10_Enterics I Flashcards
1
Q
microbiome:
define
A
- all the microbes (microbiota) in and on our bodies
- includes bacterial, viruses, and eukaryotes
- microbiota used to be called “normal flora”
2
Q
where is the microbiome?
A
- vast numbers of bacteria exposed on the body sites exposed to the environment; and many thousand species of bacteria in the microbiome
- not usually inside the tissue (blood, deep tissue, sterile)
- > 100x more genetic material in microbes than human genome
3
Q
What are the most abundant bacterial phyla in the gut microbiome?
A
- FIRMICUTES
- Staph, Strep, Bacillus, Clostridium
- BACTERIODETES
- Bacteroides, Prevotella, Porphyromonas
- ACTINOBACTERIA
- Mycobacterium, corynebacterium
- PROTEOBACTERIA
- Escherichia, and other gram negative enteric organisms
4
Q
How do gut microbiomes of humans vary?
A
Humans look similar at the phylum level, but
*EACH INDIVIDUAL VARIES AT THE SPECIES LEVEL
5
Q
Protective functions of:
Gut Microbiome
A
- Pathogen displacement
- Nutrient competition
- Receptor competition
- Production of anti-microbial factors, e.g. bacteriocins, lactic acids
6
Q
Structural functions of:
gut microbiome
A
- barrier fortification
- induction of IgA
- apical tightening of tight junctions
- immune system development
7
Q
Metabolic functions:
of gut microbiome
A
- control IEC differentiation and proliferation
- metabolize dietary carcinogens
- synthesize vitamins (e.g. biotin, folate)
- ferment non-digestible dietary residure and endogenous epithelial-derived mucus
- ion absorption
- salvage of energy
8
Q
which characteristics of the microbiota in the gut vary amongst individuals?
A
- antibiotic therapy
- birth method - c-section vs. vaginal birth
- diet - vegetarian versus a non-vegetarian
- disease states
- geographical location
- age
9
Q
how does the microbiota harm us?
A
due to breakdown in the balance betweem microbiota and host immune system
- overgrowth of pathogens (e.g. UTI, flesh-eating disease, septic shock)
- Inflammatory bowel disease
- obesity
- type I diabetes
- GI cancers - H. pylori
- Oral diseases - cavities and gingivitis
- Allergy-like (atopic) diseases
10
Q
Process of inflammation in the Gut Mucosa
A
PAMPS activate the Pathogen recognition receptors –> leads to production of proinflammatory cytokines
11
Q
**Organism, disease, and mechanism:
- shigella species
- non-typhoidal salmonella ssp
- Yersinia enterocolitica
- Campylobacter jejuni
- Escherichia coli
- Vibrio cholerae
- Vibrio vulnificus
- Salmonella typhi
- Helicobacter pylori
A
12
Q
define a pathogen:
(4 key characteristics)
A
- EVADES/ OVERCOMES defense mechanisms
- Finds niche to multiply
- Causes disease
- Ensures transmission to susceptible host
13
Q
Diagnosis of diarrheal diseases:
If symptoms include:
- Rapid onset (1-16 hours), &
- Short duration (<1 day)
A
Think: food intoxication
E.g. Staphylococcus aureus, Bacillus cereus, Clostridium perfringens
14
Q
Diagnosis of diarrheal diseases:
If symptoms include:
- Slower onset, &
- Longer duration (>1 day)
A
Think: INFECTION
- If duration is < 10 days –> likely viruses or bacteria
- If duration is > 10 days –> likely parasites or HIV
15
Q
Diagnosis of diarrheal diseases:
If symptoms include:
- No fever, or low grade fever
- No white blood cells in stool sample
A
Think: SECRETORY DIARRHEA
Consider: Viruses (e.g. rotavirus), or bacteria such as Enterotoxigenic E. Coli, Enteropathogenic E. Coli, Enterohemorrhagic E. coli, or vibrio cholerae.
16
Q
Diagnosis of diarrheal diseases:
If symptoms include:
-
fever, &
- white blood cells in the stool sample (neutrophils)
A
Think: INFLAMMATORY DIARRHEA
Consider: Campylobacter, Salmonella, Shigella, or EIEC (Enteroinvasive E. coli).
17
Q
Vibrio cholerae:
causes, transmission, symptoms, conditions for growth
A
- caused by virulence factors (cholera toxin)
- transmission:
- ONLY affects humans
- human – human transmission (Fecal-oral route), usually thru contaminated water or possibly by food
- symptoms: rice water stools, aka secretory diarrhea (no WBC or blood in stool)
- the bacteria grows in salt and fresh water
Epidemiology: 101,000 cases annually –> 2,345 deaths. Only 54 annual cases in US, 0 deaths
18
Q
What is characteristic of the secretory diarrhea caused by Cholera?
(and amplification)
A
-
Cholera is dease of fluid loss in the GI tract
- Can result from as little as 25 ug of toxin
-
Rice water stool, w/ 10-20L (or 17-20L) excreted by a cholera patient
- Filled w/ 105 - 108 bacteria/mL
- Appearance is due to lots of mucus and bacteria in the stool –> causing it to look turbid.
19
Q
Important names of scientists working on Cholera, just in case
A
- Dr. John Snow mapped the cases of cholera in London to find the cause – which was a street pump
- Robert Koch identified V. cholera bacteria as the cause of cholera outbreaks (comma bacillus) in the stools of cholera patients)
- Von Pettenkofer and Emmerich were two researchers who challenged Dr. Koch –> determined that some individuals carry genetic mutation which is resistant to cholera
20
Q
Draw the hierarchy/branching of Vibrios
A
21
Q
process of the cholera toxin infecting a cell
A
- cholera toxin binds to intestinal epitheium (enterocytes), enters cell
- A subunit permanently ribosylates the Gs alpha subunit of heterotrimeric G protein –>
- constitutive cAMP production
- high cAMP –> activates (CFTR) cystic fibrosis transmembrane regulator
- results in efflux of ions and water from the infected enterocytes
- causing secretory diarrhea
22
Q
what is the benefit to the pathogen?
A
You only have to consume a certain amount of bacteria to get sick –>
the number of bacteria amplify in the body –>
excrete into the environment
23
Q
what is the structure of the Vibrio cholerae?
A
- gram negative, comma shaped bacterium
- Tcp pili (toxin co-regulated pilus) bundle located at one pole
- has a single flagellum extending from the same space
24
Q
cholera:
diagnosis and treatment
A
- diagnosis by dark-field microscopy
- first, isolate organism on TCBS agar (Thiosulfate-citrate-bile-sucrose)
- second, test serotype using antiserum to agglutinate organisms
- treatment:
- fluid replacement w/ oral rehydration salts or intravenous fluids
- antibiotics is recommended for severely ill patients (e.g. doxycycline for first line tx for adults, azithromycin for children & pregnant women)
25
Cholera vaccines:
what is available?
* **whole killed vibrios given orally plus B subunit of cholera toxin** (not available in the US)
* oral vaccines provide protection in 52% of cases the 1st year following vaccination, and in
* 62% of cases the second year
26
name the 2 non-cholera vibrios.
how do they differ?
1. V. **parahemolyticus**
* causes shellfish poisoning
* Hemolysin causes Kanagawa phenomenon
2. **V. vulnificus**
* fatal bacteremias
* opportunistic pathogen in patients w/ underlying liver disease
27
**Kanagawa** phenomenon:
define
Production of beta-hemolysis on a special high-salt mannitol medium (Wagatsuma agar) by most strains of Vibrio parahaemolyticus, which produces a heat-stable hemolysin.
28
quorum sensing was first discovered with which bacteria?
how?
* with marine bacteria **"Vibrio fischeri"**
* isolated from light-producing organ of the squid
* V. fischeri can produce light only when large #s of bacteria were present
* Each V. fischeri can produce a very small amount of chemical molecular called **autoinducer**
29
Enterotoxigenic E. Coli:
transmission, symptoms, consequences
* human to human transmission
* sxs:
* most common cause of **traveler's diarrhea**
* **typical secretory diarrhea** (no WBC or blood in stool)
* causes infant mortality in developing countries
30
what are the 3 types of fimbriae (= Pili) of the bacteria causing secretory diarrhea?
what bacteria is associated with each?
1. **Conjugative**
* e.g. E. coli, F. pili
2. **Type IV fimbriae**
* e.g. Toxin co-regulated pilus of V. cholerae
3. **Chaperone/ Usher**
* e.g. colonization factors of Enterotoxigenic E. coli
31
what are the assembly/ structural proteins of the
## Footnote
**CHAPERONE/ USHER FIMBRIAE?**
Chaperone "CUTS" off romance
* **chaperone** (200-250 aa);
* located in periplasm
* sequesters subunits/ adhesin
* **usher** (~800-900aa)
* located in outer membrane
* sequesters subunits/ adhesins
* **tip adhesion** (~300-400aa)
* single copy at distal end of filament
* N-terminus = binding specificity
* **subunits (major and minor) - (**~150-200 aa)
* major: main filament
* minor: tip fibrillum
32
what are the **surface appendages**
of the chaperone/usher fimbriae?
1. **THICK (6-8nm) - rigid fimbriae w/ tip fibrillum**
* \> 3 subunits per turn
* e.g. E. coli CFA/ fimbriae from ETEC, or E. coli P fimbriae
2. THIN (2 nm) - flexible fibrillar structures
* 2 subunits per turn
* e.g. F18 fimbriae from ETEC
33
what is the purpose of the chaperone/ usher fimbriae?
allows the bacteria to bind to carbohydrate receptors on epithelial cells --\> results in disease
(if the fimbriae is destroyed or ineffective, then the bacteria can't cause disease)
34
epidemiology of chaperone/ usher fimbriae
points to a role as host range factors
For example, in the **human isolates of Enterotoxigenic E. coli (ETEC)** have the following chaperone/ usher fimbriae:
* CFA/I, CS1, CS2, CS3, CS4, CS5, CS6
35
E. coli and respective symptoms.
Which are pathogenic? Commensal?
Symptoms caused?
36
where are the TYPE III secretion system needle structure encoded?
* encoded on pathogenicity islands of pathogenic:
* E. coli
* Shigella
* Yersinia
* Salmonella
* Pseudomonas
37
Enteropathogenic E. coli (EPEC):
transmission, symptoms, mortality
* human to human transmission by virulence factors/ mechanisms
* symptoms:
* weanling diarrhea significantly contributes to infant mortality (developing countries)
* typical **secretory diarrhea** (no WBC or blood in stool)
38
which bacteria has the **LEE pathogenicity island**? and what is it?
* **LEE pathogenicity island**: locus of enterocyte effacement --\> encodes the proteins responsible for attaching and effacing (AE) lesions in the large intestine
* These are found on the EPEC (enteropathogenic E. coli)
39
EHEC (Enterohemorrhagic E. coli)
transmission, sxs
* transmission:
* animal to human (zoonosis)
* raw or undercooked ground meat products, raw milk and faecal contamination of vegetables
* sxs:
* Shiga toxin can cause blood in stool
* Shiga toxin can cause hemolytic uremic syndrome
40
how is E. coli O157:H7 differentiated?
differentiated by its inability to ferment sorbitol
41
which types of E. coli have the LEE genetic region?
what about STX phage?
* LEE gene --\> found in Enteropathogenic and Enterohemorrhagic E/ coli (EPEC, and EHEC)
* STX phage --\> is found in the Enterohemorrhagic E. coli (just EHEC)
42
**Shiga-like toxin:**
found in which E. coli? encoded by what? function?
1. found in Enterohemorrhagic E. coli
2. encoded by STX phage
3. Function:
* bacteria remain localized in the intestinal lumen
* upon bacterial lysis, the toxin is released and enters the blood stream
* --\>
* damage to the microvasculature --\>
* blood in stool and/or
* hemolytic uremic syndrome (HUS)
43
hemolytic uremic syndrome (HUS):
define
a group of blood disorders characterized by low red blood cells, acute kidney failure, and low platelets
sxs include: bloody diarrhea, fever, vomiting, and weakness
44
what do the following pathogens have in common?
ETEC, EPEC, EHEC, and V. cholerae
* Non-invasive
* Colonization factors
* Toxin production
* Lead to secretory diarrhea
45
What type of agar is used for detection of enteric bacterial species?
Sorbitol MacConkey agar:
Lactose + --\> E. coli, enterobacter, klebsiella
Lactose - --\> Salmonella, Shigella, Proteus
46
List 3 Lactose Positive bacteria (by MacConkey agar),
List 3 Lactose Negative bacteria
Positive:
1. E. coli
2. Enterobacter
3. Klebsiella
Negative
1. Salmonella
2. Shigella
3. Proteus
47
What is the EMB agar?
Eosin methylin blue media;
designed to discourage the growth of gram positive bacteria
