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(Amrita Vishwa Vidyapeetham University, 2014). In comparison,
species which cause complete lysis
of red blood cells are said to be beta-haemolytic (Wylie, 2014).
However some species of bacteria do
not produce any haemolysins so when colonies grown on the red
blood agar, no change is seen
(Amrita Vishwa Vidyapeetham University, 2014). These species are
classified as non-haemolytic.
Species that are haemolytic are usually Streptococcus spp. while
some strains of Staphylococci spp.
and Escherichia coli may indicate beta haemolysis (Amrita Vishwa
Vidyapeetham University, 2014).
All of the bacteria, except for bacteria in PB2, were classified
as non-haemolytic and thus do not
produce any pathogenic haemolysins. PB2 exhibited
beta-haemolysis indicating that the bacteria
present in PB2 contained haemolysins which led to the complete
destruction of red blood cells. PB2
could either be Streptococcus spp., Staphylococci spp. or
Escherichia coli.
MacConkeys agar is both selective and differential media (Wylie,
2014). It is selective for gram
negative bacteria and can differentiate those bacteria that have
the ability to ferment lactose (Amrita
Vishwa Vidyapeetham University, 2014). The crystal violet dye on
the agar inhibits gram positive
bacterial growth (Amrita Vishwa Vidyapeetham University, 2014).
By utilising the available lactose
on the medium, bacterial species that produce acid in the medium
will lower the pH of the gar below
6.8 which results in the appearance of red or pink colonies
(Amrita Vishwa Vidyapeetham University,
2014). Bacterial species such as Escherichia coli, Enterobacter
spp. and Klebsiella spp. can ferment
lactose (Wylie, 2014). Bacteria such as Salmonella spp.,
Pseudomonas aeruginosa and Shigella spp.
cannot utilise lactose present on the medium (Amrita Vishwa
Vidyapeetham University, 2014). PB1,
DW1 and DW2 were classified as non-lactose fermenting thus they
may be either part of the bacterial
species of Salmonella spp., Pseudomonas spp., Shigella spp. DC1
exhibited lactose fermentation
suggesting that it may be either Escherichia coli, Enterobacter
spp. or Klebsiella spp. DC2 and PB2
exhibited no growth which does strongly indicate whether the
bacteria is non-lactose fermenting.
Mannitol Salt agar is both a selective and differential media
and is used for the isolation of pathogenic
Staphylococcus aureus (Amrita Vishwa Vidyapeetham University,
2014). The 7.5% NaCl content on
the MSA is selective for the Staphylococcus species (Amrita
Vishwa Vidyapeetham University,2014). Only pathogenic
Staphylococcus aureus creates small colonies enclosed by yellow
zones due
to the bacterias ability to ferment mannitol which produces an
acid changing the indicating colour
from red to yellow (Amrita Vishwa Vidyapeetham University,
2014). The growth of other type of
bacteria are inhibited (Wylie, 2014). Only DC2 exhibited
mannitol fermentation suggesting that the
bacteria present is Staphylococcus aureus .
The catalase and oxidase test are biochemical tests to further
assess and identify characteristics of the
bacteria present in each sample. The catalase test specifically
facilitates the detection of enzymecatalase in bacteria (Reiner,
2010). This test allows for the differentiation between aerobic
and
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obligate anaerobic bacteria, as anaerobes are generally known to
lack catalase (Reiner, 2010).
Catalase activity is useful in differentiating between
Streptococcus spp. (catalase negative) and
Staphylococcus spp. (catalase positive) (Fidanoski &
Fidanoski, 2007). Only PB2 was classified as
catalase negative which suggests that it is of Streptococcus
spp. and is an anaerobe.
The oxidase test is used to identify bacteria that produce
cytochrome C oxidase, an enzyme of the
electron transport chain (Michigan State University, 2010). All
bacteria that are oxidase positive are
aerobic as they can use oxygen as a terminal electron acceptor
in respiration (Michigan State
University, 2010). Bacterial species may be anaerobic, aerobic
or facultative when oxidase is negative
(Michigan State University, 2010). Only DW2 was oxidase positive
and thus can be assumed that the
bacteria present in DW2 was a water-borne aerobe.
Additional biochemical analyses were conducted through the
Microbact identification test. Each strip
incorporates 12 tests which are based on the sugar utilisation
and colorimetric enzyme detection
(Thermo Scientific, 2014). This test is used on gram negative
and oxidase negative bacteria (Wylie,
2014). A code is generated from the result of the reactions in
each strip which correlate with the
percentage probability of the identity of one or more possible
bacteria present in the sample (Wylie,
2014). Only PB1, DC1, DW1 were tested using the Microbact
identification test as they were
classified as gram negative and oxidase negative.
Analysis of the Results Determined in the Investigation to
Identify the Bacteria
Peanut Butter 1 and 2 (PB1 & PB2):
The possible bacterial species present in the Brand X peanut
butter sample as stated in the
introduction are: Salmonella enterica, Escherichia coli,
Listeria monocytogenes, Campylobacter
jejuni, Shigella spp. , Staphylococcus aureus, and Streptococcus
pyogenes. The Microbact results
suggest that the bacteria in PB1 are: 98% Salmonella spp.,
