The component of the cell membranes in eukaryotes and

lecithinase reaction showed that Clostridium
perfringens produced lecithinase but Staphylococcus
epidermidis did not. These are the expected results for this test. The
ability of Clostridium perfringens to
produce lecithinase is used to differentiate it from other clostridium species using the Naglers reaction where an egg yolk
agar plate is used to identify if the lecithinase containing alpha toxin of Clostridium perfringens is present. Lecithinase
is also known as phospholipase A and hydrolyses lecithin resulting in
lysolecithin and a fatty acid (Hanahan,
Brockerhoff and Barron, 1960). Lecithin is a component of the cell
membranes in eukaryotes and the ability to break down lecithin could play a
large role in its pathogenesis. The alpha toxin of clostridium perfringens causes
gas gangrene resulting in myonecrosis, the death of muscle tissue. Clostridium perfringens produces lecithinases
as it is a soil born bacteria which when entering a host immediately start competing
with other microbes and the bodies immune system for nutrients and produces the
toxin to help it attack them, whereas Staphylococcus
epidermidis is part of the normal flora found on the body, especially the
skin, and therefore acts less aggressively towards the immune system and host


The DNase
test showed that Staphylococcus aureus
produces DNase whereas Staphylococcus
epidermidis does not. When compared to existing data these results are
expected. A paper by (Buchanan et al., 2018)
discusses the possibility for bacteria to use DNase to escape neutrophil
extracellular traps (NETs) which are made up of DNA as well as other components.
 The DNase degrades DNA by catalysing the
hydrolysis of phosphodiester linkages and would help the bacteria to escape and
avoid being destroyed by the neutrophils. There are limitations of this test
including that some MRSA stains of the bacteria do not give positive DNase results
and some other bacteria will give weak reactions to the test making it more
difficult to give an accurate result.

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The haemolysis
test showed that Streptococcus pyogenes
caused beta haemolysis, the complete destruction of the red blood cells, and Streptococcus
sanguis caused alpha haemolysis,
the partial destruction of the red blood cells. When compared to
existing data these results are expected.
Haemolysis can cause haemoglobinemia in the patient which is an excess amount
of haemoglobin found in the blood plasma of the patient due to the lysis of the
red blood cells.


For the BSAC
disc diffusion assay the control results are within the control ranges for all
four of the antibiotics, meaning that the tests were done correctly, and the
results should be reliable. S. 310258 is resistant to CFX and CXM and sensitive
to CTX and CPM, E. coli 704476/2 is sensitive to all four, E. coli 310217 is
resistant to all four, Coliform B 706498 is resistant to CFX, CTX, CPM and sensitive
to CXM. This shows the E. coli 310217 is highly resistant to the antibiotics
whereas E. coli 704476/2 is the most sensitive to the antibiotics. Antibiotics
work by targeting part of the bacteria and either killing it or preventing it
from multiplying. A common method they use, including penicillin, is by preventing
the synthesis of peptidoglycan which is used is used in the bacteria’s cell
wall.  Testing the bacteria found in a
patient is needed because even if the identity of the bacteria is known the
susceptibility to antibiotics can vary a large amount between different
strains. This test allows information about which antibiotics would be
advantageous to use and which ones would have no effect before they are
prescribed, allowing for the ideal antibiotic to be used. When antibiotics can
no longer control the growth of or kill a bacterium it is known as antibiotic
resistance. This is can happen through several ways. Mutations occurring in the
bacteria can remove the ability for the antibiotics to target it as effectively
as before or give it new ways to effectively protect itself from the antibiotics.
Bacteria can also go through the process of conjugation which is where the
bacteria transfer genetic information between each other. If a small group of
bacteria have the ability to be resistant to antibiotics they can spread this
ability to other bacteria until the whole population can no longer be killed by
the antibiotics that would have once been used. This is becoming a problem
presently due to the over prescription of antibiotics as well as people not finishing
their course of antibiotics and allowing resistant ones to survive and spread. Bacteria
that have become resistant to previously used antibiotics include; methicillin-resistant
Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). The
minimum inhibitory concentration (MIC) is the smallest concentration of an
antibiotic that can be used to prevent the bacteria from growing. The results
from these tests have been published as guidelines on the susceptibility of
different bacteria to antibiotics. While the disc diffusion test, also known as
Kirby-Bauer antibiotic testing) was the test used in this lab to show bacteria
sensitivity, other tests are also available. A disadvantage of the disc
diffusion method is that all of the results are standardised meaning that the
labs performing the tests must be very careful to accurately follow these
standards. The E-test is another method used to calculate the MIC of the
bacterium. It is a plastic reagent strip that has an antibiotic gradient covering
it which is then placed onto the inoculated agar plate to and the MIC to be
read from the scale after incubation