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Biology literature review – Effect of antibiotics on MRSA

Antibiotic resistance is one of the biggest challenges that the medical community currently faces
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g
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It occurs when these micro-organisms mutate (their DNA is changed) randomly
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This is a very serious issue; the
individual taking the antibiotic is now further susceptible to the effects of the micro-organism instead of
being cured, potentially leading to serious complications and death, and, furthermore, the individual can
pass the resistant bacteria on to others via external transmission (contamination etc
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More specifically, MRSA is an example of an antibiotic-resistant disease which
has gained noticeable interest due to the frequency of infections occurring, and it continues to rise
today
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The mutated form of Staphylococcus aureus which is resistant to the antibiotic
methicillin is called MRSA (Methicillin-resistant staphylococcus aureus), and its high prevalence in
hospitals is caused mainly by the over-use of antibiotics
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MRSA is
particularly important because it is resistant to a wide range of antibiotics and is present in greater
numbers than other antibiotic-resistant bacteria
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concord-mrsa
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php>]
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It will also attempt to highlight gaps in current research
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J Dancer [S
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oxfordjournals
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full
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The main aims of the study were to
determine the effectiveness of certain classes of antibiotics on MRSA and it “explores the molecular
mechanisms underlying a perceived increase in virulence following inappropriate therapy”
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According to the article, the average mortality rate is 36% from MRSA, compared to an all-time
high of 70% from Staphylococcus aureus prior to the introduction of antibiotics
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aureus (MSSA), suggesting that
antibiotic resistance is responsible for the greater death rate because the disease can’t be controlled
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S
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Methicillin-induced hla expression is common in strains of MRSA, and the findings show that the
antibiotic methicillin can actually increase the deadliness of the bacteria, with certain strains of MRSA
producing up to 30 times as much alpha-toxin in the presence of 10 micrograms of methicillin than in its
absence
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Antibiotics have also been shown to increase the frequency of
the SOS response in S
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The SOS response usually occurs when the bacteria are subjected
to unfavourable conditions, and is the process by which cell repair occurs through certain genes that
control DNA repair etc
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Beta-Lactam antibiotics such as
penicillin, ampicillin, cloxacillin and ceftriaxone induce the SOS response
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Effects of prolonged vancomycin administration on methicillinresistant Staphylococcus aureus (MRSA) in a patient with recurrent bacteraemia
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The results show that following a period with vancomycin
treatment, the effectiveness of the antibiotic decreased – reduced killing, reduced autolysis (selfdestruction of a cell through the action of lysosomic enzymes) and increased biofilm production –
groups of bacteria (MRSA) which adhere to a surface
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Therefore the oft-repeated advice to
always finish a course of antibiotics is not without reason, as failure to comply results in a fraction of
bacteria surviving and mutating/gaining resistance
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It also states that it is possible that over-prescription of antibiotics has had an adverse effect on
the management of MRSA infections
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However, this is not the case, with the main
method of control being the interruption of transmission through hygiene initiatives and other methods
of infection control
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The article doesn’t mention how the strength of the immune system of patients
may play a role in the effectiveness of antibiotics in places such as hospitals
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Sieradzki et al
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Sieradzki, T
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Dick et
al, April 2003 Evolution of a Vancomycin-Intermediate Staphylococcus aureus Strain In Vivo: Multiple
Changes in the Antibiotic Resistance Phenotypes of a Single Lineage of Methicillin-Resistant S
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asm
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full
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The purpose(s) of this study were to
investigate antibiotic resistance in MRSA isolates from the blood samples of a patient who underwent
vancomycin therapy
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MICs are the minimum amount of antimicrobials (in this case antibiotics) needed to inhibit visible of a
micro-organism following overnight incubation
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e
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Also, the isolates
were capable of forming colonies on agar containing low amounts of vancomycin (8-16 micrograms)
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The results are also similar to those in the previous study cited – the bacteria from later strains
were less easily killed due to further mutations/horizontal gene transmission
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The final study I will use in the review is a “supplement article” produced by George Sakoulas and Robert
C
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[George Sakoulas, Robert C
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oxfordjournals
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full
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This article claims that
vancomycin resistance is relatively rare compared to other antibiotics and it took around five decades
for vancomycin resistance to become noticeable, whereas a methicillin-resistant strain of MRSA
developed only two years after the conception of methicillin, which is a piece of background information
not found in the other article and study evaluated earlier
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5 mg/mL”, Also, according to the study ,“decreased
killing by vancomycin in vitro was associated with higher likelihood of treatment failure”
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Relationship of MIC and
bactericidal activity to efficacy of vancomycin for treatment of methicillin-resistant Staphylococcus
aureus bacteremia
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Another study (footnote no
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Furthermore, treatment with vancomycin within the previous 30 days is predictive of a higher MIC and
inferior therapeutic efficacy of vancomycin”
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Microbiological
effects of prior vancomycin use in patients with methicillin-resistant Staphylococcus aureus
bacteraemia
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] Two of these results, namely that the
effectiveness of treatment is reduced if all the bacteria are not killed, and also that the effectiveness of
vancomycin is reduced following extended periods of treatment are concordant with those mentioned
earlier in the review
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aureus over time): “An evaluation of >35,000 S
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e
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The
percentage of isolates with vancomycin MICs of 12 mg/mL ranged from 0% to 0
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However, small studies performed at individual centers in New York, Texas, and Massachusetts have
shown subtle but significant increases in vancomycin MICs in both MRSA and methicillin-susceptible S
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In the largest evaluation to date, an analysis of >6,000 S
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However, there was a significant drift toward reduced susceptibility, with an
increase in the percentage of isolates (from 19
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4% in 2004) with a MIC equal to 1
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” The first result doesn’t support the hypothesis that, over time, the antibiotic/vancomycin
resistance will increase in the bacteria over time and the MICs as a result should increase as less bacteria
is broken down, as it states there is no MIC creep/increasing vancomycin resistance
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9% in 2000 to 70
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0 mg/mL
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The apparent disparity between the results collected from the SENTRY database as
opposed to later studies is an example of controversy between earlier and later findings
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Since the study conducted at the California hospital was larger, it
would appear that it would also be more accurate

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