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NBME Micro > Microbiology: Basic Bacteriology > Flashcards

Microbiology: Basic Bacteriology Flashcards

1
Q

What color pigment does Pseudomonas aeruginosa produce?

A

Blue-green (aeruginosa: arugula is green)

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2
Q

Coxiella is considered an obligate intracellular pathogen. Name other bacteria in this class.

A

Rickettsia, Chlamydia, &; COxiella are intracellular (stay inside [cells] when it is Really CHilly &; COld)

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3
Q

What component of the cell envelope extends from the membrane to the exterior and induces TNF-α and IL-1 on gram-positive bacteria?

A

Lipoteichoic acid (in gram positive) bacteria

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4
Q

Anaerobic bacteria usually smell bad, are difficult to culture, and produce CO2 and H2 in tissue. What causes the foul smell?

A

Short-chain fatty acids

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5
Q

When an anticoagulated tube of blood from a man with fever cools, precipitate forms. Mycoplasma pneumoniae is found. What medium was used?

A

Eaton agar; M pneumoniae requires cholesterol

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6
Q

Your microbiology lab advisor wishes to use a special silver stain. What organisms may he be looking for?

A

Legionella, Helicobacter pylori, and fungi (eg, Coccidioides, Pneumocystis jirovecii)

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7
Q

Exotoxins are typically destroyed at 60°C. What are the exceptions?

A

Staphylococcal enterotoxin and Esherichia coli heat-stable toxin are exceptions

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8
Q

In patients with pharyngitis, what protein from group A Streptococcus species prevents phagocytosis by the body’s immune cells?

A

M Protein

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9
Q

What type of toxin causes sepsis and meningococcemia?

A

Endotoxin

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10
Q

What bacteria usually utilize a type III secretion system?

A

Gram ⊖ bacteria such as Pseudomonas, Salmonella, Shigella, and Escherichia coli

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11
Q

What is the chemical composition of the bacterial cytoplasmic membrane, and what are the membrane’s 2 main enzymatic functions?

A

The membrane comprises a phospholipid bilayer with embedded proteins; its main enzymatic functions are oxidation and transportation

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12
Q

What component of the cell envelope induces TNF on gram-negative bacteria?

A

Lipid A (also induces IL-1)

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13
Q

IgA protease allows bacteria to colonize mucous membranes. Describe its mechanism of action.

A

IgA protease cleaves IgA, allowing bacteria to adhere to mucous membranes

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14
Q

What cell wall structures do gram ⊖ and gram ⊕ bacteria have in common?

A

Both gram ⊕ and gram ⊖ bacteria have flagella, pili, capsules, peptidoglycans, and cytoplasmic membranes

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15
Q

Catalase degrades H2O2, preventing conversion to microbicidal products by myeloperoxidase (enzyme). Name 7 catalase-⊕ organisms.

A

Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, Escherichia coli, Staphylococci, Serratia, Burkholderia cepacia, Helicobacter pylori (Cats Need PLACESS to Belch Hairballs)

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16
Q

What cheaper and sensitive stain is used in lieu of the Ziehl-Neelsen stain to screen for mycobacteria?

A

Auramine-rhodamine stain

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17
Q

When autoclaving surgical equipment, what temperature and time setting should be used to kill bacterial spores?

A

Equipment must be autoclaved for 15 minutes at 121°C because bacterial spores are highly resistant to heat and chemicals

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18
Q

A man with an Escherichia coli infection has significant fever, hypotension, and edema. What component of the bacteria is responsible for his symptoms?

A

Lipopolysaccharide (LPS) in the outer membrane of gram ⊖ bacteria (eg, E coli); activates macrophages, complement, and tissue factor

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19
Q

What is a type III secretion system?

A

A special protein appendage produced by gram ⊖ bacteria that allows direct delivery of toxins

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20
Q

A patient with scarlet fever has erythrogenic toxins in her blood. What toxin is to blame for her symptoms?

A

Exotoxin A, which causes toxic shock-like syndrome (rash, fever, shock) and is released by Streptococcus pyogenes

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21
Q

A man recovering from trauma has a foul-smelling, necrotic skin lesion with crepitus. Mechanism of action of the causative toxin?

A

The alpha toxin of Clostridium perfringens, a phospholipase, degrades phospholipids, causing tissue and cell membrane necrosis (myonecrosis)

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22
Q

A child with whooping cough has an infection with bacteria having which mechanism of virulence?

A

Bordetella pertussis toxin overactivates adenylate cyclase, disables Gi, and impairs phagocytosis, permitting survival of the microbe

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23
Q

In endotoxin-based complement activation, which complement(s) cause(s) hypotension/edema and histamine release?

A

C3a and C5a

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24
Q

Endotoxin activation of macrophages causes release of cytokines (IL-1, IL-6, TNF-α). What are their functions?

A

IL-1 and IL-6 cause fever; TNF-α causes both fever and hypotension

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25
Q

A 56-year-old goat herder discovers a painless, black ulcer on his arm. What is the mechanism of the likely underlying bacterial toxin?

A

Edema toxin, released by Bacillus anthracis, mimics adenylate cyclase (↑ cAMP), causing edematous borders of black eschar

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26
Q

On what part of the CNS does the Clostridium tetani toxin tetanospasmin act?

A

Renshaw cells in the spinal cord (toxin prevents release of inhibitory neurotransmitters, leading to spastic paralysis)

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27
Q

A 20-year-old man recently had a splenectomy. Why should he receive Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitis vaccines?

A

Encapsulated bacteria are opsonized and cleared by the spleen; a patient without a spleen has ↓ opsonizing ability and is at risk for infection

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28
Q

What is the purpose of autoclaving surgical equipment?

A

To kill bacterial spores

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29
Q

A chest x-ray obtained from a patient with reactivated tuberculosis shows apical infiltrates in both lungs. Explain the location of these findings.

A

The lung apices have the highest partial pressure of oxygen; M tuberculosis (and all obligate aerobes) require oxygen to make ATP

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30
Q

On what 2 medical products are Staphylococcus epidermidis likely to grow on?

A

Catheters and prosthetic devices

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31
Q

Name 5 bacterial toxins coded for in a lysogenic phage.

A

Group A strep erythrogenic toxin, Botulinum toxin, Cholera toxin, Diphtheria toxin, Shiga toxin (ABCD’S)

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32
Q

What are endotoxins composed of?

A

The lipid A component of lipopolysaccharide (a bacterium’s structural part); lysis releases it

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33
Q

A 16-year-old boy has a foot infection caused by bacteria that avoid opsonization and phagocytosis through a particular virulence factor. What protein promotes this virulence?

A

Protein A; prevents opsonization and phagocytosis of S aureus by binding the Fc region of immunoglobulins

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34
Q

Name the segment of DNA that can jump from one location to another, can transfer genes from plasmid to chromosome, and vice versa.

A

Transposon

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35
Q

A catheterized pt has bacterial sepsis. Which bacterial structure, composed of polysaccharides, enabled the adhesion of the bacteria?

A

Slime (S) layer

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36
Q

How do the cell walls of gram ⊕ and gram ⊖ bacteria compare?

A

Gram ⊕: thick peptidoglycan layer and lipoteichoic acid

Gram ⊖: thin peptidoglycan layer, porin, endotoxin, lipopolysaccharide, and periplasmic space

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37
Q

In a gram-positive bacterium you identify a specialized structure composed of dipicolinic acid and peptidoglycan. What is it?

A

Most likely a spore

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38
Q

Name 3 toxins produced by Staphylococcus aureus and their associated symptoms.

A

Toxic shock syndrome toxin (symptom: rash, fever, shock); exfoliative toxin (symptom: scalded-skin syndrome); enterotoxin (symptom: diarrhea, vomiting)

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39
Q

What is the difference between enterohemorrhagic Escherichia coli and Shigella manifestations?

A

Unlike Shigella (Shiga toxin), enterohemorrhagic E coli does not invade host cells; its Shiga-like toxin inactivates 60S ribosomes and causes cytokine release → HUS/dysentery

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40
Q

Which pleomorphic gram ⊖ bacteria can be identified with a Giemsa stain?

A

Chlamydia and Rickettsia species

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41
Q

An Escherichia coli infection overactivates cellular guanylate cyclase. Describe the mechanism by which the responsible toxin causes diarrhea

A

Heat-stable toxin of enterotoxigenic E coli (ETEC) ↓ reabsorption of NaCl and water in the gut

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42
Q

What is the mechanism by which superantigens cause toxic shock syndrome?

A

Superantigens bind MHC II molecules and T-cell receptors; overwhelming release of IFN-γ, IL-2, IL-1, and TNF-α, causing shock

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43
Q

You find an intracellular organism that can live both within and outside of the host cell. Which bacteria might you identify?

A

Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis (Some Nasty Bugs May Live FacultativeLY)

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44
Q

An unimmunized 1-year-old boy is irritable, sluggish, and has a stiff neck. How do you culture the causative agent, Haemophilus influenzae?

A

On chocolate agar with factors V (NAD+) and X (hematin); the patient likely has H influenzae meningitis

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45
Q

A girl has rice-water diarrhea and is dehydrated. A toxin is to blame. What is its mechanism of action?

A

AB toxin activates Gs protein and stimulates adenylate cyclase, increasing Cl- (and water) secreted in the gut (this is Vibrio cholerae)

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46
Q

A patient tests ⊕ for tetanospasmin. Low activity of what neurotransmitters underlies the patient’s symptoms?

A

Glycine and GABA; tetanospasmin blocks inhibitory release by cleaving SNARE proteins, which mediate vesicle fusion

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47
Q

The inner leaflet of the outer membrane is composed of what?

A

Phospholipids

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48
Q

A 10-year-old girl is found to have whooping cough caused by Bordetella pertussis. How can the organisms be cultured?

A

B pertussis grows on Bordet-Gengou (potato) agar (Bordet for Bordetella) or Regan-Lowe medium (charcoal, blood, and antibiotic)

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49
Q

A 20-year-old military recruit has a headache and cough caused by Mycoplasma. Why do these bacteria not Gram stain well?

A

Mycoplasma species do not have cell walls

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50
Q

Which spirochete can be identified with Giemsa stain?

A

Borrelia

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51
Q

Deoxyribonuclease is added to a Petri dish growing Neisseria. Which process of gene transfer among bacteria will be halted?

A

Transformation (deoxyribonuclease lyses the naked DNA, thus preventing transformation)

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52
Q

Cholera toxin is encoded in a phage. Describe how the phage helps the toxin gene undergo transduction.

A

A lysogenic phage infects bacteria, inserts viral DNA into chromosomes; viral (and bacterial) DNA are excised into the capsid and can infect other bacteria

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53
Q

In patients with Pseudomonas infections, how does the catalase enzyme make these bacteria more pathogenic?

A

Catalase degrades H2O2 → H2O and O2 before myeloperoxidase can convert it to microbicidal products

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54
Q

Where in the cell wall of gram ⊖ bacteria are β-lactamases located?

A

The periplasmic space, which is only present in gram ⊖ bacteria

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55
Q

Which part of the body do bacteria that secrete IgA protease tend to colonize?

A

The respiratory mucosa; these bacteria are S pneumoniae, H influenzae type B, Neisseria (SHiN)

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56
Q

Facultative anaerobes may use O2 as a terminal electron receptor to generate ATP, but may also use what other pathways?

A

Fermentation and other pathways that are not O2-dependent

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57
Q

A patient receives a pneumococcal conjugate vaccine (PCV). How does a PCV work to promote a T-cell response?

A

In encapsulated bacteria vaccines, protein and polysaccharide are conjugated to promote a T-cell response and class switching as a result

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58
Q

An elderly woman is vaccinated only against nonconjugated polysaccharide antigens. Why is this patient at greater risk for infection when compared to conjugated vaccines?

A

Polysaccharide antigens alone are not presented to T cells; this prompts a weaker immune response, in comparison to conjugated vaccines

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59
Q

A patient has otitis media. What biofilm-producing bacteria are most likely responsible for the infection?

A

Nontypeable (unencapsulated) Haemophilus influenzae

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60
Q

What is the typical composition of the cytoplasmic membrane in gram-negative bacteria?

A

Phospholipid bilayers with embedded proteins and enzymes; only in gram-positive bacteria does lipoteichoic acid extend into the exterior

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61
Q

What are the most commonly found pleomorphic bacteria?

A

Anaplasma, Ehrlichia, Chlamydiae, Rickettsiae, Mycoplasma, Ureaplasma

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62
Q

Coxiella is considered an obligate intracellular pathogen. How does this organism get energy?

A

It obtains ATP from its host cell

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63
Q

A man is infected with bacteria that produce exotoxin A, which induces host cell death. Identify the pathogen and the exotoxin mechanism.

A

The pathogen is Pseudomonas aeruginosa; exotoxin A inactivates elongation factor (EF-2) to trigger host cell death

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64
Q

In a culture plate, some colonies representing enteric bacteria turn pink. What medium was used to identify the bacteria?

A

MacConkey agar, which is used to identify lactose-fermenting enterics (eg, Escherichia coli)

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65
Q

A patient presents with struvite stones. What is the underlying biochemical reaction that leads to the formation of such stones

A

Urease hydrolyzes urea, with release of ammonia and CO2; the increased urine pH encourages ammonium magnesium phosphate stone formation

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66
Q

Name 4 aerobes.

A

Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, Bordatella pertussis (Nagging Pests Must Breathe)

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67
Q

What are the 2 distinguishing components in the outer layer of Mycobacteria?

A

Mycolic acid and high lipid content

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68
Q

An agar plate infected with multiple bacteria is treated with alcohol. Which bacteria would survive?

A

Spore-forming bacteria (Bacillus and Clostridium); spores are resistant to alcohol

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69
Q

What type of toxin causes tetanus, botulism, and diphtheria?

A

Exotoxin

70
Q

Certain bacteria, such as Corynebacterium diphtheriae, have adenosine diphosphate- (ADP) ribosylating AB toxins. Name the functions of the A and B components.

A

B component Binds and triggers endocytosis; A component (taken up) is Active (eg, ADP ribosyltransferases and other enzymatic activities)

71
Q

What are the effects and characteristics of an endotoxin?

A

ENDOTOXINS: Edema, Nitric oxide, DIC/Death, Outer membrane, TNF-α, O-antigen, eXtremely heat stable, IL-1/IL-6, Neutrophil chemotaxis, Shock

72
Q

Legionella, Bartonella, and Ehrlichia all share what property that makes them suboptimal for Gram stain?

A

They are all primarily intracellular bacteria

73
Q

A man presents with a new heart murmur after a recent bout of pharyngitis. What would confirm the most likely diagnosis?

A

The presence of anti-streptolysin O (ASO) antibodies (he likely has rheumatic fever)

74
Q

In which type of transduction is viral DNA incorporated into the host DNA?

A

Specialized transduction (involves a lysogenic phage)

75
Q

How does Thayer-Martin agar work in the infectious disease lab to test for Neisseria?

A

It is a selective medium (contains antibiotics that permit selective growth of Neisseria by preventing the growth of other organisms)

76
Q

Transposition is done between a plasmid from vancomycin-resistant Enterococcus & S aureus. How does S aureus become vancomycin resistant?

A

Flanking chromosomal DNA is incorporated into plasmid, then into another bacterium (eg, vanA gene from Enterococcus to S aureus)

77
Q

A gram-positive bacterium produces offspring with a special keratin-like coat. How do these offspring survive?

A

By resisting dehydration, heat, and chemicals (the offspring are spores)

78
Q

A patient with a fever and rash subsequently goes into shock. What are 2 commonly tested gram ⊕ bacteria that can cause a rash and septic shock?

A

Staphylococcus aureus (via toxic shock syndrome toxin) and Streptococcus pyogenes (via exotoxin A)

79
Q

Chlamydia do not Gram stain well because they are intracellular and have ↓ levels of what acid in their cell wall?

A

Muramic acid, resulting in suboptimal staining of peptidoglycan

80
Q

What characteristic of the structure of the cell wall in bacteria provides rigid support?

A

The cell wall is composed of peptidoglycans that provide rigid support

81
Q

Excessive stimulation of the coagulation cascade by tissue factor can cause what condition?

A

Disseminated intravascular coagulation (DIC)

82
Q

A painless black ulcer develops on the arm of a 56-year-old goat herder. What unique molecule does the capsule of the bacterium contain?

A

Poly-D-glutamate, which is only found in Bacillus anthracis (diagnosis: cutaneous anthrax)

83
Q

Two plates grow the same lactose-fermenting bacteria. One is pink; the other has a green metallic sheen. What medium was used on each plate

A

Escherichia coli turns MacConkey agar pink; E coli also grows colonies with a green metallic sheen on eosin-methylene blue (EMB) agar

84
Q

Where can endotoxin be found in the cell?

A

Outer membrane of gram ⊖ bacteria (endotoxin is an integral part of the outer membrane of gram-negative bacteria)

85
Q

A plasmid is transferred from one bacterium to another. What is this transfer of information called?

A

Conjugation

86
Q

What is typically found in the core of a bacterial spore?

A

Dipicolinic acid

87
Q

What is the mechanism of diphtheria toxin?

A

Inactivates elongation factor 2 via adenosine diphosphate- (ADP) ribosylation, leading to necrosis in the pharynx, cardiac, and CNS tissue; this is Corynebacterium diphtheriae

88
Q

A teacher with unvaccinated students has had a persistent cough for 3 months. Identify the exotoxin involved.

A

Pertussis toxin, produced by Bordetella pertussis, which overactivates adenylate cyclase (causing a “100-day cough” in adults)

89
Q

Diagnostic test for rheumatic fever uses antibodies against what part of the causative agent?

A

Antibodies against Streptococcus toxin, streptolysin O (anti-streptolysin O)

90
Q

An unimmunized 7-year-old boy has a sore throat and fever. Exam reveals gray pseudomembranes in his throat. What medium should be used for culture?

A

Tellurite agar with Löffler medium (organism is likely Corynebacterium diphtheriae)

91
Q

List the structures unique to gram ⊕ bacteria and those unique to gram ⊖ bacteria.

A

Gram ⊕: lipoteichoic acid; gram ⊖: porin, periplasmic space, and outer membrane formed by endotoxins/lipopolysaccharides

92
Q

What characteristic of Mycobacterium makes it visible on Ziehl-Neelsen staining?

A

Mycolic acid in the cell wall

93
Q

A male patient with many sexual partners has purulent penile discharge from Neisseria gonorrhoeae. How is the causative organism cultured?

A

N gonorrhoeae grows on Thayer-Martin agar, a selective medium that contains vancomycin, trimethoprim, colistin, and nystatin

94
Q

What components of the cell envelope are found only in gram-negative bacteria?

A

Outer membrane, periplasm

95
Q

A febrile man with septic shock has poorly antigenic toxins in his blood found on the outer cell membrane of gram ⊖ bacteria. Induction of which cytokines caused this condition?

A

TNF, IL-1, and IL-6 (induced by endotoxin)

96
Q

Shiga-like-toxin (SLT) causes hemolytic-uremic syndrome (HUS). What is the toxin’s mechanism of action?

A

Causes enhanced cytokine release

97
Q

How does an indicator (differential) medium work? Give an example of such a medium.

A

A color change results in response to some organisms’ metabolites; Escherichia coli changes color on MacConkey agar (pH indicator) due to lactose conversion to acidic metabolites

98
Q

In endotoxin-based complement activation, which complement promotes neutrophil chemotaxis?

A

C5a

99
Q

What are exotoxins composed of?

A

Polypeptides

100
Q

A patient with cystic fibrosis has a chronic cough and confirmed biofilm-producing bacterial growth. Identify the bacteria.

A

Pseudomonas aeruginosa

101
Q

A company would like to target the Escherichia coli endotoxin with a new antibiotic. Where is this endotoxin found?

A

The outer membranes of cells of gram ⊖ bacteria (both cocci and rods)

102
Q

What glycoprotein-derived structure allows bacteria to adhere to the cell surface?

A

The fimbria (pilus)

103
Q

Bacteria with thin peptidoglycan layers turn what color(s) with counterstain?

A

Red or pink, and are gram ⊖

104
Q

In what scenario is a fluorescent antibody stain typically used?

A

To confirm syphylis (FTA-ABS); it can also be used to identify many bacteria and viruses

105
Q

Where is endotoxin (lipopolysaccharide) located in gram-negative bacteria?

A

Outer leaflet of the outer membrane

106
Q

What bacterial structural appendage, composed of protein, is known to help provide motility?

A

Flagellum

107
Q

Why do Clostridium, Bacteroides, Fusobacterium, and Actinomyces israelii have increased susceptibility to oxidative damage?

A

They lack the enzymes catalase and superoxide dismutase, and are thus susceptible to oxidative damage (anaerobes Can’t Breathe Fresh Air)

108
Q

A 10-year-old girl has had coughing fits, after which she fights to catch her breath, for 2 months. What is the mechanism of the offending toxin?

A

Bordetella pertussis disables the Gi protein (overactivates adenylate cyclase), impairing phagocytosis and allowing bacteria to survive

109
Q

Which strain of Escherichia coli has a toxin that overactivates adenylate cyclase?

A

Enterotoxigenic E coli (heat-labile toxin)

110
Q

What is the chemical composition of endotoxin?

A

Lipopolysaccharide (LPS)

111
Q

A drug company wishes to target β-lactamases. In which compartment of the bacteria would they be?

A

In the periplasm, the space between the cytoplasmic membrane and the outer membrane in gram-negative bacteria

112
Q

You are studying the effects of the lipid A component in lipopolysaccharide (LPS). How does this endotoxin differ from an exotoxin based on its release from the cell?

A

An endotoxin is released on cell lysis or by living cells (blebs detach from the outer surface membrane); exotoxins are actively secreted

113
Q

A terrified patient presents with risus sardonicus, spasticity, and lockjaw. What is the likely mechanism of the causative exotoxin?

A

Cleavage of soluble NSF attachment protein receptor (SNARE), needed for release of inhibitory neurotransmitters (exotoxin is tetanospasmin)

114
Q

In the microbiology lab you find bacteria that produce yellow “sulfur” granules (sand). What are the granules made of?

A

Bacterial filaments; the bacteria are Actinomyces israelii (israel has yellow sand)

115
Q

One pathogen can be visualized using India ink and mucicarmine. Describe the part of the organism that is stained.

A

The thick polysaccharide capsule of Cryptococcus neoformans stains red with mucicarmine

116
Q

An unmarked bacterial plate is producing urease. What organisms could be growing on the plate?

A

Proteus, Cryptococcus, Helicobacter pylori, Ureaplasma, Nocardia, Klebsiella, Staphylococcus epidermidis, Staphylococcus saprophyticus (Pee CHUNKSS)

117
Q

A patient presents with contact lens-associated keratitis. What biofilm-producing bacteria are the cause?

A

Pseudomonas aeruginosa

118
Q

Which 5 organisms can be visualized with Giemsa stain?

A

Rickettsia, Chlamydia, Trypanosomes, Plasmodium, Borrelia, Helicobacter pylori (Ricky got Chlamydia as he Tried to Please the Bored “Geisha”)

119
Q

In a patient with acute rheumatic fever, what bacterial virulence factor may be responsible for the autoimmune response?

A

M protein by group A streptococci; it has epitopes similar to those of human cellular proteins, a phenomenon known as molecular mimicry

120
Q

Many guests, especially the elderly, have developed high fever and pneumonia after a staying in a hotel with central AC. What medium is used to culture the causative organism?

A

Charcoal yeast extract agar buffered with cysteine and iron (the causative organism is Legionella)

121
Q

What glycoprotein-derived bacterial structure is known to help form an attachment between 2 bacteria during conjugation?

A

Sex pilus

122
Q

What is the primary toxic component of an endotoxin?

A

Lipid A

123
Q

What type of toxin is typically heat stable?

A

Endotoxins are stable at 100°C for 1 hour

124
Q

Proteus and Klebsiella are both urease-⊕ organisms. By what mechanism do these bacteria increase pH?

A

Urease hydrolyzes urea, resulting in release of ammonia and CO2. Ammonia reacts with the medium to increase pH

125
Q

Identify the chemical composition and the 2 main functions of the peptidoglycan layer in bacteria

A

It has a sugar backbone with cross-linked peptide side chains; it provides rigid support and protection against osmotic pressure damage

126
Q

A patient who has had a splenectomy is at risk for infection with encapsulated bacteria. Name 4 vaccines he should receive.

A

Pneumococcal (PCV13 and PPSV23), Haemophilus influenzae type B, and meningococcal vaccines

127
Q

What defines a pleomorphic bacteria?

A

No rigid cell walls

128
Q

Vaccines can be created for exotoxins but not for endotoxins. Why?

A

Exotoxins are highly antigenic (unlike endotoxins); they are able to induce antibody production, and their toxoids can be used to make vaccines

129
Q

What biofilm-producing bacteria are associated with dental plaque and infective endocarditis?

A

Viridans streptococci (Streptococcus mutans, Streptococcus sanguinis)

130
Q

Shigella and enterohemorrhagic Escherichia coli share a mechanism for causing gastrointestinal mucosal damage and dysentery. What is it?

A

Both Shiga toxin and Shiga-like toxin cleave host cell rRNA, inactivating the 60S ribosomal subunit by removing adenine from rRNA

131
Q

A 56-year-old man with diabetes has a foul-smelling foot ulcer with palpable crepitus. Which antibiotic must not be used to treat it? Why?

A

AminO2glycosides, which require O2 to enter a bacterial cell, are ineffective against anaerobes (the patient likely has an anaerobic skin infection)

132
Q

In the microbiology lab, you notice that some Sabouraud agar is growing pathogens. What is likely growing?

A

Fungi (Sab’s a fun guy!)

133
Q

Drug X is known to target polysaccharides from the bacterial capsule. What function of the bacteria is most likely affected?

A

Protection from phagocytosis

134
Q

What color pigment does Serratia marcescens produce?

A

Red (Serratia: think red Sriracha hot sauce)

135
Q

A patient has a gram ⊖ bacterial infection. On cell lysis, the release of endotoxin activates what components of the immune system?

A

Macrophages (via TLR4–CD14 interaction), complement (C3a and C5a), and tissue factor

136
Q

A homeless man is febrile and coughing up blood. A chest x-ray shows a cavitary lesion. You consider tuberculosis. What medium should be used for culture?

A

Löwenstein-Jensen agar (Mycobacterium tuberculosis is likely the causative organism)

137
Q

What components of the outer membrane are antigenic?

A

O polysaccharide component & most outer membrane proteins

138
Q

A patient tests ⊕ for tetanospasmin. What symptoms does he likely have?

A

Spastic paralysis, risus sardonicus, or trismus (lockjaw) from Clostridium tetani

139
Q

Name the 3 types of facultative anaerobic bacteria.

A

Streptococci, staphylococci, and enteric gram-negative bacteria

140
Q

A 30-year-old man has a painless syphilitic penile chancre. Why does the causative organism not react to Gram stain?

A

Treponema is too thin to be visualized on Gram staining

141
Q

What color pigment does Actinomyces israelii produce?

A

Yellow; sulfur granules appear yellow (Israel has yellow sand)

142
Q

IgA protease is secreted by which 3 bacterial species?

A

S pneumoniae, H influenzae type B, Neisseria (SHiN), which normally colonize the respiratory mucosa

143
Q

One type of conjugation process does not involve the transfer of chromosomes. How does it work?

A

In F+ to F- conjugation, plasmids are transferred from the F+ cell through a conjugal bridge; no chromosomal DNA is transferred

144
Q

Endotoxin activation of macrophages causes release of which intermediate leading to hypotension?

A

Primarily due to nitric oxide release; can also be secondary to TNF-α or C3a release

145
Q

A 30-year-old man recently underwent splenectomy and then required several specialized vaccines. What organisms should he be vaccinated against?

A

Neisseria meningitidis, Streptococcus pneumonia, and Haemophilus influenzae; patients with asplenia (No Spleen Here) have ↓ opsonizing ability and need vaccines for protection

146
Q

Which type of transduction does not retain the altered DNA in the subsequent generations of the bacteria?

A

Generalized transduction (phage DNA is not incorporated into the chromosome, and bacterial cell is lysed afterward)

147
Q

A patient with pneumonia is receiving ventilatory assistance. This patient is at risk for infection with which biofilm-producing bacteria?

A

Pseudomonas aeruginosa

148
Q

A toddler has rheumatic fever. Anti-streptolysin O titers are ⊕. What is the mechanism of by which this toxin acts?

A

Streptolysin O degrades cell membranes and lyses RBCs, causing β-hemolysis

149
Q

What are conjugate vaccines made of?

A

Capsular polysaccharide and a protein conjugate

150
Q

What color pigment does Staphylococcus aureus produce?

A

Yellow (Aureus in Latin = gold)

151
Q

A trauma victim has foul-smelling necrotic skin lesions with myonecrosis and crepitus. How does the infecting agent appear on blood agar?

A

Forms a double zone of hemolysis on blood agar by the alpha toxin of Clostridium perfringens, which causes gas gangrene by phospholipid degradation

152
Q

In an experiment, you see a cell incorporating an F+ plasmid into its own chromosomes. Name the result of this bacterial genetics process.

A

High-frequency recombination (Hfr) cell, a subtype of conjugation

153
Q

What are the mechanisms of the heat-labile and heat-stable toxins of enterotoxigenic Escherichia coli (ETEC)?

A

Heat-labile overactivates adenylate cyclase (more Cl-, H2O secretion); heat-stable overactivates guanylate cyclase (less NaCl, H2O resorption)

154
Q

Where are genes coding for the endotoxin of the bacteria located?

A

Bacterial chromosome

155
Q

You conduct an experiment in which DNA segments are transferred between chromosomes & plasmids in the same cell. Name the process.

A

Transposition

156
Q

A patient has a cough and a culture grows a gram ⊖ rod that has a positive silver stain. What is the most likely pathogen?

A

Legionella

157
Q

A baby exhibits flaccid paralysis (mainly facial) after being fed honey. What is the mechanism of the causative agent?

A

Botulinum toxin inhibits release of stimulatory acetylcholine at the neuromuscular junction by cleaving SNARE

158
Q

What is lipopolysaccharide (LPS) composed of?

A

O antigen, lipid A (the toxic component), and core polysaccharide

159
Q

Where are genes coding for the exotoxin of the bacteria located?

A

In the plasmid or bacteriophage

160
Q

Bacteria with thick peptidoglycan layers retain what dye and are deemed to be gram ⊕?

A

Crystal Violet

161
Q

A patient with rice-water stool diarrhea has an adenosine diphosphate- (ADP) ribosylating AB toxin whose primary action is overactivation of adenylate cyclase. Diagnosis?

A

Vibrio cholerae infection

162
Q

What purpose does the capsule of Streptococcus pneumoniae serve?

A

Antiphagocytic virulence factor

163
Q

An F+ bacterium & an F- bacterium participate in high-frequency recombination. What is the result for the F- bacterium?

A

The recipient cell (F-) has received new genes from the F+ cell but remains F-

164
Q

Escherichia coli grows on MacConkey agar, producing a color change. Describe the medium and how it works.

A

MacConkey agar is a pH indicator medium; it responds with a color change after conversion of lactose to acidic metabolites by E coli

165
Q

Some bacteria can take up naked DNA from the environment. Which 3 bacteria perform this process most often?

A

Streptococcus pneumoniae, Haemophilus influenzae, & Neisseria (SHiN) perform transformation most often

166
Q

In which component of the cell envelope are oxidative & transport enzymes located?

A

Cytoplasmic membrane

167
Q

Although anaerobes are pathogenic in most tissues, where are they most commonly part of the normal flora?

A

The GI Tract

168
Q

How will Ureaplasma present on Gram stain?

A

No staining; Ureaplasma lack a cell wall (similar to Mycoplasma) and do not Gram stain well

169
Q

What factor causes endotoxins to activate the coagulation cascade?

A

Tissue Factor

170
Q

A 16-year-old girl has recurrent Staphylococcus aureus, Pseudomonas, and Candida infections. What enzyme deficiency is likely?

A

NADPH oxidase deficiency, which increases susceptibility to infections with catalase-⊕ bacteria

NBME Micro (36 decks)

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