biological variation and technical variables to zone diameter variations of disc diffusion susceptibility testing
AU - Hombach, Michael
AU - Ochoa, Carlos
AU - Maurer, Florian P
AU - Pfiffner, Tamara
AU - Böttger, Erik C
AU - Furrer, Reinhard
N1 - © The Author 2015. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
PY - 2016/1
Y1 - 2016/1
N2 - OBJECTIVES: Disc diffusion is still largely based on manual procedures. Technical variations originate from inoculum preparation, variations in materials, individual operator plate streaking and reading accuracy. Resulting measurement imprecision contributes to categorization errors. Biological variation resembles the natural fluctuation of a measured parameter such as antibiotic susceptibility around a mean value. It is deemed to originate from factors such as genetic background or metabolic state. This study analysed the relative contribution of different technical and biological factors to total disc diffusion variation.METHODS: For calculation of relative error factor contribution to disc diffusion variability, five experiments were designed keeping different combinations of error factors constant. A mathematical model was developed to analyse the individual error factor contribution to disc diffusion variation for each of the tested drug-species combinations.RESULTS: The contribution of biological variation to total diameter variance ranged from 10.4% to 98.8% for different drug-species combinations. Highest biological variation was found for Enterococcus faecalis WT and vancomycin (98.8%) and for penicillinase-producing Staphylococcus aureus and penicillin G (96.0%). Average imprecision of automated zone reading revealed that 1.4%-5.3% of total imprecision was due to technical variation, while materials, i.e. antibiotic discs and agar plates, contributed between 2.6% and 3.9%. Inoculum preparation and manual plate streaking contributed 6.8%-24.8% and 6.6%-24.3%, respectively, to total imprecision.CONCLUSIONS: This study illustrates the relative contributions of technical factors that account for a significant part of total variance in disc diffusion. The highest relative contribution originated from the operator, i.e. manual inoculum preparation and plate streaking. Further standardization of inoculum preparation and plate streaking by automation could potentially increase the precision of disc diffusion and improve the correlation of susceptibility reports with clinical outcome.
AB - OBJECTIVES: Disc diffusion is still largely based on manual procedures. Technical variations originate from inoculum preparation, variations in materials, individual operator plate streaking and reading accuracy. Resulting measurement imprecision contributes to categorization errors. Biological variation resembles the natural fluctuation of a measured parameter such as antibiotic susceptibility around a mean value. It is deemed to originate from factors such as genetic background or metabolic state. This study analysed the relative contribution of different technical and biological factors to total disc diffusion variation.METHODS: For calculation of relative error factor contribution to disc diffusion variability, five experiments were designed keeping different combinations of error factors constant. A mathematical model was developed to analyse the individual error factor contribution to disc diffusion variation for each of the tested drug-species combinations.RESULTS: The contribution of biological variation to total diameter variance ranged from 10.4% to 98.8% for different drug-species combinations. Highest biological variation was found for Enterococcus faecalis WT and vancomycin (98.8%) and for penicillinase-producing Staphylococcus aureus and penicillin G (96.0%). Average imprecision of automated zone reading revealed that 1.4%-5.3% of total imprecision was due to technical variation, while materials, i.e. antibiotic discs and agar plates, contributed between 2.6% and 3.9%. Inoculum preparation and manual plate streaking contributed 6.8%-24.8% and 6.6%-24.3%, respectively, to total imprecision.CONCLUSIONS: This study illustrates the relative contributions of technical factors that account for a significant part of total variance in disc diffusion. The highest relative contribution originated from the operator, i.e. manual inoculum preparation and plate streaking. Further standardization of inoculum preparation and plate streaking by automation could potentially increase the precision of disc diffusion and improve the correlation of susceptibility reports with clinical outcome.
KW - Anti-Bacterial Agents
KW - Bacteria
KW - Disk Diffusion Antimicrobial Tests
KW - Models, Theoretical
KW - Reproducibility of Results
KW - Specimen Handling
KW - Journal Article
U2 - 10.1093/jac/dkv309
DO - 10.1093/jac/dkv309
M3 - SCORING: Journal article
C2 - 26462987
VL - 71
SP - 141
EP - 151
JO - J ANTIMICROB CHEMOTH
JF - J ANTIMICROB CHEMOTH
SN - 0305-7453
IS - 1
ER -