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What are the characteristics of Mycobacterium

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


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


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


What is the cell wall chemistry of Mycobacterium tuberculosis

composed of mycosides-glycolipids found ONLY in acid fast bacteria


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


What are Sulfatides

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


What is Wax D

complicated mycoside that acts as an adjuvant


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


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


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


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


How is Mycobacterium tuberculosis clinically diagnosed

Tuberculin Mantoux Test
• Tests skin sensitivity to TB antigens


How is Mycobacterium tuberculosis diagnosed un the laboratory

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


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


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


What are the 4 groups of Atypical Mycobacteria

Rapid growers


What are Photochromogens

produce yellow pigment when exposed to light


What are Scotochromogens

produce orange pigment in light OR dark


What are Non-photochromogens

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


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


What is Mycobacterium leprae

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


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


What are the two types of Mycobacterium leprae

1: Lepromatous leprosy
2: Tuberculoid leprosy


What is Lepromatous leprosy

• 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


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


How is Mycobacterium leprae diagnosed

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