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USMLE Step 1 Flash Cards > Microbiology > Flashcards

Microbiology Flashcards

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1
Q

Which enveloped viruses acquire the envelope from nuclear membrane of the host cell?

A

Herpesviruses (CMV, etc)

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2
Q

Infection that can cause achalasia. Common background of the patient. Mechanism.

A
  • Trypanosoma cruzi ▶️ neurotoxin ▶️ destroy myenteric plexus ▶️ intramural, parasympathetic denervation of smooth muscle
  • Patient come from central or South America
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3
Q

Coccus gram positive that can synthesize dextran from sucrose. What allow this property to do?

A 
Streptococcus viridans (mutans, sangini)
Adhere to tooth enamel ▶️ dental caries
Adhere to fibrin-platelet of damaged heart valves ▶️ endocarditis
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4
Q

What component allows to some bacteria be acid-fast? Examples

A

Mycolic acid in its cell wall

Mycobacterium, Nocardia (weak)

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5
Q

Most common organism in a cat or dog bite. Why do the wound have a characteristic odor?. Antibiotic treatment.

A
  • Pasteurella multocida
  • Mouse-like odor→indole positive (Trp ▶️ (Tryptophanase) ▶️ indole)
  • Amoxicilin-clavulanate
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6
Q

Sequence of replication of Hepatitis B virus. What polymerase does it use?

A
  • DNA double stranded→+RNA template→DNA double stranded progeny
  • Polymerase reverse transcriptase
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7
Q

Transmission pathway of Neisseria meningitidis. Once stablished a contact how can you prevent secondary cases? Which drugs do you use?

A
  • Direct contact with contaminated respiratory secretions or aerosolized droplets.
  • Antibiotic Chemoprophylaxis for close or intimate contacts preferably within 24 hours ▶️ Rifampin, Ciprofloxacin, intramuscular Ceftriaxone.
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8
Q

Gram-negative encapsulated bacteria, lactose fermenting positive, causing pneumonia in elderly patient. Hallmark of presentation and organism.

A
  • Klebsiella pneumoniae
  • Currant-jelly sputum, upper lobe pneumonia, lung tissue necrosis, early abscess formation
  • Immunocompromised ▶️ infants, elderley and specially alcoholics
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9
Q

Which is the protein that is part of peptidoglycan cell wall of a clusters of gram (+) cocci? Function.

A

Staphylococcus aureus ▶️ Protein A (virulence factor) ▶️ bind Fc portion of IgG ▶️ ❌ Complement activation ▶️ ⬇️ C3b ▶️ ❌ opsonization and phagocytosis.

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10
Q

What is the mechanism of resistance to vancomycin?, example of microorganism.

A
  • Substitution of D-lactate in place of D-alanine in the synthesis of peptidoglycan cell wall [D-ala-D-lac] (Normally binds to D-alanyl-D-alanine terminal of the cell wall peptide precursors ▶️ ❌ formation of peptidoglycan)
  • Vancomycin Resistant Enterococcus (VRE), VRSA (Staph)
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11
Q

How can occur Penicilin resistance?

A
  • Beta-lactamase (penicilinase)
  • Modify penicilin binding protein in cell wall ▶️ mechanism of MRSA ▶️ resistant to even penicilinase resistance antibiotics
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12
Q

Penicilinase resistant beta-lactam antibiotics

A

Cephalosporins, carbapenems, nafcilin, methicillin.

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13
Q

Mechanism of resistance to Tetracyclines

A
  • Efflux of drug from bacteria via active-efflux pump

- ⬆️ Protein that allow translation

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14
Q

Mechanism of resistance of aminoglycosides

A
  • Inactivation by aminoglycosides-modifying enzymes ▶️ acetylation, phosphorylation, etc.
  • Pseudomonas ▶️ ⬇️ antibiotic entry
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15
Q

In which disease or presentation you should differentiate aspergillus fumigatus vs rhizopus species? How do you differentiate them?

A
  • Fungal rhinosinusitis
  • Light Microscopy (LM):
    🔵Aspergillus ▶️ narrow hyphae branching in acute angles (V-shaped) with septations
    🔴Rhizopus ▶️ broad, ribbon-shaped, non-septate hyphae with branch at wide angles
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16
Q

Why Haemophilus influenzae cannot grow in a 5% sheep blood agar? Why does it need staphylococcus aureus to grow? How is called that phenomenom?

A

Haemophilus (“blood lover”) requires X factor (hematin), V factor (NAD+)

  • Sheep blood agar not has enough nutrients and factors
  • S. aureus cross-streaks in blood agar ▶️ secrete V factor; facilitates release release X factor from B-hemolysis ⏩ “Satellite phenomenon”
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17
Q

What confers to Hepatitis B virus the oncogenic feature? Which neoplasia associated?

A
  • Viral DNA integration into the host genome

- Hepatocellular carcinoma

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18
Q

Which are the components or regions of endotoxin? What is the toxic compound? How is it secreted?

A
  • Endotoxin=Lipopolysaccharide (LPS) ▶️ O antigen, core polysaccharide, Lipid A (toxic properties) ▶️ Sepsis
  • LPS released during division or bacteriolysis (NOT actively secreted)
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19
Q

Gram (+) cocci catalase negative, able to grow in hypertonic saline (6.5%) and bile. What is the organism, diseases and risk factors associated to the transmission? What is the other laboratory identification useful for it organism?

A
  • Enterococci (Enterococcus faecalis - 80-90%, Enterococcus faecium - 10-15%)
  • Enterococcal Endocarditis (30% of nosocomial endocarditis), UTI, wound infection
  • Genitourinary tract manipulation (cystoscopy, catheterization, instrumentation); GI tract manipulation (colonoscopy); obstetric procedures; Elderly.
  • PYR (+)
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20
Q

What is the microorganism that can cause subacute endocarditis following a dental work and its laboratory features?

A
  • Streptococcus viridans

- Gram (+), catalase (-), optochin resistant, bile insoluble

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21
Q

Function of virulence factor at the capsule of Haemophilus influenzae type b and its importance.

A
  • Polyribosil ribitol phosphate (PRP) ▶️ evasion of mucosal immunity and inhibit complement mediated killing and phagocytosis
  • Vaccine against type b PRP capsule
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22
Q

How can you identify and differentially diagnose botulism? Mechanism of action of neurotoxin.

A
  • History of eat canned food
  • 3 D´s→diplopia, dysphagia (nicotinic block), dysphonia. Also dry mouth (muscarinic block)
  • Electrodiagnostic→↓compound of muscle action potential (CMAP), continous stimulus→↑CMAP►Facilitation
  • (-) Ach release from presynaptic
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23
Q

Which gram negative rod is the most common cause malignant Otitis externa (swimmer’s ear)? Association with which patients. Other features of the organism

A
  • Pseudomonas aeruginosa
  • Elderly patients
  • Motile, aerobic Non-lactose fermenting, oxidase positive, grape-like fruity odor, exotoxin A (inactivates EF-2), phospholipase C (degrades cell membranes), pyocyanin (blue-green pigment, reactive O2 species), endotoxin
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24
Q

What mutation render to HIV resistance to HAART (both either PI’s and NTRI, NNTRI)?

A

Pol gene mutations ▶️ protease variants and structural changes in reverse transcriptase

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25
Q

Which mutation allows to the HIV evades the humoral response?

A

Env gene ▶️ structural glycoproteins (neutralizing Ab’s are directed against the epitopes of folded viral envelope glycoproteins)

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26
Q

Empiric treatment for a prosthetic valve endocarditis due to coccus gram positive catalase (+), coagulase (-). Why?

A
  • CoN Staphylococcus ▶️ slime producer ▶️ nosocomial infection and in indwelling catheter (peritoneal catheter), implantated foreign body (vascular graft), posthetic valve endocarditis
  • Vancomycin ▶️ >80% of CoN Staph are methicillin-resistant
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27
Q

Atypical pneumonia in homeless patient with CD4=188, IV drug abuse, what type of fungus do you suspect and which stain do you use to Dx?

A
  • Pneumocystis jirovecii
  • Extracellular atypical fungus
  • Methamine silver staining ▶️ cysts in frothy alveolar exudates
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28
Q

How do you identify disseminated MAC infection in a HIV+ patient? keys to differentiare from extrapulmonary tuberculosis infection. What is the prophylaxis?

A
  • MAC infection (in common - fever, weakness, weight loss, diarrhea)→anemia, hepatosplenomegaly, ↑phosphatase alkaline, ↑LDH (widespread involvement of reticuloendothelial system), MAC growth at 41°C.
  • Prophylaxis at CD4+<50 cells/uL - Azithromycin

*Tx: Clarithromycin or Azithromycin + Rifabutin or Ethambutol

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29
Q

Microorganisms associated with facial nerve palsy

A
  • Borrelia burgdorferi (Lyme disease)

- HSV-1

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30
Q

Which organism that is one of the most common causes of gastroenteritis in adults and children can be transmitted by domestic animals? What others sources of transmission?

A
  • Campylobacter jejuni (most common cause of acute gastroenteritis in children and adults in industrialized countries) ▶️ fecal-oral transmission
  • Domestic animals ▶️ cattle, dogs, chicken, sheep (common in farm and laboratory workers); Contaminated food ▶️ undercooked poultry, unpasteurized milk
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31
Q

What is a gumma and in which stage of syphilis of you expect to find it? What others features do you find in this stage?

A
  • Chronic necrotizing granuloma ▶️ painless, may ulcerate ▶️ skin, mucosas, subcutaneous tissue, bones and within organs
  • Tertiary syphilis
  • Cardiovascular syphilis ▶️ ascendent aortic aneurysms (with calcifications), aortic insufficiency (diastolic murmur, high-pitched tambour S2)

*Neurosiphylis (meningoencephalitis, tabes dorsalis, etc) classically occur in tertiary but can be present in any stage.

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32
Q

How do you differentiate with laboratory tests the both B-hemolytic streptococci?

A
  • S. Pyogenes (group A) ▶️ Bacitracin sensitive, pyrrolidonyl arylamidase (PYR) (+)
  • S. Agalactiae (group B) ▶️ Bacitracin resistant, CAMP (+), PYR (-), Hippurate test (+)
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33
Q

Which streptococcus is PYR(+) and also can grow in hypertonic salt (NaCl 6,5%) and bile? What culture medium use the former properties to isolate the organism?

A
  • Enterococcus faecalis and faecium→gamma-hemolytic (variable)
  • Bile esculin agar
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34
Q

Unique characteristic of coccidoides immitis. Where is the endemic area?

A
  • Mold (hyphae) at 25-30 grades C (environment), thick-walled spherules containing endospores at body temperature.
  • Southwestern US ▶️ California, Arizona, New Mexico, some regions of central ans south america.

*Also Dx→Sabouraud agar, serology

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35
Q

To what antibiotic is resistant Listeria monocytogenes, and then which antibiotic you should use as empiric therapy when suspect meningitis?

A
  • 3rd generation cephalosporins resistant (altered penicillin-binding proteins)
  • Ampicilin sensible
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36
Q

What type of immunity is required to clear Listeria monocytogenes and why?

A
  • Cell-mediated immunity→facultative intracellular gram (+) rod with “rocket-tails”→pass cell to cell, move intracellularly→avoid antibodies and phagocytosis
  • Susceptible group→deficient CMI►infants, chemotherapy patients, HIV(+)
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37
Q

Antimalarial drug for plasmodium falciparum erythrocytic forms contracted from africa, why?

A

Cloroquine resistant, give mefloquine

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38
Q

Treatment for chagas disease

A

Nifurtimox

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39
Q

Diagnose of Legionella penumophila. Distinctive laboratory abnormality. Diseases.

A
  • Legionella Urine antigen test
  • Culture of organism in BCYE (Buffered charcoal yeast extract)
  • Hyponatremia
  • Pontiac fever (flu-like, self-limited) or Legionaries disease (exposed contaminated water, pneumonia)

*Gram stain→many neutrophils but few or no organism

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40
Q

Gram negative rod, oxidase positive, green pigment producer (pyocyanin), that growth in moist environment. What is the microorganism and what diseases cause in that enviroment? Others features of the organism.

A
  • Pseudomonas aeruginosa
  • Swuimmer’s ear, hot tub folliculitis, burn wound
  • non-lactose fermenting, motile

*Hot tub folliculitis acquired in public or hotel swimming pool or hot tubs.

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41
Q

Stainings that can be useful to identify Cryptococcus neoformans

A
  • Methenamine silver stain→in tissue→round cells with narrow-based buds
  • India Ink→polysaccharide capsule (unique pathogenic fungus) clear, unstained zone
  • Mucicarmine→polysaccharide capsule red (bronchoalveolar washings, tissue samples, etc)
42
Q

Mechanism of production of tetanus disease. Against what is directed the vaccination?

A
  • Tetanospasmin (exotoxin of C. tetani)→heavy chain bins to ganglioside of neuronal receptor, light chain→↓release glycine and GABA from inhibitory neurons
  • Tetanus toxoid vaccination→elicitis humoral immunity specific for tetanus toxin
43
Q

Enveloped, partial double-stranded circular DNA, with a RNA-dependent DNA-polymerase

A

Hepatitis B virus

44
Q

Icosahedral core, enveloped, double-stranded linear DNA. How do these organisms acquire their envelopes?

A
  • Herpesrviridae

- The only viruses that acquire their envelopes by budding from the nuclear membrane

45
Q

What features make most probably causative organism CMV when you have a infectious mononucleosis like syndrome? what others organism associate with that presentation?

A
  • Heterophiles antibodies negative (make twice to confirm)
  • Lack of sore throat and lymphadenopathy (suggest EBV), immunocompetents
  • HHV-6, HIV, toxoplasmosis
46
Q

What strains of HPV are oncogenic and how can they cause malignancy?

A
  • HPV 16, 18, 31
  • Integrate into human genome→overexpression of viral oncogenes:
  • E6→↑degradation p53
  • E7→binds to RB1 gene and displaces transcription factors normally bound►inhibits RB1 suppressor gene→↓pRB [tumor supressor protein]
47
Q

What measure can avoid the recurrence of episodes of genital HSV-2 infection?

A

Supressive therapy→oral valacyclovir (preferred as dosed once daily, good bioavailability), acyclovir or famciclovir

*Reactivation of latent HSV-2 infection within S2, S3, S4 dorsal root (sensory) ganglia

48
Q

Most specific marker of acute for diagnosis acute Hepatitis B and why?

A

IgM anti-HBc (core)→acute phase→window period►HBsAg cleared and anti-HBs is not yet detectable

*IgG anti-HBc→recovery from disease

49
Q

What type of hematologic disturbance can occur in a mycoplasma pneumoniae infection? how can you diagnose it?

A
  • Intravascular hemolytic anemia→complement mediated→similarity between antigens in the cell membrane of mycoplasma and RBC (I-antigen)
  • “Cold agglutinins”→↑cross reacting IgM antibodies→Dx mycoplasma infection
  • Positive coombs test, ↑reticulocyte count, ↑LDH
50
Q

Extrapulmonary manifestations of mycoplasma pneumoniae

A

Steven-johnson syndrome, joint pains, encephalitis, cardiac rythm disturbances, bullous myringitis, intravascular hemolytic anemia

51
Q

E. coli virulence factor associated to meningitis? In what group of age?

A
  • K1 capsular antigens▶️prevents phagocytosis and complement-mediated lysis
  • Neonatal meningitis
52
Q

Tropism of HPV 6 and 11

A

Squamous stratified epithelium: anus, vagina, cervix, true vocal cords

*Infants can acquired respiratory papillomatosis via passage through and HPV-infected birth canal

53
Q

Diseases caused by Bartonella henselae infection and factors associated

A
  • Cat-scratch fever→veterinarian, cat scratches or bites→tender regional lymphadenopathy (axillary extremely common)
  • Bacillary angiomatosis→immunocompromise→vascular proliferations also found in viscera (falta if left untreated)
  • Culture-negative endocarditis
54
Q

Organism that cause respiratorory infections outbreaks, dry, nagging cough, chest x-ray findings worst than clinical status, needs cholesterol to grow in culture

A

Mycoplasma pneumoniae

55
Q

Pathognomonic finding of pulmonary CMV infection. Most commonly affected patients.

A
  • Prominent intranuclear inclusions sorrounded by a clear halo
  • Transplant patients
56
Q

Which organism have IgA protease?

A

Neisseria meningitidis, gonorrhoeae; Streptococcus pneumoniae, Haemophilus influenzae

57
Q

Virulent factor of staphylococcus aureus that can inhibit complement fixation

A

Staphylococcal protein A→binds to Fc portion of IgG→impair complement-mediated cell lysis

58
Q

Distinctive laboratory features of enterohemorrhagic E. coli (EHEC) O157:H7

A
  • Doesn’t ferment sorbitol→sorbitol-containing MacConkey agar to isolate
  • Doesn’t produce glucuronidase
59
Q

Which is the exotoxin of EHEC O157:H7 and its function?

A

Shiga-like toxin→inactivate 60s ribosomal subunit→stop protein synthesis►cell death

60
Q

Best test to confirm vaginitis by trichomonas vaginalis (trichomoniasis)

A

Saline microscopy (wet mount) of the discharge

61
Q

What mean that a virus exposed to a ether or other organic solvent loss its infectivity?

A

Enveloped virus

*Solvent induce disruption or dissolution of envelope (outer lipid bilayer coat). Nonenveloped viruses resistant to ether.

62
Q

Source and mechanism of damage of tetrodotoxin

A
  • Puffer fish poisoning

- Bind to voltage-gate Na channels▶️🚫Na influx▶️🚫depolarization

63
Q

Most common agent causing peumonitis in postransplanted recipient. Classification of microorganism and histopathology finding. Prophylaxis.

A
  • CMV→enveloped double-stranded DNA
  • Enlarged cells with intranuclear and intracytoplasmic inclusions (viral particles) with surrounding halo (owl’s eye)
  • Valganciclovir
64
Q

Most common exposure factor implicated in anthrax infection. Laboratory findings in Bacillus antrachis culture.

A
  • Handling animal products▶️goat hair, infected animal hides, hide-based clothes, wool
  • Large gram (+) rod, “medusa head” or serpentine colonies at standard media (microscopy)

*Woolsorters disease

65
Q

What distinctive pathogenicity factor do bacillus antrachis use?

A

Antiphagocytic D-glutamate capsule (unique in that composition - instead polysaccharide)

66
Q

Why can you find widened mediastinum in chest X ray during bacillus anthrax infection?

A

Spores inhaled▶️alveoli▶️machophage▶️germinate into vegetative cells▶️mediastinal lymph nodes▶️hemorrhagic mediastinitis⏩bloody pleural effusions, septic shock, death

67
Q

What organism produces intracellular polyphosphate granules? How can you see them? Other culture for it.

A
  • Corynebacterium diphteriae in loeffler medium and methylene blue staining
  • Cysteine-tellurite agar→black, slightly iridescent colonies
68
Q

How can you explain a finding of budding yeast that form germ tubes at 37 degrees at sputum culture?

A

Candida albicans (unique to form true hyphae) oral cavity colonization▶️usually doesn’t cause lung disease (contamination of sputum sample, not indicate disease)

69
Q

What define the tropism of enveloped virus?

A

Viral enveloped glycoprotein affinity to surface host cell surface glycoprotein

70
Q

Causes of candida vaginitis, which of them is the most common?

A
  • Antibiotic use (most common)▶️⬇️lactobacilli population▶️⬆️candida overgrowth
  • Uncontrolled diabetes mellitus
  • Systemic corticoid use
  • Pregnancy▶️⬆️estrogen levels
  • Immunosupression
71
Q

Most common cause of endocarditis in patients with prosthetic valves and septic arthritis in patients with prosthetic joints.

A

Staphylococcus epidermidis▶️coagulase-negative, susceptible to novobiocin

72
Q

An fungi that reduces the amount of ergosterol in its membrane, is most probably resistant to which antifungals?

A

Polyenes▶️amphotericin B (systemic: candida, hystoplasma, aspergillus, coccidioides, blastomyces, cryptococcus), nystatine (topical: oral candidiasis)

73
Q

Congenital infection with Parvovirus B19

A

Hydrops fetalis▶️congestive heart failure, pleural effusion and secondary pulmonary hypoplasia, ascites, pericardial effusion, severe anemia

74
Q

Which conditions would make a patient more susceptible for a vibrio cholerae gastroenteritis? Media where it can grow.

A
  • Achlorydia▶️⬇️gastric acid production (vibrio cholerae is extremely acid-sensitive)
  • Thiosulfate-citrate bile salt agar (TCBS)▶️highly alkaline selective media
75
Q

Description of a virus that cause aplastic crisis in patients with sickle cell disease

A

Nonenveloped single stranded DNA virus

Parvovirus B19

76
Q

How can EBV enter to B lymphocytes (CD19+)? What others cells can infect with same mechanism?

A
  • Viral envelope glycoprotein gp350 binds CD21 (CR2) [cellular receptor for C3d complement component]
  • Nasopharyngeal epithelial cells
77
Q

Diagnostic test of choice for Neisseria ghonorroeae and Chlamydia trachomatis

A

NAAT (nucleic acid amplification test) - urine, urethral, endocervical specimens

78
Q

Evidence of strongyloides stercolaris infection in stool. What is the infectious form?

A
  • Rhabditiform (noninfectious) larvae in the stool

- Filariform larvae (infectious)

79
Q

Most important source of protection against influenza

A

Antibodies against hemagglutinin▶️🚫binding to the host cells

80
Q

Bacteria producing dextran from sucrose may stick to what substrate? What is the organism

A
  • Fibrin platelets aggregates→colonizing during bacteremia→pre-existing valvular lesion→endocarditis (risk is low follow dental procedure with mitral valve prolapse)
  • Streptococcus viridans
81
Q

What organism do you suspect as a cause of epiglotitis in a unvaccinated child? Radiographic finding.

A
  • Haemophilus influenzae type b

- Thumprint sign

82
Q

What is the most important mechanism of immune defense against giardia lamblia? Patients at high risk of chronic infection.

A
  • CD4+ helper T lymphocytes and secretory IgA production

- IgA deficiency, X-linked agammaglobulinemia, common variable immune deficiency

83
Q

What organism is strongly associated with ecthyma gangrenosum? What condition may have the patient to predispose to it?

A
  • Pseudomonas aeruginosa bacteremia▶️perivascular invasion of of arteries and veins in dermis and subcutaneous tissue, release of exotoxins▶️exotoxin A (🚫protein synthesis), elastase (degrades elastin▶️blood vessels destruction), phospholipase C (cellular membrane destruction), pyocyanin (⬆️ROS)➡️insufficient blood flow▶️skin patches with necrosis and ulceration
  • Febrile neutropenia (Neu<500/mm3)▶️⬆️susceptibility to infections by gram (-)
84
Q

Conditions associated with pseudomonas aeruginosa infections

A

Neutropenia
Hospitalization
Indwelling catheter
Burns

85
Q

Major virulence factor of Streptococcus pyogenes and its function

A
  • Protein M
  • Inhibit phagocytosis and complement activation, mediates bacterial adherence, cytotoxic for neutrophils in the serum
  • Antigenic→target of specific humoral immunity

*Lancefield Group A streotococci are divided into >80 serogroups based on M proteins

86
Q

Similitude and difference between E. coli and Enterobacter cloacae

A
  • Both fast lactose fermenter gram negative rods, UTI organisms.
  • E. coli→convert tryptophan to indole►indole (+)
87
Q

What type of virus can make reassortment? which are they and what allow that property?

A
  • Segmented viruses
  • Influenza virus, rotavirus, orthomyxoviruses, reoviruses, bunyaviruses, arenaviruses
  • Exchange of entire genomic segments→ex, new strain in influenza virus►new epidemia or pandemia
88
Q

Most common etiology agent of endocarditis in intravenous drug user. What maneuver during auscultation do you use to hear the most probably finding and why?

A
  • Staphyloccus aureus→acute right-sided endocarditis►most probably tricuspid regurgitation results, septic embolization to lungs
  • Inspiration→↑venous return to right heart
  • Left-sided endocarditis→septic embolization to brain and systemic circulation
  • Less common agents→candida, pseudomonas
89
Q

What damages cause the clostridium difficile toxins at intestinal mucosal cells?

A

Toxin A (enterotoxin), Toxin B (cytotoxin)→inactivate Rho-regulatory proteins→ normally signal transduction and actin cytoskeletal structure maintenance►disruption of intercellular tight junctions→retraction, ↑intestinal fluid secretion

90
Q

Causal agent of “traveler’s” diarrhea, which toxin mediates it?

A

Enterotoxigenic E. coli (ETEC):

  • LT (heat labile) enterotoxin [cholera-like toxin]►(+)Gs protein→(+) adenylate cyclase→↑cAMP.
  • ST (heat stable)→(+) guanylate cyclase→↑cGMP
  • ↓reabsorption, ↑secretion of Na, H2O, electrolytes►watery diarrhea
91
Q

Which streptococcus is CAMP test positive and why?

A
  • Streptococcus agalactiae

- Produces CAMP factor→enlarges area of hemolysis formed by S aureus

92
Q

Which bacterial toxins are encoded in a lysogenic phage?

A 
ƒ- Group A strep erythrogenic toxin
- Botulinum toxin
- Cholera toxin
ƒ- Diphtheria toxin
- Shiga toxin

*ABCD’S

93
Q

Laboratory diagnosis for chlamydia trachomatis infection.

A
  • Cytoplasmic inclusions (reticulate bodies) on Iodine, Giemsa or fluorescent antibody–stained smear
  • Inside epithelial cells
94
Q

How can be the human infected by schistosoma species? Organ target and diseases caused by the different species.

A
  • Freshwater snails (incubate infectious larvae)
  • Larve penetrate intact human skin→liver (maturation):
  • Schistosoma japonicum→mesenteric venules►hepatic schistosomiasis
  • Schistosoma mansoni→menseteric venules►intestinal schistosomiasis
  • Schistosoma haematobium→urinary bladder plexus►urinary schistosomiasis
95
Q

Major virulence factor among E. coli strains that cause neonatal meningitis

A

K1 capsular antigen (polysaccharide)→prevent recognition of bacterial antigens, complement deposition, phagocytosis►survival in the blood

*Immunogenic→anti-capsular antibodies are protective against repeat infection

96
Q

Common description of the organism that cause thin, grayish-white, fishy odor discharge from vagina and clue cells from cytologic smear

A

Gardnerella vaginalis→anaerobic, gram-variable rod

97
Q

What are the clue cells and in which setting you may see them?

A

Squamous epithelial cells covered with bacterial organisms→wet mount microscopy or cytology in Gardnerella vaginalis infection

98
Q

Vaccine composition of Haemophilus influenzae type b

A

Capsular polysaccharide (polyribosylribitol - PRP) conjugated to diphteria toxin or other protein (carrier)→T cell dependent vaccine►(+) B cells to isotype switching

99
Q

Organism that can cause food poisoning and soft tissue infections, wound infections and septicemia? Source of it.

A
  • Vibrio vulnificus

- Contact contaminated water or shellfish, ingestion contaminated or raw seafood

100
Q

Which are the RNA viruses that replicate in nucleus?

A

Influenza virus and Retroviruses

101
Q

Mechanism of action of dyphteria toxin

A

AB exotoxin→ribosylation (inactivation) of EF-2→inhibit protein synthesis►cell death

102
Q

Property that allow to the Hepatitis C virus to be genetically unstable?

A

Viral RNA polymerase lack proofreading 3’→5’ exonuclease activity

USMLE Step 1 Flash Cards (9 decks)

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