أسئلة التاسعة ميكرو PPPM (قبل التعديل)

Bacterial Endospores

• Resistance endospores form under unfavorable conditions outside the body, such as starvation, desiccation, heat, or chemical agents
• Endospores aren't for reproduction; one cell produces one spore that germinates into one cell
• Sporulation occurs outside the body
• Spores have no metabolic activity and can remain dormant for many years
• Bacillus is an aerobic example
• Clostridium is an anaerobic example
• Types include central, terminal, and sub-terminal
• Shapes include oval and round
• Sizes include bulging and non-bulging
• They're resting cells highly resistant to desiccation, heat, and chemical agents

Mechanism (Sporulation)

• Nuclear material moves to one pole of the cell
• The cytoplasmic membrane invaginates to form the forespore
• Cytoplasmic membrane grows and engulfs forespore within a second membrane
• Cortex forms via deposition of dipicolinic acid and calcium
• Formation of spore coat
• Release of endospore
• The rest of the bacterial cell undergoes autolysis

Germination

• Germination occurs upon exposure to water, nutrients, and specific enzymes
• The coat degrades to allow water and nutrients to enter
• Germination turns the spore into a metabolizing, reproducing bacterium

Structure of Spore

• Contains bacterial DNA, a small amount of cytoplasm, and very little water
• Includes a cell membrane and peptidoglycan
• A thick keratin coat includes calcium

Growth Requirements of Bacteria

Bacterial Nutrition

• Nutrients are classified into basic elements and essential metabolites & growth factors
• Autotrophic bacteria use inorganic carbon sources like CO2
• Heterotrophic bacteria use organic carbon sources
• Saprophytic bacteria are an example of Autotrophic bacteria
• Pathogenic bacteria are an example of Heterotrophic bacteria
• Basic elements are needed in larger amounts for structure
  • Major elements: nitrogen, H2O, carbon
  • Minor elements: magnesium, calcium, potassium, sulphur, phosphorous
• Essential metabolites & growth factors are needed in minute (catalytic) amounts
  • Nucleotides and vitamins

Gaseous Requirements: Oxygen (O2)

• Obligate aerobes grow only in the presence of free O2 (e.g., TB)
• Obligate anaerobes grow only in the absence of O2
  • They lack peroxidase and catalase enzymes, so O2 forms toxic peroxides
  • An example is the Clostridium group
• Facultative anaerobes grow in both presence and absence of O2
  • They have two respiration systems (e.g., pathogenic bacteria)
• Microaerophiles grow best in the presence of minimal amounts of O2 (e.g., Propionibacterium acne)

Carbon Dioxide (CO2)

• CO2 is essential for the growth of most bacteria
• Normal atmospheric CO2 is sufficient (0.03%)
• Some organisms need higher concentrations (5-10%)
• High CO2 in culture media can stimulate growth (capnophilic, e.g., Neisseria & Brucella), form capsules (e.g., Pasteurella pestis, Bacillus anthracis), and produce enterotoxins (e.g., Staph aureus)

Moisture

• Bacteria are mostly water
• High water content is essential for bacterial cultivation
• Mycobacterium tuberculosis (TB) needs a high concentration of moisture

Temperature

• Temp Range includes optimum growth of organism occurs in 37C
• Psychophilic grows below the minimum temperature
• Thermophilic grows above the maximum temperature

pH

• Bacteria grow in a narrow pH range
• The optimum pH is 7.5 (neutral)
• Alkalophilic species tolerate alkaline media (e.g., Vibrio cholera)
• Acidophilic species tolerate acidic media (e.g., Lactobacillus)

Others

• Light, Osmotic pressure & mechanical factors are required

Bacterial Products: Enzymes

• Substances facilitate metabolic activity without being changed
• Enzymes need optimum temperature and pH for action
• Enzymes are proteins
  • Proteolytic enzymes break down protein
  • Saccharolytic enzymes break down carbohydrates
  • Lipolytic enzymes break down lipids
  • Respiratory enzymes are oxidases/dehydrogenases

Pigments

• Endo pigments are bound to the organism, don't diffuse, and are demonstrated on solid media
• Exo pigments diffuse into the surrounding
• Bacterial colonies with both types are colored
  • Serratia marcescens produces a red pigment
  • Staph aureus produces a golden yellow pigment
  • Pseudomonas aeruginosa produces blue (pyocyanin) or yellow pigments (fluorescens)
• Function of pigments: bacterial respiration and antibacterial action
• Bacterial pigment develops best at room temperature and appropriate pH

Toxins

• Substances produced by bacteria are harmful to the host
  • Exotoxins are diffusible toxins that diffuse into the surrounding medium
    • Exotoxins "Mainly “come from some –ve & +ve cells
    • Proteins can undergo detoxification, are strong antigens, and are coded on Plasmids or bacteriophage
  • Endotoxins remain bound to the organism and are released only when the organism disintegrates(lipid A)
    • endotoxins Come from Cell wall of most -ve cells but are not diffusible and are made of Lipopolysaccharides

Others

• Hemolysin is produced by many bacteria, such as Staph aureus
• Lipase destroys lipids
• Hyaluronidase dissolves hyaluronic acid (cement)
• Leucocidins kill leucocytes
• Also Protease, DNase & Coagulase by Staph aureus & cause clotting of plasma

Bacterial Reproduction

• Bacteria multiply by simple binary fission
  • Growth in size (elongation)
  • Division of nuclear bodies
  • Constriction originates in cell wall inwards
  • Divide into two daughter cells
• Growth on solid media produces specific colonies for each bacteria Growth on fluid media is Obligate Anaerobic, Obligate Aerobic, Facultative anaerobic, Microaerophilic The 4 phases from bacterial growth :
  • Phase of Lag -No multiplication -Bacteria ↑ in size Enzymatic synthesis
  • Phase of death = The growth phase
    • The number of organisms decreases
    • Affected mostly d.2 Rate of division
    • Can be inhibited by ATB
    • Can correlate convalescent infection
• Stage from which the inoculum affects :
  • Short E.coli 20mm vs TB long Phase
• Rate of growth can d.t type of medium accumalation toxin heat etc
• The growth fluid media affected in two phases - Turbidity - Under the surface - Both under surface
• Bacterial Growth Curve
• The bacterial growth curve demonstrates the relationship between the number of living bacteria against time
• Bacteria is cultured in fluid medium Samples are taken at regular intervals to count the number of living bacteria
  • Phase of decline = growth phase
  • Bacteria ↑ in number (Enzymatic synthesis).
  • Bacteria Could be inhibited efficiently by Antibiotic at infection
• The stage has a effect :
  • is Short for E.coli (20m) vs TB long Phase.
  • Type of organism
  • the growth fluid media is in two phases
  • diminuation of the rate d.2 materials </existing_notes>