Intestinal Flora and Pathogens Flashcards
What are the important commensural roles of the GI flora?
Aid in digestion:
Produce urease, deaminase, esterase
Producuce vitamins:
Vitamin K, Folic acid,
Thiamin (B1), Riboflavin (B2), Niacin (B3), Pantotenic acid (B5), others.
Provide continuous antigenic signal
aid in immunity to them in the blood stream
Produce gasses which aid in peristalsis
Compete for nutrients and inhibit colonization by pathogens
Describe bacterial colonisation of the GI of a newborn.
GI is sterile in utero
By vaginal birth, there is immediate exposure to the maternal vaginal and GI flora.
C-section, there is delayed colonisation and may be related to GI immunological problems.
Escherichia coli and Streptococci establish anaerobic environment, and mostly obligate anaerobic bacteria colonize and become dominant.
Breast feeding also introduces bifidobacterium
By about 12 months it has equilibrated basically the same as adult flora
What causes GI flora alterations?
What problems can this cause?
Causes: Wide sprectrum antibiotics, Dietary changes
Problems:
Nutreint absorption problems.
Vitamin deficiencies
Peristaltic problems
Increased gas productions
How many microbes are in the GI tract per gram of feces?
What are the major ones that
about 10^8 per gram
What is the general bacterial composition of the GI?
Mostly gram positive cocci and rods, but there are hundreds of different kinds.
Obligate anaerobes:
- Bifidobacterium*
- Clostridium*
- Lactobacillus*
- Eubacterium*
- Bacteroides*
- Fusobacterium*
Facultative anaerobes:
- Enterococcus*
- Enterobacteriaceae - E. coli*
Enterobacteriaceae family
Morphology
What are the major
Gram negative rods 2-4uM
Oxidase negative
Normal flora members and facultative pathogens
- E. coli
- Klebsiella
- Proteus
- Serratia
- Enterobacter
- Citrobacter
- Providencia
- Morganella
Obligate enteral pathogens
- Enterovirulent strains of E. coli
- Salmonella
- Shigella
- Yersinia
- Vibrio
- Helicobacter
- Campylobacter
Enterobacteriaceae
Morphology
Culture
Gram negative, non-spore forming rods
Flagellated, Motile
O, H, and K antigens. O: LPS antigen, H: flagella, K: capsule
Non-fastidious bacteria
Grown on selective medium
Eosin Methylene Blue agar (EMG agar)
Oxidase negative
Catalase, varies w/ species
Lactose fermentation: varies w/ species
Enterobacteriaceae
what are the major species of the genus. (6)
- Escherichia -* produces indole from tryptophan
- Klebsiella* - degrades urea
- Enterobacter*
- Proteus* - motile/swarming
- Citrobacter*
- Serratia* - produces pigment and may colonizes the respiratory tract
What is EMB agar used for?
Selective, Differential media
Inhibits gram positive growth
Inhibits swarming of proteus with detergents
Contains lactose, Lactase enzymes produce acid, causing Eosin precipitation, which then is stained by the Methylene blue.
Lactose + colonies are blue, and Lactose - colonies are pink or gray.
What are the types of infections caused by Enterobacteriaceae?
Nosocomial infections:
- Urinary infections, catheter associated
- Ventilator pneumonia
- Meningitis
- Surgery wounds
- Sepsis - Klebsiella in neonatal ICUs
Community-acquired infections
- Urinary infections - E. coli
- Pneumonia - Klebsiella
- Otitis externa - ear canal - E. coli and proteus
What causes the majority of community-acquired Urinary infections?
Uropathogenic E. coli
Source is from the normal GI flora
Infection more common in women b/c of closer proximity
Can cause pylonephritis or prostatitis
What is the unique virulence factor of Uropathogenic E. coli as compared to non-pathogenic?
The P fimriae / pili
Allow binding to the P blood group antigens found on Uroepithelial cell membranes
Hemolysins
Enterobacteriaceae
Drug resistances and mechanisms of resistance
Normal treatment
Beta-lactamase: ESBLs or MBLs, extended spectrum-BL or metallo-BL
Drug efflux pumps
Variation of membrane proteins
Cephalosporins
Carbapenems
Aminoglycosides
Fluroquinolones
E. coli
Klebsiella
Slamonella
Proteus
Typhi
Shigella
For these bacteria, which sugars can they use, which tests are positive/negative.
Legend:
*excl. Salmonella typhi
+ sugar is degraded
- sugar is not degraded
G gas is produced
What is the oxidase test?
- Determines if a bacteria has a cytochrome c oxidase enzyme
- It can therefore use oxygen for energy production by converting O2 to H2O2 or H2O with an electron transfer chain
Test: The oxidase reaction
- Reagent: blotting paper on a glass-slide freshly impregnated with a p-phenylenediamine-tetramethyl derivate
- Sample: minute amount of bacteria taken by an other slide from an individual, isolated colony from the bacterial culture
- Reading the result:
+ if colour of reagent turns to dark red or purple within 10 sec
- if colour of reagent turns to pale yellow
What important nutient is produced by Escherichia coli and used by humans?
Vitamin K
What are the obligate pathogens of the GI system?
- Enterovirulent E. coli species (ETEC, EPEC, EHEC, EIEC, EAEC, DAEC)*
- Salmonella (S. typhii, S. cholerasuis, S. enteritidis)*
- Shigella (4 species all pathogenic)*
- Yersinia enterocolitica*
- Vibrio cholera*
- Helicobacter*
- Campylobacter*
- CHESSY V*
What are the species of Enterovirulent E. coli?
All of them have the pili colonization factor (virulence factor that makes them enterovirulent strains)
ETEC: Enterotoxigenic
- releases labile toxin and stable toxin, both stimulate Cl- and bicarbonate secretion and inhibit their resorption. does not penetrate
- water stool
EAEC: Enteroaggravative
- water stool, often chronic
EPEC: Enteropathogenic
- water stool and fever
DAEC: Diffusely adherent
- water stool
EHEC: Enterohemorrhagic
- Also secretes Shiga-like toxin, inhibits 60S ribosome protein synthesis, killing enterocytes.
- Bloody stool
EIEC: Enteroinvasive
- Cell invasive virulence factor as well as shiga-like toxin.
- bloody stool with white blood cells coming from trying to clear the invaded cells.
E. coli
Morphology
Culture
Gram negative rod
2 uM
Facultative anaerobic
Non-spore forming
Peritrichous flagella.
Culture:
EMB agar: irridescent blue-green colonies
Simple agar: irridescent gray/colorless colonies.
Blood agar: gray non-hemolysing
Which bacteria express Extended spectrum beta lactamases? (ESBL)
Klebiella and E. coli
Which bacteria express MBLs? Metallo beta lactamases
Klebsiella, Pseudomonas, Acinetobacter
E. coli biochemical properties.
Glucose, Lactose, Dextrose, Maltose, Mannit, and Indol positive
Sucrose, Urease, H2S negative
Proteus
Morphology
Major biochemical characteristics
Clinical disease
Gram negative
Urease positive
Swarming motility
Fishy odor
Causes UTI
Stag horn Calculi are formed in the renal pelvis
Treat with Sulfonamides.
What are the types of extraintestinal infections caused by enterobacteriaceae?
Nosocomial infections:
Wound infections
Catheter associated UTI
Ventilator associated Pneumonia
Meningitis
Sepsis, esp in neonatal intensive care
Community acquired infections:
UTIs from E. coli
pnemonia from klebsiella
ottitis externa E. coli or Proteus.
What are Hektoen agar plates for?
Pink: Lactose, Sucrose, or Salicin acidifying
Blue: Shigella, which does NOT produce H2S
Black: Salmonella, which DOES produce H2S
The plates contain various sugar sources (lactose, sucrose, and salicin), none of which can be used by either Shigella or Salmonella, but the medium also includes peptone which can be used as a carbon source. Since most bacteria can use the sugars in preference to peptone, these “uninteresting” bacteria acidify the medium and turn a pH indicator yellow or red. Peptone metabolism by Shigella and Salmonella alkalises the medium, turning a pH indicator blue.
The presence of thiosulfate or ferric ammonium citrate in the medium produces a black precipitate in the presence of H2S, allowing Shigella – which does not produce H2S, and appears as green colonies – to be distinguished from Salmonella – which does produce hydrogen sulfide and appears as black colonies.[2]
