Glossary | Tools | Encyclopedia

Selected Descriptions of Bacteria

(Here are the descriptions of some bacteria. You will find only some of them in this lab. You may also want to consult the CDC health topics page.)

Bartonella henselae Various species of Bartonella that are pathogenic to humans are transmitted via a vector, or directly from an animal reservoir. For example, B. bacilliformis via sandflies causes Oroya fever; B. quintana via body lice causes trench fever; and B. henselae via cats causes cat scratch disease (CSD). CSD typically manifests as swellings of the lymph glands, possibly with skin lesions at the site of inoculation and possibly accompanied by fever, fatigue, and other symptoms. Immunocompromised patients may be particularly susceptible and can develop a different disease, bacillary angiomatosis, as a result of infection by B. henselae or B. quintana.

Brucella canis Species of Brucella are present in many different animals, including cattle, sheep, pigs, and dogs. Brucella abortus, found in cattle, is the most common species found in the US, and infection can occur by consuming unpasteurized milk products. Infection can also occur through abrasions of the skin when handling infected animals. Animal handlers, veterinarians, meat inspectors, and lab technicians are all potentially at risk. Brucella canis is typically found in dogs, though it's also been found in other animals. Symptoms are variable, but are flu-like in acute form, with longer-term complications such as arthritis and liver damage.

Escherichia coli Probably the most famous bacterium, E. coli is one of the most common inhabitants of the intestinal tract. Generally, they are not considered pathogenic, but they can cause disease under certain conditions. There are pathogenic strains that can cause diarrhea or other serious conditions. (Visit, where there is an animation clip of an enteropathogenic strain in action.)

Pseudomonas aeruginosa Pseudomonads are commonly found in soil, water, and other such natural environments. To healthy individuals, these bacteria do not generally constitute a health threat. They have been found to be remarkably adept at growth by using most unusual sources of nutrients such as soap residues or glue. In hospitals, P. aeruginosa has been known to cause problems in debilitated patients and is a common cause of disease in children with cystic fibrosis. These persistent creatures have been found in unlikely places such as air vents, water hoses, and even in detergent holding tanks in the very machines that are used to clean medical instruments.

Salmonella typhimurium Many strains of Salmonella are potentially pathogenic. They are commonly found in the intestinal tract of mammals, birds, and reptiles. Under some conditions, they can lead to contamination of food. The most severe illness caused by any Salmonella is typhoid fever (pathogen: Salmonella typhi). Other strains, of which S. typhimurium is one, cause less serious gastrointestinal diseases, collectively known as Salmonellosis. The bacteria invade the cells of the intestinal tract of the host (see, for an animation of how this occurs), multiply, and sometimes escape to the bloodstream and the lymphatic system. Symptoms include fever, nausea, abdominal pain, and diarrhea. Nowadays, uncooked eggs are a particularly common source of salmonellosis. Soft-boiled eggs, incompletely cooked yolk in fried eggs, or use of raw or incompletely cooked eggs in sauces and desserts can all present a risk.

Yersinia enterocolitica Yersinia enterocolitica is a species of bacteria that are often found in the intestines of many domestic animals including sheep, rabbits, pigs, cattle, horses dogs and cats. Bacteria can be transmitted in meat and milk or other contaminated food or water. They are unusual in that they can grow at 4°C, which is the temperature of refrigerators. When transmitted, the bacteria cause Yersinia gastroenteritis, or yersiniosis. The symptoms of this disease are fever, diarrhea, headache and abdominal pain. Pain is often severe and can be mistaken for appendicitis. There may be a post-infection reaction of inflamed joints. Incidences of yersiniosis is relatively rare in the US, but more common in Northern Europe.

Yersinia pestis This is the bacteria that causes the plague, which has had a huge impact on human history. In the 14th century, possibly 25% of the total population of Europe was destroyed. The plague is still with us, even in the United States. The plague is ordinarily a disease of the rat, carried both by urban and rural rodents. The bacteria is transmitted from one rat to another by fleas. However, if the host rat dies, then the fleas seek another host, and can attach to a human and transmit the disease. When the bacteria enter the human bloodstream, they multiply in the lymph and blood, causing the lymph nodes in the groin and armpit to become swollen, accompanied by fever. If untreated, death can result within a week. The plague can also become pneumonic by entering the lungs which is particularly dangerous with a nearly 100% mortality rate. This form of plague can also be contagious by air.