DISEASE TRANSMISSION AND STANDARD CLINICAL PROCEDURES
Section I. MICROBIOLOGY AND DISEASE TRANSMISSION
a. Microbiology is the study of microorganisms, including bacteria, fungi, and
b. Microorganisms, also called germs or microbes, are a common cause of
disease. They exist in almost every environment on earth. Three types of
microorganisms are bacteria, fungi, and viruses. The word "micro" implies that
microorganisms are extremely small and not visible to the unaided eye. However, when
bacteria or fungi grow into a mass, they can sometimes be seen by the unaided eye.
Most bacteria and fungi are capable of growing in or on common laboratory culture
media (nutrients). Viruses and a few bacteria require living tissue cells to support their
growth and reproduction. Bacteria, viruses in tissue culture, and some fungi grow well
at 95F (35C), whereas many fungi grow best at 77F (25C).
The three basic shapes of bacteria are coccus (spherical), bacillus (rod like), and
spirochete or spirilla (corkscrew). See figure 1-1. Cocci may be arranged in chains
(strepto), clusters (staphylo), or pairs (diplo), depending on the specific microbe. See
figure 1-2. In addition to appearing in various specific arrangements, bacilli tend to
occur in a wide variety of sizes and forms. A few bacilli produce spores that are highly
resistant to harsh environmental conditions, such as moderately high temperatures and
certain chemicals. The gram stain is often used to aid in differentiating bacteria.
Figure 1-1. Shapes of bacteria.