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Automated systems:an overview

Robin A HoweCardiff

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

93.1

75.0

94.4 95.5

66.974.7

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% A

gree

men

t

Lab 1 Lab 2 Lab 3 Lab 4 Lab 5 Total

Laboratory

Inter-laboratory ID comparisons

ID Disagree

ID Agree Genus

ID Agree

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 negative panel

Welsh Gram positive panel

Drug RangeAmikacin 4 - 32Gentamicin 1 - 8Tobramycin 2 - 8Ampicillin 4 - 32Amoxicillin/Clav 2/1 - 32/16Cefotaxime 1 - 4Cefoxitin 1 - 4Ceftazidime 2 - 16Cefuroxime 4 - 16Cephalexin 4 - 16Ciprofloxacin 0.25 - 2Aztreonam 1 - 16Imipenem 1 - 8Meropenem 1 - 8Ertapenem 0.5 - 4Colistin 1 - 4Piperacillin/Tazo 4/4 - 32/4Trimethoprim 0.5 - 4Trimethoprim/Sulfa 0.8/15.2 - 3.2/60.8Nitrofurantoin 16 - 64Levofloxacin 0.5-2

Drug RangeGentamicin 1 - 4Penicillin 0.06 - 0.25Oxacillin 1 - 4Ampicillin 2 - 16Amoxicillin/Clav 1/0.5 - 16/8Levofloxacin 0.5 - 2Ciprofloxacin 0.5 - 2Cefoxitin 2 - 8Linezolid 2 - 8Erythromycin 0.25 - 1Clindamycin 0.25 - 1Daptomycin 1 - 16Chloramphenicol 1 - 16Nitrofurantoin 16 - 64Fusidic Acid 1 - 8Rifampin 0.25 - 1Minocycline 0.5 - 2Mupirocin 1 - 4Mupirocin - HL 256Teicoplanin 1 - 16Tetracycline 0.5 - 2Trimethoprim 0.5 - 4Vancomycin 1 - 16GM-Syn 500ST-Syn 1000

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 non-fermenters, 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

TIME (hours)0 1 2 3 4 5 6 7 8 9 10 11 12 1413 1615 17 18

Raw Data

% Change

Slope

Area

SLPAR

Interpretation of Raw Data

Growth Parameters

MIC

VITEK 2 – MIC Interpretation

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 2 to 10 hours

GP ID 2 to 8 hours

NH ID 6 hours

ANC ID 6 hours

YST ID 18 hours

GN AST 2 to 18 Hours

GP AST 2 to 18 Hours

AST-YS01 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 Vitek 2 Phoenix

ID available

GPOS GNEG NH

AnO2 Yeast

GPOS GNEG

NH AnO2 Yeast

GPOS GNEG

AST available GPOS GNEG

GPOS GNEG Yeast

GPOS GNEG

Reading Continuous automated

or manual Continuous automated Continuous automated

MIC Y +/- +/- Expert system Published rules Phenotypic comparison Published rules Biochemical ID Plans for integration with non-biochemical ID systems

Epidemiological software

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