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What is Bacteria (Bacterium)
What is Bacteria? Actually, it is suppose to be What are bacteria? Bacteriology is the study of bacteria Some Basic Information - Bacteria are Prokaryotic
- Single cell
- Microscopic in size
- 0.2 to 2.0 micrometers in diameter and 2 to 8 micrometers in length
- Usually have cell wall
Size, Shape and Arrangement - Most come in one of three common and basic shapes
- Coccus (spherical)
- Single cells are known as coccus
- Pair of cells: diplococci
- 4’s: tetrads
- 8’s: sarcinae
- Chains of cells: streptococci
- Grape-like clusters: staphylococci
- Bacillus (rod)
- Single rods (bacillus)
- Rods come in various length and width
- Streptobacilli: chains
- Coccobacilli: oval-shaped cells and no straight edge
- Spiral
- Spiral: spirilla
- Spirillum
- Vibrios: these look like curved rods
- Spirochetes: these are long spirilla cells with many tight coils
- Other examples of bacteria shapes: rectangular, filamentous, square, spindle-shaped
- Some bacteria are genetically pleomorphic
- Pleomorphic: the bacteria cells can have many shapes, not just one
- Example: Corynebacterium diptheriae
Cell Structures of Bacteria - Cell Wall
- Cell wall is a tough, thick layer that forms the shape of the cell
- Its function is to protect the bacterial cell from rupture, maintain shape and serve as an anchorage for flagella
- Cell wall is different between gram (+) and gram (--) bacteria
- Characteristics of gram (+) cell structure
- Consists of many layers of peptidoglycan (sugars and amino acids bonded into one giant molecule
- Peptidoglycan
- Glycan portion
- Contains alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) molecules which form a carbohydrate backbone
- Peptide portion
- Adjacent rows of carbohydrate backbone are linked by polypeptides
- Also contains teichoic acids, which function as antigen
- Characteristics of gram (--) cell structure
- Consists of one or a very few layers of peptidoglycan and an outer membrane of protein and fat
- Periplasm holds the peptidoglycan
- Contains lipopolysacharides
- LPS (Lipid A) is referred to as an endotoxin
- Polysaccharide (O side chain) function as antigens.
- This is similar to that of teichoic acid.
- Gram negative cell do not contain teichoic acids
Why is it important to know if a bacterial pathogen is gram (+) or (--)
So that we can identify the bacterium, especially through the gram staining method |
