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Bacillus Morphology and Physiology

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1 Bacillus Morphology and Physiology
B. anthracis: anthrax of the animals and humans. B. cereus: food poisoning; opportunistic infections. Morphology and Physiology Aerobic or facultatively anaerobic. Large gram-positive rods, have square ends, arranged in long chains. Form spores. Most are saprophytic (soil, water, air, and on vegetation.)

2 B. anthracis Physiology and Structure
B. anthracis is encapsulated and non-motile. The capsule consists of polypeptide (poly-D-glutamic acid). The spores can withstand dry heat and certain disinfectants for moderate periods, and persist for years in dry earth. Animal products contaminated with anthrax spores can be sterilized only by autoclaving.

3 B. anthracis Pathogenesis and Immunity
Primarily a disease of herbivores (sheep, cattle, horses); humans are rarely affected. Being used by the terrorists as a biological warfare. In animals, portal of entry is mouth and GI tract. In humans, scratches in the skin (95% of infection), ingestion or inhalation lead to infection. Inhalation is the most likely route for infection with biological weapons (LD50: 2,500-55,000). The spores germinate in the tissue at the site of entry, and growth of the vegetative forms results in gelatinous edema and congestion. Bacillus spread via lymphatics to the blood and other tissues.

4 Spores from Germination of the carcasses spores in the soil
Grazing animals infected through injured mucous membrane Infection in humans

5 B. anthracis Pathogenesis and Immunity Virulence factors
Capsule (polypeptide) Exotoxins (A-B toxins encoded from another plasmid) Edema toxin is composed of protective antigen (B-subunit) and edema factor (has adenylate cyclase activity). This toxin complex increases vascular permeability which leads to shock. Lethal toxin is composed of protective antigen and lethal factor (a metalloprotease). This toxin stimulates macrophages to release proinflammatory cytokines.

6 B. anthracis Clinical Diseases
Cutaneous anthrax (malignant pustule): The papule rapidly changes into a vesicle, then a pustule, and finally a necrotic eschar. The infection may disseminate, giving rise to septicemia. Inhalation anthrax (wool-sorters’ disease): Mediastinitis (enlargement of mediastinal lymph nodes), sepsis, and meningitis (50% patients). Pulmonary disease rarely develops. Gastrointestinal anthrax (very rare): Can result in ulcers in the mouth and esophagus, or abdominal pain, vomiting and bloody diarrhea. May develop into septicemia rapidly with a mortality that can be 100%.

7 B. anthracis Treatment Control
Penicillin is the drug of choice. Resistant to sulfonamides and cephalosporins. Control Proper disposal of animal carcasses (burning or deep burial in lime pit). Autoclaving of animal products. Protective clothing and gloves for handling infected animals. Vaccination of domestic animals. Immunization of persons at high risk with a cell-free vaccine.

8 B. cereus and other bacillus species
Ubiquitous organisms; primarily opportunistic pathogens. B. cereus: the most important among them. Noncapsulated and motile, causing gastroenteritis: emetic form and diarrheal form. ocular infections: acute panophthalmitis occurs after traumatic, penetrating injuries of the eye with a soil- contaminated object. intravenous catheter-related sepsis. Other infections: endocarditis, pneumonitis, sepsis, meningitis, etc. Symptomatic treatment is adequate for B. cereus gastroenteritis. The treatment of other Bacillus is complicated because the course is rapid and progressive and they are resistant to multiple drugs.

9 Back

10 B. cereus food poisoning


12 Anaerobic Bacteria

13 Anaerobiosis Anaerobic bacteria will not grow in the presence of oxygen. Possible mechanisms: 1) Lack of cytochrome systems for the metabolism of O2. 2) Short of superoxide dismutase. 3) Short of catalase. 4) other unknown mechanisms. Ability of anaerobes to tolerate oxygen or grow in its presence varies from species to species. Most anaerobic clinical isolates are moderately obligate anaerobes, and have small amount of both catalase and superoxide dismutase.

14 Methods for excluding oxygen
3. Anaerobic glove chamber 1. Fluid media containing fresh animal tissue or 0.1% agar containing a reducing agent, thioglycollate. 2. Anaerobic jar

15 Non-sporeforming anaerobes
Bacteroides, Fusobacterium, Porphyromonas, Prevotella, Veillonella, Actinomyces, Propionibacterium, Peptostreptococcus 1. Non-sporeforming anaerobes constitute the predominant part of normal indigenous flora in human body. 2. Diseases caused by them are usually not transmissible and are almost autoinfection. The result is usually tissue necrosis and abscess formation. 3. Types of infections are related to the normal endogenous location of the bacteria (Table 42-1). 4. Most infections caused by them are mixed, containing 5- 6 species or more, including both anaerobes and facultative anaerobes (synergism). 5. In most cases, treatment requires drainage of the purulent material and appropriate chemotherapy (e.g., metronidazole, clindamycin, etc.)

16 Bacteroides fragilis Pleomorphic in size and shape; capsulated.
Aerotolerant; growth is stimulated in 20% bile. Constitutes less than 10% of Bacteroides species in the normal colon, however, is the most common isolate of anaerobes from infections (intra-abdominal, gynecologic, and skin and soft tissue infections; bacteremia.) Major virulence factor: capsular polysaccharides, which may cause abscess formation when injected into the rat abdomen. Resistant to penicillin.

17 B. fragilis

18 Clostridium Physiology and Structure
C. perfringens: gas gangrene; food poisoning C. tetani: tetanus C. botulinum: botulism C. difficile: pseudomembranous colitis Physiology and Structure Anaerobic. Large gram-positive rods. The spores are usually wider than the rods, and are located terminally or subterminally. Most clostridia are motile by peritrichous flagella.

19 C. perfringens Physiology and Structure Pathogenicity and Immunity
Large gram-positive bacilli. Non-motile; capsulated. Hemolytic and metabolically active. Pathogenicity and Immunity Subdivided into 5 types based on the four major lethal toxins they produce. Type A causes most of the human infections. Strains of C. perfringens are widely distributed in nature, and inhabit the intestine of humans and animals. They cause a spectrum of diseases primarily by producing toxins and enzymes.

20 C. perfringens a-toxin: lecithinase (phospholipase C) that lyses a variety of cells. Lethal, necrotizing and hemolytic. Increases vascular permeability, resulting in massive hemolysis and bleeding, tissue destruction, hepatic toxicity, and myocardial dysfunction. Other necrotizing and hemolytic toxins DNase, hyaluronidase Enterotoxin: produced primarily by type A strains.

21 C. perfringens Clinical Diseases Soft tissue infections
Portal of entry: trauma or intestinal tract. Usually caused by mixed infection including toxigenic clostridia, proteolytic clostridia and various cocci and gram-negative organisms. Three types of infections with increasing severity: Cellulitis: gas formation in the soft tissue. Fasciitis or suppurative myositis: accumulation of gas in the muscle planes. Myonecrosis or gas gangrene: a life-threatening disease.

22 C. perfringens Clinical Diseases Gas gangrene
Spores germinate vegetative cells multiply, ferment carbohydrates and produce gas in the tissue. This results in distension of tissue and interference with blood supply the bacteria produce necrotizing toxin and hyaluronidase, which favor the spread of infection tissue necrosis extends, resulting in increased bacterial growth, hemolytic anemia, then severe toxemia and death. Incubation: 1-7 days after infection. Symptoms: Crepitation in the subcutaneous tissue and muscle, foul smelling discharge, rapidly progressing necrosis, fever, hemolysis, toxemia, shock, renal failure, and death. Can be also caused by other Clostridium species.

23 C. perfringens Clinical Diseases Food poisoning
The enterotoxin causes marked hypersecretion in jejunum and ileum. Enterotoxin: a heat-labile protein (can be inactivated at ≥74 oC) produced by some strains of C. perfringens type A. It disrupts ion transport in the enterocytes. Symptoms: diarrhea, usually without vomiting or fever. Clotridium bacteremia: usually occurs in patients with tumors.

24 C. perfringens Treatment Prevention, and Control
Treatment for suppurative myositis or myonecrosis: Prompt and extensive débridement. Antibiotics (penicillin) administration. Hyperbaric oxygen may "detoxify" patients rapidly. C. perfringens food poisoning requires only symptomatic care. Prevention, and Control Preventive measures: surgical débridement and prophylactic antibiotics.

25 C. tetani Physiology and Structure Pathogenesis and Immunity
Small, motile; Spore-forming (drumstick appearance); Extremely sensitive to oxygen toxicity. Pathogenesis and Immunity Tetanospasmin is responsible for clinical manifestations of tetanus. An A-B toxin, released when the bacteria lyse. Subunit A is a zinc endopeptidase that acts on CNS: Inhibits release of an inhibitory mediator (e.g., GABA or glycine) which acts on postsynaptic spinal neurons (causing spastic paralysis).

26 C. tetani Pathogenesis and Immunity
Contamination of devitalized tissue (wound, burn, injury, umbilical stump, surgical suture) with the spores germination of the spores (aided by necrotic tissue, calcium salts, and associated pyogenic infections) release of tetanospasmin the toxin reaches CNS by retrograde axonal transport or via the bloodstream the toxin is fixed to gangliosides in spinal cord or brainstem and exerts its actions.

27 C. tetani Clinical Diseases Generalized tetanus
Incubation period: 4-5 days. Symptoms: convulsive tonic contraction of voluntary muscles. Spasms involve first the area of injury, then the muscles of the jaw (trismus or lockjaw; risus sardonicus). Other voluntary muscles become involved gradually, resulting in generalized tonic spasms (opisthotonos). Death usually results from interference with respiration. The mortality rate of generalized tetanus: ~50%. In more severe case, the autonomic nervous systems are also involved. Localized tetanus (confined to the musculature of primary site of infection) Cephalic tetanus (site of infection: head) Neonatal tetanus (infection of the umbilical wound): mortality >90%, and developmental defects are present in survivors.

28 C. tetani Laboratory Diagnosis Treatment, Prevention, and Control
Diagnosis depends on the clinical picture and a history of injury. Proof of isolation of C. tetani from contaminated wounds depends on production of toxin and its neutralization by specific antitoxin. Treatment, Prevention, and Control Prevention is much more important than treatment: Active immunization with toxoid. ‘Booster shot’ for previously immunized individuals. This may be accompanied by antitoxin injected into a different area of the body. 2. Proper care of wounds. Surgical débridement to remove the necrotic tissue. 3. Prophylactic use of antitoxin. 4. Antibiotic treatment. Metronidazole *Patients with symptoms of tetanus should receive muscle relaxants, sedation and assisted ventilation.

29 C. tetani Control Active immunization with tetanus toxoid (toxin detoxified with formalin) Aluminum salt-adsorbed toxoid DPT vaccine Course of immunization: as mentioned in C. diphtheriae. Narcotics addicts are a high-risk group.

30 C. botulinum Physiology and Structure
This species is a heterogeneous group of fastidious, spore-forming, anaerobic bacilli. Produce antigenically distinct toxins (botulinum toxins; Botox). Neurotoxic proteins with a lethal dose of 1-2 mg; liberated during the growth and during autolysis of the bacteria. A-B toxins. The subunit A is a zinc endopeptidase blocking release of acetylcholine at peripheral cholinergic synapses. Destroyed by heating for 20 min. at 100 oC.

31 C. botulinum Pathogenicity and Immunity An intoxication.
Ingestion of food (spiced, smoked, vacuum-packed, or canned alkaline foods) in which C. botulinum has grown and produced toxin the toxin acts on both the voluntary and autonomic nervous systems at synapses and neuromuscular junctions flaccid paralysis.

32 C. botulinum Clinical Diseases Foodborne botulism
Incubation period: hrs. Symptoms: double vision, inability to swallow, speech difficulty, bulbar paralysis, constipation, and abdominal pain. Bilateral descending weakness of peripheral muscle. Death occurs from respiratory paralysis or cardiac arrest. No fever. Mortality is high. Recovery may need months to years. Patients who recover do not develop antitoxin.

33 C. botulinum Clinical Diseases Infant botulism
Occurs in the first month of life. Weakness, signs of paralysis, C. botulinum and its toxin are found in feces. May be caused by ingestion of the bacteria or spores which grow in the gut and produce toxin. Feeding of honey has been implicated as a possible cause. Patients recover with supportive therapy alone. Wound botulism Develops from contaminated wounds. Symptoms similar to those of food borne botulism with longer incubation time. Less GI symptoms.


35 C. botulinum Treatment Stomach lavage and high enemas.
Trivalent (A, B, E) antitoxin administered intravenously promptly. Adequate ventilation by mechanical respirator.

36 C. botulinum Prevention and Control
Spores of C. botulinum are widely distributed in soil and often contaminate vegetables, fruits etc. Strict regulation of commercial canning has largely reduced the danger of widespread outbreaks. The chief danger lies in home-canned foods (vegetables, smoked fish or vacuum-packed fresh fish). The cans with toxic food may swell or may show innocuous appearance. The risk from home-canned food can be reduced by boiling the food for 20 min. Children younger than 1 year should not eat honey.

37 C. difficile C. difficile is responsible for antibiotic-associated gastrointestinal disease ranging from self-limited diarrhea to severe, life threatening psudomembranous colitis. It is a part of normal intestinal flora in a small number of healthy people and hospitalized patients. The spores can contaminate an environment for many months and can be a major source of nosocomial outbreaks. This organism produces two toxins: Toxin A (an enterotoxin) induces release of cytokines, hypersecretion of fluid, and development of hemorrhagic necrosis. Toxin B (a cytotoxin) causes tissue damage.

38 C. difficile Pseudomembranous colitis
Administration of antibiotics results in proliferation of drug-resistant C. difficile. Antibiotics that are most commonly associated with pseudomembranous colitis are ampicillin, cephalosporins, and clindamycin. Disease occurs if the organism proliferates in the colon and produces toxins: watery or bloody diarrhea, abdominal cramps, leukocytosis and fever. Laboratory diagnosis depends on isolation of C. difficile in the feces and detection of toxins with tissue culture cells (cytotoxicity assay). The disease is treated by discontinuing the offending antibiotic, and orally giving either metronidazole or vancomycin in severe cases.

39 C. difficile Antibiotic-associated diarrhea
25% of cases are associated with C. difficile. Mild to moderate diarrhea, less severe than the typical pseudomembranous colitis. The role of the toxins is not well understood.






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