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Transcript
Bacterial Anatomy Rashmi.S Anatomy of a Bacterial Cell Description Bacteria are Prokaryotic, unicellular that do not contain chlorophyll. Size of bacteria may range from 0.21.5 micrometer in diameter and 3-5 micrometer in length DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTES Character Nucleus: Nuclear Membrane Nucleolus Mitotic Division Cytoplasm Cytoplasmic Streaming Pinocytosis Lysosomes Golgi Apparatus Endoplasmic Reticulum Chemical Composition Sterols Muramic Acid Teichoic Acid Prokaryotes Eukaryotes Absent Absent Absent Present Present Present Absent Absent Absent Absent Absent Present Present Present Present Present Absent Present Present Present Absent Absent Classification of Bacteria based on their Shape Cocci Bacilli Vibrio Spirilla Spirochetes Actinomycetes Mycoplasma Cellular Arrangement In Cocci, Diplococci: Cocci arranged in pairs Streptococci: Arranged in chains Staphylococci: Arranged in grape like clusters In Bacilli, Coccobacilli: Oval shaped Palisades : Parallel, attached at any one end of the cell Streptobacilli: In chains Vibrio Spirilla Actinomycetes Mycoplasma Structure of a Bacterial Cell (Bacterial Anatomy) Examination of a bacterial cell reveals components of structures Some external to cell wall Others internal to cell wall Anatomy of a Bacterial Cell Demonstration of the cell wall Plasmolysis Microdissection Specific Antibodies Differential Staining Electron Microscope Structure of the cell wall Bacterial cell wall provides structural integrity to the cell. The bacterial cell wall differs from that of all other organisms by the presence of Peptidoglycan Peptidoglycan (Mucopeptide) is composed of alternating chains of .. N -Acetyl Glucoseamine and N-Acetyl Muramic acid, which is cross linked by Peptide chains Structure of Peptidoglycan Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape Based on the composition of cell wall & Staining bacteria are classified into “Gram positive” and “Gram Negative’ Gram’s Staining Gram Positive Cell wall The Gram positive cell wall is characterized by the presence of a very thick Peptidoglycan layer 20-80 nm thick Cell wall contains90% Peptidoglycan and 10%Teichoic acid Interwoven in the cell wall of grampositive are Teichoic acids and lipoteichoic acids. Teichoic acids composed of polymers of glycerol, phosphates, and the sugar alcohol- ribitol. Teichoic acids constitute for the major surface antigens. Eg: In Streptococcus pneumoniae Teichoic acid bears the antigenic determinants called the “Forssman antigen” Gram Negative Cell Wall Gram negative cell wall contains a thin Peptidoglycan layer adjacent to the Cytoplasmic membrane, In addition to the Peptidoglycan layer, the Gram negative cell wall also contains an additional outer membrane composed by Phospholipids and Lipopolysaccharide which face into the external environment. The LPS present on the Gm negative cell wall consists of 3 regions: Polysaccharide determining O antigen Core Polysaccharide Glycolipid portion /Lipid A All the three factors are responsible for the endotoxic activities……… LPS Endotoxin causes a form of Septic Shock for which there is no direct treatment Cytoplasmic Membrane It is a thin layer lining the inner surface of the cell wall. Semipermiable membrane controlling the flow of metabolites Chemically ,consists of Lipoprotein and carbohydrates. Sterols are absent Cytoplasm Colloidal system of variety of organic and inorganic solutes in Viscous watery solution No ER,& Mitochondria Contains Mesosomes Inclusions and Vacuoles Mesosomes Vesicular, convoluted invaginations of the plasma membrane Prominent in GM+ bacteria Principal sites of Respiratory enzymes Analogous to mitochondria in Eukaryotes Nucleus Bacterial nuclei “have no nuclear membrane “or the nucleolus. Genome consists of a single double stranded DNA. Might be a Circular form or may be open under certain condition to form a long chain. Plasmids Extra chromosomal DNA Circular capable of autonomous replication. Transferred from one bacterium to another . Importance Their presence confers certain special characters…… Toxigenicity Antibiotic Resistance Ability to use certain unusual components as nutrients Structures external to Bacteria Capsule Flagella Pili(Fimbriae) Capsule Viscid material secreted by bacteria around the cell surface Capsule is a sharply defined, organized structure (Eg: Pneumococcus) Loose undemarkated structure as in Lueconostoc is a Slime layer. Colorless capsule surrounding the bacterial cell Capsular Staining Most bacterial capsules are composed of Polysaccharides Eg: Klebsiella pneumoniae A few capsules are Polypeptides Eg: Bacillus anthracis Quellung Reaction Described by Neufeld(1902). Serological method of demonstrating the capsule. Suspension of capsulated bacterium is mixed with its specific anticapsular serum & examined under the microscope ,capsule appears prominent & swollen. Used to type Pneumococci. Functions of Capsules Antiphagocytic,thus contribute “Virulence”. Protects against “Lysozyme” Promote attachment of bacteria to surface(Eg: Streptococcus mutans). Permits bacteria to adhere to Medical Implants & Catheters. Toxicity to host cell – Eg: Bacteroides fragilis. Provide protection against temporary drying. Block the attachment ofBacteriophages. Applications: Used in serological typing Detection of capsule in Blood, CSF provides a rapid method of diagnosis Used in preparation of vaccines Eg: H.influenzae Flagella Unbranched, long ,filaments ,made up of protein “Flagellin” Organs of locomotion Found in all motile bacteria except Spirochetes Flagella are highly antigenic, Termed as the ‘H’ Antigen. Some of the immune responses are directed against these proteins. Structure 3-20 Micrometer. Each flagellum consists of 3 parts 1.Filament 2.Hook 3.Basal body Flagellar Arrangement Kinds of Motility: Darting motility : V.cholerae Tumbling motility: L.monocyctogenes Cork &screw motility: T.pallidum Stately motile : Clostridium spp. Serpentine motility: Salmonella (Except S.gallonarum pullorum) Detection of motility : Direct observation by hanging drop Dark field microscopy Motility media Flagellar staining Electron microscopy Immunological “H” antigen detection of Fimbriae Hair like surface appendages 0.5-10 nm thick Shorter thinner than flagella Formed of protein subunits – Pilin Functions Organs of adhesion Forms “Pellicles” Hemagglutination –Clumping of RBC’s (Escherichia,Klebsiella) Special type of Fimbriae called Sex pili,help in attachment to other bacteria Endospores Highly resistant stages of bacteria Spores germinate to form a single Vegitative cell. It is formed inside the cell . Eg: Bacillus, Clostridium Endospore Core contains the Nuclear body Surrounded by a Spore Wall. Outside this is a thick Spore cortex This is covered in turn by a tough Spore coat. Exosporium is additional outer covering, which exhibits ridges and grooves Factor responsible for the resistance of spores Presence of calcium dipicolinic acid Endospore inside bacteria Position of Spores A = oval, terminal; B = rectangular, terminal; C = rectangular, sub terminal, D = rectangular, central; E = circular, terminal; F = circular, central; G = terminal, club-shaped. Pleomorphism and Involution forms Process of exhibiting variation in the shape and size of individual cells – Pleomorphism Eg: H.influenzae Certain bacteria exhibit swollen and aberrant forms in ageing cultures – Involution forms This may be due to defective cell wall synthesis or due to Autolytic Enzymes Eg: Yersinia, Gonococcus Protoplasts,Spheroplasts and LForms Removal of bacterial cell wall by hydrolysis with Lysozyme or antibiotics like Penicillin, liberates .. “Protoplasts” from Gram positive cells “Spheroplasts” from Gram negative cell (retain the outer membrane and PG.) When Protoplasts and Spheroplasts are able to grow and divide they are called the L-Forms. First observed by Kleineberger-Nobel Named it as L forms after Lister Institute London. Eg: Streptobacillus moniliformis THANK YOU