Anaerobes Flashcards
What is an anaerobe?
An organism that cannot survive in the presence of oxygen
Anaerobes are classified into obligate and facultative anaerobes.
What is the difference between obligate anaerobes and facultative organisms?
Obligate anaerobes cannot tolerate oxygen, while facultative organisms can survive with or without it
Obligate anaerobes lack enzymes to break down toxic oxygen products.
Why can’t obligate anaerobes tolerate oxygen?
Oxygen has a direct toxic effect on them
They lack enzymes to detoxify oxygen byproducts.
What protective enzymes do aerobic organisms have?
Superoxide dismutase and catalase
These enzymes help in detoxifying harmful oxygen byproducts.
Where can anaerobes be found?
- Soil
- Freshwater
- Saltwater sediments
- Normal microbial flora
Anaerobes can be exogenous or endogenous.
What is the difference between exogenous and endogenous anaerobes?
Exogenous organisms exist outside the body, while endogenous organisms reside within the body
Infections can develop from either source.
What is a common exogenous anaerobe associated with infections?
Clostridium species
They can cause various diseases when introduced into the body.
What are acceptable samples for anaerobic bacteriology?
- Body fluids
- Abscesses
- Deep aspirates
- Transtracheal aspirates
- Direct lung puncture
- Suprapubic bladder aspirates
- Endometrial sites
Proper specimen collection is crucial for accurate results.
What are unacceptable samples for anaerobic bacteriology?
- Saliva
- Expectorated sputum
- Swabs from superficial wounds
- Vaginal/cervical/urethral secretions
- Voided or catheterized urine
Contamination with oxygen can affect anaerobic culture results.
What should be done with anaerobic specimens upon receipt in the lab?
Immediately place them in an anaerobic chamber to avoid exposure to oxygen
This step is crucial for sample integrity.
What ingredients should all primary isolation media contain?
Vitamin K, hemin, and yeast extract
These components are essential for anaerobic growth.
What is a method for anaerobic incubation?
- Anaerobic chambers
- Jar techniques
- Gas Pak
- Biobags
Each method has specific applications based on laboratory needs.
What gases are present in an anaerobic chamber?
- 5-10% hydrogen
- 5-10% carbon dioxide
- 80-90% nitrogen
These gases create an optimal environment for anaerobes.
What is a key indicator for anaerobic conditions in jars?
Methylene blue indicator
It changes color to indicate the presence or absence of oxygen.
What is a common bacteriological clue for identifying anaerobic isolates?
Foul odor when opening an anaerobic jar or bag
Specific odors are often associated with certain anaerobic bacteria.
What should be done when an anaerobic organism is suspected?
- Describe colony morphology
- Record gram staining reaction
- Inoculate pure culture
- Set up aerotolerance testing
These steps help in accurate identification.
What is the significance of double zone of hemolysis on blood agar?
Indicative of Clostridium perfringens
This characteristic can help in presumptive identification.
What should be recorded for presumptive identification?
Gram reaction and microscopic morphology
Detailed records aid in accurate diagnosis.
What is aerotolerance testing used for?
To determine whether the organism is a strict anaerobe or facultatively anaerobic
This involves incubating plates in different atmospheric conditions.
What types of plates are used in aerotolerance testing?
Blood agar plate and chocolate agar plate
Blood agar is incubated in a non-CO2 atmosphere and chocolate agar in a CO2 incubator.
What does a positive nitrate disc test indicate?
The ability of an isolate to reduce nitrate
This test is commonly used for presumptive identification of anaerobes.
What is indicated by the presence of brick-red fluorescence in certain anaerobes?
Species of Porphyromonas and Prevotella when subjected to UV light
These species fluoresce in specific colors when exposed to long wave UV light.
What is the significance of the catalase test, for anaerobes?
To differentiate between aerotolerant strains of Clostridium and Bacillus species
Clostridium species are typically catalase negative, while Bacillus species are positive.
What is the primary characteristic of Gram-Positive Spore-Forming Anaerobic Bacilli?
All classified in the genus Clostridium
These include species responsible for various clinical infections.
What are common diseases caused by Clostridium species?
Tetanus, botulism, gas gangrene, and food poisoning
C. difficile can cause antibiotic-associated pseudomembranous colitis.
What causes the symptoms of tetanus?
Release of the neurotoxin tetanospasmin
This toxin blocks neurotransmitter release, leading to muscular spasms.
What is foodborne botulism caused by?
Ingestion of exotoxins produced by C. botulinum in contaminated food
This leads to flaccid paralysis due to blockage of acetylcholine release.
What occurs in antibiotic-associated diarrhea and pseudomembranous colitis?
Overgrowth of resistant C. difficile due to antibiotic administration
This leads to bloody diarrhea and necrosis of gut mucosa.
What is the role of Gas-Liquid Chromatography (GLC) in anaerobic identification?
To analyze metabolic end products and fatty acid profiles of anaerobic organisms
This technique provides highly reproducible reports for identification.
What distinguishes preformed enzyme tests from traditional biochemical tests?
They do not require anaerobic incubation and provide results in about 4 hours
These tests utilize a code that is matched to a codebook for identification.
What type of bacteria is C. difficile?
Gram-Positive Spore-Forming Anaerobic Bacilli
What is the typical Gram stain appearance of Clostridium species?
Gram-positive, although some may stain gram variable or pink
What is the characteristic reaction of C. perfringens on Egg Yolk Agar (EYA)?
Produces an opacity within the medium
What is the characteristic appearance of C. botulinum and Fusobacterium on culture?
Lipase positive, producing a sheen resembling mother of pearl
What do organisms with proteolytic enzymes produce around their colonies?
A clear thin zone
What does the Direct Nagler test identify?
C. perfringens
What is characteristic of C. tetani on BRU/BA?
Swarming
What does a double zone of hemolysis on BRU/BA indicate?
C. perfringens
What is the appearance of lecithinase positive anaerobes on EYA?
Colony surrounded by a wide zone of opacity
What agar is used for presumptive identification of C. difficile?
Cycloserine-cefoxitin-fructose agar (CCFA)
What do C. difficile colonies produce on CCFA?
Yellow ground glass colonies
What is the characteristic odor of C. difficile growth?
Similar to a horse stable
What type of infections are caused by Gram-Positive non–spore-Forming anaerobic bacilli?
Opportunistic infections
What is a common diagnostic procedure for demonstrating Gram-positive non-spore forming filamentous bacteria?
Wet mounts and gram stains of pus
What is Bacterial Vaginosis characterized by?
Malodorous grey white discharge
What do Actinomyces species appear as under the microscope?
Straight to slightly curved rods
What is the appearance of young colonies of Actinomyces?
Spider-like or wooly
What color can Bifidobacterium colonies be?
Cream to white
What is a key feature of Mobiluncus species?
Curved bacilli
Fill in the blank: The organisms of C. perfringens are _______ positive.
Lecithinase
True or False: C. botulinum is lipase positive.
True
What color do C. difficile colonies fluoresce under UV light?
Chartreuse
What is the appearance of colonies of Mobiluncus species after 3 to 5 days?
Small, low convex, and translucent
Tiny colonies can be observed after 48 hours.
What is the morphology of Actinomyces species?
Short rods may be clubbed in a diptheroid arrangement; longer rods may be straight or wavy
They can also form small clusters or short chains.
What is the clinical significance of Propionibacterium acnes?
Can cause subacute bacterial endocarditis and bacteremia
P. acnes is a member of the normal flora of the skin.
Name some genera of Anaerobic Gram-Negative Bacilli.
- Bacteroides spp.
- Fusobacterium sp.
- Prevotella sp.
- Porphyromonas
- Veillonella
These genera are common members of the indigenous flora of the human body.
What types of infections are anaerobic Gram-negative bacilli commonly associated with?
Mixed infections, abscesses, and sepsis
For example, B. fragilis is isolated from soft tissue infections.
What is the significance of Bacteroides fragilis in clinical diagnostics?
Most commonly isolated organism of anaerobic Gram-negative bacilli from soft tissue infections
It is part of the Bacteroides fragilis group, which includes 8 closely related species.
What is the typical Gram stain appearance of Bacteroides species?
Gram-negative coccobacilli or bacilli with a pale staining, often referred to as a ‘safety pin’ appearance
This is characteristic of Bacteroides fragilis.
What is the colonial morphology of Bacteroides fragilis on BBE agar?
Gray colonies at least 1mm in diameter with browning of the media
Stippling surrounding areas of heavy growth indicates B. fragilis.
What are some clinical infections associated with Fusobacterium species?
Acute necrotizing ulcerative gingivitis (ANUG) and Vincent’s angina
ANUG is characterized by bleeding, inflammation, and necrosis of the gums.
What is the morphology of Fusobacterium species?
Fusiform appearance with tapered ends; some species display pleomorphism
Only F. nucleatum ssp. nucleatum has a consistent fusiform morphology.
What are the characteristics of anaerobic cocci in clinical infections?
Isolated from brain and lung abscesses, gingivitis, and other periodontal diseases
Anaerobic cocci include Peptostreptococcus species.
What is a notable feature of Veillonella species?
Usually found in clusters or diplococci arrangements
They are known pathogens among anaerobic Gram-negative cocci.
How can Veillonella species be presumptively identified?
Nitrate positive, anaerobic, Gram-negative coccus
They produce small, convex, translucent to transparent colonies.
