NAJRAN UNIVERSITY College of Medicine NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 4 Microbiology &Immunology Course Lecture No. 4 By Dr. Ahmed Morad Asaad Professor of Microbiology 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 2- O2 requirement 3- CO2 requirement 4- Suitable Temperature 5- Suitable pH

Nutrients According to nutrients, bacteria are classified into: Autotrophic BacteriaHeterotrophic Bacteria - They can utilize simple inorganic materials (CO 2 as the source of carbon, and ammonium salts as the source of nitrogen). ‑ Can form complex organic metabolites from these simple materials. ‑ Autotrophic bacteria may derive their energy from light (e.g. photosynthetic bacteria) or from chemical reactions by oxidation of inorganic materials (e.g. chemolithotrophic bacteria). - They require complex organic materials derived from animal and plant sources. ‑ Cannot synthesize complex organic substances from the simple inorganic materials. ‑ They derive their energy by the oxidation or fermentation of organic compounds (e.g. glucose). ‑ Most bacteria of medical importance are "heterotrophic bacteria".

O2 requirement According to O2 requirement, bacteria are classified into 4 types: TypeDefinitionExamples 1. Obligate aerobesBacteria that grow & multiply only in presence of free O 2 (i.e. O 2 is essential) Mycobacterium tuberculosis & Vibrio chlorae 2.Obligate anaerobesBacteria that can not grow in presence of O 2 (i.e. require complete absence of O 2 ) Clostridia spp.

TypeDefinitionExamples 3. Facultative anaerobes Bacteria which can utilize O 2 when present, but can also grow & multiply in its absence Most bacteria of medical Importance 4- MicroaerophilicBacteria which require low O 2 tension (lower than that present in the atmosphere) Campylobacter

What is the difference between obligate aerobic and obligate anaerobic bacteria ? In aerobic bacteria, O 2 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 O 2 will be harmful to them due to the production of those toxic materials. Thus in anaerobic bacteria, the oxidizing agent is not O 2 but other inorganic or organic compounds.

CO2 requirement ‑ Most bacteria require CO 2 in just as a small concentration as that present in air. ‑ Carboxyphilic bacteria need high CO 2 concentrations., e.g. Neisseria: requires 5% CO 2. Brucella abortus: requires 20% CO 2.

Temperature requirement According to temperature, bacteria are classified into: BacteriaTemperature range Optimum temperature Mesophilic bacteria 18 ‑ 42 º C 37 º C Psychrophilic bacteria 5 ‑ 30 º C15 ‑ 20 º C Thermophilic bacteria 25 ‑ 80 º C50 ‑ 60 º C 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.

Clinical significance of bacterial growth curve: Phases of growth curve (in vitro) Stages of diseases & infections (in vivo) The lag phase of the curveThe incubation period of the disease The logarithmic & stationary phase The clinical signs & symptoms The phase of declineThe recovery & convalescence stage