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What are the relevant gram positive rods in med micro?
- Corynebacterium diptheriae
- Bacillus anthracis
- Bacillus cereus
- Listeria monocytogenes
- Propionibacterium acnes
- Lactobacillus
- Erysipelothrix rhusiopathiae
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General features of Corynebacteria? (gram, shape, motility, capsulation, sporulation, aeration)
- Gram+
- small, slender rods that tend to stain unevenly
- nonmotile
- unencapsulated
- do not form spores
- facultative anaerobe (grow aerobically on lab media)
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Describe the epidemiology of Corynebacterium diptheriae.
- Found in throat/nasopharynx of both carriers AND those with diptheria
- Diptheria is a local infection of the throat
- Commonly spread by respiratory droplets
- Can be spread by direct contact or contaminated fomite
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Describe the pathogenesis of Corynebacterium diptheriae including mechanism of action
- Diptheria is caused by the effects of a single exotoxin (diptheria toxin), which inhibits eukaryotic protein synthesis
- Fragment B binds to cell membrane and mediates delivery of Fragment A
- Fragment A separates and causes adenylation of EF-2, rendering it inactive
- Production of diptheria toxin is a result of phage conversion
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Describe the potential diseases/infections that can result from Corynebacterium diptheriae
- 1. Upper respiratory tract infection
- Main infection
- Strictly local infection
- Produces thick gray pseudomembrane in throat WITHOUT PUS
- Often causes marked swelling of the lymph nodes in neck
- Untreated, the toxin can affect the heart and peripheral nerves
- 2. Cutaneous diptheria
- Caused by introduction of bacteria to subcutaneous tissue
- Nonhealing ulcur with gray membrane (of skin)
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What symptoms should prompt consideration of Corynebacterium diptheriae?
- Pharyngitis
- Low-grade fever
- Cervical adenopathy (neck swelling)
- Erythmia of pharynx up to gray pseudomembrane of pharynx
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Describe the laboratory identification of Corynebacterium diptheriae.
- Requires isolation of the organism and testing it for virulence (testing for diptheria toxin)
- Isolated most easily on Tinsdale's agar where it produces black colonies.
- Has distinctive banding when gram stained
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Describe the treatment and prevention diptheria?
- Prevention by the DTP vaccination would be prefereable, but if infection occurs...
- 1. Neutralization of toxin (horse serum antitoxin)
- 2. Erradication of organism (erythromycin, penicillin)
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General features of Bacillus? (gram, shape, sporulation, aeration, common locations)
- Gram+
- blunt-ended bacillus
- form endospores
- stricty or facultatively aerobic
- Most are found in soil/water
- found as airborne contaminants in med labs
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Describe the epidemiology of Bacillus anthracis
- enzootic disease of domestic sheep, goats, and horses transmitted to humans by contact with infected animal products or contaminated dust
- Majority of infections initiated by subcutaneous spore introduction through broken skin
- Less common infections initiated by inhalation of spores
- **spores may remain viable for years in pastures, wool, hair, hides, etc
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Describe the pathogensis of Bacillus anthracis
- The capsule (poly-D-glutamic acid) of B. anthracis is essential for full virulence
- Produces three exotoxins...
- 1. Edema factor (EF): causes elevation of intracellular cAMP, responsible for severe edema
- 2. Lethal factor (LF): responsible for tissue necrosis
- 3. Protective antigen (PA): mediates cell entry for LF and EF
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Describe the potential diseases/infections that can result from Bacillus anthracis
- 1. Cutaneous anthrax
- 95% of human cases
- Malignant pustules evolve on skin
- Untreated organisms may result in fatal septicemia (~20%)
- 2. Pulmonary anthrax (woolsorter's Disease)
- Caused by inhalation of spores
- Results in progressive hemorrhagic lymphadenitis (inflammation of lymph nodes)
- Mortality rate ~100% if untreated
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Describe the Laboratory identification of Bacillus anthracis
- Microscopically appear as blunt-ended bacilli singly, in pairs, or in long chains
- Do not sporulate in clinical samples, but do so in culture
- Large, grayish, nonhemolytic colonies on blood agar
- Can be distinguished from other Bacillus due to nonmotility and capsulation in vivo
- Direct immunofluorescence assay aids in ID
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Describe the treatment and prevention of Bacillus anthracis
- Sensitive to a variety of antibiotics (Penicillin not recommended)
- Multidrug therapy is recommended for inhalation anthrax
- Prevention: vaccine is available ONLY to workers in high-risk occupations
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Give information about Bacillus cereus
- Implicated in opportunistic lesions (after trauma, catheters, etc)
- Produces tissue-destructive extotoxin
- Causes food poisoning by means of enterotoxins
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General features of Listeria (gram, shape, sporulation, biochemical properties, motility, special properties)
- Gram+
- Very short/slender rods (confused with coccus)
- Non spore-forming
- catalase-positive
- distinct tumbling motility (actin-polymerization)
- Salt tolerant
- Survive/grow below 1C
- L. monocytogenes is a model organism for intracellular pathogens
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Describe the epidemiology of Listeria monocytogenes
- Listeriosis is usually foodborne (2-3% processed dairy products, 20-30% ground meats, majority of poultry are contaminated)
- Growth at 4C ∴ refrigeration does not suppress
- Listeriosis is most common in pregnant women, fetuses, newborns, the elderly, and the immunocompromised
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Describe the pathogenesis of Listeria monocytogenes
- facultative intracellular parasite
- Enters cells by normal phagocytosis
- Hemolysin Listeriolysin O allows escape from the phagosomeGrows in the cytosol, and induces polymerization of cellular actin to create a "tail" which propels it
- Transferred directly between adjacent cells
- Hemolysin phospholipase C allows escape from the double-membraned vacuole formed after cell-cell passage
- This process allows avoidance of intercellular milieu
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Describe the potential diseases/infections that can result from Listeria monocytogenes
- Septicemia and meningitis are most common
- Preggos may have mild flulike illness
- Can be transmitted to newborn from vagina (meningitis) OR to the fetus from the placenta (abortion)
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Describe the laboratory identification of Listeria monocytogenes
- Can be isolated from blood, CSF, etc
- Blood agar: small colony surrounded by narrow zone of weak β hemolysis (better observed by removing colony)
- Distinguished from streptococci by morphology, motility, and catalase production
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Describe the treatment and prevention of Listeria monocytogenes
- Variety of antibiotics are available to treat infection
- Proper food preparation and handling can prevent infection
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Give information about Propionibacterium
(spores? aeration? gram? shape/morphology? information)
- Non spore-forming, Anaerobic/microaerophilic, Gram + rods of diptheroid-like morphology
- Common inhabitants of normal skin
- rarely associated with endocarditis or plastic implant infections
- P. acnes (strict anaerobe) is cause of acne
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Give information about Lactobacillus (spores? gram? shape? information)
- non-spore forming, gram+, rods
- Part of commensal flora of human mucous membranes
- Produce large quantities of lactic acid during fermentation (maintain acidic pH)
- May play a role in dental carries
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Give information about Erysipelothrix rhusipathiae (spores? gram? shape? information)
- non-spore forming, gram+, filamentous rod
- Causes disease in animals
- Rarely associated with erysipeloid (a skin condition) in those who commonly handle animal products (eg butchers, vets, fisherman)
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