1 Cell structure.pdf

Medical Microbiology & Immunology for Dentistry Reham Aly Dwedar Professor of Microbiology & Immunology, Cairo University Dentistry Program 30 September 2024 Microbiology is...

Medical Microbiology & Immunology for Dentistry Reham Aly Dwedar Professor of Microbiology & Immunology, Cairo University Dentistry Program 30 September 2024 Microbiology is the science of minute organisms, invisible to the naked eye microbes. Microorganisms Generally unicellular = the whole organism is one cell A single microbial cell performs all the functions required to maintain itself and propagate. Microorganisms are either Eukaryotes e.g. fungi or Prokaryotes e.g. bacteria Eukaryotes Prokaryotes Size Large Small Nucleus Distinct nucleus surrounded by Absent nucleus nuclear membrane Nucleoid Enclosed organelles Present; Absent e.g., mitochondria Example Fungi Bacteria Viruses Smallest of the infective agents Have NO cell structure Obligate intracellular parasites They require biological machinery of a host cell for reproduction and survival. General Bacteriology Morphology of bacterial cell Size Shape Staining Special Arrangement Motility Capsule Sporulation  Size Bacteria are measured in micrometer (µm). Range from about 0.2-1.2 µm in width and 0.4-14 µm in length. Shape some pleomorphic  Bacterial Shape Cocci Bacilli Spiral Arrangement  Bacterial Arrangement Cocci Pairs Chains Irregular Clusters 15  Bacterial Arrangement Bacilli Pairs Chains No special arrangement 16 The arrangement of cells is determined by the planes of division. For example, the cocci that divide along a single plane produce diplococci or chains, e.g. streptococci, while those that divide on many planes produce clusters, e.g. staphylococci Staining Bacterial Structures Bacterial Cytoplasmic External Coats structures Appendages Cell membrane Nucleoid material Flagella Cell wall Ribosome Pili (Fimberia) Capsule Inclusion granules Bacteria cell is unicellular Structure of bacterial cell BACTERIAL ULTRA-STRUCTURES AND THEIR FUNCTIONS The final details of subcellular structures are best revealed by electron microscopy Bacterial Structures Bacterial Cytoplasmic External Coats structures Appendages Cell membrane Nucleoid material Flagella Cell wall Ribosome Pili (Fimberia) Capsule Inclusion granules Bacterial Ultra-Structures & their Functions Bacterial Structures Bacterial Cytoplasmic External Coats structures Appendages Cell membrane Nucleoid material Flagella Cell wall Ribosome Pili (Fimberia) Capsule Inclusion granules  1-Nucleoid: Genetic information of a bacterial cell is contained in a single circular molecule of Cytoplasmic double-stranded DNA, which constitutes the bacterial chromosome. structures: It is 1 mm long and is packed into a supercoiled state inside the cell. Cytoplasmic structures: Plasmids (+/-) In many bacteria, additional genetic information Extrachromosomal Double-stranded Circular DNA molecules Replicating independently Cytoplasmic structures: 2-Ribosomes: They are the site of protein synthesis in the cell. Ribosomes consist of protein and RNA. Prokaryotic ribosomes have ribosomes smaller than the ribosomes of eukaryotes This difference makes bacterial ribosomes a selective target for antibiotic action. Cytoplasmic structures: 3- Inclusion granules: Nutrient materials are usually stored as granules phosphates, sulphur, carbohydrates Bacterial Structures Bacterial Cytoplasmic External Coats structures Appendages Cell membrane Nucleoid material Flagella Cell wall Ribosome Pili (Fimberia) Capsule Inclusion granules Bacterial Coats Image result for bacterial capsule  1- Cell membrane: Just internal to the cell wall. Bacterial Coats Cytoplasmic membrane = plasma membrane Image result for bacterial capsule Bacterial Coats 1.The Cytoplasmic Membrane Phospholipid protein bilayer Differs from eukaryotic cells no sterols Ee plasma - Functions of cell membrane: 1. Transport of different molecules into the cell Related image diffusion and active transport. 2. Excretion of extracellular enzymes: e.g., Destructive enzymes: used to destroy harmful chemicals e.g., antibiotics e.g., penicillin-degrading enzymes.. 3. Respiration: Due to presence of respiratory enzymes thus a functional analogue of the mitochondria in eukaryotes 4. Reproduction: A septum forms by the cytoplasmic membrane to separate the cytoplasm of the two daughter cells.  Bacterial Coats Image result for bacterial capsule 2- Cell wall: The bacterial cell wall is the structure that immediately surrounds the cytoplasmic membrane. It is 10-25 nm thick, strong and relatively rigid, though having some elasticity. Structure of the cell wall ▪ The cell wall of bacteria is a complex structure. ▪ Its impressive strength is primarily due to peptidoglycan unique to bacteria ▪ Besides peptidoglycan, additional components in the cell wall divide bacteria into Gram-positive and Gram-negative Functions of the cell wall 1. It maintains the characteristic shape of the bacterium. 2. It supports the weak cytoplasmic membrane against the high internal osmotic pressure (5-25 atm). Functions of the cell wall 3. It plays an important role in cell division. 3. It is responsible for the staining affinity of the organism. Wall deficient variants: Mycoplasma ▪It is the only group of bacteria that exists naturally without cell wall. ▪ Mycoplasmas do not assume a defined recognizable shape, because they lack a rigid cell wall. ▪ These organisms are naturally resistant to cell wall inhibitors, such as penicillins and cephalosporins. Bacterial Coats Image result for bacterial capsule 3- Capsule Many bacteria synthesize large amount of extracellular polymer that collects outside the cell wall to form an additional surface layer. This layer is formed only inside the host (in-vivo).  Adherence of bacteria to human tissues. Function Virulence of many of bacteria. Capsule Specific identification of an organism. Preparation of certain vaccines. Bacterial Structures Bacterial Cytoplasmic External Coats structures Appendages Cell membrane Nucleoid material Flagella Cell wall Ribosome Pili (Fimberia) Capsule Inclusion granules External Appendages Several structures project through the cell wall of some bacteria to form surface appendages. The most commonly observed are flagella and pili. External Appendages: 1-Flagella Many bacteria move by means of flagella. They are highly antigenic. Motile bacteria tend to migrate towards regions where there is a higher concentration of nutrients and solutes (a process known as chemotaxis) and away from disinfecting substances (negative chemotaxis). External Appendages: 1-Flagella The location and number of flagella on a cell vary according to bacterial species.  External Appendages: Pili or fimbriae Pili (singular: pilus) are protein tubes that extend from the cells. They are shorter and thinner than flagella and can be observed only by the electron microscope. Functions: Adherence:. They enable bacteria to attach to the host surfaces, thus contributing to the establishment of infection. Conjugation: A special long pilus called the sex pilus (F or fertile pilus) is involved in the transfer of DNA between bacteria, a process known as conjugation. 49 Morphology of bacterial cell Size Shape Staining Motility Arrangement. Capsule Sporulation Bacterial Spores Bacteria of the genera Bacillus and Clostridium, develop a highly resistant resting phase or endospore Does not grow or reproduce, and exhibits absolute dormancy. Sporulation Sporulation is triggered by the onset of unfavorable environmental conditions : depletion of nutrients, accumulation of metabolites or changes in the growth requirements (e.g. moisture, temperature Bacterial Spores A single vegetative bacterium forms a single spore = sporulation A single vegetative bacterium emerges from a spore = germination  Viability and resistance Spores are much more resistant to disinfectants, drying and heating. Moist heat at 121°C for 10-20minutes (autoclave) is needed to kill spores while 60°C suffices to kill vegetative forms. The marked resistance of the spores has been attributed to several factors: Thermal resistance is provided by their high content of Ca2+ The impermeability of their cortex and outer coat. Their low content of water. Their very low metabolic and enzymatic activity. Bacterial Spores (Endospores) Does anyone have a question? Important question Definition and Functions of the cell wall Definition and Function of Capsule Functions of The cell membrane What is the organ of motility ? Define Bacterial endospore Compare between bacteria & Virus. Compare between human & bacterial cells.