For the safety and convenience of everyone working in the laboratory, it is
important that the following laboratory rules be observed at all times:
- Place only those materials needed for the day’s laboratory exercise on the
- Since some of the microorganisms used in this class are pathogenic or
potentially pathogenic (opportunistic), it is essential to always follow proper
aseptic technique in handling and transferring all organisms.
- No eating, drinking, or any other hand-to-mouth activity while in the lab.
If you need a short break, wash your hands with disinfectant soap and
leave the room.
- Using a wax marker, properly label all inoculated culture tubes or petri
plates with the name or initials of the microorganism you are growing,
your initials or a group symbol, and any other pertinent information.
Place all inoculated material only on your assigned incubator shelf. Culture
tubes should be stored upright in plastic beakers, while petri plates should
be stacked and incubated upside-down.
- Always clean the oil off of the oil immersion lens of the microscope with
a piece of lens paper at the completion of each microscopy lab.
- Disinfect the benchtop with isopropyl alcohol before and after each lab
period. Be sure your Bunsen burner is turned off before you spray any
- Always wash your hands with disinfectant soap.
- Familiarize yourself in advance with the procedure of the experiment to be
- Disinfect the working table with isopropyl alcohol before and after each
- The first part of each lab period will be used to complete and record the
results of previous experiments. We will always go over these results as
a class. You may wish to purchase a set of colored pencils to aid you in
recording your results in the lab manual.
- Wash your hands with disinfectant soap before leaving the lab.
Microorganisms are given specific scientific names based on the binomial
(2 names) system of nomenclature. The first name is referred to as the genus
and the second name is termed the species. The names usually come from Latin
or Greek and describe some characteristic of the organism.
To correctly write the scientific name of a microorganism, the first letter of
the genus should be capitalized, while the species name should be in lowercase
letters. Both the genus and species names are italicized or underlined. Several
examples are given below:
: L. dim. noun Bacillum
, a small rod
: L. adj. subtilus, slender
: after discoverer, Prof. Escherich
: L. gen. noun coli
, of the colon
: Gr. noun Staphyle
, a bunch of grapes; Gr. noun coccus
: L. adj. aureus
Metric Length and Fluid Volume
The study of microorganisms necessitates an understanding of the metric system
of length. The basic unit of length is the meter (m), which is approximately
39.37 inches. The basic unit for fluid volume is the liter (L), which is
approximately 1.06 quarts. The prefix placed in front of the basic unit indicates
a certain fraction or multiple of that unit. The most common prefixes we will
be using are:
||10–2 or 1/100
||10–2 m or 1/100 m
||10–3 or 1/1000
||10–3 m or 1/1000 m
||10–3 L or 1/1000 L
||10–6 or 1/1,000,000
||10–6 m or 1/1,000,000 m
||10–6 L or 1/1,000,000 L
||10–9 or 1/1,000,000,000
||10–9 m or 1/1,000,000,000 m.
In microbiology, we deal with extremely small units of metric length
(micrometer, nanometer). The main unit of length is the micrometer (mm), which
(1/1,000,000) of a meter or approximately 1/25,400 of an inch.
The average size of a rod-shaped (cylindrical) bacterium is 0.5–1.0 mm wide
by 1.0–4.0µm long. An average coccus-shaped (spherical) bacterium is about
0.5–1.0 µm in diameter. A volume of 1 cubic inch is sufficient to contain
approximately 9 trillion average-sized bacteria. It would take over 18,000,000
average-sized cocci lined up edge-to-edge to span the diameter of a dime.
In several labs, we will be using pipettes to measure fluid volume in mL.