Gram Staining Method
A staining procedure used to classify and identify bacteria as either Gram-positive bacteria or Gram-negative bacteria. Example - certian antibiotics are used to treat infections by gram-positive bacteria, and other antibiotics are used to treat infections by gram-negative bacteria. Penicillins are a group of antibiotics that are often used to treat infections by gram-positive bacteria. Not all species of bacteria can be stained by the Gram staining method. Some antibiotics treat both Gram-positive bacteria and Gram-negative bacteria.
Gram-positive
Gram-positive (Gram +) Bacteria - Bacteria that turn dark purple-blue-black color by the Gram staining method. Gram-positive bacteria do not have a secondary outer membrane, which allows the stain to penetrate the cell. Examples of Gram-positive bacteria:
- Staphylococcus epidermidis
- Staphylococcus aureus - common cause of boils
- Clostridium tetani which cause tetanus (lockjaw)
- Streptococcus pyogenes - causes a sore throat and scarlet fever
- Bacillus subtilis
- Actinomyces odontolyticus (found in mouths)
Example of antibiotics used to fight gram-positive bacteria infections:
- Novobiocin
- Linezolid (Zyvox ®)
- Daptomycin (Cubicin ®)
- Clindamycin (Cleocin ®)
Gram-negative
Gram-negative (Gram -) Bacteria - Bacteria that turn red-pink color by the Gram staining method. Opposite the Gram-positive bacteria, Gram-negative bacteria have a secondary outer membrane that prevents the dye from penetrating and staining the cell. Some examples of Gram-negative bacteria:
- Escherichia coli (E. coli)
- Pseudomonas
- Salmonella
- Legionella
- Spirochete - also spelled spirochaete
- Serratia
- Neisseria gonorrhoeae
- Klebsiella
- Proteus
- Enterobacter