Bacteria

Bacteria are small, single-celled microorganisms
They are an ancient lifeform
They possess the same basic functions as other living cells but lack chlorophyll
They usually have a single circular DNA chromosome found within the cytoplasm
They do not have membrane-bound organelles

There are three main shapes of bacteria:
- Cocci (spherical)
- Bacilli (rod-shaped)
- Spirilla (spiral shaped)

Cocci can be arranged in pairs (diplococci), chains (streptococci), clusters (staphylococci), or cubical packets (sarcinae)
Bacilli can be arranged in pairs (diplobacilli), chains (streptobacilli), or palisades (side-by-side).

Flagellum: A long, whip-like appendage responsible for bacterial motility
Ribosomes: Small organelles responsible for protein synthesis
Cytoplasm: The jelly-like substance that fills the cell
Nucleoid: The region containing the bacterial DNA
Plasma membrane: The thin, outer layer that encloses the cytoplasm and controls the passage of substances into and out of the cell
Cell wall: A rigid structure that provides support and shape to the cell
Capsule: A sticky layer that surrounds the cell wall and helps bacteria adhere to surfaces, resist phagocytosis (being engulfed by white blood cells), and evade the host's immune system
Pilus: A thin, hair-like structure that helps bacteria attach to surfaces

Gram staining is a technique used to distinguish and classify bacterial species into two groups:
- Gram-positive bacteria
- Gram-negative bacteria
The technique was developed by the Danish bacteriologist Hans Christian Gram

Gram-positive bacteria have a thick peptidoglycan layer in their cell walls, which retains the crystal violet dye, making them appear purple under a microscope. examples include S. aureus and S. pneumoniae.
Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane containing lipopolysaccharides, which does not retain the crystal violet dye as effectively. They are stained with a counterstain (usually safranin), which makes them appear pink under a microscope. Examples include E. coli and P. aeruginosa.

The systematic classification of organisms into ordered groups is called taxonomy.
The name is typically a combination of the last two ranks, genus and species.
The species name does not begin with a capital letter.
The scientific name is usually written in italics.
Generic names can be abbreviated, for example, S. aureus can be abbreviated as S. aureus.
S. aureus refers to Staphylococcus aureus.

Streptococcus mutans and Streptococcus sanguis are examples of bacteria associated with dentistry.
Streptococcus mutans is a key player in the formation of dental caries (tooth decay) and is responsible for the production of lactic acid, which erodes tooth enamel.
Streptococcus sanguis is typically found in plaque and contributes to the development of dental plaque, but generally plays a less significant role in tooth decay compared to Streptococcus mutans.
Streptococcus sanguinis may even play a protective role in oral health under certain conditions.