Automated systems:
an overview
Robin A Howe
Cardiff
Insert name of presentation on Master
Slide
AST standards
• MIC taken as standard measure of
susceptibility
– Agar dilution
– Broth dilution
– Microbroth dilution
• ISO standard
– Broth microdiluion
– Mueller-Hinton Broth
– Inoculum 5x105
cfu/mL
AST standards
• MIC taken as standard measure of
susceptibility
– Agar dilution
– Broth dilution
– Microbroth dilution
• S/I/R Breakpoints defined by
BSAC/EUCAST/CLSI
AST standards
• MIC taken as standard measure of
susceptibility
– Agar dilution
– Broth dilution
– Microbroth dilution
• S/I/R Breakpoints defined by
BSAC/EUCAST/CLSI
• MIC/BP supplemented by “expert rules”
for clinical use
The rationale for automated
systems
• More reliable AST results
– ?closer to “standard”
– Reduced scope for “user” error
– Reproducible
• Improved ID linked to AST
• Embedded expert rules
Automated systems: an overview
Identification required for
interpretation of BP & expert rules
Welsh variability in ID of
Enterobacter/Klebsiella/Serratia
Inter-laboratory ID comparisons
100%
% Agreement
90%
80%
70%
60%
50%
40%
94.4
93.1
ID Disagree
95.5
75.0
66.9
74.7
30%
20%
ID Agree Genus
ID Agree
10%
0%
Lab 1
Lab 2
Lab 3
Lab 4
Laboratory
Lab 5
Total
The rationale for automated
systems
•
•
•
•
•
More reliable AST results
Improved ID linked to AST
Embedded expert rules
Improved speed of results
Increased number of agents tested
Automated systems: an overview
Welsh Gram
positive panel
Drug
Gentamicin
Penicillin
Oxacillin
Ampicillin
Amoxicillin/Clav
Levofloxacin
Ciprofloxacin
Cefoxitin
Linezolid
Erythromycin
Clindamycin
Daptomycin
Chloramphenicol
Nitrofurantoin
Fusidic Acid
Rifampin
Minocycline
Mupirocin
Mupirocin - HL
Teicoplanin
Tetracycline
Trimethoprim
Vancomycin
GM-Syn
ST-Syn
Range
1-4
0.06 - 0.25
1-4
2 - 16
1/0.5 - 16/8
0.5 - 2
0.5 - 2
2-8
2-8
0.25 - 1
0.25 - 1
1 - 16
1 - 16
16 - 64
1-8
0.25 - 1
0.5 - 2
1-4
256
1 - 16
0.5 - 2
0.5 - 4
1 - 16
500
1000
Welsh Gram
negative panel
Drug
Amikacin
Gentamicin
Tobramycin
Ampicillin
Amoxicillin/Clav
Cefotaxime
Cefoxitin
Ceftazidime
Cefuroxime
Cephalexin
Ciprofloxacin
Aztreonam
Imipenem
Meropenem
Ertapenem
Colistin
Piperacillin/Tazo
Trimethoprim
Trimethoprim/Sulfa
Nitrofurantoin
Levofloxacin
Range
4 - 32
1-8
2-8
4 - 32
2/1 - 32/16
1-4
1-4
2 - 16
4 - 16
4 - 16
0.25 - 2
1 - 16
1-8
1-8
0.5 - 4
1-4
4/4 - 32/4
0.5 - 4
0.8/15.2 - 3.2/60.8
16 - 64
0.5-2
The rationale for automated
systems
•
•
•
•
•
•
•
•
More reliable AST results
Improved ID linked to AST
Embedded expert rules
Improved speed of results
Increased number of agents tested
Laboratory workflow
Staff skill mix
Epidemiological software
Automated systems: an overview
Available systems
• MicroScan WalkAway
• Biomerieux Vitek 2
• BD Phoenix
MicroScan
• 96 well plates
• AST based on conventional
microbroth dilution MIC
• ID currently biochemical
Microscan
• Conventional panels
• Enterobacteriaceae, gram-negative nonfermenters, staphylococci, enterococci
• Combo, MIC-only, ID-only
• Rapid panels
– 2 - 2.5 hour ID (pre-formed enzymes)
– AST for Gram negative organisms (MIC > 4
hrs)
• Synergies plus panels
– 2 - 2.5 hour ID (pre-formed enzymes)
– Broth microdilution “Read-when-ready” MIC
– Resistance detection flagged in as few as
4.5 hours
– All results finalized in 16/18 hours
• Additional
– Yeast ID, Anaerobe ID, HNID
– MICroSTREP plus ® - dry format
– ESβL plus ® -ESβL Confirmatory Panel
• Panels read by
– WalkAway® systems
– autoSCAN-4
– Manual
Microscan
• Expert rules
within LabPro
Alert system
– Pre-loaded
– customisable
Microscan
• Expert rules
within LabPro
Alert system
– Pre-loaded
– customisable
Vitek 2
• AST based on broth
susceptibility with specific
cards
• ID currently biochemical
• Growth/reactions
“continuously” monitored
Vitek 2
• ID Cards available for
–
–
–
–
–
–
Gram positives
Enterobacteriaceae
Non-Enterobacteriaceae
Neisseria/Haemophilus etc
Anaerobes
Yeasts
• AST Cards available for
– Gram positive cocci
– Gram negative bacilli
– Yeasts
• Up to 22
antibiotics tested
on each card
VITEK 2 – MIC Interpretation
Interpretation of Raw Data
Growth Parameters
MIC
Raw Data
% Change
Slope
Area
SLPAR
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18
TIME (hours)
Vitek 2
• Expert rules
within the
Advanced Expert
System (AES)
– Extensive
Knowledge Base
• >20,000 MIC
distributions
• >2,500
Phenotypes
• >200 Resistance
Mechanisms
Vitek 2
CARD Type
Time to Result
GN ID
GP ID
2 to  10 hours
2 to  8 hours
NH ID
6 hours
ANC ID
YST ID
6 hours
18 hours
GN AST
GP AST
AST-YS01
2 to 18 Hours
2 to 18 Hours
6 hours
Phoenix
• AST based on broth
susceptibility with specific
cards
• ID currently biochemical
• Growth/reactions
“continuously” monitored
Phoenix
• AST only or Combo
panels available for
– GN (Enterobacteriaceae/
Nonfermenters)
– GP (Staphylococci/
Enterococci/
Streptococci)
– Streptococci ID/AST
Phoenix
• Readings for each well taken and calculated
every 20 minutes
–
–
–
–
–
–
–
ID uses red, green, blue and UV light sources
AST measures turbidity and color change
Each well divided into pixels
Readings taken for each pixel
Entire process takes 7 minutes
Pixel data analyzed for each well
Readings for each well compared to previous
reading and baseline
• Well is complete when specific amount of
change is not seen
• Substrate/antimicrobic algorithm dependent
– Instrument will post results when enough data
collected
Phoenix
• Expert rules within BDXpert based
on CLSI/SFM/DIN/EUCAST rules
bases
Comparison of systems
Microscan
ID available
AST available
Reading
MIC
Expert system
Biochemical ID
Plans for integration with nonbiochemical ID systems
Epidemiological software
GPOS
GNEG NH
AnO2
Yeast
GPOS
GNEG
Vitek 2
GPOS
GNEG
NH
AnO2
Yeast
GPOS
GNEG
Yeast
Phoenix
GPOS
GNEG
GPOS
GNEG
Continuous automated
or manual
Y
Published rules

Continuous automated
Continuous automated
+/Phenotypic comparison

+/Published rules







Performance
• ID
– Correct to genus >95%
– Correct to Species>90%
– Difficulties with difficult organisms
• Non-fermenters
• Shigella etc
• AST
– Concordant with other methods >95%
– Specific issues with specific drug-bug combinations
& certain instruments
• VISA/VRSA
• Beta-lactams & Pseudomonas
Performance
• ID/AST performance relies on
correct ID, correct AST plus
appropriate expert interpretation
– Incorrect ID can lead to incorrect AST
• Up to 5% errors mean that results
should be examined critically
Conclusions
• Automated systems can provide
– Reliable AST integrated with ID & expert
rules
– Improved speed of results
• Caution about staff skill mix and
interpretation of results
• Microscan/ Vitek 2 /Phoenix have similar
performance overall
– Results should be examined critically