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M3 l Microbiology > B1 R&C Lec 1 : Bacterial causes of Atypical pneumonia > Flashcards

B1 R&C Lec 1 : Bacterial causes of Atypical pneumonia Flashcards

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Biology 101 flashcards
1
Q

Mention the atypical bacteria

A
  1. Mycoplasma pneumoniae
  2. Legionella pneumophila
  3. Coxiella burnetii
  4. Chlamydia pneumoniae
  5. Chlamydia psittaci
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2
Q

What are the properties of M.pneumonia?

A
  • Smallest free-living organisms.

Their most striking feature is the absence of cell wall, so:

  1. It has a variety of shapes.
  2. They stain poorly with Gram stain.
  3. Resistant to antibiotics that inhibit cell wall synthesis (e.g., penicillins and cephalosporins).
  4. The only bacteria with cholesterol in cell membrane.
  5. Can be cultured in vitro but they have complex nutritional requirements, including several lipids.
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3
Q

Describe the colonies of M.pneumonia

A

The colony frequently has a characteristic “fried-egg” shape, with a raised center and a thinner outer edge

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4
Q

How is M.pneumonia transmitted ?

A

via respiratory droplets ( only humans)

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5
Q

Explain the pathogenesis of M.pneumonia

A
  1. Rod-shaped organism with a tapered tip that contains specific proteins that serve as the point of attachment to the respiratory epithelium.
  2. Ciliary motion is inhibited and necrosis of the epithelium occurs.
  3. Cold agglutinins are cold-reactive IgM autoantibodies that can result in hemolytic anemia.

Autoantibodies are produced against red cells (cold agglutinins), brain, lung, and liver cells. These antibodies may be involved in some of the extrapulmonary manifestations of infection.

4.Hydrogen peroxide produced by the organism contributes to the damage to the respiratory tract cells.

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6
Q

Mention the Clinical findings of M.pneumonia

A
  • Gradual onset
  1. Sore throat
  2. earache
  3. nonproductive cough or with small amounts of whitish, non-bloody sputum
  • Constitutional symptoms of :

1.fever
2. headache
3. malaise
4. skin rash
5. myalgia

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7
Q

What is the Cold agglutinin disease?

A

autoimmune hemolytic anemia, in which antibodies bind red blood cells only at low body temperatures manifested by acrocyanosis (cyanotic discoloration of the hands, knees, feet, and/or distal parts of the face) in response to exposure to cold temperatures

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8
Q

When does Cold agglutinin disease resolve ?

A

spontaneously in 10 to 14 days

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9
Q

What is seen in the chest x-ray of a Cold agglutinin disease patient?

A

The rarity of findings on chest examination is in marked contrast to the prominence of the infiltrates seen on the patient’s chest Xray.

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10
Q

What is the laboratory diagnosis of M.pneumonia?

A
  1. Gram stain is not useful.
  2. Cultured on special media takes at least 10 days to grow, which is too long to be clinically useful.
  3. Positive cold-agglutinin test is presumptive evidence. Cold agglutinins are IgM autoantibodies against type O red blood cells that agglutinate these cells at 4°C but not at 37°C. The test is nonspecific; false-positive results occur in Influenza virus and Adenovirus infections.
  4. Complement fixation test for specific antibodies to Mycoplasma pneumoniae is specific for the diagnosis.
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11
Q

Which media is used to culture M.pneumonia?

A

Eaton agar

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12
Q

Which test is considered a specific diagnosis of M.pneumonia?

A

Complement fixation test for specific antibodies

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13
Q

Positive cold-agglutinin test is________ evidence.

A

presumptive

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14
Q

Which type of autoantibodies is cold agglutinins?

A

IgM autoantibodies against type O red blood cells

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15
Q

Which bacteria requires iron & cysteine for growth in culture?

A

Legionella pneumophila

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16
Q

Where does L. pneumophila environment and give examples ?

A

Habitat is environmental water sources such as air conditioners and watercooling towers.
Hospital outbreaks of have been attributed to the presence of the organism in water taps, sinks, and showers.

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17
Q

How L.pneumophila is transmitted?

A

aerosols from the water source typically from airconditioning systems, showers, and swimming pools (e.g., in hotels or cruise ships)

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18
Q

Does Person-to-person transmission happen with l.pneumophila?

A

No

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19
Q

Pathogenesis of L.pneumophila

A

The major virulence factor of the organism:

  1. Lipopolysaccharide (endotoxin). No exotoxins are produced.
  2. Intracellular replication of the organism, so cell-mediated immunity is important host defense during the infection.
20
Q

What are the predisposing factors of L.pneumophila?

A

-Older than 55 years of age.

  • Smoking damaging alveolar macrophages.
  • Chronic lung disease.

-Immunosuppressed patients.

21
Q

What is the Legionnaires’ disease?

A

vary from a mild influenza-like illness to a severe pneumonia accompanied by mental confusion, non bloody diarrhea, hyponatreamia.

22
Q

When does Legionnaires’ disease resolve?

A

Most cases resolve spontaneously in 7 to 10 days, but in older or immunocompromised patients, the infection can be fatal

23
Q

Which fever is described by “a mild, flulike self limiting form of Legionella infection that does not result in pneumonia”?

A

Pontiac fever

24
Q

What are the laboratory diagnosis of L.pneumophila in blood?

A

•Hyponatremia (serum sodium < 130 mEq/L) is common.

•Possible thrombocytopenia and leukocytosis.

25
Q

What are the laboratory diagnosis of L.pneumophila in urine?

A

•Detection of Urinary L. pneumophila antigen provides rapid diagnosis (same day test results).

•Hematuria and proteinuria are common.

26
Q

Which agar does L.pneumophila grows in?

A

charcoal yeast extract agar containing increased amounts of iron & cysteine (Slow growth > 5days).

27
Q

How L.pneumophila is detected serologically?

A

by detecting rise in antibody titer in patient’s serum (Antibody response may not be detectable until after 4 to 12 weeks of infection)

28
Q

Which organism causes Q fever?

A

Coxiella burnetii

29
Q

What are the important properties of C.burnetti?

A
  • Obligate intracellular organism because they are unable to produce sufficient energy to replicate extracellularly.
  • They stain poorly with Gram stain.
30
Q

What is the habitat of C.burnetti?

A

domestic livestock

31
Q

How is C.burnetti transmitted?

A

by inhalation of aerosols of urine, feces, amniotic fluid, or placental tissue

32
Q

C.burnetti is a ______ disease

A

Zoonotic

33
Q

Pathogenesis of C.burnetti

A

No toxins or virulence factors known.

The basis for pathogenesis by these organisms is unclear.

34
Q

Clinical findings of C.burnetti

A

*It begins suddenly with influenza like symptoms.

•This is all that occurs in many patients, but pneumonia ensues in about half

Hepatitis is frequent enough that the combination of pneumonia and hepatitis should suggest Q fever.

•Rash is rare, unlike in the other rickettsial diseases.

• Q fever is acute disease & recovery is expected even in absence of antibiotic therapy.

35
Q

What is the main organ involved with Q fever?

A

Lungs

36
Q

Which serological tests are done for C.burnetti?

A

Mainly by: Indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA) tests are most often used

  • Stain and culture rarely done because they are hazardous procedures.

*Weil-Felix test is of historic interest and is no longer performed because its specificity and sensitivity are too low.

37
Q

State the important properties of Chlamydia pneumoniae.

A

• Pleomorphic, poorly Gram stained.

• Obligate intracellular bacteria (unable to produce its own ATP).

• Absent peptidoglycan in the cell wall.

• Chlamydiae have a replicative cycle different from that of all other bacteria.

• Visible as cytoplasmic inclusion bodies on Giemsa stain or fluorescent antibody-stained smear

• Very difficult cultivation

38
Q

How is C.pneumoniae transmitted from person to person?

A

By aerosols

39
Q

Pathogenesis of C.pneumoniae

A

•No toxins or virulence factors known.

•Chlamydiae infect primarily epithelial cells of the mucous membranes or the lungs.

•They rarely cause invasive, disseminated infections.

40
Q

Clinical findings of C.pneumoniae

A

• Asymptomatic.

• General symptoms of atypical pneumonia: Fever, non-productive cough, headache and myalgia

41
Q

What does Chlamydiae form?

A

cytoplasmic inclusions (which can be seen with special stains)

42
Q

How antibodies are detected in Chlamydia?

A

•IgG and IgM serology for detecting antibody in patient’s serum is mainly used for the diagnosis.

•NAAT (nucliec acid amplification test): performed on the patient’s nasopharyngeal swab or sputum.

43
Q

What are the important properties of C. psittaci?

A

Same as C. pneumoniae :

• Pleomorphic, poorly Gram stained.

• Obligate intracellular bacteria (unable to produce its own ATP).

• Absent peptidoglycan in the cell wall.

• Chlamydiae have a replicative cycle different from that of all other bacteria.

• Visible as cytoplasmic inclusion bodies on Giemsa stain or fluorescent antibody-stained smear

• Very difficult cultivation

44
Q

How is C.psittaci transmitted?

A

•C. psittaci infects birds (e.g., parrots, psittacine, pigeons, and poultry, and many mammals).

•Humans are infected primarily by inhaling organisms in dry bird feces.

45
Q

Pathogenesis of C.psittaci

A

•C. psittaci infects the lungs primarily.

•No toxins or virulence factors known.

46
Q

Clinical findings of C.psittaci

A
  • The infection may be asymptomatic (detected only by a rising antibody titer)

-or may produce high fever and pneumonia that presents as atypical pneumonia
1. non-productive cough
2.headache
3. arthralgia
4. myalgia

47
Q

Laboratory diagnosis of C.psittaci

A

• IgG and IgM antibodies in patient’s serum.

•Cytoplasmic inclusion seen by special stains.

•Polymerase chain reaction (PCR) of respiratory specimens.

M3 l Microbiology (7 decks)

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