Mycobacteria Flashcards
What are mycobacteria and why are they unique?
Mycobacteria are a group of bacteria, including those that cause tuberculosis and leprosy, characterized by a high lipid content (waxes) in their cell wall. This waxy coat makes them resistant to disinfectants and interferes with Gram staining, making them acid-fast.
What happens during post-primary tuberculosis?
Post-primary tuberculosis is the reactivation of dormant lesions in individuals with some immunity. It mainly occurs in 5% of infected people, more commonly in those with AIDS. It is chronic and involves slow progression.
What is the Ziehl-Neelsen (Z/N) stain used for?
The Ziehl-Neelsen (Z/N) stain is a special staining procedure used for identifying mycobacteria, as they are acid-fast and resist decolorization by mineral acids.
What are non-tuberculous mycobacteria?
Non-tuberculous mycobacteria, like M. kansasii, M. avium, and M. intracellulare, cause infections similar to tuberculosis. These species are more resistant to antituberculous drugs and are more common in immunocompromised individuals.
What is primary tuberculosis?
Primary tuberculosis occurs after inhalation of tubercle bacilli, where the bacteria multiply in the lungs. The infection usually remains inapparent, forming a primary complex with lesions in the lungs, draining lymph nodes, and spreading to other parts of the body.
How is tuberculosis diagnosed in the laboratory?
Diagnosis includes microscopic examination of sputum smears stained by Ziehl-Neelsen or fluorescent dyes. Cultures on special media like Lowenstein-Jensen take 3-6 weeks to grow, and the bacteria are tested for drug sensitivity.
How is immunity to tuberculosis tested?
Immunity is tested using the tuberculin (Mantoux) test, where purified protein derivative (PPD) is injected intradermally. The size of the resulting induration (swelling) indicates previous exposure to Mycobacterium tuberculosis.
What is Mycobacterium leprae and what does it cause?
Mycobacterium leprae is the bacterium that causes leprosy (Hansen’s disease). There are two main forms of the disease: tuberculoid leprosy and lepromatous leprosy.
What is Treponema pallidum and what diseases does it cause?
Treponema pallidum is a spiral-shaped bacterium that causes syphilis, which progresses through stages: primary (chancre), secondary (rash, mucosal lesions), latent, and late syphilis.
What are the characteristics of lepromatous leprosy?
Lepromatous leprosy has many erythematous macules, papules, and nodules with severe tissue destruction. It has a high infectivity, with numerous bacilli present in the tissues.
How is leprosy transmitted?
Leprosy is primarily transmitted from person to person via respiratory droplets. In rare cases, it may also be transmitted through an animal reservoir, such as armadillos.
What are the characteristics of tuberculoid leprosy?
Tuberculoid leprosy has few erythematous plaques, peripheral nerve damage with sensory loss, and enlarged nerves. The infection has a low infectivity and very few bacilli in infected tissues.
How is syphilis diagnosed?
Syphilis is diagnosed with serological tests, such as non-treponemal tests (VDRL, RPR, Wassermann) and treponemal tests (FTA-ABS, MHA-TP). Darkfield microscopy can identify T. pallidum from lesion exudates, but it must be done immediately.
What are spirochetes?
Spirochetes are spiral-shaped, Gram-negative microorganisms that include Treponema, Leptospira, and Borrelia species. They are responsible for diseases like syphilis, leptospirosis, and Lyme disease.
What is the treatment for tuberculoid and lepromatous leprosy?
Tuberculoid leprosy is treated with dapsone and rifampin, while lepromatous leprosy requires dapsone, rifampin, and clofazimine. Prompt treatment is necessary to control the disease.
What is the treatment for Lyme disease?
Early Lyme disease is treated with doxycycline, amoxicillin, or cefuroxime. Prolonged treatment is required for neurological or musculoskeletal manifestations.
How is Lyme disease diagnosed?
Diagnosis of Lyme disease is commonly done through serology (ELISA, immunofluorescence). Microscopy and culture are not typically used due to the difficulty in identifying B. burgdorferi.
How is syphilis prevented?
Syphilis can be prevented through education on sexually transmitted infections (STIs), condom use, and periodic serological testing of high-risk individuals, including testing during pregnancy.
What is Lyme disease and how is it transmitted?
Lyme disease is caused by Borrelia burgdorferi and transmitted by Ixodes ticks. It can affect the skin, joints, nervous system, and heart.
How can Lyme disease be prevented?
Prevention includes avoiding ticks, wearing protective clothing, and using tick repellents. A vaccine against B. burgdorferi is available and targets the ospA antigen of the bacteria.
What diseases are caused by Chlamydia trachomatis?
C. trachomatis causes sexually transmitted diseases such as urethritis in men, cervicitis in women, and pelvic inflammatory disease (PID). It also causes trachoma (leading cause of blindness in some regions), inclusion conjunctivitis, and lymphogranuloma venereum (LGV).
What are the two biovars of Chlamydia trachomatis?
The two biovars of C. trachomatis are trachoma (causing blindness) and lymphogranuloma venereum (causing inguinal lymphadenopathy).
What are Chlamydia species and their unique characteristics?
Chlamydia are obligate intracellular bacteria that cannot produce their own ATP. They have a unique life cycle with two forms: the infectious elementary body and the reticulate body.
What is Chlamydia pneumoniae and what does it cause?
Chlamydia pneumoniae causes respiratory infections, ranging from pharyngitis to atypical pneumonia, often mild and subclinical. It is spread through respiratory droplets.
What is Chlamydia psittaci and how does it affect humans?
Chlamydia psittaci is primarily a bird pathogen that can infect humans, leading to pneumonia or systemic infections like endocarditis.
What is Mycoplasma pneumoniae and what does it cause?
Mycoplasma pneumoniae is the most common cause of atypical pneumonia, primarily affecting people aged 15-35. It can cause respiratory disease and rarely more severe infections like meningoencephalitis or myocarditis.
What are mycoplasmas and their characteristics?
Mycoplasmas are the smallest free-living bacteria, measuring 100-300 nm. They can grow on artificial media and are part of the normal flora in the oropharynx and genital tract, but some species are pathogenic.
What is the significance of fungal infections in immunocompromised individuals?
Fungal infections are increasing due to factors like AIDS, organ transplantation, and chemotherapy, which lower cell-mediated immunity, making individuals more susceptible to fungal infections.
How is Mycoplasma pneumoniae treated?
M. pneumoniae is treated with erythromycin or tetracycline.
What are hyphae in fungi?
Hyphae are threadlike, branching structures composed of fungal cells attached end to end.
What are dimorphic fungi?
Dimorphic fungi are fungi that can grow as either yeast or mold, depending on environmental conditions like temperature.
How are fungal infections categorized?
Fungal infections are categorized by the depth of skin affected: superficial, cutaneous, subcutaneous, and systemic.
What is the difference between molds and yeast in fungi?
Molds are multicellular and form mycelia (clumps of hyphae), while yeast are unicellular and reproduce by budding, forming pseudohyphae if they don’t separate.
What are cutaneous fungal infections?
Cutaneous fungal infections, caused by dermatophytes like Microsporum, Trichophyton, and Epidermophyton, affect skin, hair, and nails, causing conditions like athlete’s foot, jock itch, and ringworm. Treatment often involves topical imidazoles.
What are superficial fungal infections?
Superficial fungal infections include pityriasis versicolor (caused by Malassezia furfur) and tinea nigra (caused by Exophiala werneckii), which affect skin pigmentation and are treated with selenium sulfide
What is Candida albicans and what infections does it cause?
Candida albicans causes oral thrush, diaper rash, and vaginitis, and can infect various parts of the body, especially in immunocompromised individuals.
What are subcutaneous fungal infections?
Subcutaneous infections include sporotrichosis (caused by Sporothrix schenckii) and chromoblastomycosis (caused by Phialophora and Cladosporium), which typically arise from puncture wounds and can cause nodules, ulcers, and necrosis.
What are systemic fungal infections?
Systemic fungal infections are caused by dimorphic fungi like Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides immitis. They cause lung infections and may spread to the bloodstream. Diagnosis involves inhalation of spores, not person-to-person transmission.
What is Cryptococcus neoformans and what disease does it cause?
Cryptococcus neoformans is a yeast that causes meningoencephalitis, primarily in immunocompromised individuals. It is treated with amphotericin B and flucytosine.
What is Aspergillus flavus and what infections can it cause?
Aspergillus flavus is a mold that can cause hypersensitivity reactions, invasive pneumonias, and disseminated diseases in immunocompromised individuals. It also produces mycotoxins like aflatoxin, contaminating food products like peanuts.
