BSAC Standardized Disc Susceptibility Testing Method - User Group
Meeting.
Cardiff, 13 May 2010
Vitek 2 – A User
Experience.
Nathan Reading
Senior Biomedical Scientist
Sandwell and West Birmingham Hospitals NHS Trust
1 Year B.V. (before Vitek....)
• Previously....
– Disc susceptibilities for >90% isolates
•
•
•
•
•
Urines
Blood Cultures (Direct and Repeats)
Respiratory
Ocular
General – swabs etc
– Agar Dilution MIC’s
• All Pseudomonads
• Resistant gram negatives
• Ad-hoc organism/difficult infections
– Gradient Tests
• Difficult organisms
• Adhoc testing/confirmations
1 Year B.V. (before Vitek....)
Staffing required..
1 Senior BMS W.T.E.
2x BMS W.T.E.
0.5 MLA W.T.E.
Daily/Weekly Tasks
Reading Plates/Setting Up Disc Susceptibility Plates and pouring Agar
Dilution Plates/Preparing Antibiotic Stocks and Dilutions/Setting up MIC
plates/Reading MIC Plates.
Working Day
8am-5pm Weekday
8am-12pm Saturdays (All sensitivities bar MIC’s read, all sensitivities put
up bar urinary isolates)
8am-1pm Sundays (Only Blood Culture and MRSA sensitivities setup/read)
Sensitivity testing 1 Year AV
(after Vitek...)
• 1 x Senior BMS WTE
• 1x BMS WTE
• 0.6 xMLA WTE
– Reduced staff overhead
– Senior BMS freed to look after our organism collection
• All sensitivity testing complete >90% time by 4pm
• Sensitivity testing ready for release to clinician by 10-11am
• We do not release same day sensitivity testing....
– Do not wish to retract incorrect reports
– Our working days structure currently means that cards not going onto Vitek
until mid morning earliest
Sensitivity testing 1 Year AV
• Gram negatives
– UTI
• Use Chromogenic Media
• E.coli – treated as E.coli, Vitek Sens
• Coliform group – Vitek Sens and Automated ID also
– Systemic -Fermenters
• Automated ID and Sensitivity Test
– Non fermenters
• Automated ID or Basic Manual ID
• Automated Sensitivity Test
Blood Cultures
– Direct disc susceptibility – in-house dilution protocol
• Repeats by Vitek
Sensitivity testing 1 Year AV
• Gram positives
– Staphylococci
• Vitek Sensitivity
• Manual ‘traditional’ ID
• API/Vitek GP Card for discrepant organisms
– Enterococci
• Vitek Sensitivity
• Antibiogram/API/Vitek GP card if speciation needed
– Beta Haem Streptococci
• Vitek (Group B) and Discs (All others)
• Fastidious Organisms
– Discs!
Issues - Flexability
Card ‘make up’ will never perfect for every user
– Bespoke cards can be made for individuals
For our UTI’s
No Amikacin on UTI card – only Gent
We now disc test Amikacin on Gent I/R
Aminoglycoside rules cant work properly
No Mecillinam
Our clinicians want Mecillinam on all Trim R
isolates of E.coli/Kleb/Proteus can be 30%
isolates!
Issues – Antibiotic Concentrations
• Rifampicin
– Card tests at 0.25,0.5 and 2mg/L
– Calling range 0.25-4mg/L
– EUCAST/BSAC ‘S’ cut off = 0.06mg/L ‘I‘= 0.12-0.5
‘R’ =>0.5
– Card does not test low enough to determine S
using BSAC/EUCAST breakpoints
• Recent card revision did not solve this
• Now need to disc test on ad-hoc basis if clinicians
require result
Issues – Antibiotic Concentrations
• Mupirocin
– Card tests 1mg/L
• Calling range 2-8mg/L!
BSAC ranges S= ≤4 I= 8-256 R >256
– Need to disc test to differentiate I from R
• Mupirocin decolonisation may still work if Intermediate
• Recent revision to cards did not solve this.....
Detection of resistance
• Detection of Hyperproduction of K1 enzyme in
Kleb oxytoca
– No Aztreonam on UTI Card AST N144
– Need to rely on Inhibitor Resistance and
Cefotaxime which can be variable
– Offline Synergy Test
• Cefpodoxime/Cefpodoxime+Clav/Cefpodoxime+Clav+Boronic Acid
• Aztreonam disc testing
Detection of resistance
• Detection of AmpC
Detection of AmpC
• Cefoxitin Resistant
• 3rd Gen Ceph’s = S
• Check ID
– Some Chromogenic agars mis-identify Citrobacter
species (may have natural AmpC)
• Check ESBL/Confirmation Test
– Cefpodoxime/Cefpodoxime+Clav/Cefpodoxime+Clav+Boronic Acid
– If negative synergy – probable impermeability/porin loss
– If positive synergy with Boronic Acid/Clav/Cefpodozime = AmpC
Detection of Resistance
• Detection of ESBL
• Compared 296 urinary isolates screened with
HMRZ -86 a chromogenic 3rd gen Cephalosporin
– Vitek missed 11 ESBL producers out of a total of 42
– Situation improved a little on software update
• ?algorithms changed
• Still misses some low expression of ESBL
Solution ?
• All of the missed isolates (ESBL&AmpC)
reduced zone to Cefpodoxime 10ug disc
• ?Need a Vitek card containing Cefpodoxime
• 18 missed isolates E.coli/Klebsiella
• 10 ESBL Missed with routine card
• 7 AmpC Missed with routine card
• 1 K1 K oxytoca (included for interest)
Solution ?
Cefpod
Ceftaz
Ceftriax
AES Findings
Escherichia coli
17
ESBL
acquired penicillinase
>8
≤1
≤1
ESBL
Escherichia coli
10
AMP C
acquired penicillinase
>8
≤1
≤1
Inconsistent
Escherichia coli
14
ESBL
acquired penicillinase
2
≤1
≤1
Acquired Penicillinase
Escherichia coli
15
ESBL
acquired penicillinase
0.5
≤1
≤1
Acquired Penicillinase
≤1
≤1
Acquired Penicillinase
Isolate ID
CPD Routine
Zone/ Method
mm Findings
AES Findings
ACQ Penicillinase +
Impermeability (Cephamycins), <0.25
Impermeability (Cephamycins)
Klebsiella pneumoniae
14
AMP C
Escherichia coli
11
amp c
acquired penicillinase
>8
≤1
≤1
Inconsistent
Klebsiella oxytoca
18
?K1 hyper
high level natural penicillinase
2
≤1
<1
ESBL (ctx-m), high level
natural penicillinase
Escherichia coli
21
amp c
ACQ Penicillinase
2
≤1
≤1
Acquired Penicillinase
Escherichia coli
13
ampc
Acq Penicillinase
>8
≤1
≤1
Inconsistent
Escherichia coli
18
esbl
Acq Penicillinase
4
≤1
≤1
Acquired Penicillinase
Escherichia coli
18
AMP C
Acq Penicillinase
2
≤1
≤1
Acquired Penicillinase
Escherichia coli
12
AMP C
Acq Penicillinase
>8
≤1
≤1
Inconsistent
Escherichia coli
15
ESBL
Acq Penicillinase
>8
≤1
≤1
ESBL
Escherichia coli
14
ESBL
Acq penicillinase
2
≤1
≤1
Acquired Penicillinase
Escherichia coli
14
ESBL
Acq penicillinase
4
≤1
≤1
Acquired Penicillinase
Escherichia coli
14
ESBL
Acq penicillinase
2
≤1
≤1
Acquired Penicillinase
Escherichia coli
17
ESBL
Acq penicillinase
2
≤1
≤1
Acquired Penicillinase
Escherichia coli
16
ESBL
Acq penicillinase
2
≤1
≤1
Acquired Penicillinase
• *BSAC Cefpodoxime ‘S’ cut off 1mg/L
Solution ?
• 16/18 isolates all had MIC for Cefpodoxime
>1mg/L (BSAC breakpoint)
• Include Cefpodoxime on card?
– With or without CAZ,CTX?
Detection of Resistance
• What is this isolate?
• System highlights MRSA as possible mechanism –
changes Cefoxitin result from Negative to POSITIVE
Solution ?
• All isolates showing this change
– PBP 2’ Latex (Oxoid/Mast)
• 20 minute test
– If +ve therefore MRSA
– If –ve need to rule out MRSA still.
• Cefoxitin 10 disc on IsoSensitest
• MecA PCR
• Our own mini study – partially complete
– 20 isolates Oxacillin ‘R’ / Cefox Screen Changed to +ve
– 10 strains MecA negative (Internal control Nuc +ve = S.aureus)
– All 10 PBP 2’ Latex Negative
Difficult isolates
• Mucoid isolates – esp Pseudomonads
– Difficult to get a smooth inoculum
– May give false resistance/susceptibility
– Need a plan B
• MIC?
• Gradient Test?
• Discs?
More areas to investigate?
14
Vitek 2
Implentaton
12
Percentage
10
8
6
4
2
0
PERCENTAGES %I-Gent
PERCENTAGES %R-Gent
Software
upgrade
New Cards
Gentamicin and E.coli %I and %R Jan 08-Current
New and Emerging Phenotypes
• July 2009
• Our first Isolate of NDM-1 Carbapenemase in
Klebsiella pneumoniae
– Detected by Vitek 2
• Subsequent challenge with further strains
from other centres also detected as expected
• Isolates with VIM,IMP and KPC isolates also
detected.
• Carbapenemases, the new ESBL?
Summary
• Automated systems not panacea for solving
lack of AST knowledge within laboratory.
– Some users may find more questions than
answers
• BSAC method still required to fill in the gaps
– Not just fastidious organisms
• Some areas could be optimised to enhance
detection of important isolates
• Some cards need to be improved for
UK/EUCAST breakpoints
Summary – the positives
• Reduction of staff overhead
• Improved speed of results
– We at City dont make best use of all benefits of
automation
• Can be used to upskill knowledge of AST and
mechanisms of resistance
• Simple to use and well supported by the
company.