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USMLE Step 1 General > Microbiology > Flashcards

Microbiology Flashcards

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1
Q

Candida Albicans Histo

A

Yeast and Pseudohyphae Q ID: 109

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2
Q

What vaccines are conjugated polysaccharides?

A

S pneumo
H influenzae
N meningitis

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3
Q

What fungi characterized by small ovoid bodies WITHIN macrophage?

A

Histoplasmosis: disseminated disease in immunocomp’ed (HIV)

systemic (fever, weight loss)
pulm: hilar adnopathy, cavitary lesions upper lobes Hepatosplenomegaly
oral ulcers
lymphadenopathy

Q267: Aspergillus: hyphae showing V branchingCryptococcus: extracelluar. large, polysaccharide capsuleCoccidiodes: spherules containing microspores

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4
Q

Elderly man with fever, malaise, myalgia, headache, with other family members same sx = dx? What are elderly prone to developing after this? Most common orgs that cause the secondary infection?

A
  1. Influenza (lots ppl in family have) 2. Secondary bacterial pneumonia = S. pneumoniae, S aureus, Haemophilus
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5
Q

What is the only virus that is ssDNA and nonenveloped?

A

Parvovirus - Fifth’s disease- Aplastic anemia in sickle cell - Hydrops fetalis

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6
Q

What organism is best visualized using silver stain, cultured on buffered charcoal yeast extract medium with L-cystine and Fe, and can be nosocomially spread? How is it spread?

A

Legionella - contaminates water supplies, water-based cooling systems in hospitals.

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7
Q

What organism characterized by SPHERULES packed with ENDOSPORES?

A

Coccidioides: - endemic to southwestern US (Cali, Arizona, NMexico, Texas)

hyphae at 20-30 -> inhalation of spores -> spherules containing endospores at 37/body temp -> dissemination of endospores

Sx: - pulmonary disease + erythema nodosum - Immunocompromised: pulm, extra pulm, meningitis

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8
Q

Microorganisms and Regions they are Endemic

A

Coccidiodes: southwestern US Histo: Ohio and Mississippi - bird, bat dropping, cavingCryptococcus: pigeon droppings

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9
Q

Maculopapular Rash on face that spreads to trunk and extremities + postauricular LAD

A

Rubella (Measles would also have that rash)

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10
Q

What is the monospot test? What does it differentiate?

A

Monospot (+): EBV infection = heterophile Ab detected by agglutination of sheep or horse RBC: Monospot (-) = CMV mononucleosis instead

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11
Q

Congenital rubella

A

sensorineural hearing losscataractscardiac malformations (PDA)

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12
Q

Presentation of C. botulinum?

A

3D’s: Diplopia Dysphagia Dysphonia

Acquired toxin:
Food Borne: preformed toxin in bad bottles of food
Wound Borne: toxin production in wound
Infant Borne: toxin in honey - spores ingested that then mature

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13
Q

Function of Pilus

A
  1. Attachment to cell surface. 2. Conjugation thru sex pilus
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14
Q

What do the following Hep B markers represent? HBsAg, HBcAg, HBeAgAnti-HBs, Anti-HBc IgM and IgG, Anti-HBe

A

HBsAg = acute infection, persists > 6 mo = chronic inf.

HBcAg = antigen associated with core of HBV

HBeAg = marker for viral replicability and transmission

Anti-HBs = resolution of acute infection, immunity

Anti-HBc IgM = present during window phase

Anti-HBc IgG = present after recovery vs. present without anti-HBs in chronic infection; not present after vaccination

Anti-HBe = present after recovery; if present in chronic indicates low viral replicability

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15
Q

What kind of RNA virus is infectious and can induce protein synthesis?

A

SS+ RNA (single stranded, positive sense) = Rhinovirus. Q1373

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16
Q

Resistance to Aminoglycosides (Gentamicin, etc) mediated by?

A

Bacterial transferase enzymes inactivate drug by acetylation, phosphorylation, adenylation. Drug normally inhibits formation of initiation complex and cause misreading of mRNA.

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17
Q

Resistance to Penicillin mediated by?

A
  1. beta-lactamase2. altered penicillin binding protein
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18
Q

Resistance to Tetracycline mediated by?

A

Eecrease uptake or increase efflux out of bacterial cells by plasmid-encoded transport pumps

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19
Q

Resistance to Fluoroquinolones mediated by?

A

chr encoded mutation in DNA gyrase.

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20
Q

Resp Infections in Children (Q1667)

A

Croup - barking, brassy cough - parainfluenza (paramyxovirus)

Epiglottitis - drooling, difficulty swallowing - H. flu

Diptheria - pharyngeal pseudomembrane - C. diptheria

Bronchiolitis - wheezing - resp syncytial virus.

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21
Q

What does the Thayer-Martin selective medium isolate and how?

A

N. gonorrhea

Vanco = inhibit G+
Colistin (Polymyxin) = inhibit G
Nystatin = inhibit fungi
Trimethoprim = inhibit G- other than Neisseria, such as Proteus

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22
Q

What medication needs an acidic environment to kill M tuberculosis?

A

Pyrazinamide - active inside phagolysosomes.

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23
Q

How does Hep B replicate?

A

dsDNA -> + ssRNA template -> dsDNA reverse transcriptase DNA polymeraseQ376

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24
Q

How do you treat S. epidermis?

A

Vanco + Rifampin or GentamicinMost are methiciilln resistant.

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25
Q

H. flu type B causes what?

A

invasive disease - sepsis, meningitis, pneumonia, epiglottitis.

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26
Q

What viral-encoded protein would change if the virus were to gain the ability to infect human epithelial cells?

A

Glycoprotein - mediates attachment to target host cell plasmalemma receptors

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27
Q

Antibodies to polyribosyl-ribitol-phosphate (PRP) provides protection against?

A

Epiglottitis. Hib vaccine = PRP component of Hib capsule conjugated to diptheria toxin

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28
Q

What microbe causes pityriasis versicolor?

A

Malassezia furfur. KOH = spaghetti and meatballs

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29
Q

What response does inactivated vaccine vs live vaccine generate?

A

Inactivated = humoral Live = CD8

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30
Q

What does influenza vaccine help inhibit?

A

Viral entry into cell. Antibody against hemagluttinin antigen preventing it from interacting with cell receptors.

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31
Q

What cause of inflammatory diarrhea can be transferred from animals to humans?

A

Campylobacter

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32
Q

Anerobes above the diaphragm vs. below?

A

Above - ClindamycinBelow - Metronidazole

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33
Q

How does vibrio cholerae cause rice watery diarrhea? What would you expect to see on stool microscopy?

A

GN, oxidase positive, comma-shaped rod grows on alkaline media

Cholera toxin - permanently activates Gs - inc. cAMP. No leukocytes or erythrocytes visualized on microscopy since it does not invade mucosa or cause cell death…

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34
Q

Why do cephalosporins NOT work against nongonoccocal urethritis?

A

Caused by Chlamydia or Ureaplasma Urealyticum. Chlamydia - lacks peptidoglycan within cell wallUreaplasma Urealyticum - lacks a cell wall entirely

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35
Q

Ecoli virulence factors?

A
  1. P fimbrae - UTI - allows adhesion to uroepithelium
  2. K capsule - Pneumonia, Neonatal Meningitis - prevents phagocytosis and complement mediated lysis
  3. LPS - bacteremia and septic shock 4. Enterotoxins (ETEC and EHEC)
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36
Q

What is mucormycosis? What species cause it?

A

Mucormycosis
Pt: ketoacidotic diabetic and leukemic pts

Sx: infection of blood vessel walls -> paranasal sinuses, cribriform plate, frontal lobe abscesses -> facial pain, headache, black necrotic eschar, cn involvement

Dx: Mucor - nonseptated hyphae branch at wide anglesRhizopus -septated hyphae branch at 90 degrees (vs. aspergillus is 45)

Tx: Amphotericin B

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37
Q

Dimorphic Fungi

A

molds with hyphae (ambient temp, 25-30) and yeasts/single cell (body temp, 37)

Sporothri schenckii 
Coccidioides immitis 
Histoplasma capsulatum 
Blastomyces Dermatitidis
Paracoccidiodes 
Brasiliensis Q103
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38
Q

Daptomycin - Use, mech, toxicities

A

Used for invasive MRSA infections. (can’t use against GN orgs bc doesn’t penetrate their outer cell membrane; can’t use against pneumonia bc inactivated by pulm surfactant)

Mech: disrupts bacterial membrane and membrane potential by creating transmembrane channels Tox: Myopathy, increased CPK

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39
Q

How does HBV vs. HCV increase risk of HCC?

A

HCV - chronic inflam -> regenerative hyperplasia -> increases chance of genetic mutations

HBV - even when not active hepatitis, HBV inserts DNA into host genome (main cause of the increased risk) -> production of HBx protein -> stimulate cell prolif and suppress p53

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40
Q

Amphotericin B - how does it cause toxicity?

A

Binding to cholesterol in membrane. Preferentially binds ergosterol but can bind cholesterol.

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41
Q

What drugs can precipitate serotonin syndrome when given with antidepressants?

A

Linezolid
Ondansetron
Tramadol
Triptans

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42
Q

What causes spasms and muscle rigidity in neonate with unsterile umbilical cord cutting? What should have been done to prevent this?

A

Tetanus! Maternal Immunization - IgG antibodies can cross the placenta.

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43
Q

How do pufferfish cause sx?

A

Tetrodotoxin - binds to Na channels - inhibit Na influx and conduction of action potential

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44
Q

Major virulence factor of GAS

A

M protein - prevents phagocytosis

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45
Q

Name 3 bacterial virulence factors

A

IgA protease - S. pneumo, H. flu, Neisseria Protein M - GAS - prevents phagocytosis Protein A - S. aureus - prevents opsonization and phagocytosis

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46
Q

What three drugs that inhibit dihydrofolate reductase and what are they used for?

A

Trimethoprim - combined with Sulfamethaxazole against bacterial dihydrofolate reductase Methotrexate - cancer drug; targets rapidly dividing cellsPyrimethamine - antimalarial; + sulfadiazine for toxo bc inhibits parasitic dihydrofolate reductase.

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47
Q

What microbe is associated with wool sorting?

A

Bacilius Anthracis!

Woolsorter inhalation of spore -> pulm anthrax -> fever, pulm hemorrhage mediastinitis, shock Unique features of anthrax:

  1. polypeptide capsule - D glutamate instead of polysaccharide
  2. “medusa head” colonies on culture
  3. Anthrax toxin - edema, lethal factor, protective antigen
48
Q

What adverse effect is associated with ethambutol?

A

Optic neuritis - color blind, dec. visual acuity, central scotoma.

49
Q

What drug for HIV induces hyperglycemia?

A

Protease inhibitor Other adverse effects: lipodystrophy, inhibition of cytochrome p450 (ritonavir)

50
Q

How do you diagnose tetanus?

A

H&P

51
Q

MOA of raltegravir?

A

Inhibits HIV integrase. Inhibits integration of HIV into genome of the host cell. (Q8371 picture)

52
Q

What antifungal inhibits cell wall synthesis?

A

Caspofungin - inhibits cell wall synthesis by inhibiting synthesis of beta-glucan. Use: Invasive Aspergillosis, Candida

53
Q

Pathogenesis of Diptheria?

A

Toxin inhibits EF2 by ADP-ribosylation, this inhibiting protein synthesis.

54
Q

Ways to distinguish S. pneumoniae from other bacteria in the lab?

A 
GP diplococci 
Catalase negative. 
Capsule present 
Optochin sensitive. 
Bile Soluble - lysed in bile.
55
Q

Lesion associated with Pseudomonas Aeruginosa infection?

A

Ecthyma gangrenosum = cutaneous necrotic lesion after Pseudomonas invades perivascularly, and releases destruction exotoxins -> insufficiency of blood flow to patches of skin which become edematous and necrose.

56
Q

What virus does NOT acquire their envelope from the plasma membrane, but from the nuclear membrane?

A 
Herpes Viruses: 
HSV 1
HSV 2
VZV (HHV3)
EBV (HHV4) 
CMV (HHV5) 
HHV6 - roseola
HHV7 - less common cause of roseolaHHV8 - Kaposi sarcoma
57
Q

Ganciclovir and Zidovudine together will cause what adverse effect.

A

Bone Marrow suppression - neutropenia

58
Q

How does Shigella invade the GI mucosa?

A

Gain access thru the M cells of Peyer’s patch in the ileum thru endocytosis. Then shigella lyses the endosome, multiples, and spreads laterally -> causing cell death, ulceration, hemorrhage, diarrhea.

59
Q

Dx of pt who has bronchial asthma complicated by recurrent pulmonary infection and bronchiectasis; eosinophilia on labs?

A

Aspergillus Fumigatus

Allergic Bronchopulmonary Aspergillosis

60
Q

Tx for recurrent C diff

A

Fidaxomin –| RNA polymerase - impair protein synthesis, bacteriCIDAL - oral, minimal systemic absorption

61
Q

Most common cause of Bacterial Meningitis

A

S. pneumo = GP diplococcci

62
Q

What glycoprotein of HBV is NONinfectious?

A

HbSAg - noninfective envelope glycoprotein forms spheres and tubules 22 nm in diameter.

63
Q

Amphotericin B toxicity

A

Renal toxicity - - HypoK, HypoMg

64
Q

What microbe is associated with subacute sclerosing pancencephalitis?

A

Measles - SSPE develops in years after infection. Absent matrix protein -> replicates intracellularly within neurons and oligodendrocytes -> inflam, demyelination, gliosis

65
Q

Mycobacteria grow in “serpentine cords” or parallel chains due to what?

A

Cord Factor - Virulence factor - induces release of TNF alpha - neutrophil inhibition - inhibits macrophage maturation.

66
Q

Causes of painful vs. painless genital ulcers?

A

Painful - Chancroid (Haemophilus Ducreyi)- HSV-2

Painless - Primary Syphillis (chancre), Lymphogranuloma Venereum - painless genital ulcer -> painful lymphadenopathy (buboes) - Chlamydia Trachomatis

67
Q

What antiviral agent does NOT require intracellular phosphorylation to be active?

A

Foscarnet –| viral DNA polymerase (pyrophos analog)

Cidofovir –| viral DNA polymerase (nucleoside monophosphate)

Both indicated for CMV retinitis when ganciclovir fails; Acyclovir-resistant HSV

68
Q

What bacteria have no cell wall?

A

Mycoplasma.

69
Q

What picornavirus is acid-labile?

A

Rhinovirus - gets destroyed by stomach acid - does not infect GI tract. Just common cold!

70
Q

Recent vacation + Fever, Pneumonia, GI, CNS sx =

A

Legionnaires’ DiseaseWill see hyPOnatremia!

71
Q

What are the HIV structural genes and proteins they code for?

A

Env - gp120 = attachment - gp41 = fusion and entry
Gag - p24 = capsid
Pol- reverse transcriptase - protease - integrase

72
Q

Anal Ulcer in HIV(+) most likely what?

A

Squamous Cell Carcinoma - HPV!

73
Q

Efflux Pumps depend on what to pump antibiotics out?

A

H gradientATP Na gradient.

74
Q

What DNA viruses do not replicate in the nucleus?

A

Poxvirus - carries own DNA dependent RNA polymerase

75
Q

What are the DNA viruses?

A 
HHAPPPPy
Hepadna = HBV
Herpes
Adenovirus 
Parvo
Papilloma = HPV
Polyoma = JC, BK
Poxvirus = Smallpox, Cowpox, Molluscum Contagiosum
76
Q

What the DNA virus characteristics and exceptions?

A

dsDNA - except parvo ss and linear

Linear - except papilloma, polyoma - circular- and hepadna - circular and incomplete

Iscosahedral - except poxReplicate in the nucleus - except pox

77
Q

What family of virus most likely to cause aseptic meningitis?

A

Picornavirus - Enteroviruses (Echo, Coxsackie)

78
Q

Protein synthesis inhibitors - what do they do?

A

Buy AT 30, CCEL at 50.

30S inhibitors:
Aminoglycosides - inhibit formation of initiation complex
Tetracycline - inhibit tRNA binding

50S inhibitors:
Chloramphenicol - peptidyl transferase inhibitor Clindamycin - inhibit translocation
Erythromycin (Macrolides) - inhibit translocation “macroslides”
Linezolid- inhibit bacterial initiation complex

79
Q

What protein synthesis inhibitor is bacteriocidal?

A

Aminoglycoside

80
Q

Aspergillus MIcroscopy

A

Septate hyphae - 45 degrees “Acute angles for aspergillus”Conidiophore with radiating chains of spores.

81
Q

Giardia Lamblia - what’s it look like?!

A

Trophozoite - owl eye nucleus!! Cysts in the stool Presents as malabsorption - fatty rich Ghirardelli chocolates. Does not cause invasive disease.

82
Q

What are the presentations of Aspergillous?

A

Aspergillomas in Lung Cavity, esp after TB infection

Allergic Bronchopulmonnary Aspergillosis - assoc. with asthma, cystic fibrosis - causes bronchiectasis and eosinophilia

Invasive Aspergillosis - esp immunocompromised, chronic granulomatous disease Virulence = HEMATOGENOUS spread.

83
Q

What GP cocci synthesize dextrans from glucose? And what do they normally cause?

A

Viridans strep - S. mutans and S. sanguinis

  1. Dental Caries
  2. Subacute bacterial endocarditis at damaged heart valves (fibrin-plt aggregates)
84
Q

Host cell receptor/Virion protein binding specificities: - HIV- EBV- Parvovirus B19

A

HIV: CD4 and gp120
EBV: CD21 and gp350
Parvovirus: Erythrocyte P-antigen and parvovirus B19

85
Q

Culture requirements for H. flu? Can be grown with what species?

A

Chocolate agar with factor V (NAD+) and X (hematin)

Grown with S. aureus: - actively secretes NAD+- beta hemolysis -> hematin release from RBC.

86
Q

Immune Mechs against Giardia? What immunodeficiencies are predisposed to infection?

A
  1. CD4 2. IgAIgA deficiencyX-linked agammaglobulinemiaCVID
87
Q

What mediates MRSA resistance to naficillin?

A

Altered penicillin binding protein.

88
Q

HIV pt with impaired renal vision who gets a prescribed _____ and then develops seizure, Hypoca, HypoMg

A

Foscarnet

89
Q

What virus causes hepatitis and has a high mortality rate among pregnant women?

A

HEV: fecal-oral route. Nonencapsulated ssRNA virus.

Associated with waterborne epidemics.
Mild severity, no chronic hepatitis.
Does cause high mortality in pregnant patients!

90
Q

What do the toxins of Clostridium Difficile do?

A

Toxin A = enterotoxin binds to brush border - causes the inflammation and secretions

Toxin B = Cytotoxic = CYTOSKELETAL disruption via actin depolymerization = pseudomembranous colitis

91
Q

What are the NNRTI?

A

Nevirapine EfavirenzDelavirdine

92
Q

What is Reye Syndrome?

A

Aspirin in pts 5-14 yo + some infection 1. Hepatic Dysfunction: microvesicular steatosis. 2. Encephalopathy: hepatic dysfxn -> hyperammonia.

93
Q

Mechanisms of action of Acyclovir?

A

Nucleoside analog -> viral thymidine kinase -> cellular enzyme phos to acyclovir triphosphate -> incorporate into newly synthesized viral DNA and terminate DNA synthesis.

94
Q

What is the most common outcome of HBV infection?

A

Complete resolution after acute hepatitis with mild/subclinical sx. Could also - chronic hepatitis +/- cirrhosis and HCC- fulminant hepatitis with massive liver necrosis.

95
Q

Hepatitis B Virus - mechanism of injury?

A

Presence of viral HbSAg and HbCAg on cell surface stimulate CD8 cytotoxic T cell to destroy infected hepatocytes. IS NOT cytotoxic on its own.

96
Q

Enterococci usually develops after what?

A

GU manipulation (cystoscopy, surgery)

97
Q

Timeframe of TB infection

A

First week: intracellular bacterial proliferation

2-4 weeks after: Th1 response, IFNgamma, etc

98
Q

Legionella Classic Presentation

A

Pneumonia + High Fever + GI sx (diarrhea) + Headache/Confusion

Pt: Smoker, Water Source

Labs: HypoNaSputum stain showing lots of PMN, but no bacteria

Dx: Urine antigen

Tx: Resp Fluoroquinolone (Levofloxacin), Macrolide (Azithromycin)

99
Q

Cave exploration + Pulm Sx

A

HISTOPLASMOSIS. Pt: bird/bat droppings, Ohio and Mississippi valleys

Histo: macrophage filled with histoplasma (smaller than an rbc)

100
Q

Encapsulated yeast

A

Cryptococcus!

101
Q

What drug resistance is mediated by decreased bacterial catalase-peroxidase activity?

A

INH!

102
Q

Where does Kaposi Sarcoma occur? Gross and Histo?

A

Kaposi Sarcoma: skin and GI tract
Reddish/violet, flat maculopapular lesion
Hemorrhagic nodule
Spindle-shaped tumor cells with small-vessel proliferation.

103
Q

Cryptosporidium causes what?

A

Severe watery diarrhea in AIDS pts. Transmission: Oocysts in water. Gross colonoscopy: Nonulcerated inflammation, with basophilic clusters on surface of intestinal mucosal cells. Dx: Oocysts on acid-fast stain

104
Q

Unexplained oral thrush in an otherwise healthy person suggests?

A

HIV

105
Q

Most likely outcome of HCV infection?

A

Chronic stable hepatitis. Second most common is chronic hepatitis progressing to cirrhosis.

106
Q

Mechanism of Zidovudine

A

Nucleoside RT inhibitor: inhibits 3’-5’ phosphodiester bond formation. AZT has a amido group in place of 3’OH.

Competitively binds to reverse transcriptase -> bc no 3’OH -> DNA chain termination.

107
Q

What bacterial factor mediates adherence to cell?

A

Pili

108
Q

What antibiotic binds to 23sRNA of 50s ribosome?

A

Macrolide (erythromycin, azithromycin, clarithromycin)Clindamycin Prevent translocation

109
Q

Linear erythematous rash shortly after hiking trip = ?

A

Poison Ivy (Contact dermatitis) = Type IV Hypersensitivity

110
Q

How do dsDNA viruses replicate?

A

All replicate in the nucleus except poxvirus. DNA dependent DNA polymerase = replication of viral genomeDNA dependent RNA polymerase = transcription of viral DNA -> mRNA exported to cytosol -> translated by cellular ribosomes into viral proteins. Note: RNA dependent DNA polymerase = RT Nomenclature: the “dependent” part is what the polymerase is acting on.

111
Q

What pathogen has trophozoites with phagocytosed RBCs?

A

Entamoeba HistolyticaPt: fecal-oral route - cysts in water, country with poor sanitationoral-anal contact - homosexuals

Sx: bloody diarrhea, abd pain, cramping

Histo:

  1. trophozoites with phagocytosed RBCS
  2. Cysts with up to 4 nuclei
112
Q

What histological feature characterizes Rabies infection?

A

Negri bodes - eosinophilic cytoplasmic inclusions in the hippocampal neurons.

113
Q

Why give PCN with Probenecid? What other combination is similar to this?

A

Probenecid - inhibits RT secretion of PCN, most cephalosporins, and other weak acids.

Imipenem + Cilastatin. Cilastatin - inhibits renal dehydropeptidase in PCT which would inactivate imipenem.

Both Probenecid and Cilastatin, directly or indirectly, inhibit RT secretion of the drug.

114
Q

All RNA viruses replicate in the ______, except _____ and _____.

A

All RNA viruses replicate in the cytoplasm, except influenza and retroviruses.

115
Q

HIV pt with abd pain, GI complaints. Bx shows mucosal ulcerations and erosions. Histo shows large cell with ovoid nuclei and basophilic deposits.

A

CMV Colitis - reactivated in setting of HIV. “Owl eye”

116
Q

HSV Tzanck test shows

A

Multinucleated giant cells with intranuclear cowdry A inclusions.

117
Q

Opportunistic causes of diarrhea in HIV pts

A
  1. Cryptosporidium - chronic, watery diarrhea- acid-fast cysts seen in stool - esp when CD4 <200
  2. CMV colitis - mucosal ulcers and erosions- owl eye nuclei - large ovoid nuclei with centralized intranuclear inclusions
  3. MAC- necrotizing and non-necrotizing granulomas- acid fast bacilli

USMLE Step 1 General (7 decks)

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