Bacteriology: Is the study of bacteria.

Prokaryotic cells: Are simple unicellular organism without a distinct nucleus and other specialized cell structures. Example of prokaryotic cell is bacterial cell.

Eukaryotic cells: Are cells that contain nucleus, a sack like structure that encloses a cell’s genetic materials. The presence of nucleus differentiates eukaryotic cell from prokaryotic cell.

Bacteria: Are unicellular free living organisms without chlorophyll having both DNA and RNA. They are capable of performing all essential processes of life example growth, metabolism and reproduction

The genetic material (DNA, RNA) of prokaryotic cells is not membrane-bounded

Prokaryotes have no true nucleus and other membrane-bound structures known as organelles.

They normally possess just a single chromosome that is separated from other cell contents by a membrane.

The characteristics of prokaryotic cells apply to the bacteria, cyanobacteria (formerly known as blue-green algae) and archaebacteria.

Parts of a Bacterial Cell and their Functions

Bacterial cell is comprised of the following parts

Cell wall

Capsule

Flagella

Pilli (Fimbriae)

Cytoplasmic/Plasma membrane

Mesosomes

Cytoplasm

Ribosomes

Nucleoid material (DNA and RNA)

Not all bacteria possess all of these components

They both have DNA and RNA as their genetic material

They are both membrane bound

They both have ribosomes

They have similar basic metabolism

They are both diverse groups

Bacteria are classified according to a number of criteria which include

Morphology

Staining characteristics

Nature of cell wall

Ability to form spores

Ability to grow in the presence or absence of oxygen

Cocci: These are round or oval shaped bacteria. When multiplying cocci may form

Pairs (called diplococci for example meningococci and gonococci)

Chains (called streptococci example Streptococcus pyogenes)

Irregular groups or clusters (called staphylococci, example is staphylococcus aureus)

Bacilli: These are rod shaped bacteria. When multiplying bacterial rods do not usually remain attached to one another, but separate. Occasionally however, they may form

Chains, example are Streptobacilli

Branching chains, example are Lactobacilli

Mass together; example is Mycobacterium leprae

Remains attached at various angles example Corynebacterium diphtheria

Spiral: These are small regularly coiled, rigid organisms. Examples Spirillum minus

Comma shaped: These are small slightly curved rods (comma shaped). Example Vibrio cholera

Spirochaetes: These are flexible, coiled, motile organisms they progress by rapid body movement. Example, treponema species, borrelia species, and leptospires

Gram positive: When stained by Gram stain, appears blue reflecting the colour of primary stain (either gentian violet, crystal violet or methyl violet). Examples, Staphylococci species, Streptoccoci species. Clostridium tetani.

Gram negative bacteria are bacteria which appears red, after losing the colour of primary stain and adapting the colour of a counter stain (dilute carbofuchsin or safranin, or neutral red) when stained by gram stain

Examples, neisseria species, salmonella species, haemophilus species

Rigid thick wall for examples streptococcus, staphylococcus

Wall less for example Mycoplasma

Classification of Bacteria according to Ability to Form Spores

Spores are highly resistant dormant state of bacteria with dense thick walls able to withstand dehydration heat, cold and action of disinfectants.

In this kind of classification there are

Spore forming bacteria for examples bacillus species and clostridium species

Non spore forming bacteria for examples corynebacteria species like corynebactrium diphtheria

Grows in the presence of air (aerobic bacteria) for example bacillus anthracis

Grows in the absence of air (anaerobic bacteria) for example clostridium species

Bacteria fall under the group of prokaryotic cells which are simple cells as compared to eukaryotic cells.

Absence of the membranes to bind the internal organelle structures in the prokaryotes makes the major difference with the eukaryotic cells.

Bacteria are classified based on their morphology, staining characteristics, nature of cell wall, ability to form spores and ability to grow in the presence or absence of oxygen

What are the structural features of bacterial cell?

What are the differences between prokaryotic cell and eukaryotic cell?

What are the 5 criteria for classification of bacteria and give examples?

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Satish, G. (1982). The Short Handbook of Medical Microbiology. New Delhi. India: Jaypee Brothers Medical Publishers PVT Lt