General Bacteriology I PDF

General Bacteriology Part I Year:1 Semester: 1 Module:Foundation 2 Instructor information Name: Assistant prof. / Yara El sayed Marei Department: Medical Microbiology and Immunology, FOM-SCU Offic...

General Bacteriology Part I Year:1 Semester: 1 Module:Foundation 2 Instructor information Name: Assistant prof. / Yara El sayed Marei Department: Medical Microbiology and Immunology, FOM-SCU Office hours: Wednesday 10 a.m-1 p.m  INTRODUCTION Microbiology: -It is the science that deals with tiny organisms that are too small to be visible with the naked eye, but seen only by microscope. -These organisms are collectively known as ‘Microbes’ e.g: bacteria, viruses, fungi……. Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss the replication in bacteria. 6. List methods of gene transfer in bacteria Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss bacterial growth (replication) in bacteria. 6. List methods of gene transfer in bacteria Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Prokaryotic cell features (bacteria) - Unicellular -Lack membrane bound organelles as mitochondria, endoplasmic reticulum, Golgi body…… -No nucleus, nucleolus or nuclear membrane -Genome is found as a single double stranded circular DNA. -Replicate asexually by binary fission Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Prokaryote is characterized by having the following: -Nucleoid: the area of cytoplasm in which DNA is located. -Ribosomes: responsible for protein synthesis. Prokaryotic ribosomes are 70S (50 S+ 30 S) -Cell wall -Cell membrane (plasma membrane): with no sterol -Cytoplasm -Other structures: Capsule, pilli, flagella. Prokaryotic Cell Plasma Cell Wall Capsule membrane Ribosomes Nucleoid Cytoplasm (Cytosol) Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Eukaryotic cell features (Human, animals, plant and fungi) - Multicellular organisms (some fungi are unicellular). -They contain membrane bound organelles as mitochondria, endoplasmic reticulum, Golgi body…... -Ribosomes are larger 80S (60 S+ 40 S). -They have true nucleus, nucleolus and nuclear membrane -Genome consists of multiple chromosomes of linear DNA - No cell wall (except in fungi composed of chitin) -They have cytoplasmic membrane containing sterols. -They replicate asexually by budding or mitosis.  Prokaryote vs. Eukaryote Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss bacterial growth (replication) in bacteria. 6. List methods of gene transfer in bacteria Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Bacteria Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Size of bacteria Bacteria range in size from about 0.2 to 1.2 µm in Width and 0.4-14 µm in length Shape of bacteria spherical (cocci) There are three basic shapes: 1) Cocci. 2) Bacilli. rod-shaped (bacilli) 3) Spirals Some bacteria are pleomorphic (variable in shape). Arrangement of bacteria Certain cocci occur in pairs (diplococci), some in chains, spiral and others in grape-like clusters. (spirilla) Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 N.B: To determine the size, shape and arrangement of bacteria, it has to be stained then examined under the microscope. Examples of stains are:  Gram stain  Ziehl-Neelsen stain Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 When stained by Gram stain, bacteria may be: -Gram positive bacteria → appear purple in colour. -Gram negative bacteria → appear pink in colour. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 The structure of the bacterial cell 1- Cell wall 2- Cytoplasmic membrane 3-Cytoplasm 4- Capsule 5- Flagella 6- Pilli Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 1-The Bacterial Cell wall: Differs in Gram positive and Gram negative bacteria Gram positive bacterial cell wall consists of: A- Thick compact peptidoglycan layer (40–80% of weight of the cell wall)  Function: -Responsible for rigidity of the cell wall -Maintain the shape of the bacterial cell Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 -Peptidoglycan is made up of a polysaccharide backbone of alternating N-Acetylmuramic acid (NAM) and N- acetylglucosamine (NAG). N-acetylmuramic acid carries a tetrapeptide side chain consisting of four amino acids which are: L-alanine, D-glutamine, L-lysine and D- alanine. -There is a cross-bridge of five amino acids such as glycine (peptide interbridge) that serves to connect one tetrapeptide to another (by transpeptidase enzyme). Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 B-Teichoic acid: -Teichoic acids can either be covalently linked to peptidoglycan (wall teichoic acids or WTA) or connected to the lipids in the cell membrane, in which case it is referred to as lipoteichoic acid. Function: -Contributes to the overall rigidity of the cell wall -Mediates adherence to mucosal cells. -Immunogenic (induce production of TNF-α and IL-1 by macrophages) Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Gram negative bacterial cell wall consists of: A-Outer membrane B-Thin peptidoglycan layer C-Periplasmic space Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 A- The Outer membrane (OM) : - Composed of two asymmetrical inner and outer leaflets. The inner leaflet contains phospholipids, while the outer leaflet contains a unique component lipopolysaccharide (LPS). The lipopolysaccharide is made up of 3 units: - Lipid A, - the core polysaccharides and - the O antigen Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 LPS in the outer membrane is important.. Why ? -It represents the main Gram negative bacterial endotoxin. (Lipid A contributes to the toxic element of the LPS). -This Endotoxin is released when the bacterial cells are lysed during infections and elicits a strong immune response. -That is why it causes fever and endotoxic shock associated with the septicemia caused by Gram-negative organisms. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 B- A thin layer of peptidoglycan: about 5- 10 % of the cell wall C- Periplasmic space: -It contains binding proteins for amino acids, sugars, vitamins, iron, and enzymes essential for bacterial nutrition. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Function of the bacterial cell wall 1- A rigid structure that maintain the shape of the bacteria 2- Play a role in cell division 3- Determine the cell’s reaction to Gram stain Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 2- Cytoplasmic membrane: Phospholipid bilayer, no steroids Function:  Selective permeability to different molecules (control the transport of ions, nutrients and waste across the membrane)  It performs electron transport and energy production (replaces mitochondria).  Contains enzymes and carrier molecules  Contains ion pumps to maintain osmotic balance. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 3) Cytoplasm: with main component which are;  Ribosomes: 70 S (30S + 50S), site of protein synthesis.  Nucleoid: an area of cytoplasm that contains single double stranded circular DNA.  Plasmid: -Extra chromosomal double stranded circular DNA, capable of self replication independent of bacterial chromosome. -It confers additional characters as resistance to antibiotics Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 4-Capsule: usually polysaccharide. Function: -Protects against phagocytosis by phagocytic cells (antiphagocytic). -Serve as antigenic determinants (K-antigen) -Helps adherence to human tissue 5- Flagella: Long thin proteinaceous (flagellin protein) appendage attached to the cell wall and cytoplasmic membrane by a basal body and extends outwards. A = monotrichous -Single polar flagellum (monotrichous), several polar flagella at one end B = amphitrichous (amphitrichous), each end of the cell (lophotrichous) or covering the entire cell C = lophotrichous surface (peritrichious). D = peritrichous Function: organ of motility, Antigenic determinants (H-antigen). 6- Pili (fimbriae): composed of pilin protein. They are hair like filaments that extend outwards. They are shorter than flagella Function: Two types: ordinary pili (for adhesion) and sex pili (for conjugation) Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss bacterial growth (replication) in bacteria. 6. List methods of gene transfer in bacteria Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Bacterial Endospore Formation Highly resistant resting form of some Gram positive bacteria (e.g., Clostridium) formed upon exposure of vegetative (actively growing) cells to unfavorable conditions e.g. depletion of nutrients, heat and dryness. During this process, a portion of the cytoplasm and a copy of the bacterial chromosome get surrounded by a three-layered covering. It contains high calcium content and dipicolinic acid (calcium dipicolinate). The resulting endospore is extremely resistant to heat, drying, UV, chemicals and can remain viable for several years. Under favorable environmental conditions, germination of the spores to the vegetative forms occurs where endospore absorbs water, swells and the wall splits, releasing the cell inside and starts functioning as a typical bacterial cell Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss bacterial growth (replication) in bacteria. 6. List methods of gene transfer in bacteria n an isotonic environment (see Figure 17.2.517.2.5A), both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Bacterial Growth Requirements A- Physical requirements of bacteria: 1- Temperature - Most medically important species grow at a range of temperature between 25-40°C. (Mesophilic) (Optimum growth occurs at 37°C i.e. the normal body temperature) -Non-pathogenic bacteria may grow at temperatures lower than 20°C (Psychrophilic) or higher than 55°C (Thermophilic) 2- pH -Most pathogenic species of bacteria can grow at a narrow range of pH 7.2-7.6. (Neutrophilic) - However, some species grow at alkaline pH 8 (Alkalophilic) and others grow in - acidic pH 4 (Acidophilic) n an isotonic environment (see Figure 17.2.517.2.5A), both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 3- Osmosis : (Osmosis is the diffusion of water across a membrane from an area of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration) - Isotonic environment: both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. -Hypertonic environment: the water concentration is greater inside the cell while the solute concentration is higher outside. Water goes out of the cell and the cell will shrink and die -Hypotonic environment: the water concentration is greater outside the cell and the solute concentration is higher inside, Water goes into the cell and the cell will swell and burst. Most bacteria require an isotonic environment for optimum growth. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 B-Nutritional or chemical requirements 1-Oxygen: -Obligate aerobe: can grow only in the presence of oxygen. They obtain their energy through aerobic respiration -Obligate anaerobe: grow only in the complete absence of oxygen and die in its presence. They obtain their energy through anaerobic respiration or fermentation.why? As they lack the enzyme Catalase, Superoxide dismutase and Peroxidase that break down the toxic molecules (hydrogen peroxide and superoxide ion) that are produced in the presence of oxygen. -Aerotolerant anaerobe: they respire anaerobically, but can tolerate the presence of oxygen. -Facultative anaerobe: can grow in the presence or absence of oxygen, but generally better with oxygen (can perform both aerobic and anaerobic respiration) -Microaerophilic: they require low O2 conc. (lower than that present in the atmosphere) Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 2- Energy source: -Phototrophs: use (light) as their primary energy source. -Chemotrophs: use the oxidation of inorganic substances as their primary energy source. 3- Carbon source: Carbon is the structural backbone of the organic compounds that make up a living cell. Based on their source of carbon bacteria can be classified into: - Autotrophs: require only carbon dioxide as a carbon source. An autotroph can synthesize organic molecules (proteins and sugars) from inorganic nutrients. -Heterotrophs: they require preformed organic compounds as a carbon source. A Heterotroph cannot synthesize organic molecules from inorganic nutrients. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Quiz? What is meant by 1. Photoautotrophs 2. Photoheterotrophs 3. Chemoautotrophs 4. Chemoheterotrophs Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 4- Nitrogen source: Nitrogen is needed for the synthesis of such molecules as amino acids, DNA, RNA. 5- Minerals: Sulfur, Phosphorus, Potassium, magnesium, calcium and Iron 6- Trace elements Required in very minute amounts as sodium, zinc, copper. 7- Growth factors Such as amino acids , purines , pyrimidines , and vitamins that a cell must have for growth but cannot synthesize itself. Organisms having complex nutritional requirements and needing many growth factors are said to be fastidious. Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss the replication in bacteria. 6. List methods of gene transfer in bacteria Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Bacterial replication Binary fission: Most common mode of asexual reproduction. One cell divides into two equal daughter cells similar in genetic character to the mother cell. How? - Starts by elongation of the bacterial cell and duplication of the chromosomes - Then the in-growing newly formed cell membrane and cell wall forms a septum that divides the cell into two equal daughter cells. Bacterial growth Objectives: By the end of this lecture, students will be able to: 1. Differentiate between prokaryotic and eukaryotic cell 2. Describe the structure and function of bacterial cell. 3. Describe the formation and function of bacterial spores. 4. Describe the bacterial growth requirements 5. Discuss bacterial growth (replication) in bacteria. 6. List methods of gene transfer in bacteria Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Gene transfer It’s a type of sexual reproduction It involves transfer of a portion of genetic material (DNA) from a donor cell to a recipient cell followed by recombination. There are three types of gene transfer from one bacterium to another leading to bacterial genotypic variation which are: Transformation, Transduction, and Conjugation Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 1- Conjugation The donor cell contain F (fertility) plasmid that code for the formation of sex pilus (conjugation tube) that bridges the two cells when they come in contact with each other. N.B: Bacterial cells that contain an F plasmid are called “F+”. Bacteria that don’t have an F plasmid are called “F-”. One strand of the F plasmid separates and passes from F+ donor to F- recipient cell through the sex pilus. Then a complementary strand is formed by both cells. This results in the formation of an F+ recipient cell that acquires a plasmid copy. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 2- Transformation In natural transformation, pieces of DNA released from donor bacteria (when a bacterial cell dies) are taken up directly from the extracellular environment by recipient bacteria. The recipient cells become transformed and new genes are expressed. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 3- Transduction A virus that infects the bacterial cell (a bacteriophage) transfers fragments of bacterial genetic material from one bacterium (donor) to another bacterium (recipient). Bacteriophage: -They consist of a head (a protein coat with DNA inside) and a tail Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Generalized transduction: During phage replication, A piece of bacterial DNA becomes, by accident, enclosed within a phage particle instead of normal phage DNA. When this phage infects a second bacterium, the DNA from first bacterium is released and recombines with the chromosome of second bacterium. Objective 1 Objective 2 Objective 3 Objective 4 Objective 5 Thank you