10_Enterics I Flashcards
microbiome:
define
- all the microbes (microbiota) in and on our bodies
- includes bacterial, viruses, and eukaryotes
- microbiota used to be called “normal flora”
where is the microbiome?
- 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
What are the most abundant bacterial phyla in the gut microbiome?
- FIRMICUTES
- Staph, Strep, Bacillus, Clostridium
- BACTERIODETES
- Bacteroides, Prevotella, Porphyromonas
- ACTINOBACTERIA
- Mycobacterium, corynebacterium
- PROTEOBACTERIA
- Escherichia, and other gram negative enteric organisms
How do gut microbiomes of humans vary?
Humans look similar at the phylum level, but
*EACH INDIVIDUAL VARIES AT THE SPECIES LEVEL
Protective functions of:
Gut Microbiome
- Pathogen displacement
- Nutrient competition
- Receptor competition
- Production of anti-microbial factors, e.g. bacteriocins, lactic acids
Structural functions of:
gut microbiome
- barrier fortification
- induction of IgA
- apical tightening of tight junctions
- immune system development
Metabolic functions:
of gut microbiome
- 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
which characteristics of the microbiota in the gut vary amongst individuals?
- antibiotic therapy
- birth method - c-section vs. vaginal birth
- diet - vegetarian versus a non-vegetarian
- disease states
- geographical location
- age
how does the microbiota harm us?
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
Process of inflammation in the Gut Mucosa
PAMPS activate the Pathogen recognition receptors –> leads to production of proinflammatory cytokines
**Organism, disease, and mechanism:
- shigella species
- non-typhoidal salmonella ssp
- Yersinia enterocolitica
- Campylobacter jejuni
- Escherichia coli
- Vibrio cholerae
- Vibrio vulnificus
- Salmonella typhi
- Helicobacter pylori
define a pathogen:
(4 key characteristics)
- EVADES/ OVERCOMES defense mechanisms
- Finds niche to multiply
- Causes disease
- Ensures transmission to susceptible host
Diagnosis of diarrheal diseases:
If symptoms include:
- Rapid onset (1-16 hours), &
- Short duration (<1 day)
Think: food intoxication
E.g. Staphylococcus aureus, Bacillus cereus, Clostridium perfringens
Diagnosis of diarrheal diseases:
If symptoms include:
- Slower onset, &
- Longer duration (>1 day)
Think: INFECTION
- If duration is < 10 days –> likely viruses or bacteria
- If duration is > 10 days –> likely parasites or HIV
Diagnosis of diarrheal diseases:
If symptoms include:
- No fever, or low grade fever
- No white blood cells in stool sample
Think: SECRETORY DIARRHEA
Consider: Viruses (e.g. rotavirus), or bacteria such as Enterotoxigenic E. Coli, Enteropathogenic E. Coli, Enterohemorrhagic E. coli, or vibrio cholerae.
Diagnosis of diarrheal diseases:
If symptoms include:
-
fever, &
- white blood cells in the stool sample (neutrophils)
Think: INFLAMMATORY DIARRHEA
Consider: Campylobacter, Salmonella, Shigella, or EIEC (Enteroinvasive E. coli).
Vibrio cholerae:
causes, transmission, symptoms, conditions for growth
- 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
What is characteristic of the secretory diarrhea caused by Cholera?
(and amplification)
-
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.
Important names of scientists working on Cholera, just in case
- 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
Draw the hierarchy/branching of Vibrios
process of the cholera toxin infecting a cell
- 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
what is the benefit to the pathogen?
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
what is the structure of the Vibrio cholerae?
- 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
cholera:
diagnosis and treatment
- 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)
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
name the 2 non-cholera vibrios.
how do they differ?
- V. parahemolyticus
- causes shellfish poisoning
- Hemolysin causes Kanagawa phenomenon
-
V. vulnificus
- fatal bacteremias
- opportunistic pathogen in patients w/ underlying liver disease
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.
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
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
what are the 3 types of fimbriae (= Pili) of the bacteria causing secretory diarrhea?
what bacteria is associated with each?
-
Conjugative
- e.g. E. coli, F. pili
-
Type IV fimbriae
- e.g. Toxin co-regulated pilus of V. cholerae
-
Chaperone/ Usher
- e.g. colonization factors of Enterotoxigenic E. coli
what are the assembly/ structural proteins of the
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
what are the surface appendages
of the chaperone/usher fimbriae?
-
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
- THIN (2 nm) - flexible fibrillar structures
- 2 subunits per turn
- e.g. F18 fimbriae from ETEC
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)
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
E. coli and respective symptoms.
Which are pathogenic? Commensal?
Symptoms caused?
where are the TYPE III secretion system needle structure encoded?
- encoded on pathogenicity islands of pathogenic:
- E. coli
- Shigella
- Yersinia
- Salmonella
- Pseudomonas
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)
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)
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
how is E. coli O157:H7 differentiated?
differentiated by its inability to ferment sorbitol
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)
Shiga-like toxin:
found in which E. coli? encoded by what? function?
- found in Enterohemorrhagic E. coli
- encoded by STX phage
- 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)
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
what do the following pathogens have in common?
ETEC, EPEC, EHEC, and V. cholerae
- Non-invasive
- Colonization factors
- Toxin production
- Lead to secretory diarrhea
What type of agar is used for detection of enteric bacterial species?
Sorbitol MacConkey agar:
Lactose + –> E. coli, enterobacter, klebsiella
Lactose - –> Salmonella, Shigella, Proteus
List 3 Lactose Positive bacteria (by MacConkey agar),
List 3 Lactose Negative bacteria
Positive:
- E. coli
- Enterobacter
- Klebsiella
Negative
- Salmonella
- Shigella
- Proteus
What is the EMB agar?
Eosin methylin blue media;
designed to discourage the growth of gram positive bacteria
