Flashcards in GI bacteria II Deck (35):
1
What is the main ingredient in MacConkey agar?
Bile salts - inhibits growth of many bacteria except certain GI bacteria
2
Lactose fermentation on MacConkey agar is positive (red) with what bacteria?
E. coli
3
Lactose fermentation on MacConkey agar is negative (white) with what bacteria?
Salmonella, shigella
4
The indole test is positive (red color change) for what bacteria?
E. coli, vibrio spp.
5
The indole test is negative (no color change) for what bacteria?
Salmonella
6
What test is used to differentiate between salmonella and shigella?
Hydrogen sulfite production
7
Is salmonella a hydrogen sulfite producer?
Yes
8
Is shigella a hydrogen sulfite producer?
No
9
What are the characteristics of enteropathogenic E. coli (EPEC)?
1. Gram negative 2. Facultative anaerobe 3. Mmoderately invasive
10
What are the disease symptoms of enteropathogenic E. coli (EPEC)?
Water diarrhea
11
What is the pathogenesis of enteropathogenic E. coli (EPEC)?
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
12
What is the diagnosis for enteropathogenic E. coli (EPEC)?
1. Ferments lactose (red on MacConkey) 2. Indole positive 3. PCR
13
What are the characteristics of enterotoxigenic E. coli (ETEC)?
1. Gram negative 2. Facultative anaerobe 3. Non-invasive
14
What are the disease characteristics of enterotoxigenic E. coli (ETEC)?
1. "Traveler's diarrhea" 2. Watery diarrhea
15
What is the pathogenesis of enterotoxigenic E. coli (ETEC)?
1. Fimbriae - adherence 2. Toxins - increase cAMP and cGMP 3. Non-invasive, noninflammatory
16
What toxins are associated with enterotoxigenic E. coli (ETEC)?
1. LT - heat labile - AB toxin - increases cAMP 2. ST - heat stable - non-AB toxin - increases cGMP 3. Plasmid encoded
17
What is the diagnosis for enterotoxigenic E. coli (ETEC)?
1. Clinical history 2. DNA probes to detect LT and ST encoding genes
18
What are the characteristics of salmonella typhi?
1. Gram negative 2. Facultative anaerobe 3. Motile flagellated rods 4. Acid tolerant 5. Intracellular pathogen 6. Inflammatory
19
What is the epidemiology of salmonella typhi?
1. Humans are the only reservoir 2. Fecal-oral transmission 3. Infectious dose 10^5 - 10^6 bacteria
20
What is the disease progression for salmonella typhi?
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
21
What is the pathogenesis for salmonella typhi?
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
22
What is the function of M cells?
1. Sample and present intestinal contents to immune cells 2. Associated with Peyer's patches in ileum
23
What causes the typhoid fever symptoms in salmonella typhi infection?
Endotoxin released into blood stream from bacteremia
24
What is the treatment for salmonella typhi?
1. Antibiotics based on susceptibility profile 2. Fluoroquinolones, trimethoprim-sulfamethoxazole or broad spectrum cephalorsporin
25
What are the characteristics of non-typhoidal salmonella?
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
26
What is the epidemiology of non-typhoidal salmonella?
1. Numerous animal reservoirs 2. Contaminated dairy / egg / poultry 3. Human to human transmission unlikely 4. Infectious dose 10^6 - 10^8
27
What is the clinical manifestation of non-typhoidal salmonella?
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
28
What is the pathogenesis of non-typhoidal salmonella?
1. Initial stage similar to typhoidal 2. After entry can either kill macrophage or reside within macrophage
29
What characterizes non-typhoidal salmonella infection with macrophage killing?
1. Massive inflammatory response that aims to confine infection 2. Active fluid secretion
30
What characterizes non-typhoidal salmonella infection with macrophage hijacking?
1. Occurs in immunocompromised individuals 2. Systemic dissemination, bacteremia 3. Focal infections of arthritis, osteomyelitis, endocarditis
31
What is the diagnosis for non-typhoidal salmonella?
1. Serology - anti-Vi antigen Abs 2. Culture - non-lactose on MacConkey, H2S positive
32
Why is antibiotic therapy not recommended for non-typhoidal salmonella gastroenteritis infection?
1. Enhances carrier state 2. It is only for severe cases to prevent septicemia
33
What are the characteristics of campylobacter jejuni?
1. Gram negative rod, seagull shaped 2. Microaerophilic 3. Many animal reservoirs 4. Invasive - jejunum, ileum, colon
34
What is the disease progression for campylobacter jejuni?
1. Ulceration and acute enteritis - watery diarrhea 2. Sepsis 3. Long incubation time (2-11 days) 4. Sequelae - Guilliain-Barre syndrome
35