Some of the laboratory experiments included in this text may be hazardous if you handle
materials improperly or carry out procedures incorrectly. Safety precautions are
necessary when you work with any microorganism, and with chemicals, glass test
tubes, hot water baths, sharp instruments, and similar materials. Your school may
have specific regulations about safety procedures that your instructor will explain to
you. If you have any problems with materials or procedures, please ask your instructor
Safety Procedures and Precautions
The microbiology laboratory, whether in a classroom or a working diagnostic laboratory,
is a place where cultures of microorganisms are handled and examined. This
type of activity must be carried out with good aseptic technique in a thoroughly clean,
well-organized workplace. In aseptic technique, all materials that are used have been
sterilized to kill any microorganisms contained in or on them, and extreme care is
taken not to introduce new organisms from the environment. Even if the microorganisms
you are studying are not usually considered pathogenic (disease producing), any
culture of any organism should be handled as if it were a potential pathogen. With
current medical practices and procedures, many patients with lowered immune defenses
survive longer than they did before. As a result, almost any microorganism can
cause disease in them under the appropriate circumstances.
Each student must quickly learn and continuously practice aseptic laboratory
technique. It is important to prevent contamination of your hands, hair, and clothing
with culture material and also to protect your neighbors from such contamination.
In addition, you must not contaminate your work with microorganisms from the environment.
The importance of asepsis and proper disinfection is stressed throughout
this manual and demonstrated by the experiments. Once these techniques are
learned in the laboratory, they apply to almost every phase of patient care, especially
to the collection and handling of specimens that are critical if the laboratory is to make
a diagnosis of infectious disease. These specimens should be handled as carefully as
cultures so that they do not become sources of infection to others. An important
problem in hospitals is the transmission of microorganisms between patients, especially
by contaminated hands. Well-trained professionals, caring for the sick, should
never be responsible for transmitting infection between patients. Appropriate attention
to frequency and method of hand washing (scrubbing for at least 30 seconds) is critical for preventing these hospital-acquired infections (also known as nosocomial
In general, all safety procedures and precautions followed in the microbiology
laboratory are designed to:
- Restrict microorganisms present in specimens or cultures to the containers
in which they are collected, grown, or studied.
- Prevent environmental microorganisms (normally present on hands, hair,
clothing, laboratory benches, or in the air) from entering specimens or cultures
and interfering with results of studies.
Hands and bench tops are kept clean with disinfectants, laboratory coats
are worn, long hair is tied back, and working areas are kept clear of all unnecessary
items. Containers used for specimen collection or culture material are presterilized
and capped to prevent entry by unsterile air, and sterile tools are used for transferring
specimens or cultures. Nothing is placed in the mouth.
Personal conduct in a microbiology laboratory should always be quiet and
orderly. The instructor should be consulted promptly whenever problems arise.
Any student with a fresh, unhealed cut, scratch, burn, or other injury on either hand
should notify the instructor before beginning or continuing with the laboratory work. If
you have a personal health problem and are in doubt about participating in the
laboratory session, check with your instructor before beginning the work. Careful attention
to the principles of safety is required throughout any laboratory course in
General Laboratory Directions
- Always read the assigned laboratory material before the start of the laboratory
- Before entering the laboratory, remove coats, jackets, and other outerwear.
These should be left outside the laboratory, together with any backpacks,
books, papers, or other items not needed for the work.
- To be admitted to the laboratory, each student should wear a fresh, clean,
knee-length laboratory coat.
- At the start and end of each laboratory session, students should clean their
assigned bench-top area with a disinfectant solution provided. That space
should then be kept neat, clean, and uncluttered throughout each laboratory
- Learn good personal habits from the beginning:
Tie back long hair neatly, away from the shoulders.
Do not wear jewelry to laboratory sessions.
Keep fingers, pencils, and such objects out of your mouth.
Do not smoke, eat, or drink in the laboratory.
Do not lick labels with your tongue. Use tap water or preferably, self-sticking labels.
Do not wander about the laboratory. Unnecessary activity can cause accidents,
distract others, and promote contamination.
- Each student will need matches, bibulous paper, lens paper, a china-marking
pencil, and a 100-mm ruler (purchased or provided). A black, waterproof
marking pen may be used to mark petri plates and tubes.
- Keep a complete record of all your experiments, and answer all questions at
the end of each exercise. Your completed work can be removed from the
manual and submitted to the instructor for evaluation.
- Discard all cultures and used glassware into the container labeled
CONTAMINATED. (This container will later be sterilized.) Plastic or other
disposable items should be discarded separately from glassware in containers
to be sterilized.
Never place contaminated pipettes on the bench top.
Never discard contaminated cultures, glassware, pipettes, tubes, or slides in
the wastepaper basket or garbage can.
Never discard contaminated liquids or liquid cultures in the sink.
- If you are in doubt as to the correct procedure, double-check the manual. If
doubt continues, consult your instructor. Avoid asking your neighbor for
- If you should spill or drop a culture or if any type of accident occurs, call the
instructor immediately. Place a paper towel over any spill and pour disinfectant
over the towel. Let the disinfectant stand for 15 minutes, then clean the spill
with fresh paper towels. Remember to discard the paper towels in the proper
receptacle and wash your hands carefully.
- Report any injury to your hands to the instructor either before the laboratory
session begins or during the session.
- Never remove specimens, cultures, or equipment from the laboratory under
- Before leaving the laboratory, carefully wash and disinfect your hands. Arrange
to launder your lab coat so that it will be fresh for the next session.