PETRI DISH IN DIAGNOSTIC MICROBIOLOGY Basics in Diagnostic Microbiology by Dr.T.V.Rao MD

1. PETRI DISH IN DIAGNOSTIC MICROBIOLOGY
Basics in Diagnostic Microbiology
Dr.T.V.Rao MD
A Petri dish (sometimes spelled "Petrie dish" and
alternatively known, as a Petri plate, named after the German bacteriologist Julius
Richard Petri, is a shallow cylindrical glass or plastic lidded dish, Microbiologists have
many tools, to perfect the knowledge in Microbiology and to make optimal use of their
skills to diagnose many infectious diseases, PETRI DISH is the basic tool we learn
Microbiology however bacteriological diagnosis continues to be most need of the
Hospitals and important need TO DIAGNOSE MANY INFECTIOUS DISEASES, The
Petri dish continues to be most important tool to our Microbiologists, who report in the
laboratory,. An agar plate is a Petri dish that contains a growth medium, used to culture
microorganisms Individual microorganisms placed on the plate will grow into individual
colonies, each a clone genetically identical to the individual ancestor organism except for
the low, unavoidable rate of mutation. OR NON ADOPTING MICROBES AS
ANAEROBES WHEN INCUBATED WITH ENVIRONMENT OF HIGH OXYGEN, As a
post graduated in 1980 petri dish was like a Stethoscope to a practicing Doctor, I learnt
real skills through putting dedication through observation of wonders in Bacteriology and
Mycology. A Senior Microbiologist can assess how a student handles the Petri dish by
primary observation, One should know how to handle the petri dish in laboratory it is
simple can be learnt with simple practices, Sometimes we are very impressed how a
young Microbiologist handles the petri dish, Do not keep open your petri dish to the
atmosphere at your work or during poring the plates, Quickly replace the top half of the
petri dish to prevent any airborne bacteria from contaminating the experiment. Set the
petri dishes aside for 30 to 2 hours, until the agar solution cools and hardens, Label and
seal the petri dishes. Once you have introduced or inoculated the bacteria, you should
replace the lid on the petri dish and seal it with some tape. • Make sure to label each petri
dish with the source of the bacteria it contains, otherwise you won't be able to tell which
is which. You can do this using some tape and a marker. • as an extra precaution, you
can place each petri dish in a zipper-lock bag. This will provide an extra layer of
protection against any hazardous bacteria colonies that may develop, but will still allow
you to view the contents of the petri dish. Thus, the plate can be used either to estimate
the concentration of organisms in a liquid culture or a suitable dilution of that culture
using a colony counter, or to generate genetically pure cultures from a mixed culture of
genetically different organisms, using a technique known as "streaking". In this
technique, a drop of the culture on the end of a thin, sterile loop of wire, known as an
inoculator or a loop, is streaked across the surface of the agar leaving organisms behind,
a higher number at the beginning of the streak and a lower number at the end. At some
point during a successful "streak", the number of organisms deposited will be such that
distinct individual colonies will grow in that area which may be removed for further
culturing, using another sterile loop, Like other growth media, the formulations of agar
used in plates may be classified as either "defined" or "undefined" selective, enriched
media; To know a little a defined medium is synthesized from individual chemicals
required by the organism so the exact molecular composition is known, whereas an
undefined medium is made from natural products such as yeast extract, where the
precise composition is unknown. Samples can then be taken from the resulting colonies
and a microbiological culture can be grown on a new plate so that the organism can be
identified, studied, or tested. The streaking is done using a sterile tool, such as a cotton
swab or commonly an inoculation loop. Place the plates in a warm dark place to grow -
not too warm, but anything up to about 98 degrees F (37 degrees C) should be fine. In a
short time, you'll be greeted by an amazing variety of bacteria, molds, and fungi. - You’re
likely to have a huge variety of colors, sometimes fascinating shapes, and smells in your
tiny worlds. Count the number of colonies on the plate; note the differences in color,
shape, and other properties. Take the proper safety precautions. Before you attempt to
dispose of your petri dishes, you first need to take the proper safety precautions. •

2. Although most of the bacteria you grow will not be hazardous, large bacteria colonies
may pose more of a risk - so you will need to kill them before disposal using household
bleach. Protect your hands from the bleach by wearing rubber gloves, protect your eyes
with plastic goggles and protect your clothes by wearing an apron.
HOWEVER THE MAJORITY OF THE WORK WE DO IN DIAGNOSTIC LABORATORY
IN DEVELOPING COUNTRIES IS JUST ROUTING HANDLING OF THE CLINICAL
SPECIMENS FROM URINE, BLOOD SPUTUM CSF AND BODY FLUIDS IT IS JUST
ESSENTIAL THAT WE SHOULD BE GOOD AT HANDLING A PETRI DISH TO THE
OPTIMAL USE •
Ref 1 Wikipedia on culturing bacteria and fungi •
2 Basic trends in diagnostic microbiology •
Dr.T.V.Rao MD Professor of Microbiology Freelance writer
IPhoto by Dr.T.V.Rao