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Micro: Enteric Bacteria


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Which diarrheal diseases are primarliy toxin mediated?


Yersinia enterocolitis
Enterotoxigenic E. Coli: Symptoms
watery diarrhea, nausea, abdominal cramps, low grade fever

travelers diarrhea and infantile diarrhea
Describe the virulence of ETEC?
Enterotoxin (Cholera like)

LT: heat labile; similar to cholera toxin but milder

ST: heat stabile; causes increase in cGMP

has fimbriae and CFAs for colonization in the Small Intestine
ETEC: What common disease does it cause?
Traveller's diarrhea
Enteroinvasive E. Coli(EIEC): Describe its mode of infection and symptoms.
INVASION of Large intestine epithelium similar to Shigella

causes dysentery w/ fever, abd. cramping, blood and pus in stool
Enteropathogenic E. Coli: What common disease state does it cause?
Infant diarrhea
EPEC: Describe its mode of pathogenecity?
ADHERENCE to enterocytes (Small intestine)

effacement of microvilli

expresses intimin- mediates entry in to cell

bundle forming pilli for attachment
EPEC: Describe pathogenesis
ADHERENCE to sm. intestine enterocytes

EFFACEMENT of microvilli

*inflammatory response may cause ulceration
What strain of EHEC causes disease?

Where is it typically found?
the O157:H7 serotype

it is found in cattle, beef products, and fruit and veggies that have been fertilized with tainted manure
What characteristic differentiates EHEC from other strains of E. coli?
Its inability to ferment sorbitol.
Describe the symptoms caused by EHEC.

What is its primary pathogenic mehcanism?
hemorrhagic colitis, bloody diarrhea, abd. cramping

HUS - possibly because of specific LPS
What is the pathogenic mechanism of EHEC?
Shiga like TOXIN

Attachment and Effacing of microvilli leading to their death

Large Intestine
Yersinia enterocolitica: clinical presentations?
enterocolitis involving fever, diarrhea, and abdominal pain

nonenteric lymphadenitis may lead to septicemia
Yersinia enterocolitica: pathogenesis?
INVASION of M cells in small intestine

secretion of a toxin similar to E. Coli Heat stable toxin

* resevior is farm animals
T/F: S. typhii has no animal reservoir while S. enteritidis does.
How is E. Coli Diagnosed and treated?
detection is difficult, some labs may serotype

treated with fluid replacement, antibiotics

EHEC strains grow on Sorbitol agar
What are the steps involved in the pathogenesis of S. typhii?
*binds M cells of GI epithelia *endocytosed and transferred to Peyer's patch *replicates intracellularly *passes through basal lamina *taken up by macrophage and spread thru RES
A chronic carrier state is possible with S. typhii. What organ is notorious for sequestering the bacteria?
Gall bladder
EAEC: what is its primary pathogenic mechanism?
ADHERENCE to enterocytes

Heat stabile toxin called EAST that eleveates cGMP

attaching and effacing lesions
What are general characteristics of Enterobacteriaceae?
Gram(-) bacteria that are part of the normal intestinal flora

non spore formers

ferment glucose

Facultive anearobes
What are the 4 genus' of enterics?
enterobacteriaceae, vibrionaceae, pseudomonadaceae, bacteroidaceae
Vibrio Cholera: clinical manifestations?
Classic "rice water" stool diarrhea w/ high fluid output

infxn may be asymptomatic, cause mild diarrhea, or result in a carrier state
Vibrio Cholera: pathogenesis?
polar flagellum (H-ag) - motility

pili- adherance

cholera toxin

*mucinase to digest mucous layers
Describe the Cholera toxin?
two A subunits bridged by disulfide bonds and 5 identical B subunits

A1 is active subunits-enters cell upregulates adenyl cyclase --> increased cAMP leading to cause massive efflux of Na= and H20

*regulon family of genes
Vibrio Cholera: Diagnosis?
darkfeild microscope

isolation on thiosulfate-citrate-bile-sucrose(TCBS) agar

agglutination in specific antisera
Vibrio Cholera: Rx?
Rehydration orally

IV Tetracycline
Vibrio Cholera: Immunity?
post infection Abs

gastric acidity

Vibrio parahemolyticus
marine org, infects shellfish

major cause of FP in Japan and in US from eating raw shellfish

explosive diarrhea (w/o blood or mucous), cramps, nausea, vomiting

*produces a toxin
Vibrio vulnificus
found in salt h2o, infects sun bathers and those ingesting raw shellfish

can cause a fatal bacteremia

immunocompromised, liver diseased and thalassemia increase risk
Campylobacter jejuni: transmission?
transmitted by contaminated milk, H20, poultry
Camplylobacter jejuni: clinical manifestations?
bloody, pus-filled diarrhea, severe ab pain, fever

high pediatric incidence

no1 cause of gastroenteritis in developed world

*assoc. w/Guillan-Barre syndrome
Camplylobacter jejuni: bacterial characteristics?
G- curved rod



Helicobacter pylori: clinical manisfestations?
cause of gastritis, PEPTIC and DUODENAL ULCERS

makes a urease theat produces NH3 from urea

cured with Antibiotics
Shigella species: clinical manifestations?
shigellosis- fever, chills, abdominal cramps, tenesmus

blood/ pus/ mucous in stool

can cause convulsions and meningitis in infants

S. dysenteriae cause most severe infections; S.sonnei and S.flexneri most common in US
Shigella species: transmission?
man is primary host

P to P: fecal-oral transmission or by vectors(food, fingers, feces, flies)

associated w/ overcrowding and poor sanitation
Shigella species: Pathogenesis?
invades/ damages mucosa of large intestine, ulceration, and appearance of PMNS --> scarring

invasion genes are on plasmid, involves actin polymerization

non motile

Shiga toxin, INVASION
Shigella species: Describe the Shiga toxin?
A+B toxin (similar to Cholera)

inhibits protein synthesis by inactivating the 60s ribosome

also behaves as neurotoxin

*not essential for virulence
*associated w/HUS
Shigella species: diagnosis?
rectal swab
stool culture

*Shigella IS NOT Normal Flora
Shigella species: Rx and immunity?

antibiotic resistance emerging

previous infection only gives short lived immunity, no vaccine
Salmonella gastroenteritis: clinical manifestations?
diarrhea, fever, cramping, nausea, vomiting, headache

onset 24-48 hrs after ingestion

diarrhea has rotten egg smell

blood stream invasion may occur, but disease is usually self limiting
Salmonella gastroenteritis: organisms
S.typhi --> typhoid fever

S.typhimurium - most common causitive org in US

S. enterica
What are the 3 clinical sydromes that can result from infection with Salmonella species?
1. enteric fever

2. septicemic syndrome

3. gastroenteritis
Salmonella gastroenteritis: transmission?
fecal-oral route

pet turtles

chicken, raw eggs, mayonaise

unpasteurized OJ, apple cider
Salmonella gastroenteritis: pathogenesis?
attachment and invasion of mucosal (M cells) of SMALL INTESTINE, damages tissue

may produce a toxin but not major virulence factor

Salmonella gastroenteritis: diagnosis?
fecal culture on selctive/differential agar (Salm are lac-)

slide agglutination for serogroups
Salmonella gastroenteritis: Rx and immunity?
flouroquinolones (ciprofloxacin)

antimotility drugs

no vaccine
Enteric Fevers: causitive agents?
S. typhi - typhoid fever, Vi antigen (capsular polysacchride)

S. paratyphi and S.schotmulleri cause milder fevers
Enteric Fevers: clinical manifestations?
intially malaise, headache, anorexia

wk1: gradual stepwise rise in fever, constipation or diarrhea

wk2: rose spots, hi fever, septecemia

wk3: fever remits, may have ulceration and gut perforation --> bloody diarrhea
Enteric Fevers: pathogenesis?
ingested and multiply in small intestine

penetrate mucosa at distal end ileum through M cells at Peyers Patches, move through blood stream --> bacteremia

infection of gall bladder can lead to chronic carrier state or reinfection
Enteric Fevers: Transmission?
S.typhi only infects humans by direct contact or ingesting food contaminated by orgs shed by carrier (Typhoid Mary)
Enteric Fevers: Diagnosis?
isolation of org on agar or serotyping

blood is positive in wk1 of infection

stool is positive after wk1

Widal test
Enteric Fevers: Rx and immunity?
Short course, fluoroquinolones

Abs protects, infection stimulates cellular immunity

Vaccines: killed whole cells, live attenuated, IV injected capsular polysacchride
Septicemic Syndrome: organism and clinical manifestations?
S. cholraesuis

causing spiking fevers w/ frequent seeding to various organs --> abscesses, meningitis, pneumonia, osteomyelitis, endocarditis
General characteristics of Enteric Bacteria
Gram - bacilli

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