(2) Staining characteristics. There are many staining techniques used in the
identification of bacteria. Two commonly used staining procedures are the Gram stain
and the acid-fast stain.
(a) Gram stain. This staining technique was developed by Gram, a
Danish scientist. Bacteria that are stained a purple color (from crystal violet) are
referred to as gram-positive, while bacteria that are stained red (from safranine) are
called gram-negative. Interestingly, some gram-positive bacteria are more susceptible
to some antibiotics than are some gram-negative bacteria. Thus, this test is important
in determining which antibiotic might work against a certain type of bacterial infection.
(b) Ziehl-Neelsen acid-fast stain. This staining technique is used in the
identification of the particular types of bacteria responsible for causing tuberculosis and
c. Bacteria and Disease. Bacteria cause a wide variety of diseases. Many of
these are of military significance. Years ago, certain types of bacterial infections meant
death to the patient. Today, wise use of antibiotics has given the medical profession
one means of combating these types of diseases. One critical factor in dealing with
infections caused by bacteria is knowing which bacteria cause a particular disease.
This lesson will focus on identifying bacteria and related disease.
(1) Gram-positive bacteria and disease. Staphylococcus is a widespread
bacterium that causes minor infections, such as boils and abscesses, and much more
severe problems, such as food poisoning and pneumonia. Streptococcus bacteria
cause infections such as "strep throat", rheumatic fever, and some upper respiratory
infections. The pneumococcus bacterium causes pneumonia. There are several
species of Clostridium worth noting. Clostridium botulinum causes the well-known type
of food poisoning called botulism (which has about a 60 percent mortality rate).
Clostridium tetani causes tetanus (also known as lockjaw). Clostridium perfringens is
one of the organisms responsible for causing gas gangrene.
(2) Gram-negative bacteria and disease. This group of bacteria includes
such organisms as Escherichia coli, meningococcus, Pseudomonas, Neisseria
gonorrhea, Salmonella, Haemophilus influenzae, and Shigella. Escherichia coli is
normally found as a major constituent of our intestinal flora. It aids in the breakdown of
carbohydrates and helps us absorb vitamin K. This same bacterium can cause urinary
tract infections if it enters the urinary system. Since this microorganism is present in
human feces, microbiologists can detect the presence of fecal contamination in food
and water by determining if Escherichia coli (E. coli) is present in a particular sample.
Haemophilus influenzae is a type of bacteria that is commonly found in the throat and
nose of many people. It causes bronchopneumonia and sinusitis. This bacterium,
however, does not cause influenza; influenza is caused by a virus. Pseudomonas is