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Case Study

All about something.
by

Caroline Bay

on 9 May 2014

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Transcript of Case Study

Case Study No. 9:
Definition
MRSA is caused by a strain of antibiotic resistant staph bacteria, Staphylococcus aureus.

It was first identified in 1960.

Outbreaks have been frequent, occurring in 1980s-1990s and 1998-2008.

There are two types of MRSA.

Known as a "SUPERBUG".
CA-MRSA
Stands for "community associated MRSA".

Usually spreads via skin-to-skin contact.

Commonly contracted at schools, gyms, prisons, military barracks, and other close quarter situations.
HA-MRSA
Stands for "healthcare associated MRSA".

Refers to MRSA contracted in hospitals, nursing homes, etc. or by invasive procedures and related tools.
Antibiotics
Antibiotics are chemical substances that are produced by one organism and are destructive to another. They are usually derived from mold or synthetically created.

Antibiotics are only effective against bacteria, not viruses.

There are two main types of antibiotic: broad spectrum and narrow spectrum.

Broad spectrum antibiotics can target a wide variety of bacteria, no matter the bacteria's composition.
How does bacterial resistance develop?
(How did S. aureus get a hold of the mecA gene?)
Bacterial resistance
of S. aureus
Prevention
good hygiene

wash and clean wounds

avoid skin-skin contact or other people's wounds

avoid sharing personal items

shower after exercising or visiting the beach
Symptoms
chest pain
wounds that do not heal
fever and chills
deep, painful abscesses
boils, styes
rash
shortness of breath
low blood pressure
Answer: c; MRSA or methicillin-resistant Staphylococcus aureus
symptoms, treatment, and prevention
the biology
Our patient is...
Diagnosis:
Bacterial culture:
Swab and send to lab
blood agar
cefoxitin disk screen test

DNA testing:
nasal swab

Blood testing:
BD GeneOhm Staph SR assay
latex agglutination test
male, 23 years old
no existing health conditions
frequent gym use and attends large college
relatively poor hygiene
developed large pimple on hand a week ago
swelling, pain, pus has not decreased
graphic photo ahead

source: http://depts.washington.edu/hivaids/derm/case6/
Photo of patient's hand:
What does our patient have?
a) skin infection
b) HIV/AIDS
c) MRSA
d) ebola
e) none of the above
bacteria culture swab was taken and sent to the lab; the results:
source: http://www.reuters.com/article/2008/07/03/us-mrsa-idUSPAT36934720080703
i.e. tetracyclines (can treat urinary tract infections to pneumonia) and fluoroquinolones (can treat acne to stomach ulcers to gonorrhea)
Narrow spectrum antibiotics target only specific types of bacteria.
i.e. β-lactams inhibit the bacteria cell wall, which is lethal to the bacteria
includes the penicillin antibiotic group
includes ampicillin, amoxicillin, etc.

penicillin is the go-to drug to treat staph infections
source: http://www.bacteriainphotos.com/Staphylococcus%20aureus%20electron%20microscopy.html
image of S. aureus at 10,000x magnification
With MRSA, the bacteria is resistant to methicillin and most other β-lactam antibiotics.

It has developed a resistance to β-lactams by receiving the
mecA
gene.

mecA
is an extra gene that S. aureus uses to produce PBP2a, or penicillin binding protein 2a, a modified shape of original, wild-type PBP.

Methicillin and other β-lactams cannot bind to PBP2a because of PBP2a's low affinity for β-lactams, rendering the antibiotics useless.
true or false:
Phenoxymethylpenicillin
is an antibiotic.
Chemical Structure of Methicillin
source: http://www.rpi.edu/dept/chem-eng/Biotech-Environ/IMMOB/penicillin/penstart.htm
source: http://labrat.fieldofscience.com/2010/08/nanofibre-paint-that-kills-mrsa.html
Diagram of S. aureus bacterial cell wall
How do β-lactams work?
Bacterial cell walls are crucial for survival.
structure, protection against osmotic rupture
made of peptidoglycan (single or interlocking)

Antibiotics inhibit the bacteria's biosynthesis of peptidoglycan by binding to penicillin binding proteins (PBP).

Without peptidoglycan, the bacteria cannot grow and divide and the cell wall is weakened.

The inhibited bacteria die and the infection ceases.
source: https://figures.boundless.com/10149/raw/penicillin-inhibition.svg
Diagram of how beta-lactams work
A: true
It's used to treat lung infections in children, bacterial infections in the mouth, and more! Rare side effect: convulsions.
Any guesses?
Vertical Transmission
Vertical transmission is essentially natural selection with bacteria.

Beneficial mutations get passed down from parent to offspring to offspring's offspring, etc.

i.e. developing a mutation of resistance to penicillin
Horizontal Transfer
Horizontal transfer is the transferring of bits of DNA between bacteria.

These bits are called "plasmids".

Bacteria do not have to be related to share DNA.

Plasmids can easily be incorporated into the recipient's genome.
source: http://evolution.berkeley.com
Diagram of Horizontal Transfer
Furthermore, plasmids carry multiple genes so they can have the genetic coding for resistance to amoxycillin, methicillin, and common disinfectants.

Horizontal transfer speeds up the evolution of antibiotic resistance and encourages multiply-resistant strains.
source: http://evolution.berkeley.edu
Diagram of a Plasmid
source: http://mrsa-research-center.bsd.uchicago.edu/images/Cartoon_antibioticresistance_joke.jpg
Treatment
Despite being resistant to many antibiotics, there are still treatment options available for MRSA patients:

draining of skin boils and abscesses
intravenous vancomycin doses
linezolid
trimethoprimsulfamethoxazole
doxycycline
clindamycin
graphic photos ahead!
If your skin looks like this, GO SEE A DOCTOR!!
Prognosis
prognosis of good to poor depending on site and severity of infection

MRSA pneumonia and sepsis has 80% survival rate

20-40% chance of recurring infection
SCCmec
source: http://www.cdc.gov/mrsa/images/Abscess-prison_lg.jpg
source: http://blogs.plos.org/publichealth/files/2013/03/mrsa-finger-300x225.jpg
source: http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/health_tools/MRSA_revised_slideshow/webmd_rm_photo_of_spiderbite_and_mrsa.jpg
source: http://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/articles/health_tools/MRSA_revised_slideshow/princ_rm_photo_of_infected_hands.jpg

But you already might have MRSA.
colonization: the presence of bacteria, but no signs of illness or infection

1-2% of the population carry MRSA on their skin or in their nose
sources:
MRSA kills at least 19,000 Americans each year.

2007: 94,000 life-threatening infections
more photos: http://www.cdc.gov/mrsa/community/photos/index.html
DNA Sequence of mecA gene
source: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19712
Cefoxitin disk screen test
sources: http://www.bacteriainphotos.com/bacteria%20under%20microscope/mrsa%20electron%20microscopy.html
staphylococcal cassette chromosome,
mecA
's method of transport
small segment of DNA
four types
patient experiences: http://www.medicinenet.com/mrsa_infection/patient-comments-30.htm
http://www.medicalnewstoday.com/articles/216798.php
http://www.textbookofbacteriology.net/structure_5.html
http://biology.clc.uc.edu/courses/bio106/bacteria.htm
http://www.britannica.com/EBchecked/topic/1522060/methicillin
http://www.niaid.nih.gov/topics/antimicrobialresistance/examples/mrsa/Pages/default.aspx
http://www.medicinenet.com/script/main/art.asp?articlekey=84984
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0004520/
http://health.howstuffworks.com/medicine/medication/question88.htm
http://www.madehow.com/Volume-4/Antibiotic.html
http://www.mayoclinic.org/healthy-living/consumer-health/in-depth/antibiotics/art-20045720?pg=2
http://www.medicinenet.com/mrsa_infection/article.htm
http://www.health.ny.gov/diseases/communicable/staphylococcus_aureus/methicillin_resistant/community_associated/fact_sheet.htm
http://www.netdoctor.co.uk/infections/medicines/penicillin-v.html
http://www.vdh.virginia.gov/Epidemiology/Surveillance/MRSA/#ColonizationvsInfection
http://www.acep.org/Clinical---Practice-Management/Rapid-MRSA-Blood-Test-Gets-Green-Light-From-FDA/
http://www.webmd.com/news/20080102/fda-oks-1st-quick-mrsa-blood-test
http://science.howstuffworks.com/environmental/life/cellular-microscopic/question561.htm
http://mrsa-research-center.bsd.uchicago.edu/lab_researchers/faq.html
http://www.tufts.edu/med/apua/about_issue/about_antibioticres.shtml
http://www.ncbi.nlm.nih.gov/pubmed/12389036
http://www.nlm.nih.gov/medlineplus/ency/article/003334.htm
http://www.uptodate.com/contents/rapid-detection-of-methicillin-resistant-staphylococcus-aureus
http://www.microbelibrary.org/component/resource/laboratory-test/3189-kirby-bauer-disk-diffusion-susceptibility-test-protocol
http://evolution.berkeley.edu/evolibrary/news/080401_mrsa
http://blogs.plos.org/publichealth/2013/03/05/drug-resistance-in-mrsa-is-finely-tuned/
http://evolution.berkeley.edu/evolibrary/article/medicine_03
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/IMMOB/penicillin/penstart.htm
http://www.webmd.com/skin-problems-and-treatments/news/20071016/more-us-deaths-from-mrsa-than-aids

Journal articles:
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19712
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2772621/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC139644/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2065735/
video on antibiotics and resistance
Full transcript