The term gram-positive in relation to bacteria refers to the ability for the bacterial cell to uptake a gram stain into the cell wall. A gram-positive bacteria can take up the gram stain due to the large peptidoglycan cell wall, which absorbs the stain. The staining procedure colors the bacteria for ease of visibility under light microscopy. Gram-positive bacteria exist around human beings on an everyday basis as commonly occurring organisms.
Staphylococcus
Species of the genus Staphylococcus exhibit gram-positive staining due to a thick peptidoglycan layer. The peptidoglycan functions as a cell wall for the bacteria, protecting it against osmotic imbalance and giving the overall cell structure. Members of the genus Staphylococcus include Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus haemolyticus. These species commonly occur on the skin of humans, and do not cause problems. The organisms become opportunistic pathogens in immunocompromised patients or people with open wounds.
Streptococcus
Species of the genus Streptococcus have a gram-positive reaction, and in nature arrange in long chains of attached cells. Common members of the Streptococcus genus include Streptococcus mutans, Streptococcus pneumoniae, and Streptococcus pyogenes. Streptococcus mutans causes tooth decay by converting the sugars in foods into lactic acid in the mouth. This lactic acid then eats away at the enamel of the teeth and causes cavities. Streptococcus pneumoniae is the bacteria responsible for causing the lung infection pneumonia. Streptococcus pyogenes is an opportunistic pathogen similar to species of the genus Staphylococcus, and can cause "strep throat."
Clostridium
Clostridium, another commonly occurring gram-positive microorganism, consists of obligately anaerobic species. These species, unlike Staphylococcus and Streptococcus, require the absence of oxygen to grow. Common species in this genus include Clostridium botulinum, Clostridium perfringens, and Clostridium tetani. Clostridium botulinum releases a neurotoxin that causes muscular paralysis in the human body, and resides in anaerobic environments like food and soil. Clostridium perfringens infection results in the condition known as gas gangrene. According to the University of Maryland Medical Center, tissue death occurs in gas gangrene, and can lead to death of the individual. Clostridium tetani is the causative agent of tetanus, and exists mostly as spores in the soil.
Bacillus
The Bacillus genus consists of multiple species of gram-positive bacteria commonly found in nature. These organisms can exist as either strictly aerobes, or facultative anaerobes. Facultative anaerobes, unlike strict aerobes, only prefer oxygen when it is present. These organisms can also survive in the absence of oxygen. Well-known species of the genus Bacillus include Bacillus subtilis and Bacillus anthracis. Bacillus subtilis is important as a model organism for genetic experiments and modification in the laboratory. Anthrax, the common name for Bacillus anthracis, has become a household name among people as a potentially weaponized pathogen.
References
- "Biology: Concepts and Connections"; Neil Campbell, Lawrence Mitchell and Jane Reece; 2000
- "Microbiology: Sixth Edition"; Lansing Prescott, John Harley and Donald Klein; 2005
- University of Maryland Medical Center: Gas Gangrene
