厌氧性细菌

1. 厌氧性细菌

4. 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:

5. SOD: O2-+2H+ H2O2 Catalase: H2O2  H2O + O2 Peroxidase: H2O2 H2O/NAD to NADH

6. 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.

7. 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.

8. 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）

9. Clostridium tetani spore vegetative

10. Gram-positive rods that form terminal spores

11. 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.

12. 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.

13. 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.

14. 病理 • Clostridia tetani produces two exotoxins called tetanus toxins: • Tetanolysin（破伤风溶血毒素）: its virulent 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.

15. Pathogenesis of tetanospasmin • one heavy chain (H chain) • C end：binds to the gangliosides（神经节苷脂） of inhibitory neurons • N 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 g-GABA (g-氨基丁酸) and glycin (甘氨酸) • Stops inhibitory nerve impulse to skeletal muscles, resulting in persistent muscle contraction.

17. 破伤风 • 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）

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

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

20. The adult  tetanus patient shows opisthotonos

21. 防治原则 • The wound is treated by debridement (清创术) to destroy anaerobic environment.

22. 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

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

24. 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）

25. 致病因子 • 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.

26. 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.

27. Form double hemolysis circles on blood agar plates. • The α-hemolysis is caused byα-toxin while the β-hemolysis byθ-toxin.

28. Stormy fermentation（汹涌发酵） • Clostridium perfringens shows “stormy 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.

30. 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

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

33. 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

34. 预防原则 • Debridement (Gas gangrene) • A large dose of antibiotics (penicillin) • Antitoxin against alpha-toxin and hyperbaric oxygenation (高压氧疗法) • No vaccine is available

35. 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）

36. Clostridium botulinum

37. 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.

38. 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.

39. 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.

41. 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.

42. 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

43. Non-spore-forming anaerobesare strict anaerobesand 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-positive or Gram-negative cocci or rods belonging to 23 genera. 11 genera are associated with human diseases.

44. Most non-spore-forming anaerobesare 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.

45. 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.

46. 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.

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