Gram Positive Spore Forming Bacilli PDF Lecture Notes

Gram Positive Spore forming Bacilli Microbiology and immunology faculty of medicine Menofia University  Gram Positive Spore forming bacilli Aero...

Gram Positive Spore forming Bacilli Microbiology and immunology faculty of medicine Menofia University  Gram Positive Spore forming bacilli Aerobic genus Anaerobic Bacillus genus Clostridium Pathogenic Non- B. anthracis pathogenic Cl. tetani Cl. perfringens Cl. botulinum Cl. difficile &B.cereus anthracoids  Genus Bacillus aerobic gram positive, spore forming bacilli Pathogenic Saprophytic anthracoids Bacillus anthracis saprophytes in water, soil, air → B.cereus Cause opportunistic infection  Bacillus anthracis Morphology Gram positive rectangular large bacilli arranged in chains spore forming ( spore central, oval) Capsulated, non motile → any spore not stained with gram stain (appear unstained) → (McFadyean reaction) capsule stain of bacillus with polychrome methylene blue the capsule appears pink around the blue bacillus Bacillus anthracis Gram stain McFadyean reaction Cultural characters: Media: any type of media on nutrient agar → medusa head on blood agar → non-haemolytic on gelatin → liquefied, resembles an inverted fir tree. medusa head Virulence factors 1- Capsule - polypeptide –˃ antiphagocytic 2- Anthrax toxin cytotoxic Pathogenesis and Disease ANTHRAX B. anthracis is a major agent of biologic warfare (bioterrorism) caused by sending spores of the organism through the mail. Anthrax is primarily a disease of animals e.g. cattle and sheep (zoonotic) man infected accidentally especially farmers, butchers and by: 1-contact with diseased animals or their dead bodies 2-inhalation of spores 3-ingestion of infected product  Anthrax clinical presentations 1- Cutaneous 2- Pulmonary anthrax anthrax 3- Intestinal (malignant (wool sorter's anthrax pustule) disease)  Anthrax Pathogenesis and clinical presentations Cutaneous anthrax About 20% mortality Inhalation anthrax High mortality 95 % Intestinal anthrax High mortality 95 % Diagnosis: clinical signs and history of exposure. 1-specimen: skin lesions, sputum,stool and blood 2- Direct smears stained with gram stain and McFadyean stain. (morphology) 3- Cultures on nutrient or blood agar 4- Identification morphologically by gram confirmed by motility test and liquefaction of gelatin. 5- Serology ELISA to measure antibodies. 6-Rapid test: PCR-based assays For diagnosis of bioterrorism.  Bacillus Cereus Virulence factor: Heat labile and heat stable Enterotoxin Cytotoxic enzymes Disease produced by bacillus cereus Food poisoning  food poisoning Emetic type Diarrheal type Incubation period 1-5 hours 8-24 hours Short Long Food Rice Meat Pathogenesis Heat stable enterotoxin Heat labile enterotoxin Clinical picture Nausea and vomiting Diarrhea Watery non bloody Course Self limited Self limited  Genus Clostridium Characteristics : Large, Gram-positive bacilli. Spore forming. Anaerobic. Natural habitat - Soil and intestinal tract of humans and animals.  Clostridium Species 1- Cl. tetani causing tetanus 2- Cl. perfringens causing gas gangrene and food poisoning. 3- Cl. botulinum causing botulism (food poison). 4- Cl. difficile causing pseudomembranous colitis (antibiotic associated diarrhea).  Morphology 1- All 3 Cl. other than Cl. perfringens are motile non-capsulated while Cl. perfringens capsulated and non motile 2- Spore shape Cl. tetani Cl. perfringens Cl. botulinum Spherical oval oval Terminal bulging subterminal Subterminal or drum-stick central appearance Spores  Clostridium species Cl. tetani Cl. perfringens Cl. botulinum Cl. difficile  General Cultural characters: Environment: Strict anaerobes (2-5 days incubation) Media:- 1- Anaerobic media → cooked meat medium 2- Anaerobic Jar →on nutrient agar or blood agar→ β-haemolysis  Clostridium tetani Virulence factor: Tetanospasmin (neurotoxin) Action Motor nerve have no inhibitory control → increased excitability →generalized muscle spasms and hyper-reflexia → spastic paralysis. Disease: 1- classic tetanus 2- neonatal tetanus Risus sardonicus lock jaw Opisthotonus www.medicalgeek.com  Diagnosis 1-specimen:pus –discharge and wound 2-Identification Direct smear Culture Confirmatory test : Immunofluorescence stain Animal pathogenicity test  Cl. perfringens (invasive and tissue destroying ) 1-Associated with gas gangrene. 2-Cl. perfringens that produce a powerful enterotoxin cause food poisoning. 3-Their presence in water → fecal pollution  Biochemical Reactions 1-Ferment glucose ,lactose ,maltose and sucrose with production of acid and gas 2-Stormy clot reaction rapid fermentation of lactose in milk acid produced change milk colour to pink and the produced gas splits the clot  Biochemical activities 3- Nagler's reaction produce precipitation in egg yolk media due to production of lecithinase enzyme which split lecithicin to F.A causes a visible precipitate around the colonies  Virulence factors CL perfringens produces toxins and enzymes that result in spreading of infection 1- Alpha toxin Lecithinase cause cell death and necrosis. 2- Theta toxin has a haemolytic and necrotizing effect. 3- DNase, hyaluronidase and collagenase spreading factors. 4- Enterotoxin (superantigen) → food poisoning.  Diseases caused by CL perfringens 1- gas gangrene 2- food poisoning: Enterotoxin : a heat-labile protein, causing marked hyper secretion of water and electrolytes in jejunum and ileum. Symptoms: diarrhea, usually without vomiting or fever. Myonecrosis  Diagnosis 1-specimen: wound exudate 2-Identification Direct smear Culture 3-Biochemical reactions: Ferment sugars with production of acid and gas stormy clot reaction Nagler test 4-Serological test ELISA 5-PCR  Cl. Botulinum 1-The most resistant spores (100c for 5 h.) while toxin heat labile (100c for 20 m) 2-It causes botulism, which is a type of food poisoning due to ingestion of inadequately sterilized canned food as meat, tuna fish or alkaline vegetables. Canning provides proper anaerobic conditions for growth and production of exotoxin. Virulence factor : Botulinum toxin (neurotoxin) → block the release of acetylcholine leading to → flaccid paralysis.