Introduction to Microbiology and Bacterial Structure PDF

Introduction to Microbiology and Bacterial Structure Topic Outcomes At the end of the lecture, students should be able to: 1. compare and contrast prokaryotic and eukaryotic cell structures. 2. illustrate and describe the structure of a typical bacterial cell. 3. explain the medical importance of...

Introduction to Microbiology and Bacterial Structure Topic Outcomes At the end of the lecture, students should be able to: 1. compare and contrast prokaryotic and eukaryotic cell structures. 2. illustrate and describe the structure of a typical bacterial cell. 3. explain the medical importance of the various appendages of a bacterial cell. 4. illustrate and describe the detailed structure of both Gram-positive and Gram-negative cell walls. 5. explain the role of exotoxin and endotoxin. What are MICROBES? 01 Microscopic Tiny living things that are found all around us and are too small to be seen by the naked eye. 03 Do we have microbes? The human body is home to millions of microorganisms. 02 Where can we found microbes? They live in water, soil, and air. 04 Good or Bad? Some make us sick, while others are important for our health Biologic Relationships of Pathogenic Microorganisms Kingdom Pathogenic Microorganisms Type of Cells Animal Helminths (worms) Eukaryotic Protist Protozoa Eukaryotic Fungi Fungi (yeast and molds) Eukaryotic Prokaryote Bacteria Viruses Prokaryotic Non-cellular Guinea worm Cells have a nucleus or nucleoid which contains DNA; this is surrounded by cytoplasm, within which proteins are synthesised, and energy is generated. Viruses have an inner core of genetic material (either DNA or RNA) but no cytoplasm, so they depend on host cells to provide the machinery for protein synthesis and energy generation. Contains organelles (eg: mitochondria, lysosomes) True nucleus, with multiple chromosomes surrounded by nuclear membrane Eukaryotes Larger 80S ribosomes Do not contain peptidoglycan Single circular molecule of loosely organised DNA, lacking a nuclear membrane Contains NO organelles Prokaryotes Smaller 70S ribosomes Rigid cell wall - contain peptidoglycan Eukaryotic VS Prokaryotic Characteristic DNA within nuclear membrane DNA associated with histones Chromosome number Membrane bound organelles Size of ribosomes Cell wall containing peptidoglycan Example Prokaryotic Eukaryotic Eukaryotic VS Prokaryotic Characteristic Prokaryotic Eukaryotic DNA within nuclear membrane No Yes DNA associated with histones No Yes One More than one Membrane bound organelles No Yes Size of ribosomes 70S 80S Cell wall containing peptidoglycan Yes No Bacteria, archae Helminths, fungi, protozoa Chromosome number Example Prokaryote VS Eukaryote Bacterial Structure -shape Cocci Bacilli Spiral -arrangement Chain Cluster Pairs IDENTIFY B POSITIVE Gram staining NEGATIVE Gram-positive cocci Gram-positive rods Gram-negative cocci Gram-negative rods Gram-positive cocci Staphylococcus spp Streptococcus spp Streptococcus pneumoniae Gram-negative Gram negative intracellular diplococci Capsulated Gramnegative bacilli (Klebsiella) Gram stain of smear of Bacillus anthracis IDENTIFY Easy© formula (keep it simple) for common pathogenic bacteria (exceptions exist) Most cocci have the name cocci attached All cocci are Grampositive except Neisseria All bacilli are Gramnegative except DATTAL Diphtheria (Corynebacterium) Anthrax (Bacillus) Tetanus (Clostridium) Tuberculosis (Mycobacterium) Actinomycosis Leprae, Lactobacilli, Listeria Bacterial structure Flagella Appendages Pili Fimbriae External Capsule Prokaryotic cell Glycocalyx Slime layer Cell wall Cell envelope Cell membrane Cytoplasmic matrix Ribososme Inclusions Internal Nucleoid/chromosomes Actin skeleton Endospore Bacterial Structure -external Glycocalyx Gelatinous, sticky substance that surrounds the outside of the cell. When the glycocalyx of a prokaryote is firmly attached to the cell surface, it is called a capsule. When loose and water-soluble, it is called a slime layer. Protect the cell from desiccation. Capsules protect cells from phagocytosis. Slime layers enable cells to adhere to each other and environmental surfaces. Flagella Composed of a filament, a hook, and a basal body. Via taxis, flagella move the cell toward or away from stimuli such as chemicals (chemotaxis) or light (phototaxis). Endoflagella is the special flagella of spirochetes that spiral tightly around the cell instead of protruding into the environment. Endoflagella Flagella –medical importance • Some species of motile bacteria (e.g., E. coli and Proteus species) are common causes of urinary tract infections. • Flagella may play a role in pathogenesis by propelling the bacteria up the urethra into the bladder. Some species of bacteria (e.g., Salmonella species) are identified in the clinical laboratory by the use of specific antibodies against flagellar proteins. Monotrichous – single polar flagellum located at one end Ampitrichous – two flagellar one at each end Lopotrichous – two or more flagellar at one or both ends Peritrichous – flagellar all over the surface Atrichous – absence of flagella IDENTIFY Fimbriae and pili FIMBRIAE FIMBRIAE PILI Also called conjugation pili, Short, sticky, proteinaceous, An important function nonmotile extensions of some in biofilm’s slimy masses which are hollow, nonmotile tubes that connect some bacteria that help cells adhere of bacteria adhering to a prokaryotic cells for to one another and substances surface. conjugation in the environment. Bacterial Structure -cell envelope 01 03 The bacterial cell wall provides overall strength to the cell. Protects the cell from osmotic lysis Cell wall 02 Helps maintain the cell shape, which is important for how the cell will grow, reproduce, obtain nutrients, and move. 04 The cell wall can keep out certain molecules, such as toxins, particularly for Gramnegative bacteria. Peptidoglycan Also known as murein Provide rigid support for the cell Important in maintaining the characteristic shape of the cell Allow cell to withstand osmotic pressure Make up of PEPTIDES + SUGARS (GLYCAN) = PEPTIDOGLYCAN Carbohydrate backbone composed of Nacetylmuramic acid (NAG) and Nacetylglucosamine (NAM) molecules Lipopolysaccharides Composed of: LIPID A CORE POLYSACCHARIDE O POLYSACCHARIDE Teichoic acid Located outer layer of the Gram-positive cell wall and extend from it. Composed of glycerol phosphate or ribitol phosphate. Glycerol phosphate penetrates the peptidoglycan layer and is covalently linked to the lipid in the cytoplasmic membrane known as Lipoteichoic acid. Comparison -cell wall Features Gram-positive Gram negative Peptidoglycan Thicker, multilayer Thinner, single layer Techoic acid Yes No Lipopolysaccharide (endotoxins) No Yes cell wall is the outermost component common to all bacteria (except Mycoplasma species, which are bounded by a cell membrane, not a cell wall). Insert figure 4.12 Comparative cell envelopes 48 Cell wall -acid fast Acid-fast resist decolourization with acid–alcohol after being stained with carbolfuchsin. This property is related to the high concentration of lipids, called mycolic acids, in the cell wall eg: mycobacteria. Dr.P.K.Rajesh.M.D One reason why we need this info PKR 08.11.2022 Bacterial Structure -internal Spores Highly heat resistant and are not killed by many disinfectants. Boiling will not kill spores. Have a thick, keratin coat that allows them to survive many years, especially in the soil. Formed when nutrients are in short supply, but when nutrients are restored, spores germinate to form bacteria that can cause disease. Spores are metabolically inactive but contain DNA, ribosomes, and other essential components. All presentation’s materials; words, tables, figures, and designs are cited and adapted from the reference given and the internet.