Mycobacterium

Question 1

Properties of mycobacteria

Answer 1

Non spore forming, aerobic rods.

Question 2

Classification of mycobacteria

Answer 2

Tb complex
Mycobacterium Leprae
Atypical mycobacteria

Question 3

TB complex

Answer 3

Mycobacterium tuberculosis
Mycobacterium Africanum
Mycobacterium bovis

Question 4

Atypical mycobacteria

Answer 4

Photochromogenes
Scotochromogenes
Non chromogenes
Rapid Growers

Question 5

Photochromogenes

Answer 5

Mycobacterium kansasii

Mycobacterium marinum

Question 6

Scotochromogenes

Answer 6

Mycobacterium scrofulaceum

Question 7

Non-chromogenes (they are non-pigmented or have light tan or buff
coloured colonies)

Answer 7

Mycobacterium avium-intracel/ulare complex

Mycobacterium ulcerans

Question 8

Rapid growers (growth in <7days)

Answer 8

Mycobacterium fortuitum complex

Mycobacterium smegmatis

Mycobacterium phlei

Question 9

General characters of mycobacteria

Answer 9

Slender, straight or slightly curved rods with rounded ends.

Acid-fast, non-sporogenous and non-capsulated.

Z -N staining is employed for identification.

Obligate aerobes. Increased CO2 tension enhances growth.

Highly resistant to drying.

Question 10

Constituents of the cell wall

Answer 10

Lipids
Proteins
Polysaccharides

Question 11

Lipids

Answer 11

Mycobacteria are rich in lipids. These include mycolic acids (long
chain fatty acids C7s-C90), waxes and phosphatides. Lipids are largely bound
to proteins and polysaccharides. Muramyl dipeptide from peptidoglycan
complexed with mycolic acids can cause granuloma formation,
phospholipids induce caseous necrosis. Lipids are to some extent responsible
for acid fastness.

Question 12

Protein

Answer 12

Contains several proteins, those bound to a wax fraction upon injection can induce tuberculin sensitivity

Question 13

Polysaccharides

Answer 13

Can induce an immediate hyper sensitivity reaction and can serve as antigens

Question 14

Virulence factors

Answer 14

Cord factor
Sulfatides
Lipoarabinomannan
Heat shock protein

Question 15

Cord factor

Answer 15

It is a surface glycolipid
Inhibits migration of leucocytes causes chronic granuloma, and can serve as an immunologic adjuvant.

Question 16

Sufatides

Answer 16

Surface glycoprotein
Prevents fusion of phagosomes with lysosomes in microphage and allowing the bacterium escape the degradative action of lysosomal enzymes

Question 17

Lipoarabinomannan

Answer 17

Heteropolysaccharides
Inhibits microphage activation by interferon gamma
Induces macrophage to secrete TNF ALPHA WHICH CAUSES FEVER, WEIGHT LOSS, AND TISSUE DAMAGE.
Induces IL 10 which suppresses mycobacteria induced Tcell poliferation

Question 18

Heat shock protein

Answer 18

Highly immunogenic

Question 19

Pathogenesis

Answer 19

After inhalation of bacteria ~~~~~ reach alveolar space and phagocystosed by alveolar macrophage ~~~~~~~ spread to hylar lymph nodes and into blood stream ~~~~~~ non specific inflammatory response at initial focus ~~~~~~ delayed hypersensitivity ~~~~~~~ granulomatous formation ~~~~~~ Ghons complex.

Question 20

Primary infection Vs secondary infection

Answer 20

Primary infection. Secondary Infection
Lesion: Small Large
Lymphatic
Involvement: Yes Minimal
Cavity
Formation: Rare. Frequent
Tuberculin
Reactivity : initially negative Positive
Site : any part of lung
Usually lower lobe Apical region
Local spread : Uncommon. Frequent

Question 21

Types of tuberculous infection

Answer 21

Pulmonary

Exttrapulmonary :
TB plueral effusion
Tuberculosis menigitits
miliary TB
Renal and urogenital TB
Bone and joint TB
TB enteritis

Question 22

Lab Diagnosis of TB

Answer 22

Tuberculin Test
Intradermally 0.1 to 5 PPD tuberculin
Wheal: 6mm to 10mm
48 to 72 hours after injection

Question 23

Tuberculin test reactivity

Answer 23

> /= 5mm of induration : HIV, immunosupressive therapy, recent TB contact.

> /= 10mm immigrants from high prevelance countries, injection drug users. Children younger than 4 years old, AIDS patient

> /= 15mm : low risk of TB

Question 24

Specimen

Answer 24

Sputum
Broncho alveolar lavage, pleural fluid, csf, urine, stool, aspiration, blood for haematogenoud TB

Question 25

Microscopy in TB diagnosis

Answer 25

Light Mciroscopy

Fluorescent microscopy

Question 26

Light microscopy staining and findings

Answer 26

Z-N staining
Findings: Bright red, straight or slightly curved, beaded rods on green blue background.

Question 27

Reporting of sputum smear

Answer 27

10AFB/field: +++
1-10 AFB/field:++
10-100AFB/field: +
1-9 AFB/ 100 fields : exact number

Question 28

Flourescent microscopy stain

Answer 28

Auramine- rhodamine stain

TB bacilli are yellow in dark background in flourescent microscope.

Sensitive than Z-N stain

Question 29

Culture is done in which medias

Answer 29

Semi synthetic agar media
Middlebrook 7H10 7H11

Inspissated egg media : lowenstein jensen media

Broth media : 7H9 7H12

Question 30

Advantages of Bactec Rapid radiometric culture system

Answer 30

Rapid diagnosis
Determining drug susceptibility
Specificity is very high

Question 31

Disadvantage of bactec

Answer 31

Expensive
Radioactive hazards

Question 32

Treatment of TB

Answer 32

Resistant to INH and rifampicin : for 18-24 months
fluoroquinolone,
ethambutol
Pyrazinamide
Streptomycin

Resitant to all first line : second line drugs

Question 33

Prevention of TB

Answer 33

BCG vaccine

Treatment of asymptomatic tuberculin test positive patients.