Lecture 4 Vancomycin resistance VRE VISA / hVISA / VRSA

1. Lecture 4Vancomycin resistanceVREVISA / hVISA / VRSA Thursday – 1/17/2008

2. Enterococcus • Gr+ Cocci (in chains). • Two species infecting human: E. faecium and E. faecalis. • Initially considered harmless GI commensal. • Infection typically follows GI colonization. • Low pathogenicity • Yet, can cause high mortality in patients with bacteremia.

3. Enterococcus infections • E. faecalis vs. E. faecium • Nosocomial infections, mostly in debilitated patients • Common cause of nosocomial urinary tract infection • Currently 3rd leading cause of bloodstream infections. • Serious complication: endocarditis

4. Nosocomial transmission • Mode of transmission: • HCW • Environmental sources (medical devices) • Carriage: • GI tract • Duration: months - years

5. Enterococcus and antibiotic resistance • Enterococci intrinsically resistant to various antimicrobial classes • Low level aminoglycoside (low ability to penetrate cell wall) • Relative resistance to β-lactams (Cephalosporines + penicillin) (PBP5) • macrolides (low level) • TMP-SMX • Acquire high level antibiotic resistance through horizontal transfer of relevant genes. • 1980’s: emergence of beta-lactam and high gentamycin resistance. • 1986 fist report of VRE in Europe, 1989 first report in US. • Currently: alarming situation in US hospitals, rare in Europe

6. Glycopeptidesvancomycin, teicoplanin, telavancin • Antibiotic class used to treat Gram positive bacteria. • Mode of action: disruption of peptidoglycan polymerization • Bind to the amino-acids within the cell wall. (D-ala-D-ala). • Prevent the addition of new units to the peptidoglycan.

7. VRE - mechanism of resistance • Modifying enzymes • Degrading enzymes • Target Change • Efflux pumps

8. Cell wall synthesis in enterococci:

9. VanA operon Mechanism of resistance • Operons that encode enzymes for • synthesis of low-affinity precursors (D-ala-D-lac vs. D-ala-D-ala). • Elimination of normal high-affinity precursors (removing the vancomycin-binding target) • Operon encoded on a transposon

10. Glycopeptide resistance gene operons: vanA-vanE and vanG • Enterococci – acquisition of VanA, B, D, E and G phenotypes. • VanC – affords intrinsic resistance, and is chromosomal (arises in less virulent enterococci). • VanD, E, G: reported only sporadically. • VanC and VanE: D-Ala-D-Ser • VanA & VanD:resistant to vancomycin + teicoplanin. • VanA & VanB: most common • The phenotype is accomplished by multiple proteins in gene clusters.

11. The vanA gene cluster vanA(ligase) and vanH(dehydrogenase) are responsible for the synthesis of the modified depsipeptide (D-Ala-D-Lac). vanX(D,D-Dipeptidase) and vanY (D,D-Carboxypeptidase) cleave normal peptidoglycan substrates. Adapted from Courvalin et al. 2006

12. VanA type: inducible high levels of vanco-R and teicoplanin-R (Tn1546) • VanH- dehydrogenase (pyruvate->lactate) • VanA- ligase catalyses bond of D-Ala-D-Lac. • VanXandVanY- remove c-terminal D-Ala to eliminate normal precursor • VanB different in its regulation (and no vanZ, additional vanW - function unknown).

13. Mutation Plasmid transfer Transformation Genetic Mechanisms of Resistance Acquisition

14. Genetic Mechanisms of VRE • Resistant genes clustered in operons • Operons located on transposons • Transposons transmitted • Directly to chromosome • via plasmids

15. A small mobile genetic element (6625 bp) More mobile than a plasmid Plasmids that carry Tn1546 - highly efficient conjugative plasmids (~65 Kbp) Rapid spread of VRETn1546 Transposon (vanA)

16. Virulence genes associated with VRE Enterococcal surface protein variant (esp) hylEFM

17. Variant esp gene (esp- / espEfm) enterococcal surface protein • Enhanced adherence • Associated with hospital infections (VREF-100% and VSEF~50%). • Prevalent in E. faecalis strains related with infections. • Absent in community isolates. • Not more virulent in mouse model.

18. Another virulent factor: hylEfm • Significant identity with hyaluronidase genes • Hyaluronidase: a virulent factor in S. aureus, S. pneumoniae, GAS • Predominant in VREF strains • Associated with espEfm

19. Epidemiology of VRE infections

20. Prevalence of VRE among enterococci in nosocomial infections in ICU patients Bonten et al. Lancet Infect. Dis. 2001

21. E. faecium Rare, but emerging cause of infection (15% ->~30%) Most (>90%) are VRE (VREF) Colonization of hospitalized patients 1.5%-32% E. faecalis Common cause of infection (>90% ->70%). But most not VRE. Vancomycin-resistant enterococci (VRE)

22. 1986 - first case. Uncommon as nosocomial infection (<3%) only sporadic outbreaks Widely prevalent in European livestock and in healthy people in the community Inciting factor: animal use of glycopeptides Avoparcin as a growth factor since 1970s, banned in 1997. 1989 – first case. Epidemic spread: Small outbreaks Northeast -> West coast By 1995 – high endemicity in ICUs. Community reservoir – absent. Inciting factor: use of oral vancomycin. VRE: European vs. US epidemiology EuropeUSA

23. Sporadic nosocomial outbreaks. Highly prevalent in healthy humans and livestock. ‘Non-epidemicstrains’. Do not have esp gene. Endemic in US ICUs No community reservoir ‘Epidemic strains’. Contain esp gene. VRE: European vs. US epidemiology EuropeUSA

24. Vancomycin use in US vs. Europe Bonten et al. Lancet Infect. Dis. 2001

25. Bloodstream isolates of VREFSENTRY antimicrobial surveillance program Deshpande et al. Diag. Microbiol. Infect Dis. 2007

26. Genetic capitalism (the rich become richer)The success of a highly adaptive clone. Leavis et al. Curr. Opion. Microbiol 2006

27. Emergence of CC17 in the Netherlands / Top et al. JCM 2008 Is the European epidemic following the US epidemic in a 10 y delay?

28. Patient colonization GI tract Groin Skin Colonization pressure Number/density of colonized patients Admission/transfer of colonized patients Proximity of colonized patients Shared care givers Contaminated environment Stethoscopes/ BP cuffs, etc.. Antibiotic pressure Vanco Cephalosporins Antianaerobic Bacterial virulence factors esp gene Factors influencing VRE spread:

29. Suggested strategies for IC of VRE /Bonten et al. Lancet Infec Dis 2001

30. Infection Control and/or Ab control • When not clonal spread, strict IC - not efficient. • Then probably resriction of Ab classes but which? • Studies show: RF for VRE: • Vancomycin (IV - controversial) • Extended-spectrum cephalosporin • Other B-lactam-B-lactam inhibitors (controversial which) • Anti-anaerobic regimens.

31. Vancomycin resistant S. aureus (VRSA) Vancomycin intermediate S. aureus (VISA, hVISA)

32. Vancomycin resistance in S. aureus VISA (vancomycin intermediate S. aureus) • First case 1996 • MIC 4-8µg/ml • Thick cell wall(reduces vanco penetration through cell wall). • Accumulates multiple mutations that activate pathways for cell wall synthesis & change cell physiology • High fitness cost

33. hetero-VISA (hVISA) • hVISA (hetero-VISA) • Appear to be susceptible, but consists of subpopulations that have MIC≥4µg/ml • Difficult to detect.

34. VRSA - yet a very rare event • 2002 Michigan – 1st case vanA mediated since then 6 more cases. • vanA resistance in VRSA rare, most occurred in the same geographical area (Michigan) • Only very few descriptions of vanA gene cluster in MRSA, though in lab – years ago it was demonstrated. • Gene cluster found on a plasmid-specified transposon (Tn1546)

35. Currently most worrisome: • Concomitant carriage of VRE and MRSA is increasing.