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**CAM202: Microbiology > Week 3: Bacteriology of the gut I > Flashcards

Week 3: Bacteriology of the gut I Flashcards

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1
Q

Definition of diarrhoea

A

Increase in stool frequency and liquidity compared to the patient’s usual bowel habit

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2
Q

Clinical presentations of diarrhoea can be classified into:

A 
Acute = less than 14 days
Persistent = longer than 14 days
Chronic = longer than 30 days
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3
Q

Clinically, what are the two types of diarrhoea?

A

Secretory:
Watery
Usually produced in large volumes
Contains little or no blood or WBCs

Inflammatory:
Bloody
Produced in smaller volumes
Usually has WBCs

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4
Q

The nature of the causative organism in diarrhoea is dependent on which major factors?

A

Epidemiological risk factors
Patient’s age
Symptoms

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5
Q

Describe Acute Infectious Diarrhoea

A

AID is usually a self-resolving illness in immunocompetent individuals

Severe illness occurs in infants and the elderly, in immunocomprimised patients, and malnourished patients

Most deaths occurring due to acute infectious diarrhoea occur in children 5 years or younger, in developing countries

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6
Q

What are the important factor in a clinical history of someone presenting with diarrhoea:

A

Need to find out the duration and frequency of diarrhoea
Need to explore other GIT symptoms: emesis (vomiting), tenesmus (feeling of needing to pass stools/never feeling satisfied after passing stool/difficulty passing stools), cramping, nausea, anorexia.
Presence of fever
Unintended weight loss
Sexual History must be explored
Medication use - including recent Abx therapy
Recent contact with ill persons, travel, or animal contact
Consumption of raw or undercooked poultry or seafood
Immunocomprimised state (want to rule out)

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7
Q

What things should you take note of during the physical examination of a patient presenting with diarrhoea

A

Should complete a GI examination
Check hydration status: lethargy, postural hypotension, tachycardia, dry skin (e.g. loss of skin turgor - normal fluid tension of the skin), dry eyes, dry mucous membranes, sunken fontanelles (on infant’s skull)
Investigate other symptoms as indicated by symptoms - e.g. rashes, lymphadenopathy

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8
Q

What are some of the major bacterial causes of diarrhoea in humans?

A

Salmonella sp
Shigella sp
Diarrheagenic Escherichia coli (entero- haemorrhagic, -toxigenic, -pathogenic, -invasive, and -aggregative)
Yersinia Enterocolitica

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9
Q

Salmonella species: Describe the two clinical groups of salmonella

A

Typhoid Group = common causes of typhoid (enteric) fever.
Salmonella Typhi
Salmonella Paratyphi

Nontyphoid Group = serotypes other than the typhoid group

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10
Q

Describe the epidemiology and transmission of Salmonella sp

A

Infections are acquired from ingestion of faecal-contaminated food or drink. Salmonella typhi and paratyphi are transferred via person-to-person transmission. Non-typhi salmonella is transferred via animal-to-person.

Contaminated foods: poultry and beef, unpasteurised milk, eggs and fish, fruits, vegetables, baked goods, medicinal preparations can be contaminated as well

Usually large numbers of salmonellae are required to cause disease (10^8). Yet 10-100 infectious organisms can cause disease in infants, elderly and immunocomprimised.

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11
Q

Describe the Non-typhoid salmonella sp infection presentation:

And what are possible complications?

A

After 8-48 hours, typical presentation:

  • Fever
  • Colicky abdominal pain (severe tenderness and rebound tenderness)
  • Nausea, vomiting (not protracted)
  • Loose watery stools
  • Symptoms usually resolve within 2-5 days, and recovery is typically uneventful

Possible complications: bacteremia (inpatients with underlying disease), and Reiteri’s syndrome (reactive arthritis, conjunctivitis, urethritis)

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12
Q

Describe the clinical presentation of typhoid fever

List possible complications

A

(caused by Salmonella typhi and paratyphi)

Low numbers (<10^3) or organisms can cause disease. Some infected persons become chronic carriers (e.g. Typhoid Mary where the bacteria survived in the gall bladder)

Symptoms of typhoid fever typically evolve over 3 weeks:

  • Stepwise fever, with temperature-pulse dissociation (elevated fever but with normal pulse) during the 1st week.
  • Abdominal pain and rose spots on the trunk in the 2nd week.
  • Hepatosplenomegaly with intestinal bleeding in the 3rd week

Possible Complications:
Bacteraemia, Cholangitis, Pneumonia, Endocarditis, and Osteomyelitis

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13
Q

Is salmonella a nationally notifiable disease?

A

Yes

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14
Q

How is salmonella infection diagnosed?

A

Not on clinical presentation alone.

Confirmation:
- Isolation of organisms from stool and/or blood cultures using selective media

  • MacConkey agar (lactose fermentation)
  • Salmonella Shigella (SS) agar - (lactose fermentation/hydrogen sulfide)
  • Hektoen enteric (HE) medium
  • Xylose-lysine desoxycholate (XLD) agar
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15
Q

Treatment of Salmonella infection

A
  • The possibility of an underlying disease or immunodeficiency state should be considered with every patient with a severe salmonella infection
  • Empirical Abx therapy is not recommended for otherwise healthy patients
  • Elderly, immunocomprimised and children:
  • Azithromycin (ceftriaxone or ciprofloxacin IV if oral therapy not tolerated)

*Always treat cases of typhoid/paratyphoid - and follow up testing to ensure erradication

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16
Q

Which serotypes of Shigella sp are pathogenic to humans?

Which is the most commonly isolated?

A

Group A: Shigella Dysenteriae
Group B: Shigella Flexneri
Group C: Shigella Boydii
Group D: Shigella Sonnei

Shigella Sonnei (Group D) is the most commonly isolated and typically causes a watery diarrhoea

17
Q

What is the most commonly isolated Shigella ap serotype, and what disease does it typically cause in humans?

A

Shigella Sonnei (Group D serotype). Typically causes watery diarrhoea.

18
Q

What do the Shigella serovars (aside from Shigella Sonnei) typically cause in humans?

A

Bacillary Dysentery

Dysentery = inflammatory disorder of the intestine - typically the colon.

Symptoms include fever, abdominal cramping and tenesmus, and bloody diarrhoea.

*Abdo cramps, tenesmus and bloody diarrhoea are hallmarks of Shigella infection

19
Q

Describe the Epidemiology of Shigellosis

A

Occurs worldwide, but is especially common in countries lacking effective sanitation (developing countries)

Predominantly affects children 10 years and younger

Shigella (‘epidemics’) are common amongst certain populations, such as:

  • Mental or Penal Institutions
  • Daycare centres
  • Nursing homes
  • Amongst male-male sex populations
20
Q

How is Shigella transmitted?

A

Humans serve as a natural reservoir for Shigella

Generally takes a fecal-oral route

Outbreaks are commonly associated with swimming pools, spas, and fountains (faecal contaminated waters)

21
Q

Describe the Pathophysiology of Shigella Infections

A

Shigella is virulent - thus, only 50-100 organisms are sufficient to cause disease

Shigella infections are typically localised to the columnar epithelial cells of the colon (colonic mucosa).

Thus, bowel perforation or invasion of the bloodstream is extremely rare.

The bleeding (in stools) associated with Shigella infection is usually from superficial ulcerations of the mucosa, due to inflammation

22
Q

Describe the typical clinical presentation of an individual infected with Shigella sp

A

Shigella can produce variable (milder) disease, or true dysentery.

Variable Presentation:
The usual incubation period is 24-48 hours

Presentation ranges from mild watery diarrhoea with few (if any) constitutional symptoms, to asymptomatic infection

True Dysentery:
True Dysentery is preceded by watery diarrhoea lasting hours to a few days, then:
- Grossly bloody diarrhoea
- Fever, nausea, vomiting, headache, myalgia
- When severe, dehydration and even circulatory collapse can occur*

  • Children 2 or under may have associated neurologic manifestations: seizures, lethargy, and frank coma
  • In developing countries, Shigella dysenteriae is associated with hemolytic uremic syndrome (a type of haemolytic anaemia with other causes as well)
23
Q

Is Shigellosis a nationally notifiable disease?

A

Yes

24
Q

How is Shigellosis diagnosed?

A

Shigellosis is considered in every patient presenting with:
- An acute febrile illness, associated with diarrhoea, especially in patients who have dysenteric stools

Definitive diagnosis of shigellosis is made with stool culture, obtained within the first 3 days of the illness

25
Q

What type of growth medium is used for culturing Shigella?

A
  • MacConkey Agar (lactose fermentation)
  • Salmonella Shigella (SS) Agar (lactose fermentation / hydrogen sulfide production)
  • Hektoen enteric (HE) medium
  • Xylose-lysine desoxycholate (XLD) agar
26
Q

Treatment of Shigellosis

A

Primary treatment = correction of fluid and electrolyte imbalances

Candidates fr Abx treatment = All infected patients to prevent outbreaks of dysentery, even if the patient is asymptomatic when the culture results are returned.

Abx:

  • Ampicillin
  • Cotrimoxazole
  • Norfloxacin
  • Ciprofloxacin if severely ill
27
Q

Which types of Escherichia coli are Diarrheagenic in humans?

A

Usually, E.coli is harmless bowel flors, unless they have associated virulence factors.

*Differentiating pathogen from non-pathogen can be problematic

Diarrhoegenic E.coli:

  • Enterohaemorrhagic (EHEC)
  • Enterotoxigenic (ETEC)
  • Enteropathogenic (EPEC)
  • Enteroinvasive (EIEC)
  • Enteroaggregative (EAEC)
28
Q

Describe the epidemiology of Enterohaemorrhagic E. coli (EHEC, STEC, VTEC)

A

First recognised as a human pathogen in the 1980’s, and was traced back to undercooked ground beef contaminated with E.coli

There are 30 serotypes of E.coli that produce this shigella-like toxin

Carriers = cattle and other ruminants (plant-eating mammals) are the main EHEC carries

Human contact is attained via undercooking of infected meat, or infected stools contaminating water supplies to fruit and vegetables

29
Q

Describe the clinical presentation of Enterohaemorrhagic E. coli

A

After 3-4 day incubation period, get watery diarrhoea

This can progress to inflammatory (bloody) diarrhoea, accompanied by:

  • Severe abdo cramping
  • Pain
  • Vomiting
  • Low grade fever - can be used to differentiate EHEC from other organisms causing inflammatory diarrhoea

If uncomplicated, the illness typically resolves over 7-10 days.
A carrier state may last another 1-2 weeks, but also spontaneously resolves.

30
Q

What is a potential complication of Enterohaemorrhagic E. coli infection?

A

Haemolytic Uremic Syndrome (HUS)

  • Type of haemolytic anaemia
  • Symptoms and signs usually appear 5-20 days after the onset of infection, so the diarrhoea is often resolved by the time a diagnosis is established
  • HUS more commonly occurs in children, the elderly and immunocomprimised
31
Q

Is Enterohaemorrhagic E. coli infection a nationally notifiable disease?

A

Yes

32
Q

Describe the diagnostic strategy for Enterohaemorrhagic E. coli

What are some important differentials?

A

Stool samples are cultures on Sorbitol-MacConkey medium

Shiga-toxin enzyme immuoassay (EIA)

Differentials: Ischaemic collitis, inflammatory bowel disease, and intussusception

33
Q

Describe the treatment of Enterohaemorrhagic E. coli

A

Mainly supportive - maintain hydration and electrolyte balance

Empiric Abx therapy is not recommended for children because of risk of inducing H

34
Q

Describe the epidemiology of Enterotixigenic E. coli

A

ETEC is a major cause of diarrhoeal disease worldwide

Common problem for persons travelling to underdeveloped countries - common cause of travellers diarrhoea

Infectious agents are usually attained from faecal contaminated:

  • food and drink
  • leafy vegetables
  • drinking water
35
Q

Describe the typical clinical presentation of an individual infected with Enterotoxigenic E. coli

A 
Symptoms tend to occur after 24-72 hours
- Abrupt onset watery diarrhoea
- Abdominal cramping
- Vomiting
- Little-to-no fever
(*remember low grade fever is usually a sign in the direction of EHEC)
36
Q

Describe the diagnosis of Enterotoxigenic E. coli infection

A

Suspect in children/adults with frequent watery diarrhoea with few other clinical symptoms

Infected individuals usually recover completely without long-term sequelae

37
Q

Describe the treatment of Enterotoxigenic E. coli infections

A

Supportive: oral or IV fluids to rehydrate and rebalance electrolytes

If patient had been travelling in an endemic area, a single dose of ciprofloxacin for 3 days to eradicate organism is recommended

**CAM202: Microbiology (2 decks)

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