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bspharma2 > MYCOBACTERIA AND ATYPICAL PNEUMONIA > Flashcards

MYCOBACTERIA AND ATYPICAL PNEUMONIA Flashcards

1
Q

MYCOBACTERIA

A

 rod-shaped, obligate aerobic bacteria
 derive energy from the oxidation of many simple carbon compounds
 growth rate is slower than other bacteria
 do not stain readily
 cannot be classified as gram-positive or gram-negative
 acid-fast – resist decolorization by acid or alcohol

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2
Q

MYCOBACTERIA

A

 Mycobacterium tuberculosis
 Mycobacterium leprae
 Mycobacterium avium complex (M. avium-intracellulare)
 Mycobacterium bovis

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3
Q

Mycobacterium tuberculosis

A

 Koch’s Bacillus
 Culture Medium:
Inspissated Egg Media (e.g.
Löwenstein-Jensen) – contain salts, glycerol, complex organic substances (eg, fresh eggs or egg yolks, potato
flour, malachite green)

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4
Q

Mycobacterium tuberculosis
Virulence Factors

A

 Lipids (in cell wall) – responsible for
acid fastness
 Mycolic acid (long chain fatty acids C78- C90) – can cause granuloma formation; resists drying
 Cord factor - inhibits migration ofleukocytes, causes chronic granulomas
 Waxes
 Phosphatides – induce caseous necrosis
 Proteins
 elicit tuberculin reaction and antibody
production

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5
Q

Mycobacterium tuberculosis
Pathogenesis

A

Primary Complex
* granuloma (tubercle) formation due to migration of macrophages (cell-mediated immunity)
* caseous necrosis at the center of the granuloma
* formation of Ghon lesion/focus – calcified granuloma; visible under X-ray Mycobacterium tuberculosis
* formation of Ghon complex – Ghon lesion/focus
+ regional lymphadenopathy

Latent TB
* dormancy of bacilli in the granuloma

Reactivation/Secondary Tb
* reactivation of dormant bacilli due to depressed cell-mediated immunity or reinfection

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6
Q

Mycobacterium tuberculosis
Pathogenesis

A

Spread in the host via 3 ways:
1- Direct Extension
2- Lymphatic Spread – through regional lymph nodes
3- Hematogenous Spread – to all organs (miliary distribution)

Intracellular Growth
 reside principally intracellularly
in monocytes, reticuloendothelial cells, and giant cells

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7
Q

Mycobacterium tuberculosis
Clinical Findings: Primary
Complex

A

 occurs usually in childhood
 usually involves the base of the lungs
 Features:
 CXR: Ghon complex
 Positive TST

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8
Q

Mycobacterium tuberculosis
Clinical Findings: Latent TB

A

 no clinical manifestations
 Host is noninfectious

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9
Q

Mycobacterium tuberculosis
Clinical Findings: Reactivation/Secondary TB

A

Causes:
 Endogenous – dormant bacilli in the primary lesion (more common)
 Exogenous – reinfection

tubercle bacilli that have survived in the primary lesion

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10
Q

Mycobacterium tuberculosis
Clinical Findings: Reactivation/Secondary TB

A

usually involves the apex of the lung,
where O2 tension is highest

Features:
 chronic tissue lesions, formation of
tubercles, caseation, and fibrosis
 regional lymph nodes are only slightly
involved, w/o caseation
 CXR: infiltrate and cavity w/ air-fluid level

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11
Q

Mycobacterium tuberculosis Clinical
Findings:
Tuberculosis (Koch’s Disease)

A

 fatigue, weakness, weight loss, fever, and night sweats

 Pulmonary TB: chronic cough, hemoptysis

 Spinal/ TB (Pott’s disease) – involves ≥2 adjacent vertebral bodies

 Miliary TB: bloodstream dissemination, infection of many organs

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12
Q

Mycobacterium tuberculosis
Diagnosis

A

TST: Latent TB, Past Infection
Culture (Löwenstein-Jensen Medium): gold standard
Acid Fast Smear (Ziehl-Neelsen method)
Chest X Ray
Gene Xpert MTB/RIF

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13
Q

Tuberculin Skin Test (TST)

A

 a.k.a. Mantoux test
 Purified Protein Derivative (PPD)
 obtained by chemical fractionation of old tuberculin (a
concentrated filtrate of broth in which tubercle bacilli have grown for 6 weeks)
 injected on the inner surface of the forearm
 examined within 48-72 hrs after injection
 (+) result: induration/wheal formation
 due to type IV hypersensitivity

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14
Q

Tuberculin Skin Test (TST)

A

 may be negative upon isoniazid treatment
 may become positive after bacillus Calmette-Guérin (BCG) vaccination

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15
Q

Acid Fast Smear/AFB Microscopy

A

 low sensitivity (40–60%)
 Ziehl-Neelsen method
 2 sputum specimens
 collected early in the morning
 Positive = ≥1 positive sputum smear
 Negative = both sputum smears are negative

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16
Q

Chest X Ray

A

 high sensitivity but poor specificity
 for diagnosis of PTB in children who cannot expectorate (<5 y/o): CXR + TST

17
Q

Gene Xpert MTB/RIF

A

 rapid diagnosis of TB with high specificity and sensitivity
(approaching that of liquid culture)
 fully automated, real-time nucleic acid amplification technology
(PCR method)
 can simultaneously detect TB and rifampin resistance in <2 h
 has minimal biosafety and training requirements
 recommended by WHO as first-line diagnostic test in all adults and
children with S/Sx of active TB
 negative Xpert MTB/RIF result does not exclude TB

18
Q

Mycobacterium tuberculosis
Prevention

A

BCG vaccine

 ID
 from Mycobacterium bovis
 attenuated bovine organism
 given at birth
 local tissue response begins 2–3 weeks after vaccination, w/
scar formation and healing w/n 3 months
 decreasing immunity 15-20 years after initial immunization at
infancy

19
Q

Mycobacterium
tuberculosis
Treatment

A

DOTS (Directly Observed
Treatment, Short Course)

20
Q

1st LINE AGENTS for TB

A

H = isoniazid

R = rifampin

Z = pyrazinamide

E = ethambutol

21
Q

RESISTANCES

A
  • MONORESISTANT TB – one 1st line
    agent
  • RR TB – rifampicin resistant
  • POLY-DRUG RESISTANT TB – >1 1st
    line agent other than HR combined
  • MULTI-DRUG RESISTANT TB
    (MDR-TB) – at least both HR
22
Q

Mycobacterium leprae

A

 often found within the endothelial cells of blood vessels or in mononuclear cells
 Transmission:
respiratory droplets (eg, cough and sneezing)
requires prolonged and close contact

23
Q

Mycobacterium leprae Clinical
Findings:

A

Leprosy (Hansen’s Disease)

 insidious onset
 involve the cooler tissues (skin, superficial nerves, nose, pharynx, larynx, eyes, and testicles)

 Skin Lesions:
 pale, anesthetic macular lesions
 diffuse or discrete erythematous, infiltrated nodules
 diffuse skin infiltration

 Neurologic Disturbance: nerve infiltration and thickening, anesthesia,
neuritis, paresthesia
 bone resorption
 shortening of the digits (fingers)

24
Q

Mycobacterium leprae Clinical
Findings: Leprosy (Hansen’s Disease)

A

 Lepromatous Leprosy
 progressive and malignant
 nodular skin lesions with abundant acid-fast bacilli
 slow, symmetric nerve involvement
 negative lepromin skin test result
 defective cell-mediated immunity
 continuous bacteremia

 Tuberculoid Leprosy
 benign and nonprogressive
 small number of macular skin lesions with few bacilli
 sudden asymmetric nerve
involvement
 positive lepromin skin test result
 intact cell-mediated immunity

25
Q

Mycobacterium leprae Diagnosis

A

 AFB Smear
 scrapings from skin or nasal mucosa or biopsy of earlobe skin
 Ziehl-Neelsen Method

26
Q

Mycobacterium leprae Treatment

A

 Dapsone (DOC)
 Lepromatous: Dapsone + Rifampin + Clofazimine
 Tuberculoid: Dapsone + Rifampin

27
Q

Mycobacterium avium complex
(M. avium intracellulare)

A

 infrequently causes disease in immunocompetent humans
 one of the most common opportunistic infections of bacterial
origin in patients with AIDS and also in cystic fibrosis

 Pathogenesis:
 colonization of the respiratory tract or GIT
 transient bacteremia followed by invasion of tissues
 involvement of any organ

 S/Sx: fever, night sweats, abdominal pain, diarrhea, and weight
loss

28
Q

Mycobacterium bovis

A

 causes TB-like disease
 source of BCG ( Bacillus Calmette-Guerin)

29
Q

ATYPICAL PNEUMONIA

A

Systemic findings with pulmonary
component
Does not respond to β-lactam
antibiotics
Diffuse pneumonia
M. pneumoniae
L. pneumophila
C. pneumoniae Virus

30
Q

TYPICAL PNEUMONIA

A

Clinical and laboratory findings are
limited to the lungs
Respond to β-lactam antibiotics
Lobar/segmental pneumonia
S. pneumoniae
H. Influenza

31
Q

BACTERIA THAT CAUSE ATYPICAL
PNEUMONIA

A

 Legionella pneumophila
 Mycoplasma pneumoniae
 Chlamydophyla pneumoniae

32
Q

Legionella pneumophila

A

 caused an outbreak of pneumonia in persons attending an
American Legion convention (due to contaminated air- conditioning systems) in Philadelphia in 1976
 fastidious, aerobic gram-negative bacteria
 Culture Medium: Buffered Charcoal Yeast Extract (BCYE) Agar with
α-ketoglutarate, L-cysteine, and iron

33
Q

Legionella pneumophila Clinical
Findings: Legionnaires Disease

A

 atypical pneumonia: lobar, segmental, or patchy pulmonary
infiltration
 asymptomatic infection is common
 nondescript febrile illness of short duration or a severe, rapidly
progressive illness with high fever, chills, malaise, nonproductive
cough, hypoxia, diarrhea, and delirium
 high risk: smoking, alcohol misuse, diabetes mellitus, chronic
bronchitis and emphysema, cardiovascular disease, steroid and
other immunosuppressive treatment, cancer chemotherapy, and
anti–tumor necrosis factor (TNF)-α therapy

34
Q

Legionella pneumophila Clinical
Findings: Pontiac Fever

A

 after the clinical syndrome that occurred in an outbreak in Michigan
 fever and chills, myalgia, malaise, and headache
 dizziness, photophobia, neck stiffness, and confusion
 self-limiting

35
Q

Mycoplasma sp.

A

 the smallest organisms that can be free living in nature and self-
replicating on laboratory media
 no cell wall
 requires sterol in the plasma membrane

 Culture Medium: Horse Serum and Yeast Extract → “fried-egg”
appearance

36
Q

Mycoplasma pneumoniae Clinical
Findings: Walking Pneumonia

A

 mild disease
 from asymptomatic infection to serious pneumonitis, w/
occasional neurologic and hematologic (ie, hemolytic anemia)
involvement
 malaise, fever, headache, sore throat, and cough
 there may be blood-streaked sputum and chest pain

37
Q

Other Cell-Wall Defective Bacteria

A

 Mycoplasma hominis – postpartum fever, uterine tube infections

 Ureaplasma urealyticum – nongonococcal, nonchlamydial
urethritis in men

 Mycoplasma genitalium – chronic nongonococcal urethritis,
cervicitis, endometritis, salpingitis, infertility

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