Bacteriology Case Studies

Question 1

CLINICAL CASE (taken from Flash Cards):
An infant born in a rural area is brought to the EW with severe bouts of coughing throughout the day. During the visit, the
baby appears cyanotic and suffers an attack of many coughs on a single expiration followed by a deep inspiration. The coughs
produce copious greenish phlegm. Further history reveals that the infant has not been vaccinated. The physician fears that
erythromycin therapy will not be helpful at this stage of the illness.

What is the diagnosis?

What is the pathology and toxins?

What are the stages of infection?

What is the gram stain and diagnosis?

What is the treatment?

Answer 1

Clinical presentation: Whooping cough (Bordetella pertussis)

Pathology:
only human carriers, airborne transmission, bacteria adheres to cilia of respiratory epithelium via filamentous haemaglutinin and releases exotoxins.

• pertussis toxin (AB toxin) ADP-ribosylates and inactivates Gi proteins. This leads to uninhibited adenylate cyclase, resulting in increased levels of cAMP, eventually leading to increased lymphocytosis and decreased phagocytosis.
• secreted adenylate cyclase, is taken up by phagocytes, leads to increased cAMP, inhibiting bactericidal activity
• tracheal cytotoxin, kills ciliated epithelial cells, impairs mucous clearance,

violent whooping cough develops (mechanism unknown)

There are 3 stages of infection
1) cataharral stage (1-2 weeks): flu like symptoms, highly contagious
2) paroxysmal stage (3 - 8 weeks): coughing, single expiration followed by whooping inspiration
3) recovery stage (2-3 months)

Diagnosis: gram negative coccobacilli
Bordet-Gengou agar or charcoal BA with cefalexin

Vaccine: DTaP vaccine (acellular pertussis antigens)
Treatment: macrolides given BEFORE paroxysmal phase

Extra facts:
Because anti-FHA antibody production declines 15 years after vaccination, most mums cant transfer antibodies to their babies, hence infants are the most susceptible.

Infection can be life threatening for children with cardiac or pulmonary issues, and neurological sequelae (from hypoxia) usually follow.

Question 2

A 3-year-old immigrant from Mexico is admitted to the hospital with a history of a persistent cough. Upon admission, the boy’s cough becomes rapid and prolonged with intervals of high-pitched deep breaths. The peripheral white blood count is 24,000/μl, with an absolute lymphocytosis. The child does not have a history of any vaccinations.

The gram stain shows gram negative coccobacilli singly or in pairs.

What is the organism?

How is it transmitted?

What is the clinical manifestation of disease? (how does infection present and progress?)

What are the main toxins and how do they work?

Answer 2

Gram negative coccobacilli singly or in pairs (sometimes bipolar staining)

Bordetella pertussis

Highly contagious respiratory pathogen, spread by airborne droplets. Humans are the only host.

Causative agent of whooping cough (the 100 day cough).
This 3 stage disease first presents with cold-like symptoms (catarrhal stage), the 2nd stage (paroxysmal stage) characterised by paroxysmal coughing, copious mucous production and exhaustion.
The 3rd stage (convalescent stage) the cough subsides over several weeks to months.

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B. pertussis attaches to ciliated respiratory epithelial cells mediated by filamentous haemaglutinin (Fha). Once attached, tracheal cytotoxin stops the cilia from beating.

Pertussis toxin ADP ribosylates host G proteins in the early stages of respiratory infection. Pertussis toxin is an AB toxin which targets respiratory tract macrophages and promotes lymphocytosis.

Adenylate cyclase toxin and Pertussis toxin elevate intracellular cAMP levels and increase mucus secretion.

Macrolide antibiotics are preferred.

Prevention: vaccine usually given with toxoids of diphtheria and tetanus.

Question 3

Bordetella bronchiseptica could be confused with the agent of whooping cough since it occasionally causes chronic respiratory tract infections in humans, but has less intensive symptoms (rhinitis and cough). It is best described by which of the following?

a - commonly inhabits canine respiratory tract, occasional pathogen of humans, strongly urease positive

b - gram negative bipolar stained bacilli that causes diarrhoea by means of a heat-stable enterotoxin, with abdominal pain that may be mistaken for appendicitis

c - Pits agar grows in both carbon dioxide and under anaerobic conditions, and is part of the normal oral cavity flora

d - typically infects cattle, requires 5-10% carbon dioxide for growth, inhibited by dye thionine

e - typically found in infected animal bites in humans and can cause haemorrhagic septicaemia in animals

Answer 3

a - Bordetella bronchiseptica causes disease in animals (kennel cough in dogs) and occasionally respiratory disease and bacteraemia in humans. Bordetella requires enriched media and is strongly urease positive!

b -

c -

d- Brucellae are found in animals and humans, they are intracellular organisms.
Brucella abortus is typically found in cattle.
Brucellosis (unduland

e- Pasturella multocida occurs worldwide in the respiratory tract and GI tracts of domestic and wild animals. Its the most common organism in human wounds inflicted by cat and dog bites. It is one of the most common causes of haemorrhagic septicaemia in rabbits, rats, horses, sheep, fowl, cats and swine. It can affect many systems in humans, as well as bite wounds.