BACTERIA

INTRODUCTION:

            Living material is organized in unit and microorganism were living form of microscopical size and usually unicellular in structure originally classification is unsatisfied.

Prokaryotic & Eukaryotic Cells

Bacteria

n  Earth’s oldest life forms

            – between 3.5 and 3.8 billion years old

n  Most abundant life form – up to 2.5 billion individual bacteria in 1 gram of fertile soil

n  Very adaptable – found in all of Earth’s

    ecosystems

                       

v Bacteria  Characteristics

n  Unicellular

n  Circular DNA

n  No organelles

n  1/10^th the size of eukaryotic cells

n  Flagella-long hair-like structure used for movement

n  Reproduce asexually –Binary Fission

v

Classification

Bacteria can be classified in many ways. The first classification scheme was published in 1773 and many more have appered since.

Science of microbiology has developed other kind of classification but medically important classification is as follows

   

Based on several major properties

l  Morphology

l  Biochemical reaction

l  staining reaction

l  Pathogenicity

l  Based on relationship of host and microorganism

l  DNA composition 

(1) MORPHOLOGICAL

             Bacteria can be classified according to morphological characteristics like their cell shape, size and structure and their specific arrangement like motility and flagellar arrangement.

A.    According to shape:

1)cocci( spherical or oval)

             i.cocci in clustre.

                  Ex staphylococci     

         ii) cocci in chain. Ex. Streptococci

         iii) cocci in pair. Ex. Diplococcus  pneumoniae

         iv) cocci in group of four. Ex.Tetrad

2) Bacilli (cylindrical or rod shaped)

          i)coccobacilli: length of cell is greater than its breadth but not rod shaped. Ex. Brucella.

          ii) cuneiform or chinese letter arrangement: ex.corny bacteria

        iii) vibrio: comma shaped.ex. Vibrio cholerae.

        iv) spirilla: rigid piral shaped bacteria

         v) spirochetes: longer, thinner, flexible and coil shaped bacteria

3) mycobacteria:

         some bacteria have no cell wall and they called as cell wall lacking bacteria and they doent have proper shape.

 

 

(B) According to flagellar arrangement

    Monotrichous:     1 flagella

    Lophotrichous: tuft at one end

    Amphitrichous:  tuft at both ends

    Peritrichous:   all around bacteria

(2) BASEB ON BIOCHEMICAL REACTION

    Aerobic and facultative aerobic bacteria:

         (a) cocci:

               i)gram positive:

                   . Catalase positive:

                    -staphylococcus aureus

                    -staphylococcus epidermidis

                    -staphylococccus saprophyticus

                  . catalase negative:

                    -staphylococcus pyogenes

                    -staphylococcus pneumoniae

                    -viridans group streptococci

Gram negative:

      - Neisseria gonorrhoeae

      - Neisseria meningitidies

      - moraxella catarrhalis

ii) bacilli:

 (a) gram positive:

       -Bacillus anthracis

       -corne bacterium

       -mycobacterium

       -Nocardia asteroids

       -gardenrella vaginalis

(b) Gram negative:

    i)Enterobacteriaceae:

       -Escherichia coli             -Salmonella

       -Klebsiella                     -Yersinia

       -Morganella                    -shigella

  ii)Non Enterobacteriaceae( Fermentive bacilli):

       -Aeromonas

       -Vibrio

       -Pasteurella

iii) Non enterobacteriaceae (non fermentive bacilli)

      -Pseudomonas

      -Moraxella

      -Acienobacter

(3) Coccobacilli:

    -Actinobacillus           -Bartonella

    -Brucella                   -Haemophilus

    -Chlamydia                -Helicobacter

    -Ricketsiae                -legionella

(4) Mycoplasma:

     Mycoplasma pneumoniae

     Mycoplasma hominis

(5) Treponema

     Treponema pallidum

     Leptospira

     Borilia burgoferi

Aerobic bacteria:

(a)  cocci:

    i)gram positive:

         Peptostreptococcus

  ii) Gram negative:

         Bacteriodes

          Mobiluncus

(b)Bacilli:Gram negative

      -Closteridium species

      -Actinomyces

      -Lactobacillus

(3)BASED ON STAINING REACTION
        (a)Gram stain:

 1) Gram positive: after the gram stain organism which occur violet in colour.

 2) Gram negative: Which appear pink or red

      (b)Acid fast stain:

  1) Acid fast organism: after the ziehl –neelsen stain it will show pink in colour

 2) Non acid fast organism: after this stain organism will appear blue in colour

4).BASED ON PATHOGENICITY:

A)   pathogens: the organism which is able to spread disease and can cause disease.

B)    Non pathogens: which does not cause and disease; e.x: lactobacilli

C)    Commensals: normaly non pathogenic but sometime they show the disease when immunity impaired

5) BASED ON RELATIONSHIP OF HOST AND ORGANISM

1)    saprophytes: free living microbes on dead animals or decaying things that can be found in soil and water and play important role in degradation of organic matter.

2)    Parasites: that establish themselves and multiply in hosts.

3)    Commensals: microbes that live in complete live with harmony but they can produce disese when host resistance Is lowerd.E.x: normal flora organism

Bacterial anatomy

•      In the bacteria the outer layer or cell envelop or bacteria consist of two things

           (a) rigid cell wall

           (b) underlying cytoplasmic membrane or plasma membrane:

                  it includes granules, ribosomes, mesosomes and circular DNA.

v Some bacteria in addition to possess aditional structures such as gelatinous material which cover it is called as capsule and when it is too thin it is called as microcapsule.

CELL  WALL:

v Introduction:

                 most cell poseses a cell envelop consisting of cell wall and underlying cytoplasmic membrane.

v Definition:

               “the tough, rigid structure which surrounds bacterial cell it is called as cell wall”

•       Thickness: 10-20nm

•      Weight: 20-25% of dry weight of bacterial cell wall

    Peptido-glycan Polymer (amino acids + sugars)

      Unique to bacteria

      Sugars; NAG & NAM

l  N-acetylglucosamine

l  N-acetymuramic acid

      Amino acids cross link NAG & NAM

      Made of peptidoglycan – a combination of protein and polysaccharides

      Some bacteria called Gram negative bacteria have an additional layer of membrane that contains lipopolysaccharide

    - this extra layer inhibits the uptake of antibiotics – protecting the bacteria

Gram positive bacteria have a large peptidoglycan structure. As noted above, this accounts for the differential staining with Gram stain. Some Gram positive bacteria are also capable of forming spores under stressful environmental conditions such as when there is limited availability of carbon and nitrogen. Spores therefore allow bacteria to survive exposure to extreme conditions and can lead to re-infection (e.g., pseudomembranous colitis fromClostridium difficle)

Gram negative bacteria have a small peptidoglycan layer but have an additional membrane, the outer cytoplasmic membrane. This creates an additional permeability barrier and results in the need for transport mechanisms across this membrane.

A major component of the cytoplasmic membrane that is unique to Gram negatives is endotoxin. This component is essential for bacterial survival. Endotoxin has three components: the lipid, the highly conserved core polysaccharide, and the species specific O antigen (also polysaccharide). In contrast with the secreted exotoxins, endotoxin is cell-associated but MID 1 can be released during cell division or cell death. The Lipid A moiety of endotoxin is responsible for sepsis which may be fatal. Sepsis is characterized clinically by confusion, fever, drop in blood pressure and ultimately multi-organ failure.Endotoxin (also known as lipopolysaccharide-LPS):

Cell Wall function

    Determine shape of bacteria

    Strength prevents osmotic rupture

    20-40% of bacteria

    Help in division of bacteria

    Contain receptor site

    Some antibiotics effect directly: Penicillin

Cytoplasmic membrane:

    Definition:

           “thin semipermiable membrane which lies just beneath the cell wall that is called as cyto plasmic membrane”

v The whole bacterial cytoplasm is bound peripherally by very thin,elastic and semipermiable cytoplasmic membrane also known as cell membrane.

v It is 5-10nm in width

v Electron microscope shows the presence of three layer constituting a unit membrane structure.

    Chemically the membrane consist of phospholipid with small amount of protein. Sterol is absent except in mycoplasma.

    DEMONSTRATION:

Ø The seperation of membrane from cell wall is achived by readily in gram negative bacteria when they are suspended in medium of high osmotic tension.such phenomenom is called as plasmolysis

Ø Electron microscope

Function:

    Transport:

   (1) Active transport:

                  it is site of numerous enzymes (oxidase polymerase, permease) involved in the active transport of selective nutrients. It is impermiable to macromolecule nd ionised substances.

  (2) Passive transport:

                  It is act as semipermiable membrane through inward and outward passage of water and passive trnsport of molecule lipid soluble solutes take place by diffusion

    Concentration:

            it is also concentration sugar, amino acids and phosphate so that a 300-400 fold grandient exists across osmotic barrier.

    Enzymatic function:

           it also contain cytochrome oxidase, enzyme of tricarboxylic acid cycle and polymerising enzyme necessary for synthesis of cell wall

Cytoplasm

                 “Bacterial cytoplasm  is suspension of organic and inorganic solutes in viscous watery solution”

    It is not exhibiting protoplasmic streaming and it lacks endoplasmic reticulum or mitochondria. It contains ribosomes, mesosomes, inclusion and vacuoles.

All the organills which cytoplasm contains is as follows:

(1)  Ribosomes:

         Ribosomes appear as small granules and pack the whole cytoplasm. These are strung together on strands of mRNA to form polymers.

        the code of mRNA is translated in to peptides sequence t this place.

      The ribosomal particles become linked up and travels along the mRNA strand.

Function:

                 Site for protein synthesis.

    Polysomes:

         They are the group of ribosomes linked together like beads of chain by messanger RNA

v Mesosomes:

          They are vesicular, convulated or multilaminted structures formed as invagination of plasma membrane in cytoplasm .

  They are more prominent in the gram positive bacteria.

    Two types of mesosomes

      (a) septal mesosomes:

           It is attached to bacterial chrosome nd involved in dna segregation and in formation of cross wall during cell division.

      (2) Lateral mesosomes:

            They are at lateral side

Functions:

Ø They are site of respiratory enzymes

Ø Coordinate nuclear and cytoplasmic membrane division during binary fission

Ø Responsible for compartmenting DNA at sporulation

Bacterial capsule:

      “ It is an outer covering of thick jelly like material that surrounds the bacterial cell wall”

v Width: 0.2 micrometer

v Contains about 90% water and 2% solid

v The solid constitutes may be complex polysccharide (pneumococcus klebsiella, enterobacter) or polypeptides (anthrax bacillus) or hyaluronic acid (streptococcus)

    Demonstration:

     the capsule is best seen in pathological specimens like pus, blood, sputum, and exudates

(1) By ordinary stain (gram or acid fast) capsule can not be stained, it apper as halo arround the stained bacterial body.

(2) In negative staining (india pink preparation), capsule appears as clear halo around the bacterium as link can not penetrate capsule.

    Immunological method: in that stained with antiserum that swallowed by capsule so it appear as swollen under microscope so it is called as capsular awelling reaction. E.g pneumococcus

    Capsulated organism: s.pneumoniae,Bacillus anthracis, C.perfringes, pneumobacillus, H.influenzae

Function:

v Capsule serve as protective covering against antibacterial substances such as bacteriophase, phagocytes and enzymes

v Enhance bacterial virulance

v Capsular antigen is hapten in nature and specific for bacteria

Flagella

    Composed of a flagellin subunit.

    Usually sheathed  (covered).

    Rotates by way of a basal body in the bacterial cell.

    Unique to bacteria.

 Bacterial Flagella Structure:

    Composed of filament, hook, and basal body

    Flagellin protein (filament) is deposited in a helix at the lengthening tip

    Base of filament inserts into hook

    Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins

    Filament capable of rotating 360º

    Motility - movement

    Swarming occurs with some bacteria

l  Spread across Petri Dish

l  Proteus species most evident

    Arrangement basis for classification

l  Monotrichous; 1 flagella

l  Lophotrichous; tuft at one end

l  Amphitrichous; both ends

l  Peritrichous; all around bacteria

    Observe Picture in Micro Lab.

SPORES:

        “ spores are highly resistant dormant stage of bacteria formed in unfavourble environmental condition such as starvation and dessication”

v As spores are formed within the parent bacterial cell so they are also called as endospores

v During germination each spore give rise to only one vegetative bacteria

v Exospores found in fungi(conidia) formed extracellularly from end of parent cells.

Spore forming bacteria:

A.    Gram positive bacilli:

   (1) obliterate aerobic- genus bacillus.e.g B.anthracis, B.subtilis

   (2) obliterate anaerobic:genus clostridia.e.g C.tetani, C.welchii, C.botulism

B. Other bacteria:

    Gram positive coccus (porosarcina) gram negative bacilli (coxiella burnetii)

Spore morphology :

     

Sporogenesis:

           spontaneous sporulation occurs in

 condition unfavourable condition such as

 starvation, dessication, presence of

 disinfectants and in extreme temperature.

SPOROGENESIS PROCESS:

Shape and position:

    The young spore remain attached t parant cell. The precise position and shape and relative size of spores remain constant within particular bacteria.

    Spore may be central,sub terminal or terminal

A: Oval subterminal

B: Spherical terminal

C: Spherical subterminal

D: Spherical central

E: Oval terminal

F: Oval central

G: Free spore

Resistance:

    Bacterial spores are resistant to ordinary boiling, heating, and disinfectant. They can withstand boiling up to 3 hr, dry heat at 150c for 1 hr however they are destroyed by autoclaving at 121c for 15-20 min.

    The highly impervious spore coat, low water content, low metabolic activity and high concentration of calcium dipicolinate of spore make resistant to drying and heat.

Germination:

    Definition:

          “ The process of conversation of spore in to vegetative cell under suitable environment is known as germination”

There are three stages of germination

1. Activation:

    The germintion of bacterial spore do not occur even when placed in environment that favour process.

    Unless first activated by one or onother agent damage the coat of spore such as heat, abration and compound containing free sulphydryl groups.

2.Initiation:

    The process of initiation is not clear, however the spore will initiate germination in favourable condition.

    Different species of bacteria recognizes different effactors as signalling a rich medium such as L-alanine for one spesis

3. Out growth:

    With the swelling of spore wall and disintegration of cortex a single germ cell emerge after breaking open the spore coat.

    The new vegetative cell consist of spore protoplast with its surrounding wall.

    Formation of vegetative cell.

Demonstation:

l  By ordinary stain and modified Z-N stain.

    Laboratory:

       for making sterilization

Posted in: Microbiology