Medical Bacteriology Lecture 3 PDF

460 MBIO Medical Bacteriology Lecture 3 Bacterial Classification Medical Bacteriology - Lecture 7 Family Spore- Bacillaceae forming Gram Positive Rods (Spore-forming Gram-Positive Rods Ba...

460 MBIO Medical Bacteriology Lecture 3 Bacterial Classification Medical Bacteriology - Lecture 7 Family Spore- Bacillaceae forming Gram Positive Rods (Spore-forming Gram-Positive Rods Bacilli ) Bacillus 0  Family Bacillaceae Genus Bacillus General Characteristics - Gram positive - Large rod. - Arranged in chain - Spore forming - Aerobic or facultative anaerobic - Found in soil habitats around the world - Can be cultivated in ordinary nutrient medium (nonselective & selective media) - Catalase test +ve - Forming rhizoid colonies  Important species Bacillus anthracis Bacillus cereus Bacillus subtilis Bacillus mycoides Bacillus thuringiensis 1  Bacillus anthracis General Characteristics Morphology: -Large, square-ended rods in long - chain (one of the largest size pathogenic microorganisms) - Non - motile - Capsulated: The organism is stained violet, and the capsule is stained purple-pinkish in color. - Spores located in the center of the nonmotile bacilli. They are never seen in blood or tissue smears taken from infective animals. - Non hemolytic on blood agar Gram stain of B. anthracis , showing large gram-positive rods with sub terminal ellipsoidal spores in blood culture from patient (image taken from (Russell et al., 2013)) 2 3 Culture character Aerobic and facultative anaerobic growth on all ordinary media, at temp (12-43 C) with optimum temp = 37 o C. Colonies on nutrient agar media are very characteristic; the colonies appear rough, creamy, or greyish white in pigmentation, 2-3 mm in diameter with wavy or irregular margins resembling wavy curled locked hair with projection resembling what is known as medusa head. Most of the strains are non-hemolytic in blood agar media. On a 15 % gelatine stabbing culture, B. anthracis produced the very characteristic type of inverted fir tree, due to the liquefaction of gelatine, which occurs maximum at the surface and then slows down towards the bottom. In broth, there is neither turbidity nor pellicle formation, but a floccular deposit appears in the bottom NA broth of the broth, resembling fluffy cotton wool in 4 appearance. (WHY)  Biochemical reaction: B. anthracis produces acid without gases in the case of glucose–maltose–sucrose fermentation. Catalase test +ve Produce weak lecithinase* activity ( Nagler's reaction +ve ) Virulence Factors: 1- Poly-D-glutamyl Capsule; antiphagocytic (major virulence factor). 2- Anthrax exotoxin is a three-protein exotoxin (Edema factor (EF), Lethal factor (LF), Protective antigen** (PA)). Lethal toxins = PA+LF Edema toxin =. PA+EF 5 *Lecthinases are enzymes bacteria use to digest animal tissues. **PA mediates the cellular uptake of the toxic moieties LF and EF.. Pathogenesis: B. anthracis Diseases (Anthrax): Anthrax is primarily zoonotic disease of domesticated and wild animals, such as cattle and sheep. Transmitted to human after contact with infected animals or their products. Anthrax In animals, the infection most commonly occurs following ingestion of the organism and also occurs by acquisition of the organism in aerosols or via wounds. In Humans. the infection may occur in three forms of the disease : 1- Cutaneous anthrax (Skin) through wounded skin, and the disease is called malignant pustules. 2- Pulmonary anthrax (Woolsorter's disease) by inhalation of dust contaminated with the spores in the hide skin or hairs or wool. The disease is characterized by pulmonary lesion, and enlargement of the spleen. Also the disease is known as splenic fever 3- Gastrointestinal anthrax (contaminated food) 6 Laboratory diagnosis: 1.Direct smear from the blood and stained by polychrome methylene blue The poly-D-glutamyl capsule can be detected by the M'Fadyean reaction which involves staining blood smears with polychrome A tissue smear demonstrating Bacillus anthracis. Note the methylene blue (PMB), can be used to intense red stain of the large capsule of this organism. Methylene blue stain; original magnification, 400×. distinguish B. anthracis from its closest relatives. 2. Culture character and biochemical reaction. 3. Animal pathogenicity Suspension from the suspected sample or pure culture of 0.5ml of 24 hrs young broth culture is McFadyean's reaction showing short chains injected subcutaneously (s/c) into the guinea pig. of Bacillus anthracis (Blue rods )cells lying Death usually occurs within 48 hours, and many among amorphous, disintegrated capsular bacilli are seen in the blood (Smears prepared material(purple/pink-stained ) from dead animals). 7 4. Ascoli's test (thermo precipitin test): Ag-Ab reaction test This test is used on examined wools or hair on putrefied carcasses. This test depends on the detection of polysaccharide Ag of Bacillus anthracis in the examined sample. 2 cm of the suspected sample is boiled with 10 ml of sterile saline containing a few drops of 0.5% acetic acid, boiled for about 10 min, and then filtered. 0.5ml of filtrate is put into a narrow or capillary test, and then 0.5ml of anti-anthrax serum is added. Leave for 15 min at room temperature. In the positive case, a white ring (precipitate) appears at the junction of two fluids. Immunization against Anthrax Passive immunity (Ab) Active immunity (Ag) 1. Pasteur first vaccine 2. Spore Sterne vaccine 8  Bacillus cereus Reservoir: found in nature. Transmission: Foodborne, cause intoxication. It can be isolated from foods such as grains and spices (cause fried rice syndrome). Associated with food kept warm, not hot (buffets). Keeping rice warm results in germination of spores and enterotoxin formation. Pathogenesis: two possible toxins:  Emetic toxin:  Diarrheal toxin causing emetic (vomiting) syndrome causing diarrheal syndrome performed fast (1-6 hours*). The incubation period is ( 8 to 16 hours*). It is similar to S. aureus food poisoning Similar to E. coli. in its symptoms (vomiting and diarrhea) produced in meats. associated with fried rice. 9  Difference between Anthrax Bacilli and Anthracoid Bacilli* Anthrax Bacilli Anthracoid Bacilli B. anthracis B. Subtilis, B. cereus Motility Non motility Motility Capsule Capsulated Non capsulated Shape Grow in long chains Grow in short chains In nutrient broth Fluffy Cotton wool without pellicle Turbidity and pellicle formation (Turbidity) (No Turbidity) but no fluffy Cotton wool Medusa Head Colony Present Not Present Haemolysis Haemolysis absent or weak. beta haemolysis Stabbing in gelatine Inverted fir tree No Inverted fir tree liquefaction of gelatine Occurs slowly from up to down Liquefy gelatin rapidly Salicin Fermentation Ferment salicin slowly Ferment it rapidly Reduction of methylene Reduced methylene blue slowly Rapidly reduce methylen blue blue in milk Penicillin agar media No growth Growth occurs rapidly 10mg\ml pathogenicity Highly pathogenic Most of them are non pathogenic *organisms that simulate the anthrax bacillus closely, both in their morphological and cultural characters within the group of Gram-positive aerobic sporing bacilli, are termed Anthracoid bacilli 10 11