Microbiology: Lower GI and Viral gastroenteritis Flashcards
What are characteristics of Campylobacteriaceae?
Gram neg Rods
(“gull shaped”)
Microaerophilic
oxidase +
What are complications of Campylobacter Enterocolitis?
- *Guillain Barre Syndrome**
- -> likely due to autoimmunity
Reactive Arthritis (Reiters syndrome)
Also follows inflammatory diarrheas
Affects urinary tract, eyes, skin, mucus membranes
What serogroups of Vibrio cholerae produce cholera toxin?
O1 and O139
<5% of O2-O138 make CT
What are characteristics of Vibrionaceae?
Gram negative
Comma-shaped rods
Glucose fermenters
Oxidase +
What are clinical signs of Cholera gravis?
*Rice Water stool*
Peripheral pulses absent
Decreased BP
Sunken eyes
- *Poor skin turgor**
- Skin tenting
- Washer woman’s hands
Hyperventilation
Muscle cramps
No neutrophils ==> secretory diarrhea
What is the pathogenesis of V. cholerae?
- colonize small intestine using colonizing fimbriae called “toxin co-regulated pili” (Tcp-pili)
- Produce cholera toxin, leading to hypersecretion of fluid and electrolytes into intestinal lumen
What is the mechanism of cholera toxin?
A subunit:
- activates adenyl cyclase via ADP ribosylation of GTP-binding protein
B subunit:
- binds to GM1 ganglioside molecules
(same as ETEC LT)
How is cholera diagnosed?
Culture of rectal swab or stool:
- Selective agar (TCBS agar)
- Agglutination with anti-O1 or anti-O139 antiserum
Serological diagnosis:
best 2 weeks after exposure
decreases 2 months after exposure
What are clinical manifestations of Vibrio parahaemolyticus?
Acute, watery diarrhea
(occasionally bloody)
Severe cramping, abdominal pain
Vomiting
Short incubation period (hrs after exposure to undercooked or raw seafood)
How does bacterial and viral gastroenteritis differ in:
- Duration
- Nature of diarrhea
- Fecal leukocytes
- Treatment
Bacterial:
1-2 weeks duration
Mostly bloody/mucoid diarrhea
(except ETEC, v. cholerae, etc)
Fecal leukocytes present
Antibiotics in some cases and rehydration to treat
Viral:
2-3 days duration
Loose and watery diarrhea
NO fecal leukocytes
Rehydration to treat
What is the most common viral cause of gastroenteritis?
Rotavirus
What are common viruses of the GI tract?
Rotaviruses
Caliciviruses
(noroviruses and Sapoviruses)
Adenoviruses
Astroviruses
Coronaviruses
(All are non-enveloped!)
What are characteristics of Rotavirus?
dsRNA genome
(segmented)
–> Replication in cytoplasm
non-enveloped
Icosahedal double-shelled capsid
at least 4 serotypes
Reassortment between related species
Infectious after proteolytic cleavage of capsid protein VP4
(Winter diarrhea)
What are the different types of reassortment that ocurs between viruses?
- *Antigenic Drift**
- Small mutations occur
- *Antigenic Shift**
- New strain developed by interaction between strains
Who are most at risk of a rotavirus infection?
Infants (< 2yrs old)
–> by age 3, virtually every child has been exposed
Adult infection is extremely rare
Infection peaks in winter
What is the pathogenesis of rotavirus?
Infects enterocytes in small intestinal villi
–> replication damages transport system resulting in impaired Na transport and osmotic diarrhea
–> replicated virus released into intestinal lumen
What are symptoms of a rotavirus infection?
Incubation: 1-2 days
Vomiting
upset stomach
watery diarrhea
High fever (102.2+)
Loss of appetite
Severe Dehydration
Mucus in stool
May last 5-8 days
How is rotavirus diagnosed?
Virus isolation from stool
Antibody titer
ELISA
Absence of fecal leukocytes in stool
RT-PCR
What are characteristics of Noroviruses?
Icosahedral, non-enveloped
+ssRNA genome
(cytoplasmic replication)
Heat resistant
(common in shellfish, and cooking may not eliminate)
Chlorine resistant
Leading cause of food borne disease in US
(stomach flu/winter flu)
What is the pathogenesis of norovirus?
Broadening and blunting of villi of proximal small intestine with intact mucosa
- Cellular (CD8+ Tcells, neutrophils) infiltrate and cytoplasmic vacuolization
What are symptoms of a norovirus infection?
Nausea, vomiting, diarrhea, abdominal cramps, headache, fever, chills, myalgias, and/or sore throat
Vomiting more frequent than diarrhea
Stools are non-bloody, lack mucus, loose to watery
Severe dehydration and loss of electrolytes
Self-limiting with symptoms resolving spontaneously in 24-48hrs
How is norovirus diagnosed?
Absence of fecal leukocytes
RT-PCR for nucleic acids
Antigen detection, specific, but less sensitive than PCR
Rapid tests
What are characteristics of adenovirus?
ds linear DNA
Icosahedral capsid
Largest non-enveloped virus
AT least 52 serotypes known
(replicates in nucleus)
