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Micro Exam 5

Anaerobes and Mycobacterium

QuestionAnswer
Why are anaerobic organisms killed off by oxygen? they lack the enzyme to breakdown reactive oxygen species produced during respiration or aerobic metabolism.
Why do you often see mixed infections of anaerobes and aerobes? Aerobes enter a wound and use up the oxygen so the endogenous anaerobes can then fill that area that is not normally survivable by them because the oxidation potential has been lowerd.
What are the least favorable specimen types? Swabs, because they dry out easily, easily contaminated by endogenous organisms during collection, can expose the organism to oxygen for an unacceptable period of time.
How must swabs be submitted for anaerobic culture? Must be submitted in an oxygen-free transport system.
What is the ideal specimen type? whole tissue or aspiration via niddle and syringe submitted in anaerobic transport media.
How can you modify gram staining for anaerobic cultures to counterstain better? counterstain for 3-5 minutes or substitute w/ basic fuchsin to improve staining.
Would white blood cells be commonly present in anaerobic infections? Yes, most anaerobic infections produce pus so WBCs are present. C. perfringens produce theta toxin which destroys WBCs though.
What is BBE agar used for? Selective and differential for Bacterioides fragilis
What is egg yolk agar that produces lipase used for? shows what organisms are lipase positive
What is egg yolk agar that produces lecithinase used for? shows which organisms are lecithinase positive
What is the ideal environment for anaerobic incubation? "Tri-gas" environment consisting of 80-90% nitrogen, 5% hydrogen, and 5-10% CO2
What is required of anaerobic environment? Must include a method to monitor maintenance of anaerobic environment.
When should you examine culture plates for anaerobic cultures? after 48 hours and on days 3, 4, and 5 to prevent killing the organisms since they are most susceptible to oxygen in their log phase.
Clostridium spp gram stain Large, gram pos, straight-edged rods in a chain that forms spores
What is the catalase reaction of Clostridium species? Negative
Clostridium perfringens colonial morphology on Ana BAP? gray to grayish yellow, circular, glossy, dome shaped, entire, translucent colonies w/ double zone of beta hemolysis
On an egg yolk plate, what reaction is observed? Lecithinase positive
What exotoxins are produced by Clostridium perfringens? alpha toxin, Beta toxin, enterotoxin
What does the alpha toxin of C. perfringens do? Most important, mediates the destruction of host cell membranes
What does the beta toxin of C perfringens do? cytotoxic (kills cells)
What does the enterotoxin of C perfringens do? Inserts and disrupts membranes of mucosal cells
How is the Clostridium perfringens acquired? contamination of existing wound or puncture by contaminated object or ingestion of preformed toxins in vegetable or meat-based foods
What disease is caused by Clostridium perfringens' toxin-mediated destruction of muscle and other tissues after traumatic introduction of the organism? Gas gangrene
What is enteritis necroticans which is caused by Clostridium perfringens? Necrotizing enteritis, a life-threatening infection that causes ischemic necrosis of the jejunum and is more common in immunocompromised patients
What is the food poisoning implication of Clostridium perfringens? Caused by release of the toxin after ingestion of large numbers of the organism. usually a self-limiting and benign condition that manifests as abdominal cramps, watery diarrhea, and vomiting
Where is Clostridium tetani normally found? Not normal flora to humans. This is found in soil and environment more than normal flora.
How is tetanus diagnosed? based on clinical presentation rather than culture because culture may not actually be present in the wound since the disease is toxin mediated.
What toxin causes the symptoms of tetanus? testanospasmin (TeNT) which is a neurotoxic exotoxin that disrupts nerve impulses to muscles.
What is the fatality rate of tetanus even with treatement? 25% fatality
How is botulism acquired? ingestion of preformed toxins in vegatable or meat-based foods
How is infant botulism acquired? colonization of GI tract w/ potent toxin-producing organism
How is wound botulism acquired? contamination of existing wound or puncture by contaminated objects
What toxins must be produced for disease to occur in C difficile? Toxin A which is an enterotoxin (excessive diarrhea) and toxin B which is a cytotoxin.
What does detection of Clostridium septicum in the blood indicate? can be indicative of a colon tumor.
Which Clostridium are lecithinase positive? Clostridium perfringens
Which Clostridium is Lipase positive? Clostridium botulinum
What is the tx for C. difficile Typically penicillins, metronidazole, or vancomycin
What is the tx for botulism? Antibiotics are not indicated.
What is the gram stain for Actinomyces israelii? Gram positive, branching, beaded or banded, thin, filamentous rods
What is the colonial morphology on Ana BAP? White, opaque, and may resemble a molar tooth
What is the unique gram stain of Bifidobacterium species? Gram positive rods often terminating in clubs or thick, bifurcated (forked) ends. "looks like dog bones"
How are anaerobic gram positive rods typically treated? Penicillins, imipenem, cefotaime, and/or ceftizoxime
What is the gram stain appearance of Finegoldia magna? GPC in pairs and clusters that resemble staphylococci.
What is the gram stain appearance of Peptoniphilus asaccharolyticus? GPC in pairs, short chains in tetrads and small clusters that may appear as gram negative w/ age.
What is the gram stain appearance of peptostreptococcus anaerobius? gram positive, large coccobacillus often in chains
How can Peptostreptococcus anaerobius from other GPC? SPS disk inhibition zone of >12 mm
Why might Peptostreptococcus anaerobius be suppressed in blood culture vials? SPS is present in Blood culture vials
How can you diff F manga from other anaerobic GPC? it is resistant to SPS and negative for indole and nitrate
How can you diff P. asaccharolyticus from other anaerobic GPC? Indole positive and SPS resistant
How can you diff P. anaerobius from other anaerobic GPC? susceptible to SPS.
What conditions do microaerophilic streptococcus species require? 10% CO2 for growth but grow best under anaerobic conditions.
Which are the most common anaerobic bacteria? Gram negative bacilli
Which anaerobic gram negative rods are most common below the waist infections? Bacteroides fragilis
Which anaerobic gram negative rods are most common above the waist infections? Fusobacterium, Prevotella, and Porphyromonas
What is the gram stain of Bacteroides fragilis going to look like? gram negative, pale-staining, pleomorphic rods w/ rounded ends that occur singly or in pairs and resemble a safety pin oftentimes.
Bacteroides fragilis infections are commonly seen in Female genitals, GI trauma, or appendix rupture.
Fusobacterium nucleatum gram stain would appear as Gram negative, pale staining, long, slender, spindle shaped w/ sharply pointed ends
Fusobacterium necrophorum gram stain would appear as gram negative pleomorphic rods w/ round to tapered ends may be filamentous or contain round bodies. becomes pleomorphic age.
Colonial morphology of Fusobacterium nucleatum on Ana BAP? Usually nonhemolytic with fluoresces chartreuse. May be white and bread crumb-like, gray to gray-white speckled, or gray to gray-white smooth.
Colonial morphology of Fusobacterium necrophorum on Ana BAP Circular, umbonate, ridged surface, translucent to opaque, some strains may be beta hemolytic with fluoresces chartreuse
How can you differentiate B fragilis from the other two gram negative rods that are anaerobic? growth in 20% bile, catalase pos, and esculin hydrolyzing.
how can you diff F nucleatum from the other two gram neg rods that are anaerobic? F nucleatum is only indole positive.
How can you diff F necrophorum from the other two gram neg rods that are anaerobic? F. necrophorum is lipase positive and indole positive.
How is Prevotella melaninogenica from Prevotella intermedia? P. melaninogenica is indole and lipase negative while P intermedia is positive for both
Gram stain of prevotella species? Gram-negative coccobacilli
Requirement for growth of prevotella? requires vitamin K for growth (can be synthesized by S aureus so P melaninogenica can satellite around S aureus on media w/o vitamin K
Gram stain of Porphyrmonas spp? Pale-staining gram negative cocco bacilli
Gram stain of velonella spp? gram neg cocci in clusters
Biochemical reaction of veilonella? reduces nitrates
What is the basic purpose of acid fast staining? resist decolorization with acid-alcohol decolorizing agents. This is due to the cell wall's high lipid content and the mycolic acids which hlep resist decolorizing agents.
How is an acid fast stain prepared? Stain with carbolfuchsin (bright red dye), decolorize (with acid), counterstain methylene blue or brilliant green.
68 C catalase reaction for Mycobacterium tuberculosis? negative, Heat stability of catalase is negative for most causative and positive for most nontuberculosis.
What is the result of niacin accumulation test of Mycobacterium tuberculosis? Mycobacterium tuberculosis does not degrade niacin to nicotinamide like the other causative agents, so it will have a yellow color which is a positive result.
TCH inhibition differentiates what? M. bovis and M. tuberculosis (bovis will not grow in 10 mg/mL TCH)
Tween 80 Hydrolysis differentiates what? non-pathogens from pathogens
Clinical significance of Mycobacteria tuberculosis most common in the US. habitat is patients with pulmonary disease
Clinical significance of Mycobacteria bovis Humans and a wide variety of animals , but not nearly as common as M. tuberculosis
Clinical significance of Mycobacteria africanum Less common in the US, mainly seen in Africa
Biochemicals to differentiate M. tuberculosis from M. bovis Niacin, nitrate, and pyrazinamidase are negative in M. bovis and positive in M tuberculosis
Runyon group I pigment? Pigment only in light
Runyon group I description? photochromogens (slow growers
Runyon group I organisms? Mycobacteria kansasii and Mycobacteria marinum
Runyon group II pigment? Pigment in light and dark
Runyon group III pigment? No pigment
Runyon group IV pigment? no pigment, but grow within a week
Runyon group II description? scotochromogens
Runyon group III description? nonphotochromogens
Runyon group IV description? Rapid growers
Runyon group II organisms? M. scrofulaceum and M. gordonae
Runyon group III organisms? MAC
Runyon group IV organisms? M. fortuitum
Where is M. marinum found? Natural reservoirs are freshwater and saltwater. Trsmission by contact w/ contaminated water via breaks in skin or other aquatic activity involving fish
Where is M. gardonae found? Tap water, water, soil - called the tap water bacillus
M. avium complex relation to disseminated disease? most common cause of disseminated disease in AIDS patients
Clinical significance of Mycobacterium leprae causes two forms of leprosy: Tuberculoid and Lepromatous leprosies. Still endemic to certain countries with a few cases in the US per year esp. in TX, CA, LA, HI, and Puerto Rico.
Colonial morphology of Porphyromonas on Ana BAP? Dark brown to black, more mucoid than prevotella spp, fluoresces brick red (except P. gingivalis)
Colonial morphology of Prevotella spp. on Ana BAP Dark center w/ gray to light brown edges. Circular, entire convex, smooth, shiny and nonhemolytic. Fluoresces brick red.
Colonial morphology of Prevotella spp. on LKV? Black pigment
Will Porphyromonas grow on LKV? No, it is sensitive to vancomycin.
Created by: wulfmannwarrior