Bacteria are microscopic single-celled organisms that are all around us. They come in many different types, with many different ways to be categorized. One common way is by their morphology or shape. The three basic shapes of bacteria are spherical, rod shaped and spiral. Spiral-shaped bacteria can further be categorized based on the amount of spiraling they show.
Cocci are round, spherical-shaped bacteria. They can occur as a single bacterium or be arranged in a pair, chain or cluster of bacteria depending on which type of coccus it is. These bacteria cause many different types of common diseases. Among the more common cocci are Staphylococcus aureus, which appears as a cluster of cocci. Staph aureus can often be found in the nose and on the skin without causing disease, but it is also responsible for causing conditions such as boils, pneumonia, meningitis and toxic shock syndrome. Streptococcus pyogenes occurs as a chain of cocci and causes diseases that originate in the throat or skin, including strep throat and scarlet fever. Neisseria meningitidis occurs in pairs of cocci. This bacteria causes bacterial meningitis, an inflammation of the brain and spinal cord, after entering the body through the nose or throat.
Bacilli are rod-shaped bacteria that look like cylinders, arranged singly or in chains. Escherichia coli is a rod-shaped bacteria that normally lives in your intestinal tract without causing disease. However, a few strains of E. coli do cause disease that's spread typically by eating or drinking contaminated food or water; a typical symptom is diarrhea. Corynebacterium diphtheriae, another rod-shaped bacterium, infects the respiratory tract and causes diphtheria. Diphtheria causes a thick coating on the back of the nose and throat, making it difficult to swallow or breathe, followed by swelling of the neck and potentially death. Bacillus anthracis is the bacteria that cause anthrax. This rod-shaped bacterium grows in long chains and can infect you through broken skin, ingestion or inhalation.
Vibrios are one of three types of bacteria with a spiral-like shape. Vibrios are comma-shaped bacteria that look like a curved rod. They typically live in aquatic environments. Vibrio cholera moves in a darting motion by a single flagellum, a whiplike structure, and is the bacteria that causes cholera. Cholera is an intestinal infection that causes severe diarrhea and dehydration, typically transmitted by drinking contaminated water. It is a very serious disease that can lead to death if not treated promptly.
Spirilla are another subgroup of bacteria with a more rigid spiral shape. One such bacteria is Campylobacter jejuni, which causes diarrhea. Campylobacter jejuni is typically acquired in places where sanitation is poor or by eating raw or undercooked poultry. Helicobacter pylori is a similar-shaped bacteria found in your stomach. While some people infected with Helicobacter pylori have no symptoms, it is a common cause of stomach inflammation and ulcers.
Spirochetes are long, thin and flexible corkscrew-shaped bacteria. They typically move in a distinctive rotating manner that allows them to be mobile in mucus-lined tissue or where it is viscous. Two well-known spirochetes that cause disease in humans are Treponema pallidum and Borrelia burgdorferi. Treponema pallidum causes the sexually transmitted disease syphilis. Infection typically begins as a single sore at the site of infection. Additional lesions or rashes can develop elsewhere on the body if left untreated. Borrelia burgdorferi is transmitted through the bite of an infected tick and causes Lyme disease. Infection with Borrelia burgdorferi causes a typical "bull's-eye" rash. If left untreated, it can affect your heart and nervous system and cause arthritis.
- Robbins Pathological Basis of Disease; Ramzi Cotran, et al.
- Lippincott's Illustrated Reviews: Microbiology; Richard Harvey, et al.
- Todar's Online Textbook of Bacteriology; Kenneth Todar