Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
Mean Radius of Zone of Inhibition
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
1st Generation 2nd Generation 3rd Generation
Generation
Tobramycin
Polymyxin
Figure 3. Mean radius of zone of inhibitions produced
by Tobramycin and Polymyxin at each generation.
Error bars representing ±se.
Discussions
The results showed that there were significant
resistance levels due to effectiveness of Tobramycin,
and Polymxin B Sulfate in treating S. aureus. The first
generation of Staphylococcus, treated with the 20%
antibiotic solution(s) of Tobramycin and Polymyxin
showed an average radius of 0.26cm ±0.07 and 0.28cm
±0.07 zones of inhibition respectively. Second
generation of S. aureus (treated with 40% antibiotic
solution) showed an average radius of 0.69cm ±0.04
and 0.20cm ±0.09 zones of inhibition respectively.
The third generation of S. aureus (treated with 50%
antibiotic solution showed an average radius of 1.20cm
±0.1 and 0.18cm ±0.06 zones of inhibition
respectively. After statistical analysis, it was
concluded that S. aureus did not develop resistance to
Tobramycin. Polymyxin B Sulfate grew progressively
weaker to the bacteria with each new generation
grown. This drug is concluded to be the least effective
towards the bacterium. Further analysis of these results
indicates that Tobramycin is a very effective drug to
treat bacteria infections such as S. aureus. (Lucas et
al.). Although the Tobramycin used in the first
generation had smaller zones of inhibition than the
Polymyxin, the difference can be accounted for the fact
that Tobramycin did not spread as rapidly as the
Polymyxin, therefore did not kill as much bacterium. It
can be concluded that Tobramycin is much more
effective at inhibiting bacterium reproduction. Its
inhibition of translation of mRNA into a protein is
much more effective, as opposed, to Polymyxin
disrupting the outer polysaccharide layer of the
bacterium.
The experiment demonstrates the speed at
which evolutionary adaptation bacterium possesses
when put under evolutionary stress as Cirz et al. had
explained and demonstrated (Cirz et al., 2005). It
should also be noted the speed at which the mutations
occurred at on an evolutionary scale. According to
Maree et al., the resistance did occur. This happened
within three generations of the S. aureus. It is not
known whether the S. aureus was already resistant to
the Polymyxin or if it mutated in the small amount of
time that the bacterium were grown.
Acknowledgements
The authors appreciatively acknowledge
Professor Steve Teh and Dr. Tony Huntley for their
guidance and Saddleback College Biology Lab for the
contribution of S. auereus, measuring devices and other
required testing materials.
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Saddleback Journal of Biology
Spring 2008