Gastrointestinal Infections

Question 1

Helpful incubation periods

Answer 1

Most are 2-4 days
E. coli O157 is 2-6 days (really long)
Toxins are really short

Question 2

What diagnostics can you use for bacterial infections?

Answer 2

NEED selective media
Stools from patients in the hospital more than 3 days are rejected (wont be from the community)
Formed stool is rejected
Media: XLD, Camplobacter agar, MacConkey agar, Sorbital MacConkey agar
TCBS agar for Vibrio if requested

Question 3

Campylobacter

Answer 3

Gram negative, highly motile, spiral rod
C. jejuni and C. coli
Thermophilic
Microaerophilic
Isolation on blood/charcoal containing agar + antibiotics
C fetus occasionally associated with disease (non-thermophilic)
Incubation period 2-4 days
Infective dose ~10,000 cells
Prodrome of fever, myalgia, etc
Diarrhea (maybe bloody), abdominal pain and malaise
Usually self limiting (within 7 days)
Has been associated with Guillain Barre syndrome

Question 4

Salmonella enterica

Answer 4

2000 serovars
Motile (H antigen) - also O and Vi antigen
Gastroenteritis (fever, nausea, vomiting, diarrhea, abdominal pain, headache, myalgia)
Incubation period dose dependent
Symptoms in 48-72 hours
Duration 2-7 days
Not treated!! Unless less than 6 months or over 50 years
Pre-enrichment broths, XLD, HE, SS, Bismuth-sulfite agar

Question 5

O, H and Vi antigens for Salmonella

Answer 5

O: characteristic sequence of repeating polysaccharide units in LPS
H: flagellar antigens (protein) and may occur in one of two phase variations
Vi: a capsular polysaccharide (ONLY S typhi)

Question 6

Kauffmann-White antigenic scheme

Answer 6

Agglutination reactions with specific antisera against Salmonella antigens

Question 7

Why do we treat people who are less than 6 months or over 50 for Salmonella

Answer 7

Less than 6 months: do not make enough stomach acid

Over 50: acidity of stomach goes down

Question 8

Salmonella Enteric Fever

Answer 8

Caused by S. typhi
Incubation period 10 to 14 days
Bacteremic illness (myalgia and headache, fever, splenomegaly, leukopenia, abdominal pain, rash on abdomen)
Positive blood, bone marrow, urine, and stool cultures
Sequelae: intestinal hemorrhage and perforation

Question 9

XLD media

Answer 9

Selective and differential medium designed for the isolation of gram-negative enteric pathogens from clinical specimens
Contains xylose, lysine, sodium desoxycholate, sodium thiosulfate and ferric ammonium citrate
Most commonly used
For salmonella and shigella
Xylose fermentation on plate, turns yellow (shigella stays red), runs out and then salmonella will decarboxylate lysine and go back to red
Black from H2S
Typical enteric will stay yellow

Question 10

E coli O157:H7

Answer 10

Incubation period: ~3-8 days
Diarrhoea: mild to grossly bloody (haemorrhagic colitis)
Severe abdominal cramping frequent
Hemolytic uremia syndrome: up to 10% of cases (anemia / thrombocytopenia / kidney damage)
Significant mortality (~1-5%)
A number of non-0157 strains can also produce a shiga like toxin
Cows are reservoir
Virtually all do NOT ferment sorbitol
Do NOT treat

Question 11

Shiga like toxin

Answer 11

Distinguishing virulence factor for O157
Subunit toxin
A: acts at ribosomal level, inhibits protein synthesis
B: Binds glycolipid receptor in mammalian cells (renal endothelium)

Question 12

Shigella

Answer 12

TSI K/A with NO gas, Urea -, Motility -, all ferment mannitol except S. dysenteriae
Shigellosis or bacillary dysentery
Fecal-oral route, may be person to person, infective dose VERY low (10-100 organisms), animals dont harbour it
2-4 day incubation followed by fever, cramping, abdominal pain, and watery diarrhea
May be followed by frequent, scant stools with blood, mucous, and pus (due to invasion of intestinal mucosa).
Severity of disease depends upon infecting species
O antigen is similar to E. coli, so it is important to ID as Shigella before doing serotyping

Question 13

Yersinia enterocolitica

Answer 13

Swine most common source
Virulence result of tissue invasion
Rare on East Coast
Use MacConkey agar
May mimic appendicitis

Question 14

3 similarities between Vibrio/Aeromonas/Plesiomonas and Enterobacteriaceae

Answer 14

Gram negative
Facultative anaerobes
Fermentive bacilli

Question 15

2 differences between Vibrio/Aeromonas/Plesiomonas and Enterobacteriaceae

Answer 15

Polar flagella

Oxidase positive

Question 16

Vibrio

Answer 16

Comma shaped bacilli
Broad temp (18-37) and pH (7-9) range
Grow on MacConkey and TCBS
V cholerae grow without salt
>200 serogroups
Incubation period 2-3 days, need high infectious dose
Abrupt onset of vomiting and life threatening watery diarrhea
Feces changes to rice water stool

Question 17

2 serogroups of cholera responsible for epidemic cholera

Answer 17

O1 and O139

Question 18

Vibriostatic agent

Answer 18

O129

Question 19

When to think viral GI

Answer 19

No “warning signs” of bacterial infection (no high fever, bloody diarrhea, or severe abdominal pain)
Vomiting is often prominent
Incubation period longer than toxigenic disease
Entire illness usually over within 72 hours
No epidemiological clues to suggest otherwise

Question 20

What is the epidemic strain of norovirus?

Answer 20

GII.4

Question 21

Norovirus

Answer 21

ssRNA (+), non-enveloped, member of Caliciviridae family
Projectile vomiting, explosive diarrhea (both or just 1)
1-10 particles is infective dose
Fecal-oral, fomites, emesis transmission
Real time RT-PCR for detection (look for RDRP), sequencing for genotyping - cannot culture
Number 1 cause of acute gastroenteritis in adults
Short incubation, short disease
Epidemic strains each year, pandemic strains every few years

Question 22

Rotavirus

Answer 22

Reoviridae family
11 dsDNA segments, non-enveloped, 3 capsid layers
Low grade fever, vomiting, explosive non-bloody diarrhea
Can get hospitalized for dehydration (acidosis) - need IV fluids and electrolytes
Big child disease - kills a lot in developing countries
Only 100 particles needed for infection
Fecal oral and food/water borne transmission
RT PCR and Antigen testing for detection

Question 23

2 rotavirus vaccines

Answer 23

Rotarix: IV, monovalent
RotaTeq: oral, pentavalent

Question 24

Enteric Adenoviruses

Answer 24

Linear dsDNA, non-enveloped
Serogroups A-E cause resp disease
Types 40 and 41 in serogroup F cause gastroenteritis
Second only to rotavirus in infantile gastroenteritis

Question 25

Enteric Adenoviruses vs Noro/rotavirus

Answer 25

EA: longer incubation period, less fever/dehydration, more prolonged (6-9 days), children > adults, diarrhea +/- vomiting, fecal oral, PCR or antigen testing

Question 26

Astrovirus

Answer 26

``` ssRNA (+), non-enveloped Similar to rotavirus but less vomiting/fever/nausea RT-PCR but not all labs look for it Low infectious dose Fecal oral transmission ```

Question 27

Hepatitis viruses: Waterborne vs Bloodborne (types, nucleic acid, enveloped or not, transmission, risk factors, chronic or not)

Answer 27

Waterborne: Hep A and E, ssRNA (+), non-enveloped, fecal-oral, water/food risk factors, no chronic infection Bloodborne: Hep B, C, D, Hep B and D are dsDNA, C is ssRNA (+), enveloped, parenteral and sexual transmission, drug use and sexual risk factors, chronic disease possible Vaccine for A and B

Question 28

Hep A and E

Answer 28

ssRNA (+), non-enveloped, Picornaviridae family Fecal oral transmission PCR detection in early disease, then serology (IgM or IgG antibodies) 2-6 weeks incubation Usually self-limiting Risk of symptoms increases in age! Symptoms for 2-6 months: fatigue, nausea, vomiting, abdominal pain, jaundice, dark amber urine Vaccines available

Question 29

2 Vaccines for hepatitis

Answer 29

Havrix: A only Twinrix: A and B Efficacy 95%, lasts 20 years Protection in 2-4 weeks

Question 30

Clostridium difficile

Answer 30

Anaerobic, spore forming, gram + rod Major cause of nosocomial infectious diarrhea Opportunistic pathogen Without toxin genes they are a virulent (no disease) - toxin A and B Hypervirulent strain: NAP1

Question 31

How does C diff cause disease cellularly?

Answer 31

Inhibition of small GTPases (Rho/Ras/Cdc42) Actin cytoskeleton rearrangement Epithelial cell rounding Cytopathic effects

Question 32

C diff pathogenesis of inflammation (5 steps)

Answer 32

``` Neutrophil infiltration Intestinal damage Impaired permeability Fluid secretion Overall: Diarrhea and inflammation ```

Question 33

Spectrum of C diff associated disease

Answer 33

``` Asymptomatic (colonization) Antibiotic-associated diarrhea Pseudomembranous colitis Toxic megacolon Death ```

Question 34

How do we treat C diff?

Answer 34

Metronidazole for mild cases Vancomycin if its more serious - give orally If antibiotics don't work, might have to have colon removed Fidaxomicin new antibiotic (less likely to disrupt flora, but really expensive) Fecal transplants (repopulate GI tract)

Question 35

2 ways to detect C diff, 3 ways to detect its toxins

Answer 35

Organism: culture (barn yard smell, CCFA agar), EIA (need confirmation to make sure its a virulent strain) Toxins: EIA, cell culture cytotoxicity neutralization assay, nucleic acid amplification tests

Question 36

HUS

Answer 36

Hemolytic uremia syndrome Up to 10% of cases of E. coli O157:H7 Anemia / thrombocytopenia / kidney damage

Question 37

What enzyme are we looking for in EIAs for C diff?

Answer 37

Glutamate dehydrogenase

Question 38

Toxin Enzyme Immunoassays for C diff

Answer 38

Toxin B or Toxin A/B | Sometimes in combination with GDH

Question 39

Toxin neutralization for C diff

Answer 39

Use human porcine cells Take stool sample, filter bacteria out, put suspension on cells If a toxin is present, you'll see a cytopathic effect Also have to have a duplicate plate with the suspension and an anti-toxin though, and if you see survival there and death without the anti-toxin that is confirmation

Question 40

What molecular detection method do we use for C diff?

Answer 40

Real time PCR Looking for the toxin gene Limits: not detecting the production of the toxin, just seeing if it has the gene