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Culture and Sensitivity Helping the Infection Preventionist Interpret Antibiograms

Culture and Sensitivity Helping the Infection Preventionist Interpret Antibiograms. Walter Phillips, BS, MS, PhD Director of Microbiology TriStar Healthcare System. Acknowledge. I would like to acknowledge the following contributors to this presentation:

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Culture and Sensitivity Helping the Infection Preventionist Interpret Antibiograms

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  1. Culture and Sensitivity Helping the Infection Preventionist Interpret Antibiograms Walter Phillips, BS, MS, PhD Director of Microbiology TriStar Healthcare System

  2. Acknowledge I would like to acknowledge the following contributors to this presentation: • Sheldon Campbell MD, PhD, FCAP • Janet Hindler, MCLS MT(ASCP)

  3. Objectives At the conclusion of this presentation, the participant will be able to: • Discuss the purpose of an antibiogram. • Recall the acronym CLSI. • Recognize antibiograms for MRSA, VRE, ESBL and CRE. • Define MDRO.

  4. What to Test • CLSI M-100 Sx (where x is an edition number) • Issued yearly, gives guidelines • Keep up! • Don’t report everything • Conform to facility formulary • Report narrow-spectrum / inexpensive agents routinely • Reserve broad-spectrum / expensive agents for resistant isolates

  5. Group A Group B CLSI M100-S24 Table 1A.

  6. CLSI M100-S24. Table 1A..

  7. Antimicrobial Susceptibility Testing • Can I use this drug to treat this bug? • With tolerable doses, will enough drug get to the site of infection to kill the bug? • MIC • Minimal Inhibitory Concentration • broth-based, micro and macro methods • Disc Diffusion • E-test

  8. MIC Testing • Liquid media with varying dilutions of antibiotic • Lowest concentration that inhibits growth is the MIC • Minimal Inhibitory Concentration • Various formats available, automated and non-automated

  9. How to Report • Susceptible, Intermediate, Resistant (S,I, R) S - means susceptible to usual doses in accessible sites • It does NOT mean in the middle of a giant polymicrobial abscess I- means susceptible at increased doses or where the drug is concentrated • Usually means a drug to use in urineor if no better choice is available R- means resistant to usual doses • The S, I, R MIC and disk-zone cutoffs are set by CLSI using epidemiological and pharmacodynamic data. • There may be additional value in some settings to report numerical MICs.

  10. EnterobacteriaceaeCefepime MIC (µg/ml) Breakpoints (13) The interpretive criterion for susceptible is based on a dosage regimen of 1 g every 12 h. The interpretive criterion for SDD is based on dosing regimens that result in higher cefepime exposure, either higher doses or more frequent doses or both, up to approved maximum dosing regimens. SDD = “Susceptible Dose Dependent” CLSI M100-S24. Table 2A.

  11. Specimen: Wound drainageDiagnosis: TraumaStaphylococcus aureus clindamycin ≤0.5 S erythromycin ≤0.5 S oxacillin ≤0.5 S penicillin R vancomycin≤0.5 S MIC (g/ml) “Oxacillin-S and penicillin-R staphylococci are susceptible to other anti-staphylococcal ß-lactams (except amoxicillin, ampicillin, and penicillins).” Final Report with Optional Comment

  12. Specimen: BloodDiagnosis: Severe cellulitisStaphylococcus aureus ceftaroline 0.5 S clindamycin >4 R daptomycin 0.5 S doxycycline ≤1 S erythromycin >4 R linezolid 1 S oxacillin >8 R penicillin R rifampin ≤0.5 S trimeth-sulfa ≤0.5/9.5 S vancomycin 2S MIC (g/ml) “MRSA are resistant to all β-lactam agents (except ceftaroline). Doxycycline, rifampin or trimeth-sulfa should not be used alone for serious MRSA infections. Ceftaroline, daptomycin and linezolid reported per Dr. Jones request.” Final Report with Optional Comment

  13. Newer Antimicrobial Agents for MRSA - Daptomycin Staphylococcus spp. CLSI M100-S24. Table 2C.

  14. Newer Antimicrobial Agents for MRSA - Linezolid Staphylococcus spp. CLSI M100-S24. Table 2C.

  15. New Antimicrobial Agents for MRSA - Ceftaroline S. aureus CLSI M100-S24. Table 2C.

  16. Glycopeptides and Lipopeptides • Major Drugs: Vancomycin, Teicoplanin, Daptomycin • Activity: Gram-positives • Resistance Mechanisms: modification of cell-wall target; increased cell-wall thickness with drug permeability changes, undescribed mechanisms for Daptomycin

  17. Staphylococcus aureus • Major nosocomial and community-acquired pathogen • Responsible for >20% of bacteremia in US/Canada • Transmissible nosocomially and in the community. • Antibiotic resistance -- lots • Methicillin (oxacillin) resistance • Nosocomial • Community-acquired • Vancomycin resistance • Relative resistance (VISA) • High-level resistance (VRSA) • Macrolide resistance • The D-test

  18. VISA • VancomycinIntermediateS. aureus • MIC 4-8 • Accumulated changes associated with decreased fitness • Thickened cell wall by EM • Mixed large & small colony morphotypes on plates • Associated with poor clinical response

  19. VRSA • MIC ≥8 • Acquisition of vanA cluster from Enterococcus • Typically very high MICs, no loss of fitness • 1st Michigan strain: vanA cluster on a Staph conjugal plasmid, MIC>1000 • PA strain MIC=32 (?loss of cluster or ↓expression) • NY strain MIC=64 • 2nd Michigan strain 04/05: MIC >256

  20. VRE • Enterococci are naturally resistant to lots of important antibiotics • Cephalosporin's, SXT, clindamycin • Emerging resistance to penicillin's and vancomycin • Vancomycin resistant enterococci • Van A (E. faecium (most VRE isolates) and E. faecalis) • High level R to Van (> 64 mcg/ml) • Van B (E. faecium and E. faecalis) • Low level R to Van (4-32 mcg/ml) • S to teicoplanin • Van C (Other Enterococcal species) • Low level R to Van and S to teicoplanin • Not usually transmitted nosocomially • Vancomycin resistance: modified peptidoglycan precursor • VRE surveillance cultures • Routinely screen admissions to selected ICUs: stool or wound sites

  21. Definitions • MDR – multidrug-R (e.g., “NS” to at least 1 drug in ≥ 3 drug classes) • XDR – extensively drug-R (e.g., “NS” to almost all classes but retains “S” to at least one drug class) • PDR– pandrug-R (e.g., “R” to all drug classes) Definitions apply to “acquired” (vs. “intrinsic”) resistance and to drugs that might be used to treat an infection caused by the species.

  22. Specimen: Bronchoalveolarlavage Diagnosis: PneumoniaMany Acinetobacter baumannii MIC (µg/ml) amikacin >32 R amp-sulbactam >32 R cefepime >32 R ceftazidime >32 R ciprofloxacin >2 R gentamicin >10 R imipenem >8 R meropenem >8 R piper-tazobactam 128/4 R tobramycin >10 R trimeth-sulfa >4/76 R What additional drugs might we be asked to test?

  23. Specimen: Brochoalveolar lavage Diagnosis: PneumoniaMany Acinetobacter baumannii MIC (µg/ml) amikacin >32 R amp-sulbactam >32 R cefepime >32 R ceftazidime >32 R ciprofloxacin >2 R colistin1 S gentamicin >10 R imipenem >8 R meropenem >8 R minocycline<1 S piper-tazobactam 128/4 R tigecycline1 * tobramycin >10 R trimeth-sulfa >4/76 R Final Report with Optional Comment “Colistin, minocycline and tigecycline reported per Dr. Jones request. *No standard interpretive criteria for tigecycline. Infectious Diseases consult suggested.”

  24. Cephalosporin's and the like • Major Drugs & Major Activities • Narrow Spectrum: Cefazolin, Cephalexin, Cefalothin; Staph and Strep except MRSA and enterococci; susceptible Gram-negatives • Expanded Spectrum: Cefoxitin, Cefotetan; Cefuroxime; Cefaclor; add some Gram-negative and anaerobic coverage. • Broad Spectrum: Ceftriaxone; Cefixime; Ceftazidime; Cefotaxime; much better Gram-negative coverage; less Gram-positive and anaerobic activity. Ceftazidime has excellent Pseudomonas activity. • Extended Spectrum: Cefipime: better stability to some of the -lactamases • MRSA-capable:Ceftaroline, effective vs MRSA, retains decent Gram-negative spectrum. • Resistance Mechanisms: an immense variety of -lactamases; altered Penicillin Binding Proteins (PBP).

  25. Extended-Spectrum β-lactamasesESBL • Variants on enzymes found in Enterobacteriaciae, with two nastyproperties: • Have broad activity against cephalosporin's and semisynthetic penicillin's • May not be detected in vitro by typical susceptibility testing procedures • Outcome data suggests that they do cause treatment failures in vivo. • The phenotypic definition includes inhibition by clavulanic acid.

  26. ESBLS – What To Do? • Change cephalosporin-class, penicillin-class and aztreonam results to Rregardless of in vitro result. • Exceptions: • Cephamycins – not hydrolyzed • cefoxitin, cefotetan, cefmetazole • -lactam inhibitor combinations • The inhibitors do inhibit the ESBLs • ticarcillin-clavulanate • piperacillin-tazobactam

  27. KPC Carbapenemase’s • Associated with outbreaks of multi-resistant Klebsiellapneumoniae, other Enterobacteriaciae, and even Pseudomonas. • Confers resistance to all -lactams, plasmid-borne • Difficult to detect; 12% of isolates test susceptible to imipenem; ertapenem is most sensitive screening drug, or use screening breakpoint of 2 µg/ml with imipenem or meropenem (most-recent guidelines incorporate this change) • Modified Hodge test used to confirm presence of a carbapenemase (not required if using current breakpoints) • Drugs used to treat these isolates include tigecycline and colistin • Poor clinical outcomes

  28. “Routine” Cumulative antibiogram Generally…one big report, but increasing emphasis on segregating data to answer specific questions

  29. Questions?

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