click below
click below
Normal Size Small Size show me how
Micro Exam 5
Anaerobes and Mycobacterium
Question | Answer |
---|---|
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. |