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Table 3 Comparison of standard deviations of measurements with calliper, the Sirscan system adaped on-screen by the human eye and the Sirscan fully automated mode

From: Standardisation of disk diffusion results for antibiotic susceptibility testing using the sirscan automated zone reader

S. aureusATCC 29213                     
  TOB AK CN CIP LEV P FOX E DA SXT RA average         
EUCAST QC range 20-26 18-24 19-25 21-27 23-29 12-18 24-30 23-29 23-29 29-32 30-36           
Sirscan fully automated                      
   Mean value 23.2 23.4 23.6 27.8 28.1 15.9 25.0 27.8 29.4 29.4 32.7 26.0          
   Standard deviation 0.8 0.5 0.8 0.9 1.3 0.3 1.2 0.8 0.7 0.9 1.0 0.8*          
Sirscan on-screen adjusted                      
   Mean value 24.7 25.5 25.2 27.8 29.5 15.8 26.1 30.4 29.9 29.8 33.6 27.1          
   Standard deviation 1.2 0.7 1.4 1.7 1 0.4 0.9 2.2 3 1.3 0.7 1.3          
Calliper                      
   Mean value 23.4 23.2 23.8 22.7 27.2 17.2 26.1 26.2 26.7 26.2 32.9 25.1          
   Standard deviation 1 1.6 1.2 1.1 2 0.6 0.8 1.1 1.2 4.7 2.1 1.6*          
E. coli ATCC 25922                     
  TOB AK CN NA NOR CIP LEV AM AMC TPZ CXM CAZ CTX CPD CRO FEP MEM ETP SXT NF average
EUCAST QC range 18-26 19-26 19-26 22-28 28-35 30-40 29-37 16-22 18-24 21-27 20-26 23-29 25-31 23-28 29-35 31-37 28-34 29-36 23-29 17-23  
Sirscan fully automated                      
   Mean value 22.4 20.6 20.4 25.9 28.1 28.4 28.4 20.6 21.8 23.3 24.8 26.0 27.5 24.7 29.3 31.0 29.2 34.0 26.3 17.5 25.5
   Standard deviation 1.1 0.8 0.5 0.8 0.6 1.0 0.7 0.9 0.6 0.4 0.4 0.0 0.5 0.5 0.7 0.7 0.9 0.8 0.4 0.5 0.7*
Sirscan on-screen adjusted                      
   Mean value 23.2 24.5 25.1 25.9 34 37.3 35.4 25.9 23.3 27.6 26.1 27.8 31.1 29.3 32.3 35 35.9 34.3 28.4 24.8 29.4
   Standard deviation 1.5 1.3 1.4 1.3 2.4 1.6 1.5 1.8 1 1 1.2 1.2 1.9 1.2 1.3 1 1.2 1.2 1.4 1 1.4
Calliper                      
   Mean value 22.4 24.4 23.3 27.6 31.1 34.1 31.5 22.3 25.1 25.7 24.8 25.5 28.5 27.6 30.2 33.7 23.9 34.3 27.3 17.4 27.0
   Standard deviation 1.1 2.5 1.2 1.3 1 1.6 1.5 1.2 0.7 1.1 1.2 1 1.5 2.4 1.4 1.4 1.3 2.4 0.9 1.6 1.4*
P. aeruginosa ATCC 27853                     
  TOB AK CN LEV FEP CAZ TPZ IPM MEM average           
EUCAST QC range 19-25 18-26 16-21 19-26 24-30 21-27 23-29 20-28 27-33             
Sirscan fully automated                      
   Mean value 24 24.9 21.5 28 27.8 22.9 25.3 23.6 29.9 25.3            
   Standard deviation 0.8 0.7 1.4 0.6 0.4 0.3 0.7 0.5 0.3 0.6            
Sirscan on-screen adjusted                      
   Mean value 23.2 25.2 22 27.8 26.6 22.2 24.5 25 26.5 24.8            
   Standard deviation 0.8 1 0.9 1.3 1.4 0.9 1.2 0.5 0.6 1.0            
Calliper                      
   Mean value 23.5 25.0 21.6 25.9 25.8 22.2 23.9 24.9 26.4 24.4            
   Standard deviation 0.6 0.7 0.5 1.2 0.9 0.8 1.1 0.6 0.9 0.8            
  1. Standard deviations of repeat measurements of S. aureus ATCC 29213 and E. coli ATCC 25922 were significantly lower with fully automated Sirscan readings as compared to manual calliper measurements indicating better reproducibility and precision of Sirscan readings. Asterisks indicate statistically significant differences (p<0.05) of mean standard deviations using the paired t-test. Measurements were done independently and double-blinded by 19 experienced persons (technicians and laboratory physicians) with the same disk diffusion plates of EUCAST quality control strains of S. aureus ATCC 29213, E. coli ATCC 25922, and P. aeruginosa ATCC 27853. Measurements of the Sirscan fully automated mode comprise 19 independent measurements of the panels. QC, quality control; AM, ampicillin; AMC, amoxicillin-clavulanic acid; AK, amikacin; CAZ, ceftazidime; CIP, ciprofloxacin; CN, gentamicin; CPD, cefpodoxime; CRO, ceftriaxone; CTX, cefotaxime; CXM, cefuroxime; DA, clindamycin; E, erythromycin; ETP, ertapenem; FEP, cepefim; FOX, cefoxitin; IPM, imipenem; LEV, levofloxacin; MEM, meropenem; NA, nalidixic acid; NF, nitrofuratoine; NOR, norfloxacin; P, penicillin G; RA, rifampicin; SXT, trimethoprim-sulfamethoxazole.