Good Luck with the last chance!

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Good Luck with the last chance!
1930-2130 Oct. 19th, Fri
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Anaerobic Bacteria
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Obligate Anaerobes

• In the presence of oxygen, anaerobic bacteria
  produce toxic products such as superoxide and
  hydrogen peroxide, but they lack superoxide
  dismutase (SOD), catalase and peroxidase that
  detoxify these products

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SOD O2-2H ? H2O2 Catalase
H2O2 ? H2O O2 Peroxidase H2O2 ? H2O /NAD to
NADH
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• No oxidative phosphorylation
• Infection caused by anaerobes usually occurs in
  the sites with low oxidation-reduction potential
  such as periodontal pocket, intestinal tract and
  vagina.
• Anaerobes are co-infected with other facultative
  anaerobe which use up oxygen to establish a local
  anaerobic environment.

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Source of anaerobic infection

• Endogenous infection caused by anaerobes of
  normal flora which are non-spore formers.
• Exogenous infection The pathogens are usually
  anaerobic spore-formers and come from the
  environment (e.g., soil). Clostridia is the
  unique genus of anaerobic spore-formers to cause
  human diseases.

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Clostridia

• There are at least 118 species, the clinically
  important species
• Clostridia tetani
• Clostridia perfringens
• Clostridia botulinum
• Clostridia difficile

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Clostridium tetani
spore
vegetative
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• Gram-positive rods that form terminal spores

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• Culture clustering growth with hemolysis occurs
  on blood agar.

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• Biochemical activity does not ferment any
  carbohydrates.
• Resistance spores but not its vegetative form
  can tolerate boiling for 60 min and stay alive
  for several ten years in soil.

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• Clostridia tetani is found in soil. It is
  occasionally found in intestinal flora of humans
  and animals.
• Clostridia tetani is the cause of tetanus when
  the spores enter wounds.

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Process to cause tetanus
Spore-contaminated soil or other foreign objects

• Narrow deep wounds with limited blood and oxygen
  supply
• co-infection with facultative anaerobe can use up
  the local oxygen

Spores germinate and then produce tetanus toxins.
The organism still remains in the local wound.
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• Clostridia tetani produces two exotoxins called
  tetanus toxins
• Tetanolysin its virulent role remains unknown.
• Tetanospasmin it is a neurotoxin with strong
  toxicity and the most important virulent factor
  of the bacterium.

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Pathogenesis of tetanospasmin

• one heavy chain (H chain)
• C endbinds to the ganglioside receptors of
  inhibitory neurones
• N endhelps in entrance to the cells
• one light chain (L chain)
• It contains a zinc endopeptidase
• Blocks the release of inhibitory neuronal
  mediators g-GABA (g-????) and glycin
  (???)
• Stops inhibitory nerve impulse to skeletal
  muscles, resulting in persistent muscle
  contraction.

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• Typical symptoms include sardonic smile, lockjaw,
  neck rigidity, opisthotonos and dyspnea

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This baby has tetanus. The infection is usually
caused by exposing to Clostridia tetani when
cutting umbilical cord.
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This the neonatal tetanus patient displays
sardonic smile, lockjaw and dyspnea
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The adult  tetanus patient shows opisthotonos
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• Among all animal species, horses and humans, are
  most susceptible to tetanospasmin
• If not treated in time, about 20 of the patients
  are died of suffocation and respiratory failure

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• The wound is treated by debridement (???) to
  destroy anaerobic environment.

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• Although antibiotics (streptomycin and
  erythromycin) are used as part of the treatment,
  tetanus patients must be promptly treated with
  tetanus antitoxin (TAT) to neutralize free
  tetanospasmin.
• 1500 3000 U for prevention
• 100.000 200.000 U for therapy

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• Tetanus toxoid is a component of DPT vaccine
  (diphtheria toxoid, killed whole cell pertussis,
  tetanus toxoid).

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Clostridia

• There are at least 118 species, the clinically
  important species
• Clostridia tetani
• Clostridia perfringens
• Clostridia botulinum
• Clostridia difficile

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• Gram-positive rods, have capsule, can form
  terminal spores

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• Form double hemolysis circles on blood agar
  plates.
• The a-hemolysis is caused bya-toxin while the
  ß-hemolysis by?-toxin.

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Stormy fermentation

• Clostridium perfringens shows stormy
  fermentation in litmus milk. Acid turns the pH
  indicator litmus from blue to pink. The acid and
  enzymes coagulate proteins to curd. The gas
  generated in the milk breaks the coagulated
  proteins.

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Diseases

• Wound contaminated by soil (main source) and
  mammalian feces
• Gas gangrene refers to serious tissue swelling
  due to release of gas (fermentation product of
  the bacterium) and tissue necrosis

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• The death can occur within 2 days if untreated.
  Treatment includes debridement, antitoxin and
  antibiotic therapy.

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Diseases

• Common diseases
• Gas gangrene
• Food poisoning

• Other diseases
• Necrotizing Enteritis
• Cellulitis (????)
• Septicemia

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Food poisoning

• Marked hypersecretion in jejunum and ileum with
  loss of fluids and electrolytes in diarrhea.

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Necrotizing enteritis

• an acute necrotizing process in the jejunum with
  symptoms of abdominal pain, bloody diarrhea and
  peritonitis.
• The death rate of this disease is as high as
  approximately 50.

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Virulent factors

• Clostridium perfringens produces over 10 types of
  toxins. Some toxins are hemolytic, proteolytic,
  saccharolytic enzymes. Some are lethal and
  necrotic.
• alpha-toxin is the most important, it lyses
  erythrocytes, platelets, leukocytes and
  endothelial cells.

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• According to antigenic differences of 4 major
  toxins, the bacterial strains can be divided into
  AE toxic types.
• Type A is clinically the most important. Type A
  can also produce enterotoxin to cause food
  poisoning.

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• Morphology
• Stormy fermentation
• alpha-toxin (lecithinase)

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• Debridement (Gas gangrene)
• A large dose of antibiotics (penicillin)
• Antitoxin against alpha-toxin and hyperbaric
  oxygenation (?????)
• No vaccine is available

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Clostridia

• There are at least 118 species, the clinically
  important species
• Clostridia tetani
• Clostridia perfringens
• Clostridia botulinum
• Clostridia difficile

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Clostridium botulinum
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• Clostridium botulinum is a Gram-positive,
  anaerobic, spore-forming bacillus.
• It produces an enterotoxin (botulinum toxin)
  that causes food poisoning (botulism).
• According to the antigenicity of botulinum
  toxin, The microbe can be divided into AG types.
• Among the 7 types, type A and then type B
  strains cause most disease.

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• The foods that are easily contaminated by the
  toxins or spores are sausage and canned foods
  abroad, and fermented-bean preparations in
  China.
• In adult, the toxin or spore causes botulism
  (death rate 50-70).
• In infant (especially younger than 6 months),
  the toxin or spore causes infant botulism (death
  rate 1-2) .

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Pathogenesis of botulinum toxin

• Botulinum toxin is a nuerotoxin. It binds to
  other non-toxic proteins to form a complex. It is
  released, when the bacteria are dead and broken.
• When the complex enters intestines, the alkaline
  condition makes botulinum toxin released.

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• Botulinum toxin binds the cellular receptor of
  neuromuscular junction and then enters the cells
  to block the release of acetylcholine (????).
• Acetylcholine is a neurotransmitter, which
  mediates nerve impulses. Therefore, flaccid
  paralysis occurs.

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• The typical symptoms are double vision and squint
  (eye), dyscatabrosis (throat), and dyspnea. The
  patients are usually died of respiratory failure.
  
• 10 ng of Botulinum toxin can kill an adult.

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• Sample collection foods and patients feces.
• Identification of botulinum toxin in the samples

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• The patients must be promptly treated with A, B,
  E multi-valent antitoxin to neutralize the free
  toxins.
• Sometimes antibiotic therapy is needed.
• Vaccination does not protect hosts from botulism.

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• Non-spore-forming anaerobes are strict anaerobes
  and present in large numbers in intestine (95-99
  of the total bacterial mass), mouth and
  genitourinary tract as normal flora.
• These anaerobes can be divided into anaerobic
  Gram-positive or negative cocci or rods belonging
  to 23 genera. 11 genera are associated with human
  diseases.

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Non-Spore-forming Anaerobes of medical
Importance  

• Gram-negative rods
• Bacteroides, Prevotella, Porphyromonas,
  Fusobacterium
• Gram-positive rods
• Propionibacterium, Actinomyces, Eubacterium,
  Bifidobacterium
• Gram-positive cocci
• Peptostreptococcus, Peptococcus
• Gram-negative cocci
• Veillonella

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• Most non-spore-forming anaerobes are
  opportunistic pathogens, and a few of them show
  relatively stronger pathogenicity.
• Co-infection with facultative bacteria.
• Adhesion to host cells by pili.
• Production of various virulent factors such as
  enterotoxin, collagenase, hyaluronidas, protease,
  hemolysin, DNase.
• Oral, genitourinary, abdominal and perineal
  infections are most common.

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• Most infections cause chronic pyogenic
  inflammation, local abscess or tissue necrosis.
• The secretion or pus in foci are usually colored
  (black, brown, bloody, pink), putrid and
  gas-producing.

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• Direct microscopy examination to observe the
  bacteria in the smear of secretion.
• Typical bacteriological examination to isolate
  and identify the anaerobes from samples. In
  smear of secretion, bacteria can be seen, whereas
  the results of common cultivations are negative.

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• Aminoglycoside antibiotics (e.g., streptomicin)
  and some ß-lactam antibiotics are ineffective.
• Antibiotics such as nitrominazole (metronidazole)
  are used for treatment.
• No vaccines are available.