Microbiology: Intracellular bacteria, mycobacteria, and spirochetes Flashcards Preview

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Flashcards in Microbiology: Intracellular bacteria, mycobacteria, and spirochetes Deck (22):
1

Intracellular bacteria

-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

Rickettsiae

-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

Pathogenesis of Rickettsiae

-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

Rocky mountain spotted fever

-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

Epidemic Typhus

-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

Pathogenesis of epidemic typhus

-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

Chlamydiae

-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

Chlamydia trachomitis

-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

Mycobacteria

-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

Mycobacterium Tuberculosis

-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

Mycobacterium leprae

-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

Tuberculoid leprosy

-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

Chronic delayed-type hypersensitivity granulomas

-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

Tuberculin skin test

-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

Spirochetes

-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

Borrelia Burgdorferi

-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

Pathogenesis of lyme disease

-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

Lyme disease Dx

-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

Lyme disease Rx and prevention

-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

Leptospirosis

-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

Pathogenesis of leptospirosis

-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

Dx, Rx, and prevention of leptospirosis

-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