Flashcards in Micro 1 Deck (145)
What organisms naturally colonize the skin?
Yeast and gram + organisms
What organisms naturally colonize the large intestine?
Anaerobes - bacteroides (10^11 /g fecal mater)
What organisms naturally colonize the mouth?
anaerobes - density sim to lg. intestine
What organisms colonize the nose and pharynx?
Gram + and - cocci (Neisseriae and Moraxella)
Gram + rods (Corynebacterium)
The rest of the respiratory tract is sterile
What organisms normally colonize the urogenital tract?
Urethra - transiently colonized
Vagina - changes w/ age: gram + cocci (staph, strep) before puberty; Lactobacillus Acidophilus after puberty (reduces pH and maintains uniform flora)
What is the procedure for gram staining?
Crystal Violet - then rinse
Iodine - then rinse
Acetone or Isopropyl alcohol - then rinse
Safranin - rinse then dry
What is the mechanism of Gram staining?
Iodine - crystal violet complex is too large to wash out of gram +
Describe acid fast bacteria
Cell walls contain long chain fatty (mycolic) acids, do not gram stain well.
Stain w/ carbol fuchsin, decolorize w/ 3% HCl and ETOH - acid fast will remain red
What is lipoteichoic acid and where is it found?
Part of gram + cell wall - strengthens
Endotoxin - can evoke immune response from humans
Where are gram - toxins housed?
Periplasmic space - between inner cell membrane and peptidoglycan cell wall
ex: cholera toxin
Cell wall components
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Peptide bridges between NAM cross link subunits (determine thickness of wall)
Gram +: pentaglycine links D-ala and lysine
Gram -: direct link between D-ala and diaminopimelic acid
What is mycolic acid?
Component of Acid Fast Bacteria cell wall
resistant to phagocyte killing and drying
What are components of gram - outer membrane?
Lipopolysaccharides (LPS) and phospholipids
LPS: virulence factor (endotoxin), mediates inflammation, septic shock
LPS composed of
-O antigen: repeating sugars - used for typing bacteria
-fatty acid moieties - bioactive portion of LPS
What is a bacterial capsule?
Both Gram + and - bacteria
High MW polysaccharides or amino acids
production depends on enviro and growth conditions
Protection from complement mediated killing
What are pili and what are they made of?
proteinaceous structures extending from cell membrane
made of pilin, tipped w/ adhesins which bind host tissue (receptors) - virulence factor- antigenic
1. common type: mediate adhesion to host eukaryotic cells
2. sex type: join conjugating bacteria
What are flagella made of? Are they antigenic?
highly antigenic - H antigen
3 spore forming bacteria and assoc. diseases
clostridium tetani - tetanus
bacillus anthracis - anthrax
clostridium botulinum - botulism
How do Beta-Lactams work?
Inhibit final step of cell wall synthesis - transpeptidation by Penicillin Binding Proteins (PBPs)
What is the mechanism of penicillinase resistance in resistant penicillins?
Bulky side chains - sterically hinder B-lactamase binding
What coverage do beta-lactam / beta-lactamase inhibitor combo drugs offer?
Improved gram (-) and anaerobe
What classes of bacteria are highly resistant to pecinillins?
aerobic gram - bacilli
What are beta-lactamase inhibitors?
Bind beta-lactamase -> inactive compound
What are common side-effects of Penicillin drugs?
Allergic reaction - from a rash to anaphylaxis
-may be due to B-lactam ring or to side chains
Acute Interstitial Nephritis - allergic rxn in kidney
-fever, rash, eosinophilia
-non-oliguric renal failure, may progress to anuria and kidney failure
-eosinophilic cells and tubular damage seen on biopsy
Gout medication given to prolong effect of Penecillin - blocks renal elimination
Used for persistent infections - syphillis
What do cephalosporins NOT have activity against?
What drugs would most likely be used to treat community acquired intra-abdominal infections or for surgical prophylaxis?
2nd gen cephalosporins - cephamycins
Cefotetan or Cefoxitin
What is the drug of choice for community acquired pneumonia (s.pneumo)?
Cephtriaxone - 3rd gen cephalosporin
What are the SPICE organisms?
Serratia, Providencia, Indole (+) Proteus, Citrobacter, Enterobacter
-all have B-lactamase
-lab may say susceptible to 3rd gen Cephalosporin, but use may select resistant strain
-usually use cefepime or carbapenems
What cephalosporins have activity against anaerobic bacteria?
Cefotetan, Cefoxitin - 2nd gen (2B or GI) cephamycins