1. MRSA HONORS RESEARCH 1
MRSA Honors Research
Caleb Abel, Elisa Jacobs,
Jessica Phelps, Jessica Dombrowski,
& Kari Gottfried
Liberty University

2. MRSA HONORS RESEARCH 2
MRSA Honors Research
Introduction
Methicillin-resistent Staphylococcus aureus (MRSA) is rapidly becoming a major threat
to the health of people throughout the world, including in the United States. Dr. Gillen, a
microbiology professor at Liberty University, has studied MRSA for many years, and recently
released a study that included the hypothesis that one person could have two or more strains of
MRSA on them, particularly in their two nares (Gillen, 2014). As a result, we identified one
person referred to as subject #6, who had tested positive for MRSA, and who had two possible
strands of MRSA, one in each nares. We conducted experiments using antibiograms to test our
hypothesis that subject #6 had two strains of MRSA. We tested the following eight antibiotics,
Doxycycline, Streptomycin, Vancomycin, Erythromycin, Penicillin, Sulfa Drug, Oxacillin, and
Mupirocin, on both Mullen-Hinton and chrome-agar. The following Table and figures further
detail our results.
Table 1.
Biol 203-008 Student #6 Antibiotic LN S,I,R,C* RN S,I,R,C*2
1 Doxycycline (D-30) 42 S 40 S
2 Streptomycin (S-10) 13.5 I 13 I
3 Vancomycin (VA-30) 23 S 22 S
4 Erythromycin (E-15) 35.5 S 36 S
5 Penicillin (P-10) 17.5 R 10 R
6 Sulfa Drug (SXT) 33.5 S 31.5 S
7 Mupirocin (Mup) 48.5 S 46.5 S
8 Oxacillin (OX-1) 14 C 20 S
*S=Susceptible, I=Intermediate, R=Resistant, C=Can't tell

3. MRSA HONORS RESEARCH 3
Figure 1.
Results, Discussion, and Interpretation
The results of the antibiograms that we performed with the eight different antibiotics are
shown above in Table 1 and Figure 1. The disc diffusion results were all very similar. Comparing
the left and right nares, six out of eight of the antibiotics tested differed by two millimeters or
less, which is relatively insignificant. The only exceptions were Penicillin and Oxacillin. There
was an average difference in zone of inhibition sizes between each nare of 7.5 millimeters for
Penicillin, and an average difference of six millimeters for Oxacillin. Both of the averages for the
zone of inhibition for Penicillin show that the bacteria were resistant to the antibiotic. The
effectiveness of Oxacillin is more ambiguous. The average zone of inhibition size for the right
nare shows that the bacteria was susceptible to the antibiotic. However, there is no interpretation
available for zone sizes of 19 millimeters or less. Since that is the case, it is not possible to tell
whether the bacteria colonizing in the left nare is susceptible, intermediate, or resistant to
Oxacillin since the average zone size was 14 millimeters. Because there is a relatively greater
difference in these two antibiotics, it is possible that there are two separate strains of MRSA
0
10
20
30
40
50
60
Doxycyline
(D-30)
Streptomycin
(S-10)
Vancomycin
(VA-30)
Enthromycin
(E-15)
Penicillin (P-
10)
Sulfa Drug
(SXT)
Mupirocin
(Mup)
Oxacillin (OX-
1)
LN RN

4. MRSA HONORS RESEARCH 4
colonizing the nares. Further statistical tests such as the Chi-Test would have to be conducted to
support this suggestion. Based upon the results, Mupirocin would likely be the most effective
treatment for the MRSA strain in each nare. Mupirocin had the greatest zone of inhibition sizes
indicating the bacteria growing in each nare were most susceptible to this antibiotic of the ones
tested.

5. MRSA HONORS RESEARCH 5
Reference
Gillen, A. (2014). High MRSA carriage rate among nursing microbiology students. Retrieved
from http://learn.liberty.edu/bbcswebdav/pid-4299882-dt-content-rid-29014264_1/
courses/BIOL203_008_201440/Accepted%20Gillen%20Manuscript%20AiM%20MRSA
.pdf