Classification of bacteria

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					                              Classification of bacteria


                                 Learning objectives


At the end of the lecture the student should be able to:
•    Identify bacteria and its properties
•    Classify bacteria according to its shape, arrangement, gram staining, method of
     respiration.

                                     Bacteria
•    Single-celled
•    Prokaryotic (no membrane-enclosed nucleus)
•    No mitochondria or chloroplasts
•    A single chromosome
      – Double-stranded DNA
      – With no associated histones.




                                        Bacteria
•    Have a rigid cell wall made of peptidoglycan
•    The plasma membrane (in Gram-positive bacteria) and both membranes in Gram-
     negative bacteria are phospholipid bilayers but contain no cholesterol or other
     steroids.
•    No mitosis
•    Mostly asexual reproduction
•    No meiosis

•    Many bacteria form a single spore when their food supply runs low.
•    Most of the water is removed from the spore and metabolism ceases.
•    Spores are so resistant to adverse conditions of dryness and temperature that they
     may remain viable even after 50 years of dormancy.
Differences between bacteria and viruses


•   Viruses


      –   Obligate intracellular parasites
      –   No ribosomes
      –   DNA or RNA, not both
      –   seen by EM
      –   10-100s of genes
      –   Tangled phylogeny.




•   Bacteria
     – Usually free-living, but can be parasites
     – Ribosomes
     – DNA and RNA
     – seen by LM
     – 100s-1000s of genes
     – Natural phylogeny.
                            Classification of bacteria




•   According to shape
     – Coccus
     – Rod or bacillus
     – Spiral




•   According to method of energy production
     – Aerobic
     – Anaerobic




•   According to arrangement
     – Paired: diplo
     – Grape-like clusters: staphylo
     – Chains: strepto
•   According to reaction to the Gram stain.
     – Gram positive
     – Gram negative




•   According to ability to form spores
•   According to Nutritional requirements
•   According to fastidiousness
•   According to serological reactions
•   According to DNA sequencing


                                     Gram staining


•   Bacterial cells are first stained with a purple dye called
    crystal violet.
•   Then the preparation is treated with alcohol or acetone.
•   This washes the stain out of Gram-negative cells.
•   To see them now requires the use of a counterstain of a
    different color (e.g., the pink of safranin).
•   Bacteria that are not decolorized by the alcohol/acetone
    wash are Gram-positive.


Gram-Negative Rods:


•   Part of the normal flora of intestine
•   Enteric Bacteria
     – E. coli
     – Salmonella
     – Shigella
     – Yersinia
     – Pseudomonas
     – Proteus
     – Vibrio cholerae
     – Klebsiella pneumoniae
                               Gram-Negative Rods




•   Fastidious GNRs
     – Bordetella pertussis
     – Haemophilus influenzae
     – Campylobacter jejuni
     – Helicobacter pylori
     – Legionella pneumophila
•   Anaerobic GNRs
     – Bacteroides fragilis
     – Fusobacterium



                               Gram-Negative Cocci




•   Neisseria gonorrhoeae
     – The GonococcusThe Meningococcus
•   Both Gram-negative intracellular diplococci




                       Gram-positive Cocci
•   Staphylococci
     – Catalase-positive
     – Gram-positive cocci in clusters
•   Staphylococcus aureus
     – coagulase-positive
•   Staph. epidermidis
     – and other coagulase negative staphylococci




                               Gram-Positive Cocci
•   Streptococci
     – Catalase-negative
     – Gram-positive cocci in chains or pairs
•   Strep. pyogenes
•   Strep. pneumoniae
•   Viridans-type streps
•   Enterococcus faecalis


                               Gram-Positive Rods
•   Clostridia
      – Anaerobes
      – C.perfringens
      – C. tetani
      – C. botulinum
      – C. difficile
•   Bacillus cereus
      – Aerobe
•   Listeria monocytogenes
      – Faculative anaerobe



                             Non-Gram-stainable bacteria
•   Unusual gram-positives
•   Spirochaetes
•   Obligate intra-cellular bacteria


                             Unusual Gram-positives
•   Mycoplasmas
     – Smallest free-living organisms
     – No cell wall
     – M. pneumonia, M. genitalium
•   Mycobacteria
     – Acid-fast bacilli, stained by Ziehl-Neelsen stain
     – M. tuberculosis
     – M. leprae
     – M. avium


                                  Spirochaetes
•   Thin spiral bacteria
•   Viewable by phase-contrast microscopy or silver stain
     – Treponema pallidum
     – Borrelia burgdorferi
     – Leptospira
                        Obligate intracellular bacteria
•   Rickettsia
•   Coxiella burneti
•   Chlamydias
     – C. trachomatis
     – C. pneumoniae
     – C. psittaci




                             THANK YOU

				
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posted:10/29/2012
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