CLM 2 infectious dz Flashcards
What are the five basic lab techniques
- Direct Visualization
- Detection of Microbial antigens
- Examination of Host immune of inflammatory response
- Detection of Microbial Nucleotide Sequences (don’t worry about)
- Isolation of Organism in culture
How do you visualize an organism
- Gram stain
- KOH prep
- Tzanck Prep
- India ink prep
What is a gram stain of buffy coat and what can it help visualize
*The Buffy coat is the little white layer in bw the RBC that are the bottom and the serum at the top after blood is centrifuged
(Can show pair of G- intracellular diplococci consistent with suspected meningococcemia)
Gram neg is what color. What about gram positive?
Neg – red, pink
Positive – purple/blue
What is KOH prep
Skin scraping, oral or vaginal secretions on slide with drop of KOH, heated briefly with flame then examined on low power microscope
KOH dissolves host cells and bacteria, sparing fungi and elastin fibers
What would a Tzanck Smear be used for
Herpes virus multinucleated giant cells
What would India ink prep be used for and how is it done
Cryptoccoci large capsules which exclude the ink
Drop of centrifuged CSF placed on microscope slide next to drop of artist’s india ink, coverslip placed over drops
What are the different ways to detec microbial antigens/ specific etiologic agents in infectious dz
Latex agglutination Immunofluorescence Enzyme immunoassay Radioimmunoassay *note we did not focus much on this
Histopathologic exam of host tissue revealing PMN infiltration vs. Lymphocytic vs Granulomas suggest..
PMN infiltration: ACUTE bacterial process
Lymphocytic infiltration suggest more CHRONIC process: viral, fungal, TB
Granulomas suggest mycobacterial or fungal process
What are PPD or Cocci skin tests? Use? Negative tests?
Host cell mediated immune response skin test for delayed type hypersensitivity PPD for TB
Negative tests can occur if pt has depression of cell mediated immunity (anergy); consider applying control skin test to check for anergy (candida and/or mumps skin tests as control bc always +)
What is detection of microbial nucleotide sequence used for
Genetic molecular dz technique that can provide rapid ID of certain pathogens
Can also id genetic markers of antimicrobial resistance which can help guide tx
Identify species: M tuberculosis vs other mycobacterium
Dx infection: detect herpes simplex, CMV, syphilis in CSF
Detect markers of antimicrobial resistance: may help in HIV to determine if there is resistance to certain tx regimens
How is culture used in infectious disease process
One of the most common ways to identify organisms responsible for infection
Specimen sent to lab or planted on culture medium at bedside
Specific culture media needed for certain organisms (medium that selects for growth of suspected organism ie Neisseria gonorrhea)
What is an important component to using culture isolation for identifying organisms
must interpret results using information about clinical setting and method to obtain specimen
fever, cough, sob expectorated sputum
cotton swab in pus vs aspirated pus from closed abscess
“sterile” pus from brain abscess cultured on aerobic media (can be misleading if trying to grow anaerobic organisms)
Lots of room for error and confusing results (inadequate specimen, contamination, wrong medium, wrong transport medium)
*bring specimens PROMPTLY to lab
How do you determine sensitivity of organism to an antibiotic
C&S MIC (minimum inhibitory concentration)
ABX serum levels need to be over the MIC for a sig period of time in order to effectively kill bacteria
MIC determined by serially diluting abx into liquid media containing FIXED concentration of bacteria (automated)
What is the MBC and how is it determined
MBC = lowest concentration of abx that blocks growth of bacteria (no colonies)
Determined by inoculating tube with inhibited growth onto solid media plates, plates are then incubated
MIC is used more, but MBC takes things to the next level
The lower the MIC or MBC, the more effective the antibiotic
How is successful tx of infectious organisms obtained
Adequate antibiotic serum levels OVER TIME
Ratio of area under the curve to MIC is a parameter
The time above the MIC is another parameter
*want more area under the curve and longer time above MIC
How can antimicrobials be classified by pharmacodynamics
Concentration vs time dependent killing (concentration - aminoglycosides, FQ, azithromycin)
What is Sensitivity? How is it reported?
Sensitivity is the S of C&S indicates the abx an organism is sensitive to
Reported as MIC (mcg/mL) and MIC interpretation (R, I or S for resistant, intermediate, or sensitive)
*Report may also indicate usual adult dose or average cost/day
*As clinicians we should be away of geographic sensitivity/resistance
Ex: how would we make an antibiotic selection for MRSA
Senstivity report can help, but can also be misleading (clinical experience may show certain drugs not effective even if report says they are – in vitro vs in vivo)
Can antibiotic get to infected site? Ie if there is a CNS infection, must select an abx that can cross the BBB
What is a bacteriostatic agent and examples
STATIC = When MBC/MIC ≥16 for pathogen isolated
Macrolides, tetracyclines, sulfonamides, clindamycin. Linezolid, chloramphenicol
CIDAL = when MBC/MIC ≤ 4
Beta lactams, aminoglycosides, cancomycin, FQ, daptomycin, metro
What strategies can help select abx tx
- Decide if it is a bacterial infection
- Try to reasonably guess that pathogen
- Be aware of susceptibility patterns in hospital and community
- Take into account previous abx tx of pt
- Take into consideration host factors (ie is pt immunocompromised, allergies)
- Less is best
- Switch to narrow spectrum w/in 3 days after empiric tx (prevent resistance)
- When all things are equal, choose the cheapest drug
Pt has elevated WBC, Increased neutrophils and/or bands and serious illness…
BACTERIAL INFECTION!
How do you go about making a statistical guess at causative agent
Depends on anatomic site of primary infection (pulmonary, GU, GI, Skin)
Community vs. institutional setting (resistant organism or not)
What causes acute bacterial sinustitis
S pneumo, H flu, M catarrhalis
CAP, what causes it usually and what abx are they susceptible to
S penumo, H flu, M catarrhalis
Susceptible to Macrolide, FQ, doxycycline
What abx is good for community acquired MRSA
Bactrim often used first, then clindamycin
*other: vanco, minocycline, doxycycline, Linezolid, daptomycin
What are hospitalized pt likely to be colonized with
Resistant flora; be aware of what they have been treated with before and consider likelihood of resistant organisms to that antibiotic
What aspects should we be assessing when considering host factors
Site of infection (CNS, BBB etc) White count neutropenia? Age and underlying diseases renal or hepatic dysfunction, DM, CA? Duration of hospitalization Severity of pt illness
Why should we use the fewest drugs possible
Multiple drugs increase risk of adverse reactions, cost, and risks of resistant organisms
Some drugs are antagonistic rather than synergistic
What happens in the inflammatory response
- Bacteria/trauma/shock
- Activate complement system, coagulation, serum proteins
- Pro inflam cytokines and chemokines, ROS production, enzyme release
- Increase vascular perm, bacterial killin, DIC, Tachypnea, fever, leukocytosis, tachycardia, increased TPR
- Edema, tissue damage, organ failure, keukocytopenia
What is Bacteremia
Presence of organisms that can be cultred from blood
What is septicemia
Bacteremia with greater severity of s/sx: FEVER/hypothermia, tachycardia, Tachypnea, leukocytosis/leucopenia
What is sepsis syndrome. s/sx?
Even more severe than septicemia, impaired organ perfusion resulting in hypoxemia, oliguria, AMS
Severe sepsis, septic shock and refractory septic shock are even more advanced degrees of organ failure, usually accompanied by HYPOTN which may be unresponsive to fluids and/or vasopressors
s/sx: fever, chills, hyperventilation, hypothermia, AMS, hypotn, leucopenia/thrombocytopenia, END ORGAN FAILRUE (lung, kidney, liver, heart, DIC)
Outline the natural history of sepsis
Pathogenic micro organism local inflam response/local infection SIRS/sepsis SIRS + inadequate organ perfusion/sepsis syndrome Cardiovascular insuff/septic shock, respiratory insufficiency/ARDS MOSF death
What organisms commonly cause sepsis and how do you treat
Staph, strep, E. coli, enterobacter, pseudomonas
Tx:
PROMPT dx, ICU monitoring,
ABX (empirical coverage of G+ and G- until cultures available),
Judicioius fluid admin, O2, vasopressors
