General Microbiology of Bacteria

Question 1

Quickly compare Gram positive and Gram negative organisms.

Answer 1

• 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

Question 2

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

Answer 2

• 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)

Question 3

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

Answer 3

• 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)

Question 4

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

Answer 4

• 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)

Question 5

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

Answer 5

• 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

Question 6

What are the four major shapes of bacteria?

Answer 6

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

Question 7

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

Answer 7

• 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

Question 8

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

Answer 8

• 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

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

• large 50S (inhibited by erythromycin)

- small 30S (inhibited by tetracycline)

Question 11

What are the various ways bacteria can deal with oxygen?

Answer 11

• (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)

Question 12

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

Answer 12

• 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

Question 13

What are obligate intracellular organisms?

Answer 13

• 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)

Question 14

List the major types of virulence factors.

Answer 14

• 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)

Question 15

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

Answer 15

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

Question 16

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

Answer 16

• 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.)

Question 17

What is sepsis? What is septic shock?

Answer 17

• 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

Question 18

What mediates septic shock?

Answer 18

• 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

Question 19

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

Answer 19

• 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

Question 20

What are the three most common sites of bacterial infection?

Answer 20

• 1) lungs
• 2) abdomen
• 3) urinary tract

Question 21

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

Answer 21

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

Question 22

Which bacteria are encapsulated?

Answer 22

• “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)

Question 23

Which organisms are catalase positive?

Answer 23

• “PLACESS for you CATs”

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

Question 24

Which organisms are urease positive?

Answer 24

• “PUNCH KiSS”

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

Question 25

Which four organisms produce unique pigments?

Answer 25

• 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)