Gram Positive Rods Flashcards
Which three gram positive rods are endospore formers?
1) Bacillus anthracis
2) Bacillus cereus
3) Clostridium
Which two gram positive rods are regular rods that do not form spores?
1) Listeria monocytogenes (food-borne pathogen)
2) Erysipelothrix rhusiopathiae (rare zoonotic/skin infection)
Which three gram positive rods are classified as irregular/pleomorphic?
1) Corynebacterium diphtheria
2) Mycobacterium/Propionibacterium/Actinomyces (Anaerobes)
3) Nocardia asteroides
Which virulence factor of Bacillus cereus causes projectile vomiting, nausea, and cramping
Emetic enterotoxin/cerulide toxin
Binds 5-HT (serotonin) receptor, stimulating the afferent vagus nerve
T/F B. cereus emetic enterotoxin is heat-stable and proteolysis-resistant
TRUE
It is for this reason that it can be found in cooked rice/pasta dishes
T/F Emetic gastroenteritis caused by B. cereus toxin is classified as an infection
FALSE
It is classified as an intoxication because only the toxin (no organism) is consumed,
What virulence factor of Bacillus cereus causes symptoms of diarrhea, nausea, and cramps about 24 hours after ingestion that last for about a day?
Diarrheal enterotoxin.
T/F B. cereus diarrheal enterotoxin can be eliminated from contaminated food when it is cooked
TRUE
B. cereus diarrheal enterotoxin is a heat labile protein complex that can be destroyed when the food it contaminates is cooked.
_____ is a hemolysin produced by B. cereus that punches holes in cell membranes of erythrocytes?
Cereolysin
What two virulence factors produced by B. cereus act as spreading factors, allowing the organism to disseminate throughout the tissue by degrading skin, etc.?
Collagenase & Serine protease
What are the four diseases B. cereus can cause?
1) Emetic gastroenteritis (intoxication by cerulide toxin consumed in pasta/rice dishes)
2) Diarrheal gastroenteritis (Infection with cells or spores in undercooked/uncooked food)
3) Panopthalmitis (contamination of a penetrating ocular wound)
4) Disseminated infections (septicemia, CSF infxn, lung infxn, necrotizing skin lesions from collagenases/serine proteases)
Extreme overdose of B. cereus emetic enterotoxin can lead to _____ because it can impair _____
Liver failure
Emetic enterotoxin can impair mitochondrial fatty acid metabolism
What four groups are susceptible to disseminated infection by B. cereus?
1) Immucompromised
2) IVDU
3) Pts. w/ exposed wounds
4) Pts. w/ indwelling shunts
T/F Fecal cultures are useful in diagnosing B. cereus infxns?
FALSE
Not useful because B. cereus can be found as regular gut flora
What test differentiates B. cereus from the other gram positive rods?
Spore stain
Gram(+) AND positive pore stain = B. cereus
Gram(+) only = other Bacillus species
What is the treatment for systematic/skin infxns by B. cereus (4 options)?
1) Vancomycin
2) Clindamycin
3) Gentamicin
4) Ciprofloxacin
T/F Beta-lactams may be used in the treatment of B. cereus
FALSE
B. cereus produces beta-lactamase
Listeria monocytogenes is an _____ pathogen, making it protected from innate defenses, complement system, and abx. What type of immunity is important in combating Listeria because of this?
Intracellular pathogen
Cell-mediated immunity
Which virulence factor of Listeria induces phagocytosis of Listeria? What does this factor bind to?
Internalin A (InlA)
Binds to E-cadherin
What virulence factor of Listeria allows it to escape the phagosome before its fusion with the lysosome? How does this factor work?
Listeriolysin O (LLO)
LLO is a hemolysin that punches holes in cell membrane
What hemolysin produced by Listeria acts synergistically with LLO to help Listeria escape the phagosome? What does this virulence factor disrupt to accomplish this?
Phospholipase C
Disrupts signal transduction pathways
What virulence factor of Listeria directs host cell actin to polymerize behind it, propelling it, and allowing it to move from cell to cell?
ActA
Lagniappe: The movement from cell to cell reduces its exposure to the humoral immune response
What three groups are especially susceptible to Listeria?
1) Fetuses
2) Neonates
3) Immunocompromised adults
In what kind of products does Listeria thrive?
Contaminated refrigerated products (grows well at 4 degrees Celsius)
T/F The symptoms of Listeria emerge quickly
FALSE
Listeria begins with flu-like symptoms or GI problems (cramps, diarrhea) before progressing to full blown symptoms
Pregnant women infected with Listeria may be asymptomatic, but the fetus may be infected, causing _____, fetal death, or miscarriage. How does Listeria access the fetus?
Granulomatosis infantiseptica
Listeria can cross the placenta
Listeria infxn presents as _____ or _____ in the immunocompromised
Septicemia or meningitis
Gram stain of blood or CSF reveals _____
Short gram(+) rods
When cultured on blood agar, Listeria demonstrates a _____ pattern of hemolysis due to LLO and other toxins.
Beta hemolysis
When grown in broth cultures at 20 degrees Celsius, Listeria demonstrates a characteristic _____ generated from is flagellum.
Tumbling motion
What are the three treatment options for Listeria?
1) Ampicillin + gentamicin (synergism)
2) Amoxicillin
3) Bactrim (sulfamethoxazole + trimethoprim)
Drugs must be able to cross into eukaryotic cells
T/F Listeria is an obligate intracellular organism
FALSE
Its entrance into host cells is only a method of immune evasion
Diphtheria toxin has two subunits linked by _____. The A-subunit has a _____, while the B-subunit has _____ regions
Diphtheria toxin has two subunits linked by DISULFIDE BONDS The A-subunit has a CATALYTIC DOMAIN, while the B-subunit has TRANSLOCATION AND RECEPTOR BINDING regions.
What is the host cell receptor for the B-subunit of Diphtheria toxin? What does the binding of this subunit initiate?
Heparin binding epidermal growth factor (HB-EGF)
Binding initiates endocytosis of the organism
When _____, the A-subunit of Diphtheria toxin enters the cytoplasm. Once here, function does the A-subunit have?
When the pH of the endocytic vesicle drops, the A-subunit enters the cytoplasm.
Here, it catalyzes ADP-ribosylation of EF2, shutting down protein synthesis, resulting in cell death.
The A-subunit of DTx catalyzes _____, stopping _____, which causes _____.
Catalyzes ADP-ribosylation of EF2, stopping protein synthesis, which causes cell death
T/F DTx is encoded in the bacterial chromosome
FALSE
DTx is encoded by a lysogenic phage, not C. diphtheriae
_____, an iron responsive protein, is encoded by C. diphtheriae. What effect do iron levels have on this protein?
Diphtheria Toxin Repressor
Increased levels of iron decreases the amount of toxin produced
How is C. diphtheriae spread?
Respiratory route or direct contact
What symptom of Diphtheria is pathognomonic for the disease?
Exudate in the throat that forms a pseudomembrane
What are the symptoms of Diphtheria? When do they appear?
Fatigue, myalgia, sore throat 2-6 days after infection
The distinctive lymphadenopathy caused by Diphtheria, so called because of its appearance, is known as _____.
Bull neck
T/F Diphtheria exists exclusively as a local infection
FALSE
Diphtheria can disseminate through the blood. 1/10 pts. will die from a heart-related infxn
The very rare cutaneous form of Diphtheria manifests as a _____
Chronic non-healing ulcer
Diphtheria appears as _____ on a stain of nasopharyngeal sample.
Club shaped pleomorphic rods (Chinese symbols)
_____ are polyphosphate storage for Diphtheria, and are seen as pink inclusion bodies
Metachromati granules
The _____ for toxigenic Diphtheria is based on antigen-antibody precipitation on filter paper soaked in antibodies.
Elek test
T/F A Diphtheria strain showing precipitation on an Elek test has not received the gene for DTx from a lysogenic phage
FALSE
Precipitation on an Elek Test demonstrates the production of DTx by the strain. Because DTx is encoded by a lysogenic phage and not in the bacteria itself, precipitation on an Elek Test tells you the organism MUST have received the gene from a lysogenic phage.
T/F Diphtheria is susceptible to penicillin and erythromycin
TRUE
What is used as passive immunization for Diphtheria? Hint: There is a potential for serum sickness because of the source of passive immunization.
Horse anti-toxin
T/F The vaccination for Diphtieria covers other organisms.
TRUE
The diphtheria vaccine (DTaP) covers tetanus and pertussis as well.
The Schick Test is used to test an individual’s immunity to DTx. If the patient has no reaction, then _____. If the patient has a reaction of localized edema and necrosis then _____
No reaction: You have protective antibodies to DTx
Reaction (localized edema and necrosis): Time to get a booster
Nocardia asteroides is found worldwide in _____.
Soil and water
N. asteroides grows in _____ macrophages
Non-activated macrophages
N. asteroides spreads by _____.
Inhalation of dirt/dust
N. asteroides causes _____ in the immunosuppressed
Bronchopulmonary disease
T/F Diagnosis of N. asteroides infxn can be accomplished by evaluation of sputum or abscess material
TRUE
What appearance characterizes N. asteroides when it is cultured on blood agar?
Orange, waxy, wrinkled colonies
T/F N. asteroides appears as filamentous slender rods that are non-acid-fast
FALSE
N. asteroides does appear as filamentous slender rods, but they are PARTIALLY acid-fast, not non-acid-fast.
What two treatment options are available for infxns by N. asteroides?
1) Sulfonamides
2) Amikacin + Beta-lactam
