Term
| What are the defining features of Viral pathogens? |
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Definition
1) Obligate intracellular pathogens
2) DNA or RNA, NOT BOTH
3) No independent energy source
4) Selectivity
5) Insensitive to antibacterial/antifungal antibiotics |
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Term
| How can you distinguish between Bacterial and Eukaryotic pathogens? |
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Definition
1) DNA enclosed by nuclear membrane (only Eukaryotic)
2) Chromosome # (Eukaryotic >1)
3) Membrane-bound organelles (Eukaryotic only)
4) Ribosomes (70S bacteria and 80S eukaryote)
5) Peptidoglycan in cell wall (Bacteria only EXCEPT Mycoplasma spp.)
6) Sterols in plasma membrane (Eukaryotes ONLY except for Mycoplasma spp., Helicbacter pylori and Borrelia burgdorferi) |
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Term
| Which 3 bacterial species are the only ones to have Sterol in their plasma membranes? |
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Definition
1) Mycoplasma spp
2) Heliobacter pylori (ulcers)
3) Borrelia burgdorferi (limes) |
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Term
| What are the 3 basic bacterial morphologies? |
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Definition
1) Cocci
2) Rods
3) Spriochete |
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Term
| How does Penicillin act in Murein biosynthesis? |
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Definition
Peptidoglycan cross-linking is carried out by transpeptidases (Penicillin binding proteins)
Penicillin (also cephalosporin) binds PBPs and prevents cross-linking of last G residue in one chain and penultimate D-alanine in anther chain.
Beta-lactam ring on drug resembles structures of D-Ala and blocks cross-linking |
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Term
| Explain how a Gram stain is carried out in the lab. |
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Definition
1) Stain with crystal violet (both purple)
2) Mordant-iodine to complex (both still purple)
3) Decolorize with EtOH (Gram(-) becomes clear) because
4) Counterstain with Safranin (Gram- turns red, while Gram + stays purple) |
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Term
| What structures are unique to Gram-positive bacteria? |
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Definition
Remember, important Gram + bacteria include Streptococcus spp (gram + cocci in pairs)
Staphylococcus spp (gram+ cocci in clusters)
Clostridium spp.
1) Lipoteichoic acid in Glycerol backbone of Murein.
2) Teichoic acid in Ribitol backbone of Murein. |
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Term
| What type of bacteria contain LPS and what is its structure? |
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Definition
Gram (-) enterics
3 regions; Lipid A (endotoxic), Core (conserved) and O antigen (bile and complement resistance/highly variable) |
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Term
| How are Gram (-) bacteria serotyped? |
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Definition
O antigen (variable, outermost portion of LPS)
H antigen (flagella)
K antigen (capsular antigen)
example) E. coli O157:H7 |
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Term
| What is a lipooligosaccharide (LOS)? |
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Definition
| Found on some gram (-) bacteria, LOS is like LPS, but without the "O antigen" for complement/bile resistance. |
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Term
| What are advantages/disadvantages of Gram (-) (Shigella spp, Salmonella spp.,Vibrio cholerae., E. coli) vs. Gram (+) bacteria? |
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Definition
Advantages: protection from environment and some antibiotics
Disadvantage: expensive to make, hard to secrete proteins through 2 membranes (need Porins) |
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Term
| What are the unique features of Mycobacteria? |
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Definition
Detected by Acid-fast stain (gram stain does not work)
1) Waxy envelope (Mycolic acids with phenolic glycolipids) provide resistance to desiccation from person to person and phagocytosis)
Examples include M. tuberculosis and M. leprae |
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Term
| How do you visualize Spirochetes? |
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Definition
Visualized by dark-field microscopy (too narrow to see by normal microscopy)
Examples include Borrelia burgdorferi and Treponema pallidum (Syphilis) |
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Term
| What are the unique features of Rickettsiae spp.? |
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Definition
-Obligate intracellular bacteria that are vector-borne and transmitted by feas, ticks, lice, ect.
- Generate some energy but also use host cell for some.
- Gram (-) but too small to stain
- Examples include R. rickettsii (rocky mountain spotted fever) and R. typhi (endemic typhi) |
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Term
| What are the unique features of Chlamydiae and Clamydophila spp.? |
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Definition
- Obligate intracellular bacteria with complex life cycles
- Energy parasites with 2 membranes (like gram -), but NO PEPTIDOGLYCAN.
-Exist in EBs (infective) and RB (non-infective forms)
- Examples include
Chlamydiae trachomatis (blindness),
Chlamydophila psittaci (psittacosis/form of pneumonia)
Chlamydophila pneumoniae (pneumonia) |
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Term
| Which types of bacteria lack peptidoglycan-containing cell walls? |
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Definition
Chlamydiae (2 membranes like gram (-)
Mycoplasma |
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Term
| Which type of bacteria CANNOT generate metabolic energy but still maintains independent protein synthesis? |
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Definition
| Chlamydiae (2 membranes but no peptidoglycan) |
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Term
| Which types of bacteria are intracellular pathogens (can't grow outside cell)? |
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Definition
Chlamydiae and Rickettsiae (except Rochalimaea quintana)
Also need energy from host |
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Term
| What are the unique features of Mycoplasma spp.? |
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Definition
1) Very small, lacking cell walls and possessing sterols in PM
2) Lack of cell wall affects antibiotic sensitivity.
3) Major pathogenic version is M. pneumoniae (atypical pneumoniae) |
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Term
| What are the "Molecular Koch's Postulates"? |
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Definition
1) Property of virulence gene should be associated with virulance gene.
2) Innactivated should prevent virulence
3) Wild type should re-establish virulence.
Virulence factors including toxins, adhesion and capsules as measured by ED50 (dose to kill 50%), ID50 (dose to 50% sick), LD50 (50% fever) |
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Term
| What about bacterial organelle structure influence selective toxicity in drug action? |
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Definition
70 S Ribosomes allow selective targetting.
Fungi, Parasites and Humans all have 80S |
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Term
| Why are Rickettsia and Chlamydiae obligate intracellular pathogens? |
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Definition
| They are "energy thieves" and cannot make their own energy |
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Term
| What purpose does the bacterial capsule serve? |
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Definition
| Resistance against phagocytosis and biofilm (can form around medical devices and antibiotics may not penetrate) |
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Term
| How does a bacteria make its cell wall? |
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Definition
1) In cytoplasm, UDP-GlcNAc and UDP-MurNac and pentapeptides are made.
2) In plasma membrane, monomers are combined and attached to lipid carrier
3) Lipid carrier takes dimer to periplasm, where lipid carrier inserts into growing chain
4) Chains of peptidydoglycan cross-link |
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Term
How do the following drugs work to inhibit bacterial cell wall synthesis?
1) Bacitracin
2) Avancomycin
3) Penicillin |
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Definition
1) Bacitracin inhibits recycling of lipid carrier
2) Avancomycin (gram +) interferes with incorporation into growing chain
3) Penicillin inhibits crosslinking |
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Term
| Why are some bacteria gram (+) vs. gram (-) |
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Definition
1) Gram (+) have plasma membrane and thick peptidoglycan layer (why they don't de-stain)
Tichoic and Lipotichoic are importance for adherence to mammalian cells are not NOT FOUND in gram (-)
2) Gram (-) also has plasma membrane, with thinner peptidoglycan layer, a second outer membrane (extracellular O antigen/intracellular Lipid A/core polysacharide and Porin proteins), and a periplasmic space in between. |
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Term
| What are 5 important factors for bacterial growth? |
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Definition
1) Temp
2) pH
3) O2 (redox) conditions
4) Nutrients (i.e. iron)
5) Osmolarity |
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Term
| How does human lactoferrin and transferrin inhibit bacterial growth and how do bacteria adjust for this? |
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Definition
1) Bind up iron so bacteria can't have it
2)
- Bacteria can produce their own iron-binding molecules (Siderophores)
- Neisseria spp. can bind human transferrin and lactoferrin and use bound iron. |
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Term
| What types of bacteria are Microaerophiles? |
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Definition
| Special group of aerobes that require lower conc. of O2 than found in air (Campylobacter spp. causing GI disease/diarrhea and fever) |
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Term
| Distinguish between Faculative anaerobes, Aerotolerants and Strict Anaerobes. |
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Definition
1) Faculative will ferment when there is no O2, but use O2 when it is available (E. coli- this is why you shake them)
2) Aerotolerants will grow in presence of O2, but will ALWAYS use fermentation (Streptococcus spp.)
3) Strict anaerobes grow only in the absence of O2 (Clostridium spp). |
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Term
| Provide an explanation for why some bacteria are anaerobic. |
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Definition
Anaerobes need LOW REDOX POTENTIAL, so they normally cannot survive in human tissues
1) Lack catalase, which mean they cannot break down H2O2
2) Lack SOD so they can't detoxify O2-
3) Enzymes that require reduced environment |
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Term
| What conditions allow anaerobes to survive in tissues? |
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Definition
1) Circuilatory issues (heart disease)
2) Tight orthopedic casts (hypoxia)
3) Co-presence of facultative anaerobes such as E. coli |
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Term
| Where do you often find anaerobic bacterial species in the human body? |
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Definition
1) Skin (Propionibacterium spp.)
2) Mouth (Porphyromonas gingivalis)
3) Vagina (Lactobacillus, Prevotella bivia)
4) Colon (Bacteroides fragilis) |
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Term
| What are the medically important Gram (+) bacterial species? |
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Definition
1) Sporeforming rods: Clostridium spp.
2) Non-sporeforming rods: Actinomyces spp. (granulomatous infection)
3) Cocci: Peptococcus, Peptostreptococcus |
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Term
| What are the medically important Gram (-) bacterial species? |
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Definition
1) Non-sporeforming rods: Bacteroides-like group, Fusobacterium spp.
2) Cocci= Veillonella spp. |
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Term
| What physiological conditions might lead to anaerobic infection? |
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Definition
1) Low tissue redox from circuilatory problems
2) Antibiotic therapy (C. dif)
3) Bite wounds
4) Aspiration of mouth flora into lungs
5) Spillage of intestinal contents into peritoneal cavity due to GI perforation. |
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Term
| What are characteristics of Nonclostridial Anaerobic Infections? |
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Definition
No Exotoxins
1) Abscess
2) Polymicrobic
3) Highly antibiotic-resistant bacteria
4) Mix with facultative anaerobes
5) Difficult to treat because abscess may have no blood supply for antibiotic delivery, and antibiotics may be ineffective anyways (DRAIN IT)
6) Low Virulence but can be fatal
7) Slow-growing, fastidious and produce fermentation gases (odor is a clue). |
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Term
| What are the Characteristics, Virulence Factors, Entry Tactics and Diseases associated with Bacteroides-like Bacteria? |
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Definition
1) Gram-negative Anaerobic rods (Nonclostridial) found as normal flora in colon, vagina and mouth
- Bile-senstive, pigmented, species are called Porphyromonas and Prevotella
2)
- Antiphagocytic capsule
- LPS from Porphyromonas and Prevotella is endotoxic
- Proteases for tissue spreading
- only 0.5% of gut flora, but most associated
3) Endogenous infections when they breech epithelium via surgery, wounds or ruptures (must be accompanied by low tissue redox)
- NOT CONTAGIOUS
4) Bacteroides fragilis- Peritonitis and then abscess
Prevotella bivia- female genital tract can cause PID and infertility
Prevotella melaninogenica and Porphyromonas gingivalis- found in mouth and can cause respiratory tract infections
- If they enter blood, they can cause bacteremia (rapidly fatal) |
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Term
| How do you treat Bacteroides-like infections? |
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Definition
| Surgical drainage and use of antibiotics effective (metronidazole) |
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Term
Histotoxic Clostridia
B
V
E
D
T |
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Definition
B) Gram (+), anerobic, spore-forming rods found in GI, soil or both.
- C. perfringens 90% of time
- C septicum with GI cancer
V) Exotoxin secretion
- alpha-toxin from C. perfringens is a lecithinase (PLC) that disrupts mammalian cell membranes.
E) Both endogenous and exogenous infections
- Enter into vegetative cells or spores into wound ruptures and tumors.
- Low redox conditions
D)
- Gas gangrene (clostridial myonecrosis)
- Enter circulation and can be rapidly fatal
- Anaerobic cellulitis (only cutaneous/subcutaneous tissue)
- Simple wound infections/Organ infections (uterine)
- C. perfringens type A food poisoning (enterotoxin-diarrhea)
T)
- Remove affected tissue with surgery with antibiotics
- Hyperbaric O2
- Keep wounds clean! |
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Term
Why are Bacterial Endospores so resistant to heat, radiation, chemicals and drying?
What are 4 examples of such bacteria? |
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Definition
Pathogens like Baciilus (aerobic or facultative) and Clostridium (anaerobic) release endospores which have
1) low internal water (low metabolism so can last 100 year) and are
2) rich in DNA stabilizing proteins.
Examples include:
Anthrax: Bacillus anthracis
Tetanus: Clostridium tetani
Infections from histotoxic clostridia
C. dif |
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Term
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Definition
B) Gram (+), anaerobic, spore-forming rod.
V) Tetanus neurotoxin inhibits inhibitory neurotransmitter release resulting in muscle contraction
E) Implantation of spores at wound or at childbirth via umbilical stump (requires low redox and has long incubation time)
D) Toxin migrates along nerves to CNS and causes convulsive muscle contractions of voluntary muscles of jaw, back and extremities. Respiratory failure causes death
T) Tetanus anti-toxin, or prevent with "toxoid," which is inactive form in DPT vaccine that confers resistance (normally, toxin levels are too low to mount an immune response)
- Should immunize moms to pass antibodies on. |
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Term
| True or False: The GI flora is dominated by anaerobic bacteria. |
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Definition
| True! Bacteroides dominate and are 4 orders of magnitute greater than Coliforms. |
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Term
| Why are B. fragilis strains associated with GI issues? |
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Definition
| Bacteroides-like bacteria that produces exotoxin in GI tract |
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