The method of recognition and bacterial classification by Gram Tincture was invented by the Danish scientist Christian Gram in 1884 and from there derives its name. What does it consist of?
It consists of adding a specific series of pigments and mordants to a laboratory sample, thus achieving a pink or violet staining, depending on the type of bacteria : Gram positive responds to the pigment and will appear under a purple microscope; while Gram negatives resist staining and will make it red or pink.
This difference in response accuses a different composition of the cell envelope, since the gram-positive ones have a thick layer of peptidoglycan (murein), which gives them great resistance but makes them retain the dye much better. The Gram – negative however, have a double membrane lipid in its container, thus requiring a peptidoglycan layer much thinner and hence, are not stained in the same manner.
This method reveals a natural bacterial typology, useful when identifying the species and especially the antibiotic required to combat it . Although gram-positive bacteria are a varied and majority group, with the presence of mobile (flagellated) and even photosynthetic organisms, gram-negative ones are responsible for numerous of the most lethal known diseases of bacterial origin .
Examples of gram-positive bacteria
- Staphylococcus aureus . Responsible for abscesses, dermatitis, localized infections and possible gastroenteritis.
- Streptococcus pyrogenes . Causing suppurative infections in the respiratory tract, as well as rheumatic fever.
- Streptococcus aglactiae . Common in cases of neonatal meningitis, endometritis and pneumonia.
- Streptococcus faecalis . Usually in bile and urinary tract infections, it inhabits the human colon.
- Streptococcus pneumoniae . Responsible for pneumonia and respiratory tract infections, as well as otitis, meningitis and peritonitis.
- Streptococcus sanguis . Causing endocarditis, when it enters the bloodstream through lesions in its habitat, mouth and dental mucosa.
- Clostridium tetani . Bacteria responsible for tetanus enter the body from the ground due to trauma to the extremities.
- Bacillus anthracis . It is the well-known anthrax bacteria, both in its cutaneous and pulmonary version.
- Clostridium botullinum . Causing the classic and infant botulism, it lives on the ground and in poorly preserved foods.
- Clostridium perfringes . This bacterium secretes toxins that destroy the cell wall, and is responsible for gas gangrene, necrotizing enteritis and endometritis.
Examples of gram-negative bacteria
- Neisseria meningitidis . Dangerous bacteria that cause meningitis and meningocococemia, colonize the human airways and ascend to the meninges by blood.
- Neisseria gonorrhoeae . Known for being the cause of gonorrhea, a common sexually transmitted disease.
- Escherichia coli . Inhabitant of the human colon, is involved in the so-called “traveler’s diarrhea”, as well as in neonatal meningitis, sepsis and urinary infections.
- Salmonella typhi . Bacteria responsible for the disease known as typhoid fever, is usually transmitted by fecal-oral route: water pollution, poor disposal of excreta or defective hygiene.
- Salmonella enteritidis . It usually causes enterocoitis and septicemia with abscesses if it passes from the intestine to the blood.
- Haemophilus influenzae . Bacillus usually aerobic, is responsible for numerous meningitis, otitis, sinusitis, bronchopneumonia, cellulite and septic arthritis.
- Bordetella pertussis . Causing the disease known as pertussis, high infant mortality.
- Brucella abortus . It causes brucellosis, a disease of cattle that is transmitted to man by contact with animals or by ingestion of unpasteurized dairy products.
- Francisella tularensis . Responsible for the so-called “rabbit fever” or tularemia, it is transmitted to man by vectors (mites or other exoparasites) of rabbits, deer and similar animals.
- Pasteurella multocida . Anaerobic bacillus, transmitted by the bite of infected domestic animals, such as dogs and cats. It spreads through the skin and infects the respiratory system, also causing cellulite.