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Microbiology > GI Infections > Flashcards

GI Infections Flashcards

1
Q

Define Gastroenteritis

A

Rapid onset diarrhoeal illness, lasting <2 weeks with diarrhoea (loose or unformed stool) ≥3/day or ≥200g of stool which is either viral or bacterial in aetiology

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2
Q

Define diarrhoea.

A

loose or watery stool, ≥3 times in 24 hours, acute/chronic/persistent

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3
Q

What is the difference between acute, persistent and chronic diarrhoea?

A
  • Acute <14 days (may be viral or bacterial)
  • Persistent 14-29 days
  • Chronic >30 days (may be due to parasites and non-infectious aetiology)
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4
Q

What is small and large bowel diarrhoea?

A
  • Small bowel diarrhoea = watery, crampy abdominal pain, bloating and gas; inflammatory cells rare
  • Large bowel diarrhoea = small volume, painful, occur with blood/mucous; inflammatory cells common
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5
Q

What are the RFs for gastroenteritis?

A
  • Food borne
  • Exposure-related
  • Host-related
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6
Q

What are the exposure-related RFs for gastroenteritis?

A
  • Outbreak situation (>2 cases of common food source or exposure)
  • Travel history (exposure to poor settings and water facilities)
  • Occupational exposure / Health-care related exposure (recent ABx  c. diff)
  • Animal contacts (pets, farms, zoos)
  • Reptile contact (specifically)
  • Institution/childcare facility
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7
Q

What are the host-related RFs for gastroenteritis?

A
  • Young children and elderly
  • Immunosuppressed patients
  • MSM (men who have sex with men)
  • Anal-genital, oral-anal, or digital-anal contact
  • Haemochromatosis or haemoglobinopathy
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8
Q

Describe the epidemiology of GI infections.

A
  • There is an underreporting of GI infections (most are self-limiting <24 hours, patients do not seek healthcare)
  • Viral (i.e. norovirus) >>> bacterial
  • Developing countries have outbreaks (especially cholera in war torn countries)
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9
Q

What is the mechanism of disease?

A
  • (1) Secretory diarrhoea (from toxin production):
    • Cholera toxin:
      • Subunit production
      • cAMP opens Cl- channels at the apical membrane of the enterocytes causing an efflux of Cl- to lumen with loss of water and electrolytes → profoundly dehydrated
    • Superantigens:
      • Superantigens bind directly to TCRs and MHC molecules; outside the peptide binding site: there is massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response) → secretory diarrhoea
  • (2) Inflammatory diarrhoea
  • (3) Enteric fever – host responses in bacteraemia are…
    • Inflammatory (exudative) diarrhoea
    • Enteric fever: interstitial inflammation
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10
Q

How do we diagnose GI infections?

A
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11
Q

What are the extra-intestinal manifestations of GI infections? What are the causative organisms?

A
  • Salmonella, Yersinia → aortitis, osteomyelitis, deep tissue infection
  • Campylobacter, Yersinia → haemolytic anaemia
  • Shigella, Campylobacter, Yersinia → Glomerulonephritis
  • STEC, Shigella → HUS
  • Yersinia, Campylobacter, Salmonella, Shigella → erythema nodosum
  • Salmonella, Shigella, Campylobacter, yersinia, (giardia, Cyclospora cayetanensis) → reactive arthritis
  • Listeria, salmonella (infants <3m) (also enteroviruses) → meningitis
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12
Q

Describe staphylococcus aureus?

A
  • 1/3 population chronic carriers, 1/3 transient
  • Spread by skin lesions on food handlers
  • Appears in tetrads, clusters on gram stain → yellow colonies on blood agar
  • SUPERANTIGEN: produces enterotoxin, an exotoxin that can act as a superantigen in the GI tract, releasing IL1 and IL2 causing prominent vomiting and watery, non-bloody diarrhoea
  • Mx: self-limiting
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13
Q

What are the gram +ve rods: spore forming bacteria?

A

Bacillus cereus

Clostridia

Listeria monocytogenes:

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14
Q

Describe bacillus cereus.

A
  • Gram-positive rods: spore forming
  • Bacillus cereus: food poisoning
    • Spores germinate in reheated fried rice (heat-stable emetic toxin – not destroyed by reheating)
    • Gram +ve rod-spores
    • Heat-labile diarrhoeal toxin (food is not cooked to a high enough temperature)
    • Watery non-bloody diarrhoea; self-limiting
    • Rare cause of bacteraemia in vulnerable population
    • Can cause cerebral abscesses
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15
Q

What are the types of clostridia? What is the source? What do you ingest? What does it do? How do we treat it?

A
  • Clostridia (gram +ve anaerobe)
    • Clostridium botulinum: botulism
      • Source: canned or vacuum-packed food (honey in infants)
      • Ingestion of preformed toxin (inactivated by cooking)
      • Blocks ACh release from peripheral nerve synapses: paralysis
      • Treatment with antitoxin
      • Clostridium pefringens: food poisoning
        • Source: reheated food (meat)
        • Normal flora of colon but not small bowel, where the enterotoxin acts (superantigen)
        • Incubation is 8-16hrs
        • Watery diarrhoea, cramps, vomiting lasting 24hrs
      • Clostridium difficile: pseudomembranous colitis
        • Produces 2 toxins – Toxin A and Toxin B
          • Toxin A = enterotoxin = inflammation
          • Toxin B = cytotoxin = virulence factor (more dangerous than A)
        • 3% of community, 30% of hospitalised patients
        • Antibiotic related colitis (any but mainly cephalosporins, cipro and clindamycin)
        • Infection control – isolate and hand-washing
        • Treatment: PO vancomycin, stop antibiotics where possible
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16
Q
A

Pseudomembranous colitis - C.diff

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17
Q

Describe listeria monocytogenes infection.

A
  • Bad for pregnant women
  • Outbreaks of febrile gastroenteritis
  • ß-haemolytic, aesculin positive with tumbling-weed motility
  • Source: refrigerated food (“cold-enhancement”), unpasteurized dairy, vegetables (grows at 4ºC)
  • Symptoms: Watery diarrhoea, cramps, headache, fever, little vomiting
    • At risk: perinatal infection, immunocompromised patients, elderly (confused)
      • Treatment: ampicillin, ceftriaxone, cotrimoxazole
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18
Q

Describe the enterobacteriaceae, what is the source toxins, types? What should be avoided?

A
  • Facultative anaerobes, glucose/lactose fermenters (LF), oxidase-negative
  • Escherichia coli (Traveler’s diarrhoea)
    • Source: food/water contaminated with human faeces.
    • Enterotoxins:
      • Heat labile stimulates adenyl cyclase and cAMP
      • Heat stable stimulates guanylate cyclase
      • Act on the jejunum/ileum not on colon
        • ETEC; toxigenic → main cause of traveller’s diarrhoea
        • EPEC; pathogenic → infantile diarrhoea
        • EIEC; invasive → dysentery
        • EHEC; haemorrhagic → O157:H7 EHEC: shiga-like verocytotoxin causes HUS
        • Avoid antibiotics
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19
Q

Describe salmonella infections. What are the antigens, species …

A
  • Non-lactose fermenters, H2S producers (black colonies), TSI agar, XLD agar, selenite F broth
  • Antigens:
    • Cell wall O (groups A-I)
    • Flagellar H
    • Capsular VI (virulence, antiphagocytic)

Three species – distinguished by disease caused

  • S type
  • S. enteritidis
  • S cholerasuis
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20
Q

Differentiate between S.typhi and S enteritides.

A
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21
Q

Describe shigella infection. What are the antigens? How does it spread? What does it cause? How should it be managed?

A
  • Non-lactose fermenters, non H2S producers, non-motile
  • Antigens:
    • Cell wall O antigens
    • Polysaccharide (groups A-D): S. sonnei, S. dysenteriae, S. flexneri (MSM)
      • The most effective enteric pathogen (low infectious dose 50)
      • No animal reservoir (human → human transmission)
      • No carrier states
      • Dysentery
        • Invading cells of mucosa of distal ileum and colon
        • Producing enterotoxin (Shiga toxin)
        • Avoid antibiotics (ciprofloxacin if required)
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22
Q

What are vibrios? What are the types?

A
  • Curved, comma shaped, late lactose fermenters, oxidase positive
    • Vibrio cholerae
    • Vibrio parahaemolyticus
    • Vibrio vulnificus
23
Q

Describe Vibrio cholerae

A
  • O1 group: epidemics, biotypes El Tor, Cholerae and serotypes Ogawa, Inaba, Hikojima
  • Non O1 group: sporadic or non-pathogens
  • Faeco-oral transmission inc. shellfish, oysters, shrimp
  • Colonisation of small bowel and secretion of enterotoxin with A and B subunit, causing persistent stimulation of adenylate cyclase
  • Causes massive diarrhoea (rice water stool) without inflammatory cells

Treat the losses: electrolyte replacement and fluids

24
Q

Describe Vibrio parahaemolyticus

A
  • Ingestion of raw or undercooked seafood (i.e. oysters)
  • Major cause of diarrhoea in Japan or when cruising in the Caribbean
  • Self-limited for 3 days
  • Cholerae: grows in salty 8.5% NaCl
  • Treat with doxycycline
25
Q

Describe Vibrio vulnificus

A
  • Cellulitis in shellfish handlers and fatal septicaemia with D+V in HIV patients
  • Treat with doxycycline
26
Q

Describe campylobacter.

A
  • Curved, comma or S shaped; Microaerophilic
  • C. jejuni at 42 ºC
  • Oxidase positive, motile
  • Self-limiting but symptoms can last for weeks (20 days) – only tx if immunocompromised (macrolide)
  • Transmitted via contaminated food and water with animal faeces (poultry, meat, unpasteurised milk)
  • Enterotoxin (watery diarrhoea) with invasion (+/- blood)
  • Symptoms: Watery, foul smelling diarrhoea, bloody stool, fever and severe abdominal pain → treat with erythromycin or cipro if in the first 4-5days
  • Extra outcomes: GBS, ReA, Reiter’s
27
Q

Describe Yersinia enterocolitica

A
28
Q

Describe mycobacteria.

A
  • Will appear as gram variable
  • Always think of TB
29
Q

Describe entamoeba histolytica.

A
  • Motile trophozoite in diarrhoea; Non-motile cyst in non-diarrhoeal illness
  • Killed by boiling, removed by water filters; 4 nuclei
  • No animal reservoir
  • Ingestion of cysts: trophos in ileum which colonize cecum and colon causing a “flask shaped” ulcer
  • Symptoms: dysentery, flatulence, tenesmus or in chronic form: weight loss +/- diarrhoea, liver abscess
  • Diagnosis
    • Stool microbiology (wet mount, iodine and trichrome)
    • Serology in invasive disease
      • Treat: metronidazole and paromomycin in luminal disease
30
Q

Describe Giardia lamblia.

A
  • Trophozoite “pear shaped”; 2 nuclei
  • 4 flagella and a suction disk
  • Ingestion of cyst from faecal-contaminated water and food
    • Excystation at duodenum, tropho attaches, no invasion but malabsorption of protein and fat
      • Travellers (cruise), hikers, day care, mental hospitals, MSM
      • Symptoms: Foul smelling non-bloody diarrhoea, cramps, flatulence, no fever
      • Diagnosis: stool micro, ELISA, “string test”
      • Treatment: metronidazole
31
Q

Describe Cryptosporidium parvum

A
  • Infects the jejunum
  • Severe diarrhoea in the immunocompromised (can cause outbreaks)
  • Oocysts seen in stool by modified Kinyoun acid fast stain
  • Treatment: reconstitution of immune system. Self-limiting
32
Q

Describe norovirus.

A
  • Outbreaks
  • Low ID load (18-1000 viral particles) – lick lips on an infected ward is enough!
  • Environmental resilience (0-60 degrees)
  • No long-term immunity
  • G2.4 currently predominant strain
33
Q

Describe rotavirus

A
  • dsRNA “wheel like”
  • Replicates in mucosa of small intestine
  • Secretory diarrhoea, no inflammation
  • Watery diarrhoea by stimulation of enteric nervous system
  • By age 6 most children worldwide have antibodies to at least one type
  • Exposure to natural infection twice confers lifelong immunity
    • Huge economic burden worldwide
34
Q

Describe adenovirus.

A
  • Types 40/41 cause non-bloody diarrhoea usually <2yrs of age. Any type in immunocompromised
  • Diagnosis: stool EM, antigen detection, PCR
    • Poliovirus
    • Enteroviruses (coxsackie, ECHO)
    • Hepatitis A
      • Transmitted via faecal-oral route but main presentations from other systems
35
Q

How should infection be prevented and controlled?

A
  • Targets for promotion
    • Breastfeeding, improved weaning practice
    • Clean water for drinking
    • Safe disposal of stools of young children
    • Precautions when travelling
    • Food handling
    • Public health notification
    • Good handwashing
36
Q

Explain the use of vaccines?

A
  • Cholera: serogroups O1 (Inaba, Ogawa, biotypes El Tor and classical), O139
    • Inactivated, whole cell, contains all above + B subunit of toxin (PO)
    • Live attenuated (PO) not recommended
    • Campylobacter: military, infants, traveller, candidate vaccines exist
    • ETEC: inactivated and live vaccines in trials
    • Salmonella typhi: Vi capsular PS (IM) and (PO) live
    • Rotavirus
      • Rotarix: live attenuated human strain monovalent, 2 (PO) doses
      • Rotateq: pentavalent, 3 (PO) doses, one bovine and four human strains
      • Rotashield and intussusception (8-20 weeks)
      • Age of vaccine is 6-12 weeks
37
Q

Explain the need for Public Health.

A
  • Notifiable diseases = Campylobacter, Clostridium species, Listeria monocytogenes, Vibrio, Yersinia
  • Each trust to notify to local Health Protection Unit
  • Identify outbreaks in areas
  • Environmental Health Officers to inspect premises and take samples from environment and food
38
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Staphylococcus aureus?

A
39
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Norovirus?

A
40
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Clostridium Perfringens?

A
41
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Enteric Viruses?

A
42
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Listeria monocytogenes?

A
43
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Enterotoxigenic E.coli?

A
44
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Nontyphoidal Salmonella?

A
45
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Campylobacter spp?

A
46
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Shigella spp?

A
47
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Vibrio parahemolyticus?

A
48
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Enterohemorrhagic E.coli?

A
49
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Yersinia spp?

A
50
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Giardia lamblia?

A
51
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Cyclospora cayetanensis?

A
52
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Cryptosporidium parvum?

A
53
Q

What is the

  • incubation period
  • Pathogen
  • Duration of illness
  • Food RFs
  • Type of Diarrhea

for Clostridium difficile?

A

Microbiology (19 decks)

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