BSAC Standardized Disc Susceptibility Testing Method - User Group Meeting.

Cardiff, 13 May 2010

Vitek 2 – A User Experience.

Nathan ReadingSenior 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 TasksReading 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 Weekday8am-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 - FlexabilityCard ‘make up’ will never perfect for every user– Bespoke cards can be made for individuals

For our UTI’sNo Amikacin on UTI card – only Gent

We now disc test Amikacin on Gent I/RAminoglycoside rules cant work properly

No MecillinamOur 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 ?

• *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?

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.