Clinical Microbiology — SCT II [Vol. 3]

Question 1

What are the possible portals of entry of Francisella tularensis? Specify at least 4

Answer 1

1. Tick bite
2. Conjunctiva
3. Skin abrasions
4. Respiratory tract
5. Gastrointestinal tract

Question 2

How do humans acquire bucellosis? What do the bacteria replicate in the human body?

Answer 2

VIa contaminated milk products or through skin abrasions (contact with animals)

Organisms spread to the mononuclear phagocytes of the reticuloendothelial system (lymph nodes, liver, spleen, bone marrow)

Question 3

What are the reservoirs of the different Brucella species, respectively?

Answer 3

B. abortus: cattle
B. melitensis: goat, sheep
B. suis: swine
B. canis: dog

Question 4

What is the mechanism of action of cholera toxin?

Answer 4

Cholera toxin activates the adenylate cyclase enzyme in cells of the intestinal mucosa leading to increased levels of intraceullar cAMP, and the secretion of large amount of water and electrolytes into the lumen of the small intestine

Question 5

What is the principle of the treatment of cholera?

Answer 5

Rapid intravenous or oral replacement of the lost fluid and ions.

In severe cases: administration of tetracycline (in addition to rehydration)

Question 6

Mention 4 diseases caused by Haemophilus influenzae

Answer 6

1. Purulent meningitis
2. Epiglottits (obstructive laryngitis)
3. Otitis media and sinusitis
4. Pneuomnia
5. Cellulitis
6. Arthritis

Question 7

Which disease is caused by Haemophilus ducreyi?

Answer 7

Chancroid (soft chancre or ulcus molle), which is an STD (sexually transmitted disease)

Question 8

What can serve as source of infections caused by Pseudomonas aeruginosa?

Answer 8

Pseudomonas species are normally present in the environment and can be isolated from the skin, throat, and stool of some healthy persons.

They often colonize hospital food, sinks, taps, mops, and respiratory equipment

Question 9

Mention 4 diseases that are frequently caused by Pseudomonas aeruginosa

Answer 9

1. Urinary tract infections
2. Wound infections (burns)
3. Otitis externa
4. Pneuomonia, sepsis (immunosuppression)

Question 10

Mention at least 3 drugs which may be effective to treat infections caused by Pseudomonas aeruginosa

Answer 10

Certain pencillins: piperacillin/tazobacatam combination

A 3rd generation cephalosporin: ceftazidim

A 4th generation cephalosporin: cefepime

Certain aminoglycosides: gentamicin, amikacin

Carabapenems: imipenem, meropenem

Question 11

What are the frequent sources of infection for Legionella pneumophila?

Answer 11

1. Air conditioners
2. Water taps
3. Showers
4. Evaporators

Question 12

Which 2 diseases are caused by Legionella pneumophila?

Answer 12

1. Legionellosis, legionnairs’ disease (atypical pneumonia)
2. Pontiac fever (mild, flu like illness without pneumonia)

Question 13

List 3 important virulence factors of Bordatella pertussis

Answer 13

1. Pertussis toxin
2. Filamentous hemagglutinin
3. Adenylate-cyclase toxin
4. Tracheal cytotoxin

Question 14

What is the precise definition of bacterial food poisoning?

Answer 14

Acute disease, usually with vomiting and diarrhea, usually caused by preformed toxins produced by bacteria contaminating the food

The period between consumption of food and the appearance of symptoms is short (<4-6 hours)

Question 15

Mention 3 bacterium species causing food poisoning

Answer 15

1. Staphylococcus aureus
2. Bacillus cereus
3. Clostridium perfringens
4. Clostridium botulinum

Question 16

Which bacterium has the highest germ number in the colon?

Answer 16

Bacteroides fragilis

Question 17

Mention 4 bacterial genera that are obligate anaerobes

Answer 17

1. Clostridium
2. Bacteroides
3. Prevotella
4. Porphyromonas
5. Fusobacterium
6. Actinomyces
7. Bifidobacterium
8. Peptostreptococcus
9. Propionibacterium

Question 18

Which is the most important gas gangrene Clostridium? What is its main virulence factor?

Answer 18

Clostridium perfringens
Alpha-toxin (lecithinase)

Question 19

Mention 3 Clostridium species causing gas gangrene! How are they acquired?

Answer 19

1. Clostridium perfringens
2. C. novyi
3. C. septicum
4. C. histolyticum
5. C. tertium
6. C. bifermentans
7. C. sporogenes

The site of infections is usually a wound that comes into contact with Clostridium spores that germinate in an anaerobic environment

Question 20

How can tetanus be prevented in patients who have wounds possibly contaminated with C. tetani spores?

Answer 20

Wound should be cleaned and debrided; tetanus toxoid booster injection given; tetanus immunoglobulin (TETIG) in previously unvaccinated patients and in case of heavy contamination of wound; pencillin may be added prophylactically

Question 21

What are the main symptoms of tetanus? Specify at least 3

Answer 21

1. Spastic paralysis: muscle spasms
2. Lockjaw (trismus)
3. Rhisus sardonicus (grimace of the face)
4. Opisthotonus (spasm of the back)
5. Respiratory paralysis

Question 22

What is the mechanism of action of botulinum toxin?

Answer 22

Blocks release of acetylcholine in peripheral nerve synapses

Question 23

What are the main symptoms of botulism? Specify at least 3

Answer 23

1. Flaccid paralysis: diplopia (double vision)
2. Dysphagia (difficulty to swallow)
3. Dysphonia (hoarseness)
4. Respiratory paralysis

Question 24

What kind of therapy is used to treat botulism?

Answer 24

Treatment: respiratory support + trivalent antitoxin

Question 25

Explain whether or not antibiotic treatment is useful in botulism

Answer 25

Not, because antibiotics are not effective against performed toxins