Gram Positive Bacilli: Examples of Human Diseases

Page content

The Cell Wall

Bacteria are classified as either gram positive or gram negative. This is based on a staining technique, which uses the uptake of the dyes gentian violet and iodine. Gram positive bacteria take up the dye and will appear blue or violet, while gram negative bacteria will appear pink.

Gram positive bacteria stain purple, because they have a different cell wall than gram negative bacteria. The Gram positive cell wall contains a high level of peptidoglycan, which is a polymer composed of sugars and amino acids. This cell wall functions as an organelle and interacts with the bacteria’s environment, particularly the infected host’s tissue. The cell wall also plays a role in cell shape, protects against mechanical and osmotic damage, and functions as a transporter, allowing molecules to cross the cell membrane.

Human Disease

A number of gram positive bacteria are associated with human diseases and are classified not only by their gram stain but also by their shape. These include Cocci and Bacilli. Cocci have a spherical shape and can be either Staphylococcus (appearing like a bunch of grapes) or Streptococcus (forming a chain). Bacilli have a rod shape and can be either spore forming or non spore forming.

Spore Forming Bacilli

A spore forming species of the bacteria bacillus is B. anthracis, which causes anthrax. It can infect the skin, lungs and gastrointestinal system, with infection in the lungs and gastrointestinal tract often being fatal. Treatment is usually handled with penicillin, but if the disease is resistant, fluroquinolones or tetracycline’s can be used. These spores are highly resistant, surviving for decades, even in harsh conditions.

Clostridium Tetani is a gram positive anaerobe which forms spores. It is known to cause tetanus and produces a neurotoxin. It resides in soil, human intestines, animal bites and rusty metal. The toxins can lead to contracture, and death occurs through respiratory failure. There is a vaccine available for tetanus.

Non Spore Forming Bacilli

Listeria are bacillus form of bacteria which do not form spores. Listeria monocytogenes is often found in contaminated water, soil and plants. It is a rare but potentially fatal food-borne infection. It is a bacterium which can exist in both cold temperatures and at body temperature. It has been found in uncooked meats, uncooked vegetables and unpasteurized dairy foods. It is a bacterium which affects the elderly, pregnant women and the sick. Treatment is usually with ampicillin and ciprofloxacin.

Corynebacterium diphtheria causes diphtheria, a highly contagious disease. It infects the throat and tonsils These bacteria can produce an exotoxin, which irritates the throat and causes secretions to form. This can suffocate the patient. A vaccine is available to prevent diphtheria.


Merck Manual: Infectious Diseases

The Classification and Identification of Bacteria of Medical Importance.

Microbiology: Bacillus