What’s New in the 2011 CLSIStandards for Antimicrobial

Susceptibility Testing (AST)?

BDDSProduct Specialist蕭玉翎Lynn Hsiao

投影片資料來源投影片資料來源投影片資料來源投影片資料來源

BY Janet A. Hindler, MCLS MT(ASCP)

CLSI AST Standards

January 2011• M100-S21 Tables (2011)*

– M100-S20-U (June 2010)• Revised carbapenem breakpoints

(Enterobacteriaceae)

• M02 A10 Disk Diffusion Method (2009)**

• M07-A8 MIC Method (2009)**

• M11-A7 Anaerobe MIC Testing (2007)

* M100 updated at least yearly

**M02, M07 updated every 3 years

Summary ofChanges

M100-S21. pp. 13.

CLSI AST Standards

Major Changes 2011 (1)• Revisions

– Enterobacteriaceae – cefazolin breakpoints (again!)

– Enterobacteriaceae – carbapenem breakpoints (June 2010)

– Pseudomonas aeruginosa – aztreonam and cephalosporin breakpoints (reassessed)

– Appendix A - Verification (Confirmation) of unusual AST results

• Additions– Table– inducible clindamycin resistance Streptococcus spp.

ββββ-hemolytic Group

– Anaerobe Tables

– Intrinsic Resistance Table - Enterobacteriaceae

Listing Information in Boldface Type inM100-S21…

Old comment:

• “NOTE: Information in boldface type is considered tentative for one year.”

Revised comment:

• “NOTE: Information in boldface type is new or modified since the previous edition.”

M100-S21 Table 1A. pp. 32and throughout.

To Be used with CLSI M11-A7

Enterobacteriaceae

Enterobacteriaceae - CarbapenemsRevised… Breakpoints (MIC μg/ml)

• *FDA breakpoint

• Corresponding disk diffusion breakpoints also revised

M100-S21 Table 2A. pp. 45.First published M100-S20-U (June 2010)

New CLSI Specific Carbapenem

Dosage Comment

“Because of limited treatment options for infections caused by organisms with carbapenem MICs or zone diameters in the intermediate range clinicians may wish to range, design carbapenemdosage regimens that use maximum recommended doses and possibly prolonged intravenous infusion regimens as has been reported in the literature.”

CLSI M100-S21. pp. 45.References for this suggestion in M100-S21. pp. 58.

Will tests for carbapenemases (e.g.,Modified Hodge Test) be needed with therevised breakpoints?

• No. For patient management, tests for carbapenemases are not necessary

• If requested, tests for carbapenemasesmay be done for infection control and epidemiological surveillance purposes

– Modified Hodge Test – phenotypic test for carbapenemase activity

– PCR for known carbapenemases

M100-S21 Table 2A-S2. pp. 50.

Revised breakpoint

Exmp. OLD Breakpoints - MeropenemS, I, R Reporting Strategy

1 Perform MHT if MIC 2-8 μμμμg/ml (imipenem or meropenem) or 2-4 μμμμg/ml (ertapenem) and “R” to at least one 3rd gen cephalosporin

2 Recommendation changed from CLSI M100-S20 January 2010; now report all carbapenems “R” if MHT positive

OLD Meropenem

Breakpoints (μμμμg/ml) CLSI M100-S21. Tables2A-S2, 2A-S3. pp. 54.

Exmp. NEW Breakpoints - MeropenemS, I, R Reporting Strategy

• 1 MHT not needed for routine patient reporting; may perform for Infection Control or Epidemiological Surveillance but DO NOT change “S” or “I” to “R” on patient report if MHT positive

NEW Meropenem

Breakpoints (μμμμg/ml)

CLSI M100-S21Table 2A-S2. pp. 50.

Carbapenem Resistant

Enterobacteriaceae (CRE)Two mechanisms of resistance

– Carbapenemase - β-lactamase that hydrolyzes carbapenems

– Cephalosporinase combined with porin loss

• Some cephalosporinases (e.g., AmpC β-lactamasesor ESBLs) have low-level carbapenemase activity

• Porin loss limits entry of the carbapenem into the cell

Identification of CRE is important from aninfection control perspective regardless of the

mechanism of resistance

What criteria can we use to categorize anisolate of Enterobacteriaceae as “CRE”

for infection control purposes?

• 1 isolate must fulfill criteria for at least one drug

Not in M100-S21.

JH comment.

Revised

breakpoints (μμμμg/ml)

What about Proteus / Providencia /Morganella and imipenem?

• New comment:

• “(21) Imipenem MICs for Proteus spp., Providencia spp., and Morganella morganiitend to be higher (eg, MICs in the new “I” or R” range) than meropenem or doripenemMICs.These isolates may have elevated MICsby mechanisms other than production of carbapenemases.”

M100-S21 Table 2A. pp. 45.

Why not use ertapenem to categorize anisolate of Enterobacteriaceae as “CRE”

for infection control purposes?

• Most isolates “I” or “R” to ertapenem but “S” to other carbapenems may not pose the same infection control risk as isolates ”I” or “R” to other carbapenems

• Substantial number of Enterobacteriaceae are “I” or “R” to ertapenem only and would be flagged as “CRE”– Enterobacteriaceae with chromosomal β-lactamase + porin

loss often “I” or “R” to ertapenem and “S” to other carbapenems

Bennett et al. 2010. DMID. 66:445.Woodford et al. 2007. Int J Antimicrob Agents. 29:456.

Not in M100-S21.JH comment.

Why should we try to implement revisedcarbapenem breakpoints for

Enterobacteriaceae?• Increasing numbers of isolates of

Enterobacteriaceae with decreased carbapenem susceptibility due to a variety of resistance mechanisms

• New information suggests old susceptible breakpoints may not reliably predict drug efficacy

• Will allow identification of CRE which can be communicated to infection control with minimal delay

EnterobacteriaceaeRevised (again!) Cefazolin Breakpoints

• a Breakpoints are based on a dosage regimen of 2 g every 8 h.• b Cephalothin interpretive criteria should only be used to

predict results of the oral agents, cefadroxil, cefpodoxime, cephalexin, and loracarbef. Older data which suggest that cephalothin results could predict susceptibility to some other cephalosporins may still be correct but there are no recent data to confirm this.

CLSI M100-S21 Table 2A. pp. 43.

T/R = test/report group

What are the test / report issues forcefazolin and cephalothin with urine

isolates of Enterobacteriaceae?• Most labs do not test both cephalothin and

cefazolin

• If results from testing cefazolin (with new breakpoints) are used to predict activity of oral narrow-spectrum cephalosporins for uncomplicated urinary tract infections…“resistance” will be overcalled in many isolates– Revised cefazolin breakpoints are based on

serum and not urine concentrations of drug

• Best to test / report cephalothin

Pseudomonas aeruginosa

Pseudomonas aeruginosa

Beta-lactam Breakpoints (1)• ♦ Reevaluation but no change in breakpoints for

cefepime, ceftazidime, aztreonam

• ♦ Added dosage information (ceftazidime and aztreonam dosages are different than those for Enterobacteriaceae)

M100-S21 Table 2B-1. pp. 61.

Pseudomonas aeruginosa

Beta-lactam Breakpoints (2)

• Deleted breakpoints for:

– Ceftriaxone, cefotaxime - limited indications (e.g., urinary tract infections)

– Ceftizoxime, cefoperazone, moxalactam - no longer available in USA

• Currently reexamining breakpoints for:

– Carbapenems

– Extended-spectrum penicillins

– ββββ-lactam / ββββ-lactamase inhibitor combinations

Gram-positive bacteria

Staphylococcus spp. (Table 2C)Enterococcus spp. (Table 2D)

Streptococcus spp. β-hemolytic Group (Table 2H-1)Streptococcus spp. Viridans Group (Table 2H-2)

• Added comment:

“Daptomycin should not be reported for isolates from the lower respiratory tract”

Staphylococcus spp.

Staphylococcus spp.Test/Report

• Added minocycline

• Therapy option for MRSA

• New (2011) IDSA Guidelines for treatment of MRSA at http://www.idsociety.org)

•M100-S21 Table 1A. pp. 30.

Staphylococcus spp.Penicillin and β-lactamase Testing (1)

• Revised comment:

“(11) ….. Perform an induced ββββ-lactamase test on all S. aureus isolates for which the penicillin MICs are ≤0.12 μμμμg/mL or zone diameters ≥ 29 mm before reporting the isolate as penicillin susceptible. Rare isolates of staphylococci that contain genes for ββββ–lactamase production may not produce a positive induced ββββ-lactamase test. Consequently, for serious infections requiring penicillin therapy, laboratories should perform MIC tests and induced ββββ-lactamasetesting on all subsequent isolates from the same patient. PCR testing of the isolate for the blaZ ββββ-lactamase gene may be considered.”

M100-S21 Table 2C.pp. 70.

Continuing issues for Staphylococcusspp. that test penicillin-S…(1)

• Perform an induced ββββ-lactamase test on penicillin-S Staphylococcus spp.– An induced ββββ-lactamase test does not always

detect S. aureus capable of producing ββββ-lactamase

– Revised comment in CLSI M100- S21 suggests blaZ PCR may be considered

– Very recently determined blaZ PCR not optimal• Variations of gene and need multiple primers

• Some blaZ do not produce functional ββββ-lactamase

– CLSI exploring other phenotypic ββββ-lactamasemethods

CLSI January 2011 Agenda Book.

Continuing issues for Staphylococcusspp. that test penicillin-S…(2)

• For now, a lab strategy might be to:– Report penicillin if “R”

– Suppress penicillin if “S” (except for S. lugdunensis) and add note “Contact lab if penicillin results needed” needed

– May get requests to test isolates from serious infections as endocarditis, osteomyelitis

– Upon request, test:• Induced ββββ-lactamase test

• ?blaZ PCR

• ?Other

• …and test subsequent isolates on the patient

Streptococcus spp.Beta-hemolytic Group

Streptococcus spp.Beta-hemolytic Group – Penicillin

• Revised comment:

• “(3) Penicillin and ampicillin are drugs of choice for treatment of beta-hemolytic streptococcal infections. Susceptibility testing of penicillins and other ββββ-lactams approved by the FDA for treatment of ββββ-hemolytic streptococcal infections need not be performed routinely, because nonsusceptibleisolates (ie, penicillin MICs > 0.12 and ampicillin MICs > 0.25 μμμμg/mL) are extremely rare in any ββββ-hemolytic streptococcus and have not been reported for Streptococcus pyogenes. If testing is performed, any ββββ-hemolytic streptococcal isolate found to be nonsusceptible should be re-identified, retested, and, if confirmed, submitted to a public health laboratory.”

M100-S21 Table 2H-1. pp. 100.

Group B Streptococcus spp.

Penicillin “Non-susceptible”• Japan - 1995-2005

– 14 isolates w/ penicillin MICs 0.25-1 μμμμg/ml– Modified penicillin binding proteins (PBP2X and others)– Elevated MICs to other ββββ-lactams

Kimura, et al, 2008. AAC 52:2890.• USA CDC - 1999-2005 (n=5631)

– Four isolates with PBP2X mutations in “hot spot” similar to Streptococcus pneumoniaeDahesh, et al. 2008. AAC 52:2915.

• Penicillin MICs for isolates from a patient on long term penicillin therapy went from 0.06-0.25 μμμμg/ml

Gaudreau et al. 2010. J Antimicrob Chemother. 65:594.

Streptococcus spp.

Beta-hemolytic Group*

Erythromycin / Clindamycin

* Groups A, B, C, G (large colony types)

**requires induction to show resistance

Inducible Clindamycin ResistanceStreptococcus spp. β-hemolytic Group

• “D Zone” Test:– Routine disk diffusion

method– Place 2 μμμμg clindamycin 12

mm from edge of 15μμμμg erythromycin disk.

• Broth microdilution test:– 1 μμμμg/mL erythromycin and

0.5 μμμμg/mL clindamycin in same well

Bowling et al. 2010. JCM. 48:2275.

Recommendations for Prevention of Perinatal

Group B Streptococcal (GBS) Disease

…from CDC GBS

Guidelines

Check CDC GBS website for additional guidelines for AST

Check for inducibleclindamycin R if….erythromycin-R andclindamycin-Swebsite for additional

guidelines for AST

Revised Appendix A

M100-S21 App. A. pp.144-145

Actions to take for 3 categories ofresults….

Example: Confirm vancomycin-NS(MIC >32 μg/ml) Streptococcus mitis

Example: Confirm ceftriaxone-R

(MIC >32 μg/ml) Salmonella spp.

M100-S21 App. B. pp.147

What do we mean by “intrinsic” vs.“acquired” resistance?

• Intrinsic resistance = inherent or innate (not acquired) resistance, which is reflected in wildtype antimicrobial patterns of all or almost all representatives of a species. Intrinsic resistance is so common that susceptibility testing is unnecessary.

• Acquired resistance = antimicrobial resistance in a bacterium that was previously susceptible that occurs as a result of:– Chance gene mutation– Acquisition of R genes from another bacterium

M100-S21 App. B. pp. 147.

Morganella morganii (outpatient urine)

ampicillin R

Cephalothin R

Cefuroxime S??

Ciprofloxacin R

Nitrofurantoin S??

trim-sulfa R

Refer to intrinsic resistance profiles to “evaluate theaccuracy of testing methods”Results inaccurate?? - M. morganii are intrinsically“R” to cefuroxime and nitrofurantoin

What should we do?

What should we do when AST resultsdo not match intrinsic “R” profile?

• Check for any obvious errors

• Consider impact to patient care: