MORPHOLOGY OF BACTERIA

CELL

•Structural and functional unit of all the living organisms

•Also known as “Building Block of Life”.

•Coined by Robert Hooke in 1965.

• Two third of a cell made up of water and rest consists of protein, lipids , carbohydrates

DIFFERENCE BETWEEN PROKARYOTES AND EUKARYOTES

Structure Prokaryotes Eukaryotes
Nucleus Absent Present
Nuclear membrane Absent Present
Nucleolus Absent Present
Chromosome One More than one
Deoxyribonucleoprotein Absent Present
Division By Binary Fission By Mitosis
Bacteria and Blue –green algae Fungi , slime moulds,Protozoa
Cytoplasm
Mitochondria ,Golgi Apparatus, Lysosomes , Endoplasmic Reticulum All are absent All are present

BACTERIA

•Single celled  ,prokaryotic  microscopic organism

•Possess both DNA and RNA

•Can survive in extremes of temperature , pH , oxygen and atmospheric pressure.

SIZE OF BACTERIA CELL

•Unit of measurement in bacteriology is micron(micrometre )

•1µm=1/1000 mm(millimetre)

•1 nm(nanometre)=1/1000µm

•1Å=1/10 nm

•Medically Important Bacteria

•0.2-1.5µm in diametre

•3-5µm in length

For example •Staphylococcus(1µm in diameter) •E.coli(1-3µin diameter)

SHAPES OF BACTERIA

ARRANGEMENT OF SHAPE

ANATOMY OF BACTERIAL CELL

•Outer layer- 2 components

•Rigid cell wallCytoplasmic membrane

Cytoplasm– Gel like substance enclosed within cell wall

•Contains cytoplasmic inclusions ,ribosomes , mesosomes and nucleoid

Additional structures – Plasmid ,slime layer, capsule , flagella , fimbriae ,spores.

CELL WALL

•Outermost layer, encloses cytoplasmic membrane

•10-25 nm thick

•Protects from osmotic shock and physical damage

•Several antibiotics may interfere with cell wall synthesis e.g. Penicillin

•Chemical nature of cell wall helps to divide bacteria into two broad groups –

 Gram positive and Gram bacteria

DEMOSTRATION OF CELL WALL

•Microdissection

•Reaction with specific antibodies

•Mechanical rupture of cell

•Differential staining procedures

•Electron Microscopy

CHEMICAL STRUCTURE OF BACTERIAL CELL WALL

Chemically it is composed of mucopeptide(peptidoglycan or murein) scaffolding formed by N-acetyl glucosamine and N-acetyl muramic acid molecules alternating in chains which are cross linked by peptide chains

GRAM POSITIVE CELL WALL

GRAM NEGATIVE CELL WALL

DIFFERENCE BETWEEN CELL WALL OF GRAM POSITIVE AND GRAM NEGAIVE BACTERIA

Character Gram positive Gram negative
Thickness Thicker Thinner
Periplasmic space Absent Present
Lipids Absent or small Present
Teichoic acid Present Absent
Peptidoglycan 16-18 nm 2nm

CELL WALL DEFICIT

•Don’t possess stable morphology

•Occur as round or oval bodies or interlacing filaments

•Cell wall synthesis becomes defective either spontaneously or as a result of drug like penicillin

•Bacteria loses their distinctive shape

•Such cells are called L forms, Protoplast , Spheroplast

CYTOPLASMIC MEMBRANE

•Thin layer 5-10 nm , separates cell wall from cytoplasm

•Acts as a semipermeable membrane : Controls inflow and outflow of metabolites

•Composed of lipoproteins with small amounts of carbohydrates

CYTOPLASM

•Colloidal system of variety of organic & inorganic solutes in viscous watery solution

•Contains : Ribosomes, Mesosomes, Intracytoplasmic inclusions

NUCLEUS

•No nucleolus

•No nuclear membrane

•Oval or elongated bodies

PLASMID

•Extranuclear  genetic elements consisting of DNA

•Transmitted to daughter cells during binary fission

•May be transferred from one bacterium to another

•Not essential for life of the cell

CAPSULE AND SLIME LAYER

•Viscous layer secreted around cell wall

•Polysaccharide/polypeptide in nature

•Capsule have sharply defined structure e.g. S.pneumoniae

•Slime layer has loose undermarcated secreation e.g. leuconostoc

•Some bacteria may have both a capsule and a slime layer e.g. Streptococcus salivarius

FUNCTION OF CAPSULE

•Prevents bacteria from phagocytosis

•Helps in adhesion

DEMOSTRATION OF CAPSULE

•Serological method

•Staining method

FLAGELLA

•Organs of locomotion

•Composed of proteins called flagellin

•3 to 20µm in length and 0.01-0.013µm in width.

STRUCTURE OF FLAGELLA

Bacterial flagellum is composed of 3 parts:

1)Filament – •Longest portion which extends from cell surface to the tip

2) Basal body – •Portion embedded in cell

3) Hook – •Short ,curved segment •Links filament to its basal body •Acts as flexible coupling

DEMOSTRATION OF FLAGELLA

•Electron microscopy

•Phase Contrast microscopy

•Dark ground microscopy

TYPE OF ARRANGEMENT OF FLAGELLA

FIMBRIAE

•Thin , hair like structure on the surface of many gram negative bacteria

•acts as organ of adhesion(attachment)

•0.5 µm in long and less than 10 nm thick

•Made up of proteins called pilins

PILLI

•Eight morphological pili are known

•Classified as common or sex pili

•Self aggregating monomers of pilin

Sex Pilli •Found on male bacteria

•Help in attachment to female bacteria

•Genetic material is transferred by hollow conjugation tubes

SPORES

•Small oval or spherical structures

•Highly resistant resting stages formed during adverse environment

•Very resistant to heat , radiation and drying and can remain dormant for hundreds of years

           Demonstration •Gram stain •Modification of Ziehl-Neelsen Technique

           Structure •Bacterial spore comprises of several layers. •From innermost towards the outermost , the layers are : •Core –Cortex – Coat – Exosporium

TYPES OF BACTERIAL SPORES

STEPS OF SPORULATION

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