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Clinical Microbiology > Gastrointestinal Infections > Flashcards

Gastrointestinal Infections Flashcards

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1
Q

Helpful incubation periods

A

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

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2
Q

What diagnostics can you use for bacterial infections?

A

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

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3
Q

Campylobacter

A

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

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4
Q

Salmonella enterica

A

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

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5
Q

O, H and Vi antigens for Salmonella

A

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)

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6
Q

Kauffmann-White antigenic scheme

A

Agglutination reactions with specific antisera against Salmonella antigens

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7
Q

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

A

Less than 6 months: do not make enough stomach acid

Over 50: acidity of stomach goes down

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8
Q

Salmonella Enteric Fever

A

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

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9
Q

XLD media

A

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

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10
Q

E coli O157:H7

A

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

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11
Q

Shiga like toxin

A

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

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12
Q

Shigella

A

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

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13
Q

Yersinia enterocolitica

A 
Swine most common source
Virulence result of tissue invasion
Rare on East Coast
Use MacConkey agar
May mimic appendicitis
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14
Q

3 similarities between Vibrio/Aeromonas/Plesiomonas and Enterobacteriaceae

A

Gram negative
Facultative anaerobes
Fermentive bacilli

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15
Q

2 differences between Vibrio/Aeromonas/Plesiomonas and Enterobacteriaceae

A

Polar flagella

Oxidase positive

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16
Q

Vibrio

A 
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
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17
Q

2 serogroups of cholera responsible for epidemic cholera

A

O1 and O139

18
Q

Vibriostatic agent

A

O129

19
Q

When to think viral GI

A

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

20
Q

What is the epidemic strain of norovirus?

A

GII.4

21
Q

Norovirus

A

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

22
Q

Rotavirus

A

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

23
Q

2 rotavirus vaccines

A

Rotarix: IV, monovalent
RotaTeq: oral, pentavalent

24
Q

Enteric Adenoviruses

A

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

25
Q

Enteric Adenoviruses vs Noro/rotavirus

A

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

26
Q

Astrovirus

A 
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
27
Q

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

A

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

28
Q

Hep A and E

A

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

29
Q

2 Vaccines for hepatitis

A

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

30
Q

Clostridium difficile

A

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

31
Q

How does C diff cause disease cellularly?

A

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

32
Q

C diff pathogenesis of inflammation (5 steps)

A 
Neutrophil infiltration
Intestinal damage
Impaired permeability
Fluid secretion
Overall: Diarrhea and inflammation
33
Q

Spectrum of C diff associated disease

A 
Asymptomatic (colonization)
Antibiotic-associated diarrhea
Pseudomembranous colitis
Toxic megacolon
Death
34
Q

How do we treat C diff?

A

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)

35
Q

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

A

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

36
Q

HUS

A

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

37
Q

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

A

Glutamate dehydrogenase

38
Q

Toxin Enzyme Immunoassays for C diff

A

Toxin B or Toxin A/B

Sometimes in combination with GDH

39
Q

Toxin neutralization for C diff

A

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

40
Q

What molecular detection method do we use for C diff?

A

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

Clinical Microbiology (25 decks)

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