•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

•Single celled  ,prokaryotic  microscopic organism

•Possess both DNA and RNA

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

•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)

•Outer layer- 2 components

•Rigid cell wall •Cytoplasmic 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.

•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

•Microdissection

•Reaction with specific antibodies

•Mechanical rupture of cell

•Differential staining procedures

•Electron Microscopy

•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

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

•Contains : Ribosomes, Mesosomes, Intracytoplasmic inclusions

•No nucleolus

•No nuclear membrane

•Oval or elongated bodies

•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

•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

•Prevents bacteria from phagocytosis

•Helps in adhesion

DEMOSTRATION OF CAPSULE

•Serological method

•Staining method

•Organs of locomotion

•Composed of proteins called flagellin

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

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

•Electron microscopy

•Phase Contrast microscopy

•Dark ground microscopy

•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

•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

•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

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