Overview of the Nebraska Public Health Laboratory:

Nebraska Public Health
2008 CLSI M100-S18 update
Paul D. Fey, Ph.D. Associate Professor/Associate Director
Josh Rowland, M.T. (ASCP) State Training Coordinator
• Discuss 2008 M100S18 major changes
– Organism specific
– KPC carbapenemase
• Other AST issues and
questions from
discussion group
Issue 1-New Appendices
• Appendix A -ESBL screening
• Appendix B -Staphylococcus aureus
susceptibility testing issues
• Appendix C -Coagulase-negative
Staphylococcus susceptibility testing issues
• Appendix D -Screening for high-level
Aminoglycoside resistance within the enterococci.
Tables 1 and 1A-Antibiotic reporting
• Starting pages 24 (Disk diffusion) and 86 (MIC). Tables 1
and 1A.
• Changes Table 1:
– Tobramycin moved from group B (selective reporting) to group A
(primary) in Enterobacteriaceae and Pseudomonas aeruginosa.
– Ticarcillin moved from group A to group B in Enterobacteriaceae
and Pseudomonas aeruginosa.
– Macrolides, Clindamycin, Trimethoprim/sulfa. moved to group A
under Staphylococcus.
– Note that Daptomycin is MIC only-do not use disk diffusion disks
– Acinetobacter spp. Ampicillin-sulbactam, ciprofloxacin,
levofloxacin and gentamicin, tobramycin moved to group A.
Tables 1 and 1A-Antibiotic reporting
• Starting pages 24 (Disk diffusion) and 86 (MIC).
Tables 1 and 1A.
• Changes table 1A
– Note that “Streptococcus spp. other than
Streptococcus pneumoniae” column has been split into
two columns: 1) Streptococcus spp. Beta-hemolytic
group (Groups A, B, C, and G) and 2) Streptococcus
spp. Viridans group (Small colony forming b-hemolytic
colonies [ S. anginosus] are included in this group).
Haze in zone of inhibition
• New comments on M2-disk diffusion tables about appropriate
methods to read zones of inhibition to certain antibiotics—i.e.
Proteus mirabilis and swarming, trimethoprim-sulfamethoxazole
testing, etc. Please read all comments if disk diffusion is common in
your laboratory.
• Page 52—”Organisms that show hazy growth throughout the zone of
inhibition around the clindamycin disk should be reported as
clindamycin resistant, whether or not they show a D-zone.”
• To detect any type of colonies that may show resistance-Page 52”When testing linezolid, disk diffusion zones should be examined
using transmitted light. Organisms with non-susceptible results
should be confirmed using an MIC method.”
Streptococcus pneumoniae
• If you are performing disk diffusion to detect
resistance in Streptococcus pneumoniae, read
page 66.
– “Penicillin MICs should be determined for those
isolates with oxacillin zone diamters < 19 mm,
because zones of < 19 mm occur with penicillinresistant, intermediate, or certain susceptible strains
based upon the meningitis and oral penicillin V
interpretive criteria given in M7, Table 2G. Isolates
should not be reported as penicillin-resistant or
intermediate based solely on an oxacillin-zone < 19
Streptococcus pneumoniae
• Significant reporting changes regarding penicillin
– Interpretive standards for parenteral penicillin nonmeningitis, meningitis, and oral penicillin nonmeningitis.
– On meningitis isolates, only report meningitis
interpretive standards.
– On non-meningitis isolates (e.g. pneumonia or blood),
report both meningitis and non-meningitis interpretive
Streptococcus pneumoniae isolated
from blood-penicillin MIC of 1
Ceftriaxone (meningitis)- <0.5 S
Ceftriaxone (non-meningitis)- <0.5 S
Erythromycin->1 R
Levofloxacin- <0.5 S
Penicillin (meningitis)-1 R
Penicillin (non-meningitis)-1 S
Penicillin oral (non-meningitis)-1 I
Vancomycin-0.5 S
• Based on therapy
category, different
interpretive standards.
• Multiple comment
suggestions in the CLSI
• These changes must
reflected in your
Staphylococcus aureus changes
• Page 111. Cefoxitin MIC test to detect methicillin
resistance—only reliable for S. aureus and S.
– “The results of cefoxitin MIC tests can be used to
predict the presence of mecA-mediated resistance in
S. aureus and S. lugdunensis. Isolates for which
cefoxitin MICs are > 8 mg/ml should be reported as
resistant. Isolates for which the cefoxitin MICs are < 4
mg/ml should be reported as oxacillin susceptible.”
Staphylococcus aureus changes
• Page 114-Erythromycin-resistant and clidamycinsusceptible isolates. New approved way to
detect inducible resistance to clindamycin. Well
containing 4 mg/ml erythromycin and 0.5 mg/ml
clindamycin—growth in the well indicates
resistance to clindamycin.
KPC carbapenemase
• Enzyme capable of hydrolyzing carbapenems (imipenem,
ertapenem, meropenem, doripenem).
• Isolated primarily on the east coast of US in ICUs.
• Klebsiella pneumoniae and other Enterobacteriaceae.
• KPC not easily detected using commercial susceptibility
systems—some isolates have an MIC of 2 to the
carbapenems (still susceptible)
• KPC enzymes hydrolyze expanded-spectrum
cephalosporins as well—therefore, all Enterobacteriaceae
isolates that have an ESBL phenotype should be
screened for a carbapenemase.
KPC carbapenemase
• Ertapenem most useful carbapenem to detect KPC.
• If ertapenem is not on your panel, suggest that all
ESBL/AmpC-like Enterobacteriaceae (i.e. expandedspectrum cephalosporin resistant) be tested with
ertapenem (and other carbapenems) by disk diffusion or
MIC method (E-test).
• If isolate has MIC of > 2 mg/ml (susceptible isolates
should have an MIC of < 0.5 mg/ml), contact physician
and send isolate to reference laboratory.
– Modified Hodge test
– PCR for KPC

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