Lab.1
Spore forming, G +ve aerobic bacilli:
Bacillus species:
General characteristics and morphology:
The genus bacillus includes large aerobic, gram-positive rods occurring in chains. Most members of this genus are saprophytic organism prevalent in soil, water and air, and on vegetation, such as Bacillus cereus and Bacillus subtilis. Some are insect pathogens.
B. cereus can grow in foods and produce an enterotoxin and cause food poisoning.
B. anthracis which causes anthrax, is the principal pathogen of the genus.
This genus form heat-resistant spores, chemical disinfected and UV-light, and it can be killed by exposing to moist heat and at 121°C for 20 min. and 1 hr. in 160°C dry heat. The spores are found in air, soil and water. They are straight bacilli with round or square ends producing endospore, centrally located in non motile spp. and of the same width of bacillus body.
B. anthracis are non motile, non hemolytic arranged in chains (Streptobacilli) encapsulated.
B. subtilis are motile, hemolytic, spore can survive 50 years in soil.
Bacillus anthracis:
This causative organisms of anthrax in cattle, sheep and other animals, it is infected for man, generally by spore entering through injured skin causing cotaneous anthrax or by inhalation of spores causing pulmonary anthrax from infected animal or intestinal anthrax which is rare and cause when man eat the meat of animals dying by anthrax.
1. Morphology:
G +ve, anarerobic, large arranged in filamentous chain, but may form single or in pairs in animal blood, it forms spores, non motile, surrounded by irregular capsule when stained by polychrome.
Methelin blue (McFadyeans reaction) ? methylen blue (cell), Capsule ? red color.
2. Culture characteristics:
Aerobic, temp. range for growth from 15-45°C at 37°C, grow on ordinary nutrient agar colonies are irregular round, 2-3 mm in diameter, grayish and give the medusa head appearance, colonies on blood are non-hemolytic, stabbing semi solid medium showing non-motile bacteria, whereas related non pathogenic spp. are motile by swarming B. subtilis.
3. Specimens:
Blood for serological test (Ascoli test [precipitation test]) and culturing, sputum, pus from local lesions.
4. Biochemical’s test:
Catalase +ve, no hemolysis, form acid from glucose fermentation sucrose and maltose, no gas, nitrate reduce to nitrite.
Bacillus cereus:
It is the same of B. anthracis except in:
It is non capsulated.
Motile.
Produce b-hemolytic in blood agar.
Spore forming, G +ve bacilli, obligate anaerobe:
Clostridia:
General characteristics and morphology:
Clostridia are G +ve, obligate anaerobic, rod or bacilli in shape, some sp. Are motile eg. Cl. botulinum, the natural habitat is soil, intestinal tract of human where they live as saprophytes, the pathogens sp. are:
Cl. tetani [causative agent of tetanus].
Cl. perfringes [causative agent of gas gangrene].
or Cl. welchii
Cl. botulinum [causative agent of botulism]
Cl. difficile [causative agent of pseudomembranous
colitis (PMC) or antibiotic associated
colitis (AAC)].
The pathogenicity of Cl. is attributed to their exotoxin. Cl. is G +ve bacilli, spore forming, and the spore of Cl. are usually wider than the diameter of bacillui in which they are formed. The spores are locate as the following:
Terminally ? Cl. tetani (drum stick).
Subterminally ? Cl. botulinum.
Centrally ? Cl. perfringes.
Lab. Diagnosis:
- Culture characteristics:
Cl. can grow only in anaerobic, the optimum temp. is 37°C for 24-48 hr. Cl. can grow in ordinary nutrient medium and more rapidly on fresh blood agar.
- How to provide anaerobic conditions?
A reducing agent is added to liquid media eg. Glucose 4%.
By using gas pack system: Water is added to disposable aluminum foil packet containing:
Sodium borohydrate.
Sodium bicarbonate.
Cobalt chloride.
Citric acid.
The packet is immediately put in the jar, reaction then take place to supply hydrogen and carbon dioxide, so the main purpose of this system is to provide anaerobic conditions and supply CO2 10%.
Anaerobic jar: O2 is removed by either composition or replaced by inert gas like N2 and also CO2 10% is provided.
- Colony forms:
Cl. perfringes produce large colony with entire margin.
Cl. tetane produce small colony, many Cl. produce a zone of hemolysis on blood agar like Cl. prefringes.
Classification of B. according to O2 requirement:
Aerobic B.: Required O2 in their growth and will not grow under anaerobic conditions eg. Pseudomonas.
Anaerobic B.: Do not required O2 in their growth and fail to growth on surface of solid media eg. Cl. tetani.
Facultative anaerobic B.: Can grow either aerobically or anaerobically, but prefer anaerobic growth like Streptococci and E. coli.
Microerophilic: Required O2 in their growth, but fail to grow on the surface of solid media and exhibit low growth under anaerobic conditions (needs O2 5-7%) eg. Helicobacter pylori.
Capnophilic: Required CO2 in their growth like Clostriduim and Enterococcal fecalis.