Gram Positive Rods PDF

Gram positive Rods Genus Bacillus  General characteristics Large gram positive (young/fresh culture) bacilli with square end.  Some are gram negative in old culture Aerobic or facultative anaerobe Spore former Majority are harmless, saprophyticus  Natural habitat...

Gram positive Rods Genus Bacillus  General characteristics Large gram positive (young/fresh culture) bacilli with square end.  Some are gram negative in old culture Aerobic or facultative anaerobe Spore former Majority are harmless, saprophyticus  Natural habitat – Saprophytes, widely distributed in natural environment (mainly in soil and water) – Contaminants of operating rooms and surgical dressings, Bacillus…  Species of Medical Importance – Bacillus anthracis – Bacillus cereus Bacillus anthracis  Distinguishing Features – produces a single antigenic type of capsule and several exotoxins. – Capsule is polypeptide (poly-D-glutamate) that prevent phagocytosis – Potential biowarfare agent  Reservoir Bacillus anthracis – B. anthracis is responsible for the disease anthrax. Virulence factors – Capsule, plasmid encoded – Anthrax toxin (AB toxin) consists three distinct components/Thermostable proteins – Edema factor (EF) - is an adenylate cyclase – Lethal factor (LF) - kills cells – Protective antigen (PA) - mediates entry of LF or EF into eukaryotic cells Pathogenesis B. anthracis causes anthrax which is mainly a disease of sheep, cattle, goats and other herbivores with humans becoming infected only after coming into contact with infected animals or their skins. Human infections (zoonosis) can occur from handling infected animals or coming into contact with skins containing anthrax spores, – e.g. when using skins as clothing, water-carrying containers, or sleeping mats Other sources of infection include animal hair, bones, and the bedding of infected animals. Diseases Depending on the source and site of infection, B. anthracis can cause:  Cutaneous anthrax (commonest form): – Bacilli enter damaged skin, producing a blister (‘malignant pustule’) which usually ulcerates and eventually forms a dry black scab surrounded by oedema.  Pulmonary anthrax (wool sorter’s disease) – Life-threatening pneumonia – Caused by inhaling large numbers of B. anthracis spores Diseases…  Enteric anthrax (Gastrointestinal anthrax) – Rare – A severe form of gastroenteritis with fever, − Edema and blockage of gastrointestinal tract can occur, vomiting and bloody diarrhea, due to ingesting infected meat. – Septicaemia often develops. – Meningoencephalitis: Usually as a complication of septicaemia and occasionally as primary anthrax meningoencephalitis. Laboratory Diagnosis Specimen: fluid or pus from a local lesion, blood, and sputum. Microscopic Stained smears from the local lesion or of blood from dead animals often show chains of large gram-positive rods. Loeffler’s polychrome (McFadyean) methylene blue stained smear – Square ended blue-black bacilli surrounded by a pink/purple capsule Anthrax can be identified in dried smears by immunofluorescence staining techniques. Laboratory…  Culture – When grown on blood agar plates, the organisms produce non-hemolytic gray to white mucoid colonies with a rough texture and a ground-glass appearance. – Comma-shaped outgrowths may project from the colony. – Grow on nutrient medium under aerobic conditions  Biochemical test: – Ferment glucose, maltose, sucrose with acid production but not gas – Positive for Nitrate reduction test, Catalase test, starch Prevention & control  Treatment ciprofloxacin or doxycycline.  Prevention Disposal of animal carcasses by burning or by deep burial in lime pits Decontamination of animal products Wearing of protective clothes & gloves for handling infected materials  Eg. Animal’s hair, hide bone Immunization of domestic animals with live attenuated vaccines, Toxoid vaccine  Bacillus cereus  Distinguishing Feature – spores  Reservoir – found in nature  Transmission – Foodborne, intoxication – Major association with fried rice from Chinese restaurants – Associated with food kept warm, not hot (buffets)  B. cereus is predominantly responsible for food poisoning in humans  produces toxins that cause disease that is more an Pathogenesis B. cereus produces enterotoxins that causes food poisoning It causes two possible toxins: – the emetic type: associated with fried rice, and preformed fast (1–6 hours), similar to S. aureus with vomiting and diarrhea – the diarrheal type: associated with meat dishes and sauces. 18 hours, similar to E. coli; LT: increasing cAMP → watery diarrhea  Diseases – Gastroenteritis Lab diagnosis  Suspected food (eg. rice, meat, vegitable) and vomitus of patients are cultured on ordinary media.  Smear from colonies show large gram positive sporing bacilli  B. cereus, unlike B. anthracis, is motile, non-capsulate, and produces haemolytic colonies on blood agar.  is non-lactose fermenting, producing pale colonies on MacConkey agar.  On egg-yolk agar, B. cereus gives a strong lecithinase reaction  Mannitol egg-yolk phenol-red polymyxin agar (MYPA) is Prevention and control Treatment – self-limiting – Antimicrobials with activity against B. cereus include gentamicin, erythromycin, vancomycin and clindamycin. Prevention – Rice should not be kept warm for a long period of time  Genus Clostridium  General characteristics – Large, gram positive (-ve or variable in old cultures) – Majority are motile, but C. perfringens is non-motile – Anaerobic, rod shaped, spore forming (central, sub- terminal or terminal spores), – Ferment organic compounds Acid, gas production during fermentation of sugars Foul smelling products from fermentation of amino acids and fats General char…  Produce extra-cellular enzymes – Degrade biological molecules – Role in invasion and pathogenesis – play an important role in nature in biodegradation and the carbon cycle  Cause tetanus, botulism, pseudo-membranous colitis, food poisoning and gas gangrene  Most are saprophytes  Found in soils, aquatic sediments, skin, intestinal tract, and feces of animals  Include four medically important Spp: Classification of Clostridia  Based on shape and position of spore  Based on biochemical properties  Predominantly saccharolytic Clostridia (eg.C. perfringens)  Predominantly proteolytic Clostridia (eg. C. butulinum A,B,F)  Slightly proteolytic Clostridia (eg. C. tetani)  Sacchrolytic Clostridia (eg. C. butulinum C,D,E)  Neither proteolytic nor saccharolytic Clostridia (eg, C. cochlearua) C. perfringens  Distinguishing Features  Large gram-positive, spore-forming rods (spores rare in tissue  Anaerobic: “stormy fermentation” in milk media  Double zone of hemolysis  oval, sub-terminal and non-bulging spores  Non-motile bacteria  Virulence factor: – Exotoxin, Enterotoxin, and hydrolytic substance Based on surface antigens and major lethal toxins (,,,) produced, five types of C. perfringens (A–E) Pathogenesis Spores germinate under anaerobic conditions in tissue. Vegetative cells produce: – Alpha toxin (phospholipase C) is a lecithinase. It disrupts membranes, damaging RBCs, platelets, WBCs, endothelial cells → massive hemolysis, tissue destruction, hepatic toxicity. Twelve other toxins damage tissues. Enterotoxin produced in intestines in food poisoning: disrupts ion transport → watery diarrhea, cramps (similar to E. coli); resolution