Intro to Infectious Diseases Flashcards
Conceptually understand how the MIC is calculated and how it is used clinically
minimum inhibitory concentration (MIC) is the lowest concentration of an antimicrobial that prevents visible growth of the organisms after 24 hours of incubation on growth media.
Determines the susceptibility of a pathogen to a particular antimicrobial.
IgM
First circulating antibody to appear in response to initial exposure of antigen
Detection of highly elevated IgM usually indicates an acute infection
effective in agglutinating antigen and compliment activation
largest immunoglobulin. ~10% of immunoglobulins
IgG
Most abundant circulating antibody (~75%)
Crosses blood vessels. Crosses the placenta and confers passive immunity to fetus
protects against bacteria, viruses, toxins and triggers the complement system
IgA
prevents attachment of pathogens to epithelial surfaces found in many bodily secretions. Present in breast milk which protects infants from GI infections.
~0.2% of immunoglobulins.
IgD
Mostly on the surface of B cells.
Function as antigen receptors to help B cell activated and initiate B cell differentiation.
Does not activate complement and does not cross placenta
~0.2% of immunoglobulins.
IgE
Attaches to mast cells and basophils, releases histamine in response to allergic reactions.
Causes type 1 hypersensitivity reactions (anaphylaxis)
~<0.1% of immunoglobulins
Antibiogram
Collection of susceptibility reports (typically over one year). Consolidated into a single table that displays the % of pathogens that were susceptible to drugs.
Mechanisms of resistance
Enzymatic Inactivation of Antibiotic
Decreased Permeability
Altered Drug Target site
Antibiotic Efflux
Enzymatic Inactivate of Antibiotic
Beta-lactamase production: produce enzymes that hydrolyze the β lactam ring by breaking the amide bond, rendering the antibiotic inactive.
Aminoglycoside-modifying enzymes (AMEs): Acetylation, Nucleotidylation and Phosphorylation; impairs cellular uptake and/or binding to ribosome.
Decreased Permeability
Gram (-) bacteria contains porin channels in the outer membrane which permit diffusion of essential nutrients and small hydrophilic molecules, including antibiotics. Porin channels be be closed or down regulated due to mutations or acquired genes.
Altered Drug Target Site
Penicillin binding proteins (PBP): alterations in PBP prevents β-lactam antibiotics to bind to their drug target site.
Mutations in the binding site (Vancomycin)
Alterations in binding sites for DNA gyrase or topoisomerase IV (Fluoroquinolone resistance)
Antibiotic Efflux
The efflux pump on the cell membrane is used by bacteria to remove antibiotics out of the cell. (P. aeruginoa and E.coli)
Variables that may propagate resistance
Overuse of antibiotics: Over-prescribing in the outpatient setting, preventing potential bacterial complications, and reducing provider liability
Inappropriate use of antibiotics: Antibiotics prescribed for non-bacterial infections, Wrong dose, Broad spectrum agents used (when narrow spectrum is preferred), Low dose of antibiotics in food.
