Chapter 16- Anaerobic bacteria Flashcards
1
Q
Obligate aerobe
A
Only aerobic growth; oxygen required for growth of the microorganisms
2
Q
Facultative anaerobe
A
Both aerobic and anaerobic growth can occur; greater growth in the presence of oxygen. The organisms thrive in the presence of oxygen, but also grow in its absence by relying on fermentation or
anaerobic respiration, if there is a suitable electron acceptor other than oxygen and the organism is able to
perform anaerobic respiration
3
Q
Obligate anaerobe
A
Only anaerobic growth; cannot grow in the presence of oxygen (oxygen is toxic to these bacteria)
4
Q
Aerotolerant anaerobe
A
Anaerobic growth; but growth continues in the presence of oxygen. These bacteria do not use oxygen, but are indifferent to its presence and are not harmed by it
5
Q
Microaerophilic
A
Aerobic growth; oxygen required in low concentrations.They require about 1%–10% oxygen concentration, well below the 21% found in the atmosphere.
6
Q
Capnophilic
A
Aerobic growth, CO2 required in high concentrations.They also use a low concentration of oxygen, lower than that found in the atmosphere
7
Q
Anaerobic bacteria as normal flora
A
Anaerobes can be found anywhere with a mucous membrane. The oral cavity, lower female genital tract, and GI tract are the locations that are the biggest sources of anaerobic organisms. Other locations include the urethra, skin, upper respiratory tract, and conjunctiva
8
Q
Clinical clues suggesting anaerobic infections (6)
A
- An infectious process next to mucosal surfaces that have normal anaerobic flora particularly in gastrointestinal tract, female genital tract and oral cavity
- Anaerobes are often associated with tissue necrosis and abscess formation
- The presence of a foul odor or gas is highly suggestive of an anaerobic infection
- A patient’s failure to respond to antibiotics that are not active against anaerobic bacteria are suggestive of anaerobic infection
- Gram stain smears showing a polymicrobial flora and organisms with morphologic features of anaerobes are indicative of anaerobic infection- don’t form normal colonies in culture
- Formation of anaerobic environments- wounds, abscesses, especially after surgery
9
Q
Gas gangrene
A
When some anaerobes grow in tissue, they can produce gas-results in pockets of air in tissue that can be visualized on imaging
10
Q
Gram stain of anaerobic abscess
A
Anaerobic samples are dense with organisms that may contain many different morphologies
11
Q
How are specimens for anaerobic culture collected?
A
Samples must be collected so as to avoid contamination by anaerobic normal flora of mucosal surfaces. Therefore, the optimum specimens are fluids that are sterile- they don’t contain anaerobes as normal flora. Anaerobic transport media is always used to protect the sample from oxygen, which can be toxic to the microorganisms
12
Q
Which specimens are used for culture of anaerobes?
A
Optimum specimens are normally sterile fluids (e.g. blood, pleural and peritoneal fluids, and aspirates). Samples from mucosal surfaces are not acceptable for anaerobic culture (i.e. sputum, urine, etc)- most of the time you grow normal flora
13
Q
Anaerobic transport media
A
Anaerobe samples must be transported in specific media, as if they are transported in normal air, the bacteria will die. The tissue/swab sample is placed in a closed tube containing gel media. When placed in the gel, it undergoes an enzymatic reaction to remove oxygen from the tube and preserve the sample
14
Q
Anaerobic chamber
A
Materials are introduced through the small doors in the air-lock chamber. The operator works through arm ports in airtight sleeves. Chamber is filled with 85% N2, 10% H2 and 5% CO2. It allows the microbiologist to perform the techniques for isolation and identification of anaerobic bacteria without ever exposing the sample to air
15
Q
Anaerobic jars and sealed boxes
A
When water is mixed with the chemical packet containing sodium bicarbonate and sodium borohydride, hydrogen and carbon dioxide are generated. The hydrogen and atmospheric oxygen in the jar react with a palladium catalyst and combine to form water. The oxygen is thus removed, creating an anaerobic atmosphere for the bacteria. Atmosphere contains < 5% oxygen, about 18% CO2 and no hydrogen. An anaerobic indicator is placed in the jar to monitor the atmospheric conditions. Anaerobic jars are used for cultivating anaerobic bacteria on primary plating media or subculture plates
16
Q
Anoxomat
A
This is a jar evacuation and replacement system- the air is vacuumed out of the jar. This can be done very quickly and is automated. It produces an atmosphere that is 80% nitrogen, 10% hydrogen and 10% carbon dioxide. Uses a palladium pouch
17
Q
OxyPlate
A
Each individual petri plate is sealed to become an anaerobic chamber. The culture medium in the plate contains an enzyme, oxyrase, which combines oxygen with hydrogen, removing oxygen as water is formed. It isolates anaerobes without the need for anaerobic jars, chambers, or pouches
18
Q
Anaerobic indicators (2)
A
Oxidation –Reduction Indicators:
1. Methylene blue: Blue 🡪 colorless under anaerobic conditions
2. Resazurin: Pink 🡪 colorless under anaerobic conditions
19
Q
Methylene blue
A
An anaerobic indicator. The dye stains blue in the presence of air. It loses color when oxygen leaves the environment
20
Q
What are anaerobic indicators used for?
A
When using anaerobic jar techniques (anaerobic jars, anoxomat), anaerobic indicators are necessary to determine whether an anaerobic atmosphere is being maintained in the jar
21
Q
Anaerobic culture media
A
Anaerobes almost always need additional nutrients (hemin and vitamin K usually). Media contain hemin and Vitamin K to enhance anaerobic growth. Selective media is important because most anaerobic infections are polymicrobial. There are multiple types of agar that can be used
22
Q
Types of anaerobic culture media (7)
A
- Anaerobic blood agar (CDC)
- Bacteroides bile esculin agar (BBE)
- Kanamycin-vancomycin laked sheep blood agar (KVL)
- Phenylethyl alcohol agar
- Egg yolk agar
- Colistin Nalidixic Acid agar (CNA)
- Broths with reducing agents
23
Q
Anaerobic blood agar (CDC)
A
General purpose medium for cultivation of all anaerobic bacteria
24
Q
Bacteroides bile esculin agar (BBE)
A
An enriched, selective, and differential medium used for the isolation and presumptive identification of Bacteroides fragilis group. BF bacteria produces a dark pigment when it grows
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KVL agar
KVL stands for Kanamycin, Vancomycin, and Laked Blood Agar. It's an enriched, selective and differential medium used for the isolation of anaerobic bacteria especially Bacteroides sp and Prevotella sp. Prevents growth of facultative Gram negative and Gram positive bacteria. Laked blood enhances pigment formation.
26
Phenylethyl alcohol agar
An enriched and selective blood agar medium used for isolation of most anaerobic organisms (Gram positive and Gram negative) from mixed cultures. This includes Clostridium and Bacteroides. Inhibition of facultative anaerobic Gram negative bacteria such as Enterobacterales.
27
Egg yolk agar
The lipid concentration from eggs in included in the agar. If the organism breaks down the lipids, it produces a white precipitate around the streak of bacteria. It is used to detect proteolytic enzymes (lipase and lecithinase) produced by Clostridium sp. Lecithinase produces an opaque zone around the colony, while lipase forms a blue green sheen on agar surface around colony
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Colistin Nalidixic Acid agar (CNA)
Inhibits Gram negative organisms and is used to grow most Gram positive anaerobic and facultative anaerobic bacteria
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Broths with reducing agents
Used to culture anaerobic bacteria. Thioglycollate and cooked meat can be used to grow anaerobic bacteria
30
Aerotolerance
The capacity of an organism to tolerate the presence of oxygen in the air. In microbiology, the aerotolerance of a microorganism can be tested through the Aerotolerance Test, which makes use of thioglycollate broth.
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Aerotolerance test
Before attempting to identify a possible anaerobic bacterium, it first must be demonstrated to be an anaerobe. A colony is inoculated to an anaerobic blood agar plate which is incubated anaerobically for 48 hours, and to a chocolate agar plate incubated under conditions of increased CO2. Isolates growing only on the plate incubated anaerobically are obligate anaerobes. Isolates growing on the aerobically incubated plate but significantly better anaerobically are aerotolerant anaerobes.
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Gram negative coccobacilli species (3)
Bacteroides sp, Prevotella sp and Porphyromonas sp
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Gram negative rods species
Fusobacterium sp. The rods are very uniform, thin and straight with tapered ends
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Gram negative cocci species
Veillonella sp
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Gram positive rods species (2)
Actinomyces sp form Gram positive branching rods. Clostridium sp form Gram positive rods that sometimes form spores
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When does spore production occur in bacteria?
Spore production occurs when an organism is stressed
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Gram positive cocci species (6)
1. Peptostreptococcus
2. Peptococcus
3. Fingoldia
4. Parvimonas
5. Anaerococcus
6. Peptoniphilus
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Species of the Bacteriodes fragilis group (10)
1. B. fragilis – most common anaerobe in human infections
2. B. thetaiotaomicron – 2nd most common Bacteroides sp
3. B. distasonis
4. B. vulgatus
5. B. ovatus
6. B. eggerthii
7. B. merdae
8. B. stercoris
9. B. uniformis
10. B. caccae
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Bacteroides fragilis group
They are normal flora of the colon, but they can cause infections when their membranes are disrupted. For example, with colon cancer, bacteroides in a stool culture or an abdominal bacteroides abscess can be concerning for colon cancer
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Bacteriodes fragilis group infections
Infections are commonly caused by entry into normally sterile body sites especially after surgery, trauma, or disease (i.e. bacteremia, soft tissue infection)
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Bacteriodes fragilis virulence factors (2)
1. Endotoxin: fever, dilation of blood vessels, shock, and blood clotting
2. Polysaccharide capsule: antiphagocytic
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Identifying characteristics of bacteroides fragilis group (5)
1. Gram negative coccobacilli
2. Growth in presence of 20% bile
3. Bile-esculin positive (ability to hydrolyze esculin)
4. Most Bacteroides species are vancomycin (since they are gram negative) and kanamycin resistant and variable in sensitivity to colistin.
5. Indole negative
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Which antibiotics are bacteroides fragilis group species resistant to?
B. fragilis group are Vancomycin, Kanamycin, and Colistin resistant.
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Why does B. fragilis grow on BBE agar?
B. fragilis group hydrolyze esculin to form dextrose and esculetin. This compound reacts with the ferric ions contained within the medium, turning the medium around the colonies a dark brown to black color. Thus, the tolerance to the bile and hydrolysis of esculin provide the means to presumptively identify B. Fragilis group
45
B. fragilis differentiation disks
Vancomycin, kanamycin, and colistin disks are used to differentiate bacteria based on their susceptibility to these antibiotics. B. fragilis is one example of bacteria that is resistant to vancomycin, kanamycin, and colistin disks
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Prevotella melaninogenica
Produces melanin, which creates black colonies in culture. It is normal flora of the oropharynx, nose, and gastrointestinal and urogenital tracts. However, it is associated with infections such as periodontitis, head, neck, and lower respiratory tract infections
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Infections caused by Prevotella species (3)
1. Periodontitis (gum infection), can cause tooth abscesses as well
2. Head and neck infections
3. Pneumonia
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Virulence factors of Prevotella melaninogenica
endotoxin, proteinases
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Identification characteristics of Prevotella melaninogenica (5)
1. Pigmented colonies (black) on blood containing agar
2. Brick red fluorescence under UV light
3. Inhibited by 20% bile (therefore no growth on BBE agar)
4. Most Prevotella species are Vancomycin and Kanamycin resistant (will grow on KVL) and variable in sensitivity to Colistin
5. Indole negative
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Prevotella species
Composed of over 20 different species, including Prevotella melaninogenica. These species are gram negative coccobacilli
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Porphyromonas species
Composed of more than 10 species, makes up the normal flora of the oropharynx, nose, and gastrointestinal and urogenital tracts
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Infections caused by Porphyromonas species
Oral infections, head and neck infections
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Virulence factors of Porphyromonas species
endotoxin and proteinases
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Identification factors of Porphyromonas species (5)
1. Pigmented colonies (black) on blood containing agar
2. Brick red fluorescence under UV light
3. Inhibited by 20% bile (no growth on BBE agar)
4. Porphyromonas species are generally sensitive to vancomycin and resistant to colistin (will not grow on KVL agar)
5. Indole positive
55
Indole test
Screens for the ability of an organism to degrade the amino acid tryptophan and produce indole. Tryptophan is an amino acid that can undergo deamination and hydrolysis by bacteria that express tryptophanase enzyme. The presence of indole when a microbe is grown in a medium rich in tryptophan demonstrates that an organism has the capacity to degrade tryptophan.
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How do Porphyromonas species differ from Prevotella species?
Porphyromonas will not grow on KVL agar, but Prevotella will grow. This is because Porphyromonas species are generally sensitive to vancomycin, a component of KVL agar
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Fusobacterium species
There are 9 of these species. They are normal flora of the upper respiratory and gastrointestinal tract. Two important species are F. nucleatum (causes serious pulmonary infections) and F. necrophorum (lung and liver abscesses, necrosis). F. nucleatum is the most common isolate but F. necrophorum causes more serious infection.
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Infections caused by Fusobacterium species
Causes pulmonary, blood, sinus, and dental infections in addition to brain abscesses. Also, Lemierre’s syndrome
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Virulence factors of Fusobacterium species
endotoxin and leukotoxin (lyses blood cells)
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Lemierre’s syndrome
A complication of bacterial pharyngitis/tonsillitis and involves an extension of the infection into the lateral pharyngeal spaces of the neck with subsequent septic thrombophlebitis of the internal jugular vein(s)- the veins may become swollen or inflamed due to a blood clot. Septic emboli may also lodge in the lungs, liver, endocardium, or joints. This syndrome was common in the age prior to the development of antibiotics
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F. nucleatum
F. nucleatum is a Fusobacterium species that causes serious pulmonary infections. It is the most common Fuscobacterium isolate and forms "bread crumb colonies" in culture
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Identification characteristics of Fuscobacterium species (3)
1. Most strains inhibited by 20% bile (will not grow on BBE agar)
2. Resistant to vancomycin, sensitive to kanamycin and colistin (will not grow on KVL agar)
3. Indole positive
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General characteristics of anaerobic Gram negative cocci
Anaerobic gram negative cocci are obligately anaerobic. They typically grow in pairs but can also form chains and clumps. In general, they are normal flora of oral, genitourinary, respiratory and gastrointestinal tracts of humans. Typically part of mixed bacterial infection but sometimes sole bacterium-
BF tends to be the only group causing a solo infection. Their virulence factor is the endotoxin
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3 most common genera of anaerobic gram negative cocci
1. Veillonella species – most common infections are mouth and urogenital
2. Acidaminococcus species – most common infections are in gastrointestinal tract
3. Megasphaera species - most common infections are in gastrointestinal tract
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General characteristics of anaerobic gram positive cocci
These species are obligately anaerobic. They can grow in pairs, chains, or clumps, an some appear coccobacillary. They are normal flora of the human intestines, female genital tract, oral cavity, respiratory tract, and skin. Associated with polymicrobial abscesses and infections of skin and soft tissue, mouth, bones, joints, respiratory tract, and female genital tract.
Virulence factors are adhesion factors and biofilm production
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6 most common anaerobic Gram positive cocci genera
1. Peptococcus (niger is only species)
2. Peptostreptococcus species
3. Finegoldia species
4. Parvimonas species
5. Anaerococcus species
6. Peptoniphilus species
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Finegoldia magna
Anaerobic gram positive cocci associated with the Finegoldia species. It is the most pathogenic and most frequently isolated. Typically associated with infections of skin, soft tissue, bone and joints
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Peptostreptococcus anaerobius
Anaerobic gram positive cocci associated with the Peptostreptococcus species. It causes infections of the abdominal cavity and female genital tract
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Anaerococcus prevotii
Anaerobic gram positive cocci associated with the Anaerococcus species. It causes infections of the abdominal cavity and female genital tract
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Parvimonas micros
Anaerobic gram positive cocci associated with the Parvimonas species. It is an oral cavity pathogen
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Identifying characteristics of gram positive cocci (2)
1. Pigment production: olive green colonies that become black (no fluorescence)
2. Susceptibility to Sodium Polyanethol Sulfonate (SPS): > 12 mm
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Sodium Polyanethol Sulfonate (SPS)
A constituent in culture media used to grow bacteria from blood samples from patients suspected of bacteremia
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Gram positive rods species that do not form spores (6)
1. Actinomyces species
2. Cutibacterium (Propionibacterium) species
3. Mobiluncus species
4. Lactobacillus species
5. Bifidobacterium species
6. Eggerthella (Eubacterium) species
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Clostridium species
There are over 20 of these species. Some are are normal gastrointestinal flora of humans and animals, and others are found in soil water and dust. Most species are obligate anaerobes but a few are aerotolerant. They produce a variety of exotoxins. Because of spore production, they are very resistant to disinfection processes
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Clostridium species morphology
They form large Gram positive rods, but some species may appear Gram negative as they are easily decolorized. They may also form spores, seen as a hollow area under the microscope
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Clostridium staining
Malachite green spore stain is used, with safranin used as counterstain. The bacteria appear red and bluish green
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Clostridium perfringens
One of the most important pathogens in genus. They are normal flora of the gastrointestinal tract and female genital tract. Infections are acquired through trauma or ingestion. Virulence factors are enterotoxin (affects gastrointestinal tract) and exotoxins (A-E) that can cause severe tissue damage (histotoxins)
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Infections caused by Clostridium perfringens (3)
1. Gas gangrene (myonecrosis – breakdown of muscle tissue)
2. Post-abortion sepsis
3. Food poisoning (from meats and gravy)
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Gas gangrene
Also referred to as myonecrosis- destruction of muscle. In addition to the death of tissue, there is a bad smelling discharge and the skin becomes discolored. Diabetics and patients with circulatory disorders are more prone to infection
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Clostridium perfringens food poisoning
One of the most common causes of foodborne illness in the United States. Nearly 1 million cases of foodborne illness each year. The bacteria produce a toxin inside the intestine that causes illness- diarrhea and abdominal cramps begin within 6 to 24 hours (typically 8 to 12 hours). The illness usually begins suddenly and lasts for less than 24 hours. Beef, poultry, gravies, and dried or pre-cooked foods are common sources- occurs when foods are prepared in large quantities and kept warm (at unsafe temperatures) for a long time before serving.
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Clostridium perfringens Identifying characteristics (6)
1. Double zone of beta-hemolysis on blood agar
2. Reverse CAMP test positive
3. Lecithinase positive – Lipase negative
4. Nagler test positive (anti-lecithinase)
5. Tributyrin test negative
6. Subterminal spores but difficult to induce
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Beta-hemolysis
C. perfringens produces a double zone of beta-hemolysis on blood agar, which means there are 2 rings of empty areas surrounding the bacterial colonies
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Reverse CAMP test
The reverse CAMP test is a method to identify Clostridium perfringens using β-hemolytic streptococci (Streptococcus agalactiae). The test is called reverse CAMP test because the CAMP factor produced by S. agalactiae is used for the detection of Clostridium perfringens from other Clostridium species. A CAMP positive Group B Streptococcus is streaked in the center of sheep blood agar, and Clostridium perfringens is streaked perpendicular to it. After incubation, a “bow-tie” zone of enhanced hemolysis pointing towards Streptococcus agalactiae is seen (positive result). This is because of how alpha toxin produced by Clostridium perfringens interacts with CAMP factor and produce synergistic hemolysis
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Detection of lecithinase activity
Can be done using egg yolk agar or the Nagler test. Lecithinase is a type of phospholipase found in various species of bacteria
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Nagler test
Antitoxin is added on half of the plate. If the antitoxin prevented the lecithinase from growing, this is a positive Nagler test. A positive test is represented by an opaque zone around the colony (the enzyme lecithinase is an exotoxin). C. perfringens is one example of Nagler positive bacteria. The test uses an egg yolk agar plate
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Lipase test
Used to detect the ability of bacteria to produce the exoenzyme lipase and hydrolyze lipids. A positive result is a blue green sheen on the agar surface around the colony
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Clostridium tetani
Found in soil, water and dust. Puncture wounds are perfect anaerobic environments for C. tetani to grow. Gunshots, burns, and animal bites can also be infected with tetanus. The tetanospasmin toxin that the bacteria produces causes tetanus, and spores enter the body through these wounds. There is very little necrosis.
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C. tetani virulence factor
The bacteria produces tetanospasmin, a neurotoxin that affects spinal cord resulting in involuntary muscle contractions. Contractions begin with neck and jaw (lock jaw) and progress to a backward arching of back muscles. The muscles become stuck in the contracted positions, and lockjaw is the most common symptom
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Treatment and prevention of tetanus
Antitoxin and vaccine (DPT: diphtheria, pertussis and tetanus trivalent vaccine). Booster is recommended every 5 years.
Antibiotics are not used as treatment
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Tetanus
The organisms can enter through large, small, or even unrecognized wounds. Deep, infected punctures are most susceptible, as it creates the perfect anaerobic environment. The toxin is produced locally, and passes through the bloodstream or along nerves to the CNS. The motor neurons of the spinal cord and of the brainstem become hyperactive, because the toxin specifically attacks inhibitory cells. Spasms of the jaw, facial and neck muscles, and dysphagia are typical early symptoms
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How does the tetanospasmin toxin impact cells?
The toxin is transported to the CNS and into an inhibitory neuron. It blocks vesicle fusion and release of glycine or GABA, which blocks the function of inhibitory neurons. Therefore, the fusion and release of acetylcholine cannot be stopped, and the cell is stimulated so the muscle contracts continuously
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Identifying characteristics of C. tetani (3)
1. Round terminal spores resembling drumsticks
2. Lecithinase and Lipase negative
3. Generally not cultured; diagnosis made by signs and symptoms and toxin detection in blood
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Clostridium botulinum
Found in soil water and dust. Causes botulism when people are exposed to the botulinum toxin. There are 4 types- food, infant, wound, and iatrogenic botulism
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Food botulism
Caused by ingestion of preformed toxin in spoiled, home-canned foods in which the spores are not destroyed
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Infant botulism
Most common type of botulism. Infants have underdeveloped gut microbiota, and spores that they digest can then grow in the intestine and produce the toxin. Ingestion of honey in a child under one year old can cause botulism. Infants who are affected may seem "floppy" due to muscle weakness
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Wound botulism
Occurs in wounds contaminated with spores. An increase in cases has been seen with IV drug use
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Iatrogenic botulism
Medically induced botulism- occurs when someone is given too high of a dose of botulin toxin for excessive muscle activity or cosmetic use
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Botulinum toxin
The virulence factor of C. botulinum. It is a neurotoxin that binds to the synapse of motor nerve fibers, resulting in acute (flaccid) paralysis and death. The toxin blocks exocytosis of acetylcholine, which means that stimulation of nerve activity is blocked and paralysis results. There is an antitoxin to treat these symptoms
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Clostridium botulinum Identifying characteristics (3)
1. Lecithinase and Lipase positive
2. Spores are oval/subterminal and resemble tennis rackets
3. Diagnosis usually based on signs and symptoms and detection of toxin in stool and blood
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Symptoms of botulism
Double vision, droopy eyelids, trouble speaking, swallowing, or breathing. Untreated botulism can be fatal if the muscle weakness affects the respiratory muscles
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Clostridium difficile
Normal flora of gastrointestinal tract in small percentage of population and as many as 30% of hospitalized patients. High carriage rate in intestines of patients who have received broad spectrum antimicrobial agents that have eliminated normal intestinal flora. Causes antibiotic associated pseudomembranous colitis and diarrhea- the diarrhea can cause severe dehydration and parts of the colon can die, which would require surgery and could be a sepsis risk. People with a healthy microbiome are at low risk
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C. diff virulence factors
Produces enterotoxin A and cytotoxin B. Enterotoxin impacts the GI tract, while cytotoxins cause inflammation in cells or destroys cells
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C. diff infections are diagnosed by (5)
1. Growing toxin producing bacteria from stool sample
2. Detecting toxin in stool using tissue culture monolayers
3. Detecting toxin in stool using immunoassays
4. Detecting glutamate dehydrogenase (GDH) antigen
5. Molecular detection of C. difficile toxin gene
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How are C. diff spores destroyed?
Chlorine bleach is the only thing that destroys the spores- it needs to be on the spores for 10-15 minutes
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Pseudomembranous colitis
A medical condition in which the colon gets inflamed in association with excessive intake of broad spectrum antibiotics. Symptoms include watery diarrhea, abdominal pain with cramping, fever, mucousy stools, nausea, and dehydration
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Identifying characteristics of C. diff (3)
1. Culture from stool using Cycloserine-cefoxitin-fructose agar (CCFA). Selective and differential agar. Colonies fluoresce a green-yellow color under UV light. The organism is slow growing, so cultures take awhile
2. Lecithinase and Lipase negative
3. Spores oval/subterminal
107
How is the C. diff toxin detected from a stool sample?
EIA tests or cell culture can be used, although culture is relatively slow. The toxin gene can also be detected in a stool sample using molecular detection (PCR). One issue is that PCR may be detecting the toxin in people who are just colonized by the organism
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Clostridium septicum
Normal flora of gastrointestinal tract, suggests colon cancer when found in blood cultures- a disruption to the GI tract can release the organism into the blood. Occasionally cause of gas gangrene due to histotoxins. Virulence factor is histotoxins.
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Identifying characteristics of Clostridium septicum (2)
1. Swarming “Medusa head” colonies- bacillus anthracis does this as well
2. Lecithinase and Lipase negative
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Actinomyces species
There are 20 species, with actinomyces israelli being the most common pathogen. It is normal flora of animal and human mucous membranes. Virulence factors - fimbriae
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Actinomyces israelli
Causes “lumpy jaw”, abdomen and chest infections and pelvic infections in women with intrauterine devices. The infection may begin in a membrane, like in the mouth, and work its way outward through sinus tracts- small tunnels that open onto the surface of the skin or mucous membranes. Yellow discharge is produced through the skin- called sulfur granules due to the color
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Identifying characteristics of actinomyces species (3)
1. Gram positive filamentous, branching rods. A sulfur granule may be gram stained
2. Colony – molar tooth morphology
3. Catalase and indole - negative
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How would you differentiate an anaerobic Actinomyces species from an aerobic actinomycete like Nocardia?
Nocardia acid fast stain
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Cutibacterium (Propionibacterium)
4 species, with cutibacterium acnes being the most common species. They are normal flora of the skin, mouth and gastrointestinal tract - most commonly isolated anaerobic Gram positive bacillus. Opportunistic pathogen – plays role in acne and is recovered from infections of prosthetic devices (i.e. CSF shunts and prosthetic joints especially shoulder). Also can cause corneal ulcers after cataract surgery. Virulence factors are production of enzymes that can cause tissue damage
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Why are shoulder joint infections so serious?
Shoulder joint infections are more serious- the surgery requires cutting through the armpit, which contains multiple nooks and crannies for the organism to hide in
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Identifying characteristics of Cutibacterium acnes (2)
1. Described as anaerobic diphtheroid (palisading)- non-sporulating, pleomorphic Gram-positive bacilli
2. Catalase and indole positive
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Acne formation
The Cutibacterium acnes organism lives in the hair follicles. If the follicle becomes clogged with sebum and shed keratin, the bacteria can infect it and cause inflammation (acne) and scarring. The inflammation begins mildly, but scarring occurs with more severe inflammation
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Mobiluncus species
Normal flora of female genital tract unless it’s the predominant bacterium. Associated with bacterial vaginitis, pelvic inflammatory disease and abdominal infections. Virulence factors: ability to adhere to epithelial cells
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Identifying characteristics of the Mobiluncus species (3)
1. Stains Gram negative but has cell wall structure of Gram positive
2. Curved rod
3. Catalase and indole negative
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Lactobacillus species
Normal flora of GI tract and female genital tract (during childbearing years). Helps to maintain an acidic environment in the vagina to keep other organisms in check. If the population of lactobacilli decreases the risk of bacterial vaginitis increases. Rarely pathogenic – often used as probiotic (Lactobacillus acidophilus)
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Identifying characteristics of the Lactobacillus species (3)
1. Aerotolerant anaerobe
2. Alpha hemolytic colonies on blood agar
3. Catalase negative
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Bifidobacterium species
Normal flora of oral and gastrointestinal tract. Mostly nonpathogenic; probiotic (B. lactis regularis). Identifying characteristics: Bifurcated Gram positive rods and catalase negative and indole positive. The rods are divided into 2 branches or forks
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Eggerthella (Eubacterium) species
Normal flora of oral cavity and intestinal tract, mostly nonpathogenic. Identifying characteristics- Gram positive rod, catalase and indole negative
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Definitive identification methods (4)
1. Biochemical test batteries
2. Metabolic end product analysis using gas liquid chromatography
3. Cell wall fatty acid profiling by gas liquid chromatography
4. Mass spectrometry (MALDI-TOF)
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Treatment of anaerobic infections
Drainage of abscesses, elimination of foreign bodies, debridement of necrotic tissues and other surgical measures are frequently done- gets rid of the anaerobic environment. Antimicrobial susceptibility testing is not routinely performed (fastidious nature of bacteria and slow growth). Presumptive identification is important to help guide therapy
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Metronidazole mechanism of action
Metronidazole is converted in anaerobic organisms by the redox enzyme pyruvate-ferredoxin oxidoreductase. The nitro group of metronidazole is chemically reduced by ferredoxin and the products are responsible for disrupting the DNA helical structure, therefore inhibiting nucleic acid synthesis
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Gram negative rods susceptibility to antimicrobials
Bacteroides fragilis group produce beta-lactamases so are resistant to penicillins and most cephalosporins (are susceptible to ampicillin/sulbactam and piperacillin/tazobactam). Susceptible to metronidazole and carbapenems.
128
Non-spore forming Gram positive rods susceptibility to antimicrobials
In general susceptible to penicillins, metronidazole, and carbapenems (exceptions are Actinomyces and Cutibacterium (Propionibacterium) which are resistant to metronidazole)
129
Clostridium species susceptibility to antimicrobials
Susceptible to penicillins, cephalosporins, metronidazole and carbapenems. Variable susceptibility to clindamycin depending on species. Vancomycin is used to treat Clostridium difficile.
130
Anaerobic cocci (Gram positive and Gram negative) susceptibility to antimicrobials
Susceptible to penicillins and clindamycin.
