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BACTERIA

DOMAIN BACTERIA

  • PHENOTYPIC CATEGORIES
      • Gram negative with cell walls
      • Gram positive with cell walls
      • Bacteria without cell walls

 

 

 

 

CELL WALL DEFICIENT BACTERIA 

  • These are bacteria which lose their cell walls during adverse growth conditions but revert to their original shape when placed in favorable growth conditions.
  • L-forms ( Lister institute )
  • Result from:
      • Spontaneous mutation
      • Effects of chemicals ( penicillin)

MYCOPLASMA

  • These are bacteria lack cell walls thus appear in various shapes – PLEOMORPHIC
  • Mycoplasma pneumoniae

 

  • All cocci are gram positive except :
      • Neisseria
      • Veillonella
      • Branhamella
  • All bacilli are gram negative except:
      • Corynebacterium
      • Clostridium
      • Bacillus
      • Mycobacterium

STAINING

  • Because bacteria are colorless and transparent they are usually stained  to give color to the organisms so that it will be easier to view them under the microscope.

PREPARATION FOR STAINING

    1. Smear
    2. Air dry
    3. Fixation ( heat fixation and methanol fixation )

 

 

PURPOSES OF FIXATION

      • to kill microorganisms
      • to preserve the morphology of bacteria
      • to anchor the smear to the slide

 

TYPES OF STAINING

  • SIMPLE STAINING
    • Simple staining  is  used to determine cell shape, size, and arrangement. It uses only one kind of stain.

 

  • DIFFERENTIAL STAINING
    • Differential staining methods usually require more than one stain. These procedures permit the differentiation of cell types or cell structures. 
          • Gram staining
          • Acid fast staining
  • SPECIAL STAINING (STRUCTURAL STAINING)
    • Special staining procedures are done to observe capsules , spores and flagella.

 

GRAM STAINING

  • The Gram stain procedure which was developed by Dr. Hans Christian Gram in 1883,  distinguishes between Gram positive and Gram negative groups by coloring these cells red or violet. 
  • Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.  Gram negative bacteria stain red, which is attributed to a thinner peptidoglycan wall, which does not retain the crystal violet during the decoloring process.

 

GRAM VARIABLE BACTERIA

  • Gram variable bacteria are neither consistently blue nor red on gram staining
  • Ex: Mycobacterium

ACID FAST BACTERIA

  • Acid fast bacteria have a high lipid content ( mycolic acid )in their cell walls, hence cannot be stained using the gram stain.
    • ZIEHL-NEELSEN STAIN
      • differential staining procedure that specifically stains all members of the genera mycobacteria.
      • utilizes heat and phenol (carbolic acid) to help the penetration of the dye, basic fuchsin, to the inside of mycobacterial cells, which are impermeable to basic dyes in routine stains.
      • The high lipid and wax content of the mycobacterial cell walls is thought to be the reason for such impermeability.
      • Reagents
        • Carbol fuschin (basic dye)
        • Mordant (heat)
          • Softens the waxes to allow dye to penetrate the wall
        • Acid alcohol (decolorizer)
          • Methylene blue (counter stain) or Malachite green
    • KINYOUN ACID FAST STAINING PROCEDURE
      • The  Kinyoun method of staining does not require heating, thus is called cold method.  Instead, the concentration of carbol fuschin used is increased.

 

STRUCTURAL STAINING PROCEDURES

  • CAPSULE STAINS
    • Capsule stain is a type of differential stain which uses acidic and basic dyes to stain background & bacterial cells respectively so that presence of capsule is easily visualized.  
    • The India ink  method uses the dyes, crystal violet and india ink (nigrosin). The capsule is seen as a clear halo around the microorganism against the black background. This method is used for demonstrating Cryptococcus.
  • FLAGELLA STAINS
  • ENDOSPORE STAINS

 

  • MOTILITY of bacteria is associated with the presence of flagella and axial filaments.
    • Most spiral shaped bacteria and one half of bacilli are motile.
    • Cocci  are  nonmotile.
    • METHODS FOR DEMONSTRATING MOTILITY
      • inoculation in semisolid medium
      • hanging drop method

 

ATMOSPHERIC REQUIREMENTS

  • AEROBES utilize molecular oxygen for energy.
  • OBLIGATE AEROBES require an atmosphere containing 20-21% O2.
      • Mycobacteria, fungi
  • MICROAEROPHILES require lower concentrations of O2 (5%).
      • Neisseria gonorrheae
      • Campylobacter spp.
  • ANAEROBES do not require O2 for life and reproduction.
  • OBLIGATE ANAEROBES  can only grow in an anaerobic environment.
  • AEROTOLERANT ANAEROBES grow better in the absence of O2 but can survive in its presence.
  • FACULTATIVE ANAEROBES can survive in the presence or absence of oxygen.
      • Enterobacteriaceae
      • Streptococci
      • staphylococci

UNIQUE OR RUDIMENTARY BACTERIA

  • RICKETTSIA
    • The rickettsiae are a diverse collection of obligately intracellular Gram-negative, non-sporeforming highly pleomorphic  bacteria found in ticks, lice, fleas, mites, chiggers, and mammals.
    • These bacteria cause arthropod borne diseases such as Rocky Mountain Spotted Fever.
  • CHLAMYDIAS
    • Chlamydias are obligate intracellular pathogens transmitted by inhalation of aerosols or by direct contact between hosts.
    • They are referred to as energy parasites because they can produce ATP's.
    • Chlamydia trachomatis is one of the most common causes of sexually transmitted urethritis.
  • MYCOPLASMAS
    • Mycoplasmas are the smallest of the cellular microbes.
    • Mycoplasmas lack cell walls thus are pleomorphic.
    • They cause atypical pneumonia and genitourinary infections
    • They produce fried egg shaped colonies when cultured.

PHOTOSYNTHETIC BACTERIA

      • Purple bacteria
      • Green bacteria
      • Cyanobacteria

ARCHAEA

  • These are “ancient” microorganisms that are able to live in extreme environment.
  • They possess cell walls without peptidoglycan.

 

REFERENCE:

Engelkirk, P. G. (2018). Burton's microbiology for the health sciences 11th ed.(ch 1). Philadelphia: Lippincott Williams & Wilkins.