Microbiology Flashcards
What is the VDRL test composed of?
Mixing the patients serum with a mixture of cardiolipin, cholesterol, and lecithin antigens. Aggregation or flocculation (clumping) indicates the presence of anticardiolipin antibodies in the patient’s seum. This is a positive syphilis test.
Note that anticardiolipin Abs is NOT specific to treponema. It can also be seen in TB, Lupus, etc.
What is the pathogenesis of the C. diff enterotoxins?
2 toxins, A and B bind to receptors on intestinal mucosal cells and are internalized. They inactivate Rho-regulatory proteins involved in signal transduction and actin cytoskeletal structure -> disruption of intercellular tight junctions -> increased paracellular fluid secretion.
widespread inflammation and neutrophil recruitment -> apoptosis
Which spreads more rapidly - measles (rubeola) or Rubella (togavirus)?
Rubella.
BOTH start on the face and spread down but rubella often spreads faster and doesn’t darken/coalesce. Question stems will likely make note of this.
They might also make a point to state that there is posteriorauricular lymphadenopathy to clue you in to rubella
What is the classic triad of congenital rubela?
Congenital cataracts
Sensorineural deafness
Patent Ductus Arteriosus
Which virus family bud through and acquire the lipid bilayer envelope from the host cell nuclear membrane?
Herpesviruses (which include CMV!)
_____ prevent bacterial cell wall synthesis by inhibiting peptidoglycan synthesis.
Vancomycin and Bacitracin
_____ prevent bacterial cell wall synthesis by inhibiting peptidoglycan cross-linking.
Penicillins, Cephalosporins, Carbapenems
How do penicillins work?
D-Ala-D-Ala structural analog AKA a beta-lactam ring!: bind penicillin binding proteins (transpeptidases) and therefore block transpeptidase cross-linking of peptidoglycan in the cell wall.
How does vancomycin work?
Inhibits cell wall peptidoglycan formation by binding D-Ala D-Ala of cell wall precursors. They are NOT susceptible to beta-lactamases.
What sexually transmitted disease causes multiple extremely painful ulcers termed chancroids with a gray yellow exudate?
H. ducreyi
Organisms often clump in long parallel strands “school of fish”
What IS an acid fast stain? What organisms are acid fast +?
hydrochloric acid and alcohol after staining with carbolfuschin an aniline dye
Hepatic abscessed in developmental countries are likely to be _______ in origin, while in underdeveloped countries they are ________ in origin.
Developed = bacterial (e.g. staph aureus) Underdeveloped = parasitic (entomoeba histolytica, echinococcal).
What is viral phenotypic mixing?
When a host cell is coinfected with 2 viral strains and progeny virions contain unchanged parental genome from one strain nucleocapsid (or envelope) proteins from the other strain.
Because there is no change in the underlying viral genomes (i.e. no genetic exchange), subsequent progeny will revert to having only one type of surface protein.
Pneumonia-like sx + hyponatremia and/or diarrhea and/or neuro symptoms =?
Legionella
Severe coughing spells with post-tussive emesis = ?
Pertussis (whoopingcough)
This would be the “paroxysmal”/second phase of the infection
How does staph aureus evade phagocytosis?
Synthesizes protein A in its peptidoglycan cell wall that binds the Fc portion of IgG preventing opsonization/binding of complement.
Pneumonia + hepatitis = ?
Pneumonia + hepatitis + undulating fever = ?
Pneumonia + hepatitis = Q fever (coxiella)
Pneumonia + hepatitis + undulating fever = Brucella
What is the most common cause of viral meningitis? What will you find in the CSF?
Enteroviruses (e.g. coxsackie, polio, echovirus)
What 3 organisms present with rashes on the hands and feet?
- Syphilis (treponema pallidum)
- RMSF (rickettsia rickettsii)
- Hand foot mouth (coxsackie A)
_______ can make dextran from sucrose allowing it to adhere to sites of endothelial or valvular damage via fibrin and platelet adhesions.
Strep viridans (green jester on the donkey in sketchy video)
Hepatitis ___ infections can cause an aversion to smoking.
A
So. weird.
What can HPV in men cause (esp in immunocompromised patients)?
Anal squamous cell carcinoma - a visible ulcerative mass that causes pain, itching, and rectal bleeding
An organism being “PYR positive” is the same thing as saying it is ______ sensitive.
Bacitracin-sensitive
e.g. Strep pyogenes
______ is a highly contagious disease that presents with an intensely pruritic rash (usually worse at night) in the flexor surfaces of the wrist, lateral surfaces of fingers and palms.
Excoriations with small, crusted, red papules scattered around affected areas.
Scabies
Diagnosis is confirmed with skin scrapings from excoriated lesions that show mites, ova, and feces under LM.
What are the 3 primary organisms causing necrotizing fasciitis?
- Strep pyogenes
- Staph aureus
- C. perfringens
Group B strep and A. hydrophila also possible
_________ caused by ________(organism) is characterized by a blanching sand paper/goose pimple rash that appears on the neck, armpits, and groin and then generalizes to the body sparing the mouth (circumoral pallor). It is also often associated with a grey-white exudate pharyngitis.
Scarlet Fever
Strep pyogenes
What is the most common cause of fungal meningitis?
Cryptococcus neoformans
How will Allergic bronchopulmonary aspergillosis (ABPA) present and what lab findings will you see?
Corticosteroid-dependent asthmatics develop an allergic sensitivity to aspergillus. ABPA patients will have very high serum IgE, eosinophilia, and IgG Abs to aspergillus.
Can progress to bronchiectasis.
Hep B ______ is necessary for Hep D infection.
Surface antigen (surface antigen coats the Hep D viral particles)
Fungus in Great Lakes = ?
Blastomyces dermatidis
Cat bites most commonly transmit which 2 organisms?
- Pasteurella multicoda
2. Bartonella henselae
Dog bites most commonly transmit which 3 organisms?
- Pasteurella multicoda
- Streptococci
- Staph aureus
Fungus caused by bats = ?
Histoplasma capsulatum (remember the sketchy scene in the cave with the scientist and canary!)
What virulence factor causes gram-negative sepsis/septic shock?
LPS (lipopolysaccharide) endotoxin
Specifically, the Lipid A portion is responsible for the toxic properties
It is released during destruction of the bacterial cell wall or cell division. It is heat stable.
How can you distinguish Grave’s hyperthyroidism from a Toxic Adenoma of the thyroid?
TA will have lid lag and staring gaze to excessive adrenergic receptor expression.
TA will also present as nodular lesions while Grave’s will have a diffusely enlarged thyroid.
How will a PDA murmur sound?
Continuous
Best heard under the clavicle along the left sternal border
Maximal intensity at S2
Why does squatting improve cyanosis in Tetralogy of Fallot?
Squatting increases peripheral systemic vascular resistance (afterload) and decreases the degree of right to left shunting across the VSD.
What is the metyrapone stimulation test?
Tests the HPA axis integrity by blocking cortisol synthesis by inhibiting 11-beta-hydroxylase, which converts 11-deoxycortisol to cortisol in the zona fasciculata.
Reduction in cortisol levels following metyrapone administration causes an increase in pituitary ACTH secretion -> increased production of 11-deoxycortisol is metabolized by the liver to 17-hydroxycorticosteroid that accumulates int he urine.
FAILURE of the test indicates primary or secondary adrenal insufficiency.
Chlamydia infections generally start with a _______ ulcer but patients present with:
Initially painless
Patients present with painful lymphadenitis
H. influenzae requires which two factors to support growth on agar or blood?
X factor - Hematin
V factor - NAD+
If you have sheeps blood you can co-infect with s. aureus which actively secretes V factor (NAD+) into the media. This is known as the “satellite phenomenon”
High fever THEN maculopapular rash, think…
HHV-6/Roseola
Rash usually starts on the trunk and then spreads to face and extremities.
Fever is occasionally so high that it can cause seizures
What shape do cryptococcus neoformans take on?
Budding yeast
Genital ulcer without pain differential?
Chlamydia trachomatis
Treponema pallidum
How does H. influenzae b the most invasive/virulent?
Expresses polyribosylribitol (PRP) capsule which inhibits complement-mediated phagocytosis.
How do bacteria generate resistance against aminoglycosides (most common)?
Aminoglycosides interfere with aminoacyl binding site of the 30S ribosomal subunit. Bacterial methylation of the aminoglycoside-binding portion of the ribosome prevents the aminoglycoside from binding and inhibiting protein translation.
Hemorrhagic lymphocytic pleocytosis with elevated protein in CSF =?
Herpes Simplex Virus (encephalitis)
What viral infection are lung transplant patients curiously more at risk for?
CMV
Valganciclovir often given as prophylaxis
What aspect of E.Coli is responsible for the virulence of neonatal meningitis?
K1 capsular antigen
When are VDRL/RPR tests often falsely negative in syphillis infections?
First few weeks (i.e. primary infection, painless chancre)
What drugs treat anaerobic infections above the diaphragm? below?
Above = clindamycin Below = metronidazole
Hepatitis ___ is associated with a high mortality rate in pregnant women. How is it spread? What is it’s genome?
Hep E
Spread fecal-oral route
ssRNA
What are the stool findings in acute diarrhea? (watery/noninflammatory, inflammatory, enteric)
Non-inflammatory = watery no RBCs and no leukocytes
Inflammatory = leukocytes +/- RBCs
Enteric = fecal mononuclear leukocytes (note the only example of this is Salmonella typhi)
Gram positive cocci in ____ = staph
Gram positive cocci in ____ = streptococci (Group A, Group B, or enterococcus, viridans, pneumo, gallolyticus)
clusters = staph chains = strep
What are the top 3 organisms involved in septic abortions?
- Staph aureus
- E.coli
- Group B strep
Symptoms of rabies? Most common reservoir?
Hydrophobia Pharyngeal spasms/dysphagia Aerophobia Agitation Flaccid paralysis
Bats
Bacteroides fragilis is an anaerobic gram negative that has been shown to favor intrabdominal ______.
Abscesses
What is the main virulence factor of neisseria meningitidis?
Lipo-oligosaccharide (LOS), an analogue of LPS. i.e. an endotoxin that causes toxicity when released into the plasma via shedding of the outer membrane in bacterial lysis.
C-fos and C-jun are ____-binding proteins involved in leucine zipper motifs.
DNA
What are the symptoms of carcinoid syndrome?
Excessive release of serotonin causing:
Episodic cutaneous flushing
Bronchospasm/wheezing
Diarrhea
Mycoplasma pneumonia lacks a cell wall and therefore does not…
Gram stain
What eye muscles are innervated by the oculomotor nerve (CN III)
Inferior, superior, medial rectus
Levator palpebrae
Iris sphincter and ciliary muscle
What is the ONLY double stranded RNA virus? What does it cause?
Reovirus family (i.e. Rotavirus! or Colorado tick fever) It is also segmented #1 cause of severe diarrhea in kids
What is a major side effect of calcineurin inhibitors? What are they and what are they used for?
Cyclosporine and tacrolimus - block T cell activation by inhibiting IL-2 (i.e. are immunosuppressants)
They are highly nephrotoxic!!!
Mass effect in the cavernous sinus can impinge which nerves?
Oculomotor Ophthalmic Trochlear Maxillary Trigeminal
High grade fibrillary astrocytoma aka ______. What is a tip off that you have that?
Glioblastoma
Crosses midline
A B12 deficiency will cause ______ methylmalonic acid and _____ homocysteine.
A folate deficiency will cause ______ methylmalonic acid and ________ homocysteine.
B12 = increased, increased
Folate = normal, increased
In the CAH pathway, which is the only enzyme deficiency that leads to increased potassium?
21 alpha hydroxylase
Where in the brain do you often find schwannomas?
Cerebellar-pontine junction
High yield characteristics of meningioma:
Adult
F > M (something to do with estrogen??)
Derived from arachnoid cells -> attaches to meninges
Causes seizures from mass effect
Whorled appearance + psammoma bodies on histology
High yield characteristics of glioblastomas:
Adult
Derived from astrocytes
Can cross midline ("butterfly glioma")
GFAP +
Pseudopalisading cells lined upHigh yield characteristics of schwannomas:
Adult Benign tumor of schwann cells Cerebellar pontine junction S-100 positive Can cause bilateral acoustic neuroma (NF2) Generally affects CN VIII
High yield characteristics of oligodendroglioma:
Adult Malignant tumor of oligodendrocytes Calcified tumor in the white matter (usually frontal lobe) May present with seizures Fried egg appearance on histo
High yield characteristics of pilocytic astrocytoma:
Kids (most common in them) Benign tumor of astrocytes Cystic lesion with mural nodule Rosenthal fibers (eosinophilic fibers) on histo GFAP +
High yield characteristics of medulloblastoma:
Kids
Malignant tumor derived from granular cells in cerebellum which means:
derived from neuroectodermal tissue
Small, round, blue cells: Homer-wright rosettes
Poor prognosis due to spread through CSF
High yield characteristics of ependymoma:
Kids
Malignant tumor of ependymal cells
Occurs (usually) in 4th ventricle -> hydrocephalus
High yield characteristics of craniopharyngioma:
Kids/young adults
Arises from epithelial remnants of Rathke’s pouch
Supratentorial mass
Optic chiasm compression -> bitemporal hemianopsia
Calcifications on imaging
Benign but tend to recur
What is the BUN/Cr ratio in prerenal azotemia? Why?
> 20
Prerenal azotemia occurs due to reduced blood flow and thus GFR (often due to hypotension). The kidneys try to maintain volume by holding onto Na+ and BUN, thus BUN goes up while Cr is still excreted and FeNa (fraction of sodium excreted) goes down, i.e. < 1%
Note that in prerenal azotemia, the kidneys themselves still work, so urine will still be correctly concentrated (e.g. 500mOsm)
What BUN/Cr/FeNa values would you expect in intrinsic renal failure? Why?
The kidneys themselves are damaged, so BUN and Na will not be successfully reabsorbed ->
BUN/Cr < 15, FeNa >2% and urine will not be properly concentrated, so < 350 mOsm
What BUN/Cr/FeNa values would you expect in post renal failure? Why?
Due to obstruction (e.g. BPH, stone, congenital abnormality, etc.) Will generally present like intrinsic renal failure, but BUN and Na reabsorption is more variable
Difficulty in concentrating urine (<350 mOsm)
Note, that this will happen only if BOTH kidneys are obstructed
What is Filgrastim?
GCSF (granulocyte count stimulating factor)
How long can hepatic glycogenolysis last you before gluconeogenesis begins?
24 hours
How does Wiskott-Aldrich look on labs?
WATER
Wiskott Aldrich
Thrombocytopenia
Eczema
Recurrent (encapsulated, viral, and fungal) infections
Low/normal IgG IgM
HIGH IgE IgA
X-linked recessive
Leukocytes and platelets unable to recognize actin cytoskeleton
Low voltage ECG with “electrical alternans” = ?
Cardiac tamponade
