Microbiology Lesson 10: Mycobacteria PDF

LESSON 10: Mycobacteria LECTURER: Dr. Eunice L. Estella INTRODUCTION: TUBERCULOSIS 1 MYCOBACTERIUM TUBERCULOSIS COMPLEX Tuberculosis is an airborne disease. M. tuberculosis​ M. caprae​ Abo...

LESSON 10: Mycobacteria LECTURER: Dr. Eunice L. Estella INTRODUCTION: TUBERCULOSIS 1 MYCOBACTERIUM TUBERCULOSIS COMPLEX Tuberculosis is an airborne disease. M. tuberculosis​ M. caprae​ About 1 million Filipinos have active tuberculosis. M. bovis​ M. microti​ This is the third highest prevalence rate in the world. M. bovis BCG​ M. canettii​ It is a highly curable disease, yet it is the number one killer M. africanum​ M. pinnipedii among all infectious diseases. 2 NONTUBERCULOUS MYCOBACTERIA (NTM) Every day, more than 70 people lose their lives to tuberculosis in the Philippines. A. MYCOBACTERIUM TUBERCULOSIS COMPLEX Many more patients develop drug-resistant tuberculosis A1. PATHOGENESIS which are more expensive and difficult to treat. A1.1 MYCOBACTERIUM TUBERCULOSIS I. GENERAL CHARACTERISTICS STATISTICS Mycobacterium tuberculosis is a cause of most cases of ORGANISMS THAT BELONG TO THE GENUS human tuberculosis, particularly in developed countries. MYCOBACTERIUM ARE: An estimated 1.7 billion people or ⅓ of the world’s 1 AEROBIC population are infected with M. tuberculosis. Although some may grow in reduced oxygen concentrations. MODE OF TRANSMISSION 2 NON-SPORE FORMING Inhalation of a single viable organism has been shown to Except for M.marinum lead to infection, although close contact is usually 3 NON-MOTILE necessary. 4 VERY THIN, SLIGHTLY CURVED OR STRAIGHT RODS ○ Immunocompromised state 0.2 to 0.6 um x 1 to 10 um Among those who because infected with tuberculosis, only SOME SPECIES MAY DISPLAY A BRANCHING 15-20% develop the disease. 5 MORPHOLOGY ○ The disease usually occurs some years after the initial 6 CELL WALL CONTAINS N-GLYCOLYL MURAMIC ACID infection, when the patient’s immune system breaks Mycobacterium have an unusual cell structure. down for some reason other than the presence of ○ They have N-glycolyl muramic acid instead of tuberculosis bacilli in the lungs. N-acetyl muramic acid. ○ In a small percentage of the infected host, the disease It has a very high lipid content which creates a becomes systemic, which affects a variety of organs. hydrophobic permeability barrier. Because of this structure, Mycobacteria are difficult to A1.2. MYCOBACTERIUM BOVIS stain with commonly used basic aniline dyes. After ingestion of Milk from Infected cow, Mycobacterium ○ Such as those used in gram-staining. bovis may penetrate the gastrointestinal mucosa or invade 7 GENERALLY CONSIDERED GRAM POSITIVE the lymphatic tissue of the oropharynx. Even though these organisms are not generally stained by BACILLUS CALMETTE-GUERIN (BCG) gram. An attenuated strain of M. bovis, bacillus Calmette-Guérin RESIST DECOLORIZATION WITH ACIDIFIED ALCOHOL 8 (BCG). (3% HCl) ○ It has been used to immunize susceptible individuals After prolonged application of a basic fuchsin dye or with against tuberculosis. heating of the dye after its application. Because Mycobacteria are the classic examples of This important property of Mycobacteria which derives intracellular pathogens, and the body’s response to BCG from their cell wall structure is referred to as Acid hinges on cell-mediated immunoreactivity, immunized Fastness. individuals are expected to react more aggressively against ○ Acid Fastness— a characteristic that distinguishes all antigens that elicit cell-mediated immunity. mycobacteria from other genera. In rare cases, an unfortunate individual's immune system is GROW MORE SLOWLY THAN MOST OTHER HUMAN so compromised that it cannot handle the BCG, and so 9 PATHOGENIC BACTERIA BECAUSE OF THEIR systemic BCG infection may develop. HYDROPHOBIC CELL SURFACE. Another important feature. A2. SIGNS AND SYMPTOMS OF TUBERCULOSIS Because of this hydrophobicity, organisms tend to clump, so that nutrients are not easily allowed into the cell. A single cell’s generation time may range from approximately 20 to 36 hours for Mycobacterium ulcerans. ○ Generation time— the time required for a cell to divide into two independent cells. The slow growth results in the formation of visible colonies in 2 to 60 days at optimum temperature. II. MAJOR GROUPS OF MYCOBACTERIA Mycobacteria can be divided into two major groups. Signs and Symptoms of Tuberculosis ○ Based on fundamental differences and epidemiology and association with the disease. This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 1  MICROBIOLOGY | Lesson 10: Mycobacteria Tuberculosis may mimic other diseases such as pneumonia, ○ Caseous— consistency is like cheese. neoplasm, or fungal infections. In addition, clinical manifestations in patients infected with A4.2 MENINGEAL OR MILIARY (DISSEMINATED) M. tuberculosis complex may range from asymptomatic to TUBERCULOSIS acutely symptomatic. Symptomatic patients can have systemic symptoms: ○ Either pulmonary signs or symptoms ○ Signs or symptoms related to other organ involvement such as the kidney. ○ Or a combination of these features. Cases of pulmonary disease caused by M. tuberculosis complex are clinically, or radiologically, and pathologically indistinguishable. Primary tuberculosis typically is considered a disease of the respiratory tract. Miliary Tuberculosis of the Lung COMMON PRESENTING SYMPTOMS INCLUDE In some patients infected with primary active tuberculosis, 1 Low-grade fever 4 Anorexia (loss of appetite) the disease may spread via the lymphatic system or 2 Night sweats 5 Weight loss hematogenously. 3 Fatigue ○ Millary— disseminated tuberculosis. This most often occurs in patients with depressed or PULMONARY TUBERCULOSIS ineffective cellular immunity. A patient who presents with pulmonary tuberculosis usually has a productive cough, along with low-grade fever, chills, A4.3 OTHER ORGAN INVOLVEMENT myalgias (aches), and sweating. In a small percentage of patients, organs besides the lungs However, these signs and symptoms are similar to other can become involved after infection with M. tuberculosis diseases such as influenza, acute bronchitis, and complex organism. pneumonia. ○ These organs include the: Genitourinary Tract A3. SPECTRUM OF DISEASE The Cervical Lymph Nodes The Nervous System (results in Meningitis) Bone And Joints (Arthritis and Osteomyelitis), Also found in the Peritoneum and Pericardium. A5. DIAGNOSIS A5.1 TUBERCULIN TEST OR PURIFIED PROTEIN DERIVATIVE (PPD) TEST Spectrum of Disease: Tuberculosis TB Disease Pathway TB DISEASE PATHWAY Upon respiratory infection with an M. tuberculosis complex Tuberculin test organism, the cellular immune system T-cells and 1 One way to diagnose tuberculosis. macrophages migrate to the lungs, and the organism are Based on the premise of after infection with M.tuberculosis. phagoctized by the macrophages. However, these organisms are capable of intracellular BASIS OF TEST— PD Test 2 multiplication in the macrophages. Individual develops a delayed hypersensitivity cell-mediated So often, the host is unable to eliminate the organism and immunity to certain antigenic components of the organism. 3 the result is the systemic hypersensitivity to Mycobacterium antigens. DISADVANTAGE: SENSITIVITY AND SPECIFICITY — PD Test Granulomas (a hard tubercle) form in the lung from the Disadvantage: The PPd test is not 100% sensitive or lymphocytes, macrophages, and cellular pathology specific. 4 including giant cell formation, or the cellular fusion A positive reaction to the skin test does not necessarily displaying multiple nuclei. signify the presence of disease. Different interpretative criteria are used for different patient A4. POSSIBLE OUTCOMES populations. A4.1 TISSUE NECROSIS (CASEOUS NECROSIS) If the Mycobacterium antigen concentration is high, the hypersensitivity reaction may result in tissue necrosis caused by enzymes released by the macrophages. In this case, low granuloma forms, and the solid/semi-solid caseous material is left at the primary lesion site. This transcript is strictly confidential and is intended for AVR 5TH FLOOR group members only; please don’t share or distribute! 2  MICROBIOLOGY | Lesson 10: Mycobacteria PROCEDURE — PD Test has been incubated overnight with a mixture of synthetic peptides simulating two proteins in M. tuberculosis. The test assesses responses to multiple antigens can be performed in a single patient visit Less subject to reader bias and error An important feature is that the results of the assay are unaffected by previous BCG vaccination. Flow of the procedure for PD Test. B. NONTUBERCULOUS MYCOBACTERIA (NTMs) A culture extract of M. tuberculosis is injected 1 Includes all mycobacterial species that DO NOT BELONG to intracutaneously. Mycobacterium TB complex. After 48 to 72 hours, an infected individual shows a Currently approx. 130 species NTM are recognized. delayed hypersensitivity reaction to the PPD. This is Present everywhere in the environment. characterized by: 2 Sometimes colonize the skin, respiratory and GI tracts of ○ Erythema (redness) healthy individuals. ○ Most importantly: Induration — firmness as a Little is known about how infection is acquired. result of influx of immune cells) The diameter of the induration is measured and then MODE OF TRANSMISSION 3 interpreted as to whether the patient has been infected with Trauma M. tuberculosis. Inhalation of infectious aerosols and ingestion Few diseases are nosocomial or are acquired as an RESULTS AND INTERPRETATION — PD Test iatrogenic infection. NTMs are NOT usually transmitted from person to person (in TUBERCULIN TEST contrast to MTM) nor does the isolation of these organisms ≥ 5 mm necessarily mean they are associated with the disease HIV positive process. Recent contact with an active TB patient INTERPRETATION OF (+) NTM CULTURE Nodular or fibrotic changes on chest X-ray Complicated Organ transplant Because these organisms are widely distributed in nature and their pathogenic potential varies greatly from one ≥ 10 mm specie to another. Recent arrivals (