Bacteria and Antibiotic Resistance Lab Report All the instructions and questions included in the attached fil BACTERIA AND ANTIBIOTIC RESISTANCE LAB INSTRU

Bacteria and Antibiotic Resistance Lab Report All the instructions and questions included in the attached fil BACTERIA AND ANTIBIOTIC RESISTANCE LAB
INSTRUCTIONS
Please read the following lab case study. You will need a ruler for one part of the lab.
Please write your answers in the boxes that are provided. The sections for each of this
lab are intended to be completed in order.
PART 1: DOES JIMMY HAVE MRSA?
Of course Jimmy always had cuts and scrapes—he was a five-year-old boy! He’d been
playing in the neighborhood playground and cut his lip when he fell off the jungle
gym. This time though, his lip swelled up and he developed a fever. When his mother
took him to the doctor, the pediatrician said the cut was infected and had prescribed
cephalothin, an antibiotic related to penicillin, and recommended flushing the cut
regularly to help clear up the infection. Two days later, Jimmy was in the hospital
with a fever of 103°F, coughing up blood and having trouble breathing. The
emergency room doctors
told the family that
Jimmy had developed
pneumonia. They
started him on IV
antibiotics, including
ceftriaxone and
nafcillin, both also
relatives of penicillin.
Figure 1. Example of a Kirby-Bauer plate. Note the lawn of
bacteria covering the plate and the antibiotic disk at the center. A
clear zone of inhibition has formed, which indicates that the
bacteria have not grown in the area in which the antibiotic has
diffused out of the antibiotic disk. To determine the extent of
antibiotic susceptibility or resistance, measure the diameter of the
zone of inhibition
Jimmy’s doctors decided
to check for MRSA
(methicillin-resistant
Staphylococcus aureus).
He hasn’t gotten better,
and MRSA is resistant to
most of the penicillin
derivatives. To test for MRSA, the doctors took a swab from the site of Jimmy’s
wound. They then isolated bacteria from the swab and tested it biochemically. A
Kirby-Bauer disk diffusion test was performed next.
To do this test, paper disks containing different antibiotics are placed on agar petri
plates. Agar is a gelatinous material that has nutrients required for the growth of
bacteria. The suspected bacteria are spread in a thin layer on the agar plate. The
bacteria is grown until it has “lawned,” or completely coated with microbes to make a
thick hazy layer over the agar surface. The area around each disk is examined for a
clear zone where the microbe’s growth has been inhibited (Fig. 1). Jimmy’s Kirby-
Bauer test results are shown in figure 2.
Figure 2. Jimmy’s test results (bottom). The control plate (top) was isolated from a patient not infected
with MRSA. PE: penicillin, ME: methicillin, CE: cephalothin, VA: vancomycin, CTL: control disk that
contains no antibiotic. The Kirby-Bauer method is standardized so that no zone of inhibition is scored
as a zero, and all others include the disk as part of the zone.
Measure the zones of inhibition in centimeters (in science we use the metric system)
for each plate in Figure 2. Record your results in the table below.
Disk
Zone Size – Control
Zone Size – Jimmy
PE
VA
ME
CE
CTL
1. Why is a control disk included on each of the Kirby-Bauer plates?
2. Why is a control sample included in this laboratory test?
3. Does Jimmy have MRSA? How did you come to this conclusion?
4. What antibiotic should Jimmy’s doctors prescribe? Explain your choice.
PART 2: DID JIMMY INFECT HIS FAMILY?
Jimmy’s doctors have prescribed a new antibiotic based on his Kirby-Bauer results,
and he’s quickly recovering. However, his now doctors have a new question. Did
anyone catch Jimmy’s MRSA? MRSA and other forms of Staphylococcus aureus can
be spread through direct skin-to-skin contact. Jimmy’s doctors are also
epidemiologists, scientists that study the incidence, spread, and cause of disease. It’s
not surprising that Jimmy’s doctors would be concerned about his family.
The first MRSA cases arose in the 1970s. However, MRSA isn’t the first variety of
Staphylococcus aureus (commonly shortened to S. aureus or staph) to become
resistant to antibiotics. Penicillin-resistant strains first arose in the mid-1940s, shortly
after penicillin was widely introduced to treat staph infections. Initially, these
resistant varieties arise in hospitals and other health care settings where antibiotic use
is common. However, as time elapses, infection with resistant strains can be acquired
in the community, independent of health care environments. After penicillin
resistance in S. aureus became common, doctors began to treat infections with
methicillin. Similarly, methiciliin resistance was first observed in health care settings
and then rapidly spread to the community. Complicating this issue of resistance,
individuals can asymptomatically carry and shed these bacteria for years, making
identification of sources of outbreaks difficult. And, as can be seen in Jimmy’s case,
these antibiotic-resistant infections can be very severe, even causing death.
To answer their question about Jimmy’s family, his doctors took nasal swabs from
each of his asymptomatic family members and their isolates were subjected to KirbyBauer tests. The results can be seen in Figure 3.
Figure 3. Test results from Jimmy’s family. The control plate was isolated from a patient not infected
with MRSA. PE: penicillin, ME: methicillin, CE: cephalothin, VA: vancomycin. The Kirby-Bauer
method is standardized so that no zone of inhibition is scored as a zero, and all others include the disk
as part of the zone
Measure the zones of inhibition in centimeters for each plate in Figure 3. Record your
results in the table below.
Disk
Zone Size –
Mother
Zone Size – Sister
Zone Size –
Father
Zone Size –
Control
PE
VA
ME
CE
CTL
5. Do any of Jimmy’s family members carry MRSA? Explain your answer.
PART 3: VRSA, THE FUTURE
With the introduction of vancomycin to treat MRSA, vancomycin-resistant
Staphylococcus aureus (VRSA) strains have also arisen.
6. In what setting is VRSA most likely to first arise?
7. Predict what a Kirby-Bauer VRSA plate would look like.
8. What might the emergence of VRSA mean for future treatment of S. aureus?
Adapted from:
Leonard, M. (2012, December 3). Antibiotic Resistance: Can we ever Win? National
Center for Case Study Teaching in Science. Retrieved from
http://sciencecases.lib.buffalo.edu/cs/
References:
Chambers, H.F. & DeLeo, F. R. (2009). Waves of resistance: Staphylococcus aureus in
the antibiotic era. Nature Reviews: Microbiology, 7, 629-641. doi:
10.1038/nrmicro2200

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