Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Molecular mimicry wikipedia , lookup
Triclocarban wikipedia , lookup
Human microbiota wikipedia , lookup
Marine microorganism wikipedia , lookup
Disinfectant wikipedia , lookup
Magnetotactic bacteria wikipedia , lookup
Trimeric autotransporter adhesin wikipedia , lookup
11/24/13 BACTERIAL CELL SHAPES AND SIZES BACTERIAL CELL STRUCTURE coccus e.g. Staphylococcus aureus bacillus e.g. Escherichia coli Microbiology Lecture 2 spirillum Professor T.J. Foster GRAM STAIN e.g. Treponema pallidum Mixed culture showing (1) spherical cocci (2) rod-shaped bacilli and (3) spiral or helical-shaped bacteria (Gram stained). THE GRAM STAIN • CRYSTAL VIOLET + IODINE FORM COMPLEX • WASH ETHANOL • COUNTERSTAIN FUSCHIN • GRAM POSITIVE, PURPLE CRYSTAL VIOLET-IODINE RETAINED • GRAM NEGATIVE, RED CRYSTALVIOLET-IODINE WASHED OUT Escherichia coli, Gram negative rod. Staphylococcus aureus, Gram positive coccus Mixtures of Gram positive and Gram negative bacteria 1 11/24/13 STRUCTURE OF THE BACTERIAL (PROKARYOTIC) CELL • NO MITCHONDRIA – FUNCTIONS PERFORMED BY CYTOPLASMIC MEMBRANE G G M G M G M M Disaccharide repeat G G M G M G M Peptido -glycan M • RIBOSOMES FREE IN CYTOPLASM G – NO ENDOPLASMIC RETICULUM M G M G M G M • HAPLOID – SINGLE CIRCULAR CHROMOSOME – NO NUCLEAR MEMBRANE • CELL WALL PEPTIDOGLYCAN G, N-acetyl glucosamine M, N-acetyl muramic acid – UNIQUE WALL POLYMER Peptidoglycan LYSOZYME, an enzyme that cleaves polysaccharide G G M G G M M G G M M G Peptide bridge Amino acid Peptidogycan Disaccharide N-acetyl muramic acid N-acetyl glucosamine M M G M PENICILLIN, an antibiotic inhibits formation of peptide cross bridge 2 11/24/13 NAG NAM Summary of Peptidoglycan Structure NAG NAM Two tetrapeptide Chains crosslinked Two tetrapeptide chains cross-linked by peptide bridge FUNCTION OF CELL WALL FUNCTION OF CELL WALL • MECHANICAL STRENGTH • STRUCTURAL INTEGRITY • MECHANICALSTRENGTH • STRUCTURAL INTEGRITY – DISRUPT PEPTIDOGLYCAN – CELLS BURST – HIGH INTERNAL OSMOTIC PRESSURE – DISRUPT PEPTIDOGLYCAN – CELLS BURST – HIGH INTERNAL OSMOTIC PRESSURE Protoplast Bacterial cell Wall Lysozyme Isotonic solution 3 11/24/13 GRAM-POSITIVE BACTERIAL CELL WALL FUNCTION OF CELL WALL Lipoteichoic acid Wall teichoic acid negatively charged polymers • MECHANICALSTRENGTH • STRUCTURAL INTEGRITY Proteins Covalently bound to peptidoglycan – DISRUPT PEPTIDOGLYCAN – CELLS BURST – HIGH INTERNAL OSMOTIC PRESSURE Protoplast Peptidoglycan H2O Lysozyme Isotonic solution Cytoplasmic membrane Hypotonic Protoplast bursts Gram-Positive Bacterial Wall Structure Protein Attached covalently to cell wall peptidoglycan. Lipoteichoic acid Cytoplasm GRAM-POSITIVE BACTERIAL CELL Thick single-layered cell wall Nuclear material (no nuclear membrane) Wall teichoic acid Thick Peptidoglycan Cytoplasmic Membrane. Lipid bilayer Dividing cell Membrane proteins 4 11/24/13 GRAM-NEGATIVE BACTERIAL CELL WALL Lipopolysaccharide (endotoxin) Gram-Negative Bacterial Wall Structure Porin Fimbria (pilus) Polysaccharide chain Lipopolysaccharide LPS, endotoxin Outer Membrane Outer membrane Pore Outer membrane protein porin Thin peptidoglycan Periplasmic space Peptidoglycan Periplasm Cytoplasmic membrane Cytoplasmic membrane Cytoplasm GRAMNEGATIVE BACTERIAL CELL WALL Molecules and Structures on the Surface of Gram-Negative Bacteria Outer Membrane PeptidoGlycan Periplasm Cytoplasmic Membrane Cytoplasm 5 11/24/13 Lipopolysaccharide (Endotoxin) eg. There are 100s of different serotypes of the species Salmonella enterica FIMBRIAE (PILI) Flagellum Polysaccharide chain (highly variable) Defines O (somatic) antigen Core polysaccharide fimbriae Lipid A (toxic moiety) Outer membrane Promotes adhesion to mammalian cells eg intestinal epithelium, Vibrio cholerae Tip of Pilus of Escherichia coli FimG tip protein – adhesin Pilus of Escherichia coli Tip fibrillum 3 nm thick tip fibrillum Composed of 2 proteins 7 nm thick helical rod. Subunits of FimA Attached to outer membrane basal structure (not shown) Shaft. Identical FimA subunits Attached to outer membrane by usher 6 11/24/13 Flagella Flagellum Movement towards substrate chemotaxis Flexible. Beating flagella Motility Peritrichous Rotates polar Motility; Polar Number and arrangement of flagella characteristic of species CAPSULE • Outer layer • Polysaccharide usually (sometimes polypeptide) • Unstructured : loose association • Promotes virulence in pathogenic (diseasecausing) bacteria – Inhibits phagocytosis by leucocytes – Streptococcus pneumoniae. – Bacillus anthracis • Cap+ virulent • Capnon-virulent Capsule Bacillus anthracis Streptococcuss pneumoniae Polysaccharide capsule 7 11/24/13 CAPSULE SPORES Bacterial cell • Resistance to heat and dessication Capsule • Clostridium Bacillus 8 11/24/13 Infections of Humans by Spore-Forming Bacteria. Tetanus Clostridium tetani. Obligate anaerobe. Commensal of intestine of horses. Spores in soil. Contaminate deep wound. Anaerobic environment. Germination. Synthesize tetanus neurotoxin. Enters nerve cells. Inactivate neurons that trigger muscle relaxation. Spasms - face, then limbs. Vaccine (lecture 8) You should take some time to reflect on the differences in structure, composition & organization of prokaryotic and eukaryotic cells, referring back to earlier lectures on cell biology. Anthrax Bacillus anthracis Aerobic. Ingestion or inhalation of spores. Pneumonia or septicaemia. Poly-D-glutamic acid capsule and potent “Lethal Toxin” essential virulence factors Biological weapon : bioterrorism It is very important that you know the detailed structure of the cell wall of Gram-positive and Gram-negative bacteria. Not only is this knowledge of fundamental importance in its own right, but it is essential for the full understanding of susceptibility of and resistance of microbes to antimicrobial drugs (lecture 3), and of interactions between pathogenic bacteria and the mammalian host (lecture 4). Note the different mechanisms of action of penicillin in inhibiting the formation of peptidoglycan (lecture 3), and lysozyme, an enzyme which destroys peptidoglycan. Lysozyme is part of the innate immunity of mammals (lecture 7/8) Several appendages are found on bacterial cells that are of importance in colonization of the host (fimbriae or pili of Gram-negative bacteria and surface proteins of Gram-positive bacteria – see lecture 4). The capsule of Streptococcus pneumoniae is a major virulence factor because it prevents phagocytosis of bacteria by neutrophils, unless there are specific antibodies present that bind to the capsule (see lecture 7/8). Lipopolysaccharide of Gram- negative bacteria is an important antigenic determinant (lecture 7) but is also toxic (it is called endotoxin) and is of importance in the pathogenesis of diseases caused by Gram-negative bacteria (lecture 4) and is recognized by the host as a signal that infection is occurring – triggering inflammation The ability of some Gram-positive bacteria to form spores is the reason why the autoclave must be used to completely sterilize media and materials for laboratory use (lecture 1). Spores are very important in the dissemination of the bacteria that cause tetanus and anthrax, the latter is currently of concern because of the possibility of using it for bioterrorism. Further Reading Campbell does not have much detail on the structure of prokaryotes Chapter 4 of Totora is an excellent chapter covering this lecture in some depth. Todor’s On-line Textbook of Bacteriology 9