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91. Microbiology p176-186


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Bacterial Strucutre & Cell Walls
Where is beta-lactamase in bacteria? What does it do?
Beta-lactamases are found in the periplasm of gram negative bacteria. The enzyme hydrolyzes beta-lactam antibiotics, conferring resistance.
Which gram-positive organism lacks a polysaccharide capsule?
Bacillus anthracis - has D-glutamate instead of polysaccharide
What are spores made of and what do they do?
Keratin-like coat, dipicolinic acid. Provide resistanceto dehydration, heat and chemicals
What helps organisms adhere to indwelling catheters?
The glycocalyx (composed of polysaccharide)
What is the major surface antigen of gram-positive cell walls and what does it do?
Teichoic acid - unique to gram-positive bacteria. Induces TNF and IL-1
What is specific to gram-negative bacterial cell walls?
Endotoxin/LPS (lipopolysaccharide)
Bacterial Growth Curve
p. 177
Describe the four phases of bacterial growth.
1) Lag phase of metabolic activity without division. 2) Log phase of rapid cell division. 3) Stationary phase in which nutrient depletion slows growth. 4) Death due to prolonged nutrient depletion and buildup of waste products.
Main Exotoxin and Endotoxin Features
p. 177
What are exotoxins and endotoxin chemically?
Exotoxins are polypeptides, while endotoxins are lipopolysaccharides.
Where do bacteria keep their exotoxin or endotoxin genes?
Exotoxin genes on plasmids or bacteriophages; endotoxin genes on bacterial chromosomes.
Which is more fatal – exotoxin or endotoxin?
Exotoxin is highly fatal (~1 microgram), while you need 100Â’s of micrograms for endotoxin to prove lethal.
Which has greater heat stability – endotoxin or exotoxin?
Endotoxin – stable at 100°C for 1 hour, while endotoxin is rapidly destroyed at 60°C (EXCEPT Staph enterotoxin)
True or False: We can vaccinate against exotoxins and endotoxins.
False: We do have toxoids vaccines against exotoxins for diseases like tetanus, botulism and diphtheria, but there are no vaccines against endotoxins.
Bugs with Exotoxins
p. 178
Which bugs have Exotoxin that acts by ADP ribosylation?
Corynebacterium diphtheriae (which then inactivates EF-2). Also Escherichia coli, Vibrio cholerae, and Bordetalla pertussis (all these then stimulate adenylate cyclase).
Which bug has exotoxin that blocks the release of acetylcholine? What symptoms does that cause?
Clostridium botulinum. Anticholinergic symptoms, CNS paralysis, floppy baby, and a wrinkle-free forehead if injected!!
Which bug has exotoxin that blocks glycine release? What does that cause?
Clostridium tetani. Causes “lockjaw”.
How does Staph aureus cause toxic shock syndrome?
The toxin is a superantigen that binds to MHC II protein and T-cell receptor à induces IL-1 and IL-2 à TSS
Endotoxin (especially lipid A)
p. 178
How could bacterial infection cause disseminated intravascular coagulation?
Endotoxin can activate Hageman factor --> initiates coagulation cascade --> DIC
How could bacterial infection cause hypotension?
Endotoxin activates macrophages to release nitric oxide (--> vasodilationà hypotension); can also activate alternate complement pathway C3a, --> hypotension (N.B. also edema).
How does bacterial infection cause fever?
Endotoxin activates macrophages to release IL-1 and TNF --> fever.
Gram Stain Limitations
p. 178
--- are too thin to be visualized. Use darkfield microscopy and fluorescent antibody staining instead.
--- lack a cell wall
--- stain with silver
Legionella pneumophila
Fermentation patterns of Neisseria
p. 179
What are the two Neisseria species?
N. meningitidis, N. gonorrhoeae
How are the Neisseria species differentiated?
MeninGococci ferment Maltose & Glucose; Gonococci ferment only Glucose
Pigment-producing Bacteria
p. 179
--- produces a yellow pigment
Staphylococcus aureus (Latin aureus = gold)
--- produces a blue-green pigment
Pseudomonas aeruginosa
--- produces a red pigment
Serratia marcescens (think red marachino cherry)
IgA Proteases
p. 179
IgA proteases allow organisms toÂ…
Â… colonize mucosal surfaces
Name 4 organisms with IgA proteases
Strep pneumoniae, N. meningitidis, N. gonorhoeae, H. influenzae
Gram-positive Lab Algorithm
p. 180
What are the lab steps for ID'ing Staphylococcus aureus?
1st gram stain --> get purple/blue cocci (= positive); 2nd catalase test --> positive (staphylococcus clusters); 3rd coagulase test --> positive (differentiates S. aureus from the coagulase-negative S. epidermidis and S. saprophyticus)
What are the 4 types of gram-postive rods?
Corynebacterium, Listeria, Bacillus, Clostridium
When do you test for bacitracin sensitivity or resistance?
For beta-hemolytic strep. Bacitracin-sensitive --> Group A beta-hemolytic Strep pyogenes. Bacitracin-resistant --> Group B (Bad!) beta-hemolytic Strep agalactiae
Name 4 laboratory features of Streptococcus pneumoniae
alpha hemolytic (green – partial hemolysis), positive Quellung reaction, optochin-sensitive, and bile-soluble
Once you see gram-negative rods under the microscope, what is your next diagnostic test?
test lactose fermentation
What are the 3 fast lactose fermenters:
Klebsiella, E. coli, and Enterobacter
How do you distinguish among lactose non-fermenters?
Perform an oxidase test
Which are oxidase-positive?
Which are oxidase-negative?
Shigella, Salmonella, or Proteus
What are the gram-negative cocci?
What are the gram-negative coccoid rods?
H. influenzae, Pasteurella, Brucella, Bordetella pertussis
Special Culture Requirements
p. 180
Use chocolate agar and factors V & X for ---
Hemophilus influenzae
Factor V has --- and Factor X has ---
NAD, hematin
Thayer-Martin (VCN) media to culture ---
Neisseria gonorrhoeae
Bordet-Gengou (potato) agar to culture ---
Bordetella pertussis
Tellurite plate, Loffler's medium, blood agar for ---
Corynebacterium diphtheriae
Lowenstein-Jensen agar for growing ---
Mycobacterium tuberculosis
Pink colonies on MacConkey's agar are ---
Lactose-fermenting enterics (Klebsiella, Eschericihia, or Enterobacter
Charcoal yeast extract agar buffered with increased iron and cysteine to grow ---
Legionella pneumophila
Sabouraud's agar to culture ---
p. 181
Stain used to diagnose Whipple's disease
PAS (Periodic Acid Schiff)
PAS stains ---
glycogen, mucopolysaccharides
Ziehl-Neelsen stains ---
Acid-fast bacteria
India ink stains ---
Cryptococcus neoformans
Congo red stains -- and exhibits ---
Amyloid, apple-green birefringence in polarized light
Giemsa's stains what 4 organisms?
Borrelia, Plasmodium, trypanosomes, Chlamydia
Conjugation, Transduction, Transformation
p. 181
Which process can involve eukaryotic DNA?
DNA transferred from 1 bacterium to another is
DNA transferred by a virus from 1 cell to another
Generalized transduction can transfer --
Any gene
Specialized transduction transfers ---
only certain genes (that's why it's special!)
Obligate Aerobes
p. 181
"Nagging Pests Must Breathe" helps you remember what?
obligate aerobes: Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, Bacillus
Aerobic bacteria commonly found in burn wounds, nosocomial pneumonia, and pneumonias in cystic fibrosis patients?
Pseudomonas aeruginosa (an obligate aerobe)
What bug likes the lungsÂ’ apices and why?
Mycobacterium tuberculosis – because the apices have the highest partial pressure of oxygen
Obligate Anaerobes
p. 181
If you hear crepitus, indicating gas in tissue, what type of infection do you suspect?
Anaerobic bacterial infection, such as Clostridium, Bacteroides, or Actinomyces (CBA)
Which bugs are anaerobic and why?
Clostridium, Bacteroides, and Actinomyces. Air causes them oxidative damage, because they lack catalase and/or superoxide dismutase.
Why are aminoglycoside antibiotics ineffective against anerobic bacteria?
"AminO2glycosides" require O2 to enter into bacterial cells; anaerobic bacteria aren't where the oxygen is
Intracellular Bugs
p. 181
Name the 2 obligate intracellular organisms
Rickettsia, Chlamydia - "They stay inside (cells) when it's Really Cold"
Why do they need the host's cell?
They can't make ATP
Name 7 facultative intracellular organisms
Mycobacterium, Brucella, Francisella, Listeria, Yersinia, Legionella, Salmonella
Encapsulated Bacteria
List 4 examples of encapsulated bacteria
Streptococcus Pneumoniae, Haemophilus influenzae, Neisseria meningitidis, Klebsiella pneumoniae
What is the main virulence factor of encapsulated bacteria and why?
Polysacharide capsule is antiphagocytic
What is a necessary component of humoral immune response to encaps. Bacteria?
What vaccines are available for encapsulated bacteria?
Pneumovax, H. influenzae, meningococcal
What serves as vaccine antigen?
What laboratory test can be used to detect the presence of encapsulated bacteria?
Quellung reaction - capsule swells when specific anticapsular antisera are added - "Quellung = capsular swellung"
What complications/clinical signs is pneumococcus associated with?
"Rusty sputum", sepsis in sickle cell anemia, and splenectomy
Spores: Bacterial
p. 182
What kind of bacteria form spores and when?
Certain gram-positive rods when nutrients are limited
Name 3 spore-formers
Bacillus anthracis, C. perfringens, C. tetani = gram positive soil bugs
T or F: Spores are highly resistant to destruction by heat and chemicals
Spores have ___ acid in their core
T or F: Spores are metabolically active
False. Spores have no metabolic activity
What disinfecting procedure kills spores?
Autoclaving (ex/ surgical equipment)
Alpha-hemolytic Bacteria
p. 182
What organisms are alpha-hemolytic?
Pneumococci, viridans strep
Pneumococci are catalase ___ and optochin ___
Pneumococci are catalase sensitive and optochin sensitive
Viridans strep are catalase ___ and optochin ___
Viridans strep are catalase sensitive and optochin resistant
Beta-hemolytic Bacteria
p. 182
What organisms are beta-hemolytic?
Staph aureus, strep pyogenes, strep agalactiae, lysteria monocytogenes
Staph aureus is catalase ___ and coagulase ___
Positive, positive
Strep pyogenes is catalase ___ and bacitracin __
negative, sensitive
Strep agalactiae is catalase __ and bacitracin__
negative, resistant
Where is Lysteria monocytogenes found, and what is its characteristic pathology and laboratory appearance?
Unpausterized milk, miningitis in newborns, tumbling motility
p. 182
What are catalase and coagulase tests used for?
Catalase is used to distinguish staph (+) from strep (-), coagulase is used to distinguish S. aureus (+) from S. epidermis (-) and S. saprophyticus(-)
How is catalase a virulence factor?
It degrades H2O2, an antimicrobial product of PMNs that is a substrate for myeloperoxidase
Staph aureus
p. 182
What is the function of protein A?
Virulence factor - binds to Fc-IgG and inhibits complement fixation and phagocytosis
TSST is a ___ (type of virulence factor) that binds to ___ (2 types of receptor) and causes ___ of ___ (type of cells) leading to ___ (disease)
TSST is a superantigen that binds to MHC II and T-cell receptor and causes polyclonal activation of T-cells leading to toxic shock syndrome
3 toxins of S. aureus and a syndrome caused by each
TSST- 1 - toxic shock syndrome, exfoliative toxin - scalded skin syndrome, enterotoxins - rapid-onset food poisoning
T/F - S. aureus causes acute bacterial endocarditis
T/F - S. aureus causes skin disease and organ abscesses, but not pneumonia
False - causes all 3
T/F - S. aureus food poisoning is due to bacterial infiltration of the intestinal wall
False - it is due to ingestion of preformed enterotoxin
Strep Pyogenes
p. 182
T/F: strep pyogenes is catalase negative and bacitracin sensitive
3 pyogenic manifestations of strep pyogenes
pharyngitis, cellulitis, impetigo
Which is not a toxigenic manifestation of strep pyogenes: scarlet fever, rheumatic fever, TSS, acute glomerulonephritis
Rheumatic fever and acute glomerulonephritis are immune-mediated
List 5 signs and symptoms characteristic of rheumatic fever
PECCS: polyarthritis, erythema marginatum, chorea, carditis, subcutaneous nodules
p. 183
T/F: Enterococci are penicillin G sensitive and show variable hemolysis
F - they are resistant, but do have variable hemolysis
Lancefield group D includes ___ and ___, which can be differentiated through ___ (lab test)
Enterococci and non-enterococcal Group D strep. Enterococci can grow on 6.5% NaCl, and non-enterococci cannot.
Lancefield grouping is based on ___ on the bacterial cell wall
C carbohydrate
Viridans Strep
p. 183
Viridans Strep are ___ hemolytic
Strep mutans causes ___
dental caries
S. sanguis causes ___
bacterial endocarditis
How do you differentiate viridans strep from S. pneumoniae in the laboratory?
Both are alpha-hemolytic, but viridans strep is resistant to optochin (live in the mouth, not afraid of-the-chin)
p. 183
T/F: Clostridia are gram-positive, spore-forming, microaerophilic bacteria
False - they are obligate anaerobes
Name 4 types of Clostridia and disease caused by each
Tetanus - tetanic paralysis, Botulinum - flaccid paralysis, Perfringens - gangrene, Difficile - diarrhea
How does Clostridia cause tetanic paralysis?
Exotoxin blocks glycine (inhibitory neurotransmitter) release from Renshaw cells in spinal chord leading to tetanic paralysis
How does C. botulinum cause flaccid paralysis?
Preformed, heat - labile toxin inhibits ACh release
T/F: C. perfringens produces alpha-toxin, a globulin that causes myonecrosis, gas gangrene, or hemolysis
False - alpha-toxin is a lecithinase
What causes pseudomembranous colitis? How is it treated?
Cytotoxin, an alpha toxin produced by C. diff, usu after antibiotic use (clindamycin ar ampicillin). Treat with metronidazole.
p. 183
Exotoxin is encoded by ___ and ihibits ___ by ADP-ribosylation of ___
beta-prophaage, protein synthesis, EF-2
T/F: Symptoms of diphtheria include pseudomembranous pharyngitis, lymphadenopathy, and hematuria
Does not cause hematuria
Lab tests for Diphtheria
Gram-positive, club-shaped rods with metachromatic granules; grow on tellurite agar
ABCDEFG of diphtheria
ADP ribosylation, Beta-prophage, Corynebacterium, Diphtheriae, EF-2, Granules
p. 184
Anthrax is caused by ___ (bacteria)
Bacillus anthracis
T/F: Bacillus anthracis is spore-forning and gram negative rod
FALSE - it is a gram-positive rod
What is the progression of anthrax?
Contact leads to malignant pustule (painless ulcer) which can progress to bacteremia and death
What is woolsorter's disease?
Life-threatening pneumonia caused by inhalation of spores
Characteristic lesion of anthrax
Black skin lesions - vesicular papules covered by black eschar
Actinomycis Vs. Nocardia
p. 184
Actinomycis, Nocardia are gram___ rods that form long-branching filaments resembling fungi
What air requirement do actinomysis and nocardia have?
Actinomyces is an anaerobe and nocardia is an aerobe
A vs. N (pick one): pulmonary infection in immunocompromized
A vs. N (pick one): oral/facial abscess with sulfur granules that may drain through sinus tracts in skin
A vs. N (pick one): Normal oral flora
A vs. N (pick one): Weakly acid fast
What treatment do you use for actinomycis? For nocardia?
SNAP - sulpha for nocardia; actinomyces use penicillin
Penicillin and gram-neg bacteria
p. 184
Gram negative bugs are ___ to benzyl penicillin G and ____ to penicillin derivatives such as ampicillin
resistant, may be susceptible
T/F: Vancomycin can enter gram-negative bacteria
False - gram-negative outer membrane layer inhibits entry of penicillin G and vancomycin
Bugs causing food poisoning
p. 184
Reheated rice
Bacillus cereus
Contaminated seafood
Vibrio parahemolyticus and vulnificus
Meats, mayonaise, custard
S. aureus
Reheater meat dishes
C. perfringens
Improperly canned food
C. botulinum
Undercooked meat
E. coli 0157:H7
Poultry, meat, eggs
Diarrhea, bugs causing watery, bugs causing bloody
p. 184
Ferments lactose and causes non-bloody diarrhea
enterotoxigenic E. coli
Comma-shaped organism
Vibrio cholerae
Does not ferment lactose, motile, bloody diarrhea
Does not ferment lactose, nonmotile, very low ID50, bloody diarrhea
Comma or S-shaped, growth at 42 degrees, bloody diarrhea
Campylobaxter jejuni
Transmitted by seafood
Vibrio parahemolyticus
Transmitted through pet feces (puppies), bloody diarrhea
Yersenia enterocolitica
Rice-water stools
Vibrio cholerae
4 non-bacterial causes of non-bloody diarrhea
Virus - rotavirus, norwalk virus; protozoan - Cryptosporidium and Giardia
Ferments lactose and causes bloody diarrhea
E. coli 0157:H7
Protozoan cause of bloody diarrhea
Entamoeba histolytica
p. 185
Lab tests for enterobacteriaceae
Ferment glucose, oxidase negative
T/F: Enterobacteriaceae includes E.coli, Salmonella, Klebsiella, Enterobacter, Serratia, Proteus, and Pseudomonas
False - does not include Pseudomona
Describe O, K, and H antigens
O - somatic, polysacharide of endotoxin; K - capsular, related to virulence; H - flagellar, found in motile species
Haemophilus Influenzae
p. 185
Name 4 diseases caused by H. influenzae
epiglottitis, meningitis, otitis media, pneumonia
T/F - H. influenzae is a large gram-negative rod
False - it is a small (coccobacillary) gram-negative rod
H. influenzae is transmitted by ____ and invasive disease is caused by capsular type ___. It produces ___ protease.
aerosol, B, IgA
Culture on ___ agar requires ___ and ___
Chocolate agar, Factor V (NAD), X (hematin)
T/F: H. influenzae causes the flu.
False - influenza virus causes flue
Use ___ to treat H. influenzae meningitis and ___ for prophylaxis of close contacts.
Ceftriaxone, rifampin
T/F: H. influenzae vaccine contains type D capsular polysacharide conjugated to enterotoxin
False: vaccine contains type B capsular polysacharide conjugated to diphtheria toxoid or other protein
When is the H. influenzae vaccine given?
Btw 2 and 18 months of age
Legionella Pneumophilia
p. 185
Legionella Pneumophilia is a gram___ rod
Legionella pneumophila will grow on ___ yeast extract with ___ and ___, and should be treated with ___
Charcoal, iron, cysteine, erythromycin
T/F: Legionella pneumophilia is transmitted through environmental water source habitat.
T/F: Legionella is transmitted person to person.
False - no person to person transmission
(ubiquitous in man and natural water environments)
Pseudomonas Aerugenosa
p. 185
T/F: Pseudomonas Aerugenosa is anaerobic gram-negative rod found in water sources
False - it is AERobic (AERuginosa)
Name 5 infections commonly caused by Pseudomonas
Pneumonia (esp. in CF), sepsis, external otitis, UTI, hot tub folliculitis
T/F: Pseudomonas Aerugenosa ferments lactose and is oxidase-negative
False - P. Aurugenosa does not ferment lactose and is oxidase negative
Blue-green pigment produced by P. Aerugenosa
What 2 toxins does P. Aerugenosa produce?
Endotoxin (causes fever and shock), exotoxin A (inactivated EF-2)
What is the treatment for P. aeruginosa
Aminoglycoside plus extended-spectrum penicillin (piperacillin, ticarcillin)
What kind of injury makes a person especially susceptible to P. aeruginosa infection?
Helicobacter Pylori
p. 185
What conditions does H. pylori cause and is a risk factor for?
Causes gastriti and 90% of duodenal ulcers, risk of peptic ulcer, gastric carcinoma
T/F: H. pylori is a gram-negative rod that creates an alkaline environment
What is a test for H. pylori?
Urease breath test
What is the treatment for H. pylori?
Triple therapy - bismuth, metronidazole, and tetracycline or amoxicyclin OR more expensive metronidazole, omeprazole, and clarithromycin
What 2 bacteria are urease positive?
H. pylori and Proteus
Lactose - fermenting enteric bacteria
p. 185
What culture technique differentiates lactose fermenting from non-fermenting bacteria?
Lactose fermenters grow pink colonies on MacConkey's agar (Lactose is KEE)
Ferments lactose
Does not ferment
Ferments lactose
Ferments lactose
Ferments lactose
Salmonella Vs. Shigella
p. 186
Non-lactose fermenter
Invades futher, disseminates hematogenously
More virulent
Shigella (10e1 innocumlum compared to 10e5 innoculum for Salmonella)
Symptoms prolonged with antibiotic treatment
Has an animal resevoir
Invade intestinal mucosa causing bloody diarrhea
What immune cell type predominantly responds to Salmonella?
How is Shigella transmitted?
4 f's: food, fingers, feces, and flies
Cholera and Pertussi toxins
p. 186
How does Vibrio Cholerae toxin work?
Permanently activates Gs causing rice-water diarrhea
How does Pertussis toxin work?
Permanently disables Gi, causing whooping cough, also promotes lymphocytosis by inhibiting chemokine receptors
What do Pertussis toxin and Choleratoxin have in common?
Act via ADP ribosylation that permanently activates adenyl cyclase, resulting in increased cAMP
Zoonotic Bacteria
p. 186
Name 5 common zoonotic bacteria
"Bugs from your pet": Borrelia burgdorferi, Brucella, Francisella tularensis, Yersinia pestis, Pasteirella multocida
Borrelia burgdorferi
Lyme disease; tick bite; Ixodes ticks that live on deer and mice
Brucellosis/undulant fever; dairy products, contact with animals -- "Undulate and Unpasteurized products give you Undulant fever"
Francisella tularensis
Tularemia; tick bite; rabbits, deer
Yersenia pestis
Plague, flea bite; rodents, esp. prarie dogs
Pasteurella multocida
Cellulitis; animal bite; cats, dogs
Gardnerella vaginalis
p. 186
What symptoms are associated with G. vaginalis infection?
Vaginosis - greenish vaginal discharge, fishy smell, not painful
What is Mobiluncus?
An anaerobe commonly involved in G. vaginalis infections
G. vaginallis should be treated with ___
What are the laboratory characteristics of G. vaginalis?
Pleiomorphic, gram-variable rod; clue cells - vaginal epithelial cells covered with bacteria are visible under a microscope

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