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Classification+structure+function

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    Classification+structure+function Classification+structure+function Presentation Transcript

    • Classification, Structure and Functions of Bacteria Dr Kamran Afzal Asst Prof Microbiology
    • I. Classification of Bacteria
    • Taxonomy
      • Taxonomy
        • Organizing, classifying and naming organisms into groups - according to specific criteria
        • Formal system originated by Carl von Linné (1701-1778)
        • Bergey’s manual of systemic bacteriology (1927, 1984 and 2001)
    • Taxonomy
      • D omain
      • K ingdom
      • P hylum
      • C lass
      • O rder
      • F amily
      • G enus
      • s pecies
      • Taxonomic ranks
      • Kingdom – Prokaryotae
      • Phylum – Gracilicutes
      • Class – Scotobacteria
      • Order – Eubacteriae
      • Family – Enterobacteriaceae
      • Genus – Escherichia
      • Species - coli
    • Species and Subspecies
      • Species
        • Collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantly
      • Strain
        • A population of microbes descended from a single individual or pure culture (biovars, morphovars)
      • Type
        • Subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type)
    • Naming Micoorganisms
      • Binomial (scientific) nomenclature
      • Gives each microbe 2 components of its name
        • Genus - noun, always capitalized
        • species - adjective, lowercase
      • Both italicized or underlined
        • Staphylococcus aureus ( S. aureus )
        • Bacillus subtilis ( B. subtilis )
        • Escherichia coli ( E. coli )
    • Classification Systems
      • Phylogenetic Classification System
        • Groups reflect genetic similarity and evolutionary relatedness
      • Phenetic Classification System
        • Groups are based on convenient, observable characteristics – Morphology
          • Cell shape and arrangement
          • Colony morphology
          • Cell wall structure (Gram staining)
      • Special cellular structures
        • Microscopic morphology
      • Biochemical characteristics
      • Serological Tests
        • Use group specific antiserum isolated from the plasma of animals that have been sensitized to the organism
      • Chemical analysis
      • Nutritional requirements
        • Autotrophs, heterotrophs
      • Genetic and molecular analysis
        • DNA composition
          • G _ C , A _ T
        • DNA analysis using genetic probes
        • Nucleic acid hybridization
        • Nucleic acid sequencing
        • rRNA analysis
        • Microarray
    • Major Groups of Disease Producing Bacteria
      • Gram positive cocci
      • Staphylococcus, Streptococcus,
      • Enterococcus, Peptostreptococcus
      • Gram negative cocci
      • Neisseria gonorroae,
      • Neisseria meningitidis
      • Gram positive rods
      • Corynebacterium, Listeria, Actinomyces,
      • Nocardia
      • Endospore-forming Gram positive rods
      • Bacillus, Clostridium, Erysepelothrix
      • Gram negative rods – Facultative anaerobic
      • Escherichia, Klebsiella, Proteus, Providencia
      • Salmonella, Shigella, Yersinia, Vibrio, Haemophilus
      • Gram negative rods - Aerobic/Microaerophilic
      • Campylobacter, Helicobacter, Spirillium
      • Bordetella, Brucella, Pseudomonas
      • Gram negative rods - Anaerobic
      • Bacteroides
      • Fusobacterium
      • Spirochetes
      • Treponema, Borrelia, Leptospira
      • Cell wall deficient Bacteria
      • Mycoplasma, Ureaplasma
      • Acid fast bacteria
      • Mycobacteria
    • II. Structure of Bacteria
    • Typical shapes of bacteria Most bacteria retain a particular shape; a few are pleomorphic
    • Characteristic grouping
    • General properties of bacteria
      • Non-membrane bound organelles
      • More complex than viruses but less than living, cellular organisms
      • Ribosomes smaller
      • Inherited information held in single circular chromosome
      • Bacteria range in size 0.3 to 14 micron
      • Variable oxygen requirement
      • Possess cell wall and an outer membrane in Gram -ve
      • Can be grown in the lab given proper nutrition and oxygen in culture media
    • Typical prokaryotic structures
    • Capsule
      • Protection
        • Dehydration
        • Immune mechanisms
      • Glycocalyx - polysaccharide, protein
        • Capsule if organized
        • Slime layer if not
      • Contributes to virulence
    • Cell wall
      • Survival dependent on integrity of cell wall
      • Role in cell division
      • Chemical composition - Unique to bacteria
          • Peptidoglycan - Main structural component
          • Strengthening components
          • Teichoeic acid
          • Lipid A – endotoxin
          • Mycolic acid - AFB
      • Significance of Gram-positive vs Gram-negative
        • Antibiotic sensitivity
        • Sensitivity to lysozyme
        • Sensitivity to alcohol
    •  
      • Gram-positive
        • Peptidoglycan is a thick layer external to the cell membrane
      • Gram-negative
        • Peptidoglycan is thin and covered by an outer membrane (OM)
    •  
    • Teichoic acids
      • Gram +ve only
      • Glycerol, Phosphates and Ribitol
      • Attachment for Phages
    • Cell membrane
      • Phospholipid bilayer
        • Carrier proteins - Porins allow molecules to pass through outer membrane
        • Generally require energy to move against the concentration gradient
        • Outer membrane is made of lipopolysaccharide
        • (LPS)
    •  
    •  
    •  
    • Lipopolysaccharide (LPS)
      • G -ve bacteria only
      • Structure
        • Lipid A
        • Polysaccharide
      • Functions
        • Endotoxin: Toxic; kills mice, pigs, humans
          • G- septicemia; death due to LPS
        • Pyrogen: causes fever
        • Adjuvant: stimulates immunity
      • Heat resistant: hard to remove
      • Appearance of Colonies
        • Mucoid: Smooth (lots of LPS or capsule)
        • Dry: Rough (little LPS or capsule)
      • O Antigen of Salmonella and E. coli
        • 2,000 different O Ags of Salmonella
        • 100’s different O Ags of E. coli
          • E. coli O157
        • O Antigens differ in Sugars, not Lipid A
    •  
    • Flagella
      • Movement
        • Bacteria vary in the way flagella are attached
        • Running, tumbling, swarming
        • Can move toward or away from light or chemical stimuli
        • Flagellin protein is unique to prokaryotes
      • Arrangement
        • Monotrichous; 1 flagella
        • Lophotrichous; tuft at one end
        • Amphitrichous; both ends
        • Peritrichous; all around bacteria
    •  
    • Fimbriae and Pili
      • Adhesion
        • Fimbriae
      • Conjugation
        • Pili
    • F-Pilus for Conjugation
      • 80% Water + 20% Salts-Proteins
      • Nucleoid with single, circular, supercoiled DNA molecule
      • No organelles (Mitochondria, Golgi, etc.)
      • Ribosomes - Involved in protein synthesis
      • Many bacteria have plasmids
        • Small, extra-chromosomal, circular piece of DNA
        • Genes present may not be required but may be advantageous (antibiotic resistance, resistance to metals)
      Cytoplasm and Internal components
    • Endospores
      • Resistant structure
        • Heat, irradiation, cold
        • Boiling >1 hr still viable
      • Takes time and energy to make spores
      • Location important in classification
        • Central, Sub-terminal, Terminal
      • Bacillus stearothermophilus spores
        • Used for quality control of heat sterilization equipment
      • Bacillus anthracis spores
        • Used in biological warfare
    • Endospores
    •  
    • Cell wall
      • Which are more sensitive to Penicillin?
        • Gram +ve
        • Gram -ve
      • Alcohol/Acetone affects which more?
        • Gram +ve
        • Gram -ve
    • III. Functions of Bacteria
      • Decompose organic waste
      • Produce industrial chemicals such as ethyl alcohol and acetone
      • Produce products used in manufacturing (e.g., cellulase) and treatment (e.g., insulin)
      • Produce fermented foods such as vinegar, cheese, yogurt, butter, pickles and bread - Anaerobes
      • Used to produce antibiotics to kill other bacteria
        • Streptomycin
        • Erythromycin
        • Chloromycetin
        • Kanamycin
      • Recycling of nutrients
        • Cyanobacteria
          • Replenish supply of oxygen in atmosphere
        • Autotrophic bacteria
          • Convert carbon dioxide in the air to the organic compounds that are passed to consumers in food chains and webs
      • A lot of bacteria are normal flora (commensals) of humans
      • A few are pathogenic - disease-causing