Microbiology: Intracellular bacteria, mycobacteria, and spirochetes Flashcards
1
Q
Intracellular bacteria
A
- Includes Rickettsiae, Chlamydiae, and Mycobacteria
- These cannot reproduce outside of their host cells
- Can be acquired directly from blood (rickettsia), mucosa (M tuberculosis), and enterally
2
Q
Rickettsiae
A
- Small GN coccobacilli (obligate intracellular) that do not stain w/ gram stain but do stain w/ giemsa
- Energy parasites that have ATP transport system to use host ATP supplies
- Transmitted by arthropod vectors (ticks, mites, fleas, lice)
- Cause rocky mountain spotted fever
- Targets endothelial cells
- Separated into groups based on Ag composition: spotted fever group, typhus group, and scrub typhus group
3
Q
Pathogenesis of Rickettsiae
A
- Inoculated into dermis of skin by a tick bite or an open wound
- Bacteria spread through blood stream and infect epithelia, causing destruction of the endothelial cells due to replicating bacteria
- The bacteria attach to the cells, are phagocytosed, and then replicate (binary fission) in cytoplasm
- Can move within the endothelial cells via F actin
- Release and spread as filopodia
- Leakage of fluid from brain can lead to encephalitis
- Immune cells produce INF-g and TNF-a activate killing of the bacteria by autophagosome and subsequent lysosome fusion
4
Q
Rocky mountain spotted fever
A
- Caused by rickettsia rickettsii
- Fever 4-10 days after tick bite, along w/ muscle pain, headache, lymphadenopathy (swollen lymph nodes)
- Rash from extremities to trunk (sometimes on palms and soles)
- Dx by culture (requires BSL-3 condition), also microimmunofluorescence (MIF) against outer membrane proteins and LPS (followed by western/PCR to confirm)
- Rx is doxycycline
5
Q
Epidemic Typhus
A
- From louse-borne rickettsia prowazeckii (closest relative to mitos)
- Contains microcapsule and slime layer, life cycle requires lice (reservoirs: humans, flying squirrels)
- Bacteria enter blood from scratching caused by the lice, allowing them to infect endothelial cells
- Usually occurs in crowded, unsanitary places
6
Q
Pathogenesis of epidemic typhus
A
- Bacteria can multiply within endothelial cells, causing vasculitis and thrombosis
- 1 week after infection there is fever, severe headache, and myalgia (muscle pain). 5 days later there is petechial rash under arms which radiates outward to entire body
- Dx is clinical presentation + potential conditions for lice, detection of Abs to rickettsial Ags in serum, isolation from culture
- Prevention: delousing, vaccination, Rx w/ choloramphenicol or tetracycline
7
Q
Chlamydiae
A
- Small intracellular obligate rods with a specific form of LPS, no peptidoglycan (GN, susceptible to osmosis), and are ATP parasites
- 2 main genera: chlamydia and chlamydophila
- They form metabolically inactive infectious elementary bodies (EB, to enter cells) and metabolically active but noninfectious reticulate bodies (RB, to replicate within the cells)
- EBs are resistant to harsh conditions like spores
8
Q
Chlamydia trachomitis
A
- Growth: EB binds to receptors on susceptible (nonciliated) epithelial cells and are internalized by endo/phagocytosis
- EBs become RBs in endosome, bacteria prevents fusion of endosome w/ lysosome to avoid degradation
- RBs replicate by binary fission in endosome and become EBs again, and are eventually released by lysis or extrusion
- Immune system does not produce lasting immunity
- Causes UTI, trachoma (roughening of inner surface of eyelids), conjunctivitis (pink eye), pneumonia, an lymphogranuloma venereum (LGV, swollen ilial lymph nodes)
- Divided into 3 biological variants (biovars): trachoma, LGV, mouse neumonitis
- Human biovars divided into serovars (serological variants) based on their outer membrane protein
- Dx by molecular amplification, Rx by doxycycline or erythromycin
9
Q
Mycobacteria
A
- Obligate intracellular aerobic rods that are non-motile, non-spore forming
- Complex lipid-rich cell wall (very hydrophobic), containing mycolic acids (responsible for acid fast stain)
- Composition of cells wall responsible for acid fastness, slow growth, resistance to detergents and antibios, and antigenicity
- On top of the mycolic acids in cell wall it also has arabinogalactan, and mannose-capped lipoarabinomannan
- Can survive and replicate within phagocytes, making them inaccessible to circulating Abs (requires cellular)
10
Q
Mycobacterium Tuberculosis
A
- Weakly GP acid fast rods
- Capable of intracellular growth in alveolar macrophages
- Disease primarily host response to infection
- IC, alcohol/drug patients are most likely to acquire
- Humans are only reservoir, spread by infectious aerosols
- Disease usually isolated to pulmonary infection
- Dx by skin test, microscopy, culture, and PCR
- Rx is long to prevent drug-resistant strains. Used Isoniazid (INH), ethambutol, pyrazinamide, and rifampin for 2 months. Followed by 2 months of INH+rifampin (used in prophylaxis as well)
11
Q
Mycobacterium leprae
A
- Weakly GP acid fast rods
- Cannot be cultured on artificial media
- Contains capsule for intracellular growth
- Disease mostly from host response
- Lepromatous, but not tuberculoid, disease is highly infectious
- Spread by direct contact or inhalation of infected aerosols
- Can cause tuberculoid form of leprosy or lepromatous form
- Dx from microscopy (only sensitive to lepromatous form), skin testing for tuberculoid leprosy
- Rx for tuberculoid form: rifampficin and dapsone for 6 mo
- Rx for lepromatous form: add clofazimine to tuberculoid Rx and extend Rx to 12 mo
12
Q
Tuberculoid leprosy
A
- Causes a strong cellular response but weak humoral response
- Infected tissues have many lymphocytes and granulomas but few bacteria
- Bacteria causes large production of IL2 and IFN-g resulting in activation of macrophages
13
Q
Chronic delayed-type hypersensitivity granulomas
A
- Host immune response to intracellular bacteria is cause of tissue injury and disease (bacteria resist dying in phagosomes)
- As a result they can persist and cause chronic inflammation, causing granulomas surrounding the bacteria
- This results in deposition of scar tissue (in TB much of the respiratory difficulty is caused by replacement of normal tissue w/ scar tissue
14
Q
Tuberculin skin test
A
- Extracted + purified outer cell wall Ags are injected to see exposure to M tuberculosis
- Induration can be 5, 10 or 15 mm. The larger the induration the more difficult it is to pass the test (i.e. only ppl who fail w/ induration of 5 are IC, evidence from CXR)
15
Q
Spirochetes
A
- Thin, helical GN bacteria
- Can swim via flagella
- 2 main pathogenic families: Lyme borreliosis (lyme disease) and Leptospirosis
- They call cause mulit-system inflammatory disorder
16
Q
Borrelia Burgdorferi
A
- Causes Lyme disease
- GN but stain w/ aniline (giesma)
- Genome contains linear chrom plus linear and circular plasmids
- World-wide tick borne illness (usually in summer, most frequent tick-transmitted illness in US)
- B burgdorferi found in US and Europe, other two strains (B garinii and B afzelii found in Europe and Asia)
- Reported in 49 states, mostly in Northeast, Midwest, Pacific West and Southeast
- Life cycle is: larva-> nymph-> adult (feeds on blood of deer and humans)
- Lives in Ixodes ticks, which is the vector of transmission
- Grows in Kelly’s medium
17
Q
Pathogenesis of lyme disease
A
- Causes erythema chronic migrans (ECM) or erythema migrans (EM)
- Characterized by flat reddened area w/ central clearing (usually develops 2-23 days after infection at site of tick bite)
- This starts as a red macule that expands to become a ring-like lesion
- Accompanying it are malaise, fatigue, headache, fever, chills, myalgias/arthralgias, arthritis, lymphadenopathy
- Bacteremia occurs in untreated patients within days to weeks
- Once sepsis occurs other symptoms may arise: cardiac dysfunction (myopericarditis, CHF), nephritis, and neurologic signs (facial palsy, meningitis, encephalitis)
- Possible to develop late lyme disease consisting of arthritic (most common), neurologic, musculoskeletal and/or cardiac complications weeks-years after exposure due to deposition of Ag-Ab complexes
18
Q
Lyme disease Dx
A
- CDC defines it as: EM + laboratory confirmation or one late manifestation
- CDC criteria for Dx: isolation of bacteria, or demonstration of IgM/IgG levels to spirochetes, or increase in Ab btw acute/convalescent serum samples
- Clinical manifestations often used for diagnosis, along w/ indirect immuno-fluorescnece assay (IFA, measures IgM) + western to confirm
- Culturing is possible but low-yield (under dark field microscopy)
19
Q
Lyme disease Rx and prevention
A
- Early administration of amoxicillin, doxycycline or ceftriaxone lessens likelihood and severity of late complications
- Patients w/ recurrent arthritis or PNS diseases required prolonged IV antibios
- 3 stages in infection: 1) skin lesions and flu symptoms, 2) arthritis with cardiac abnormalities, chronic meningitis, neuritis, and 3) dementia, nerve demyelination, destruction of bones + joints
- Prevention: tight fitting clothes, avoid animals (no vaccine), use alcohol on skin
20
Q
Leptospirosis
A
- Caused by leptospira interrogans
- Fine, tightly coiled spirals, curved at ends to form hooks
- Seen under dark field microscopy
- Motile, obligate aerobe, is culturable
- World wide zoonotic disease (sources are pets/livestock contamination of water)
- Enters through skin abrasions or mucous membranes
- Infects all tissues from blood
21
Q
Pathogenesis of leptospirosis
A
- Can present as a sub-clinical mild flu and fever w/ myalgia and then remit
- Or can progress to systemic infection (Weill’s disease) w/ fever, jaundice, renal and hepatic failure, vasculitis, myocarditis, hepatitis, meningitis and death
- Once in blood from skin or mucosa, it progresses to liver, kidneys, CNS
- Causes hemorrhage, necrosis, jaundice
- Acute phase lasts 3-10 days, followed by afebrile period, followed by recurrence of fever and severe symptoms
22
Q
Dx, Rx, and prevention of leptospirosis
A
- Culture of blood and/or CSF w/in 10 days of onset, use urine after 10 days
- Seen w/ dark field microscopy or giemsa stain
- Can use microscopic agglutination test (MAT) w/ serum
- Rx is IV penicillin or doxycycline, tetracycline to treat renal infection
- Prevented by vaccinating livestock, preventing contamination of water
