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Microbiology > General Microbiology of Bacteria > Flashcards

General Microbiology of Bacteria Flashcards

1
Q

Quickly compare Gram positive and Gram negative organisms.

A
  • Gram positive: thick peptidoglycan wall with extensive cross-linking; absorbs crystal violet and stains blue
  • Gram negative: thin peptidoglycan wall with less cross-linking; extra outer phospholipid bilayer with lipopolysaccharide (LPS); crystal violet gets washed out, allowing absorption of safranin and stains red
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2
Q

What is the general structure of a Gram positive bacteria? Gram negative?

A
  • positive: cytoplasm –> cytoplasmic membrane –> thick peptidoglycan wall (this wall is directly in contact with the underlying cytoplasmic membrane)
  • negative: cytoplasm –> cytoplasmic membrane –> thin peptidoglycan wall (not directly in contact with the underlying membrane, there is a periplasmic space between the two) –> phospholipid bilayer w/ lipopolysaccharide (LPS)
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3
Q

What is teichoic acid? What about murein lipoprotein? Where is each found?

A
  • each is found in the peptidoglycan wall
  • Gram positive bacteria have teichoic acid, which is an important antigenic determinant
  • Gram negative bacteria have murein lipoprotein, which links the wall to the unique 3rd outer membrane (the phospholipid bilayer with LPS)
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4
Q

Explain the composition of the peptidoglycan wall. Which enzyme is involved in its structure?

A
  • the wall is made up of repeating disaccharides, with each disaccharide having a 4 amino acid tail/extension
  • these disaccharides get cross-linked via the enzyme transpeptidase (this enzyme is inhibited by penicillin)
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5
Q

Explain the composition of the Gram negative’s unique outer layer.

A
  • this is a phospholipid bilayer containing lipopolysaccharide (LPS)
  • the LPS has an outer layer containing the O-antigen (it is the antigenic determinant) and an inner layer containing lipid A, which is the Gram negative endotoxin
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6
Q

What are the four major shapes of bacteria?

A
  • cocci (circular)
  • bacilli (rod-shaped; coccobacilli are short bacilli)
  • spiral forms (spiral, “s”, or comma shaped)
  • pleomorphic (lacking a distinct shape)
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7
Q

Name the six classic Gram positive pathogens. What are two others?

A
  • Streptococcus: cocci, forms strips
  • Staphylococcus: cocci, forms clusters
  • Bacillus: bacilli, spore-forming
  • Clostridium: bacilli, spore-forming
  • Corynebacterium: bacilli, not spore-forming
  • Listeria: bacilli, not spore-forming
  • Actinomyces and Nocardia: branching filamentous
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8
Q

Name the major Gram negative bacteria that are cocci or spiral shaped. Pleomorphic?

A
  • Gram negative cocci: Neisseria (and Moraxella) (both are diplococci)
  • Gram negative spiral: the spirochetes (Treponema, Borrelia, Leptospira)
  • pleomorphic: Chlamydia and Rickettsiae
  • this means the majority of Gram negative organisms are rods
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9
Q

Are Mycobacteria Gram negative or Gram positive? What do we use to stain them with? What about for Mycoplasma?

A
  • Mycobacteria are weakly Gram positive bacilli; they stain much better with acid-fast staining
  • Mycoplasma are neither positive nor negative; they lack a peptidoglycan cell wall and only have a simple cell membrane
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10
Q

What are the two bacterial ribosomal subunits? Which antibiotic inhibits each?

A
  • large 50S (inhibited by erythromycin)

- small 30S (inhibited by tetracycline)

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11
Q

What are the various ways bacteria can deal with oxygen?

A
  • (by “dealing with oxygen,” we mainly mean dealing with oxygen radicals)
  • organisms can have catalase, peroxidase, and/or superoxide dismutase
  • catalase and peroxidase deal with hydrogen peroxide (2H2O2 into 2H2O and O2)
  • superoxide dismutase deals with superoxide radicals (2O2- and 2H+ into H2O2 and O2)
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12
Q

Obligate aerobes vs. facultative anaerobes vs. microaerophilic bacteria (aerotolerant anaerobes) vs. obligate anaerobes

A
  • obligate aerobes require oxygen for energy production; they use glycolysis, TCA cycle, and the ETC; they have catalase, peroxidase, and superoxide dismutase
  • facultative anaerobes are aerobes that can survive w/o oxygen if need be; they have catalase and superoxide dismutase
  • microaerophilic bacteria (AKA aerotolerant anaerobes) are anaerobes that can tolerate low levels of oxygen; they have superoxide dismutase
  • obligate anerobes have zero tolerance for oxygen; they lack any of the enzymes
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13
Q

What are obligate intracellular organisms?

A
  • these can’t make their own ATP and must steal it from their host
  • examples: Chlamydia and Rickettsia (these are the two major pleomorphic Gram negatives)
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14
Q

List the major types of virulence factors.

A
  • flagella (movement)
  • pili (AKA fimbriae; adhesion, invasion)
  • capsules (prevent phagocytosis)
  • endospores (only Bacillus and Clostridium)
  • biofilms (extracellular polysaccharide network allowing adhesion to prosthetic devices and protection from antibiotics/antibodies)
  • facultative intracellular organisms (inhibit phagosome-lysosome fusion, allowing survival within phagocytes)
  • exotoxins (released by most Gram positives and V. cholera and E. coli)
  • endotoxins (Gram negative’s lipid A component of the LPS outer membrane)
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15
Q

Which organisms are facultative intracellular organisms? Which are obligate intracellular organisms?

A
  • facultative: LISTEn SALly YER FRiend BRUCE Must LEave; Listeria monocytogenes, Salmonella typhi, Yersinia, Francisella tularensis, Brucella, Mycobacterium, Legionella
  • obligate: Chlamydia and Ricketssia
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16
Q

What are the different types of exotoxins? Which major bacteria secrete each?

A
  • neurotoxins (act on nerves/motor end plates)
  • enterotoxins (result in osmotic diarrhea); infectious disease via cholera, E. coli, Campylobacter jejuni, shigella; food poisoning via ingestion of S. aureus’ or B. cereus’ enterotoxins
  • pyogenic exotoxins (stimulate cytokine release, causing fever, rash, and toxic shock syndrome); S. aureus, Strep pyogenes
  • tissue invasive exotoxins (destroy tissue, DNA, collagen, fibrin, RBCs, WBCs, etc.)
17
Q

What is sepsis? What is septic shock?

A
  • sepsis: bacteremia that causes a systemic immune response (patients “look sick”); increased or decreased temp, elevated WBC, elevated HR, elevated breathing rate
  • septic shock: sepsis resulting in dangerous drops of BP and organ dysfunction; septic shock has a 40% base mortality rate that increases with the number of systems involved
18
Q

What mediates septic shock?

A
  • in response to the sepsis, activated immune cells release “endogenous mediators of sepsis”; the main one being TNF (AKA cachectin because it causes cachexia)
  • TNF triggers the release of IL-1, resulting in vasodilation, hypotension, and organ dysfunction
19
Q

Which major systems can be affected by septic shock? What will result from each?

A
  • vascular: vasodilation; hypotension, organ hypoperfusion
  • cardiac: myocardial depression; decreased CO, hypotension, organ hypoperfusion
  • kidneys: acute renal failure; decreased urine output, volume overload, toxin accumulation
  • lungs: ARDS (adult respiratory distress syndrome); hypoxia
  • liver: hepatic failure; toxic accumulation, hepatic encephalopathy
  • brain: encephalopathy; altered mental status
  • coagulation system: DIC (disseminated intravascular coagulation); disseminated clotting and bleeding
20
Q

What are the three most common sites of bacterial infection?

A
  • 1) lungs
  • 2) abdomen
  • 3) urinary tract
21
Q

Which three organisms are obligate aerobes? Which three are obligate anaerobes?

A
  • obligate aerobes: “Nagging Pests Must-Breathe”: Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis
  • obligate aerobes: “Can’t Breathe Air”: Clostridium, Bacteriodes, Actinomyces
22
Q

Which bacteria are encapsulated?

A
  • “SHiNE SKiS”
  • Strep. pneumonia, H. influenza, Neisseria MENINGITIDIS, E. coli, Salmonella, Klebsiella, Strep. agalactiae (group B Strep)
  • (note that the first 3 organisms are also the 3 organisms that produce IgA protease to colonize the respiratory mucosa)
23
Q

Which organisms are catalase positive?

A
  • “PLACESS for you CATs”

- Pseudomonas aeruginosa, Listeria, Aspergillus, Candida, E. coli, Staph. aureus, Serratia

24
Q

Which organisms are urease positive?

A
  • “PUNCH KiSS”

- Proteus, Ureaplasma, Nocardia, Cryptococcus, H. pylori, Klebsiella, Staph. epidermidis, Staph. saprophyticus

25
Q

Which four organisms produce unique pigments?

A
  • Pseudomonas aeruginosa: blue-green (pyocyanin)
  • Staph. aureus: yellow (aureus = gold)
  • Actinomyces israelii: yellow (think of Israel’s yellow sand)
  • Serratia marcescens: red (think of maraschino cherries)

Microbiology (16 decks)

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