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Transcript of Case Study
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".
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.
Stands for "healthcare associated MRSA".
Refers to MRSA contracted in hospitals, nursing homes, etc. or by invasive procedures and related tools.
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?)
of S. aureus
wash and clean wounds
avoid skin-skin contact or other people's wounds
avoid sharing personal items
shower after exercising or visiting the beach
wounds that do not heal
fever and chills
deep, painful abscesses
shortness of breath
low blood pressure
Answer: c; MRSA or methicillin-resistant Staphylococcus aureus
symptoms, treatment, and prevention
Our patient is...
Swab and send to lab
cefoxitin disk screen test
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
Photo of patient's hand:
What does our patient have?
a) skin infection
e) none of the above
bacteria culture swab was taken and sent to the lab; the results:
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
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
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:
is an antibiotic.
Chemical Structure of Methicillin
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.
Diagram of how beta-lactams work
It's used to treat lung infections in children, bacterial infections in the mouth, and more! Rare side effect: convulsions.
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 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.
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.
Diagram of a Plasmid
Despite being resistant to many antibiotics, there are still treatment options available for MRSA patients:
draining of skin boils and abscesses
intravenous vancomycin doses
graphic photos ahead!
If your skin looks like this, GO SEE A DOCTOR!!
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
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
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
Cefoxitin disk screen test
staphylococcal cassette chromosome,
's method of transport
small segment of DNA
patient experiences: http://www.medicinenet.com/mrsa_infection/patient-comments-30.htm
video on antibiotics and resistance