Gram Positive Rods PDF

Gram Positive Bacilli Microbiology Department Dr. Mohamed Elmutasim 9th of Feb. 2023 Objective: To study diseases caused by Gram positive bacilli diagnosis and management  Gram positive bacilli Classification of Gram-positive rods: There are five medically important genera o...

Gram Positive Bacilli Microbiology Department Dr. Mohamed Elmutasim 9th of Feb. 2023 Objective: To study diseases caused by Gram positive bacilli diagnosis and management  Gram positive bacilli Classification of Gram-positive rods: There are five medically important genera of gram-positive bacilli: Bacillus, Clostridium, Corynebacterium, Listeria, and Gardnerella. Endospore-forming ability: Bacillus and Clostridia are spore-forming rods, while Listeria, Gardnerella, and Corynebacterium are not. Gaseous (oxygen requirements): Bacillus species are obligate aerobes, whereas Clostridium species are obligate anaerobes.  Gram positive bacilli Some Gram-positive rods have a unique shape based on spores’ position, branches’ presence, etc. : -Actinomyces appear as irregular, branching gram-positive rods, -Corynebacteria appear as V or L club-shaped, -Clostridium tetani appear as drum-stick appearances, and -Nocardia appears as branching filaments.  Bacillus cereus Disease: Bacillus cereus causes food poisoning Habitat: Domestic animals, soil, and rice grains are the main reservoirs of this organism. Transmission: acquired by eating “reheated rice.” The spores germinate when rice is kept warm for many hours. Diagnosis: Bacillus cereus is an aerobic, spore-forming, Gram- positive bacillus.  Bacillus cereus The organism produces two toxins, one is like cholera toxin, and the another is like staphylococcal enterotoxin. The main symptoms of Bacillus cereus food poisoning are nausea, vomiting, and non-bloody diarrhea.  Bacillus anthracis Diseases: due to Anthrax toxin Anthrax occurs in three main forms: 1- Cutaneous (malignant pustule) painless ulcer with black eschar (crust, scab). Local edema is striking. Untreated cases progress to bacteremia & death.  Bacillus anthracis 2-Pulmonary (woolsorter's disease): Begins with symptoms resembling influenza, rapidly progresses to hemorrhagic mediastinitis, bloody pleural effusions, septic shock & death. 3- Gastrointestinal: Vomiting, abdominal pain & bloody diarrhea  Bacillus anthracis Habitat is soil. Transmission is by: - Contact with infected animals - Inhalation of spores from animal hair & wool. Transmission: Aerobic Gram-positive, Spore-forming rods Poly-D-glutamate Capsule (amino acids NOT polysaccharides)  Corynebacterium diphtheriae Disease: Diphtheria The disease starts with high temperature, chills, sore throat & enlargement of neck lymph nodes. Grayish membrane is seen on the throat, which cannot be removed. If membrane is pulled away bleeding. Pseudomembrane in throat caused by death of mucosal epithelial cells due to diphtheria toxin.  Corynebacterium diphtheriae Habitat is the human throat. Transmission is via respiratory droplets. Diagnosis: Club-shaped gram-positive rods arranged in V or L shape. Granules stain metachromatically. Aerobic Non–spore-forming organism.  Corynebacterium diphtheriae Treatment: Antitoxin made in horses neutralizes the toxin. Penicillin G kills the organism. No significant resistance to penicillin. Prevention : Toxoid vaccine: Toxoid is formaldehyde-treated toxin Given to children in combination with tetanus toxoid & pertussis vaccine (DTaP).  Listeria monocytogenes Diseases: Meningitis & sepsis in newborns & immunocompromised adults. Gastroenteritis. Habitat: Organism colonizes the GI & female genital tracts It is widespread in animals, plants & soil. Transmission is across placenta or by contact during delivery. Outbreaks of sepsis in neonates & gastroenteritis are related to ingestion of unpasteurized milk products, e.g., cheese.  Listeria monocytogenes Listeria grows well at cold temperatures called "cold enhancement." Predisposing factors : - Reduced cell-mediated immunity - Immunologic immaturity (neonates). Prevention: Pregnant women & immunocompromised patients should not ingest unpasteurized milk products or raw vegetables. Trimethoprim-sulfamethoxazole can prevent listeriosis  Clostridium tetani Disease: Tetanus It produces exotoxin Tetanus toxin (tetanospasmin) Habitat is the soil. Transmission: Organism enters through traumatic breaks in the skin Diagnosis: Anaerobic Gram-positive Spore-forming rods Spore is at one end ("terminal spore") so organism looks like a "tennis racket."  Clostridium tetani Treatment: Hyperimmune human globulin to neutralize toxin. Penicillin G and spasmolytic drugs (e.g., Valium). No significant resistance to penicillin. Prevention: Toxoid vaccine (toxoid is formaldehyde-treated toxin). Given to children in combination with diphtheria toxoid and pertussis vaccine (DTaP).  Clostridium perfringens Diseases: -Gas gangrene due to alpha toxin (lecithinase) -Food poisoning due to enterotoxin Habitat is soil and human colon. Transmission: Gas gangrene : contamination of wound with soil or feces. Food poisoning : ingestion of contaminated food. Diagnosis: Anaerobic, gram-positive Spore-forming rods.  Clostridium perfringens Treatment: Gas gangrene Penicillin G plus debridement of wound (no significant resistance to penicillin). Food poisoning symptomatic treatment. Extensive debridement of the wound plus administration of penicillin decreases probability of gas gangrene. There is no vaccine.  Clostridium botulinum Disease: Botulism due to Botulinum toxin flaccid paralysis. Habitat is the soil. Transmission: Organism & toxin transmitted in improperly preserved food Diagnosis: Anaerobic Gram-positive Spore-forming rods Prevention: -Observing proper food preservation techniques: - Cooking all home-canned food - Discarding bulging cans.  Clostridium difficile Disease: Pseudomembranous colitis due to: Antibiotics normal flora of colon C. difficile to overgrow & produce large amounts of exotoxins. Habitat is the human colon. Transmission is fecal–oral Diagnosis: Anaerobic Gram-positive Spore-forming rods. Actinomycetes: Actinomyces israelii Disease: Actinomycosis (abscesses with draining sinus tracts) Habitat is human mouth, especially anaerobic crevices around the teeth. Transmission occurs during dental disease or trauma. It aspirated into lungs, causing thoracic actinomycosis. Retained intrauterine device predisposes to pelvic actinomycosis. Diagnosis: Anaerobic Gram-positive filamentous, branching rods.  Nocardia asteroides Disease: Nocardiosis (especially lung and brain abscesses). Habitat is the soil. Transmission is via airborne particles, which are inhaled into the lungs. Diagnosis: Aerobic Gram-positive filamentous, branching rods. Weakly acid-fast. Thank You