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Flashcards in Section 2: Mycobacteria Deck (26)
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1

What are the characteristics of Mycobacterium

-Nonmotile
-Aerobic
-Non spore forming
-Cell morphology= bacilli
-Cell wall is 40% lipid
-Acid fast

2

What is Mycobacterium tuberculosis

Discovered as a causative agent ofTB by Robert Koch in 1882
• At the time TB killed I in 7 people, currently infects I in 3 worldwide. Total about 2 billion, kills about 3 million

3

What are the characteristics of Mycobacterium tuberculosis

-Thin pleomorphic rods
-No capsules
-Appear "beaded" when stained due to high lipid content of cell wall
• Very resistant to drying and chemicals
• Can remain alive and viable for weeks or months - Obligate aerobe
-Colony morphology is unique-rough irregular
-Growth is very slow, divide every 12 to 24 hours

4

What is the cell wall chemistry of Mycobacterium tuberculosis

composed of mycosides-glycolipids found ONLY in acid fast bacteria

5

What is Cord Factor

formed by the union of 2 mycolic acids with a disaccharide (trehalose)
• Cord factor is found only in virulent strains of M tuberculosis
• Its presence results in a parallel growth of the bacteria, so they appear as cords.
• Exactly how leads to virulence is unknown

6

What are Sulfatides

mycosides that resemble cord factor with sulfates attached to the disaccharide • Inhibit lysosome function in phagocytic cells

7

What is Wax D

complicated mycoside that acts as an adjuvant

8

What is the epidemiology of Mycobacterium tuberculosis

-Tuberculosis is primarily a disease of humans
-Transmitted by close person to person contact via aerosolized droplets
• Large droplets are trapped on mucosal surfaces and removed
• Small droplets containing 1-3 M tuberculosis organisms can reach alveoli and establish an infection
-Transmission via objects is also possible
-A person with untreated, active tuberculosis can infect an estimated 20 other people per year

9

What is the pathology of Mycobacterium tuberculosis (long)

-Primary infection
• Bacteria inhaled in droplet nuclei, land in the lower respiratory tract
• Infiltration of macrophages and neutrophils
• Phagocytosed bacteria are taken to regional lymph nodes
• Bacteria are not killed, multiply and survive in the phagocytes= intracellular
• Move through the lymphatic system to infect other tissue
• Some macrophages do successfully destroy bacteria and present antigens to helper T cells to activate cell mediated immunity
• T cells enter circulation and search forM. tuberculosis.
• When T cells encounter bacteria they release lymphokines to attract and activate macrophages. • Activated macrophages can now destroy M tuberculosis
• Activated macrophages attack, lung tissue becomes damaged and local necrosis of lung tissue occurs
• Foci of the infection is called the Ghon complex and the necrosed tissue is called caseous necrosis The entire structure is called a granuloma or a tubercle
• Within the tubercle bacteria are kept from spreading, but remain viable
• As cell mediated immunity develops

10

What is the secondary infection of Mycobacterium tuberculosis

• Most cases ofTB occur after the bacteria are dormant for some time
• The infection can occur in any of the organ systems "seeded" during the primary infection
• The temporary weakening of the immune system causes reactivation-many AIDS patients develop TB in this way
• I /3 of HIV infected person are also infected with M tuberculosis worldwide

11

What are sites of reactivation

• Pulmonary TB-most common site. Areas of infection grow, liquidity and cavitate. Clinically= weight loss, night sweats, cough with blood
• CNS -TB causes meningitis and forms granulomas in the brain
• Genital infection
• Bone infections-usually involves the spine, destroying intervertebral discs (Pott's disease) • Joint infection
• Skin infection
• Miliary TB-tiny millet-seed sized tubercles (granulomas) are disseminated all over the body. The kidneys, liver, lungs and other organs are filled with tubercles

12

How is Mycobacterium tuberculosis clinically diagnosed

Tuberculin Mantoux Test
• Tests skin sensitivity to TB antigens

13

How is Mycobacterium tuberculosis diagnosed un the laboratory

w-Isolation of tubercle bacilli using selective media
-Use of biochemical tests
-Acid fast stain

14

What is Mycobacterium bovis

• Pathogen of cattle
• Can be transmitted to humans in raw milk
• Human infection with M bovis is often not pulmonary, causes infection of bone, cervical lymph nodes

15

What are atypical Mycobacteria

• Atypical = non-tuberculosis
• Found in many places in the environment: tap water, fresh and ocean water, milk, bird droppings, soil, and house dust.
• The manner in which these bacteria are transmitted is not completely understood.
• There is no evidence of person to person transmission

16

What are the 4 groups of Atypical Mycobacteria

Photochromogens
Scotochromogens
Non-photochromogens
Rapid growers

17

What are Photochromogens

produce yellow pigment when exposed to light

18

What are Scotochromogens

produce orange pigment in light OR dark

19

What are Non-photochromogens

-Closely related toM tuberculosis
-Usually infects birds (can infect other animals)
-Major cause of bacterial infection in HIV patients

20

What are Rapid Growers

See growth in 2-3 days
-M. phlei-widely distributed in soil and dust and on plants
-M smegmatis-originally isolated from human smegma

21

What is Mycobacterium leprae

• Acid fast rod shaped bacteria
• CANNOT be grown in laboratory culture, intracellular microbe

22

What is the epidemiology of Mycobacterium leprae

• Children more susceptible
-Cell mediated immune response is not as strong
• Males more susceptible
-Bacteria grows in cooler body temperature, testes often infected
• Transmission
-Poorly understood, not highly infectious. Attempts to infect human volunteers have failed.
-Direct contact
-Found in respiratory secretions, so droplet transmission is possible
-Very slow grower, incubation is from 3-10 years

23

What are the two types of Mycobacterium leprae

1: Lepromatous leprosy
2: Tuberculoid leprosy

24

What is Lepromatous leprosy

Progressive
• Most severe, patient can't mount cell-mediated immune response
• Infects every organ, but the primarily the skin, nose, testes and nerves
• Large numbers of bacteria present
• Changes are seen mostly in skin

25

What is Tuberculoid leprosy

Less severe, patients can mount a cell-mediated response
• Skin damage is not as excessive and disease is milder and non-progressive
• Nerve involvement is common, but in patches.
• Most frequently enlarged nerves are closest to the skin, the auricular, the ulnar, the posterior tibial and the peroneal.
• Difficult to find bacteria in tuberculoid leprosy

26

How is Mycobacterium leprae diagnosed

Unable to grow M leprae in laboratory culture, must grow in
• Mouse food pads
• Armadillos