Presentation on theme: "Obligate aerobe acid-fast rods TUBERCULOSIS OVERVIEW, CAUSE, AND PATHOGENESIS Tuberculosis, MTB, or TB (short for tubercle bacillus) common, and in many."— Presentation transcript:
TUBERCULOSIS OVERVIEW, CAUSE, AND PATHOGENESIS Tuberculosis, MTB, or TB (short for tubercle bacillus) common, and in many cases lethal infectious disease caused by various strains of mycobacteria usually Mycobacterium tuberculosis Mycobacterium tuberculosis, was identified and described on 24 March 1882 by Robert Koch Tuberculosis may infect any part of the body most commonly occurs in the lungs pulmonary tuberculosis
Tuberculosis holds a special place in medical history Can humble master clinicians challenge public health authorities treatable and preventable WHO over 8 million cases 2 million deaths occur worldwide each year 25% to 33% of the world’s population with silent latent infection with M. tuberculosis
Tuberculosis in the United States is now largely a disease of the disadvantaged Tuberculosis in the United States is now largely a disease of the disadvantaged In 2006, there were 13,767 reported cases of TB in the United States In 2006, there were 13,767 reported cases of TB in the United States cases were reported in every state cases were reported in every state drug-resistant cases drug-resistant cases co-infection with M. tuberculosis and HIV co-infection with M. tuberculosis and HIV estimated 10 to 15 million persons remain latently infected estimated 10 to 15 million persons remain latently infected
Mycobacterium tuberculosis slightly curved or straight rod-shaped bacillus requires special acid-fast stains to be visualized It is closely related to M. bovis primarily pathogen of cattle and related animals M. tuberculosis is also related to M. leprae leprosy
Tuberculosis is spread from person to person through the air by droplet nuclei 1 to 5 m in diameter that have been expulsed into the air Cough is the primary means by which tubercle bacilli are aerosolized singing, sneezing, or speaking may contribute to a lesser extent Droplet nuclei small enough to remain suspended in the air for long time The probability of transmission depends on numerous factors source case exposed contact air space shared
Usual pathogenesis of tuberculosis. About 5% of infected persons develop clinical disease within the first year of infection; another 5% develop reactivation later during their lives.
TB pathogenesis begins when a droplet containing viable tubercle bacilli is inhaled Bacilli then spread through the pulmonary lymphatics reach lymph nodes may become enlarged Efferent lymphatics then carry bacilli into the systemic circulation the lungs, the brain, kidneys, and bones Tubercle bacilli replicate relatively slowly dividing time within 18 to 24 hours 20 minutes for most common pathogens Thus, the process of local, lymphatic, and eventual systemic spread described above typically requires several weeks
PULMONARY TUBERCULOSIS Worldwide, tuberculosis remains the most common cause of death Pulmonary tuberculosis is the most common manifestation and the form of the disease usually responsible for its transmission The usual patient with pulmonary tuberculosis presents with a history of several weeks of a progressive illness The most important pulmonary symptom is cough Constitutional complaints coexist and may predominate fever, chills, night sweats, weight loss, appetite loss, and easy fatigability
HIV and TB HIV has greatly increasing the risk of TB Diagnosis of TB in patients with HIV can be difficult Suspicion of TB is an indication for HIV antibody testing
Laboratory diagnosis 1- Mantoux skin test (Tuberculin) 2- Chest X-ray 3- Isolation of Mycobacterium species Löwenstein–Jensen medium (L.J medium) Löwenstein–Jensen medium (L.J medium) microscopic positive results for acid-fast bacilli microscopic positive results for acid-fast bacilli 4- Identification of microbial genetic material molecular methods such as PCR molecular methods such as PCR
Positive skin test - tuberculosis indicates exposure to organism indicates exposure to organism does not indicate active disease does not indicate active disease
The Mantoux skin test consists of an intradermal injection of one-tenth of a milliliter (ml) of PPD tuberculin.
The size of induration is measured 48–72 hours later. Erythema (redness) should not be measured.
Mantoux test injection site in a subject without chronic conditions or in a high-risk group clinically diagnosed as negative at 50 hours
Skin testing for tuberculosis, using the Mantoux test.
Microscopic Examination of Mycobacterium The Mycobacteria are aerobic acid fast, non-motile, non- spore forming rods M. tuberculosis is a non-spore forming, non capsulated straight or slightly curved rod, measuring 1-4µm x 0.2-0.6 µm The most common pathogens that cause disease to man are M. tuberculosis, M. bovis, M. africanum, and M.microti
Laboratory diagnosis M. tuberculosis acid fast bacteria – sputum TB in Sputum
M. tuberculosis is best demonstrated by using the Ziehl -Neelsen technique or a fluorescence technique. When stained by ZN, they appear as thin pink rods arranged singly or in groups. Once stained, they resist decolorization with 2% H2SO4 and alcohol or 3% HCl in 95% ethyl alcohol (Acid-fast, Alcohol fast).
Cultural Characteristics and colony morphology M. tuberculosis is strict aerobic grows very slowly (2-4 weeks) egg enriched medium Lowenstein-Jensen medium giving dry creamy colored colonies Other selective media as Middlebrook 7H10, 7H11 agar and 7H9 broth used for primary isolation antibiotic susceptibility testing M. tuberculosis is a non chromogen does not grow on media contain p-nitrobenzoic acid these characteristics help to differentiate them from M. avium, M. intracellulare, and M. kansasii
The optimum temperature for growth is at 37C The culture must be incubated up to 12 weeks M. tuberculosis produces rough, and tough colonies on glycerol and pyruvate egg media They are niacin producers and grow under aerobic conditions at 37 C
TB Culture Cultivation and culture characteristics of Tubercle bacilli on Lowenstein Jensen medium (raised dry cream colored colonies)
Antibotic treatment - tuberculosis extensive time periods (e.g. 9 months) extensive time periods (e.g. 9 months) organism grows slowly, or dormant organism grows slowly, or dormant two or more antibiotics two or more antibiotics e.g. rifampin and isoniazid e.g. rifampin and isoniazid resistance minimized resistance minimized
Tuberculosis and Drug resistance Multiple drug resistant (MDR) resistant to first line drugs Extremely drug resistant (XDR) Resistant to some of the second line drugs Nearly un-treatable