Intro to Bacteriology and Antibiotic Strategies Flashcards
Gram positive cocci in pairs?
Pneumococcus = S. pneumoniae
Gram positive cocci in chains?
Streptococcus pyogenes = Group A Strep
Gram positive cocci in clusters?
Staphylococcus
Gram Positive Rods
Bacillus species
Gram Negative Cocci
Neisseria (meningitis)
Gram Negative Rods
Campylobacter (bacterial gastroenteritis)
Can spirochetes be visualized with the gram stain?
No
Do bacteria have organelles?
No, have one supercoiled circular chromosome and small plasmids. Smaller ribosomes
Gram negative cell wall
Inner lipid bilayer, thin cell wall, outer lipid bilayer
Gram positive cell wall
Inner lipid bilayer, thick peptidoglycan cell wall
Components of the peptidoglycan cell wall
N-acetyl glucosamine and N-acetyl muramic acid, NAG and NAM, form parallel structures which are cross linked by peptide strands.
Porin Channels
Located on outer membrane of gram negative bacteria, allow nutrients to flow in.
Lipopolysaccharide
An endotoxin that is part of the outer bilayer of a gram negative bacteria, causes a cytokine cascade in host when released upon death of the organism.
Normal bacteria of the skin
Staphylococcus epidermidis
Normal bacteria of the upper respiratory tract
anaerobic cocci, viridans streptococci
Environmental Factors of Infection
Overcrowding, climate, antibiotic use
Host Factors of Infection
Immunocompromised state, extremes of age, breach in barriers
Inhibitors affecting peptidoglycan synthesis
Penicillin, cephalosporin, carbapenems, monobactams
How does penicillin work?
Inhibits cross-linking of peptidoglycans on the cell wall, causes a fragile outer coat, guts spill out.
How does the structure of penicillin cause it to work?
Beta lactam (peptide bond with 4 membered ring). Has 2 alanines hidden in the molecule, which will bind to active site of transpeptidase, which is built for 2 alanines.
Beta-lactamase
An enzyme that confers penicillin resistance buy cutting open the beta lactam ring.
Transposition of drug resistance genes
A drug resistance gene can be flanked by insertion elements where endonucleases will cut. This will create a circular piece of DNA that can be transported to a new plasmid. Polygenic plasmids can be created this way, leading to MDR plasmids.
Vancomycin, bacitracin
Also affects peptidoglycan synthesis by inhibiting the polymerization of NAG and NAM. Recognizes the double-alanine sequence for binding.
Resistance to vancomycin
1) Decrease the penetration of vancomycin to its target (gram negativity, vanc. can’t pass outer membrane).
2) Alter the target of the antibiotic. Bacteria have Vanc receptor which causes D-ala-D-lactate formation instead of Ala-Ala. Vancomycin has no target.
Inhibitors affecting cell wall membranes
Polymyxins (cationic detergent), polyene antibiotics (amphotericin B, binds to sterols), azoles (depletes cell of ergosterol)
Resistance mechanism to tetracyclines
Moved out to the cell
Resistance to aminoglycosides
Transport in to cell is dependent on ETC, so anaerobes are resistant. Most commonly, aminoglycosides can be inactivated by an enzyme encoded in a plasmid or on the chromosome.
Inhibitors affecting DNA-dependent DNA polymerase activity
Quinolones (inhibit gyrase/topoisomerase), Nalidixic acid (gyrase inhibitor), Mitomycin (cross-links DNA), Metronidazole (damages DNA with free radicals)
Inhibitors affecting DNA-dependent RNA polymerase activity
Rifampicin, actinomycin D
Folic acid antimetabolites
Sulfonamides and trimethorprim, cells need folate to build amino acids and DNA.
Synergy, Indifference, Antagonism
Look this up.
What is necessary for aminoglycosides to work?
Protein synthesis. Administer streptomycin with a protein synthesis inhibitor and antagonism occurs.
