Fully automated disc diffusion for rapid antibiotic susceptibility test results: a proof-of-principle study.
Antibiotic resistance poses a significant threat to patients suffering from infectious diseases. Early readings of antibiotic susceptibility test (AST) results could be of critical importance to ensure adequate treatment. Disc diffusion is a well-standardized, established and cost-efficient AST procedure; however, its use in the clinical laboratory is hampered by the many manual steps involved, and an incubation time of 16-18 h, which is required to achieve reliable test results.



We have evaluated a fully automated system for its potential for early reading of disc diffusion diameters after 6-12 h of incubation. We assessed availability of results, methodological precision, categorical agreement and interpretation errors as compared with an 18 h standard. In total, 1028 clinical strains (291 Escherichia coli , 272 Klebsiella pneumoniae , 176 Staphylococcus aureus and 289 Staphylococcus epidermidis ) were included in this study. Disc diffusion plates were streaked, incubated and imaged using the WASPLab TM automation system.



Our results demonstrate that: (i) early AST reading is possible for important pathogens; (ii) methodological precision is not hampered at early timepoints; and (iii) species-specific reading times must be selected. As inhibition zone diameters change over time and are phenotype/drug combination dependent, specific cut-offs and expert rules will be essential to ensure reliable interpretation and reporting of early susceptibility testing results.
Institut für Medizinische Mikrobiologie, Universität Zürich, 8006 Zürich, Schweiz.
Michael
M
Hombach
Institut für Medizinische Mikrobiologie, Universität Zürich, 8006 Zürich, Schweiz.
Marion
M
Jetter
Institut für Medizinische Mikrobiologie, Universität Zürich, 8006 Zürich, Schweiz.
Nicolas
N
Blöchliger
Institut für Medizinische Mikrobiologie, Universität Zürich, 8006 Zürich, Schweiz.
Natalia
N
Kolesnik-Goldmann
Institut für Medizinische Mikrobiologie, Universität Zürich, 8006 Zürich, Schweiz.
Erik C
EC
Böttger
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D057205:Automation, Laboratory; D001424:Bacterial Infections / Q000382:microbiology; D052978:Disk Diffusion Antimicrobial Tests / Q000295:instrumentation / Q000379:methods*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects; D004927:Escherichia coli Infections / Q000382:microbiology; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects; D013212:Staphylococcus epidermidis / Q000187:drug effects
D000900:Anti-Bacterial Agents