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Microbiology > Corbett - Gram + rods > Flashcards

Corbett - Gram + rods Flashcards

1
Q

What is the mechanism of action of Corynebacterium diptheriae?

A

Basically there are two subunits within in the toxin, A and B. B binds to the cell. Once inside the cell, the A subunit becomes active and ADP-ribosylates the elongation factor 2 (EF2), thus inactivating it and killing the cell.

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2
Q

Clinical significance of diptheria

A
  • causes respiratory issues such as sore throat and infection of the nasopharynx.
  • classic sign is the “bull-neck” that accompanies the massively enlarged lymph nodes.
  • you will see a dense, gray, psuedomembrane that covers parts of the oropharynx.
  • it is possible to have cardiac and neurological symptoms as well
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3
Q

How do you ID diptheria?

A

You have to grow it on a Tinsdale agar that has tellurite on it to inhibit other flora. This will yield black colonies with halos.

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4
Q

How do you treat diptheria?

A
  • you can use diptheria antitoxin to neutralize the toxin, which comes from horses and can causes serum sickness in 10% of patients.
  • prompt antibiotics such as erythromycin or penicillin.
  • Prevent diptheria through use of inactivated toxoid vaccine.
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5
Q

How is diptheria spread?

A

Respiratory droplets

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6
Q

How does one typically get Anthrax (bacillus anthracis)?

A

Usually spread through animal products such as sheep.

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7
Q

What are the virulence factors for anthrax?

A

Edema toxin - causes increased amount of cAMP
Lethal toxin - causes tissue necrosis
Protective antigen - allows entry into the cell.

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8
Q

Clinical significance of anthrax?

A

Depending on the size of the particles it can either be cutaneous or pulmonic.

  • If large particles then it will cause a cutaneous, painless, swollen pustule with a black Eschar. If left untreated it could cause sepsis.
  • If small particles, they can travel down into the lungs and cause hemmorhagic lymphadenitis, which will kill you. Basically you will bleed out of your lungs.
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9
Q

ID of bacillus anthracis (Anthrax)

A

Gram stain

  • gram +
  • centrally located endospores that look like chains of bamboo
  • on a blood agar they form gray comma shaped colonies. Nonhemolytic, nonmotile.
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10
Q

Treatment of anthrax

A

Cutaneous - doxycycline, ciprofloxin, erythromycin
Inhalation anthrax - multi drug treatment.

Prevention - cell free vaccine is available for high risk individuals.

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11
Q

How is listeria monocytogenes transmitted?

A

Food borne - especially in poultry and cheeses.

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12
Q

In what population is listeria particularly prevalent?

A

Pregnant woman and their children

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13
Q

How does listeria monocytogenes exert its effect?

A

They get phagocytized. Once inside phagocyte, they escape the vacuole using listeriolysin O to break down the capsule. Then it uses the cells actin and creates a tail to allow it to propel into neighboring cels.

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14
Q

Clinical significance of listeria?

A

Healthy people - diarrhea and fever
Newborns - meningitis and septic arthritis
Pregnant women - flu-like symptoms

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15
Q

ID of listeria monocytogenes?

A

Blood agar - beta-hemolysis with blue-green sheen.
- non-spore forming.

Tumbling motility in hanging drop is key

Production of catalase

“Umbrella Motility” in semi-solid nutrient agar

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16
Q

Treatment of listeria?

A

Ampicillin

- prevent with proper food handling.

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17
Q

How is clostridium perfirigens spread?

A

Spores are found in the soil and often drug users use dirty needles.
- also it is part of the normal flora of the large intestine and vagina.

18
Q

How does clostridium perfirigens exert its affects?

A

Main virulence factor is exotoxin A, which lyses ECs, RBCs, and WBCs.

19
Q

Clinical significance of clostridium perfirigens?

A

Myonecrosis occurs, which is basically the break down of muscle. This causes air to get into the muscle, known as crepitus.

  • you will see swelling of the limb as well as erythema and blistering.
  • anaerobic cellulitis on the skin and potential for necrotizing fasciitis.
  • food poisoning
20
Q

ID of clostridium perfirigens ?

A

Cultured anaerobically on blood agar, will have unique “double zone” of hemolysis.

21
Q

Treatment of clostridium perfirigens?

A
  • surgical treatment with debris event of devitalized tissue
  • hyperbaric oxygen therapy
  • Penicillin
22
Q

How does one get clostridium botulinum?

A

It is found in soil and aquatic sediments. These spores frequently contaminate vegetables and meat.
- in question stem if it mentions canning your own vegetables then it is probably clostridium botulinum.

23
Q

How does botulinum toxin exert its effects?

A
  • there are three types of neurotoxins - A, B, and E.
  • There are two chains, the light chain buds off and cleaves the SNARE proteins, which inhibits Acetylcholine release from the vesicles.
  • Flaccid paralysis results.
24
Q

Clinical significance of botulinum toxin

A
  • It will cause paralysis starting from the head and moving downward. So, you might get blurry vision, then difficulty swallowing etc. Eventually you might get respiratory failure.
25
Q

Why are babies particularly at risk for botulinum?

A

Because they can get it easier than we can from contaminated honey.

26
Q

Treatment of botulinum toxin

A
  • Immediate antitoxin with trivalent A, B, or E horse botulinum immune serum or human serum.
  • penicillin
27
Q

How does clostridium tetani (tetanus) spread?

A
  • common in barnyards, gardens, soils, work sites.

- Common in puncture wounds

28
Q

How does clostridium tetani (tetenus toxin) exert its affect?

A

There are A and B fragments as usual. The B fragment delivers the A fragment to the neuron cytoplasm. The A fragment blocks NT release at inhibitory synapses such as GABA and glycine. This causes sever prolonged muscle spasms.

29
Q

Clinical significance of tetanus

A

Spastic paralysis precipitated by external stimuli. Early stages affect the jaw.

  • you will see risus sardonicus (creepy smile)
  • you will see opisthotonos (back and neck straightening/bending back)
30
Q

ID of tetanus

A

Usually treat based on clinical presentation

- Racquet shaped bacillus on gram stain

31
Q

Treatment for tetenus

A

Immunization every 10 years.

32
Q

What does Clostridium difficile look like on gram stain?

A

Large gram + rod

  • anaerobe
  • spore forming
33
Q

How does Clostridum difficile damage the colon?

A

It is the toxins that they make that cause damage. The two major toxins are toxin A (TcdA) and toxin B (Tcd B).

34
Q

WHat are the two main toxins of Clostridium difficile

A

Toxin A and toxin B

35
Q

What is the mechanism of action of the C diff toxins?

A

Causes Rho inactivation, which increases secretion of fluids and electrolytes and decreased permeability in the intestinal mucosa.

36
Q

Risk factors associated with C. Difficile associated diarrhea?

A

6 As:

Acquire the spores - fecal-oral route
Antibiotics 
Advanced age
Admitted to hospital
Acute illness
Acid suppression
37
Q

How does one acquire clostridium?

A

Spores are usually ingested somehow. Then all of the ones that weren’t spores, but were vegetative, are killed. But the spores stay as spores until they get into an environment where they can germinate properly. This usually occurs in the intestines.

38
Q

Which antibiotics are more likely to cause C. Diff?

A

Clindamycin

39
Q

How do antibiotics increase the risk of getting C diff?

A

They disrupt the barrier function of the normal colonic flora.

40
Q

Clinical features associated with clostridium difficile.

A 
Water diarrhea 
Cramping and abdominal pain
Anorexia
Malaise and fever
Tenderness
Dehydration
Fever
Peritonitis
Pseudomembranes in the colon
Thickening of the walls of the colon
41
Q

B1/NAP1/027 strain

A

New strain of C diff that has higher concentrations of toxin A and B. There is also a 3rd toxin. High resistance to Fluoroquinoolones.

42
Q

How. Do you make a diagnosis of C diff?

A

Stool culture
Immunoassay for toxin A and B
PCR

Microbiology (14 decks)

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