Microbiology: Lower GI infections Flashcards
What are characteristics of picornaviruses?
non-enveloped, icosahedral capsid
(2, 3, 5-fold symmetry)
+ssRNA
RNA is infectious
What is the picornavirus replication cycle?
- virus binds to cellular receptor and genome is uncoated
- RNA is translated in cytoplasm. Virus RNA is a single strand producing a polyprotein that is self-cleaving, and self-assembling.
- Viral +RNA is copied to form -RNA, which are copied again to make replications of +RNA (by viral RNA pol)
- Newly synthesized virus particles are assembled and released from cell by lysis
What is the Cytopathic Effect?
It is the in vitro cellular response to enterovirus infection
–> infected cells shrivel up and die
What are characteristics of poliovirus?
it is a picornavirus
- 3 serotypes (1, 2, and 3) - no common antigen
- Identical physical properties
- Humans are only susceptible hosts
What are the options for poliovirus vaccination?
**Salk:** Inactivated polio vaccine formalin inactivated (killed)
Sabin: Oral polio vaccine
attenuated (live)
Why is poliovirus 3 risky to vaccinate against wth live attentuated virus?
It is at risk of reversion and infecting host with virus
What are characteristics of Clostridia?
Anaerobic
Spore-forming
Gram + rods
Agents of:
Botulism
Tetanus
Gas Gangrene,
Food poisoning,
pseudomembranous colitis
What are the virulence factors of C. difficile?
Toxin A: an enterotoxin
- *Toxin B**: potent, necrotizing cytotoxin
- believed to be responsible for clinical manifestations
What is C. difficile-associated disease?
Associated with pseudomembranous enterocolitis
-> ranges frmo milid diarrhea to a severe, necrotizing process involving the large intestine
–> occurs as a complication of antibiotic therapy
What are treatments for C. difficile infection?
Stop antibiotics that lead to C. diff overgrowth
Give oral metronidazole (or vancomycin if necessary)
–> remember, Abx not useful against spores and recurrence is possible
Fecal transplants for recurring illness
What lab tests are used to Dx C. difficile?
Stool culture for C. diff
Toxin testing for C. diff
Molecular PCR tests
What are the main types of foodborne illness?
-
Intoxications caused by toxin pre-formed in food
- short incubation period (3-6hrs)
- C. botulinum, S. Aureus, B. cereus
- *2. Intoxications by toxins manufactured in body**
- Live organisms ingested
- C. perfringens, ETEC, V. cholerae
- *3. Intestinal invasive diseases**
- Salmonella, Campylobacter
What are three common pre-formed toxins that cause food poisoning?
1. Botulinum Toxin: Produced by C. botulinum
in smoked, vacuum-packed, or canned foods
Spores germinate and produce toxin
Ingested toxins produce flaccid paralysis
2. Staphylococcal Enterotoxin: Superantigens produced by S. aureus that stimulate excessive amounts of cytokines –> Nausea, vomiting
3. Bacillus cereus toxin: Emetic toxin often occurs after eating fried rice
What are two possible results of Bacillus cereus infection?
- Emetic form: Intoxication
(occurs w/fried rice) - Diarrheal form: Infection
Ingestion of bacteria from food
Bacteria make heat labile enterotoxin in gut, producing diarrhea
What are characteristics of Clostridium perfringens food poisoning?
- Common in USA, freq. with cooked beef or other meat
- Occurs after large number of vegetative cells are ingested and sporulate in the gut –> enterotoxin produced
- Incubation period 8-12hrs, usuallly a self-limiting disease
What is the only entamoebiasis infection considered to be pathogenic?
Entamoeba histolytica is only pathogenic amoebae
- However, presence of non-pathogenic amoebae indicates fecal contamination and where commensal non-pathogenic amoebaes are found, pathogenic are likely to be as well
What is amebiasis?
- Amebiasis is infection with Entamoeba histolytica
- Invasion of trophozoites into intestinal or extra-intestinal tissue
What is a Cyst Passer?
A patient infected with Entamoeba histolytica, who presents without symptoms
What is the pathogenesis of amebiasis?
E. histolytica secretes enzymes that lyse tissue
- Small ulcers form –> ulcers deepen –> capillaries rupture –> parasite feeds on tissue and blood and multiplies
Ulcers present as “flask shaped” uclers
–> start in sigmoid colon and move deeper into colon as disease progresses
What are symptoms of intestinal amebiasis?
Incubation period (1-4months) is variable
Symptoms first occur with diarrhea leading to amoebic dysentery with mucoid, bloody stools
Lactose Intolerance (may be permanent)
Acute:
weight loos
Abdominal pain
tenesmus
fever
Chronic:
constipation alternating with diarrhea
What is pathogenesis of extra-intestinal amebiasis?
- Ulcers perforate bowel
- Trophozoites may be carried to:
Liver
Brain
kidney
skin
others - Causes ulcerations and abcesses in these organs
- Amebic abcesses are sterile with no cysts present
Trophozoites found in periphery of ulcer
What are symptoms of extra-intestinal amebiasis?
- Depends on organ infected
Liver: RUQ pain, fever, hepatomegaly, elevated diaphragm, mas in RUQ
Lung: cough, bloody sputum, possibly trophozoites
How is amebiasis diagnosed?
Intestinal:
Direct microscopy of mucus sample
- trophozoites can be seen
–> sometimes ingesting RBCs
Extra-intestinal:
Needle aspiration of abscess
- red/white, pinkish color
- Examine pus for motile trophozoites
- Gram stain pus for bacteria (should be sterile)
Serology: (best for extra-intestinal)
Gel diffusion
Hemagglutination
ELISA
What is treatment for amebiasis?
Metronidazole
Other options:
Tinidazole
Paromomycin
What is the pathogenesis of giardia lamblia?
Fecal to oral transmission, often due to drinking infected water
Cycsts can survive form months (even in chlorinated water)
Once ingested, can form a physical obstruction oto absorption by adhering to epithlia of small intestine
What are symptoms of Giradia infection?
Range from none to acute, explosive diarrhea to malabsorption
Incubation period: 1-14 days
Acute:
Diarrhea
Abdominal Pain
Nausea and vomiting
bloating
Flatulence
Steatorrhea
Chronic:
malabsorption
weight loss
debilitation
How is Cryptosporidium parvum contracted?
Waterborne spores
Found in swimming pools and unpasteurized apple cider
What are clinical features of cryptosporidium parvum?
Asymptomatic in healthy people
Life-threatening in immunocompromised
- -> watery diarrhea, vomiting, abdominal pain
- *Chronic wasting disease** that can be assoc. with pulmonary disease
How is Cryptosporidiosis diagnosed and treated?
Dx:
Acid fast staining of stool
Immunofluorescenct antibody staining is best
Treatment:
Nitazoxanide may help
otherwise, no established therapy
How is Cyclospora cayetanensis contracted?
Transmission through water and fresh produce
Most common in tropical and subtropical areas
(Nepal)
What are clinical features of Cyclospora infection? Treatment?
Watery diarrhea - WBC negative
(can be severe)
Incubation period of ~1week
Untreated infections can last 10-12 weeks
Treat with Trimehtroprim/sulfa
What are causes of Bloody Diarrhea?
IBD (Ulcerative Colitis)
Infectious (EHEC, E. histolytia, yersinia, shigella)
Ischemic colitis
Radiation proctitis
