Microbiology PDF

Microbiology Dr. Sajjad Mohsin Definitions: Microbiology: Is the study of microscopic organisms (microorganisms). Microorganisms included: 1. Bacteria: simple, single cell (unicellular microorganism). 2. Viruses: Obl...

Microbiology Dr. Sajjad Mohsin Definitions: Microbiology: Is the study of microscopic organisms (microorganisms). Microorganisms included: 1. Bacteria: simple, single cell (unicellular microorganism). 2. Viruses: Obligatory intracellular microorganisms. 3. Fungi: a. Unicellular microorganism (yeast) b. Multicellular filamentous complex (mold). 4. Parasites: a. Unicellular microorganisms (protozoa) b. Multicellular, more complex (Worms, arthropods) DIVISIONS OF MICROBIOLOGY A. Microbiology could be divided according to the microorganisms into: 1. Bacteriology: study of bacteria. 2. Mycology: study of fungi. 3. Phycology: study of algae. 4. Protozoology: study of protozoa. 5. Virology: study of viruses. 6. Parasitology: study of parasites. B. Microbiology can also be divided into the more fundamental branches. These branches are: 1. Pure microbiology 2. Applied microbiology (biotechnology) C. Microbiology could be divided according to the health status into 1. Etiology: identification of the causative agent of diseases. 2. Epidemiology: study the spread and the distribution of diseases. 3. Immunology: study the immune system. 4. Infection control: control of spread of infectious disease. 1  Microbiology BENEFICIAL APPLICATIONS (Why do we Study MICROBIOLOGY?) A. Define the causative agents of the infectious diseases B. Define the beneficial microflora. Studying the microflora includes: 1. Beneficial metabolic functions. 2. Antagonistic effect of microflora which prevents invasion pathogens C. Environmental importance: 1. Decomposers, 2. Produce oxygen, 3. Food chain & 4. Sewage treatment. D. Industrial importance: 1. Food industry, 2. Brewing industry, 3. Genetic engineering, and 4. Pharmaceutical industry 4. Genetic engineering Cell morphology of microorganisms Bacteria are complex and highly variable microbes. They come in four basic shapes: spherical (cocci), rod-shaped (bacilli), arc-shaped (vibrio), and spiral (spirochete) (Figure 1(A)). 2  Microbiology Figure 1.. (A) Basic shape of bacteria. (B) Fungal spores. (C) Fungal hyphae. (D) Morphology and structure of viruses: 1. Poxvirus, 2. Paramyxovirus, 3. Orthomyxovirus, 4. Coronavirus, 5. Togaviridae, 6. Adenovirus, 7. Bullet-shaped virus, 8. Herpes virus, 9. T2 bacteriophage, 10. Reovirus, 11. Papovavirus, 12. Picornavirus, 13. Picodnavirus, 14. Tobacco mosaic virus. Fungi are divided into unicellular and multicellular according to the number of cells that make up the organism. Unicellular fungi, such as Saccharomyces and other yeast- like fungi, are usually round or oval. Multicellular fungi have hyphae and spores. The hyphae and spores of different fungi are shaped differently (Figure 1.3(B) and (C)). Many viruses are spherical or almost spherical, some are rod-shaped (often seen in plant viruses), filamentous (e.g., freshly isolated influenza virus), bullet-shaped (e.g., rabies virus), brick-shaped (e.g., poxvirus), and tadpole-shaped (e.g., bacteriophage) (Figure 1.3(D)). Eukaryotic Cells vs. Prokaryotic Cells 3  Microbiology Eukaryotic Cells vs. Prokaryotic Cells 4  Microbiology Bacterial cell wall (comparison between gram positive and negative cell wall). Gram-positive’ and ‘gram-negative’ are terms used to broadly categorize two different types of bacteria. This distinction is made based on the structure of their cell walls, and their reaction to Gram staining. Gram-positive bacteria have cell walls made of a thick layer of peptidoglycan. The cell walls of gram-negative bacteria contain only a thin layer of peptidoglycan, but they also have an outer membrane that is absent in gram-positive bacteria. Gram staining is a technique that uses violet dye to distinguish between gram-positive and gram-negative bacteria. If the bacteria are gram-positive, the thick, peptidoglycan layer in their cell walls will retain the dye and they will stain violet. If the bacteria are gram-negative, the dye will leak out of the thin peptidoglycan layer, and the bacteria will stain red. Gram positive vs. gram negative bacteria 5  Microbiology 6  Microbiology Multiplication of Bacteria Bacterial multiplication is a consequence of growth that leads to proliferation of a single bacterial cell into two daughter cells. Bacteria are multiplied by binary fission. The time required for this multiplication process is called “Generation Time” and it is different from one bacterial species to another. Colony :- is a clump of organisms growing on the surface of solid medium. Members of the bacterial colony are ancestor of one father cell 7  Microbiology Generation Time: is the time required for a single bacterial cell to give rise to two daughter cells under optimum conditions. Generation time is variable and depends on the bacterial species. For example, the generation time for Escherichia coli is about 20 minutes, whereas the generation time is longer (about 20 hours) for Mycobacterium tuberculosis and about 20 days for Mycobacterium leprae. Bacterial Growth Curve The Criteria of Bacterial Growth Curve shows 4 distinct Phases: 1. Lag phase: Usually, the multiplication of bacteria does not start immediately after the introduction of a new bacterium onto a new medium. It takes some time to multiply. The time between inoculation of the bacterium and the beginning of multiplication is known as lag phase. In the Lag Phase, there is no increase in the number of cells However, there is increase in metabolic activity. In the lag phase, they are preparing for reproduction. 2. Log phase: This phase is characterized by rapid exponential increase in cell number (1→ 2 → 4 → 8 →16 → 32 → 64 → 128 → etc). a. Log phase is a period of rapid reproduction. During this log phase, the population constantly doubled. b. In the Log phase, bacteria are antibiotics most sensitive and more prone to environmental factors. 3. Stationary phase: In the Stationary phase, the bacterial exponential increase stops completely. In the Stationary phase, the number of viable bacteria = the number of dead bacteria within the medium. This is due to depletion of essential nutrients, water, oxygen, change in pH of the medium, and etc. At the stationary phase, accumulation of toxic metabolic wastes starts to occur. 4. Decline phase: During this phase, the bacterial population declines due to death of cells. The decline phase starts due to (a) accumulation of toxic products and autolytic enzymes and (b) exhaustion of nutrients. 8  Microbiology Factors Affecting Growth of Bacteria: A variety of factors affect growth of bacteria: 1. Oxygen: Bacteria require oxygen for energy production. Bacteria can be divided into four groups based on Oxygen requirements: a. Aerobes (Obligate aerobes) : which can grow only in the presence of oxygen (20% O2, e.g., Pseudomonas aeruginosa). b. Anaerobes: Obligate anaerobes are the bacteria that can grow only in the absence of oxygen (e.g., Clostridium botulinum and Clostridium tetani). c. Facultative anaerobes: These bacteria are ordinary aerobes but can also grow without oxygen (e.g., E.coli). Facultative anaerobes bacteria can adjust their O2 requirements depending on the conditions. Most of the pathogenic bacteria are facultative aerobes. d. Microaerophilic - require the presence of small amounts of oxygen (2% - 10%). 2. Carbon dioxide Examples of such bacteria include H. influenzae, Brucella abortus, etc. 3. Temperature The optimum temperature for most of the pathogenic bacteria is 37оC. Bacteria divided into three groups according to growth temperature : Psychrophiles: These bacteria are cold loving microbes that grow within a temperature range of 0 – 20оC. Most soil and water saprophytes belong to this group. Mesophiles: These are moderate temperature loving microbes that grow between 25оC and 40оC. Most pathogenic bacteria belong to this group. 9  Microbiology Thermophiles: These are heat loving microbes. They can grow at a high temperature range of 55–80оC. 4- pH Most pathogenic bacteria grow between pH 7.2 and 7.6 5. Light 6. Osmotic pressure 10