L3 - Bacterial Structure.pdf

L3 - Bacterial Structure Dr. Janita Pinto September 1, 2024 www.gmu.ac.ae COLLEGE OF  PHARMACY Learning objective...

L3 - Bacterial Structure Dr. Janita Pinto September 1, 2024 www.gmu.ac.ae COLLEGE OF  PHARMACY Learning objectives On completion of this unit, the student will be able to: Describe the morphology of bacteria Describe the structure of bacterial cell wall & Geor Shape of Bacteria Cocci – spherical/ oval shaped major groups Bacilli – rod shaped Vibrios – comma shaped Spirilla – rigidLoading… spiral forms Spirochetes – flexible spiral forms Actinomycetes – branching filamentous bacteria Mycoplasma – lacks cell wall 9/14/2 016  fimbriae (pili) - in Helps Structure of A Bacterial Cell endurance. Outer layer – two components: Rigid cell wall Cytoplasmic (Cell/ Plasma) membrane – present beneath cell wall Cytoplasm – cytoplasmic inclusions, ribosomes, mesosomes and nucleus Additional structures – plasmid, slime layer, capsule, flagella, fimbriae (pili), spores  Woundinwall eptid in bustoric emijte CELL WALL both game ram ↓ Outermost layer, encloses cytoplasm 1. Confers shape and rigidity Composed of complex polysaccharides (peptidoglycan/ mucopeptide) - formed Alternating int encies & by N acetyl glucosamine (NAG) & N Loading… acetyl muramic acid (NAM) alternating in eptidogylan chains, held by peptide chains. (NAG) N-Acetyl The carboxyl group of each N-acetyl muramic acid is attached via a peptide (NAM) The S carboxyl Seminar an bond to a chain of four amino acids. group is via a peptidea of 4 bonds to a chain amino alids.  CELL WALL 4. In Gram-negative cells a typical sequence is: L-alanine; D-glutamic acid; meso Gram-negative) diaminopimelic acid; D-alanine D-abanine Gram-positive) 5. In Gram-positive cells the meso diaminopimelic acid is replaced by L-lysine. a lysine 6. The tetrapeptide chains on adjacent glycan strands are joined by peptide bonds to give a cross-linked polymer.  Cell Wall- Antimicrobial agents acting Lysozome against on peptidoglycan protection 1. Enzymes (for example, lysozyme, lysostaphin): bacteria invanding Many body fluids such as tears and saliva contain the enzyme lysozyme as a protection against invading bacteria. Lysozyme breaks linkages between N-acetyl muramic acid and N- acetylglucosamine. 9/14/2 016  are zeols dynamic Cell Wall- Antimicrobial agents acting on peptidoglycan 2. Antibiotics (for example, penicillins, cephalosporins, bacitracin, vancomycin, teicoplanin): Beta-lactam antibiotics act by preventing the cross-linking of peptidoglycan during synthesis. Bind to penicillin-binding proteins (PBPs), which are carboxypeptidases and transpeptidases responsible for final stages of cross linking. Enzyme inhibition leads to a build up of precursors and release of autolytic enzymes. They form spheroplasts and lysis of the cells results due to fragile outer cell walls. ‹#›  structural (ring Cell Wall- Antimicrobial agents acting on peptidoglycan 2. Antibiotics (for example, penicillins, cephalosporins, bacitracin, vancomycin, teicoplanin): - MRSA (methicillin resistant Staphylococcus aureus) has an additional PBP with lower binding affinity for b-lactams. Bacitracin interferes with a lipid carrier responsible for transporting cell-wall precursors across the membrane from the cytoplasm.  Cell Wall- Antimicrobial agents acting on peptidoglycan 2. Antibiotics (for example, penicillins, cephalosporins, bacitracin, vancomycin, teicoplanin): Glycopeptides are large polar molecules unable to penetrate the Gram-negative outer membrane. Loading… They are only active against Gram-positive bacteria and act by binding to the end of peptide chains, preventing cell-wall growth. Teichoie neids exacts essential lations ~ only inram positive  Gram negative cell wall course) The Gram-negative cell wall is composed of an outer membrane linked to thin, mainly single-layered peptidoglycan by lipoproteins. The peptidoglycan is located within the periplasmic space that is created - between the outer and inner membranes. The outer membrane includes porins, which allow the passage of small hydrophilic molecules across the membrane, and lipopolysaccharide molecules that extend into extracellular space.  Lipopolysaccharide The lipopolysaccharide (LPS) of the outer membrane of the cell wall of gram-negative bacteria is endotoxin. The LPS is composed of three distinct units: (1)A phospholipid called lipid A, which is responsible for the toxic Endotoxin structure effects. T (2) A core polysaccharide of five sugars. (3)An outer polysaccharide consisting of up to 25 repeating units of three to five sugars. This outer polymer is the important somatic, or O, antigen of several gram-negative bacteria that is used to identify certain organisms in the clinical laboratory.  Summary of differences between Gram positive & Gram negative bacteria Property of bacteria Gram Positive Gram Negative Thickness of wall 20-80 nm Gnickers 10 nm Number of layers in wall 1 2 Peptidoglycan content >50% 10-20% Teichoic acid in wall + - Lipid & lipoprotein content 0-3% 58% Protein content 0% 9% Lipopolysaccharide 0 13% Sensitive to penicillin Yes Less sensitive 9/14/2 016 (Induces fore in the body)  Other Cytoplasmic Components Intracytoplasmic inclusion bodies:. Volutin granules & – are used for storage of phosphorus and energy and consist of polymetaphosphate;. Glycogen granules – are food and energy stores and accumulate under conditions of nitrogen starvation;. Lipid granules – consist of poly-b-hydroxybutyric acid and are storage products. Sulfur/iron granules – some cells can accumulate magnetite (Fe3O4) (Inclusion) bodies Extensions of plasma  Additional Organelles. Plasmid – Extranuclear genetic element consisting of DNA Plasmids replicate faster than the main bacterial genome and so cells usually contain multiple copies. All plasmids contain the information required for replication but some also contain information for cell to cell transfer (called conjugative plasmids). Transmitted to daughter cells during binary fission Confer certain properties e.g. the production of toxins, pili, bacteriocins, siderophores and enzymes responsible for antibiotic resistance. 1. Flagella – Additional Organelles – Long (3 to 12 µm), filamentous surface appendages – Organs of locomotion (movement) – Chemically, composed of proteins called flagellins – The number and distribution of flagella on the bacterial surface are characteristic for a given species - hence are useful in identifying and classifying bacteria  & Additional Organelles 4. Fimbriae/ Pili – No movement – Thin, hairlike appendages originating from cytoplasmic membrane – Found on the surface of many Gram-negative bacteria – 10-20µ long, acts as organs of adhesion (attachment) - allowing bacteria to colonize environmental surfaces or cells and resist flushing – Made up of proteins called pilins. Pili can be of two types – – Common pili – short & abundant Sex pili - small number (one to six), very long pili, helps in conjugation (process of transfer of DNA)  Additional Organelles 5. Spores – – Highly resistant resting stages formed during adverse environment (depletion of nutrients – Very resistant to heat, radiation and drying and can remain dormant for hundreds of years. Catanus) – Formed by bacteria like Clostridia, Bacillus The center of the endospore, the core, exists in a very dehydrated state and houses the cell's DNA, ribosomes and large amounts of calcium dipicolinic acid. 9/14/2 016  Importance of spores Extreme resistance makes them difficult to eradicate from pharmaceuticals and food. – Sterilization processes are designed for the elimination of spores. A number of species are dangerous pathogens. ( – Bacillus anthracis - anthrax borg – Clostridium tetani - tetanus – Clostridium perfringens - gangrene – Clostridium botulinum - botulism Issue of dormancy (longevity in the environment) makes them a problem with respect to germ warfare. Spore-forming bacteria are commercially important as producers of antibiotics – for example bacitracin, gramicidin and polymyxin – and of insecticides.  Cell Walls of Acid-Fast Bacteria Mycobacteria (e.g., Mycobacterium tuberculosis) have an unusual cell wall, resulting in their inability to be Gram- stained. These bacteria are said to be acid-fast because they resist decolorization with acid–alcohol after being stained with carbol fuchsin. This property is related to the high concentration of lipids, called mycolic acids, in the cell wall of mycobacteria.  (negative) positive) Learning Resources Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 8th ed. Elsevier Ltd; 2016. ISBN: 978-0-323-29956-5. https://www.clinicalkey.com/#!/content/book/3-s2.0- B978032329956500080X Barer MR, Irving W, Swann A, Perera N. Medical Microbiology: A Guide to Microbial Infections. 19th Ed. Elsevier Ltd; 2018, ISBN: 978-0-7020-7200-0. https://www.clinicalkey.com/#!/content/book/3- s2.0-B9780702072000000023 Additional Reading Levinson W. Review of Medical Microbiology and Immunology. 14th 9/1/2024 ed. USA. McGraw Hill; 2014. ISBN-13: 978-007-1818-117.