Mycobacterium tuberculosis

Non-motile, non-spore-forming, aerobic, have high amounts of Guanine and Cytosine in their DNA, slow-growing, and most are weakly Gram-positive. They have lipid-rich cell walls that are: — Acid-fast — Resistant to detergents and antibiotics — Contain antigens that stimulate the host immune response. Layers of the Cell Wall: — Cytoplasmic membrane — Peptidoglycan layer - tends to stain weakly Gram-positive — Arabinogalactan layer is a branched polysaccharide macromolecule that comprises arabinose and galactose residues; it links to the peptidoglycan layer, below. — Mycolic acids, which comprises long-chain fatty acids; these acids contribute to the low permeability of Mycobacteria cell walls. Be aware that some authors describe an outer capsule or capsule-like material. Primary cause of tuberculosis 18-hour doubling time Produces non-pigmented colonies Mycobacterium tuberculosis grows on Lowenstein-Jensen agar. Cord factor (aka, trehalose dimycolate) is a lipid component of the cell wall that contains mycolic acids and gives virulent strains of Mycobacterium tuberculosis a "serpentine cord" arrangement. Obligate human pathogens; humans are its only reservoir. Transmitted in respiratory droplets, especially sputum produced by individuals with severe secondary pulmonary infections. HIV-positive individuals and those with other cellular immunodeficiencies, including organ transplant recipients, are more susceptible to serious infection. Intracellular pathogen. Virulence factors promote bacterial survival and replication in host cells: — Secretion systems and adhesins facilitate host cell invasion — Inhibition of phagosome-lysosome fusion allows the bacteria to avoid degradative lysosomal enzymes — Resistance to reactive oxygen species and nitric oxide, which are otherwise bactericidal — Prevention of cellular apoptosis, which allows the bacteria to replicate intracellularly; it is thought that, when the host cell is no longer useful, the bacteria promote necrosis, which facilitates their spread to new tissues and/or new hosts. — In summary, these virulence factors promote long-term survival of the pathogen; thus, tuberculosis is a disease of chronic inflammation. Treatment for tuberculosis is complex, and involves long-term use of multiple antibiotics. Detection: — Microscopy is a fast way to identify Mycobacteria by their acid-fast cell walls. — Nucleic acid-based tests are then used to determine the specific species of Mycobacterium. — Cultures taken from respiratory secretions can also be useful; however, remember that Mycobacteria have slow growth rates. — Molecular probes and mass spectrometry can be used to identify Mycobacteria. Infection sites Hematogenous or lymphatic spread of Mycobacterium tuberculosis can lead to disseminated infections or localized infections in specific organs. When the lesions are very tiny, this is called "Miliary tuberculosis." The most common site of infection. Characterized by granulomas and scarring; secondary infections can produce caseation and cavitation. Symptoms include fever, night sweats, chest pain, coughing up blood, fatigue, and weight loss. Pulmonary tuberculosis is often accompanied by infection of nearby lymph nodes. Most commonly nodes in the cervical region — "Scrofula" Infected nodes tend to be non-tender, firm, and discrete. As infection progresses, nodes may form a mass of nodules. Associated with renal transplants. Accounts for approximately 30% of extrapulmonary tuberculosis. Patients often have sterile pyuria (elevated white blood cell count without evidence of bacterial growth) and microscopic hematuria. Be aware that tuberculosis can spread through the urinary tract and to the genital tract. Most commonly effects the thoracic vertebrae, especially in children and young adults. Spinal tuberculosis, aka, Pott's disease, often produces Kyphosis or other deformities. Most often occurs after ingestion of contaminated milk or swallowed respiratory tract mucus. Infection can involve the gastrointestinal tract, often where the ileum and cecum meet, as well as the peritoneum and abdominal lymph nodes. Ulcerative lesions are common. Characterized by subcutaneous nodules on the anterior surface of the lower extremities. Most lethal form of infection. Tends to affect young children and HIV-positive adults. Associated with hyponatremia (low blood sodium concentration). Associated with cattle; zoonotic infection when contaminated meat or unpasteurized milk is consumed. Mycobacterium bovis bacillus Calmette-Guerin (BCG) is a derivation of Mycobacterium bovis. — Used in a childhood vaccine to prevent some forms of tuberculosis infection. Tuberculosis-causing strain endemic to West Africa. Mycobacterium tuberculosis culture (CDC/Dr. George Kubica). Histology (Mark Braun, MD: http://medsci.indiana.edu/c602web/602/c602web/toc.htm). M. tuberculosis (National Institute of Allergy and Infectious Diseases (NIAID)). M. tuberculosis in sputum (https://www.medicalimages.com/stock-photo-image-image9922493.html; Medical Images RM / GLORIA BAPTIST). Chest (CDC). Mycobacterium tuberculosis culture (CDC/Dr. George Kubica). Pulmonary caseation (Wikipedia; Author Yale Rosen). Kyphosis (Permission from MusicNewz).