Vancomycinresistant Staphylococcus aureus VRSA: A Michigan anomaly

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Vancomycin-resistant Staphylococcus aureus
(VRSA) A Michigan anomaly?

• James T. Rudrik, Ph.D.
• Microbiology Section Manager
• Bureau of Laboratories
• Michigan Department of Community Health
• rudrikj_at_michigan.gov
• 517-335-9641

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A History of Resistance

• Penicillin G - introduced in 1941
• Between 1942 and 1958 gt70 of all S. aureus
  isolates were resistant
• Methicillin - first penicillinase-resistant
  semisynthetic penicillin introduced in 1960
• Isoxazolyl Penicillins 1961 - Oxacillin,
  Cloxacillin, Dicloxacillin, Flucloxacillin
• Nafcillin 1961
• 1961 First report of naturally occurring
  Methicillin resistance

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Vancomycin

• Introduced in 1958
• Quickly replaced by other drugs
• Ototoxicity
• Nephrotoxicity
• Mississippi mud
• Resurrected as treatment for MRSA

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Prevalence of S. aureus

• 32 (89.4 million) and 0.8 (2.3 million) of U.S.
  population is colonized with S. aureus and MRSA,
  respectively
• Intensive care MRSA infections 2 in 1974, 22
  in 1995, 64 in 2004
• 292,000 hospitalizations for S. aureus infection
  annually, 126,000 related to MRSA
• 94,000 serious MRSA infections, 19,000 deaths,
  86 health-care associated, 14 community
  associated
• JID 2006193172-79, CID 200642389-91, EID
  200511868-72, JAMA 20072981763-771

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Vancomycin Resistance

• Enterococci rare until reported in large
  numbers from Europe and UK in late 1980s.
  Subsequent spread in US
• Alteration of peptidoglycan precursors that
  eliminate vancomycin binding site
• Potential for resistance in Staph, particularly
  MRS strains

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VRSA Cases
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VRSA Cases
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Infection Control Measures

• Enhanced Contact Precautions
• Single patient room
• Gown and gloves for each patient interaction
• Dedicated staff and equipment
• Masks with eye protection
• Thorough cleaning and disinfection
• Outpatient setting
• Dedicated room or separate area
• Last appointment of the day

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Summary

• Patient risks for acquiring VRSA
• Presence of MRSA
• Preceding vancomycin therapy
• VRE faecalis colonization
• Underlying conditions like chronic skin ulcers
  and diabetes
• Investigation identified no VRSA transmission
• IC measures appear adequate to prevent
  transmission

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Where did VRSA come from?Why are so many cases
in Michigan?

• All nine VRSA isolates are unique and occurred by
  independent genetic events
• Presence of VanA phenotype in S. aureus is the
  result of acquisition of genetic material from
  VRE

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Definitions

• Transposon Segments of DNA that can move around
  to different positions in the genome of an
  organism.
• May cause mutations
• jumping genes
• Plasmid - extrachromosomal DNA separate from the
  chromosomal DNA and capable of autonomous
  replication. In many cases, it is typically
  circular and double-stranded.
• May transfer between organisms

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Vancomycin resistance in Enterococci

• VanA mediated by Tn1546
• Carried on an Inc-18 type plasmid
• - Conjugative, broad-host-range plasmid

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Transfer of vanA from VRE to S. aureus
Dan Ferber. 2003. Science 3021488.
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Transfer of vanA from VRE to S. aureus
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VRSA Characteristics
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MI VRSA Characteristics
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Inc18-Type vanA Plasmids
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Results for VRE
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Summary

• Inc18-Like vanA plasmid associated with 5 of the
  7 MI VRSA cases
• Inc18-Like vanA plasmid
• Found more often in MI than other geographical
  locations
• Found more often in E. faecalis than other
  species of VRE
• No evidence of Inc18-type vanA plasmid in PA VRSA
• vanA plasmid is not Inc18-type in NY case