GI bacteria II

Question 1

What is the main ingredient in MacConkey agar?

Answer 1

Bile salts - inhibits growth of many bacteria except certain GI bacteria

Question 2

Lactose fermentation on MacConkey agar is positive (red) with what bacteria?

Answer 2

E. coli

Question 3

Lactose fermentation on MacConkey agar is negative (white) with what bacteria?

Answer 3

Salmonella, shigella

Question 4

The indole test is positive (red color change) for what bacteria?

Answer 4

E. coli, vibrio spp.

Question 5

The indole test is negative (no color change) for what bacteria?

Answer 5

Salmonella

Question 6

What test is used to differentiate between salmonella and shigella?

Answer 6

Hydrogen sulfite production

Question 7

Is salmonella a hydrogen sulfite producer?

Answer 7

Yes

Question 8

Is shigella a hydrogen sulfite producer?

Answer 8

No

Question 9

What are the characteristics of enteropathogenic E. coli (EPEC)?

Answer 9

1. Gram negative 2. Facultative anaerobe 3. Mmoderately invasive

Question 10

What are the disease symptoms of enteropathogenic E. coli (EPEC)?

Answer 10

Water diarrhea

Question 11

What is the pathogenesis of enteropathogenic E. coli (EPEC)?

Answer 11

1. Interacts with intestinal cells via BfpA (bundle forming pillus A) 2. Type III secretion system, injects Tir into host cytosol 3. Intimin binds to Tir 4. F actin causes loss of microvilli - diarrhea 5. No toxins

Question 12

What is the diagnosis for enteropathogenic E. coli (EPEC)?

Answer 12

1. Ferments lactose (red on MacConkey) 2. Indole positive 3. PCR

Question 13

What are the characteristics of enterotoxigenic E. coli (ETEC)?

Answer 13

1. Gram negative 2. Facultative anaerobe 3. Non-invasive

Question 14

What are the disease characteristics of enterotoxigenic E. coli (ETEC)?

Answer 14

1. “Traveler’s diarrhea” 2. Watery diarrhea

Question 15

What is the pathogenesis of enterotoxigenic E. coli (ETEC)?

Answer 15

1. Fimbriae - adherence 2. Toxins - increase cAMP and cGMP 3. Non-invasive, noninflammatory

Question 16

What toxins are associated with enterotoxigenic E. coli (ETEC)?

Answer 16

1. LT - heat labile - AB toxin - increases cAMP 2. ST - heat stable - non-AB toxin - increases cGMP 3. Plasmid encoded

Question 17

What is the diagnosis for enterotoxigenic E. coli (ETEC)?

Answer 17

1. Clinical history 2. DNA probes to detect LT and ST encoding genes

Question 18

What are the characteristics of salmonella typhi?

Answer 18

1. Gram negative 2. Facultative anaerobe 3. Motile flagellated rods 4. Acid tolerant 5. Intracellular pathogen 6. Inflammatory

Question 19

What is the epidemiology of salmonella typhi?

Answer 19

1. Humans are the only reservoir 2. Fecal-oral transmission 3. Infectious dose 10^5 - 10^6 bacteria

Question 20

What is the disease progression for salmonella typhi?

Answer 20

1. 13 day incubation 2. Fever with headache 3. Typhoid fever (4 weeks) with sustained bacteria 4. GI symptoms - colonization of gall bladder, reinfection of intestines 5. Shed in stool

Question 21

What is the pathogenesis for salmonella typhi?

Answer 21

1. Adherence to M cells and enterocytes 2. Type III secretion system 3. Ssps - salmonella secreted invasion proteins cause membrane ruffling of M cell 4. Escape from vacuole 5. Bacteremia from T3SS invasion into macrophages

Question 22

What is the function of M cells?

Answer 22

1. Sample and present intestinal contents to immune cells 2. Associated with Peyer’s patches in ileum

Question 23

What causes the typhoid fever symptoms in salmonella typhi infection?

Answer 23

Endotoxin released into blood stream from bacteremia

Question 24

What is the treatment for salmonella typhi?

Answer 24

1. Antibiotics based on susceptibility profile 2. Fluoroquinolones, trimethoprim-sulfamethoxazole or broad spectrum cephalorsporin

Question 25

What are the characteristics of non-typhoidal salmonella?

Answer 25

1. Gram negative facultative anaerobe 2. Motile flagellated rods 3. Acid tolerant 4. Intracellular pathogens 5. Same as typhoidal but not as human adapted 6. Inflammatory

Question 26

What is the epidemiology of non-typhoidal salmonella?

Answer 26

1. Numerous animal reservoirs 2. Contaminated dairy / egg / poultry 3. Human to human transmission unlikely 4. Infectious dose 10^6 - 10^8

Question 27

What is the clinical manifestation of non-typhoidal salmonella?

Answer 27

1. 6-48 hours post ingestion 2. Nausea and vomiting with abdominal cramps and watery diarrhea for 3-4 days 3. Fever 50% of cases 4. Dysentery type diarrhea possible 5. Spontaneous resolution of watery diarrhea within 7 days

Question 28

What is the pathogenesis of non-typhoidal salmonella?

Answer 28

1. Initial stage similar to typhoidal 2. After entry can either kill macrophage or reside within macrophage

Question 29

What characterizes non-typhoidal salmonella infection with macrophage killing?

Answer 29

1. Massive inflammatory response that aims to confine infection 2. Active fluid secretion

Question 30

What characterizes non-typhoidal salmonella infection with macrophage hijacking?

Answer 30

1. Occurs in immunocompromised individuals 2. Systemic dissemination, bacteremia 3. Focal infections of arthritis, osteomyelitis, endocarditis

Question 31

What is the diagnosis for non-typhoidal salmonella?

Answer 31

1. Serology - anti-Vi antigen Abs 2. Culture - non-lactose on MacConkey, H2S positive

Question 32

Why is antibiotic therapy not recommended for non-typhoidal salmonella gastroenteritis infection?

Answer 32

1. Enhances carrier state 2. It is only for severe cases to prevent septicemia

Question 33

What are the characteristics of campylobacter jejuni?

Answer 33

1. Gram negative rod, seagull shaped 2. Microaerophilic 3. Many animal reservoirs 4. Invasive - jejunum, ileum, colon

Question 34

What is the disease progression for campylobacter jejuni?

Answer 34

1. Ulceration and acute enteritis - watery diarrhea 2. Sepsis 3. Long incubation time (2-11 days) 4. Sequelae - Guilliain-Barre syndrome

Question 35

What are the features of Guillain-Barre syndrome?

Answer 35

1. Acute immune-mediated polyneuropathy 2. Progressive, fairly symmetric muscle weakness accompanied by absent or depressed deep tendon reflexes