Two main functions of microbiology laboratory: Diagnostic : detection, isolation and identification of etiologic agents; and/or immunoassay (serology). Therapeutic: antimicrobial susceptibility testing as guide to appropriate therapy. CLT 209 Exam 4 What is etiologic agent of each disease? What is vector of vectorborne diseases? Zoonoses? What is the ?White Plague? and the ?Great Pox?? What is AFB? What is significance of AFB-positive smear in TB? What is PPD use for? What are unique characteristics of chlamydiae, rickettsiae, & mycoplasmas? What are primary laboratory means by which these diseases diagnosed? What are typical signs of rickettsioses? What is trichoma? LGV? What are the five ?classical? STI?s? What is the MIC, and how used in antimicrobial therapy? What is primary use of antimicrobial susceptibility testing? What are disadvantages of inappropriate use of antimicrobials? Antimicrobials and Antimicrobial Therapy Fundamental principle: selective toxicity Prokaryotic vs eukaryotic cells Most agents antibacterial, several are antifungal, few are antiviral Narrow vs broad spectrum Bacteriostatic vs bactericidal Principles of Antimicrobial Therapy Optimal agent: one with narrowest spectrum of activity, fewest side effects, and lowest toxicity. Administered in dosage and schedule that will achieve a level at the site of infection equal to, or several times greater than, Minimum Inhibitory Concentration (MIC). Physician must consider individual patient: Site of infection Age Status of liver and kidney function Pregnancy Hypersensitivity Idiosyncrasy Drug interactions Disadvantages of improper use of antimicrobials: Toxicity Hypersensitivity Alteration of indigenous flora Selection of resistant strains Antimicrobial Susceptibility Testing Purposes: 1. Initiation of appropriate therapy 2. Modification of existing therapy 3. Determination of susceptibility patterns in local environment Methods: 1. Broth dilution ? yields MIC value 2. Agar diffusion ? yields SIR value Antibiogram: a species? susceptibility pattern; useful as guide to empirical therapy Macro broth dilution susceptibility test: Macro broth dilution susceptibility test: Micro broth dilution (MicroTiter) susceptibility test: Kirby-Bauer, 1966, Disc Agar Diffusion Method Kirby-Bauer disk agar diffusion susceptibility test: Correlation of MIC value with zone diameter: SIR Interpretation S (susceptible) = MIC < therapeutic concentration; expected to respond to agent at usual dosage and schedule. R (resistant) = MIC > achievable level by usual dosage and schedule. I (intermediate) = MIC ? expected level at site of infection by usual dosage and schedule; may respond to high dosage. Susceptibility Testing Panels Panel for GP and GN isolants Panel for specific species Example: P. aeruginosa Panel for urinary or CSF isolants Prevention of Antimicrobial Resistance in the Healthcare Setting www.cdc.gov/drugresistance/healthcare/
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