MRSA - Infectious agent

1. MRSA
METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS
Figure 1. Methicillin-resistant Staphylococcus aureus bacteria (MRSA) under a
scanning electron microscope

2. Domain Bacteria
Kingdom Eubacteria
Phylum Firmicutes
Class Bacilli
Order Baciallales
Family Staphylococcaceae
Genus Staphylococcus
Species Staphylococcus aureus
Sub Species Methicillin-resistant
Staphylococcus aureus
Taxonomy
Figure 2. Example of a phylogenetic tree for MRSA

3. Structure
• Gram positive spherical bacterium
• Yellow in colour
• Forms grape like clusters as the cell division
happens in multiple planes
• Has a cell wall of peptidoglycan that contains
multiple glycine residues
• No Flagella making the organism immobile
Figure 3. Staph. aureus

4. Metabolism
• Can uptake a number of nutrients including
glucose, mannose, mannitol, sucrose, lactose
and others.
• Uses aerobic respiration or fermentation which
produces lactic acid for energy production
• Due to the production of products such as lactic
acid, Mannitol Salt Agar can be used as a selective
medium
Figure 4. Staph Epidermidis On Mannitol Salt Agar

5. • MRSA is resistant to beta-lactam antibiotics due to
the process of natural selection.
• Resistance makes MRSA infection more difficult to
treat with standard antibiotics which makes it more
dangerous.
• As it is frequently in contact with humans it can show
resistance to a growing number of therapies.
• mecA is the gene responsible for resistance to beta-
lactam antibiotics
Resistance to antibiotics
Figure 5. A zone of Inhibition is evident around the
oxacillin disk for S. aureus, left, but not for
Methicillin-resistant S. aureus (MRSA), right.

6. MRSA evades the immune system by:
• Expressing cell surface toxins
• Secretes proteins that inactivate complement cascade
• Bind and inactivate antibodies and reduce effectiveness
• Neutrophil chemotaxisis
• Inhibiting opsonisation
• Neutralizing antimicrobial peptides

7. Why does MRSA spread easily in hospitals?
MRSA is easily spread by skin to skin contact with somebody infected with the organism, as well
as coming into contact with carrier material (e.g. towel)
In hospitals patients are more at risk due to
◦ Weakened immune system
◦ Frequent catheter insertions
◦ Use of a ventilator
Contributing factors in hospitals
◦ Overcrowding, Understaffing, movement of patients from ward to ward, Failure to discharge
elderly patients back into the community
Figure 6. The Unknown Killer: MRSA

8. • MRSA is one of the most common hospital acquired
infections
• In healthy humans it is an inhabitants the skin and
mucous membranes in the nose
• Approx. 30% of normal healthy population is infected
with S. aureus as it can asymptotically colonize the skin
of human hosts
• If a break in the skin occurs it can allow the bacterium
to enter the wound and cause an infection
Figure 7. The Unknown Killer: MRSA

9. Figure 1. Methicillin-resistant Staphylococcus aureus bacteria (MRSA) under a scanning electron
microscope (2013) [Image] At: www.naturesalternativepdx.com (Accessed on 27/10/2015)
Figure 2. Example of a phylogenetic tree for MRSA (2008) [Image] At:
http://bioweb.uwlax.edu/bio203/s2008/seubert_heid/Classification.htm (Accessed on 27/10/2015)
Figure 3. Staph. aureus (2013) [Image] At: https://www.studyblue.com/notes/note/n/mis-study-
guide-2013-14-professor/deck/8688414 (Accessed on 27/10/2015)
Figure 4. Staph Epidermidis On Mannitol Salt Agar (2015) [Image] At: http://imageck.com/19916552-
staph-epidermidis-on-mannitol-salt-agar.html (Accessed on 27/10/2015)
Figure 5. A zone of Inhibition is evident around the oxacillin disk for S. aureus, left, but not for
Methicillin-resistant S. aureus (MRSA), right. (2006) [Image]
http://www.antimicrobialtestlaboratories.com/Zone_of_Inhibition_Test_for_Antimicrobial_Activity.ht
m (Accessed on 27/10/2015)

10. Figure 6. The Unknown Killer: MRSA (2012) [Image] At:
https://www.behance.net/gallery/3997835/Infographic (Accessed on 27/10/2015)
Figure 7. The Unknown Killer: MRSA (2012) [Image] At:
https://www.behance.net/gallery/3997835/Infographic (Accessed on 27/10/2015)