Saran's Learn Microbiology

  GLYCOCALYX ·     Some bacterial cells have a gelatinous, sticky substance that surrounds the outside of the cell. This substance is known as a Glycocalyx (Plural: Glycocalyces), which literally means “Sweet cup” or “Sugar coat”. ·    Glycocalyx may be composed of Polysaccharides or Polypeptides, or both Polysaccharides and Polypeptides. Its chemical composition varies widely with the species. These chemicals are produced inside the cell and are extruded onto the cell’s surface. ·      When the Glycocalyx of a bacterium is composed of organized repeating units of organic chemicals firmly (strongly) attached to the cell’s surface, the Glycocalyx is called a Capsule. In contrast, a loose, water-soluble Glycocalyx is called a Slime layer. ·    Glycocalyx is the currently accepted term used to refer to all Polysaccharide-containing substances found external to the cell wall, from the thickest Capsules to the thinnest Slime layers. ·        Capsules is not present in all bacteria

  PILI ·        Pili are long hair like tubular microfibers like structure. ·        Pili are present on some Gram negative bacteria only. ·        Based on Hemagglutinating ability and Mannose sensitivity, Pili are classified into four types. They are i.        Type I - Occur in Escherichia coli, Klebsiella, Shigella and Salmonella . They are mannose sensitive. ii.      Type II - Present in Salmonella gallinarum and Salmonella pullorum,  devoid of any hemagglutinating or adhesive properties. iii.    Type III - Present in some strains of Klebsiella, Serratia , etc. They agglutinate RBC only after heating and are mannose resistant. iv.    Type IV - Mannose resistant and occur in Proteus . ·        Pili are made up of protein called Pilin. ·        Comparatively, Pili are longer than Fimbriae and shorter than Flagella. ·        Approximate length of Pili is 0.5 µm – 2.0 µm. ·        Number of Pili per cell is very less. It is usually 1 to 10 per cell. They ar

  BACTERIAL SURFACE APPENDAGES ·        Bacterial Surface Appendages are Proteinaceous tubular or fibrous structure found on the surface of the bacterial cells. ·        The main functions of Bacterial surface appendages are Locomotion, Adhesion, Attachment and Assisting in Genetic exchange. ·        The three Surface appendages of bacteria are Flagella, Fimbriae and Pili.   FLAGELLA ·   Bacterial flagella are thread-like or whip-like appendages intricately embedded in the cell envelope. ·      Flagella are responsible for conferring motility to the bacteria. They do not have any role in surface attachment. ·        Flagella are 20 - 30 μ m in diameter and 15 μ m in length. ·        Flagella are many times longer than Pili and Fimbriae. ·        Flagella are made up of protein called Flagellin. ·        Flagella are helical and non-straight in nature. ·        Flagella are interior in the originated from the Cytoplasmic membrane. ·        The formation of Flagel