2 0 1 4 The Very Latest from the CLSI AST Subcommittee.swacm.org/annualmeeting/2014/handouts/20140904... · The Very Latest from the CLSI ... •Discuss new developments for the January

Susan E. Sharp, Ph.D., DABMM, FAAM Director - Regional Laboratory

Director - Regional Microbiology/Molecular Infectious Diseases Diagnostics Laboratory

Kaiser Permanente

Associate Professor - Department of Pathology Oregon Health & Sciences University

Portland, OR

The Very Latest from the CLSI

AST Subcommittee.

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http://www.swacm.org/index.htm

OBJECTIVES

•Review significant changes made in the 2012/2013 M100

documents.

•Review changes in this year’s 2014 CLSI M100-S24

document.

•Discuss new developments for the January 2015 CLSI

M100-S25 guideline.

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CLSI AST Standards – January 2014

M100-S24 Tables (2014)*

M02-A11 Disk Diffusion Method (2012)^

M07-A9 MIC Method (2012)^

* M100 updated every year

^ M02, M07 updated every 3 years

Summary of Major Changes

Changes to CLSI documents are summarized in the front of each document.

Recent breakpoint addition/revision dates are listed in the front of M100 document.

Information listed in boldface type is new or modified since the previous edition of M100 document.

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Significant changes in 2012

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Staphylococcus spp. – Penicillin - 2012

The story…..

> 90% of staphylococci are penicillin “R”

Penicillin rarely considered for treatment of staphylococcal infections

– …HOWEVER - Penicillin might be considered for infections requiring lengthy therapy (e.g., endocarditis, osteomyelitis) - IF penicillin were known to be “S”

Some Staphylococcus spp. that test “S” to penicillin by MIC or disk diffusion may actually possess a β-lactamase (BL) that may cause the patient to fail penicillin therapy.

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CLSI Previous recommendation (2011):

– If the isolate tests “S” for penicillin, perform the induced nitrocefin BL test before reporting penicillin as “S.

– PCR for the blaZ gene (codes for BL) may be considered

Penicillin Breakpoints

MIC (µg/ml) Zone (mm)

S I R S I R

≤0.12 - ≥0.25 ≥29 - ≤28

7 Reference: M100-S21 (2011) - Table 2C. Page 70

Staphylococcus aureus (BL) - 2012

Induced nitrocefin BL test usually, but not always, detects staphylococcal BLs

– Other BL tests are more sensitive for the detection of BL than the nitrocefin test:

– Cloverleaf test

– Penicillin disk zone edge test

blaZ gene PCR is also not optimal for BL

– As there are several types of blaZ genes

all types may not be detected by a single PCR assay

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– Cloverleaf test





9

?

?




– Cloverleaf test





10

?

?

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Cloverleaf Assay

for BL in S. aureus

• 5% sheep blood agar

• S. aureus ATCC 25923 as the indicator organism

• 1 unit penicillin disk

• Negative (pen-S) strain

• Isolates A-D are all BL +

(pen-R)

• Some difficulties reading

Reference: CLSI Agenda Book January 2011.

A

B

C

D

BL negative

“Cloverleaf”

12

β-lactamase positive

β-lactamase negative

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Staphylococcus aureus - 2012 Disk Zone Edge Test (10 U penicillin disk and standard disk diffusion method)

Fuzzy / “beach” =

β-lactamase negative,

Penicillin - S

Sharp / “cliff” =

β-lactamase positive,

Penicillin - R

S. aureus

supplemental QC:

Neg - ATCC 25923

Pos - ATCC 29213

Reference: M100-S22. Table 2C Supplemental Table 1. Page 83

Staphylococcus aureus 3 Lab BL Study Results (N=348), 2012

Test Sensitivity Specificity

Cefinase 77% 100%

Cloverleaf 100% 100%

Penicillin disk zone edge 96% 100%

14 Reference: CLSI Agenda Book January, 2011

Staphylococcus spp. –

Penicillin Optional Strategy - 2012

Report penicillin as “R” if tests resistant

Suppress penicillin if it tests as “S” and consider a note: “Contact laboratory if penicillin results needed.”

– If penicillin results are needed, perform:

Nitrocefin BL test (un-induced)

– If positive report as penicillin “R”

– If negative

» Penicillin zone edge test

> If Beach = Report Penicillin-S

> If Cliff = Report Penicillin-R

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S. aureus

Isolates where penicillin zones are ≥29 mm or penicillin MICs are ≤0.12 µg/ml, perform a penicillin ‘disk zone edge test’ before reporting as penicillin susceptible.

NOTE:

– S.lugdunensis isolates where penicillin zones are ≥29 mm or penicillin MICs are ≤0.12 µg/ml, perform an induced nitrocefin assay or other CLSI reference method on isolates before reporting as penicillin susceptible.

The penicillin disk zone edge test was shown to be inferior as compared to the induced nitrocefin assay and should not be used with S.lugdunensis.

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2012

Inducible clindamycin resistance in Streptococcus:

b-Streptococcus

– If performing susceptibility testing on these organisms, you should include inducible-clindamycin resistance testing.

S.pneumoniae

– The clinical significance of this mechanism of clindamycin resistance is not known for S.pneumoniae, but inducible clindamycin resistance can be detected using D-zone testing.

– If testing S.pneumoniae to clindamycin and the isolate is clindamycin-S, a test for inducible clindamycin resistance should be performed.

17 | © 2011 Kaiser Foundation Health Plan, Inc. For internal use only. October 29, 2014

NEW IN 2013

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Staphylococcus

All cephalosporins/many penicillins in the 2012 Table 2C were removed.

– Deleted all β-lactam breakpoints except penicillin, oxacillin [cefoxitin], and ceftaroline.

A statement is provided to indicate that results for cephalosporins and other b-lactam antibiotics can be predicted from the results of penicillin, oxacillin MIC, cefoxitin MIC, or cefoxitin disk diffusion testing.

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Staphylococcus spp.

M100-S22, 2012. Table 2C.

Staphylococcus spp.

2013 - Eliminated breakpoints for:

Penicillins

BL/BL inhibitor combos

Cephalosporins

Carbapenems

M100-S22, 2012. Table 2C.

Staphylococcus

Rationale for deleting these breakpoints for staphylococci:

– The 2012 breakpoints were most likely inaccurate.

They were ‘Grandfathered’ into the staphylococcal tables with other major table over-hauls in the early 2000’s.

Can deduce all anti-staphylococcal b-lactam results from penicillin and oxacillin [cefoxitin] results.

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Staphylococcus spp. β-Lactam Breakpoints Remaining

Penicillin

– Represents penicillinase-labile penicillins

Oxacillin (MIC only; no more DD)

– Represents penicillinase-stable penicillins

Cefoxitin

– Surrogate for oxacillin

Ceftaroline (added 2013)

– Cephem with anti-MRSA activity

Staphylococcus - β-Lactams Use Pen and Oxa (FOX) results to predict results for other ß-lactams

Test Results

Predicts Penicillin

Oxacillin (cefoxitin)

S S

Susceptible to: All penicillins ß-lac / ß-lactamase inhibitor combos Cephems Carbapenems

R S

Resistant to: Penicillinase-labile penicillins Susceptible to: Penicillinase-stable penicillins ß-lac / ß-lactamase inhibitor combos Cephems Carbapenems

R R Resistant to: All ß-lactams (except cephems with anti-MRSA activity, e.g., ceftaroline)

amoxicillin, ampicillin,

carbenicillin,mezlocillin

penicillin, piperacillin

ticarcillin

cloxacillin, dicloxacillin

flucloxacillin, methicillin

nafcillin, oxacillin

Staphylococcus - β-Lactams Oxa (FOX) results to predict results for other ß-lactams

Oxacillin Test

Results Predicts

S

(Do not report the penicillinase-labile penicillins)

Susceptible to: Penicillinase-stable penicillins ß-lac / ß-lactamase inhibitor combos Cephems Carbapenems

R Resistant to: All ß-lactams (except cephems with anti-MRSA activity, e.g., ceftaroline)

cloxacillin, dicloxacillin

flucloxacillin, methicillin

nafcillin, oxacillin

NEW 2013 AST QC Guidance

Table 3C. Disk Diffusion: Reference Guide to QC Frequency

Conversion from Daily to Weekly QC

Routine QC is performed each day the test is performed unless an alternative quality control plan has been established.

CLSI document M02-A11 Section 15.7 describes a QC plan using a 20-30 day protocol that if successfully completed allows a user to convert from daily to weekly quality control.

– < 1/20 or < 3/30 weekly QC testing

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NEW AST QC: 3x5 (15) Plan

Statistics

– Out-of-control results could be due to either systemic or random errors

– Systemic errors = likely to get >2 outliers out of 15 results

– Random (allowable) errors = very high probability of getting 1 outlier of 15 results due to random error (which is OK)

1/15 error: Deemed likely a random error

>2/15 errors: Deemed possible systematic error continue tests

<3/30 errors: Deemed likely random error

>4/30 errors: Deemed likely systematic error investigate

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NEW AST QC 3x5 (15) Plan

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Test 3 replicates of each QC

strain for 5 days using individually

prepared inoculum

Fail.

Continue to

include QC

each test

day. Take

corrective

action. Test another 3

replicates for 5

days

Pass. Convert

to weekly QC.

Pass. Convert

to weekly QC.

0-1 of 15 out

of range?

2-3 of 15 out

of range?

> 4 of 15 out

of range?

TOTAL: 2-3

of 30 out of

range?

> 4 of 30 out

of range?

Intrinsic Resistance Tables: 2013

Enterobacteriaceae

– Added imipenem with note that Proteus species, Providencia species and Morganella species may have elevated MICs by mechanisms other than by production of carbapenemases. Isolates that test “S” should be reported as “S”.

– Added in a Note 2 information that Enterobacteriaceae are also intrinsically resistant to clindamycin, daptomycin, fusidic acid, glycopeptides (vancomycin, teicoplanin), linezolid, macrolides (erythromycin, clarithromycin, azithromycin), quinupristin-dalfopristin, and rifampin.

Added Non-Enterobacteriaceae

Added Staphylococci

Added Enterococcus spp.

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NEW IN 2014

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Vancomycin / Staphylococci 2014

Table 2C:

– Vancomycin disk diffusion

– Previously you could use it for detecting “R”

VRSA due to the vanA gene will show no zone of inhibition around a 30-mg vancomycin disk

Any isolate with > 7mm zone must be tested with a MIC method before reporting as “S”

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- Staphylococcus species

No DD criteria !

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- Staphylococcus species

No DD criteria !

Routine QC recommendations/organism:

– Those that appear for each organism group will be streamlined.

– These new guidelines can be used for both weekly QC as well as individual drug QC.

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Streamlined QC 2014

P.aeruginosa : Table 2B-1

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CURRENT:

Routine QC Recommendations (See Tables 3A and 4A for acceptable QC ranges.)

Escherichia coli ATCC® 25922

Pseudomonas aeruginosa ATCC® 27853

Escherichia coli ATCC® 35218 (for b-lactam/b-lactamase inhibitor combinations)

NEW for 2014:





Acinetobacter : Table 2B-2

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CURRENT:





NEW for 2014:



Escherichia coli ATCC® 25922 (for tetracyclines and SXT)


Burkholderia : Table 2B-3 Stenotrophomonas : Table 2B-4

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CURRENT:





NEW for 2014:



Escherichia coli ATCC® 25922 (for chloramphenicol, minocycline, and SXT)


Other non-Enterobacteriaceae : Table 2B-5

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CURRENT:





NEW for 2014:



Escherichia coli ATCC® 25922 (for chloramphenicol, tetrayclines, sulfonamide and SXT)


Enterobacteriaceae : Table 2A

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CURRENT:




NEW for 2014:




Pseudomonas aeruginosa ATCC® 27853 (carbapenems)

Method Susceptible

Susceptible-Dose

Dependent Resistant

MIC ≤ 2 µg/mL 4–8 µg/mL ≥ 16 µg/mL

Zone Diameter

(Disk Diffusion) ≥ 25 mm 19–24 mm ≤ 18 mm

Enterobacteriaceae and cefepime

ISSUE: When the cephalosporin breakpoints to the Enterobacteriaceae were change

(lowered) in 2010, cefepime was also reviewed but the committee at that time left the

breakpoint unchanged at < 8 / 16 / > 32 ug/ml.

RESULT: The committee after MUCH discussion in 2013 voted to change cefepime

breakpoints for the Enterobacteriaceae for M100-2014 and introduce SDD.

Previous – 2013

Revised – 2014

Method Susceptible Intermediate Resistant

MIC ≤ 8 µg/mL 16 µg/mL ≥ 32 µg/mL

Zone Diameter

(Disk Diffusion) ≥ 18 mm 15–17 mm ≤ 14 mm

“Cefepime Breakpoint Change for Enterobacteriaceae and

Introduction of the Susceptible-Dose Dependent (SDD)

Interpretive Category”

Pages 18-21 of the 2014 M100-S24

(discussion of this new reporting criteria)

SDD

Cefepime SDD

Why were the cefepime breakpoints reconsidered

(20102014)?

The issue of new breakpoints for cefepime became apparent for

several reasons: Previous breakpoints were based on a higher dose of cefepime than is often

used.

Clinical failures were noted for isolates with cefepime MICs of 4 and 8

µg/mL, especially when lower doses of cefepime were used.

There are limited new drugs in the pipeline that show activity against

multidrug-resistant gram-negative bacteria: There is a need to optimize use of drugs currently available.

Designing susceptibility reports to correlate better with dosages of the drug

used is one way to help accomplish this goal.

Interpretive Criteria

Susceptible Dose Dependent – Definition:

The SDD category implies that susceptibility of an isolate is dependent on the dosing regimen that is used in the patient.

In order to achieve levels that are likely to be clinically effective against isolates for which the susceptibility testing results are in the SDD category, it is necessary to use a dosing regimen that results in higher drug exposure than the dose that was used to establish the susceptible breakpoint.

Consideration should be given to the maximum approved dosage regimen, because high exposure gives the highest probability of adequate coverage of an SDD isolate.

Cefepime SDD

Accompanying “NOTE” states: – The SDD interpretation is a new category for antibacterial

susceptibility testing, although it has been previously applied for

interpretation of antifungal susceptibility test results (see CLSI

document M27-S4).

– The concept of SDD has been included within the intermediate

category definition for antibacterials. However, this is often

overlooked or not understood by clinicians and microbiologists when

an intermediate result is reported.

– The SDD category may be assigned when doses well above those

used to calculate the susceptible breakpoint are approved and used

clinically, and where sufficient data to justify the designation exist

and have been reviewed.

– When the intermediate category is used, its definition remains

unchanged.

Cefepime SDD

NOTE: – The SDD interpretation is a new category for antibacterial susceptibility

testing, although it has been previously applied for interpretation of

antifungal susceptibility test results (see CLSI document M27-S4).

– The concept of SDD has been included within the intermediate category

definition for antibacterials. However, this is often overlooked or not

understood by clinicians and microbiologists when an intermediate

result is reported.

– The SDD category may be assigned when doses well above those used

to calculate the susceptible breakpoint are approved and used clinically,

and where sufficient data to justify the designation exist and have been

reviewed.

– When the intermediate category is used, its definition remains

unchanged.

Cefepime SDD

SDD is recommended instead of

“intermediate” when reporting cefepime results

for Enterobacteriaceae isolates because:

– There are multiple approved dosing options for

cefepime, and

– SDD highlights the option of using higher doses to

treat infections caused by isolates when the

cefepime MIC is 4 or 8 µg/mL or the zone is 19 to

24 mm.

Cefepime SDD

Why is SDD being used now?

It has become apparent that there is a growing need to refine susceptibility reporting to maximize clinicians’ use of available drugs.

Intermediate too often means “resistant” to clinicians because they do not appreciate the full definition of “intermediate.”

SDD is more specific and it conveys what we know—a higher dose can be considered for isolates with MICs (or zones) that fall in this interpretive category.

SDD is already well established for use in antifungal susceptibility testing.

It is anticipated that reporting a cefepime SDD result will encourage clinicians to consider the possibility that cefepime may be an option for treatment.

Antibiotic stewardship programs, which emphasize dosing regimen and duration of therapy options, are increasing awareness of appropriate use of antibiotics. Personnel from these programs should be able to describe the significance to clinicians of an SDD result for cefepime.

Cefepime SDD

How should this change be implemented?

Meet with the appropriate practitioners at your institution (members of the antimicrobial

stewardship team, infectious disease staff, pathology group, pharmacy, etc.) to inform them of these

changes and agree on a plan to inform your clinicians of this change.

Talk to the manufacturer of your antimicrobial susceptibility testing device to determine how to

implement the revised breakpoints on your device.

– NOTE: Because the US Food and Drug Administration (FDA) has not revised the cefepime

breakpoints and commercial manufacturers must use FDA breakpoints, the manufacturer cannot

adopt the new CLSI cefepime breakpoints. However, for most systems, you can manually change

the breakpoints and implement following a verification study.

Work with your laboratory information system staff to report “SDD” or “D” for

Enterobacteriaceae when the cefepime MIC is 4 or 8 µg/mL. Make certain that SDD will be

transmitted to the hospital information system and appropriately displayed on reports viewed by

clinicians.

Distribute user-specific educational materials to laboratory staff and clinicians receiving

antimicrobial susceptibility testing results from your laboratory. Examples of these materials can be

found on the CLSI Subcommittee on Antimicrobial Susceptibility Testing webpage at www.clsi.org.

What coming in 2015?


Quality Control -

Continuing to look at ways to decrease routine QC testing

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Currently = The M2/M7 text and flowchart clearly indicates that you must perform 5 consecutive days of repeat QC “if” you can not attribute the out-of-range result to a specific issue.

– If you can contribute it to a particular issue (e.g., contamination, used the wrong QC strain, etc.), you only have to do one repeat and if ‘in’, you may continue weekly QC testing.

However, the above does not address the 0-5% of out-of-range results which would be expected due to random error (as ranges are established based on > 95% agreement).

– One suggestion is to use retrospective data from the same lot of materials to satisfy the 5 replicate repeat. This would not be a "statistical" change, only a change in approach.

Also considering to allow for multiple replicates in one day to determine more quickly if there is a problem (as laboratories may still be testing patient specimens while troubleshooting).

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Out-of-Range QC – 2015 (p.216-217 M100-S24)

Out-of-Range QC – 2015

Adding a new section in M2/M7 for Troubleshooting out-of-range results:

If the cause can be identified –

– Correct the issue, document the reason, and retest the strain on the day the error is observed.

– If the repeated result is within range, no further corrective action is required.

If the cause can not be identified -

– If the 4 previous QC results have been acceptable using the same lots of materials (e.g., agar plates, disks, MIC trays/plates/panels), these 4 results, along with the current repeat, may be used to ‘retrospectively’ satisfy the requirement for 5 repeats.

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Out-of-Range QC – 2015

Example - If the cause can not be identified:

If the 4 previous QC results were acceptable (same lots) and you now obtain an out-of-range result, repeat the QC as soon as possible and if this repeat is within range, the corrective action was successful and you can resume weekly testing.

– If the repeat is out-of-range you must take additional corrective action, and daily QC must be continued until the problem is resolved.

If 4 previous QC results were not acceptable or not available (e.g., new lot recently put into use), test sufficient QC replicates to satisfy the requirement for a total of 5 results.

– Up to 3 QC replicates can be tested/day if individual inocula are used.

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Week Day MIC panel Lot # Results Action

1/1 Mon 1234 2

1/8 Mon 1234 8

1/15 Mon 1234 8

1/22 Mon 1234 4

1/29 Mon 1234 16 Out of range. Repeat QC testing same day.

1/30 Tues 1234 2 In range. 5/6 acceptable in range QC tests for

E.coli ATCC 25922 and ampicillin with lot 1234.

Resume weekly QC testing.

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If you have an out of range QC result upon weekly QC testing, you will be able to

repeat the QC once - if in range, and if the last 4 times you previously tested were

also in range (same lot #s) you can go back to weekly QC testing (example below).

Example 1 - Cause can not be identified E.coli ATCC 25922 ampicillin: range 2-8 ug/ml

Week Day MIC panel Lot #

Results Action

1/1 Mon 8999 4

1/8 Mon 4567 2

1/15 Mon 4567 8

1/22 Mon 4567 16 Out of range. Repeat QC testing same day.

1/22 Tues 4567 4 In range. 3 acceptable in range QC tests for E.coli

ATCC 25922 and ampicillin with lot 4567. Repeat

QC for 2 more consecutive days.

1/22 Wed 4567 8 In range.

1/22 Thur 4567 2 In range. 5/6 acceptable in range QC tests for

E.coli ATCC 25922 and ampicillin with lot 4567.

Resume weekly QC testing.

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You may also repeat the QC testing prospectively - do as many as you need to get

the 5/6 to be in range (same lot #s) (e.g.; 2 retrospective and 3 prospective). If all

within range, you and can go back to weekly QC (example below).


Week Day Lot # Results Action

1/1 Mon 4002 4

1/8 Mon 7891 2

1/15 Mon 7891 8

1/22 Mon 7891 16 Out of range. Repeat QC testing x3 same

day from different starting dilutions.

1/22 Tues (1st) 7891 4 3 replicates from different starting dilutions

are in range. 5/6 acceptable in range QC

tests for E.coli ATCC 25922 and ampicillin

with lot 7891. Resume weekly QC testing.

1/22 Tues (2nd) 7891 2

1/22 Tues (3rd) 7891 8

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You may also do up to 3 replicates per day (same lot #s) using

different starting dilutions (example below).


Using retrospective data to go to weekly testing:

– If you have been performing intermittent QC testing of a drug each time you test patient organisms, you will be able to use those contemporary (within the last year) retrospective results in order to collect data that can be used for going to weekly QC testing.

– For example, if you have QC tested a drug approximately 2x/month for the last year (but requests are starting to pick up), you can use the most recent 20 QC tests to document your ability to go to weekly QC testing for the drug.

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Streamlined QC – 2015 M2/M7 (?)

Streamlined QC 2015 M2/M7 (?)

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Date

tested

LOT # disk/MHA

Results OK

(Y/N)

11/13/13 123/258 Y

12/12/13 123/456 Y

12/22/13 123/456 Y

1/1/14 123/003 Y

1/15/14 456/003 Y

1/29/14 456/003 Y

2/5/14 456/225 Y

2.26.14 456/225 Y

3/3/14 456/258 Y

3/26/14 456/258 Y

4/16/14 456/459 Y

4/20/14 788/459 Y

5/1/14 788/459 Y

5/17/14 788/560 Y

6/6/14 788/560 Y

6/18/14 788/777 Y

7/3/14 788/777 Y

7/30/14 909/777 Y

8/16/14 909/889 Y

8/25/14 909/889 Y

20 days consecutive QC testing days

= all acceptable begin weekly QC

Salmonella M100-S15

The pefloxacin (5ug) disk test was approved to screen for fluoroquinolone resistance for use in countries that cannot readily perform MIC testing.

– Screening breakpoint were approved at <23mm (resistant), >24mm (susceptible).

– The M100 will state that the pefloxacin disk test is the preferred method for fluoroquinolone resistance screening in Salmonella spp.; however, these disks are not currently available in the U.S. and may not be for some time.

Breakpoints for azithromycin with Salmonella Typhi were approved for resistant isolates seen (1o outside the US).

– The new breakpoints will be published in 2015 M100 document and will be: <16mg/ml (>13mm)-Susceptible; >32mg/ml (<12mm)-NonSusceptible


M-45 Guideline – third edition:

Revisions will be coming in this third edition for susceptibility testing with fastidious organisms.

– Includes 5 new organism groups (Lactococcus, Micrococcus and assorted related genera [Kocuria, Nesterenkonis, Dermacoccus and Kytococcus spp.], Rothia, Aerococcus and Gemella).

– Other existing groups will have additional antibiotics added or modified.

– Plesimonas shigelloides will be moved to the M100 document (enterobacteriaceae) and out of the Aeromonas group in M-45.

– Will look to harmonize the b-lactam breakpoints of Aeromonas to those of the Enterobacteriaceae in the M100 document.


SDD - Susceptible Dose-Dependent

The CLSi will consider developing SDD breakpoints for the following b-lactam antibiotics with the enterobacteriaceae:

– aztreonam

– cefotaxime

– ceftriaxone

– cefoxitin

– ceftazidime

They will also consider the possibility of developing SDD breakpoints with Pseudomonas aeruginosa:

– ceftazidime

– aztreonam

– cefepime


Carbapanemase detection

The CLSI will develop the CarbaNP as a standardized reference test for detection of carbapenemases in GNRs.

– It is based on in vitro hydrolysis of carbapenems by bacteria containing carbapenems, which is detected by a changes in pH using the indicator phenol red [red (-) to yellow(+)].

– This standardized protocol should be published in the 2015 M100-S15 guidelines.

M100 document - miscellaneous:

Will remove 12 drugs from Table 1 (‘antimicrobials suggested for routine testing and reporting’) in the M100-S15 document as they are no longer available for use in the U.S.

The CLSI will also be looking at placing new, clarified information (with pictures!) for reading ‘trailing’ endpoints in broth microdilution microtiter tray assays.

The 2015 M100-S15 document will have an updated national anaerobe antibiogram table (from isolates testing from 2010-2012).


New Antibiotics

Oritavancin

A new lipogycopeptide antibiotic for use in acute soft skin and tissue infections caused by resistant Gram positive cocci.

It is reported that this drug may be given as a single bolus dose that may work as well as 7-10 days of twice daily vancomycin therapy for these organisms.

The committee may look to see if a vancomycin disk testing might work as a screening test for susceptibility to this new antibiotic.


All cephalosporins/many penicillins in the 2012 Table 2C were removed for 2013.

– Deleted all β-lactam breakpoints except penicillin, oxacillin [cefoxitin], and ceftaroline.

A statement is provided to indicate that results for cephalosporins and other b-lactam antibiotics can be predicted from the results of penicillin, oxacillin MIC, cefoxitin MIC, or cefoxitin disk diffusion testing.

67

Remember this? Staphylococcus – 2013

Oxacillin Test Results

Predicts

S

Susceptible to: Penicillinase-stable penicillins ß-lac / ß-lactamase inhibitor combos Cephems (= cephalosporins) Carbapenems

R Resistant to: All ß-lactams (except cephems with anti-MRSA activity, e.g., ceftaroline)

MSSA and Ceftriaxone Etest issue: CLSI & ASM White Paper

A recent paper Pickering, et al, (“Common Occurrence of Ceftriaxone-

Resistant, Methicillin-Sensitive Staphylococcus aureus at a Community Teaching

Hospital”), published in Clinical Infectious Diseases has been RETRACTED.

– The paper reported that although the rate of ceftriaxone resistance in methicillin-susceptible S.aureus (MSSA) in the literature is ~3%, at their institution 60% of MSSA isolates tested non-susceptible to ceftriaxone.

– The authors went on to state that ceftriaxone susceptibility cannot be predicted by testing oxacillin (or cefoxitin) as suggested by the CLSI M100-S23 document

Indication that they found MICs to oxacillin of <0.5 mg/mL in all of their ceftriaxone-R isolates.

– They concluded that MSSA isolates should be tested for susceptibility to ceftriaxone before this agent is used to treat serious MSSA infections. Again, this article has been RETRACTED.


The reason behind this retraction is that the authors used Etest to perform ceftriaxone MIC testing on the MSSA isolates (did not use standardized microbroth dilution [BMD] methods).

– Based on additional studies, it is now apparent that the ceftriaxone Etest will over call resistance in MSSA as compared to standardized BMD testing.

The CDC acquired 16 of the MSSA/“ceftriaxone non-susceptible” isolates from the Pickering study.

– These 16 isolates were tested by ceftriaxone BMD at the CDC and all of the isolates had results in the susceptible range (MIC range 2-4mg/mL).

– Although there are no current CLSI breakpoint MIC values for ceftriaxone with the staphylococci (the 2012 CLSI M100 breakpoint for susceptible was <8mg/mL), the FDA susceptible breakpoint for ceftriaxone with staphylococci is <4mg/mL.



In addition, the microbiology laboratory at Massachusetts General Hospital (MGH) did additional studies with 30 MSSA from their patient population with ceftriaxone.

– BMD MIC: 29/30 isolates MIC of 2 or 4 (1 isolate had an 8mg/ml) when tested

– Etest: all isolates had MIC results as follows:

4 mg/ml (3 isolates)



>32 mg/ml (4 isolates)

– Thus, the Etest showed many major errors as compared to BMD testing and should not be used to test staphylococci to ceftriaxone.

It should also be pointed out that the ceftriaxone Etest is not approved for testing against Staphylococcus isolates in US.



Per FDA breakpoints; 17/20 isolates non-S/CRO


FDA breakpoint: < 4

Previous 2012 CLSI breakpoint: < 8


Massachusetts General Hospital Study

Take home…

A recent paper (Pickering, et. al.) published in CID stating that MSSA isolates were 60% resistant to ceftriaxone HAS BEEN RETRACTED.

Current CLSI M100 documents stating that oxacillin (cefoxitin) testing can be used for predicting the susceptibility of ceftriaxone for staphylococci can and should be used.

The ceftriaxone Etest is not FDA approved for testing against staphylococci and will overcall resistance in MSSA if used.

There is a need for reference confirmatory testing of any new resistance seen.



Summary -

CLSI updates AST tables (M100) each January.

CLSI updates documents that describe how to perform reference disk diffusion (M02) and reference MIC (M07) tests every 3 years (new ones due out in 2015).

Changes to CLSI documents are summarized in the front of each document.

Information listed in boldface type is new or modified since the previous edition.

Recent breakpoint addition/revision dates are listed in the front of M100.

Minutes of CLSI AST Subcommittee meetings and other materials are available at www.clsi.org.

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http://www.clsi.org/

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Watch for the January 2015 M100-S25 document!

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Documents

2 0 1 4 The Very Latest from the CLSI AST Subcommittee.swacm.org/annualmeeting/2014/handouts/20140904... · The Very Latest from the CLSI ... •Discuss new developments for the January