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Gram positive rods.Form endospores. (heat & cold resistance spores) Either strict aerobes or aerotolerant anaerobes (that is, they can grow in the presence of O2 BUT dont require it). Two medically important bacillus spp. B.anthracis & B.cereus. Most of the bacillus spp. Are found in soil, water and as airborne contaminants in medical laboratory.Bacillus anthracis, cause Anthrax is most important member of this genus.
General Characteristics of Bacillus
On blood agarLarge, spreading, gray-white colonies, with irregular marginsMany are beta-hemolytic (helpful in differentiating various Bacillus spp. from B. anthracis) Spores seen after several days of incubation, but not
typically in fresh clinical specimensLaboratory Characteristics of Bacillus
Properties of Bacillus anthracisLarge gram + rod.Square ends, frequently found in chains.Antiphagocytic capsule is composed of D-glutamate. (This is unique capsules of other bacteria are polysaccharide). Nonmotile, other members of the genus are motile.Culture on blood agar.3 forms of anthrax:Cutaneous Painless ulcer with a black eschar. pulmonary inhalation of sporesgastrointestinal ingested spores
Laboratory diagnosisCultured on blood agar, B.anthracis forms large, grayish, nonhemolytic colonies with irregular borders.A direct immunofluorescence assay aids in the identification of the organism.
Q. Whats the reason that Spore are usually not seen in smears of exudate?
Laboratory diagnosisAns. Because spores form when nutrients are insufficient and plentiful in infected tissue.
B.anthracis gram stain. Arrow points to Skin lesion, a necrotic lesion covered one large gram+ rod within long chain. by a crust caused by lethal factor.
Edema and necrosis around eyeInhalation anthrax with bilateral pneumonia, more severe in left lower lung.
Bacillus anthracisviewed under fluorescence microscope
Laboratory diagnosis andClinical features
Cause food poisoning.Spores on grains such as rice.Two symptoms a. Short incubation (4hrs) const. nausea & vomiting. b. Long incubation (18hrs) watery, nonbloody diarrhea.Lab. Diagnosis not usually done.Only symptomatic treatment is given.
Quest. Recognize anthracis VS cereus
Clostridium spp. characteristicsGram positive.Large rods that produce endospores.Most spp. Are motile.All clostridia are anaerobic.Cultured on blood agar.
Clostridium botulinumCause botulism (food poisoning e.g. canned meat).There are eight immunologic type of toxins (e.g. Botox)Clinical findings: *flaccid paralysis, diplopia (double vision), dysphagia and respiratory muscle failure.No fever are present.
Laboratory diagnosisUsually organisms not cultured.Use mouse protection test for botulinum toxin detection, theyll die unless protected by antitoxin. Or by using ELISA assay.Egg yolk emulsion agar
Laboratory diagnosis andClinical featuresCause tetanus (lockjaw).Germination of spores favored necrotic tissue.Has one antigenic type (tetanospasm) unlike botulinum has eight.Clinical findings: *Spastic paralysis, Risus sardonicus & opisthotonos (back spasm) due to rigid contraction of the jaw muscle.Diagnosis is based on clinical findings.Diazepam (valium) as a treatment to prevent spasm.
Tetanus. Note the marked hyperextension of the back, a position calledopisthotonus.Caused by tetanus toxin, an exotoxin that inhibits the release of mediators of the inhibitory neurons in the spinal cord
Laboratory diagnosis andClinical featuresCause two distinct disease, food poisoning & gas gangrene (myonecrosis).Associated with war wounds, automobile, motorcycle an accidents and septic abortion (endometritis) inner layer of the uterus.Clinical findings pain, edema, cellulitis and necrosis (gangrene).When cultured unaerobically produces a unique double zone of B-hemolysis. Egg yolk agar used to demonstrate the presence of the lecithinase (alpha toxin). Other biochemical test as sugar fermentation (glucose) and organic acid production such as acetic acid.
Gas gangrene. Note large area of necrosis on lateral aspect of foot. Necrosis mainly caused by lecithinase produced byClostridium perfringens. Gas in tissue is a feature of gangrene produced by this anaerobic bacteria. A large gas and fluid-filled bulla is seen near the ankle.Clostridium perfringens Gram stain Arrow points to a large gram-positive rod
Laboratory diagnosis andClinical featuresCause antibiotic associated pseudomembranous colitis. e.g. clindamycin, cephalosporin and ampicillin.Clinical findings: AAD antibiotic associated diarrhea, usually nonbloody, fever and abdominal cramping often occur.Two types of tests usually used to detect the exotoxins, 1st ELISA for stool samples. 2nd PCR assay. The presence of a pseudomembrane in the colon can be detected by endoscopy.
Pseudomembranous colitis. Note yellowish plaque-like lesions in sigmoid colon that inhibits a signal transduction protein, leading to death of enterocytes.
Important Features of Pathogenesis by ClostridiumSpecies