The Most Common Bacteria
There are many types of bacteria, and scientists have spent many years culturing and studying their properties. The scientific name for the most common bacteria is Escherichia coli. E. coli was discovered by Theodore Escherich. This bacterium is found in the intestinal tract of every individual and helps breakdown food. It is also found in hot springs and radioactive waste, so it can exist in widely diverse environments. E. coli are highly concentrated in stool and can contaminate the urinary tract, resulting in infection. E. coli have a Gram- negative rod.
The scientific name for the bacteria that are found on skin and other mucus membranes is Staphylococcus. Staphylococci have two varieties, Staphylococcus aureus and Staphylococcus epidermidis. Staph epidermidis is found on skin and mucus membranes and does not typically cause disease. It does need to be distinguished in the laboratory from Staph aureus, however, which can cause serious infections. Staph aureus is present in the nasal passages, as well as the skin. The color of Staph aureus is golden yellow on blood agar, which is why it is named “aureus.” Staph epidermidis grows white colonies on blood agar. Staph epidermidis is named for its predominant presence on the skin.
There are several varieties of Streptococci. Streptococci pyogenes is a Group A Strep, which can cause sore throat, particularly when an individual’s immune system is depressed. Another variation is Streptococci pneumonia, which can cause pneumonia and other respiratory problems. Streptococci are distinguished by their hemolytic action on blood agar. Group A Strep cause a breakdown in blood, giving a clear area around the colony growing on blood agar. These are called beta-hemolytic strep.
Salmonella and Shigella
Salmonella species and Shigella species inhabit the rectum and stool. They are often found as contaminants in food or acquired by handling animal manure. Salmonella is found in raw chicken and eggs and is a major source of food poisoning. Shigella can attach to the intestinal wall, causing bleeding. Both Salmonella and Shigella infections can cause severe diarrhea. These are easily transmitted person-to-person, so handwashing is essential.
Salmonella was named after the man who discovered it, Daniel Salmon. Shigella derives its name from a Japanese microbiologist, Kiyoshi Shiga. Salmonella and Shigella are both Gram-negative rods.
Another bacteria that can cause severe diahrrea is Campylobacter. Patient stool specimens cotaining these bacteria will be liquid and may have blood in them. Campylobacter is a curved-shaped Gram-negative organism.
Klebsiella species is a Gram-negative rod and is often found in hospital patients. Klebsiella pneumonia affects the lungs and can cause pneumonia.
Proteus are Gram-negative rods that are commonly found in the intestinal tract, along with E. coli. Proteus mirabilis is prolific in soil and water and can become infective when an open sore or cut becomes dirty.
Pseudomonas aeruginosa is a Gram-negative rod and has low virulence. It is highly opportunistic, infecting those with depressed immune systems, and can cause life threatening infections. It can easily exist on surfaces and can be found in hospital equipment, including hot tubs.
Albert Neisser, a German bacteriologist, discovered a unique Gram-negative diplococcus with a slightly flattened side. The bacteria, Neisseria, were named after him. There are two varieties that are common and disease producing. One is Neisseria meningiditis, which causes meningitis in adults. The other is Neisseria gonorrhoeae, which causes gonorrhea, one of the most common venereal diseases.
Clostridium difficile is a type of Gram-positive bacteria that can exist in the absence of oxygen. It can cause severe diarrhea and often follows antibiotic treatment. In these cases, the antibiotics have wiped out the normal flora of the body and C. diff can then become prolific. In order to reestablish normal flora, probiotics are often needed.