MCB 2010 Miami Dade College Microbiology Paper

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ldentification of Escherichio coli and Bacillus cereus from mixed culture #21
using morphological differentiation and biochemical methods
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\rene Anez
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MCB 2010 Laboratory
Dr.
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n Gines-Candelaria
Aprilgth,2019
ldentification of bacteria in unknown suspension #21
7
Table of Contents
Abstract
2
lntroduction
2
Materials and Methods
5
Results
6
Discussion..
13
References.
14
ldentification of bacteria in unknown suspension #21
2
Abstract
The purpose of this experiment was to identify 2 different unknown bacteria from mixed culture # 21,. A
list of 12 possible organisms was provided (Table 1) and it was stated that the mixture would have one
coliform and one non-coliform organism. Using a microbe chart as guide of the morphological and
biochemical characteristics of these 12 bacteria, a dichotomous key was constructed and used as the
strategy to identify the two microorganisms (Figure L). ln order to correctly identify the bacteria, Gram
(F-
stain, cellular morphology and arrangement, culture in selective and differential mediurli, and
biochemical tests were performed. After the organisms were correctly identified, one separate
biochemical test was conducted with each bacterium to confirm the initial identification. After following
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the dichoto rmous key it was determined that the given bacterial suspension consisted of Escherichia coli
and Bacillus cereus.
lntroduction
Microbiology is one of the most important branches of the biological sciences. The study of
microorganisms is crucial, as they can be found practically everywhere (Leboffe and Pierce 34) and are
a
very important pillar of ecological interaction, because they are “the basis of every food chain on this
planet” (Kellenberger, 2001). Microorganisms play an important role in our daily life and most of the
time we are unaware of it. lt is thanks to microorganisms and their ability to ferment different
substrates that we can enjoy dairy products like cheese and yogurt, sausages and beverages that include
wine and beer and that can in general increase the shelf life of food products (Talon 2017l,. We “depend
on microbes (in our) intestines for digestion and the synthesis of some vitamins” (Tortora, 2). Even
though microorganisms can be beneficial, they can also cause disease and is important to learn to
differentiate them {Tortora, 2).
a
ldentification of bacteria in unknown suspension
For microbiologists
#21
3
to properly identify bacterial species and genera, using only morphological
characteristics is not sufficient (Kellenberger,ZAOtl, it is necessary to perform additional tests, that
include biochemical and physiological characteristics of bacteria.
Bacteria can use a lot of different compounds to grow. They are capable of using “an enormous variety
of hydrocarbon substrates” (Baron, 1996). This allows for a very large metabolic diversity and for finding
bacteria practically everywhere, at the same time it allows us to use these differences to corectly
identify them using metabolic and biochemical tests. Since bacteria have such a large metabolic diversity
and are also very well suited to survive various environmental changes thanks to the survival of mutants
(Baron, 1996), whenever encountered with unknown bacteria it is incredibly important to develop a
strategy that allows for identification of all possible organisms. This strategy is a dichotomous key, that
allows for the identification of all possible organisms in as little steps as possible. Even though this
project was conducted in the microbiology laboratory, and the time given for identification was of
multiple weeks, the time for correct identification in most scenarios is of great importance. For example,
in case of a bacterial infection, the attending physician needs to know the bacterium that is causing the
infection and the sensibility or resistance of this bacterium to different antibiotics to be able to develop
an efficient treatment plan. Because time is of great importance and because it also allows
to use
less
resources, dichotomous keys are often used in microbiology laboratories. Therefore, after receiving the
list of possible microorganisms (Table 1) the first step was to create a dichotomous key (Figure 1) using
microbe chart as guide.
Following the dichotomous key to perform the appropriate biochemical tests with the unknown
bacteria, it will be possible to correctly identify both organisms given in the bacterial suspension #21.
4
ldentification of bacteria in unknown suspension #21
Table 1: List of possible organisms in the obtained sample
Organisms
Non-coliform
Coliform
Klebsiello pneumonioe
Escherichio coli
E nte robo cte r a e rog e n e s
Sal monel I a typhi m uri u m
Shigello flexneri
P se
ud om ono s ae ru
g i nosa
Bacillus cereus
Alkaligenes faecolis
Proteus vulgaris
Micrococcus luteus
Stophylococcus dureus
Bocillus subtilis
*Source: Gin6s-Candelaria, Edwin. “MCB 20101- Morphological and Physiological Characteristics of
Unknown Bacteria”. Miami Dade College. 23 Oct 2018.
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