厌氧性细菌

Obligate Anaerobes （专性厌氧菌）

In the presence of oxygen, anaerobic bacteria produce toxic products such as superoxide and hydrogen peroxide, but they lack superoxide dismutase (SOD ，超氧化物歧化酶 ), catalase （过氧化氢酶） and peroxidase （过氧化物酶） that detoxify these products:

SOD: O2-+2H+ H2O2

Catalase: H2O2 H2O + O2

Peroxidase: H2O2 H2O /NAD to NADH

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 （兼性厌氧菌） which use up oxygen to establish a local anaerobic environment.

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 （芽孢梭菌） is the unique genus of anaerobic spore-formers to cause human diseases.

Clostridia

There are at least 118 species, the clinically important species:

Clostridia tetani （破伤风芽孢梭菌） Clostridia perfringens （产气芽孢梭

菌） Clostridia botulinum （肉毒梭菌） Clostridia difficile （艰难梭菌）

Clostridium tetani

sporespore

vegetativevegetative

Gram-positive rods that form terminal spores

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.

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.

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.

Process to cause tetanus

病理 Clostridia tetani produces two exotoxi

ns called tetanus toxins: Tetanolysin （破伤风溶血毒素） : its virul

ent role remains unknown. Tetanospasmin （破伤风痉挛毒素） : it is

a neurotoxin with strong toxicity and the most important virulent factor of the bacterium.

one heavy chain (H chain)C end ： binds to the gangliosides （神经节苷脂） of inhibitory neuronsN end ： helps in entrance to the cells

one light chain (L chain)It contains a zinc endopeptidase （锌内肽酶）Blocks the release of inhibitory neuronal mediators -GABA (- 氨基丁酸 ) and glycin ( 甘氨酸 )Stops inhibitory nerve impulse to skeletal muscles, resulting in persistent muscle contraction.

Pathogenesis of tetanospasmin

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

Typical symptoms include sardonic smile（苦笑面容） , lockjaw （牙关紧闭） , neck rigidity, opisthotonos （角弓反张） and dyspnea （呼吸困难）

破伤风

This baby has tetanus. The infection is usually caused by exposing to Clostridia tetani when cutting umbilical cord.

This the neonatal tetanus patient displays sardonic smile, lockjaw and dyspnea

The adult tetanus patient shows The adult tetanus patient shows opisthotonos

防治原则 The wound is treated by debridement

( 清创术 ) to destroy anaerobic environment.

Although antibiotics (streptomycin and erythromycin ，链霉素、红霉素 ) 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

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

Clostridia

There are at least 118 species, the clinically important species:

Clostridia tetani （破伤风芽孢梭菌） Clostridia perfringens （产气芽孢梭

菌） Clostridia botulinum （肉毒梭菌） Clostridia difficile （艰难梭菌）

致病因子 Clostridium perfringens produces ove

r 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.

According to antigenic differences of 4 major toxins, the bacterial strains can be divided into A~E toxic types.

Type A is clinically the most important. Type A can also produce enterotoxin to cause food poisoning.

• Form double hemolysis circles on blood agar plates.

• The α-hemolysis is caused byα-toxin while the β-hemolysis byθ-toxin.

Stormy fermentation （汹涌发酵） Clostridium perfringens shows “stor

my fermentation” in litmus milk. 该菌分解乳糖产酸。 Acid turns the pH indicator litmus ( 石蕊 ) from blue to pink. The acid and enzymes coagulate proteins( 酪蛋白 ) to curd. The gas ( 氢气和二氧化碳 ) generated in the milk breaks the coagulated proteins.

Diseases

Wound contaminated by soil (main source) and mammalian feces

Gas gangrene （气性坏疽） refers to serious tissue swelling due to release of gas (fermentation product of the bacterium) and tissue necrosis

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

Food poisoning

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

十二指头肠

空肠

回肠

预防原则

Debridement (Gas gangrene) A large dose of antibiotics (penicillin) Antitoxin against alpha-toxin and hy

perbaric oxygenation ( 高压氧疗法 ) No vaccine is available

Clostridia

There are at least 118 species, the clinically important species:

Clostridia tetani （破伤风芽孢梭菌） Clostridia perfringens （产气芽孢梭

菌） Clostridia botulinum （肉毒梭菌） Clostridia difficile （艰难梭菌）

Clostridium botulinum

According to the antigenicity of botulinum toxin( 肉毒毒素 ), The microbe can be divided into A~G types.

Among the 7 types, type A, B and E strains cause most disease.

Pathogenesis of botulinum toxin Botulinum toxin( 肉毒毒素 ) 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.

Botulinum toxin binds to the cellular receptor of neuromuscular junction and then enters the cells to block the release of acetylcholine ( 乙酰胆碱 ).

Acetylcholine is a neurotransmitter, which mediates nerve impulses. Therefore, flaccid paralysis （松弛性瘫痪 ） occurs.

The typical symptoms are double vision and squint ( 眯眼 ), dyscatabrosis ( 咽下困难 ), and dyspnea （呼吸困难） . The patients are usually died of respiratory failure.

10 ng of Botulinum toxin can kill an adult.

Non-Spore-forming Anaerobesof medical Importance  

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

•Non-spore-forming anaerobes are strict anaerobes and

present in large numbers in the intestine (95-99% of the

total bacterial mass), mouth and genitourinary tract as

normal flora.

•These anaerobes can be divided into anaerobic Gram-p

ositive or Gram-negative cocci or rods belonging to 23 g

enera. 11 genera are associated with human diseases.

• 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( 会阴 ) infections are most common.

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 （腐烂的） and gas-producing.

• 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.

1. Aminoglycoside antibiotics (e.g., streptomicin) and

some β-lactam antibiotics are ineffective.

2. Antibiotics such as nitrominazole ( 比如 metronidaz

ole) are used for treatment.

2. No vaccines are available.