Bacteria are highly versatile, single-celled organisms that inhabit virtually all environments. The human body is widely colonized by bacteria, which live in the nose, mouth, intestine, vagina and on the skin. Bacteria may be broadly categorized by shape. Bacterial types based on shape include the spherical cocci, the rod-like bacilli and the spiral-shaped spirilla.
Cocci
The cocci include a broad array of bacterial organisms. Many types of cocci prove disease-causing or pathogenic in humans. The medical reference text, "Principles and Practice of Infectious Diseases," reports Staphylococcus aureus as a common cause of a variety of human infections including impetigo, boils, food poisoning, toxic shock syndrome, pneumonia, and bloodstream and bone infections. Streptococci are also common human pathogens, especially group A strep, group B strep and pneumococcus. Common streptococcal infections include strep throat, scarlet fever, pneumonia, meningitis, cellulitis, necrotizing fasciitis, bloodstream infections, and ear and sinus infections. "Todar's Online Textbook of Bacteriology" notes that other important disease-causing cocci include Neisseria meningitidis, a common cause of meningitis, and Neisseria gonorrhoeae, the causative agent of the sexually transmitted disease gonorrhea.
Bacilli
A wide variety of bacilli normally inhabit the human intestine, including species of Lactobacilli, Bifidobacterium and Escherichia. However, many types of bacilli can also cause human disease. The Centers for Disease Control and Prevention reports that Salmonella and Shigella commonly cause food poisoning among Americans. Salmonella and Shigella cause approximately 40,000 and 14,000 cases, respectively, of food-borne diarrheal illness in the United States each year. Another bacillus, E. coli, remains the leading cause of bladder and kidney infections, reports the National Institute of Diabetes and Digestive and Kidney Diseases. Spore-forming bacilli in the Clostridium group of bacteria cause tetanus and botulism. The reference text, "Principles and Practice of Infectious Diseases" reports other common pathogenic bacilli include Klebsiella pneumoniae, Pseudomonas aeruginosa, Haemophilus influenzae, Bordetella pertussis and Yersinia pestis. Bordetella pertussis is the bacterium that causes whooping cough. Yersinis pestis is the causative agent of plague.
Spirilla
Although spirilla prove less prevalent than cocci or bacilli, these spiral-shaped bacteria are important causes of human infectious disease. Treponema pallidum is the causative agent of the sexually transmitted disease syphilis. The Centers for Disease Control and Prevention reports approximately 13,500 new cases of syphilis occurred in the United States in 2008. Untreated syphilis among pregnant women commonly causes fetal death or infection among newborn babies. Borrelia burgdorferi is the causative agent of Lyme disease. The bite of an infected tick provides the route of transmission. According to the Centers for Disease Control and Prevention, nearly 250,000 cases of Lyme disease occurred in the United States from 1992 to 2006.
References
- Todar's Online Textbook of Bacteriology: Bacterial Pathogens of Humans
- Todar's Online Textbook of Bacteriology: Pathogenic Neisseria
- Todar's Online Textbook of Bacteriology: The Composition of the Normal Flora
- Centers for Disease Control and Prevention: Salmonellosis
- Centers for Disease Control and Prevention: Shigellosis
