Lecture 9 Flashcards
What are coliforms?
group of gram-negative, facultative anaerobic rod bacteria | ferment lactose to acid and gas
What can we use coliforms for?
used to test contamination of water or food due to feces
What is diarrhea?
the excessive discharge of fluids from bowel | it is a symptom, not a disease
What are the 2 types of diarrhea?
secretory (watery) and dysentery
What is secretory diarrhea?
loss of electrolytes and fluids from small intestine
What is dysentery diarrhea?
significant local tissue damage or inflammation of GI tract = causes blood in fluids of diarrhea
Where does dysentery diarrhea mostly occur?
large intestine
Where does secretory diarrhea mostly occur?
small intestine
In a disease where it causes both secretory and dysentery diarrhea, which one usually happens first?
secretory first then bloody second
What are the two most common causes of diarrhea? (viral/bacterial) Which is more severe?
most common = VIRAL gastroenteritis || 2nd most common = bacterial gastroenteritis = more severe than viral
How do toxic and invasive bacteria differ from each other?
invasive bacteria invade tissues of intestine and toxic bacteria don’t invade but produce toxins that target intestine
Which type of diarrhea is more serious?
dysentery diarrhea
What is Enterobacteriaceae?
group of gram- pathogens that causes infectious diseases having diarrhea as a symptom
What is Vibrionaceae?
another family of bacteria that causes diseases with diarrhea as a symptom
Which Enterobacteriaceae causes only secretory diarrhea?
enterotoxigenic E. coli (ETEC) ; enteropathogenic E. coli (EPEC) ; enteroaggregative E. coli (EAggEC)
Which Enterobacteriaceae causes only dysentery diarrhea?
enteroinvasive E. coli (EIEC) ; enterohemorrhagic E. coli (EHEC) ; Shigella
Which Enterobacteriaceae causes both types of diarrhea?
Salmonella Typhimurium and Yersinia enterocolitica
Which Vibrionaceae causes only secretory diarrhea?
Vibrio cholerae
Which Vibrionaceae causes both types of diarrhea?
Vibrio parahaemolyticus and Campylobacter jejuni
Which E. coli strain is similar to Shigella?
enteroinvasive E. coli (EIEC)
What are the main characteristics of enteric bacteria that causes secretory bacteria?
gram- rods, infection in small intestine, does NOT invade, produces enterotoxins targeting small intestine; reservoir = animals or environment; no use of antibiotics for treatment
What are the main characteristics of V. cholera?
gram- curved rods ; motile with single polar flagella (Class II) ; facultative anaerobes
Which test can we use to distinguish between Vibrionaceae and Enterobacteriaceae? What are their differences in this test?
oxidase reaction = Vibrios are positive and Enterobacteriaceae are negative
What class of flagella do motile Enterobacteriaceae have?
Class I = petrichous flagella
Where are Vibrio cholera usually found?
in aquatic/marine environments associated with algae and marine invertebrates
What disease does Vibrio cholera commonly cause?
cholera
What are the serotypes of V. cholera based off algae?
the O antigen
What do serotypes refer to?
the different reactivity of species with different antibodies
What is the O antigen part of?
part of the LPS on outer cell membrane
What are the 2 main strains of the O antigen and which one is more virulent?
O1 and O139; O1 = more virulent
What is the O1 antigen divided into?
the Classic and El Tor biovar (indicates a difference at the biochemical level)
Is cholera a new or old disease?
old
What is required of a disease in order to consider it a pandemic?
needs to affect at least 2 continents
How many cholera pandemics have occurred thus far?
7
How does one get infected with cholera?
one ingests seafood or drinks water contaminated with V. cholera which will get into GI tract to the small intestine
What is “rice water stool”?
refers to the 2 layers (“water” and “rice”) of stool sample from a patient with secretory diarrhea
What is the mortality rate in untreated patients?
60%
What are the 4-5 virulence factors of V. cholera?
flagella, capsule, Tcp, pili, cholera toxin, other unknown factors
What type of toxin is the cholera toxin?
AB toxin
In what strain is the capsule found? Is this strain the more or less virulent one of the two?
O139 which is the less virulent strain
What role does the dehydration pili play?
with the early interactions with the host cell
Why is there no antibiotic resistance in V. cholera?
because no antibiotics is used for treatment
Why is the flagella considered to be a virulence factor?
with no flagella, bacterium cannot cause disease and becomes attenuated
What does attenuated mean?
weakened in force or effect
What vaccines are available against V. cholera?
still under development but there is one that provides limited protection for a short time
Why do we not administer antibiotics to patients with secretory diarrhea caused by V. cholera? (2 reasons)
don’t want to kill off normal flora || don’t want to kill V. cholera because could have toxins inside their cells that if lysed = high amounts of it will be released
When would one every administer antibiotics against V. cholera?
to reduce toxic production and rapidly eliminate the pathogen
What is the main treatment against cholera?
oral rehydration therapy
What is oral rehydration therapy?
prevents dehydration by intaking water that contains salts and glucose
How can one prevent contamination of food due to V. cholera?
freeze food (kills most of bacteria), proper hygiene and good food preparation practices
Who first identified E. coli?
Theodore Escherich
What are the main characteristics of E. coli?
Gram– rods; facultative anaerobes, oxidase negative, motile
What is the reservoir for E. coli?
humans and animals
What are the 5 strains of enteric pathogenic E. coli causing intestinal diseases?
ETEC, EPEC, EAggEC, EIEC, and EHEC
What does ETEC stand for? What does it cause?
enterotoxigenic E. coli causes Traveler’s diarrhea
What does EPEC stand for? Who does it affect?
enteropathogenic E. coli affecting infants (pedia) under 1
What does EAggEC stand for? Who does it infect?
enteroaggregative E. coli affecting AIDS patients and newborns under 6months
What do EAggEC form that make it difficult to treat?
biofilms
What does EIEC stand for? What is it similar to?
enteroinvasive E. coli = similar to Shigella
What does EHEC stand for? What parts of the world is it most common for it to cause an infection and why?
enterohemorrhagic E. coli || H= hamburgers = ground beef»_space; more common in nations that like to eat ground beef
Do all EHEC strains invade? If no, which one doesn’t?
no, strains that cause hemorrhagic colitis don’t invade
Which Enterobacteriaceae invade?
EIEC and usually EHEC
What does ETEC contaminate?
water and fresh vegetables
Why is the disease ETEC causes called “Traveler’s diarrhea”?
our immune systems are naturally used to specific species present in the water/food we eat everyday in our home area but different regions/places have different strains of species = immune system not used to them and reacts = causes diarrheal symptoms
What are the virulence factors of ETEC?
2 heat-labile toxins (LT-I and LT-II), 2 heat-stable toxins and 1 adhesin
Which virulence factor is closely if not similar to the cholera toxin? Why?
LT-I as ETEC most likely took the gene from V. cholera; they both use the same pathogenic mechanism
Which disease is similar to cholera? Which is milder than the other and why?
Traveler’s diarrhea is a milder form of cholera because V. cholera may produce more toxins (not yet identified) that ETEC
What toxins does EPEC produce?
none have yet been identified
What are the virulence factors of EPEC?
adhesins, Type III secretion system-Tir receptor, some secreted proteins can be potential toxins
What does EPEC cause?
diarrhea in infants and small children (p=pedia)
Which virulence factor plays a key role in infection?
Type II secretion system with Tir receptor
What is the consequence due to infection of EPEC?
microvilli destruction in small intestine leads to inability to absorb food (malabsorption)
What does EAggEC cause?
persistent diarrhea in people in both developed and developing countries
Why is EAggEC called enteroaggregative? How does this explain the infection it causes?
bacteria aggregate and form biofilms on epithelium of small intestine = hard to treat due to biofilm = explains why diarrhea is persistent (lasts long time)
What toxins does EAggEC produce?
hemolysin and enterotoxin
What are symptoms of EAggEC-mediated diarrhea?
secretory diarrhea with vomiting, low-grade fever, dehydration
What is the main form of treatment for all diseases covered for diarrhea?
oral rehydration therapy
Are there any vaccines available to treat EAggEC-mediated diarrhea?
still under development
