GI infections (bacterial) Flashcards
In developing nations, GI infections are major source of __ &__ where in developed nations they are a source of ___
morbidity and mortality
- especially children
just morbidity
Outbreaks of GI infections are usually due to what kind of contamination?
food and water contamination
in the developing world, how many cases of GI infections are there a year and how many deaths?
~ 1 billion cases / year resulting in 4-6 million deaths (12,600 / day)
What bacterial pathogen causing GI infection has a very long incubation period?
E-coli 0157
A very short incubation period for GI disease is indicative of..
preformed toxin having been ingested
In 1g of stool, there are approximately how many bacteria?
10^11
When are stool samples from a patient rejected?
- If they’ve been in the hospital more than 72 hours
2. If its not actually diarrhea
What are the 4 main types of selective media (plus one bonus one for Vibrio) that are used to culture stool samples?
XLD, Campylobacter agar, MacConkey agar, Sorbitol MacConkey agar
On request, TCBS agar for Vibrio
What is the morphology of Campylobacter sp. ?
Gram -ve, highly motile, spiral rod
What are the three species of Campylobacter? How can they be differentiated?
Campylobacter jejuni, Campylobacter coli, and C. fetus
C. jejuni is positive for a hippurate test
C. fetus is non-thermophilic unlike the other 2
- rarely causes disease
How does campylobacter rank in terms of causes of community acquired diarrheal diseases?
it’s by far #1
What conditions do Campylobacter require for growth?
Thermophilic (25 to 43º C) - except C. fetus
- allows you to differentiate between it and other bacteria that won’t grow at elevated temps
Microaerophilic
What additions to the agar need to be made to grow Campylobacter?
needs to contain blood or charcoal
-also usually has antibiotics
Whats the incubation period and infective dose for Campylobacter?
Incubation period: usually 2-4 days
Infective dose 10^3 – 10^4 cells
What are typical symptoms of a campylobacter infection?
Fever, myalgia, etc..
Diarrhea (can be bloody)
Abdominal pain
What is the prognosis of a Campylobacter infection?
usually self limiting and resolves in about a week
- people are not normally treated for this
What rare disease has Campylobacter been associated with?
Guillain-Barre syndrome
How many true species of Salmonella are there? what are they ?
just 3 really
S. enterica, S. bongori, S. subterranea
How many serovars of S. enterica are there?
about 2000
What is a special virulence adaptation of Salmonella?
Motile because of peritrichous flagella (H antigen).
What two serovars of S. enterica are non-motile?
S. gallinarum and S. pullorum
What is the Kauffmann-White antigenic scheme?
A way to classify Salmonella based on agglutination reactions with specificantisera against Salmonella antigens
What are 3 types of antigens found on Salmonella that are used for Kauffmann-White profiling?
O, H and Vi antigen
What is O antigen ?
characteristic sequence of repeatingpolysaccharide units in LPS.
What is the H antigen?
flagellar antigens (protein) and mayoccur in one of two phase variations.
What is the Vi antigen? where is it found?
Capsular polysaccharide found only in the Salmonella typhi serovar
What is the relationship between infective dose and incubation period for Salmonella gastroenteritis?
Incubation period is dose dependent - couple of days on average
When do symptoms usually appear for a Salmonella infection?
after about 48 to 72 hours
What are some symptoms of Salmonella gastroenteritis?
Nausea and vomiting Diarrhea Myalgia Fever Abdominal pain
What is the typical duration for an infection with Salmonella Gastroenteritis?
2-7 days
Are people treated for Salmonella?
Yes if they are under 6months or over 50 years
Why are certain people treated for Salmonella?
Under 6 months: don’t produce enough stomach acid
Over 50: stomach acid isn’t acidic enough
What is Salmonella Enteric Fever? What causes it?
Bacteremic illness caused by S. typhi in the blood
What is the incubation for Salmonella Enteric Fever?
10-14 days
What is the best specimen to collect to diagnose Salmonella Enteric fever?
Bone marrow sample
- can use blood and urine, almost never find it in stool by the time the patient is presenting with symptoms
What are some symptoms of Salmonella Enteric Fever? (6)
- myalgia and headache
- fever
- splenomegaly
- leukopenia
- abdominal pain
- Rose spots (macular rash on abdomen)
What are two possible sequelae of SEF?
intestinal haemorrhage and perforation
What is the first step in culturing Salmonella?
Need to grow up the number of organisms in a pre-enrichment broth
- inhibits the growth of other organisms in the sample
What are the 2 types of pre-enrichment broth? How long do you grow it in there for?
- Selenite
- Tetrathionate
No longer than 16 hours
What 4 types of selective and differential media can be used to culture Salmonella?
XLD, HE, SS agar, Bismuth-sulfite agar
What is XLD media? What does it contain? What is it used for?
Contains xylose, lysine, sodium desoxycholate, sodium thiosulfate and ferric ammonium citrate
also has an excess of lactose and sucrose
Selective & differential media for the isolation of gram negative enteric pathogens cultivated from clinical specimens
What 3 reactions occur on XLD media
1) xylose fermentation,
2) lysine decarboxylation
3) hydrogen sulfide production
Enterics (with the exception of Shigella) ferment what sugar rapidly?
xylose
XLD media is used to differentiate what two pathogens from other enteric gram negatives?
Salmonella and Shigella
How does XLD media work?
Initially Salmonella will ferment the xylose and the colonies will turn yellow due to the acid production
- For shigella, the colonies will remain red as it doesn’t ferment xylose
Gradually the Salmonella colonies will revert back to red as xylose is depleted and lysine decarboxylation is maxed out
- this is prevented from happening in other enterics with the addition of excess lactose and sucrose
Salmonella then produces hydrogen sulfide under alkaline conditions which results in the formation of colonies with black centers, whereas, under acidic conditions, this black precipitation is inhibited
- results in black colonies
What would a typical enteric look like on XLD media
would turn yellow and remain that way
What does shigella look like on XLD media?
red, no change in colony colour
What does Salmonella look like on an XLD plate?
goes from yellow back to red and eventually to the formation of black spotted colonies
What is the incubation period for E.coli 0157?
3-8 days
What symptoms are typical of an E. coli 0157 infection?
Diarrhea which can range from mild to grossly bloody
- severe cases = hemorrhagic colitis
Severe abdominal cramping
What can occur in up to 10% of cases of E.coli 0157 ?
hemolytic urea syndrome (HUS)
What is HUS? What is the mortality?
anemia / thrombocytopenia / kidney damage Significant mortality (~1-5%)
Who is more susceptible to developing HUS?
very young and very old
What does E.coli 0157 produce that makes it so virulent?
Shiga like toxin
What kind of toxin is shiga-like toxin? How does it act?
Subunit toxin:
A: acts at ribosomal level, inhibits protein synthesis
B: binds glycolipid receptor in mammalian cells (renal endothelium)
What is a reservoir of E.coli 0157 and why?
Cows because they lack the receptor for the shiga like toxin
Can other non-0157 strains of E. coli also produce shiga like toxin?
yeppp
What 2 features are used to distinguish the 0157 strains of E. coli from others? What kind of agar is used? What test ?
Virtually all 0157 strains DO NOT fermentsorbitol, whereas most non-0157 strains do
0157 strains are also ß-glucuronidase negative
Latex agglutination is used to confirm 0157 strains
Uses Sorbitol-MacConkey agar
What are the 4 species of Shigella and their group
S. dysenteriae (Group A)
S. flexneri (Group B)
S. boydii (Group C)
S. sonnei (Group D)
What is the results of a TSI slant for Shigella?
K/A (red /yellow)
Except for S. dysenteriae, all Shigella ferment…?
mannitol
Are Shigella motile?
no
What is the result of a Urea test for Shigella?
Negative
What does Shigella cause in humans?
Shigellosis or bacillary dysentery.
How is Shigella transmitted?
Via the fecal oral route or person to person
What is the infective dose for Shigella?
VERY low, 10-100 organisms only
Is Shigella a zoonotic disease?
no
What is the incubation period like for Shigella
Mid range : 2-4 days
What are some symptoms of an infection with Shigella? Early and later symptoms
Early: fever, cramping, abdominal pain, and watery diarrhea
Later: frequent, scant stools with blood, mucous, and pus (due to invasion of intestinal mucosa).
What determines the severity of Shigellosis?
the invading pathogen
- S. dysenteriae is the worst
What is the basis for the grouping of the Shigella species?
O antigen
- the K antigen is heat labile
Why is it important to ID a bacteria as either Shigella or E. coli prior to serotyping?
Because the O antigens are very similar
What is the virulence factor produced by Shigella? Which species?
Shiga toxin
Produced by S. dysenteriae
- in smaller amounts by S. flexneri and S. sonnei.
Which bacteria mimics appendicitis ?
Yersinia enterocolitica
What is a major source of pathogenic strains of Yersinia enterocolitica?
Swine
What kinds of agar can be used to culture Y. enterocolitia?
CIN agar (Cefsulodin-Irgasan-Novobiocin) We use MacConkey agar
What makes Y. enterocolitica so virulent?
the extent to which it can invade host tissue
In what ways are Vibrio and Aeromonas similar to Enterobacteriaceae? (5)
- Gram-negative
- Facultative anaerobes
- Fermentative bacilli
- Cause gastrointestinal disease
- found primarily in water sources
In what two ways are vibrio and aeromonas different from the enterobacteriaceae ?
- Oxidase positive
2. Have polar flagella
What is the shape of Vibrio?
Comma shaped bacilli
What are the 3 species of Vibrio that are clinically significant to humans?
V. cholerae, V. parahaemolyticus, V. vulnificus
What is the range of temperatures across which Vibrio sp. will grow? What about the pH ?
Both temp and pH ranges are very broad
18-37ºC
pH 7.0 - 9.0 (useful for enrichment)
What two media types (among other simple media) will Vibrio grow on?
MacConkey agar
TCBS (Thiosulfate Citrate Bile salts Sucrose) agar
What is special about the growth conditions of V. cholera that can be used to distinguish it from other species of Vibrio?
It can grow without salt while other strains are halophilic
How many serogroups are there for V. cholera? How are they classified?
> 200 based on the O antigen
Which two serotypes of V. cholera are responsible for epidemic cholera?
01 and 0139
the 01 serotype of V. cholera can be subdivided into how many biotypes? what are they called?
two, called El Tor and classical
What is special about certain members of the 01 serotype of V. cholera?
Some don’t produce cholera enterotoxin (atypical or nontoxigenic O1 V. cholerae)
What is 0129?
a vibriostatic agent
What is the incubation period for V. cholera like?
mid range: 2-4 days
What is the infectious dose like for V. cholera? What can affect this?
High infectious dose: >10^8 CFU
10^3 -10^5 CFU with achlorhydria or hypochlorhydria(lack of or reduced stomach acid)
What are the symptoms of a V. cholera infection?
Abrupt onset of vomiting and life threatening watery diarrhea (15-20 L a day of fluid loss)
What changes symptom wise as the cholera infection persists?
As more fluid is lost stool changes to rice-water stools: Colorless Odorless No protein Speckled with mucus
