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34 Cards in this Set

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What are the general characteristics of Mycobacteria?
unique cell wall structure - resembles G+ bacteria but does not fall into G+ category
slow-growing (3-8 wks to obtain colony)
acid-fast staining characteristics

2 medically important species:
Describe the structure of Mycobacteria.
Cell wall composed of complex branched lipid and sugar molecules

lipid component comprises 60% of cell wall weight

cell wall contains mycolic acids - waxy long-chain fatty acids that make bacteria resistant to degradation and attack
What are general characteristics of M.tuberculosis?
facultative intracellular pathogen capable of causing lifelong infection

strictly aerobic

causes Tuberculosis
estimated that 1/3 of the world population is infected with M.tuberculosis
How do people become infected with M.tuberculosis?
person with pulmonary tuberculosis coughs, generating aerosolized droplets containing M.tuberculosis

aerosol particles with bacteria inhaled by uninfected person and lodge in the terminal air spaces in the lung, where bacteria are taken up by alveolar macrophages

bacteria survive and multiply within macrophages

bacteria survive within macrophages by preventing acidification of phagosome

organism spreads to local lymph nodes and disseminates to remote sites
How do people develop a primary infection of Tuberculosis?
primary infection is controlled by host immune response and is usually asymptomatic, but organism is rarely completely eradicated

cellular immune response results in formation of tubercles, which are microscopic granulomas that consist of giant cells, epithelioid cells, and lymphocytes

dying macrophages release their toxic products, resulting in necrosis of the center of the tubercle - called caseating granulomas
How do people develop Tuberculosis disease?
10% of infected patients undergo reactivation, leading to clinical signs and symptoms of tuberculosis

factors that increase probability of progression to disease: advanced age, alcoholism, HIV infection, malnutrition, immunosuppressive drugs

reactivation is what leads to cough, spreading organism to the next host
What are the characteristics of Tuberculosis disease?
fever, weight loss, night sweats

2 main groups:
pulmonary TB - most common, productive cough with blood-tinged sputum, cavities at apex of lung
extrapulmonary TB - disease occurs at other organs or sites; in order of frequency, the following organs may be involved: lymph nodes, pleura, genitourinary tract, bones and joints, meninges, peritoneum

Miliary TB - widely disseminated TB infection not controlled by immune system, hepatomegaly, splenomegaly, lymphadenopathy
How is Tuberculosis diagnosed?
PPD skin test:
PPD = purified protein derivatives composed of partially purified transport proteins and porins from the mycobacterial cell wall that are important antigens

Chest X-ray

laboratory detection of mycobacterium - growth of M.tuberculosis from clinical specimens such as sputum
How are Tuberculosis infections treated?
slow growth makes M.tuberculosis resistant to almost all antibiotics

6-9 month regimens with multiple antibiotics used:
What are the general characteristics of Mycobacterium leprae?
obligate intracellular pathogen - does not grow in cell-free cultures

causes Leprosy

very slow division times - divides once every 11-13 days
What are the pathogenic mechanisms of M.leprae?
direct human to human transmission

organism surrounded by dense, inert lipid capsule - secretes no toxins

directly causes nerve demyelination by killing Schwann cells
What clinical diseases are caused by Mycobacterium leprae?
Tuberculoid Leprosy - strong cellular immune reaction, few bacteria in tissues, low humoral response, hypopigmented anesthetic macular skin lesions with raised edges and depressed center, large palpable peripheral nerves, neuronal damage leads to muscle atrophy and contractures, especially of hands and feet

Lepromatous Leprosy - strong humoral response, abundance of bacteria in macrophages, raised skin lesions of any shape, septal perforation and nasal collapse lead to saddle-nose, nerve involvement leads to loss of peripheral sensation
How is M.leprae diagnosed?
does not grow on media or culture

diagnosed by histologic examination of biopsy of skin lesion
How is M.leprae treated?
6-12 months of dapsone and rifampin +/- clofazimine
What are general characteristics of Spirochetes?
G- bacteria with characteristic spiral shape

cannot be viewed by Gram stain

visualized by darkfield microscopy or direct fluorescent antibody (DFA)

3 important genera:
Borrelia - Lyme's disease
Leptospira - leptospirosis
Treponema - syphilus
What are the medically important species of Borrelia?
Borrelia burgdorferi (Lyme disease):
transmitted to humans exclusively through contact with ticks during blood meal

Borrelia recurrentis (relapsing fever):
transmitted to humans via ticks and lice
Describe the life cycle of Lyme disease spreading ticks.
Spring - eggs deposited
Summer - eggs become larvae, larvae feed on mice, birds, small mammals
Fall and Winter - no feeding
Spring - larvae become nymphs, feed on squirrels, birds, and small mammals
Winter - nymphs become adults and feed on deer and large mammals
Spring - lay eggs and start cycle again
What characteristic of Borrelia burgdorferi enables the bacteria to persist in two very different environments, ticks and animals?
Outer surface proteins (Osp) functions thought to play a role in this

Osp A and B are plasma-encoded and primarily expressed while organism is in the tick

Osp C is upregulated during tick feeding
Describe the clinical disease caused by Borrelia burgdorferi.
infection progresses through 3 stages:

1. Early infection, stage 1 - after tick bite, erythemia migrans (EM) rash expands outward and has central clearing at site of the bite, lesion due to cutaneous spread of organism outward from site of inoculation

2. Early infection, Stage 2 - days to weeks after onset of EM, organisms disseminate to the blood, leading to arthralgias, fever, chills, malaise, meningitis, cranial nerve palsies, and cardiac arrhythmias

3. Late infection, Stage 3 - months after infection, arthritis, encephalopathy
How is Borrelia burgdorferi diagnosed?
diagnosis made by recognition of clinical symptoms, then confirmed via serologic testing (ELISA with confirmatory western blotting)

visualized by Giemsa, Wright, and acridine orange stains

difficult to grow in culture
How is B.burgdorferi treated?
early disease and arthritis - oral doxycycline or amoxicillin

neurologic abnormalities and cardiac involvement - IV ceftriaxone
What are general characteristics of Borrelia recurrentis?
causes recurrent fever and malaise every 4-14 days

Tick-bourne relapsing fever (TBRF)

Louse-bourne relapsing fever (LBRF)
Describe infections caused by Leptospira interrogans.
obligate aerobic spirochete

causes infections in rats, cattle, dogs

transmitted to humans following exposure to water contaminated with animal urine (ingestion, cuts in skin, exposure of conjunctiva)
What are the clinical symptoms of Leptospira infection?
Primary phase - fever, chills, headache, muscle pains; symptoms reside after a week as bacteria are cleared from bloodstream

Secondary phase - 1-3 days later recurrence of symptoms, 15% of pts develop meningitis
Describe the general characteristics of Treponema pallidum.
causes syphillis

There are other Treponema diseases usually seen in tropical climates that are not sexually transmitted and manifest as infectious skin lesions:
T.pallidum subspecies pertenue causes yaws
T.pallidum subspecies endemicum causes bejel
T.carateum causes pinta
Describe the general characteristics of Rickettsiaceae.
obligate intracellular bacteria
small G- coccobacilli
zoonotic infections - transmission is often by insect vectors

4 important genera:
What are the medically important species of Rickettsia?
R.rickettsii - Rocky Mountain spotted fever
R.typhi - murine typhus
R.tsutsugamushi - scrub typhus
R.prowazekii - epidemic typhus
R.akari - rickettsialpox
What are the pathogenic mechanisms of Rickettsia rickettsii?
requires host cell nucleotide cofactors and ATP to multiply

transmitted to humans via tick bites

uses bacterial protein OmpA to attach to endothelial cells and induces its own engulfment by endothelial cells, bacteria replicates in the cytoplasm

disseminate via lymphatics and bloodstream
How is Rickettsia rickettsii treated?
Doxycycline is drug of choice

treatment should not be withheld for pending diagnostic tests
What are the general characteristics of Coxiella burnetii?
cause of Q fever - fever, pulmonary infiltrates, NO rash

harbored by sheep and other animals

spread by aerosols during birth of lambs or other animals

most cases are self-limiting
What are the general characteristics of Ehrlichia chaffeensis?
transmitted by ticks

infects monocytes and macrophages, grow within phagolysosome

pt. presents with fever, headaches, myalgias, thrombocytopenia, leukopenia

minority of pts develop a rash
What are the general characteristics of Anaplasma phagocytophilum?
transmitted by ticks

causes human anaplasmosis

infects neutrophils

higher mortality rates than erhlichiosis
What are the general characteristics of Chlamydia and Chlamydophila?
complicated intracellular and extracellular life cycles

3 medically important species:
Chlamydia trachomatis - causes STD chlamydia
Chlamydophila pneunomiae - causes pneumonia
Chlamydophila psittaci - causes pneumonia
What are general characteristics of Mycoplasma pneumoniae?
smallest free-living and self-replicating organisms

lack a cell wall - thus, do not Gram stain

tightly adheres to cilia and microvilli on surface of bronchial epithelium

common cause of community-acquired pneumonia