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NAJRAN UNIVERSITY College of Medicine. Microbiology &Immunology Course Lecture No. 4. By. Dr. Ahmed Morad Asaad Professor of Microbiology. Bacterial physiology and metabolism Bacteria have certain requirements In order to grow and multiply. These requirements include: 1- Nutrients
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NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 4 By Dr. Ahmed MoradAsaad Professor of Microbiology
Bacterial physiology and metabolism Bacteria have certain requirements In order to grow and multiply. These requirements include: 1- Nutrients 2- O2 requirement 3- CO2 requirement 4- Suitable Temperature 5- Suitable pH
Nutrients According to nutrients, bacteria are classified into:
O2 requirement According to O2 requirement, bacteria are classified into 4 types:
What is the difference between obligate aerobic and obligate anaerobic bacteria? • In aerobic bacteria, O2 is utilized as the final oxidizing agent. • 2 H2O + 2 O2 → 2 H2O2 + O‑2 (Toxic substances) • Aerobes and facultative anaerobes contain certain enzymes, e.g. superoxide dismutase, catalase and peroxidase, which protect them from the effect of these toxic materials. • Anaerobic organisms do not possess these protective enzymes and the presence of O2 will be harmful to them due to the production of those toxic materials. • Thus in anaerobic bacteria, the oxidizing agent is not O2 but other inorganic or organic compounds.
CO2 requirement • ‑ Most bacteria require CO2 in just as a small concentration as that present in air. • ‑ Carboxyphilic bacteria need high CO2 concentrations., e.g. • Neisseria: requires 5% CO2. • Brucellaabortus: requires 20% CO2.
Temperature requirement According to temperature, bacteria are classified into: What is the type of bacteria of medical importance in relation to temperature?
pH requirement • ‑Most bacteria of medical importance can grow and multiply within a pH range of 7.2 ‑ 7.6. • ‑Some bacterial species require: • Acidic pH for their maximal growth (e.g. lactobacilli). • Alkaline pH (e.g. Vibrios).
Bacterial growth curve When bacteria are transferred to a suitable fluid medium and the number of viable bacterial/ml is calculated at regular time intervals, a growth curve will be obtained which can be divided into 4 phases:
1- The lag phase : ‑ During this phase, there is no or little bacterial multiplication. - It is the period between inoculation of the medium with the organism and beginning of active multiplication. ‑ In this phase the organism adapts itself to the new environment by synthesizing new enzymes and macromolecules required for metabolism.
2- The logarithmic (exponential) phase : • - It is the most active phase of bacterial growth. • - The number of bacteria increases steadily by time. • - This phase continues until : • The available nutrients are exhausted, and/or • The toxic waste products are accumulated.
3- The stationary phase : • -During this phase the rate of bacterial growth is slow due to exhaustion of nutrients and accumulation of waste metabolites. • -The number of dying bacteria = the number of newly formed bacteria.
4- The phase of decline : -When exhaustion of nutrients and accumulation of waste products continue, the number of dying bacteria exceeds the number of newly formed bacteria.
