E. Coli Flashcards
E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae are all what type of bacterium?
Gram negative facultative anaerobic rods so they ferment glucose, they are oxidase negative, and reduce nitrates to nitrite (dipstick test!)
What antigenic structures are used in serotyping E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae?
K (capsular) antigens: capsular polysaccharide (Klebsiella)
H (flagellar) antigens
O antigens: O-side of LPS chains
How are E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae cultured and identified?
Fecal samples on MacConkey
Normally sterile samples cultured on rich media
ID by biochemical tests or serology
On a KIA slant what does it mean if the results are Y/Y?
Lactose fermentation; E. Coli
On a KIA slant what does it mean if the results are R/Y?
Glucose fermentation; Shigella
On a KIA slant what does it mean if the results are Black?
Hydrogen Sulfide production; Proteus
On a KIA slant what does it mean if the results are R/R?
No fermentation; Pseudomonas
On a KIA slant what does it mean if the results have a bottom gap?
H2 production; E. Coli
What is a big problem for the treatment of E. Coli, Salmonella, Shigella, and other Opportunistic Enterobacteriaceae?
Plasmid-mediated antibiotic resistance, although antibiotics are generally not needed
What percentage of infectious diarrhea is caused by viruses?
90
If diarrhea persists more than 10-14 days what is it most likely?
A parasite
If diarrhea is chronic what should begin to be considered?
HIV; it is a big problem in AIDS patients
Mycobacterium avium intracellulare, CMV
What diseases does E. Coli cause?
Diarrhea and dysentery, a variety of opportunistic infections (#1 cause of UTIs) including septicemia and meningitis in neonates
Where is E. Coli important (regionally)?
In the US and developing world
Why do resident E. Coli flora not cause diarrhea?
They lack PAIs
What are the cultural characteristics of E. Coli?
Lac+, ferments glucose with gas (H2), does not produce H2S, motile
What are the cultural characteristics of Salmonella?
H2S+, Gas + (except S. typhi) Lac -, Glu +
What are the cultural characteristics of Shigella?
H2S-, Gas -, Lac -, Glu +
What are the 5 types of E. coli?
Enterotoxigenic (ETEC) Enteroinvasive (EIEC) Enterohemorrhagic (EHEC) Enteropathogenic (EPEC) Enteroaggregative (EAEC)
What is EHEC caused by?
Mostly by O157:H7; Undercooked beef, fruits, unpasteurized juices, lettuce, spinach, sprouts, and human to human
What are the symptoms of EHEC?
Little fever, acute onset cramps, watery diarrhea that becomes bloody within 24 hours (noninflamm, no leukocytes); Lasts up to 8 days
What is the pathogenesis of EHEC?
Low infectious dose (~100), Shiga toxin (Stx) which is an AB toxin that cleaves 28S RNA of the ribosome where the lysogenic phage is encoded
What is the important syndrome that follows in about 2-7% of patients? (EHEC)
HUS; HUS and EHEC is the MCC of pediatric acute renal failure; think young and elderly; also anemia. DONT TREAT with abx because it is exacerbated
What is the locus of enterocyte effacement for EHEC?
It is a PAI with a type 3 secretion system, it delivers E. coli receptor to host cell, makes pedestal for attachment, and responsible for the diarrhea
How is EHEC diagnosed?
O157:H7 cannot use sorbitol so:
White on Sorbitol MacConkey agar
other STEC and E. coli are red/pink
RADT for Stx in stool
Why are Abx CI’d in EHEC?
Believed to stress bacteria leading to increased phage expression of Stx
What is ETEC?
Traveler’s diarrhea
What are the virulence factors for ETEC?
CFA I or II for attachment
What are the symptoms of ETEC?
High volume watery diarrhea (but nowhere near as much as cholera)
What are the 2 toxins of ETEC process?
Heat labile toxin (LT) lie cholera toxin (same mech too as cholera too!); and Heat stabile toxin (ST); net effect is both lead to hyper secretion of chloride and water
What is EIEC?
Very similar to shigella (Lac-, nonmotile) and produces Dysentery similar to Shigellosis
What is the virulence of EIEC?
High infectious dose, actin tails actually push it through from cell to cell (more in shigella)
What are EPEC symptoms?
Profuse, watery infant diarrhea in developing countries
What is the virulence of EPEC?
Clustered micro colonies in SI that degenerate with loss of brush border and microvilli, pedestal because of LEE, no Stx, ST, or LT; attachment and effacing lesion
Why is E. coli hospital acquired?
Because they are commonly isolated, and are multi drug resistant and can cause sepsis
What is associated with an encapsulated strain (K1 antigen)?
Neonatal meningitis
What us UPEC?
Uropathic E. Coli, it causes >90% of UTIs; more common in females than males; symptoms are same as a UTI; Dx made by bacterial in urine (10^5 in females and 10^3 in males); virulence includes a P fimbriae (PAP pili) and a capsule (K antigen)
Salmonella and Shigella are both what type of pathogens?
Frank pathogens (isolation is always significant)
What disease is Salmonella a significant source of?
Gastroenteritis from food poisoning
What disease is S. Typhi known for?
Typhoid fever, a disseminated disease. It does NOT cause gastroenteritis
What culturing characteristics will be found with Salmonella?
Gram -, Lac -, Glu +, produces gas (not typhi), and H2S +
What is the only significant species of Salmonella?
S. Enterica
What is Salmenellosis caused by?
S. Enteriditis, Typhimurium, and other non-Typhi; Enteriditis and Typhimurium are the two most frequent
What is Salmonellosis and where does it come from?
It is GE that is grossly underreported, caused by meat products, dairy, poultry and EGGS, pet turtles/reptiles, and human - human transmission
Describe what happens after consumption of S. Enteritidis.
Bacteria swim through intestinal mucosa layer and reach the small bowel; they are encoded with PAI Type 3 system and inject effectors into M cells that form membrane ruffles that endocytose bacteria, bacteria cross to basal membrane and enter lamina propria - inflammatory response ensues
When do symptoms of Salmonellosis begin and what do they consist of?
20-72 hours post consumption and with N/V followed by abdominal cramps and diarrhea lasting 3-4 days (fever in half, diarrhea can be loose to dysentary) - abx usually not necessary
Can Disseminated Salmonellosis happen?
Yeah, but it’s rare
What does disseminated salmonellosis consist of and who gets it?
Bactermia, sepsis; osteomyelitis; endocarditis; renal problems. AIDS and Hodgkin’s patients (bacteremia), sickle cell children (osteomyelitis), and the elderly/very young
What is Typhoid fever caused by, and how is it spread?
S. Typhi, fecal-oral route, exclusively human reservoir (infected food handler)
How does S. Typhi infect?
Invade M cells, survive in macrophages because the Vi capsule antigen inhibits neutrophil uptake - then spreads to mesenteric lymph nodes and RES in macrophages - then spread to blood (sepsis). Perforations of GI tract at necrotic peyer’s patches can lead to hemorrhage
What are the symptoms of Typhoid Fever?
Insidious, rising fever with headache and abdominal pain (slow pulse and confusion, diarrhea late if at all, death possible by ruptured spleen); chronic gallbladder infection is possible
Where is typhi cultured from?
From blood or feces
Is there a vaccine for typhi?
Yea
What are the 3 types of Shigella?
Dysenteriae, Sonnei, Flexneri
Where is S. Dysenteriae found and what does it cause?
Central/South America (produce 1000x Stx compared to other shigella); HUS, and high fatality rate
Where is S. Sonnei found?
70% in US, mostly children
Where is S. Flexneri found?
2nd MC US, MC Worldwide, Gay men (STD)
How is shigella transmitted?
It is a frank pathogen, human reservoir, fecal-oral route, most common in children, institutions, and gay men (The Penn State Special…)
What are the culture findings for Shigella?
Gram -, non-motile rod, Lac -, Glu +, no gas, no H2S, Leukocytes in stool samples
What is shigellosis?
Acute inflammatory colitis and bloody diarrhea - dysentery like EIEC (Sonnei is often less bloody and more watery)
How does shigella infect?
Very low infectious dose (10-100 cfu), entry into M cells of the gut and escape the phagocytic vesicle, extension to neighboring enterocyte and rarely leaves the GI tract
How is shigella cultured?
On standard enteric media
What is Yersinia Enterocolitica?
A gram - coccobaccilli with bipolar staining
Where is Y. Enterocolitica found?
Animal pathogens; human outbreaks linked to consumption of milk and pork in US
What does Y. Enterocolitica cause?
Gastroenteritis, relatively rare, abdominal pain can mimic appendicitis = “pseudoappendicits”; self limiting
What does Klebsiella Pneumoniae cause?
a “currant jelly” pneumonia (encapsulated), found in alcoholics (aspiration)
What does Proteus and Morganella cause?
UTI’s
