Microbiology of the Lower GI Tract - Bacterial Gastroenteritis Flashcards
What are the main GI defense systems in the intestine?
peyer’s patches and normal flora
What percetage of foodborne illness outbreaks in the US are caused by bacteria?
40%
When does true food poisoning occur?
when you eat food containing pre-formed toxins
Which will have a shorter incubation period - food poisoning or a food-associated infection?
food posoning - only the amount of time it takes for the toxin to get into your system
with food-associated infections, the bacteria need to proliferate and make their toxin/cause damage, so it takes longer
Are the toxins causing food poisoning endotoxins or exotoxins? What;s the special term for them because they affect gut epithleial cells?
exotoxin = called an enterotoxin
What ar ethe three main bacteria that cause food poisoning with pre-formed toxins in food?
staph aureus
bacillus cereus
clostridium botulinum
Describe the morphology of stpah aureus.
gram positive cocci in clusters
coagulase positive, catalase positive
What are the symptoms of staph aureus food poisoning and what’s the incubation period?
nause,a vomiting, stomach cramps, and diarrhea for 1-3 days after an incubation of 1-7 hours after you eat the food
self-limiting
once the toxin is gone, the illness is gone
How can you make a positive diagnosis of staph aureus food poisoning? Is this necessary?
toxin=producing staph aureus can be identified in stool or vomit
most conclusive test is to link the illness with a specific food and test the food
this is not necessary unless you’re tracking an outbreak
How many different toxins can stpah aureus make to cause food poisoning?
7
The staph aureus toxins can survive incredibly high temps. How about the bacteria itself?
It’s one of the most resistant non-spore forming human pathogens which can survive in dry state at temps between 15-45
but no, it cannot survive at the high temps that the toxin can
What foods typically harbor staph aureus and its toxin?
food that has sat around for a long time - enough time for the bacteria to make the toxin
potato salad, processed meats, pastries that sit out on bakery shelves
What does bacillus cereus look like?
box=car shaped gram positive rod
Why is bacillus cereus particularly an issue in hospitals?
it produces biofilms that can adhere easily to invasive devices
Why does bacilus cereus cause a chronic persistent infection?
because of it’s biofilm - it can periodically release more B cereus into the bloodstream
What can bacillus cereus do that staph aureus cannot in terms of contagion?
forms spores
Describe the morphology of bacillus cereus.
gram positive large bacilli
endospore forming
If bacilus cereus motil?
yes - mostly
What is bacillus cereus relationship with osygen?
facultative anaerobe
What hemolysis does bacillus cereus exhibit?
beta hemolytis
Where in the enviornment are B cereus spores common? How does this affect the food involved?
Common found in the soil - most often in plant foods that grow close to the ground like legumes, cereals (rice) and spices
Why was bacillus cereus food poisoning such a problem in the 70s
chinese restauraunts would let the leftover rice sit over night to make fried rice, giving the present bacteria time to make toxins
What are the two forms that bacillus cereus food poisoning can take?
emetic type
diarrheal type
Which occurs after a hosrter incubation period - emetic or diarrheal?
emetic after 1-6 hours
diarrhea after 6-15 hours
What is the duration for both the emetic type and diarrheal type?
24 hours
WHat is the mechanism behind the emtic type? What toxin is used?
the pre-formed CEREULIDE toxin (low molecule weight ionophoric peptide) will form holes in the cells membranes, causing irritation
What is the mechanism behind the diarrheal type? What toxin?
get watery diarrhea and abdominal cramps due to a large molecular weight enterotoxin that causes intestinal fliud secretion by several mechanisms
NOT pre-formed (which is why it takes longer to develop the diarrheal form)
Why do you need to warn the lab if you suspect a B cereus infectios cause of gastroenteritis?
Because of its ubiquity, B cereus is often irgnored or dismissed as a contaminant when found in a culture specimen
Describe the morphology of clostridium botulinum?
a gram positive bacilli with a terminal spore (looks like a matchstick)
What is clostridum botulinum’s relationshipw ith O2?
obliate anerobe
What are the three general forms of botulinism?
- foodborne botulinism from ingestion of toxin in food
- wound botulism
- infant botulism from ingesting the spores
What are the symptoms of botulism?
it’s not really a GI illness because diarrhea isn’t prominent
more neurological - makes a neurotoxin that irreversibely blocks the release of ACh from the motor end place leading to muscle weakness and paralysis - get blurred vision, double vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth and muscle weakness
What are the treatment options for foodborne botulism?
ventilator if respiratory failure
antitoxin is paralysis isn’t complete
remove contaminated foof if it’s still iikely in the gut
What are the symptoms of infant botulism?
has an incubation period for the spores to produce the toxin-forming bacteria
baby will be lethargic, feeding poorly, constipated with weak cry and poor muscle tone
What are the comon food reservoirs for the toxin in clostridium botulium?
innappropriately canned foods
What’s a common food reservoir for the C. botulinum spores?
honey - so don’t give it to babies untilt hey’re older than 1
What are the five main bacteria that are primarily transmitted through food but do not cause real food poisoning?
- clostridium perfringens
- salmonela enterica
- campylobacter jejuni
- listeria monocytogenes
- vibrio parahaemolyticus
the big three are at the top
Of the big three: C. jejuni, salmonella, and C. perfringens, which one uses and enterotoxin and how to the other two do it?
C. perfringens uses an enterotoxin and C. jejuni and Salmonella both invade the intestinal cells
Describe the morphology of clostridium perfringens.
gram positive bacilli
spore forming
What is clostridium eprfringens’ relationship with O2?
ogligate anaerobe
What characteristic distinguishes clostridium perfringens from other species of clostridium (botulinum and difficile)?
it’s non-motile
What symptoms are present and what symptoms are absent in clostridium perfringens?
diarrhea and abdominal cramps present, but no feer or vomiting
true or false: clostridium perfringens infections can be passed from human to human
no
How do you make a positive diagnoiss of clostridium perfringens?
detectoin of toxin or high amounts of bacteria in the feces
What are the morphological characteristics of campylobacter jejuni?
gram negative spirilli
What is capylobacter’s relationship with O2?
microaerophilic
True or false - campylobacter jejuni is non-motile
false - it’s motile
True or false - campylobacter is cold sensitive
true
How is campylobacteriosis spread?
it’s a zoonosis, meaning a disease that is transmitted to humans from aniamsl or animal products
in this case it’s in poultry
Since campyllobacter jejuni is microaerophilic and cold sensitive, how must it be cuultured?
very carefully
use karmali agar, which is a selective agar with vancomycin and cefoperazone to kill everything else
What are the main symptoms ofcampylobacter jejuni? After how long an indubation period?
diarrhea, cramping and fever plus maybe abdominal pain after a 2-5 day incubation
symptoms can last a week
can have vomiting and diarrhea can be bloody
What is the general mechanism of te symptos in campylobacter infections?
inflammatory response to cell invasion
What is the possible complication of campylobacter jejuni?
guillain-barre
What serotypes of salmonella will cause typhoid fever?
S. parathyphi A
S. typhi
What serotypes of salmonella will cause gastroenteritis known as salmonellosis?
S. Enteritidis
S. Typhimurium
Describe the morphology of S. Enteritidis?
Gram negative bacilli with multiple flagella
Does S. enteritidis form spores?
nope
S. Enteritidis is H2S ____ and lactose _____
H2S positive and lactose negative
What agar is used to differentiated salmonella and shigella? How?
Salmonella Shigella agar
it has bile salts that inhibit gram postivies. Also contaisn an indicator that will show red with lactose-fermenting organisms. FUrthermore, ferric citrate is added for indication of H2S, which will show up black.
So S. Enteritidis will be black (H2S positive and lactose negative)
What are the symptoms of salmonellosis? After how long of an indubation period?
diarrhea, fever and abdominal cramps after 12 hours to 3 days
How long do the symptoms last in salmonellosis?
4-7 days
What is a possible complication with salmonellosis?
reactive arthritis
True or false: the salmonellosis symptoms are caused by an invasion mechanism.
true
What are the common food sources of salmonella?
raw eggs
food service workers
unpasteurized milk
unwashed produce
What animal reservoir is there for salmonella?
turtles
Dexcribe the morphology of vibrio species
gram negative vibrio (curved rod) with one flagella
What is vibrio’s relation to O2?
facultative anerobe
Is vibrio oxidase positive or negative? Why is this special?
it’s oxidase positive, which distinguishes it form enterics which are oxidase negative
How do we test for vibrio’s oxidase positivity?
we use Kovac’s oxidase reagent on the plate which will turn oxidase positive organisms blue
Vibrio cholerae is the famous one, but which one will also cause gastroenteritis?
vibrio parahaemolyticus
What are the symptoms from vibrio parahaemolyticus?
fairly ild bloody diarrhea, stomach cramps, fever, nausea and/or vomiting that last less than a week
What are the two enterotoxins Vibrio parahaemolyticus uses?
hemolysins TDH or TRH
note that any strains of V. parahaemolyticus that doesn’t have these toxins wno’t cause disease
What will these toxins do for the vibrio
form pores in the RBCs and epithelial cells, disrupting gut homeostasis
What food is the most common reservoir for vibrio parahaemolyticus?
uncooked fish and shellfish
Describe the morphology of listeria monocytogenes.
Gram positive (!) bacillus with a flagella
Does listeria form spores? Oxidase positive or negative?
Non-spore forming
oxidase negative
note - it’s non-fastidious
Listeria wins the prize for what?
leading cause of death by foodborne illness
What hemolysis does listeria display?
beta-hemolysis (but the zone of discoloration is really only direclty under the colonies, so you can miss it0
In what populations is listeria particularly concerning?
older adults, PREGNANT WOMEN, newborns and immunocompromised
it’s considered an opportunistic infection
What are the symptoms of listeriosis?
fever, muscle aches, stiff neck
fever and chills if pregnant
can progress to meningitis and sepsis in vulnerable populations
How do you diagnose listeriosis?
you an’t do a stool sample, so you have to positvely ID the bacterium in a normally sterile site like the CSF
Does listeria invade?
yes - if you have the classic clinical symptoms, the disease has already reached the invasive stage
How does listeria spread throughout the body? What organ is a particular target?
It enters immune cells and then spreads around through a trojan horse effect
the liver is a major target
Once the listeria excapes from the vacuole and enters cytoxol of the cell, how does it move around?
uses actin polymerization -
actin rockets
What are the common food reservoirs for listeria?
sprouts deli meats and hot dogs smoked seafood soft cheese raw milk
why we make pregnancy suggestions against these foods
Shigella is most closely related to what other bacteria?
E coli
What are the three types of shigella we learned?
shigella sonnei (most common) shigella flexnori (bascillary dysentery) shigella dysenteriae (rarest, but most severe dysentery)
What are the symptoms of shigella sonnei?
diarrhea - bloody
fever
cramps
start 1-2 days after exposure and resolve in 507
What is dysentery?
it’s frequent, small bowel movements with blood and mucus accompanied by rectal pain and spasms - tenesmus
How do amebic and vacillary dysentery differ?
amebic is gradual onset while bacillary is sudden
fever, chills and pus occur with bacillary and not amebic
prostration is generally worse with bacillary
the chourse is chronic in amebic and acute in bacillary
What is the morphology of shigella?
gram negative bacillus which is non-motile (shigella have no flagella)
Shigella is H2S ____ and lactose _____
H2S negative and mainly lactose negative
Does shigella form spores?
no
How do Shigella get around if they don’t have a flagella?
they use actin rockets
Is shigella invasive?
yes
What’s the possible complication of shigella?
hemolytic uremic syndrome
S. flexnori can also cause reactive arthritis
What is the toxin for shigella called - it’s what leads to the dysentery?
shiga toxin - also called verotoxin
What are the four general diases caused by E coli?
Diarrhea
Urinary tract infections
Neonatal Sepsis
Gram negative sepsis
What is hte mophology of e coli?
gram negative bacillus that’s motile
What’s e coli’s relation to O2?
facultative anaerobe
Does e coli form spores?
no
E colis i lactose _____
positive
True or false: E coli is a very comon GI commensal and most straings are no pathogenic.
true
What must occur for E coli to become pathogenic?
needs to gain the ability to make a toxin
What are the two strains that will cause GI disease?
Enterotoxigenic (ETEC)
Enterohemorrhagic (EHEC) - also called shiga-toxin producing E coli (STEC)
ETEC is associated with what disease?
traveler’s diarrhea
also diarrhea in kids
the enterotoxin from E coli activates what signalling molecule to result in water entry to the lumen?
adenylate cyclase
What are the symptoms of ETEC and EHEC?
profuse watery diarrhea which can progress to bloody for EHEC fever nausea but no vomiting chills headache, muscle aches, bloating
What’s the complication of ETEC and EHEC?
HUS
True or false: antibiotics are recommended for E coli.
false
What are the main food reservoirs for E coli?
uncooked meat and unwashed vegetables - especially greens
What is the primary reservoir for Vibrio cholerae?
water
What two serogroups of vibrio cholerae produce cholera toxin and thus cholera?
O1 and O139
How does the cholera toxin work?
It activates adenylate cyclase to increased cAMP. THIs decreases Na absorption and increases Cl excretion intot he lumen with water following
Describe the diarrhea that occurs in cholera?
it’s acute profuse watery diarrhea described as rice-water stools
also get vomiting, tachycardia, loss of skin elasticity , dry mucous membranes, low blood pressure and dehydration in general
How cna you confirm a case of cholera?
only by isolation of the causative orgnaism from the diarrheic stools of infected people
What’s the biggest factor for treatment of cholera?
rehydration therapy is the mainstay
antibitoics only for severe cases
What is the reservoir for S. typhi causing typhoid fever?
untreated water
True or false: typhoid fever (S. typhi) only affects humans.
true
Is a vaccine available for S typi?
yes
What are the symptoms of Typhoid fever
It’s a life-threatening illness
it starts in the GI tract and then enters the bloodtresam. you get high fevers, weakness, headache, stomach pain, diarrhea OR constripation, sometimes a rash of flat, rose-colored spots
Can a person become a carrier for S typhi even after symptoms clear?
yup
Do you use antibiotics in typhoid fever?
yes
What are some examples of low-inoculum organisms?
only need tens to hundreds ot virions/cysts/bacteria….
shigella, giardia, entamoeba, norovirus
What are some examples of hihg-inoculum organisms?
needs tens or thousands….
vibrio cholerae, C. perfringens
What is the morphology of C diff?
gram positive bacilli - motile
Does clostridium difficile form spores?
oh yeah - endospores
What’s C diff’s relation to O2?
obligate anaerobe
How does C diff primarily cause disease?
exotosin causes cell death, shallow ulcers and pseudomembranes
How do you diagnose C diff?
difficult to culture since it’s an obligate anaerobe, so you need to detect the toxins
scoping is dangerous because of risk for perforations
