Methicillin resistant S.aureus (MRSA)

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Methicillin resistant S.aureus (MRSA)
Dr Ritabrata Kundu Professor of
Pediatrics Institute of Child Health, Calcutta
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DEFINITIONS

• Staphylococcus aureus gram positive coccus.
• Resistant to penicillin by enzyme ? lactamase
  or penicillinase.
• Penicilllinase resistant penicillin like
  methicillin (MSSA).
• Methicillin resistant S. aureus (MRSA) by
  altering the penicillin binding protein
  (PBP2a).

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Characteristics of the ?-Lactam Ring
6-Aminopenicillanic acid
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Antibiotic inactivation due to enzymatic cleavage
of beta lactam ring by beta lactamase
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Modified penicillin binding protein (PBP) site
makes methecillin inactive
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Types of MRSA

• Nosocomial MRSA increasing prevalance
• Community acquired MRSA (CA MRSA)
• VISA Since 1996
• VRSA June 2002

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Pathogenesis

• S. aureus colonizes nares, axillae, vagina etc.
• Mucin appears to be the critical host surface.
• Spread by
• ? Direct contact with infected people.
• ? Indirect contact by touching contaminated
  object.
• ? Not through the air.
• Presence of foreign material or devices.

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Clinical presentation of CA MRSA

• Skin infections
• Bacteriocin
• High salt tolerance
• Panton-Valentine Leukocidin (PVL)
• Necrotising pneumonia
• Other presentation
• Toxic shock syndrome like illness
• Osteomyelitis
• Mediastinitis

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Furunculosis
Cellulitis
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Clinical Presentation of Nosocomial MRSA

• Pneumonia Ventilator associated pneumonia
  (VAP).
• Bacteremia 16 of all nosocomial bacteremias.
• Metastatic involvement of bones, jts, kidneys
  and lungs.
• Endocarditis.
• Surgical site infections (SSI).

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Risk factors for MRSA carriage

• Previous colonization (nasal/cutaneous)
• Age gt 60 yrs
• Exposure MRSA infected/colonized patient
• Host factors
• H/o ICU stay/surgery in last 5 yrs
• Prolonged hospital staygt21 days
• Open skin lesion
• Increased antibiotic exposure
• Chronic medical illness
• l Diabetes mellitus Type I
• l Patients on hemodialysis
• Impaired immune function
• AIDS
• Quantitative/Qualitative leukocyte dysfunction

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Why increased incidence of MRSA colonization?

1. Cephalosporine/Quinolines/? lactams are readily
   excreted in sweat.
2. CA MRSA carry small SCC mec type IV gene which
   grows and spreads faster.
3. Bacteriocins reduces other commonsel flora.
4. CA MRSA higher tolerance to salt helps to survive
   as skin flora.

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Susceptibility of MRSA
Nosocomial MRSA CA MRSA Multiresistant Sucep
libility to variety of non beta lactam
antibiotic Current antibiotic in use
Erythromycin Vancomycin Clindamycin Daflo
pristin-quinupristin Tetracycline Linezolid
Aminoglycosides Tigecycline (Tygacil) Cotrimoxa
zole Daptomycin Quinolones
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Non beta lactam antibiotics
Clindamycin Bacteriostatic, should not be used
treat serious infection. Inducibe
resistance. Rifampicin Should not be used
alone. Gentamycin Added for synergy. Ciproflox
acilin Not consistently associated with high
cure rate. Teicoplanin A derivative of
vancomycin.
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• Empirical antibiotic therapy for suspected
  staph. infection
• Prevalance of MRSA in the community.
• Presence/absence of health care associated risk
  factors.
• Severity and type of clinical presentation.

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Suggested initial empiric therapy with suspected
Staph. infection in pts with healthcare
associated risk factor
First line agents Second line
agents Severe infection Vancomycin Linezolid,
Quinupristin/ dalfopristin,
Daptomycin For empiric treatment add
penicillinase resistant penicillin Non
severe infection Penicillinase resistant Linezoli
d pencillin
Cotrimoxazole First generation
Clindamycin cephalosporine
Tetracycline Vancomycin
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Suggested initial empiric therapy with suspected
Staph. infection in pts. with out healthcare
associated risk factor
First line agents Second line
agents Severe infection Vancomycin Linezolid,
Quinupristin/ dalfopristin, Daptomycin
Penicillnase resistant
penicillin PLUS one of the following
Cotrimoxazole, Clindamycin, Te
tracycline Non severe infection Penicillinase
resistant Cotrimoxazole penicillin Clindamy
cin First generation Tetracycline
cephalosporine
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Infection Control Methods for Methicillin
Resistant Staphylococcus
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Institute of Child Health, Calcutta Golden
Jubilee Celebration 22-26 January 2006 Thanks and
warm welcome to all of you
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Prevent antimicrobial resistance at healthcare
settings

1. Prevent infection.
2. Diagnose and treat infections effectively.
3. Use antimicrobial wisely.
4. Prevent transmission decolonisation with
   mupirocin.