The bacterial recognition and classification method by Gram’s 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 ones respond to the pigment and will appear purple under the microscope; while Gram-negatives resist staining and will do so in red or pink.
This difference in response shows 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 in 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 motile (flagellated) and even photosynthetic organisms, gram-negative bacteria are responsible for many of the deadliest known bacterial diseases.
Examples of gram-positive bacteria
- Staphylococcus aureus. Responsible for abscesses, dermatitis, localized infections and possible gastroenteritis.
- Streptococcus pyrogens. Causing suppurative infections in the respiratory tract, as well as rheumatic fever.
- Streptococcus agalactia. Frequent in cases of neonatal meningitis, endometritis and pneumonia.
- Streptococcus faecalis. Common in biliary and urinary tract infections, it inhabits the human colon.
- Streptococcus pneumonia. 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 versions.
- Clostridium botullinum . Causing classic and infant botulism, it inhabits the soil and poorly preserved food.
- 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 causes meningitis and meningococcemia, colonizes the human airways and ascends the meninges by blood.
- Neisseria gonorrhoeae . Known for being the cause of gonorrhea, a common sexually transmitted disease.
- Escherichia coli . A regular inhabitant of the human colon, she is involved in so-called “traveler’s diarrhea”, as well as neonatal meningitis, sepsis, and urinary tract infections.
- Salmonella typhi . Bacteria responsible for the disease known as typhoid fever, is usually transmitted via the faecal-oral route: water contamination, poor disposal of excreta or poor hygiene.
- Salmonella enteritidis . It usually causes enterocoitis and sepsis with abscesses if it passes from the intestine into the blood.
- Haemophilus influenzae . Bacillus, usually aerobic, is responsible for numerous meningitis, otitis, sinusitis, bronchopneumonia, cellulitis, and septic arthritis.
- Bordetella pertussis . Causing the disease known as pertussis, with 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.
- Francisella tularensis . Responsible for the so-called “rabbit fever” or tularemia, it is transmitted to man through vectors (mites or other types of exoparasites) of rabbits, deer and similar animals.
- Pasteurella multocida . Anaerobic bacillus, transmitted by the bite of infected pets, such as cats and dogs. It spreads through the skin and infects the respiratory system, also causing cellulite.