Essential Medical

Dr. Abdelraouf A. Elmanama Medical laboratory Sciences Department Faculty of Health Sciences Chapter 2 Bacterial Morphology and Structure SIZE OF

Unit for measurement :

Micron or micrometer, μm: 1μm=10-3mm Size: Varies with kinds of bacteria, and also related to their age and external environment. Shape of Bacteria

 Cocci: sphere, 1μm  Bacilli: rods , 0.5-1 μm in width -3 μm in length  Spiral : 1~3 μm in length and 0.3-0.6 μm in width Cocci Bacilli

Spiral Structure of Bacteria Essential structures Cytoplasm nuclear material

Special structures Capsule Flagella Pili Spore Cell wall

 Location: outermost portion. 15-30 nm in thickness, 10%-25% of dry weight. 1884: Christian Gram: First publication for the Gram stain method)

Cell wall :Common layer

 A backbone of N-acetyl glucosamine and N- acetylmuramic acid: Both discovered in Gram positive and Gram negative bacteria.  A set of identical tetrapeptide side chain attached to N-acetyl-muramic acid: different components and binding modes in Gram positive and Gram negative bacteria.  A set of identical peptide cross bridges: only in Gram positive bacteria NAM NAG NAM NAG

CH2OH CH2OH CH2OH CH2OH H O H O H O H O O H H O H H O H O O H H O H O O H H H H H H H3C H NH H NH H3C H NH H NH C–H C–H O=C O=C O=C O=C

C=O CH3 CH3 C=O CH3 CH3 H– N H– N L–Ala L–Ala D–Glu D–Glu H H L–Lys Gly–Gly–Gly–Gly–Gly–N L–Lys Gly–Gly–Gly–Gly–Gly–N D–Ala D–Ala C=O C=O 图附

Special components of Gram positive cell wall

- Special components of Gram negative cell wall

Functions of Cell Wall

 Maintaining the cell's characteristic shape- the rigid wall compensates for the flexibility of the phospholipid membrane and keeps the cell from assuming a spherical shape  Countering the effects of osmotic pressure  Providing attachment sites for bacteriophages  Providing a rigid platform for surface appendages- flagella, fimbriae, and pili all anchored to the wall and extend beyond it  Play an essential role in cell division  Be the sites of major antigenic determinants of the cell surface。 Wall-less forms of Bacteria.

 When bacteria are treated with: 1) enzymes that are lytic for the cell wall e.g. lysozyme or 2) that interfere with biosynthesis of peptidoglycan, wall-less bacteria are often produced.  Usually these treatments generate non-viable organisms. Wall-less bacteria that can not replicate are referred to as protoplasts (if an outer membrane is not present).  Occasionally wall-less bacteria that can replicate are generated by these treatments (L forms). Bacteria L form

 Bacteria with defective cell wall-bacteria ( L form) (L-forms" after the Lister Institute): protoplast Cell membrane Function of Cell membrane

a. Selective permeability and transport of solutes into cells b. Electron transport and oxidative phosphorylation c. Excretion of hydrolytic exoenzymes d. Site of biosynthesis of DNA, cell wall polymers and membrane lipids. Mesosomes

 Mesosomes are specialized structures formed by convoluted invaginations of cytoplasmic membrane, and divided into septal and lateral mesosome. Cytoplasm

 Composed largely of water, together with proteins, nucleic acid, lipids and small amount of sugars and salts  Ribosomes: numerous, 15-20nm in diameter with 70S; distributed throughout the cytoplasm; sensitive to streptomycin and erythromycin site of protein synthesis  Plasmids: extrachromosomal genetic elements  Inclusions: sources of stored energy, e,g volutin Ribosomes

 Ribosomes are the protein synthesizing factories of the cell.  They translate the information in mRNA into protein sequences. Plasmid

Plasmids are: • Small， • Circular， • Extrachromosomal， • Double-stranded DNA molecules • They are capable of self-replication and • Contain genes that confer some properties， such as resistance，virulence factors • Plasmids are not essential for cellular survival. Inclusions of Bacteria

Inclusions are aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell.

Inclusions accumulate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions. Granules Nucleus

 Lacking nuclear membrane, absence of nucleoli, hence known as nucleic material or nucleoid, one to several per bacterium. Bacterial chromosome

Single Circular Compacted Capsules and slime layers

 These are structures surrounding the outside of the cell envelope.  When more defined, they are referred to as a capsule when less defined as a slime layer.  They usually consist of polysaccharide; however, in certain bacilli they are composed of a polypeptide (polyglutamic acid). They are not essential to cell viability and some strains within a species will produce a capsule, whilst others do not. Capsules are often lost during in vitro culture. Capsules and slime layers Function of Capsules and slime layers(1)

 Attachment :These structures are thought to help cells attach to their target environment.  produces a slime layer in the presence of sucrose.  This results in dental plaque and many bacteria can stick to tooth surfaces and cause decay once S. mutans forms a slime layer.  Vibrio cholerae, the cause of cholera, also produces a which helps it attach to the intestinal villi of the host. Function of Capsules and slime layers(2)

 Protection from phagocytic engulfment. Bacterial pathogens are always in danger of being "eaten" by phagocytes.  (Host cells that protect you from invaders.) Streptococcus pneumoniae, when encapsulated is able to kill 90% of infected animals, when non-encapsulated no animals die.  The capsule has been found to protect the bacteria by making it difficult for the phagocyte to engulf the microbe. Function of Capsules and slime layers(3)

Resistance to drying. Capsules and slime layers inhibit water from escaping into the environment. Function of Capsules and slime layers(4)

Reservoir for certain nutrients. Glycocalyx will bind certain ions and molecules. These can then be made available to the cell. Function of Capsules and slime layers(5)

Depot for waste products. Waste products of metabolism are excreted from the cell, and will accumulate in the capsule. This binds them up, and prevents the waste from interfering with cell metabolism. Flagella.  Some bacterial species are mobile and possess locomotory organelles - flagella.  Those that do are able to taste their environment and respond to specific chemical foodstuffs or toxic materials and move towards or away from them (chemotaxis).  Flagella are embedded in the cell membrane, extend through the cell envelope and project as a long strand.  Flagella consist of a number of proteins including flagellin.  They move the cell by rotating with a propeller like action. Relative Speeds of Organisms Organism Kilometers per hour Body lengths per second Cheetah 111 25 Human 37.5 5.4 Bacteria 0.00015 10

Flagella

 The diameter of a flagellum is thin, 20 nm, and long with some having a length 10 times the diameter of cell.  Due to their small diameter, flagella cannot be seen in the light microscope unless a special stain is applied.  Bacteria can have one or more flagella arranged in clumps or spread all over the cell. Flagella

Mono/trichous Amphi/trichous Lopho/trichous Peri/trichous Flagella

Used in Identification of Bacteria Contribute to Pathogenesis Motility of bacteria Pili

 Pili are hair-like projections of the cell , They are known to be receptors for certain bacterial viruses.  Chemical nature is pilin  Classification and Function a. Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion b. Sex pili: longer and coarser, only 1-4, related to bacterial conjugation Sex pili

 A donor bacteria will attach to a recipient via the sex . Then a copy of part of the donor bacterium's genome passes through the sex pilus into the recipient.  Conjugation, as it is called, is one explanation for the rapid spread of drug resistance in many different species of bacteria. Common pili or fimbriae

 Pili have also been show to be important for the attachment of some pathogenic species to their host.  Neisseria gonorrheae, the causative agent of gonorrhea, has a special pili that helps it adhere to the urogenital tract of its host. The microbe is much more virulent when able to synthesize pili.

 Endospores are highly resistant resting structures produced within cells.  They are common to organisms which live in soil and may need to wait out some rough times such as >100°C heat, radiation, drying or chemical agents ; under favorable conditions , a spore germinates into a vegetative cell  Spores are commonly found in the genera and Clostridium. DPA and survival

 Dipicolinic acid, DPA.  Spores can survive for a very long time, and then regerminate.  Spores that were dormant for thousands of years in the great tombes of the Egyption Pharohs were able to germinate and grow when placed in appropriate medium.  There are even claims of spores that are over 250 million years old being able to germinate when placed in appropriate medium.  These results have yet to be validated. Spores

 The mechanisms that account for this include the dehydration of the protoplast and the production of special proteins that protect the spores DNA.

Are capable of detecting their environment and under favorable nutrient conditions germinating and returning to the vegetative state. Spore

 Used in Identification of Bacteria  Contribute to Pathogenesis  Resistance to adverse environmental conditions Methods Microscopy

 Light Microscope  Electron Microscope  Dark-field Microscope  Phase Contrast Microscope  Fluorescence Microscope Methods Staining Methods

Simple staining; Differential staining ( Gram stain, Acid-fast stain), Special staining( Negative stain, Spore stain, Flagella stain)