What is bacteria? By

Younes Rashad

Bacteria is a single-celled organism which can only be seen through microscope.

Bacteria comes in different shapes and the size of bacteria is measured in micro-meter (which is a millionth part of a meter).

Bacteria are found everywhere and in all type of environments.

Prokaryotic (no membrane-enclosed nucleus)

No mitochondria or chloroplasts

A single chromosome

Have a rigid cell wall made of peptidoglycan.

Many bacteria form a single spore when their food supply runs low. Spores are so resistant to adverse conditions of dryness and temperature that they may remain viable even after 50 years of dormancy.

Bacteria Identification

Cultural properties

Morphology

Gram Staining

Oxygen requirement

Nutrition

Morphology Bacilli (Rod-shaped bacteria)

Cocci ) Sphere-shaped bacteria)

Spirilla ) Spiral-shaped bacteria)

Gram Staining• In 1884, Hans Christian Gram, a Danish doctor working in Berlin, accidentally

stumbled on a method which still forms the basis for the identification of bacteria.

• Gram reaction is based on the structure of the bacterial cell wall.

• The primary bacterial stain of the Gram's method is crystal violet.

Gram +ve Gram -ve

• In Gram-positive bacteria, the purple crystal violet stain is trapped by the layer of peptidoglycan which forms the outer layer of the cell.

• In Gram-negative bacteria, the outer membrane prevents the stain from reaching the peptidoglycan layer in the periplasm.

Gram +ve bacilli

ThickClostridium spp.,

ThinListeria spp.

 BranchedActinomycetes and Nocardia,

Gram +ve cocci

Clusters Staphylococcus spp.

Chain Streptococcus spp,.

 Tetrad Micrococcus spp

Gram-negative bacilli

Thin rods

enterobacteriaceae,

such as E. Coli

Coccobacilli Haemophilus spp.

such as H. influenzae

Curved Vibrio spp.

Thin needle shape Fusobacterium spp.

Gram-negative cocci

Diplococci

Neiseria spp .

Coccobacilli Acinetobacter spp ,.

Oxygen requirement

Aerobic (Need Oxygen)

Bacteria that can grow and live in the presence of oxygen.

Anaerobic (Do not need Oxygen)

Bacteria that do not grow and live in the presence of oxygen.

Nutrition

Autotrophic Bacteria (Bacteria that used chemical energy to create their own food)

Heterotrophic Bacteria (Bacteria that must ingest biomass to obtain their energy and nutrition)

Endospores Under conditions of starvation, especially the lack of carbon and nitrogen sources, a single endospores form within

some of the bacteria. The process is called sporulation. An endospore is not a reproductive structure but rather a resistant, dormant survival form of the organism.

It is resistant to high temperatures (including boiling), most disinfectants, antibiotics, low energy radiation, drying, etc. The endospore can survive possibly thousands of years.

Endospore stain of

Bacillus anthracis

Endospore stain of Clostridium tetani

Capsule

• The capsule is made up of polysaccharides (complex carbohydrates).

• Capsules are to keep the bacterium from drying out and to protect it from phagocytosis (engulfing) by larger microorganisms.

• The capsule is a major virulence factor in the major disease-causing bacteria, such as Escherichia coli and Streptococcus pneumoniae. Nonencapsulated mutants of these organisms are avirulent, i.e. they don't cause disease.

FlagellaMotile bacteria move using flagella

If the flagellum is located at the end of the cell, the cell is said to have monotrichous polar distribution. (A)

Lophotrichous distribution is a pattern in which bacteria appear to have a tuft of hair at one or both ends. (B)

Amphitrichous bacteria have a single flagellum at each pole. (C)

Peritrichous flagella are distributed uniformly over the surface of each bacterial cell. (D)

COLONY MORPHOLOGYA colony is defined as a visible mass of microorganisms all originating from a

single mother cell.

Wild-type Myxococcus xanthus

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