2. Contents
1. Introduction
2. Evolution of MRSA
3. Genetics of MRSA
4. How do you get MRSA?
5. MRSA statistics
6. Clinical manifestations
7. Diagnosis and treatment
8. Ongoing research
9. Prevention
3. 333
MRSA evolved into a notorious bug through the process of natural
selection.
INTRODUCTION
Methicillin Resistant Staphylococcus
aureus
Gram positive cocci in clusters
Phylum: Firmicutes
Normal flora of human skin and
respiratory tract
MRSA: resistant to beta-lactam antibiotics
ORSA: Oxacillin Resistant S. aureus
Scanning electron micrograph of a
human neutrophil ingesting MRSA
4. 444
The emergence of this super bacterium afforded a very costly lesson:
Bacteria have the ability to mutate!
EVOLUTION OF MRSA
5. 555
Different SCCmec genotypes confer different antibiotic resistance rates
to MRSA.
GENETICS OF MRSA
Staphylococcal cassette chromosome mec (SCCmec)
Genomic island containing mecA gene
Six genotypes of mec Right Extremity Junction (MREJ): types I – VI
MREJ types I – III: Hospital acquired MRSA
MREJ types IV and V: Community acquired MRSA
6. 666
PBP2a protein enables bacterial cell wall synthesis in the presence of
beta-lactam antibiotics.
GENETICS OF MRSA
mecA gene
Exogenous gene acquired by S. aureus
Encodes penicillin binding protein 2a (PBP2a)
Confers resistance to all beta-lactam antibiotics
7. 777
MRSA bacteria usually spread via skin-to-skin contact with someone
who has an MRSA infection or who is colonized by the bacteria.
HOW DO YOU GET MRSA?
Hospital associated MRSA infections (HA-MRSA)
Healthcare workers
Immunocompromised patients
Implanted medical devices
Surgical wounds or burns
Community associated MRSA infections (CA-MRSA)
Crowded environments
Misuse of antibiotics
Veterinarians, livestock handlers, and pet owners
Athletes and children
Contaminated beach waters
9. 999
CLINICAL MANIFESTATIONS
Skin and soft tissue infections (SSTI)
Boils
Entry of bacteria often through open
wounds
Usually develops as a painful bump
on the skin
Further develops into a pus-filled
swelling
Abscess
Larger pus filled lump develops
underneath the skin
Typical MRSA boil
Skin abscess caused by MRSA
10. 101010
SSTIs are generally picked up from the community.
CLINICAL MANIFESTATIONS
Skin and soft tissue infections (SSTI)
Impetigo
Bullous impetigo
Non bullous impetigo
Folliculitis and cellulitis
Extensive erythema and indurations
Itchy red spots that develop into sores
Infection of the hair follicles Infection of the deeper layers of skin on leg
11. 111111
If the MRSA penetrates into the deeper parts of the body or into the
blood, they can cause fatal infections.
CLINICAL MANIFESTATIONS
Invasive MRSA infections
Sepsis
Urinary tract infections
Endocarditis
Pneumonia
Septic bursitis
Septic arthritis
Osteomyelitis
Meningitis
Toxic Shock Syndrome
Symptoms: High fever, chills, general sense of feeling unwell, dizziness, muscular
aches, swelling and tenderness
www.cdc.gov/mrsa/
12. 121212
However, initial treatment of MRSA infection is often based on the
symptoms.
DIAGNOSIS OF MRSA
Standard culture (2-4 days)
Sub culturing on solid media
Oxacillin susceptibility test
Antibiotic sensitivity profile
Rapid latex agglutination test (15 mins)
Detection of a variant penicillin binding
protein (PBP2a)
Latex particles sensitized with a
monoclonal antibody against PBP2a
Mueller Hinton Agar showing MRSA
resistant to oxacillin disc
Positive test: Visible agglutination
13. 131313
DIAGNOSIS OF MRSA
Conventional gel based PCR
Target gene: mecA-femB
Requires culturing of MRSA
Real time multiplex PCR
Target gene: SCCmecA
genomic island
Detection from direct
specimens
www.indmedica.com
14. 141414
TruArray MRSA still awaits the FDA approval for its use in diagnostics.
DIAGNOSIS
TruArray MRSA: Akonni Biosystems (4 hrs)
Direct detection from nasal swabs
Polymerase Chain Reaction (PCR)
Fluorescent labelling of SA/MRSA DNA
15. 151515
The decolonization treatment does not require hospitalization.
TREATMENT
Screening for MRSA: Swab test
Before or after hospitalization of a patient
Before a planned surgery or Caesarean section
MRSA positive patients Strict isolation
Suppression or decolonization treatment
Skin - Antibacterial body wash or powder
Nose – Antibacterial nasal cream
Scalp – Antibacterial shampoo
Decolonization regimen: daily for 5 consecutive days
16. 161616
Once established, MRSA invasive infections are often incurable, even
when appropriate antibiotics are used.
TREATMENT
Skin and soft tissue infections
Boils or abscesses: incision and drainage
Folliculitis or cellulitis: Antibiotic course (5-10 days)
Surgical wounds or burns: Antibiotic course (7-14 days)
Invasive MRSA infections
Combination of two or more antibiotic injections (approximately 6 weeks)
Routinely prescribed antibiotics
HA-MRSA: vancomycin, teicoplanin, linezolids, daptomycin, quinpristin-
dalfopristin, tigecycline and fifth generation cephalosporins
CA-MRSA: co-trimaxazole, tetracyclines and clindamycin
Vancomycin Intermediate-resistant Staphylococcus aureus (VISA)
17. 171717
ADEP-antibiotic drug combination and super antigen based vaccines
generate hope for complete sterilization in MRSA infections.
ONGOING RESEARCH
Nature (November 2013)
Professor Kim Lewis (Boston)
Combination of conventional antibiotics with acyldepsipeptide
(ADEP)
Journal of Infectious Diseases (December 2013)
Microbiologist Patrick Schlievert (Iowa)
Super antigen based vaccines for MRSA studied in rabbits
Awaits FDA approval for clinical trials
18. 181818
Hospital staffs should maintain very high standards of hygiene and
take extra care when treating patients with MRSA.
PREVENTION
HA-MRSA
Effective hand washing technique
Regular cleaning of patient areas
with antibacterial solutions
Use of disposable gloves
Isolation of MRSA positive patients
Strictly minimal transfer of patients
between wards
19. 191919
SPREAD THE WORD! NOT THE GERMS!
PREVENTION
CA-MRSA
Regular hand wash & frequent
showers
Short and clean fingernails
Do not share personal items
Cover wounds with a dressing
