Enteric Gram Negative Rods Flashcards
What is the purpose of colonizing on MaConkey agar?
What is the color change and what does it indicate?
To isolate gram negative enteric rods
if the rods can ferment lactose, it will turn pink
What are general characteristics for all Enterobacteriaceae species?
Gram stain?
Odixase test?
- Gram negative bacilli
- Oxidase negative
How could you identify a sample of Escherichia coli?
gram stain?
Urease?
Motility?
Citrate?
Indole?
MacConkey?
location of colonization?
- gram stain
- Gram negative rod with or without capsule
- Urease (-)
- Motility (+)
- Citrate (-)
- Indole (+)
- MacConkey agar
- lactose fermenter
- location of colonizaton
- colonize urethra, vagina & colon
- exogenous species cause disease, not endogenous
- colonize urethra, vagina & colon
What are the 5 major causes of E. coli virulence?
- Surface antigens
- O, H, F, K
- Adhesins
- Colonization factors (CFAI, CFAII, CFAIII)
- P pili, AAF I & III, Dr fimbrae
- Capsule
- some are encapsulated
- K1 cause neonatal meningitis
- Endotoxin
- LPS
- Exotoxin
- ETEC: heat stable (STa, STb), heat labile (LT-I, LT-II)
- EHEC: Shiga-like toxins (Stx-1 & Stx-2)
What disease is characterized by the following symptoms?
Dysuria, frequqncey, suprapubic pain
Can result in fever & back pain
What bacteria is likely responsible?
What are the common virulence factors?
UTI
E. coli (#1 cause UTI)
If fever & back pain –> kidneys (pyelonephritis)
Virulent factors: P pili, AAF I & III, Dr fimbrae
In addition to UTIs and Gastroenteritis, what other infections can be caused by E. coli?
- Pneumonia
- rare to cause community pneumonia
- GNB (including E. coli) = ~70% nosocomial pneumonia
- Neonatal meningitis
- K1 capsule associated
- 2nd leading cause in neonates
- Bacteremia/Septicimia
- most common source bacteremias
Which 5 E. coli strains cause Gastroenteritis? Specify which part of the GI tract they infect.
- Enterotoxigenic (ETEC)
- small intestine
- Enteropathogenic (EPEC)
- small intestine
- Enteroaggregative (EAEC)
- small intestine
- Shiga toxin producing (STEC)
- large intestine
- Enteroinvasive (EIEC)
- large intestine
Enterotoxigenic E. coli (ETEC)
Plasmid toxins?
symptoms? Duration?
How acquired?
- Heat labile (LT-1 & LT-II) & stable (STa & STb) toxins
- genes CFA/I, CFA/II, CFA/III
- LT-1 = like cholera toxin (increase in cAMP)
- STa = increase in cGMP = fluid loss
- 1-2 days watery diarrhea, cramps, vomiting
- persists 3-4 days
- Fecally contaminated food/water
- mainly in young children
Enteropathogenic E. coli (EPEC)
Virulence?
symptoms? Duration?
- Bfp, intimin, Tir allow attachmen to intestina epithelial cells
- attachment leads to microvillus destruction (A/E histopathology)
- A/E encoded by 40 genes on a pathogenicity island
- Wateyr diarrhea from malabsorption due to micovilli destruction
- major cause non-bloody infant diarrhea in poor countries
- can lead to poor growth in children
Enteroaggregative E. coli (EAEC)
Virulence?
symptoms? Duration?
- AAF I-III mediated adherence adn induce mucus secretion
- leads to biofilm formation
- evade clearance, persist in GI tract
- leads to shortening of microvilli
- leads to biofilm formation
- Persistent watery diarrhea with vomiting
- chronic diarrhea and growth retardation in children
Shiga toxin producing E. coli (STEC)
Virulence?
symptoms?
Source?
Complication?
- All STEC produce Shiga toxin
- Enterhemorrhagic E. coli (EHEC) is a subset of STEC
- Some are LEE positive
- O157:H7- common, diagnosis based on Shiga toxin production
- Destruction intestinal villue (A/E lesions)= fluid loss
- Common in rich countries
- From undercooked meat, vegetables, unpasteurized milk, water
- person to person spread
- mild - bloody diarrhea associated with sever abdominal pain
- ~8% show HUS w/ kidney problems
Enteroinvasive E. coli (EIEC)
Virulence?
symptoms?
Source?
Complication?
- Mostly poor countries, rare in US
- Plasmid mediated destruction of colonic epithelial cells
- fever, cramp, waery diarrhea; may lead to dysentery
- resembles Listeria/Shigella
Write down this chart
How could you identify a sample of Salmonella?
Gram stain?
SS Agar?
Motile?
- Gram stain?
- gram negative rod
- SS Agar?
- black colonies due to production of H2S
- Motile?
- yes, motile
Nontypoidal Salmonellosis pathogenesis?
- invate GI tract through pagocytic microfold (M) cells in Peyers Patches.
- Trigger membrane ruffles that trap and induce endocytosis
- Massive PMN infiltration– limits salmonella mostly to GI
- induces epithelial cells to secrete IL-8 (PMN attractant)
- PMN toxicant damage mucosa & caue inflammatory diarrhea
What disease is characterized by the following symptoms?
What is the bacteial cause?
10-14 incubation– gradually increasing fever
myalgia, malaise, anorexia
rose spots (trunk & chest), hepatosplenomegaly, bradycardia
Can lead to GI bleeding & perforation due to hyperplasia and ulceration
Enteric Fever
Salmonella Typhi
consider w/ recent travel to endemic areas
Pathogenesis of Shigella
- invade colonicm mucosa through M cells in Peyer’s Patches
- Spread via actin tail & release inflammatoyr mediators
- transmigration PMN into colon (necrosis)
- Doesn’t spread from colon
How does the Shiga toxin work?
An A-B5 toxin, B binds to Gb3, sends A into cytosol
A cleaves 28S rRNA in 60S and inhibits tRNA binding
inhibits protein synthesis & kills cell
Most impacted = intestinal epithelial cells & kidney cells
What disease is characterized by the following symptoms?
What bacteria is responsible?
STI (40-70 yr olds)– but also seen in children/sexually inactive
1-4 week incubation; 1 or more S/C nodes
painless slowly enlarging lesions
Granuloma inguinale
Klebsiella granulomatis
How would you identify a sample of K. granulomatis?
gram stain?
Culture?
MIcroscopic examination?
- Gram negative bacilli
- never been cultured in vitro
- use lesion material fo rmicroscopic examination
- Donovan bodies (bacteria within macrophages)
How would you identify a sample of Bacteroides fragilis?
Gram stain?
Natual colonization?
Colony appearance?
What disease dose it cause?
- Gram stain
- small pleomorphic anaerobic gram negative rod
- GIT normal flora
- Anaerobic colonization = black growth due to esculin hydrolysis
- Causes intra-abdominal abscess
- foul smelling wound with presence of gas
How would you identify a sample of Fusobacterium nucleatum?
Gram stain?
Natural colonization location?
Diseases it causes?
- pleomorphic anaerobic gram negative rod
- indigenous ot human oral cavity
- diseases
- periodontal plaques
- polymicrobial infections
