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USMLE Step 1 > Microbiology > Flashcards

Microbiology Flashcards

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1
Q

What are the four classes of dermophytes?

A
  1. Trichophytin
  2. Microsporum
  3. Epidermophytin
  4. Malassezia furfur
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2
Q

What are the common yeast organisms? Name 3.

A
  • Candida albicans
  • Cryptococcus neoformans
  • Pneumocystis jirovecii
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3
Q

What is a common mould organism?

A

Aspergillus fumigatus

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4
Q

What are some common dimorphic fungal organisms? Name 5.

A
  • Histoplasma capsulatum
  • Blastomyces dermatitidis
  • Coccidioides immitis
  • Paracoccidioides brasiliensis
  • Sporothrix schenkii
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5
Q

What are the treatments for Candida infections?

A

Vulvovaginitis: topical azoles, nystatin

Oral/Esophageal thrush: oral fluconazole, caspofungin

Systemic infections: oral/IV fluconazole, caspofungin, or amphotericin B

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6
Q

What are the three possible manifestations of Aspergillus infection?

A
  1. Allergic bronchopulmonary aspergillosis (ABPA)
    >> Common in asthma and cystic fibrosis
    >> Can cause bronchiectasis and eosinophilia
  2. Aspergillomas: esp. after TB infection
  3. Invasive aspergillosis (systemic)
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7
Q

What are the microscopic characteristics of Aspergillus fumigatus?

A

Narrow septate hyphae branching at acute angles

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8
Q

What are the microscopic characteristics of Mucor and/or Rhizopus speciies?

A

Broad, irregularly-shaped non-septate hyphae branching at right angles

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9
Q

What is the treatment for Aspergillus infection?

A
  • Voriconazole
  • Lipid amphotericin B
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10
Q

What are the common clinical manifestations of Rhizopus/Mucor infections?

A

Invasion via the cribiform plate leads to rhinocerebral infections
>> Frontal lobe abscesses
>> Black necrotic eschar on the face
>> Cranial nerve involvement

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11
Q

What is the treatment for Mucor/Rhizopus infections?

A
  • Surgical debridement
  • Amphotericin B
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12
Q

What are the prophylactic drugs for PCP?
When should we start giving them in an AIDS patient?

A
  • TMP-SMX (Bactrim)
  • Pentamidine
  • Dapsone
  • Atovaquone

>> Start prophylaxis when CD4+ count <200cells/mm3 in HIV patients

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13
Q

How do we prevent cryptococcal meningitis in AIDS/HIV patients?

A

Fluconazole

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14
Q

What are the clinical manifestations of Sporothrix schenkii infection?

A
  • Local pustule from skin trauma, usually by a (rose) thorn
  • Painless ulcerating ascending lymphangitis
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15
Q

How can we treat Sporothrix schenkii infection?

A
  • Oral potassium iodide
  • Itraconazole
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16
Q

What are some common infections caused by dermatophytes?

A
  • Tinea pedis (athlete’s foot)
  • Tinea cruris (groin – jock’s itch)
  • Tinea corpus (body – ringworm)
  • Tinea capitus (head – ringworm)
  • Tinea unguium (nails – onychomycosis)
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17
Q

What are the treatment for typical superficial dermatophyte infection?

A
  • Topical terbinafine
  • Topical azoles
  • If extensive or if involving the scalp or hair
    >> Oral terbinafine
    >> Oral azoles
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18
Q

What is the treatment for onychomycosis (tinea unguium)?

A
  • Oral terbinafine
  • Oral atroconazole
  • Oral fluconazole
    >> 6 weeks - 6 months: hands
    >> 12 weeks - 12 months: feet/toes
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19
Q

Where are the endemic locations of Histioplasma capsulatum?

A
  • Mississippi River Valley
  • Ohio River Valley
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20
Q

What are the endemic locations of Blastomyces dermatiditis?

A
  • States East of the Mississippi River
  • South to Central America
  • North to Canada
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21
Q

What are the endemic locations of Coccidioides immitis?

A
  • California
  • Southwestern United States (Texas)
  • San Joaquin Valley
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22
Q

What are the endemic locations of Paracoccidioides brasiliensis?

A

Latin America

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23
Q

What is the route of transmission of Histioplasma capsulatum?

A

Bird and bat droppings
>> Contact/inhalation

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24
Q

What is the microscopic feature of Histioplasma capsulatum?

A
  • Smaller than RBCs
  • Hides in macrophages
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25
Q

What is the microscopic feature of Blastomyces dermatitidis?

A
  • Broad-based budding
  • Same size as RBCs
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26
Q

Which systems are mainly affected in the case of blastomycosis infection?

A
  • Lung
  • Skin
  • Bone
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27
Q

What is the microscopic feature of Coccidioides immitis?

A
  • Spherule much large than RBCs
  • Filling with endospores
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28
Q

What is the natural life course of Coccidioides immitis?

A

Barrel-shaped arthroconidia >> airborne >> inhalation >> enters lung >> switches to spherules (NOT YEAST!) >> explodes with endospores

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29
Q

Which systems are mainly affected in the case of coccidioides infection?

A
  • Lungs
  • CNS
  • Skin
  • Bones and Joints
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30
Q

What is the route of transmission of Coccidioides immitis?

A

Inhalation

  • Case rate increased after earthquakes as spores in the dust are thrown up in the air and easily inhaled
  • “San Joaquin Valley” Fever
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31
Q

What is the microscopic feature of Paracoccidioides brasiliensis?

A
  • Much bigger than RBCs
  • Multiple “captain-wheel” budding formation
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32
Q

What are the general treatment plans for systemic mycoses?

A

Localized infections

  • Fluconazole
  • Itraconazole

Systemic infections
- Amphotericin B

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33
Q

What are the possible causes of systemic mycoses?

A
  • Histioplasma capsulatum
  • Blastomyces dermatiditis
  • Coccidioides immitis
  • Paracoccidioides brasiliensis
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34
Q

Which organism causes tinea versicolor?

A

Malassezia furfur (a dermatophyte)

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35
Q

What are the presenting clinical features of tinea versicolor?

A

Hypopigmented and/or hyperpigmented patches on the trunk and proximal limbs

  • Light macules coalescing to form large scaling plaques
  • Not usually pruritic
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36
Q

What is the microscopic feature of Malassezia furfur?

A

“Spaghetti and meatball” appearance on KOH prep

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37
Q

What is the treatment for tinea versicolor?

A
  • Topical miconazole
  • Topical selenium sulfide
  • Oral azoles if severe
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38
Q

What is the treatment for Malassezia furfur infection?

A
  • Topical miconazole
  • Topical selenium sulfide
  • Oral azoles if severe
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39
Q

What infections are associated with birds?

A
  • Histoplasma capsulatum
  • Cryptococcus neoformans
  • Chlamydophila psittaci
  • Viruses
    >> H5N1 Influenza
    >> West Nile Virus
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40
Q

Which anti-HIV medication is known for causing bone marrow suppression?

A

Zidovudine

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41
Q

What cell wall features are unique to Gram-positive organisms?

A
  • Thick peptidoglycan wall
  • Lipoteichoic acid
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42
Q

What cell wall features are unique to Gram-negative organisms?

A
  • Thin peptidoglycan wall
  • 2 membranes
  • Lipopolysaccharides (LPS) endotoxin in the outer membrane
  • Periplasmic space between the two membranes, containing beta-lactamase
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43
Q

What test is useful in determining capsular organisms?

A

Quellung reaction

  • Anticapsular serum is added to the bacteria
  • Capsule will appear swollen under microscopy
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44
Q

Name some encapsulated bacteria.

A

Even Some Pretty Nasty Killers Have Shiny Bodies.

  • Escherichia coli (certain strains)
  • Streptococcus pneumoniae
  • Pseudomonas aeruginosa
  • Neisseria meningitidis
  • Klebsiella pneumoniae
  • Haemophilus influenzae type B
  • Salmonella typhi
  • Group B streptococcus

+ Cryptococcus neoformans: fungus that causes meningitis in AIDS patients and is also an encapsulated organism.

  • *The SHiN organisms are very important to remember, and are common causes of infections and death in asplenic patients:**
  • Streptococcus pneumoniae
  • Haemophilus influenzae type B
  • Neisseria meningitidis
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45
Q

What are the differences in the ribosomes of prokaryotes and eukaryotes?

A

Prokaryotes

  • 50S and 30S subunits
  • 70S ribosomes

Eukaryotes

  • 60S and 40S subunits
  • 80S ribosomes
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46
Q

What are the differences between generalized and specialized transduction?

A

Generalized transduction

  • “Packaging” event
  • Lytic phages
  • Parts of bacterail chromosomal DNA become packaged into viral capside
  • Phage infects another bacterium >> transfer of genetic material

Specialized transduction

  • “Excision” event
  • Lysogenic phages
  • After incorporation of viral DNA into bacterial chromosome, when the phage DNA is excised from the bacterial DNA for production of viruses after activation of the viral infection, flanking bacterial genes are excised WITH it.
  • DNA is packaged into phage viral capside
  • Phage infects another bacterium >> transfer of genetic material
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47
Q

What are the 5 bacterial toxins encoded in a lysogenic phage?

A

ABCDE

  • Shiga-like toxin
  • Botulinum toxin
  • Cholera toxin
  • Diphtheria toxin
  • Erythrogenic toxin of Streptococcus pyogenes
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48
Q

Name some bacteria that do not Gram stain well.

A

These Microbes May Lack Real Colour.

  • Treponema
  • Mycobacteria
  • Mycoplasma
  • Legionella pneumophila
  • Rickettsia
  • Chlamydia
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49
Q

Name the microorganisms that are stained by Giemsa stain.

A

Certain Bugs Really Try His Patience.

  • Chlamydia
  • Borrelia
  • Rickettsia
  • Trypanosomes
  • Histoplasma
  • Plasmodium
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50
Q

What is periodic acid-Schiff (PAS) stain used for?

A

Staining of:

  • Mucopolysaccharides
  • Glycogen

>> Whipple’s disease by Tropheryma whipplei

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51
Q

What organisms can be stained by Ziehl-Neelson (carbol fuchsin) stian?

A
  • Mycobacterium
  • Nocardia
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52
Q

What organism can be stained by India Ink?

A

Cryptococcus neoformans

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53
Q

What organisms can be stained by silver stain?

A
  • Fungi (e.g. pneumocystis)
  • Legionella
  • Helicobacter pylori
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54
Q

Which bacteria can form spores?

A
  • Bacillus: anthracis, cereus
  • Clostridium: perfringens, tetani, botulinum
  • Coxiella burnetii
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55
Q

Which bacteria have the ability of transformation (i.e. taking up naked DNA from a lysed cell by a living microorganism and incorporating that naked DNA into its own chromosomal DNA)?

A

SHiN

  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Neisseria meningitidis

>> These three organisms are also mainly responsible for infections and deaths in asplenic individuals, and are also available as capsular conjugate vaccines.

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56
Q

Name the bacterial structure.

Mediates adherence of bacteria to the surface of a cell

A

Fimbria

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57
Q

Name the bacterial structure.

Protects against phagocytosis

A

Capsule
>> Organized and firmly adherent glycocalyx

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58
Q

Name the bacterial structure.

  • Rgiid support to bacterial cell
  • Protects against osmotic pressure differences
A

Peptidoglycan layer of the cell wall

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59
Q

Name the bacterial structure.

  • Space between the inner and outer cellular membranes
  • Unique to Gram-negative bacteria
A

Periplasmic scpae

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60
Q

Name the bacterial structure.

  • Bacterial form providing resistance to heat, chemicals and dehydration
  • Formed mainly by Bacillus and Clostridium species
  • Also formed by Coxiella burnetii
A

Spores/endospores

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61
Q

Name the bacterial structure.

Forms attachment between two bacteria during conjugation (transfer of DNA material)

A

Pilus
>> Sex pilus
>> F-pilus

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62
Q

Name the bacterial structure.

  • Genetic material within bacteria that contains genes for antibiotic resistance
  • Not a part of the chromosomal DNA
A

Plasmid

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63
Q

Name the four main methods of bacterial genetic transfer.

A
  1. Conjugation
  2. Transposition (by transposons)
  3. Transformation (uptake of naked DNA from a lysed cell by a living microorganism)
  4. Transduction (generalized VS. specialized)
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64
Q

What are the properties of a superantigen? Which bacteria are famous for producing superantigens?

A
  • Exotoxins that are able to bind to MHC II receptors and TCRs simultaneously
  • This induces a polyclonal expansion of T-cells and thus a massive immune response, triggering release of large amounts of cytokines

  • *Bacteria famous for producting superantigens:
  • Staphylococcus aureus
  • Streptococcus pyogenes (Group A Streptococcus)**
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65
Q

What are the exotoxins produced by Staphylococcus aureus?

A
  • Alpha-toxin: hemolysis
  • Beta-toxin: sphingomyelinase C
  • Gamma-toxin
    >> A+B = Hemolysin
    >> B+C = Leukocidin
  • Delta-toxin: hemolysis
  • Panton-Valentine leukocidin: bicomponent toxin especially found in MRSA
  • Superantigens
    >> Enterotoxins A-E: food poisoning
    >> TSST-1: toxic shock syndrome (tampons; high fever, hypotension, diffuse rash)
    >> Epidermolytic/exfoliative toxins: scalded skin syndrome
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66
Q

How does endotoxin induce damage in the host tissue?

A

1. Macrophage activation

  • IL-1 and IL-6: fever
  • TNF-alpha: fever, hypotension, cell death and cachexia
  • Nitric oxide: hypotension
  • Mediates the occurrence of septic shock

2. Complement activation

  • C3a: hypotension, edema
  • C5a: neutrophil chemotaxis

3. Tissue factor release

  • Activates the coagulation cascade
  • Can lead to disseminated intravascular coagulopathy (DIC_
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67
Q

Name four exotoxins that work by inhibiting protein synthesis.

A
  1. Diphtheria toxin of Corynebacterium diphtheriae (inhibits EF-2)
  2. Exotoxin A of Pseudomonas aeruginosa (inhibits EF-2)
  3. Shiga toxin of Shigella species (inactivates 60S subunit of host ribosomes)
  4. Shiga-like toxin of EHEC (inactivates 60S subunit of host ribosomes)
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68
Q

Name 4 exotoxins that work by increasing fluid secretion (and thus usually causing watery diarrhea).

A
  1. Heat labile (increases cAMP) and heat stable (increased cGMP) toxins of ETEC
  2. Cholera toxin of Vibrio cholera (increases cAMP and thus increases Cl- and H2O efflux in the gut)
  3. Anthrax toxin of Bacillus anthracis (mimics adenylate cyclase)
  4. Pertussis toxin of Bordetella pertussis (disables Gi protein >> increases cAMP)
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69
Q

What toxin is secreted by Corynebacterium diphtheriae and what is its mechanism of action? What are its clinical effects?

A
  • Diphtheria toxin
  • Inhibits protein synthesis by inhibiting elongation factor 2 (EF-2)
  • Clinical features
    >> Pseudomembranous pharyngitis
    >> Cardiac cell damage
    >> Nerve cell damage
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70
Q

What toxin is secreted by enterhemorrhagic Escherichia coli (EHEC), and what is its mechanism of action? What are its clinical effects?

A
  • Shiga-like toxin (verocytotoxin)
  • Inactivates the 60S subunit of the hosts’ ribosomes by cleaving adenine from rRNA, and thus inhibiting protein synthesis
  • Enhances cytokine release >> hemolytic uremic syndrome (HUS)
    >> Hemolytic anemia
    >> Thrombocytopenia
    >> Acute renal failure
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71
Q

What toxin is secreted by Shigella species, and what is its mechanism of action? What are its clinical effects?

A
  • Shiga toxin
  • Inactivates 60S subunit of the hosts’ ribosomes by cleaving adenine from rRNA, and thus inhibits protein synthesis
  • Clinical effects:
    >> GI mucosal damage – dysentery
    >> Enhances cytokine release – hemolytic uremic syndrome (HUS)
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72
Q

What toxin is secreted by Pseudomonas aeruginosa, and what is its mechanism of action? What are its clinical effects?

A
  • Exotoxin A
  • Inhibits elongation factor 2 (EF-2) and thus inhibits protein synthesis
  • Causes host cell death
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73
Q

What toxin is secreted by enterotoxigenic Escherichia coli (ETEC), and what is its mechanism of action? What are its clinical effects?

A
  • Heat stable and heat labile toxins
  • Heat labile toxin overstimulates adenylate cyclase >> increases intracellular cAMP
  • Heat stable toxin overstimulates guanylate cyclase >> increases intracellular cGMP
  • Clinical effects
    >> Watery diarrhea
    >> ETEC is the leading cause of traveller’s diarrhea

RMB: Los Angeles and Singapore!

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74
Q

What toxin is secreted by Bacillus anthracis, what are its components and what are their mechanisms of action? What are the clinical effects?

A
  • Anthrax toxin
    >> Edema factor
    >> Lethal factor
    >> Protective factor
  • Edema factor mimics adenylate cyclase and thus increases intracellular cAMP
  • Leads to the characteristic edematous borders of the black eschar in cutaneous anthrax
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75
Q

What toxin is secreted by Vibrio cholerae, and what is its mechanism of action? What are its clinical effects?

A
  • Cholera toxin
  • Permanently activates Gs proteins and thus overstimulates adenylate cyclase >> increased intracellular cAMP levels >> increased Cl- and H2O efflux
  • Causes watery diarrhea
    >> Rehydration is life-saving in cholera!
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76
Q

What toxin is secreted by Bordetella pertussis, and what is its mechanism of action? What are its clinical effects?

A
  • Pertussis toxin
  • Disables Gi proteins >> adenylate cyclase work uninhibited >> increased intracellular cAMP levels
  • Whooping cough
    >> Seen in children
    >> Whoops on inspiration
    >> Coughs on expiration
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77
Q

What toxin is secreted by Clostridium perfringens, and what is its mechanism of action? What are its clinical effects?

A
  • Alpha toxin
  • A phospholipase (lecithinase) causing lysis of cell membranes and tissue damage
  • Clinical effects
    >> Gas gangrene
    >> Myonecrosis
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78
Q

What toxin is secreted by Clostridium tetani, and what is its mechanism of action? What are its clinical effects?

A
  • Tetanospasmin
  • Cleaves SNARES that are required for neurotransmitter release >> inhibits release of GABA and glycine from the neurons (esp. in the Renshaw cells of the spinal cord)
  • Clinical effects
    >> Spastic paralysis
    >> Risus sardonicus
    >> Lock-jaw
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79
Q

What toxin is secreted by Clostridium botulinum, and what is its mechanism of action? What are its clinical effects?

A
  • Botulinum toxin
  • Cleaves SNARES that are required for neurotransmitter release >> prevents release of ACh at neuromuscular junctions mainly
  • Clinical effects: flaccid paralysis
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80
Q

What are the exotoxins produced by Streptococcus pyogenes?

A
  1. Streptolysin O: oxygen labile
  2. Streptolysin S: oxygen stable
  3. Erythrogenic/pyrogenic toxins A, B and C (superantigens)
    >> Scarlet fever
    >> Streptococcal toxic shock syndrome
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81
Q

What organism causes pseudo-appendicitis?

A

Yersinia enterocolitica

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82
Q

What are the 3 components of anthrax toxin?

A
  • Edema factor
  • Lethal factor
  • Protective antigen
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83
Q

Name 7 bacteria that produce enterotoxins (exotoxins that causes gut electrolyte and water imbalances leading to diarrhea).

A
  1. Staphylococcus aureus
  2. Shigella species
  3. Enterohemorrhagic E. Coli (EHEC) – O157:H7
  4. Enterotoxigenic E. Coli (ETEC)
  5. Vibrio cholerae
  6. Yersinia enterocolitica
  7. Clostridium perfringens, Clostridium difficile
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84
Q

What is the mechanism of resistance in MRSA?

A

Altered penicillin-binding protein

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85
Q

What bacterium is known to produce large golden colonies?

A

Staphylococcus aureus

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86
Q

What bacterium is known to produce blue-green pigments?

A

Pseudomonas aeruginosa

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87
Q

What bacterium is known to produce yellow sulfur granules?

A

Actinomyces israelii
>> Anaerobic
>> Not acid-fast
>> Gram-positive branching filaments

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88
Q

What bacterium is known to produce red pigments?

A

Serratia marcescens

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89
Q

What is the first and second most common cause of uncomplicated urinary tract infection (UTI) in young women?

A
  1. Escherichia coli
  2. Staphylococcus saprophyticus (catalase +ve, coagulase -ve, novobiocin resistant)
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90
Q

What vaccinations are available against Streptococcus pneumoniae?

A
  • Pneumococcal conjugate vaccine (PCV13): for infants
  • Pneumococcal polysaccharide vaccine (PPSV23): for adults
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91
Q

What are the indications for pneumococcal vaccination for adults?

A
  • Age 65 years of above
  • Age 2-64 years with chronic illness
  • Smoker
  • Asthmatic
  • Disease that decreases immune response
    >> Leukemia
    >> Lymphoma
    >> Renal failure
    >> HIV infection
    >> Asplenia
  • Medication that decreases immune response
    >> Steroids
    >> Chemotherapy
    >> Radiation therapy
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92
Q

What virulence factor does Staphylococcus aureus have other than exotoxins?

A

Protein A

  • Binds to Fc-IgG
  • Inhibits complement activation and thus disrupts opsonization
  • Disrupts phagocytosis
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93
Q

What important virulence factors do Streptococcus pneumoniae have?

A
  • Capsule
    >> There is no virulence if the pneumococcus has no capsule
  • IgA protease
    >> IgA protects mucosal surfaces from bacterial infection
    >> IgA protease cleaves IgA, providing a survival advantage for the pneumococci that is trying to colonize the respiratory mucosae
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94
Q

What are the classical presenting features for pneumococcus pneumonia?

A
  • Sudden onset of chills
  • Lobar consolidation
  • “Rusty colour” sputum
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95
Q

What infections does Streptococcus pneumoniae usually cause?

A

MOPS

  • Meningitis
  • Otitis media (especially in children)
  • Pneumonia
  • Sinusitis
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96
Q

What are some classes of Viridans Streptococcus?

A
  • Strep. mutans
  • Strep. salivarius
  • Strep. anginosus
  • Strep. mitis
  • Strep. sanguinis
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97
Q

What types of infections/diseases can Streptococcus pyogenes cause?

A

Pyogenic diseases

  • Pharyngitis
  • Cellulitis/impetigo
  • Systemic infections: pneumonia, bacteremia, necrotizing fasciitis

Toxin-mediated diseases

  • Streptococcal toxic shock syndrome
  • Necrotizing fasciitis

Immunological diseases

  • Rheumatic fever (following strep throat)
  • Acute post-streptococcal glomerulonephritis (following either pharyngitis or skin infection)
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98
Q

What is the diagnostic criteria for rheumatic fever?

A

Jones Criteria
>> 2 major criteria OR 1 major criterium plus 2 minor criteria

Major criteria

  • Joints: polyarthritis
  • <3: pancarditis (endo/myo/peri)
  • Nodules: subcutaneous/Aschoff nodules
  • Erythema marginatum
  • Sydenham chorea

Minor criteria

  • Fever
  • Arthralgia
  • Elevated ESR or CRP
  • Prolonged PR interval on ECG
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99
Q

What are some clinical features for Scarlet fever?

A
  • Scarlet sandpaper-like rash
  • Strawberry tongue
  • Circumoral pallor
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100
Q

What infections can Group B streptococcus (Streptococcus agalactiae)?

A

Babies/Neonates

  • Pneumonia
  • Meningitis
  • Sepsis

Pregnant Women

  • Asymptomatic bacteruria
  • Urinary tract infection
  • Post-partum endometritis
  • Bacteremia

Non-Pregnant Women

  • Bacteremia
  • Skin and soft tissue infections
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101
Q

Name the three most common organisms causing neonatal sepsis.

A
  • Group B streptococcus
  • Escherichia coli
  • Listeria monocytogenes
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102
Q

Where are Viridians streptococci usually found?

A

Normal flora of the oropharynx

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103
Q

Where is Streptococcus agalactiae usually found?

A

Normal flora of the vagina in 25% of women
>> Asymptomatic carriers

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104
Q

Where are enterococci usually found?

A

Normal colonic flora

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105
Q

What infections do enterococci usually cause?

A
  • Urinary tract infections
  • Biliary tract infections
  • Subacute bacterial endocarditis
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106
Q

How does the Lancefield grouping classify streptococci?

A

By the differences in the C carbohydrate on the bacterial cell wall

107
Q

What condition is Streptococcus bovis associated with?

A

COLON CANCER

>> Bacteremia
>> Subacute endocarditis

108
Q

What organisms are most commonly implicated in subacute endocarditis?

A
  • Viridans streptococci
  • Enterococci
  • Streptococcus bovis
  • Staphylococcus epidermidis (coagulase-negative staphylococcus)
  • HACEK organisms
    >> Haemophilus
    >> Actinobacillus
    >> Cardiobacterium
    >> Eikenella
    >> Kingella
109
Q

What are some clinical manifestations of Corynebacterium diphtheriae infection?

A
  • Pseudomembranous pharyngitis with grayish-white membraneous exudate
  • Lymphadenopathy
  • Myocarditis
  • Arrhythmias
110
Q

How does one diagnose Corynebacterium diphtheriae infection?

A
  • Culture of gram-positive club-shaped rods with metachromatic (blue/red) granules
  • Elek test for diphtheria toxin
  • Black colonies on cystine-tellurite agar
111
Q

What is the capsule of Bacillus anthracis made of?

A

D-glutamate
>> B. anthracis is the only bacterium with polypeptide capsule

112
Q

Name the obligate anaerobes.

A

Anaerobes Can’t Breathe Air.

  • Clostridium
  • Bacteroides
  • Actinomyces

>> Treat with metronidazole and/or clindamycin

113
Q

Name the obligate aerobes.

A

Nagging Pests Must Breathe.

  • Nocardia
  • Pseudomonas aeruginosa
  • Mycobacterium
  • Bacillus: actually a facultative anaerobe….
114
Q

What are the clinical manifestations of infection with Bacillus anthracis?

A

Cutaneous anthrax

  • Boil-like papule >> Ulcer with black eschar – PAINLESS with necrotic centre
  • Uncommonly progresses to bacteremia and death

Inhalation/Pulmonary anthrax
- Flu-like symptoms
- Fever
- Pulmonary hemorrhage
- Mediastinitis
- Shock
>> Mediastinal widening on CXR
>> Woolsorter’s disease

115
Q

What are the clinical features of tetanus infection?

A
  • Trismus (Lock-jaw)
  • Risus sardonicus
  • Spastic paralysis
116
Q

Which populations does Listeria monocytogenes mainly affect?

A
  • Infants
  • Elderly
  • Immunocompromised
  • Pregnant women
117
Q

What infections does Listeria monocytogenes mainly cause?

A

Pregnant women

  • Amionitis
  • Septicaemia
  • Spontaneous abortions

Neonates/Infants

  • Granulomatous infantiseptica
  • Neonatal meningitis

Elderly
- Meningitis

Healthy individuals

  • Gastroenteritis
  • Usually self-limiting

>> Listeria is the only gram-positive organism that produces LPS.

118
Q

What are the microscopic characteristics of Listeria monocytogenes?

A
  • Facultative intracellular microbe
  • Taken up by monocytes
  • Rocket tails
  • Tumbling motility
119
Q

Which antibiotic can be used to treat Listeria monocytogenes?

A

Ampicillin

120
Q

Which antibiotic can be used to treat Actinomyces?

A

Penicillin

121
Q

Which antibiotic can be used to treat Nocardia?

A

Sulfonamides

122
Q

What is the most common cause of meningitis?

A

Streptococcus pneumoniae

123
Q

What is the most common cause of osteomyelitis?

A

Staphylococcus aureus

124
Q

Name the gram-negative cocci.

A
  • Neisseria meningitidis (maltose fermenter)
  • Neisseria gonorrhoeae (maltose non-fermenter)
  • Morexella catarrhalis
125
Q

Name the gram-negative coccoid rods.

A
  • Haemophilus influenzae
  • Bordetella pertussis
  • Pasteurella
  • Brucella
126
Q

Name the gram-negative lactose fermenter rods.

A

Fast fermenters

  • Escherichia coli
  • Klebsiella
  • Enterobacter

Slow fermenters

  • Citrobacter
  • Serratia
127
Q

Name the gram-negative lactose nonfermenting rods.

A

Oxidase positive
- Pseudomonas

Oxidase negative

  • Shigella
  • Salmonella
  • Proteus
128
Q

Name the gram-negative curved bacteria.

A
  • Campylobacter jejuni
    >> Grows in 42oC
    >> Predisposes to Guillain-Barre syndrome
  • Vibrio cholerae
    >> Grows in alkaline medium
    >> Comma-shaped

These are oxidase positive.

129
Q

What infections can Neisseria gonorrhoeae cause?

A
  • Urethritis
  • Sexually transmitted infection
  • Pelvic inflammatory disease
  • Septic arthritis
  • Fitz-Hugh-Curtis syndrome
130
Q

What infections can Neisseria meningitidis cause?

A
  • Meningitis
  • Meningococcemia
  • Waterhouse-Friderichsen syndrome (adrenal hemorrhage)
131
Q

What drugs are used to prophylaxis against Neisseria meningitidis?

A
  • Rifampicin
  • Ciprofloxacin
  • Ceftriaxone
132
Q

What is the treatment for Neisseria gonorrhoeae infection?

A
  • Ceftriaxone
  • Azithromycin/doxycycline for Chlamydia trachomatis co-infection
133
Q

What is the treatment for Neisseria meningitidis infection?

A
  • Ceftriaxone
  • Penicillin G

>> Immediate and empirical treatment! —- NEVER WAIT FOR CULTURE

134
Q

What infections does Haemophilus influenzae usually cause?

A

EMOP

  • Epiglottitis
  • Meningitis
  • Otitis externa
  • Pneumonia
135
Q

Which culture medium is used for Haemophilus influenzae?

A

Chocolate agar with Factor V and Factor X

136
Q

What is the treatment for Haemophilus influenzae infection?

A

Mucosal infections

  • Amoxicillin
  • +/- Clavulanic acid

Meningitis

  • Ceftriaxone
  • Rifampicin prophylaxis for close contacts
137
Q

Which culture medium and stain is used for Legionella pneumophilus?

A
  • Stain: silver stain
  • Culture medium: charcoal yeast extract medium with iron and cysteine
138
Q

What is the mode of transmission of Legionella pneumophila?

A
  • Aerosol transmission
  • NOT person-to-person
139
Q

What are the clinical manifestations of Legionella pneumophila infections?

A

Legionnaire’s disease

  • Fever
  • Severe pneumonia
  • GI symptoms
  • CNS symptoms

Pontiac fever
- Mild flu-like syndrome

140
Q

What infections does Pseudomonas aeruginosa usually cause?

A

PSEUDOmonas

  • Pneumonia
  • Sepsis
  • Otitis Externa
  • Urinary tract infection
  • Diabetic Osteomyelitis
  • Wound and burn infections
  • Hot tub folliculitis
  • Ecthyma gangrenosum: rapidly progressive necrotic cutaneous lesions
141
Q

What is the treatment for Pseudomonas aeruginosa?

A
  • Aminoglycoside
  • Fluoroquinolones
  • Anti-pseudomonal penicillins: piperacillin, ticarcillin
  • Anti-pseudomonal cephalosporins: cefepime, ceftazadime, cefoperazone
  • Imipenem, meropenem
142
Q

What is Helicobacter pylori a risk factor for?

A
  • Peptic ulcer disease
  • Gastric adenocarcinoma
  • Lymphoma
143
Q

What microbiological tests help identify Helicobacter pylori?

A
  • Gram-negative curved rod
  • Urease +
  • Catalase +
  • Oxidase +
144
Q

What is the treatment for Helicobacter pylori infection?

A

Triple therapy
>> Proton pump inhibitor
>> Clarithromycin
>> Amoxicillin OR Metronidazole

Quadruple therapy
>> Proton pump inhibitor
>> Bismuth
>> Metronidazole
>> Tetracycline

145
Q

What is the most common cause of travellers’ diarrhea?

A

Enterotoxigenic E. coli

146
Q

What are the features of hemolytic uremic syndrome?

A
  • Hemolytic anemia
  • Thrombocytopenia
  • Acute renal failure
147
Q

What is the treatment for Escherichia coli infections?

A
  • Mainly supportive
  • Antibiotics
    >> Fluoroquinolones
    >> Azithromycin
    >> TMP-SMX
148
Q

What is the treatment for Clostridium difficile infection?

A
  • Metronidazole
  • Oral vancomycin
    >> Not absorbed systemically
    >> Will not cause nephrotoxicity
149
Q

What are some important microbiological differences between Salmonella and Shigella?

A
  • Salmonella has flagella; Shigella doesn’t
  • Salmonella produces hydrogen sulfide; Shigella doesn’t
  • Salmonella is found in a lot of animals
    Shigella is found only in human and primates
150
Q

What are the characteristic features of typhoid fever, and what is the causative organism?

A
  • Rose spots on the abdomen
  • Fever
  • Headache
  • Diarrhea
  • Can remain in the gallbladder and cause a carrier state

>> Salmonella typhi
>> Found only in humans

151
Q

What is the characteristic clinical finding for Klebsiella pneumonia?

A

Red current jelly sputum

152
Q

What infections does Klebsiella usually cause?

A
  • Aspiration pneumonia in diabetics and alcoholics
  • Nosocomial UTI
153
Q

What is the source of infection of Yersinia enterocolitica?

A
  • Pet feces (e.g. puppies)
  • Contaminated milk
  • Contaminated pork
154
Q

What are the clinical manifestations of Yersinia enterocolitica infection?

A
  • Bloody diarrhea
  • Mesenteric adenitis >> can mimic Crohn disease or appendicitis
155
Q

What are the bacteria that can cause food poisoning?

A

Gram-positive bacteria

  • Staphylococcus aureus (picnics)
  • Bacillus cereus (reheated rice)
  • Clostridium perfringens (reheated meat)
  • Clostridium botulinum (canned food)

Gram-negative bacteria

  • E. coli O157:H7 (burgers)
  • Salmonella (poulty, meat and eggs)
  • Vibrio parahemolyticus/vulnificus (seafood)
156
Q

What are the toxins produced by Clostridium difficile?

A
  • Toxin A: enterotoxin >> diarrhea
  • Toxin B: cytotoxin >> pseudomembranous colitis
157
Q

Which antibiotics are associated with Clostridium difficile infection?

A
  • Clindamycin
  • Ampicillin

>> Any antibiotic can do it

158
Q

Name the bacteria.

  • Clue cells
  • Fishy discharge
  • Bacterial overgrowth
A

Gardnerella vaginalis

159
Q

What drugs can cause photosensitivity?

A

SAT for a photo

  • Sulfonamides
  • Amiodarone
  • Testosterone
160
Q

What are the signs and symptoms of cystitis?

A
  • Dysuria
  • Frequency
  • Urgency
  • Suprapubic pain

>> WBCs and often RBCs in urine
>> No casts: need involvement of the kidney for casts

161
Q

What patient populations are at increased risk for urinary tract infections?

A
  • Women (especially pregnant women)
  • Men with congenital abnormalities
    >> Hypospadias
    >> Epispadias
  • Vesicoureteral reflux
  • Elderly men, especially those with enlarged prostates
  • Any condition that causes stasis of urine
  • Diabetics
162
Q

What are the signs and symptoms of pyelonephritis?

A
  • Fever
  • Chills
  • Flank pain
  • Hematuria
  • WBC casts: WBCs in the renal tubules and compressed >> moulded in the tubules to form casts
163
Q

How does one diagnose urinary tract infections?

A
  • History: women with dysuria and frequency without vaginal discharge – 90% UTI
  • Leukocyte esterase test
    >> Positive LE indicates inflammation in the urinary tract (not only specific to UTIs)
  • Nitrite test
    >> Detects the presence of Enterobacteriaceae
    >> Can be negative in the presence of UTI if caused by other organisms
164
Q

What are the common causative organisms for UTIs?

A
  1. Escherichia coli (80% of all UTIs)
  2. Staphylococcus saprophyticus (10-15% of all UTIs)
  3. Klebsiella pneumoniae
  4. Proteus mirabilis/Proteus vulgarus
    >> Enterobacter cloacae
    >> Serratia marcescens
    >> Pseudomonas

KEEPPSS

  • Klebsiella pneumonia
  • Escherichia coli
  • Enterobacter cloacae
  • Proteus mirabilis/Proteus vulgarus
  • Pseudomonas aeruginosa
  • Staphylococcus saprophyticus
  • Serratia marcesens
165
Q

What condition is associated with Proteus infection of the urinary tract?

A

Struvite/staghorn/ammonium-magnesium-phosphate renal stones

166
Q

What antibiotics are commonly used to treat urinary tract infections?

A
  • SMP-TMX (sulfonamides)
  • Aminopenicillins
  • Fluoroquinolones
  • Nitrofurantoin
167
Q

What is the mechanism of action of sulfonamides?

A
  • Competitive inhibitor of dihydropteroate synthase
  • Inhibits folate production
  • Bacteria cannot absorb folate from the external environment
  • Bacteria must make their own folate acid
168
Q

What organisms do sulfonamides cover?

A
  • Gram negatives
  • Gram positives
  • Nocardia
  • Chlamydia
  • Usually used for UTI
  • Also used for skin infections
169
Q

What are the common side effects of sulfonamides?

A
  • Hypersensitivity (sulfa allergy)
  • Hemolysis in patients with G6PD deficiency
  • Nephrotoxicity: tubulointerstitial nephritis
  • Photosensitivity
  • Stevens-Johnson syndrome
  • Kernicterus from in utero exposure
  • Drug interaction: displacement of drugs (e.g. warfarin) from albumin
170
Q

What are the mechanisms of resistance of bacteria against sulfonamides?

A
  • Decreased drug uptake
  • Altered target enzyme (dihydropteroate synthase)
  • Increased PABA synthesis
171
Q

What drugs can cause Stevens-Johnson syndrome?

A
  • Penicillins
  • Sulfa drugs
  • Seizure drugs
    >> Carbamazepine
    >> Phenyotoin
    >> Ethosuximide
    >> Lamotrigine
    >> Phenobarbital
  • Allopurinol
172
Q

What is the mechanism of action of trimethoprim?

A
  • Inhibits dihydrofolate reductase
  • Often used in combination with sulfamethoxazole
  • Inhibits folate synthesis
173
Q

What are the indications for use of TMP-SMX?

A
  • Urinary tract infections
  • Prophylaxis in recurrent UTIs
  • Shigella
  • Salmonella
  • Treatment and prophylaxis for Pneumocystis jirovecii pneumonia (PCP)
  • Prophlaxis for toxoplasmosis
174
Q

What the side effects of trimethoprim?

A

Conditions associated with low folate levels

  • Megaloblastic anemia
  • Leukopenia
  • Granulocytopenia
175
Q

What is the mechanism of action for fluoroquinolones?

A

Inhibits DNA gyrase and topoisomerase IV

176
Q

What drugs should be avoided when taking fluoroquinolones?

A
  • Antacids
  • Any supplements containing:
    >> Calcium
    >> Magnesium
    >> Iron
177
Q

What are the main indications for fluoroquinolone use?

A
  • Gram-negative infections of the urinary and gastrointestinal tract
  • Pseudomonas infections
  • Neisseria infections
  • Some gram-positive infections, especially for later generations (e.g. levofloxacin)
178
Q

What are the side effects of fluoroquinolones?

A
  • GI upsets
  • Headache
  • Dizziness
  • Superinfections
  • Tendonitis (Achilles tendon) and tendon rupture
  • Leg cramps and myalgias
  • Prolonged QT interval

>> Contraindicated in pregnant women, nursing mothers and children under 18 years due to possible damage to cartilage
>> The only exception to use of FQ in children is in recurrent lung infections in cystic fibrosis

179
Q

What is the mechanism of resistance against fluoroquinolones?

A
  • Chromosomal-encoded mutations of DNA gyrase
  • Plasmid-encoded resistance
  • Efflux pumps
180
Q

What is the mechanism of action of nitrofurantoin?

A

Inactivates bacterial ribosomes

>> Reduced by bacterial proteins to a reactive intermediate

181
Q

What is the indication for nitrofurantoin use?

A

Mild UTI: usually cystitis caused by E. coli and S. saprophyticus
>> NEVER pyelonephritis
>> NEVER Proteus infections

182
Q

What is the mechanism of action of metronidazole?

A

Forms free radial toxic metabolics
>> Bactericidal
>> Anti-protozoal

183
Q

What are the indications for metronidazole use?

A

GET GAP on the Metro.

  • Giardia lamblia
  • Entamoeba histolytica etc.
  • Trichomonas vaginalis etc.
  • Gardneralla vaginalis
  • Anaerobes: Clostridium, Bacteroides
  • H. Pylori
184
Q

What are the side effects of metronidazole?

A
  • Disulfuram-like reaction
  • Headaches
  • Metallic taste
185
Q

What are the drugs that can cause a disulfuram-like reaction if taken with alcohol?

A

PM PMT in SinGapore

  • Procarbazine
  • Metronidazole
  • Cefoperazone, cefamandole and cefotetan
  • First generation Sulfonylureas
  • Griseofulvin
186
Q

What drugs are used to treat anaerobic infections?

A
  • Below the diaphragm: metronidazole
  • Above the diaphragm: clindamycin
187
Q

Name the three spirochetes.

A

BLT

  • Borrelia burgdoferi
  • Leptospira interrogans
  • Treponema
188
Q

What is the characteristic shape of Leptospira interrogans, and what is the classic origin of infection?

A
  • Question-mark shape
  • Contact with contaminated water of animal urine
189
Q

What are the clinical manifestations of Leptospira infections?

A

Leptospirosis

  • Early phase: flu-like symptoms
  • Asympatomatic phase
  • Later phase: jaundice from liver damage, renal failure, meningitis and conjuntival suffusion with photophobic
  • *Weil disease**
  • Jaundice
  • Azotemia
  • Fever
  • Hemorrhage
  • Anemia
190
Q

What is the causative organism of Lyme disease? Where in the U.S. is it most commonly found?

A

Borrelia burgdoferi
>> Most commonly found in northeastern United States

191
Q

What is the vector for Borrelia burgdoferi?

A

Ixodes ticks (also vector for Babesia)

Natural reservoir: mouse

192
Q

What are the symptoms of Lyme disease?

A

Stage 1 symptoms

  • Erythema chronicum migrans (“Bull’s eye” red rash)
  • Flu-like symptoms
  • May have facial nerve palsy

Stage 2 symptoms
- Cardiac symptoms
>> AV nodal block
>> Myopericarditis
- Neurological symptoms
>> Facial nerve palsy (usually bilateral)
>> Encephalopathy
>> Polyneuropathy

Stage 3 symptoms

  • Chronic large joint monoarthritis
  • Migratory polyarthritis
  • Subactue encephalitis/encephalopathy
193
Q

What is the treatment for Lyme disease?

A
  • Doxycyline
  • Ceftriaxone
194
Q

What are the symptoms of syphilis?

A

Primary syphilis
- Usually singular/isolated painless chancre

Secondary syphilis

  • Systemic/disseminated disease
  • Maculopapular rash involving the palms and soles
  • Condyloma lata: warty lesions at moist areas

Tertiary syphilis
- Gummas: chronic granulomas
- Aortitis of the ascending aorta: tree barking due to vasa vasorum destruction
- Neurosyphilis
>> Tabes dorsalis
>> Argyll Robertson pupil
>> Charcot joints

195
Q

How does one diagnose syphilis?

A
  • Direct visualization by dark-field microscopy in primary syphilis
  • Serological testing
    >> Nonspecific: VDRL/RPR
    >> Specific: FTA-ABS
196
Q

What is the treatment for syphilis?

A

Penicillin G
>> If allergic to penicillin: doxycycline

197
Q

What are the clinical features of congenital syphilis?

A
  • Sabre shins
  • Saddle nose
  • Hutchinson teeth
  • Mulberry molars
  • CNVIII deafness
198
Q

What conditions are associated with rash involving the palms and soles?

A

Kawasaki CARS

  • Kawasaki disease
  • Coxsackie A viral infection
  • Rocky Mountain Spotted Fever
  • Secondary syphilis
199
Q

What are the possible causes of a false positive VDRL test?

A

Missed Positive VDRL

  • Malaria
  • Pregnancy
  • Viruses: EBV (mono), hepatitis
  • Drugs
  • Rheumatic fever and Rheumatoid arthritis
  • Lupus and Leprosy
200
Q

Name the zoonotic organism.

  • Cat-scratch fever
  • Bacillary angiomatosis
A

Bartonella

>> Regional lymphadenopathy
>> Bacillary angiomatosis in immunocompromised (similar to Kaposi sarcoma)

201
Q

Name the zoonotic organism.

  • Lyme disease
  • Ixodes ticks
A

Borrelia burgdoferi

>> Shares Ixodes ticks with Babesia

202
Q

Name the zoonotic organism.

  • Recurrent fever
  • Ticks and lice
A

Borrelia recurrentis

203
Q

Name the zoonotic organism.

  • Undulant fever
  • Unpasteurized dairy products
A
  • Brucella* species
    • Gram negative coccoid rods
204
Q

Name the zoonotic organism.

  • Bloody diarrhea
  • Pets and livestock
  • Grows in 42oC
A

Campylobacter jejuni

205
Q

Name the zoonotic organism.

  • Severe pneumonia
  • Parrots and other birds
A

Chlamydia psittaci

206
Q

Name the zoonotic organism.

  • Q-fever
  • Spores from tick feces and cattle placenta
A

Coxiella burnetii

207
Q

Name the zoonotic organism.

  • Headache, muscle aches and fatigue
  • Blunts immune system >> opportunitistic infections (e.g. Candida)
  • Lone Star ricks
A

Ehrlichia chaffeensis

208
Q

Name the zoonotic organism.

  • Tularemia
  • Deer
  • Tick bites
  • Rabbits
A

Francisella tularensis

209
Q

Name the zoonotic organism.

  • Jaundice
  • Azotemia
  • Hemorrhage
  • Conjunctival suffusion
  • Animal urine
A

Leptospira interrogans

210
Q

Name the zoonotic organism.

  • “Glove and stocking” loss of sensation
  • Leonine facis
  • Armadillos
A

Mycobacterium leprae

211
Q

Name the zoonotic organism.

  • Cellulitis
  • Osteomyelitis
  • Cat and dog bites
A

Pasteurella multocida

212
Q

Name the zoonotic organism.

  • Epidemic typhus
  • Louse
A

Rickettsia prowazekii

213
Q

Name the zoonotic organism.

  • Rash over the palms and soles
  • Dermacentor ticks
A

Rickettsia rickettsii

214
Q

Name the zoonotic organism.

  • Endemic typhus
  • Fleas
A

Rickettsia typhi

215
Q

Name the zoonotic organism.

  • Bubonic plague
  • Fleas
  • Prairie dogs
  • Rats
A

Yersinia pestis

216
Q

Name the bacterium.

  • Fishy smell discharge
  • Bacterial overgrowth
  • Clue cells
A

Gardnerella vaginalis

217
Q

Name the bacterium.

  • Fever
  • Spread by ticks
  • Rash on palms and soles
A

Rickettsia rickettsii

>> Rocky Mountain Spotted Fever

218
Q

Name the bacterium.

  • Fever
  • Spread by louse and fleas
  • Central rash spreading outwards
A

Rickettsia prowazekii and typhi

219
Q

Name the bacterium.

  • Infertility
  • Ectopic pregnancy
  • Urethritis
A

Chlamydia trachomatis

220
Q

Name the bacterium.

  • Transmitted by aerosols
  • Treated with doxycycline or azithromycin
  • Interstitial pneumonia
A
  • Chlamydophila pneumoniae/Mycoplasma pneumoniae*
221
Q

Name the bacterium.

  • Spore former
  • Negative Weil-Felix
  • Q-fever
A

Coxiella burnetii

222
Q

How does primary TB present?

A
  • Asymptomatic
  • Fever
  • Chest pain and cough
  • Usually CXR is normal
  • Most common CXR finding if present: hilar lymphadenopathy
223
Q

What is the difference between Ghon focus and Ghon complex?

A
  • Ghon focus: calcified lung scar
  • Ghon complex: Ghon focus + calcified hilar lymph node
224
Q

What are the possible causes of a positive PPD (purified protein derivative) test?

A
  • Current infection
  • Past exposure
  • BCG vaccine
225
Q

What are the possible causes of a negative PPD skin test?

A
  • No infection
  • Anergy
    >> Steroids
    >> Immunocompromised
    >> Malnutrition
    >> Sarcoidosis
226
Q

How can primary TB in immunosuppressed patients present?

A
  • Significant and potentially lethal lung infection
  • Severe bactermia
  • Miliary tuberculosis (multiple organ seeding)
227
Q

How does secondary TB present?

A
  • Reactivation of latent TB
  • Fibrocaseous cavitary lesions
    >> Cheese-like caseous necrosis
  • Much more symptomatic than primary TB
    >> Fever
    >> Weight loss
    >> Night sweats
    >> Hemoptysis
  • Includes extrapulmonary TB
    >> CNS lesions: parenchymal tuberculoma, meningitis etc.
    >> Pott’s disease
    >> Lymphadenitis
    >> Renal disease
    >> Gi disease
    >> Miliary TB
228
Q

What culture medium is used for MTB culture?

A
  • Lowenstein-Jensen agar
  • Takes 2-4 weeks to culture
  • More rapid diagnosis: acid-fast stain on early morning sputum for 3 consecutive days
  • Interferon Gamma-Release Assay
229
Q

What is the treatment for latent TB?

A

6-9 months of isoniazid (INH)

230
Q

What is the treatment for active primary or secondary TB?

A

First two months

  • Rifampin
  • Isoniazid
  • Pyrazinamide
  • Ethambutol

Following four months

  • Rifampin
  • Isoniazid
231
Q

What patients are at risk for Mycobacterium kansasii infections?

A
  • Chronic bronchitis
  • Emphysema
    >> COPD patients
    >> Causes pulmonary TB-like symptoms
232
Q

Which drug is used for prophylaxis of MAI in AIDS patients? When should one start?

A

Azithromycin
>> CD4 count <50 – START!

233
Q

What are the clinical manifestations of Mycobaterium leprae infection?

A

Tuberculoid

  • Few hypoesthetic, hairless skin plaques
  • High cell-mediated immunity with Th1 cell response

Lepromatous

  • Diffuse skin involvement
  • Leonine (lion-like) facies
  • “Glove-and-stocking” sensory loss >> repeated trauma >> deformity of the digits
  • Communicable
  • Low cell-mediated immunity with Th2 cell response
234
Q

What is the source of infection of Mycobacterium leprae?

A
  • Person-to-person
  • Armadillos

>> CANNOT BE GROWN IN VITRO

235
Q

What is the treatment for Mycobacterium leprae infection?

A

Tuberculoid leprosy

  • 6-12 months
  • Dapsone + rifampin

Lepromatous leprosy

  • 2-5 yeras
  • Dapsone + rifampin + clofazimine
236
Q

What is the mechanism of action of isoniazid?

A

Inhibits synthesis of mycolic acids

237
Q

What are the side effects of isoniazid?

A
  • Hepatotoxicity
  • Peripheral neuropathy
    >> Prevented by giving B6 (pyridoxine) supplements
  • Drug-induced lupus
238
Q

What are the 4 Rs for Rifampin?

A
  • RNA polymerase inhibitor
  • Ramps up cytochrome P450
  • Red/orange body fluids
  • Rapid resistance if used alone
239
Q

What are the indications for rifampin?

A
  • Treatment of TB
  • Treatment of leprosy
  • Prophylaxis against:
    >> Neisseria meningitidis
    >> H. influenzae type B
240
Q
A
241
Q

What are the side effects of pyrazinamide?

A
  • Hyperuricemia
  • Hepatotoxicity
242
Q

What is the mechanism of action of ethambutol?

A

Decreasing carbohydrate polymerization of mycobacterium cell wall
by blocking arabinosyltransferase

243
Q

What are the side effects of ethambutol?

A

OPTIC NEUROPATHY

(red-green colour blindness – reversible)

244
Q

What organism is associated with:

Rabbit hunters?

A

Francisella tularensis

245
Q

What organism is associated with:

Pet prairie dog?

A

Yersinia pestis

246
Q

What organism is associated with:

Ixodes tick?

A
  • Borrelia burgdoferi
  • Babesia
247
Q

What organism is associated with:

Lymphadenopathy + a new kitten?

A

Bartonella

248
Q

What organism is associated with:

a dog bite?

A

Pasteurella multocida

249
Q

Which Rickettsial species has properties unique from the other Rickettsial organisms? What are those unqiue properties?

A

Coxiella burnetii

  • No vector
  • Transmitted by aerosolized droplets
  • Endospore
  • No rash – instead causes interstitial pneumonia
  • Negative Weil-Felix test
250
Q

What are the nonenveloped viruses?

A

Give a PAPP smear and CPR to the naked heppy.

  • Papillomaviruses
  • Adenoviruses
  • Parvoviruses
  • Polyomaviruses
  • Caliciviruses
  • Picornaviruses
  • Reoviruses
  • Hepeviruses
251
Q

What would happen to the Mycobacterium tuberculosis organisms within the first week of infection/after exposure?

A

Aerosol infection of the lower lung fields >> phagocytosis by alveolar macrophages >> sulfatide virulence factor by M. tuberculosis allows for intracellular bacterial proliferation >> cell lysis from continuous proliferation >> MTB organisms released and infect other macrophages

Eventually antigen-carrying macrophages migrate to the lymph nodes and induce a T-helper lymphocyte response – 2-4 weeks after exposure

252
Q

Describe the process of epithelioid transformation of macrophages in M. tuberculosis infection.

A

MTB is a facultative intracellular organism that is relatively indigestable

When macrophages ingest something that is relatively indigestable, they lose their motility, and accumulate at the site of the injury >> transform into epithelioid cells –> usually in a chronic granuloma caused by infection with fungi or MTB

253
Q

Which type of tuberculosis infection are Ghon foci found?

A

Primary tuberculosis infection >> granulomatous inflammation sites that are walled off when they are too big to be destroyed

254
Q

What cells are predominantly involved in the eradication of Mycobacterium tuberculosis?

A

Cell-mediated Th1-mediated immune response as immunoglobulins from B-cells are unable to reach the organism; this response occurs 2-4 weeks after exposure

  • Th1 cells recruit macrophages and more Th-1 cells
  • Th2 cells recruit and activate B-cells and inhibit Th-1 cells and are therefore of no help
255
Q

What is the treatment for tuberculoid M. leprae infection?

A

Localized infection mediated by Th1-cells

Rifampin + Dapsone x 6 months

256
Q

What is the treatment for lepromatous M. leprae infection?

A

Diffuse infection mediated by Th2 cells

Dapsone + rifampin + clofazimine x 2-5 years

257
Q

Which organisms are catalase positive?

A

PLACESS

  • Pseudomonas
  • Listeria
  • Aspergillus
  • Candida
  • E. coli
  • Staphylococcus aureus
  • Serratia

>> Those with chronic granulomatous disease, which is a X-linked mutation affecting NADPH oxidase, are at increased risk for recurrent infections of these bacteria and fungi —– nitroblue tetrazolium test negative (neutrophils fail to turn blue) and dihydrorhodamine test abnormal

258
Q

What is the action of NADPH oxidase?

A

Usually functions within activated phagocytes to produce reactive oxygen species, which are then broken down by catalase in catalase-positive organisms

259
Q

What is the action of coagulase?

A

Activates prothrombin, and thus converts fibrinogen to fibrin >> fibrin-coating of the organism and thus offers resistance against phagocytosis

Staphylococcus aureus expresses coagulase.

260
Q

What is lecithinase?

A

The toxin and major virulence factor of Clostridium perfringens, also known as alpha toxin

  • Has activity of phospholipase C
  • Increases platelet aggregation and adherence molecule expression on leukocytes and endothelial cells
  • Results in vaso-occlusion and ischemic necrosis of affected tissues
261
Q

What are the capsulated bacteria?

A

Even Some Pretty Nasty Killers Have Shiny Bodies

  • Escherichia coli
  • Streptococcus pneumoniae
  • Pseudomonas aeruginosa
  • Neisseria meningitidis
  • Klebsiella pneumoniae
  • Haemophilus influenzae type B
  • Salmonella typhi
  • Streptoccocus group B
262
Q

What is the action of shiga toxin?

A

Inactivate **60S **ribosome by removing adenine from tRNA

263
Q

Why does no effective immunity develop despite the presence of antibodies in HCV infection?

A

HCV has six or more genotypes and multtiple subgenotypes

  • The genetic difference in the encoding of its two envelope glycoproteins has led to the development of a hypervariable region of the envelope glycoprotein that is especially prone to frequent mutation
  • There is no proofreading 3’ –> 5’ exonuclease activity buil into the virion-encoded RNA polymerase >> many mistakes and therefore many mutations
  • There are usually several dozen subspecies of hepatitis C virus typically present in the blood of an infected individual at any one time. The production of host antibodies lags behind the production of new mutant strains of HCV and effective immunitty against infection is not conferred.
  • The tremendous antigenic variety of HCV has signifiantly slowed efforts to develop a vaccine against the virus.
264
Q
A

USMLE Step 1 (14 decks)

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