This document summarizes information about methicillin-resistant Staphylococcus aureus (MRSA), including its evolution, genetics, transmission, clinical manifestations, diagnosis, treatment, ongoing research, and prevention. MRSA evolved through natural selection to become resistant to beta-lactam antibiotics. It carries a genetic element called SCCmec that confers this resistance. MRSA can cause a range of infections through skin-to-skin contact and spread in both healthcare and community settings. Diagnosis involves culture and identification of the mecA gene which encodes resistance. Treatment depends on the site and severity of infection, utilizing antibiotics like vancomycin or decolonization regimens. Ongoing research explores new drug combinations

1. Scourge of MRSA
Divya Mathew
Friday, 21st
February 2014

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

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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

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The emergence of this super bacterium afforded a very costly lesson:
Bacteria have the ability to mutate!
EVOLUTION OF MRSA

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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

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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

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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

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MRSA STATISTICS
 AIIMS report on MRSA

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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

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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

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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/

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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

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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

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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

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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

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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)

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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

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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

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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

20. Thank You!