Lec. No. 7 Dr. Manahil Classification of Bacilli 1. Gram positive bacilli A- Spore forming a- aerobic genus Bacillus. b- anaerobic genus Clostridium B- Non-spore forming Including the following genera: - Corynebacterium. - Erysipelothrix. - Lactobacillus. - Listeria. 2. Acid fast bacilli. Genus Mycobacterium 3. Gram negative bacilli Including many genera as: a-Escherichia. b-Klebsiella. c-Shiggella. d-Salmonella. e-Proteus. f-Serratia. g-Pseudomonas.
Gram positive bacilli spore forming
1. Genus bacillus More than 70 species present in the genus. This genus includes large aerobic, gram positive rods occurring in chains. Most members are saprophytic organisms. Bacillus anthracis is the principal pathogen of the genus which cause anthrax.Bacillus anthracis Morphology Cultural characteristics Pathogenesis Anthrax is primarily a disease of cattle, sheep and horses. Humans become infected incidentally by contact with infected animals or their products. The portal of entry in animals is the mouth. In human, the infection is usually acquired by the entry of spores through injured skin, by inhalation of spores, or rarely the mucous membrane. - The spores germinate in the tissues at the site of entry.
The virulence factorsThe major factors responsible for the virulence of B. anthracis are the capsule, edema toxin and lethal toxin.The poly–D-glutamic acid capsule is anti-phagocystic.Anthrax toxin is made up of three proteins: protective antigen (PA), edema factor (EF), and lethal factor (LF).Protective antigen serves as a necessary binding molecule for EF and LF.Edema results from the combination of PA and EF (edema toxin), whereas death occurs when PA and LF combined (lethal toxin). The toxin has affinity for the cells of the RES.
Clinical types of Anthrax 1. Cutaneous (Malignant pustule) A pruritic papule develops 1-7 days after entry of the organisms through a scratch. The papule rapidly changes into a vesicle that coalesce and a necrotic ulcer develops. The lesions typically are 1-3cm in diameter and have a characteristic central black eschar.
Marked edema occurs. Major symptoms are headache, fever, and malaise.
2. Inhalation anthrax (Pulmonary; wool sorter's disease) The incubation period may be up to 6 weeks. The disease is more fatal than cutaneous type. Common in workers in wool factories. It is due to inhalation of dust containing spores. The inhaled spores can remain latent in the nasal passages or reach the lower airways. Alveolar macrophages ingest the inhaled spores and transport them to the mediastinal lymph nodes. The second stage of disease is more severe, with a rapidly worsening course of fever, edema, and massive enlargement of the mediastinal lymph nodes. Mediastinal symptoms are seen in half of patients.
3. Gastrointestinal type This type is rare in humans, and gastrointestinal anthrax is uncommon. Enteritis with bloody diarrhea occurs with high fatality rate. The organisms may be isolated from the stool.
The complication of Anthrax About 5% of the patients with cutaneous, inhalation and gastrointestinal type develop meningitis. The generalized symptoms may be mild as fatigue, fever, and are followed by sudden onset of acute illness with cyanosis, sever pyrexia and disorientation followed by circulatory failure, shock, coma and death, all within a few hours. Human anthrax is classified as: A- Industrial B- Non-industrial