L14: mycobacterial infections

Question 1

Mycobacterium tuberculosis morphology

Answer 1

Acid fast, mycolic acids, unusual lipids
Obligate aerobes
Slender slightly curved rod shaped bacillus
Non-motile

Question 2

Mycobacterium tuberculosis virulence factors

Answer 2

NO classic virulence factors or toxins

Question 3

Agents that cause TB infection

Answer 3

Mycobacterium tuberculosis complex:

Mycobacterium tuberculosis: Human only reservoir: respiratory person-to-person

Mycobacterium bovis: cattle, consumption of unpasteurized milk, infected animals/humans

Mycobacterium africanum: west african countries, may be spread through food, opportunistic

Question 4

higher risk for TB infection

Answer 4

prolonged exposure, crowded housing conditions, close contact, children infected by caregivers, alcoholism, IVDU, malnutrition, DM, immunosuppression, silicosis: pneumoconiosis (inhalation of silica dust)

Question 5

mycobacterium tuberculosis infects

Answer 5

very old or very young, bimodal distribution, immunocompromised

Question 6

TB presentation ins infants and immunocompromised

Answer 6

hematogenous dissemination→ meningitis, other sx

Question 7

TB presentation in older patients

Answer 7

failure of immune system→ reactivation of latent infection

Question 8

TB MOA

Answer 8

Droplets→ alveoli→ phagocytosis by macrophages→ prevents fusion with lysosomes while allowing nutrient containing vesicles to merge
Innate and cell-mediated host response→ self-destruction of cells and tissues

Question 9

general symptoms of TB

Answer 9

insidious onset, nonspecific cough, weight loss, night sweats
Immune competent: confined to lungs, contained in a few weeks, most resolve TB infection

Question 10

Immediate resolution of TB

Answer 10

cleared by alveolar macrophages, no active case of TB

Question 11

Primary active TB

Answer 11

Restricted to lower lung, (+)skin test

granuloma→ +/- progression and calcification→ CXR: tubercles, ghon bodies

Question 12

Progressive primary TB/Active TB

Answer 12

Immune system can’t stop bacteria from multiplying
One/both upper lobes involved
Contagious, exp: immunocompromised

Question 13

Latent infection TB

Answer 13

Well patients with inactive TB bacteria
May be viable in lesions for long periods
No symptoms, not contagious

Question 14

how to kill TB

Answer 14

pasteurization as they’re heat sensitive

Question 15

Skin testing of TB

Answer 15

MTB protein derivative (PPD): Mantoux skin test

Measures size of induration after 48-72 hours

Question 16

what’s a “booster”?

Answer 16

a person with past TB infection but minimal PPD reaction→ 2nd skin test

Question 17

why is TB difficult to stain/culture

Answer 17

Unusual lipids + mycolic acids

slow growth phenotype

Question 18

how to stain TB

Answer 18

Acid fast→ resist decolorization→ Ziehl-Neelsen or Kinyoun stains

Question 19

MTB

Answer 19

TB test: stimulates isolated T cell to produce IFN-gamma→ quantify

Question 20

GeneXpert

Answer 20

TB nucleic acid amplification test: presence of MTB and rifampin resistance

Question 21

non TB mycobacterial agents (2)

Answer 21

Mycobacterium avium Complex (MAC) and Mycobacterium kansasii

Question 22

Mycobacterium avium Complex (MAC) and Mycobacterium kansasii morphology

Answer 22

Weakly G+ aerobic bacilli
Acid fast
Slow growing
Opportunistic

Question 23

how MAC and MK presents in middle aged/older male smokers

Answer 23

cavitary lesions resemble TB

Question 24

how MAC and MK presents in Elderly female non-smokers

Answer 24

patchy or nodular CXR

Lady windermere’s syndrome

Question 25

other MAC and MK presentation

Answer 25

Solitary pulmonary nodule

Question 26

how MAC and MK presents in AIDs patients

Answer 26

Disseminated disease: no organ spared | HAART and abx prophylaxis→ less infections

Question 27

how to definitively identify MAC/MK

Answer 27

PCR for 16S rRNA sequence

Question 28

MAC/MK on culture

Answer 28

acid fast

Question 29

MAC and MK are spread by

Answer 29

Any water source, soil, plants: ingestion | NO person-to-person transmission: no isolation required

Question 30

Mycobacterium abscesses

Answer 30

Especially in cystic fibrosis: drug resistance=hard to treat | Rare in normal population

Question 31

Cell wall of TB

Answer 31

peptidoglycan layer Mycolic acids Lipoarabinomannan Cord factor

Question 32

Mycolic acids

Answer 32

long chain fatty acids prevent dehydration, resist H2O2

Question 33

Lipoarabinomannan

Answer 33

mycoside: glycolipid mycolic acid + disaccharide

Question 34

Cord factor

Answer 34

inhibits cell mediated immunity, scavenges reactive oxygen intermediates (ROI)

Question 35

Insidious TB reactivation

Answer 35

cough, weight loss, ever, fatigue, night sweats, chest pain

Question 36

Lesions in TB reactivation

Answer 36

caseous lesions with necrosis→ erosion→ discharge TB bacilli into bronchi→ contagious

Question 37

Miliary TB reactivation

Answer 37

Erode blood vessels→ hematogenous spread to other body sites: any organ→ miliary TB (massive spread)