MRSA and VRSA in the Hospital Environment

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MRSA and VRSA in the Hospital Environment
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http//www.sanger.ac.uk/Info/Press/gfx/040624_stap
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What are MRSA, VRSA and VISA

• MRSA refers to methicillin/oxacillin resistant
  Stapylococcus aureus
• VRSA refers to vancomycin resistant S. aureus
  which require 32µg/mL for inhibition
• VISA refers to vancomycin intermediate S. aureus
  which require 16µg/mL

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Bacteriological Characteristics of MRSA and VRSA
S. aureus

• Gram cluster forming coccus
• Nonmotile, nonsporeforming facultative anaerobe
• Catalase and usually Coagulase
• Pathogens of humans, and causes a wide range of
  pus forming infections
• Resistant to penicillins, cephalosporins, and
  vancomycin

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Pathogenesis of MRSA and VRSA

• Important cause of Hospital acquired infections
• Pneumonia
• Surgical wound infections
• Bloodstream infections
• Urinary tract infections

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Virulence Factors

• MRSA, VRSA, and VISA share all of the same
  virulence factors with antibiotic susceptible S.
  aureus.
• Additionally, VISA strains show longer doubling
  times and reduced autolytic activities
• VRSA and MRSA produce penicillin binding proteins
  2 and 2
• Reduced cross linking in cell walls through
  glutamine amidation.

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Risk Groups

• People in the healthcare setting with weakened
  immune systems
• HIV patients
• Elderly
• Infants
• Post Surgical patients
• Dialysis patients

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MRSA History

• Emergence of Resistance to penicillin in 1948
• Emergence of Resistance to Methicillin 1961
• Both occurred a few years after the introduction
  of the antibiotics

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VRSA and VISA History

• The First VISA(Vancomycin intermediate) infection
  occurred in 1997 in Michigan
• To Date 16 VISA cases have occurred in the United
  States
• First VRSA case Michigan in 2002
• Only 6 cases have been reported in the United
  States (3 in Michigan)

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Antibiotic Resistance Acquisition

• MRSA resistance come from the mecA gene found on
  a mobile genetic element stapyloccal cassette
  chromosome mec SCCmec
• Emerged has emerged in five phylogenetically
  distinct lineages
• Origin is unknown and SCCmec is found in no other
  bacteria other than staphylococci
• Hypothesized mecA acquistion was acquired through
  horizontal transfer with other Gram genera

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Antibiotic Resistance Acquisition

• VRSA strains resistance comes from the vanA gene
  on a transposable element (TN1546) carried on a
  plasmid
• Likely transferred from Vancomycin-resistant
  enterococci

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Antibiotic Resistance Acquisition

• VISA strains have thicker than usual cell walls
  which may deplete the vancomycin available (not
  mediated by vanA)
• Acquired through mulitple mutations
• Cell wall synthesis
• Increased uptake of nutrients
• Flow of metabolites

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MRSA in Dialysis patients

• 5,287 cases of invasive MRSA cases reported by
  the Active Bacterial Core Surveillance in 2005
• 813 in dialysis patients with 45.2 cases per
  1000 patients
• 70 of infections in those age 50 or greater
• 86 Bloodstream infections
• 17 mortality rate

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Methicillin (oxacillin)-resistant Staphylococcus
aureus (MRSA) Among ICU Patients, 1995-2004
Source National Nosocomial Infections
Surveillance (NNIS) System
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MRSA Cases by Infection Type

• 3

12 Minnesota Clinics obtained 937 samples of MRSA
(median age 68) 37 Soft tissue or skin
infections 22 Respiratory tract 20 Urinary
Tract 9 Bloodstream 1 Otitis 11 Other
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VRSA Incidence and Epidemiology

• Only 6 cases have been reported in the United
  states as of 2005
• Because of this little epidemiology data is
  available for analysis
• The incidence of VRE has increased over the past
  decade

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Vancomycin-resistant Enterococi Among ICU
Patients, 1995-2004
Source National Nosocomial Infections
Surveillance (NNIS) System
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What is Being Done?
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Data Collection and Statisical Analysis

• CDCs National Healthcare Safety Network (NHSN),
  monitors Healthcare-associated infections in 300
  hospitals
• CDCs Dialysis Surveillance Network(DSN)
• Active Bacterial Core Surveillance(ABCs) System
• From 2003-present, invasive MRSA infections are
  monitored in nine sites across the United States
  currently participate in the ABCs MRSA
  surveillance, representing a population of about
  16.3 million persons.

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Standard Prevention
Gowning
Washing
Patient Isolation
Gloving
Masking
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Treatment of MRSA

• Vancomycin and two newer antimicrobial agents,
  linezolid and daptomycin
• Skin infections may be treated with incision and
  drainage

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Treatment of VRSA

• Responds to a few FDA approved drugs but testing
  must be done to check for the best response.
• rifampin, gentamicin, imipenem, chloramphenicol,
  trimethoprim-sulfamethoxazole, and tetracycline.

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CA-MRSA

• Community acquired MRSA
• Those who havent been hospitalized in the past
  year or had a medical procedure performed i.e.
  dialysis
• Usually manifest in otherwise healthy people as
  pimples or boils
• Median age 23
• More commonly have Panton-Valentine leucocidin
  gene than its hospital acquired counterpart,
  which can cause a cytotoxin that causes leukocyte
  destruction and tissue necrosis

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References

• Todar, K. Staphylococcus Todars Online
  Textbook of Bacteriology. http//www.textbookofba
  cteriology.net.
• Massachusetts Department of Public Health
  Division of Epidemiology and Immunization.
  STAPHYLOCOCCUS AUREUS withRESISTANCE TO
  VANCOMYCIN(VISA/VRSA) Infection Control
  Guidelines for Long-Term Care Facilities.
  http//www.mass.gov/dph/cdc/epii/ltcf/visaguide.pd
  f. 2001.
• What is the CDC doing about MRSA?
  http//www.cdc.gov/ncidod/dhqp/ar_mrsa_CDCactions.
  html. 2006.
• VISA/VRSA Vancomycin-Intermediate/Resistant
  Stapyloccus aureus.
• http//www.cdc.gov/ncidod/dhqp/ar_visavrsa.html.
  2006
• CDC. Information about MRSA for the Healthcare
  Personnel. http//www.cdc.gov/ncidod/dhqp/ar_mrsa_
  healthcareFS.html. 2004.
• Tenover, Fred C., Biddle, James W., and
  Lancaster Michael V. Increasing Resistance to
  Vancomycin and Other Glycopeptides in
  Staphylococcus aureus. Emerging Infectious
  Diseases. 72. 2001.
• Timothy S. Naimi Kathleen H. LeDell Kathryn
  Como-Sabetti Stephanie M. Borchardt David J.
  Boxrud Jerome Etienne Susan K. Johnson
  Francois Vandenesch Scott Fridkin Carol
  O'Boyle Richard N. Danila Ruth
  LynfieldComparison of Community- and Health
  Care-Associated Methicillin-Resistant
  Staphylococcus aureus InfectionJAMA 2003 290
  2976-2984
• Stapylococcus aureus Resistant to Vancomycin ---
  United States, 2002. MMRW Weekly. 51(26)
  565-567 2002.
• Robinson, Ashley and Enright, Mark. Evolutionary
  Models of the Emergence of Methicillin-Resistant
  Stapylococcus aureus. Antimicrobial Agents and
  Chemotherapy. 47(12) 3926-3934. 2003.