Usmle Microbiology: Gram-Positive Rods

Front 1

Gram-Positive Rods: Species

Back 1

1. Bacillus spp. 2. Clostridium spp. 3. Corynebacterium diptheria 4. Listeria monocytogenes

Front 2

Bacillus Species

Back 2

1. B. anthracis 2. B. cereus

Front 3

Bacillus anthracis: Identification

Back 3

1. Nonmotile (as opposed to other Bacillus spp.) 2. Forms Medusa's head colonies on blood agar

Front 4

Bacillus anthracis: Virulence Factors

Back 4

1. Capsule 2. Anthrax toxin 3. Spores

Front 5

Bacillus anthracis: Virulence Factors-Capsule

Back 5

1. Glutamic acid polymer 2. Prevents phagocytosis and lysis (from antibody + complement)

Front 6

Bacillus anthracis: Virulence Factors-Anthrax Toxin

Back 6

1. A-B toxin; Protective Factor + Edema OR Lethal Factor 2. Caused localized edema and cell death 3. Highly toxic

Front 7

Bacillus anthracis: Disease

Back 7

1. Cutaneous anthrax 2. Pulmonary anthrax 3. Gastrointestinal anthrax

Front 8

Bacillus anthracis: Disease-Cutaneous Anthrax

Back 8

1. Initial itching papule at inoculation site 2. Forms ulcer that can lead to necrosis (eschar) with massive edema, septicemia, and possible death 3. Inoculation of spores or bacteria from soil or animal products into a superficial wound or abrasion

Front 9

Bacillus anthracis: Disease-Pulmonary Anthrax

Back 9

1. Inhalation of spores from contaminated items (e.g. wool, fur, and hides) 2. Virus-like respiratory illness with high mortality rate due to respiratory failure

Front 10

Bacillus anthracis: Disease-Gastrointestinal Anthrax (Transmission)

Back 10

1. Ingestion of bacteria in contaminated meat 2. GI symptoms 3. Rare

Front 11

Bacillus anthracis: Epidemiology

Back 11

1. Occupational disease of individuals who handle wool, furs, and hides 2. Cutaneous disease most common 3. GI disease rare in humans, but seen in developing countries

Front 12

Bacillus cereus: Epidemiology-Habitat

Back 12

1. Soil (ubiquitous) 2. Foods: A) Grains B) Vegetables C) Dairy

Front 13

Bacillus cereus: Pathogenesis

Back 13

1. Spores survive initial cooking, but germinate into toxin-producing vegetative cells in the absence of prompt refrigeration 2. Reheating inactivates heat-labile toxin (preventing immediate diarrhea), but spares heat-stable toxin (emetic form) and vegetative cells (future diarrheal form)

Front 14

Bacillus cereus: Disease

Back 14

Food poisoning: 1. Emetic form 2. Diarrheal form

Front 15

Bacillus cereus: Disease-Food Poisoning (Emetic Form Transmission)

Back 15

Ingestion of preformed heat-stable enterotoxin in reheated foods (e.g. rice and beans)

Front 16

Bacillus cereus: Disease-Food Poisoning (Emetic Form Clinical Manifestation)

Back 16

1. Rapid onset: 1-5 hours (similar to S. aureus) 2. Symptoms: A) Nausea B) Vomiting C) Abdominal cramps

Front 17

Bacillus cereus: Disease-Food Poisoning (Diarrheal Form Transmission)

Back 17

Ingestion of multiplying bacteria, which produce heat-labile enterotoxin in GI, from contaminated meat, vegetables, or sauces

Front 18

Bacillus cereus: Disease-Food Poisoning (Diarrheal Form Clinical Manifestation)

Back 18

1. Slow onset: 10-15 hours (similar to Clostridium perfringens) 2. Symptoms: A) Diarrhea B) Severe cramps

Front 19

Bacillus cereus: Prevention

Back 19

Refrigeration of foods after cooking

Front 20

Clostridium Species

Back 20

1. C. perfringens 2. C. tetani 3. C. botulinum 4. C. difficile

Front 21

Clostridium perfringens:

Back 21

Soft tissue infections, gas gangrene, food poisoning, necrotizing enteritis, septicemia

Front 22

Clostridium tetani: Epidemiology-Habitat

Back 22

1. Soil, water, sewage 2. Normal flora of many animals
- Rare in US due to vaccine

Front 23

Clostridium tetani: Identification

Back 23

1. Small rods with tennis racquet shape due to presence of terminal spore 2. Strict anaerobe (very sensitive to oxygen)
- Toxin would not be detected (its bound to motor neurons and internalized by cells)

Front 24

Clostridium tetani: Virulence Factors

Back 24

1. Tetanospasmin 2. Spore

Front 25

Clostridium tetani: Virulence Factors-Tetanospasmin

Back 25

1. A-B type 2. Neurotoxin 3. Blocks release of inhibitory neurotransmitters (e.g. GABA, glycine) 4. Results in spastic paralysis due to unregulated excitation

Front 26

Clostridium tetani: Disease

Back 26

Tetanus; severe, unopposed muscle contraction. Most evident in the jaw - lockjaw.

Front 27

Clostridium tetani: Prevention

Back 27

1. Vaccination with tetanus toxoid as part of DPT or DT vaccine 2. Formaldehyde-inactivated 3. Boosters: every 10 years and after probable exposure

Front 28

Clostridium botulinum: Identification

Back 28

Detection of botulinum toxin in patient specimens or food via immunoassay. Anaerobic

Front 29

Clostridium botulinum: Virulence Factors

Back 29

1. Botulinum toxin 2. Spore

Front 30

Clostridium botulinum: Virulence Factors-Botulinum toxin

Back 30

1. A-B type 2. Neurotoxin 3. Blocks release of ACh at cholinergic synapses, leading to flaccid paralysis 4. Recovery period prolonged because nerve endings must regenerate

Front 31

Clostridium botulinum: Disease

Back 31

1. Food botulism 2. Infant botulism

Front 32

Clostridium botulinum: Disease-Adult Botulism

Back 32

1. Food-borne; ingestion of preformed toxins (e.g. canned goods) 2. Symptoms (variable onset): A) Weakness B) Dizziness C) Blurred vision D) Fixed/dilated pupils E) Dry mouth F) Flaccid paralysis G) Death via respiratory paralysis

Front 33

Clostridium botulinum: Disease-Infant Botulism

Back 33

1. Contaminated honey 2. C. botulinum colonizes GI and produces toxin in vivo 3. Infants
Symptoms: A) Initially nonspecific (failure to thrive, constipation) B) Progress to: i. flaccid paralysis (floppy baby syndrome) ii. respiratory arrest (1% to 2% of patients)

Front 34

Clostridium difficile: Epidemiology-Habitat

Back 34

Part of normal GI flora in some individuals

Front 35

Clostridium difficile: Identification

Back 35

1. Detection of toxin in stool samples via immunoassay 2. Ability to kill cultured cells (i.e. cytotoxicity test)

Front 36

Clostridium difficile: Virulence Factors

Back 36

1. Antibiotic resistance 2. Enterotoxin (Toxin A) 3. Cytotoxin (toxin B) 4. Adhesion factor 5. Sporulation

Front 37

Clostridium difficile: Virulence Factors-Enterotoxin or Toxin A

Back 37

Promotes fluid secretion and intestinal hemorrhage (similar to cholera toxin)

Front 38

Clostridium difficile: Virulence Factors-Cytotoxin or Toxin B

Back 38

Damages mucosal membranes by depolymerizing cellular cytoskeleton

Front 39

Clostridium difficile: Disease

Back 39

Pseudomembranous colitis

Front 40

Clostridium difficile: Disease-Pseudomembranous Colitis

Back 40

1. Profuse, foul-smelling, liquid (sometimes bloody) diarrhea 2. Leukocytes in stool 3. Fever 4. Abdominal pain

Front 41

Clostridium difficile: Transmission

Back 41

1. Endogenous (normal flora) 2. Exogenous via spores (e.g. nosocomially on hands/fomites)

Front 42

C. diphtheriae: Epidemiology and Identification

Back 42

1. Uncommon in the US due to vaccine 2. Small, pleomorphic irregular-staining gram-positive rods that contain metachromatic granules 3. Tellurite medium

Front 43

C. diphtheriae: Pathogenesis

Back 43

1. Diptheria toxin (encoded by a bacteriophage). 2. A-B toxin. A subunit is an ADP-ribosyltransferase that inactivates elongation factor EF-2 -> which inhibits protein synthesis

Front 44

C. diphtheriae: Clinical symptoms

Back 44

1. Exudative pharyngitis (dysphagia, fever, malaise) 2. Thick pseudomembrane

Front 45

L. monocytogenes: Characteristics

Back 45

1. Short gram-positive rod that exhibits tumbling motility at room temp and is easily grown on agar, even at cold temperatures. 2. Ubiquitous in nature - animals, soil and asymptomatic colonizers of the human GI.

Front 46

L. monocytogenes: Pathogenesis

Back 46

1. Ingestion and subsequent transmucosal uptake of GI cells. 2. Evades phagocytosis by invading cells

Front 47

L. monocytogenes: Clinical symptoms

Back 47

1. Early onset disease (granulomatosis infantisptica); due to transplacental transmission. Marked by miscarriage or birth complications by sepsis, multiorgan abcesses and granulomas
2. Late onset disease; transmitted during childbirth. Results in meningitis or meningoencephalitis.
3. Adult listeriosis (pregnant, elderly or immunocompromised) can present bacteremia, sepsis or meningitis.