History and biology
To become vancomycin-resistant, vancomycin-sensitive enterococci typically obtain new DNA in the form of plasmids or transposons which encode genes that confer vancomycin resistance. This acquired vancomycin resistance is distinguished from the natural vancomycin resistance of certain enterococcal species including E. gallinarum and E. casseliflavus.
High-level vancomycin-resistant E. faecalis and E. faecium are clinical isolates first documented in the 1980's. In the United States, vancomycin-resistant E. faecium was associated with 4% of healthcare-associated infections reported to the Centers for Disease Control and Prevention National Healthcare Safety Network from January 2006 to October 2007. VRE can be carried by healthy people who have come into contact with the bacteria, usually in a hospital (nosocomial infection), although it is thought that a significant percentage of intensively farmed chicken also carry VRE. Other regions have noted a similar distribution, but with increased incidence of VRE. For example, a 2006 study of nosocomial VRE revealed a rapid spread of resistance among enterococci along with an emerging shift in VRE distribution in the Middle East region, such as Iran. Treatment failures in enterococcal infections result from inadequate information regarding glycopeptide resistance of endemic enterococci due to factors such as the presence of VanA and VanB. The study from Iran reported the first case of VRE isolates that carried VanB gene in enterococcal strains from Iran. This study also noted the first documented isolation of nosocomial E. raffinosus and E. mundtii in the Middle East region. 
Mechanism of acquired resistance
Six different types of vancomycin resistance are shown by enterococcus : Van-A, Van-B, Van-C, Van-D, Van-E and Van-G. The significance is that Van-A VRE is resistant to both vancomycin and teicoplanin, Van-B VRE is resistant to vancomycin but susceptible to teicoplanin, and Van-C is only partly resistant to vancomycin, and susceptible to teicoplanin.
The mechanism of resistance to vancomycin found in enterococcus involves the alteration of the peptidoglycan synthesis pathway. The D-alanyl-D-lactate variation results in the loss of one hydrogen-bonding interaction (four, as opposed to five for D-alanyl-D-alanine) being possible between vancomycin and the peptide. The D-alanyl-D-serine variation causes a six-fold loss of affinity between vancomycin and the peptide, likely due to steric hindrance.
Treatment of infection
Cephalosporin use is a risk factor for colonization and infection by VRE, and restriction of cephalosporin usage has been associated with decreased VRE infection and transmission in hospitals. Lactobacillus rhamnosus GG (LGG), a strain of L. rhamnosus, was used successfully for the first time to treat gastrointestinal carriage of VRE. In the US, linezolid is commonly used to treat VRE.
- Antibiotic resistance
- Drug resistance
- Methicillin-resistant Staphylococcus aureus (MRSA)
- "Vancomycin-resistant Enterococci (VRE) in Healthcare Settings". VRE in Healthcare Settings - HAI. CDC. Retrieved 2015-06-09.
- Gould, Dinah; Brooker, Christine (2008-08-20). Infection Prevention and Control: Applied Microbiology for Healthcare. Palgrave Macmillan. ISBN 9781137045928.
- "VRE and the Clinical Laboratory - HAI". Healthcare-associated Infections. CDC. Retrieved 2015-06-09.
- Robinson, D. Ashley; Feil, Edward J.; Falush, Daniel (2010-03-16). Bacterial Population Genetics in Infectious Disease. John Wiley & Sons. ISBN 9780470600115.
- Hidron AI, Edwards JR, Patel J, et al. (November 2008). "NHSN annual update: antimicrobial-resistant pathogens associated with healthcare-associated infections: annual summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2006-2007". Infect Control Hosp Epidemiol 29 (11): 996–1011. doi:10.1086/591861. PMID 18947320.
- "Diseases and Organisms in Healthcare Settings". Healthcare-associated Infections (HAIs). CDC. Retrieved 2015-06-09.
- Kouchak, Farideh; Askarian, Mehrdad (2012). "Nosocomial Infections: The Definition Criteria". Iranian Journal of Medical Sciences 37 (2): 72–73. PMC 3470069. PMID 23115435.
- Nilsson, Oskar (2012). "Vancomycin resistant enterococci in farm animals – occurrence and importance". Infection Ecology & Epidemiology 2. doi:10.3402/iee.v2i0.16959. PMC 3426332. PMID 22957131.
- Fathollahzadeh, Bahram; Hashemi, Farhad B.; Emaneini, Mohammad; Aligholi, Marzieh; Nakhjavani, Farrokh A. (2006). "Frequency of Vancomycin-Resistant Enterococci from Three Hospitals in Iran" (PDF). Daru 14 (3): 141–146. Retrieved 2015-12-30.
- Fong, I. W.; Drlica, Karl (2007-11-15). Antimicrobial Resistance and Implications for the 21st Century. Springer Science & Business Media. ISBN 9780387724188.
- Mendez-Vilas, A. (2011). Science and Technology Against Microbial Pathogens: Research, Development and Evaluation, Proceedings of the International Conference on Antimicrobial Research (ICAR2010), Valladolid, Spain 3 - 5 November 2010. World Scientific. ISBN 9789814354868.
- Ahmad, Iqbal; Aqil, Farrukh (2008-11-21). New Strategies Combating Bacterial Infection. John Wiley & Sons. ISBN 9783527622948.
- Grayson, M. Lindsay; Crowe, Suzanne M.; McCarthy, James S.; Mills, John; Mouton, Johan W.; Norrby, S. Ragnar; Paterson, David L.; Pfaller, Michael A. (2010-10-29). Kucers' The Use of Antibiotics Sixth Edition: A Clinical Review of Antibacterial, Antifungal and Antiviral Drugs. CRC Press. ISBN 9781444147520.
- "Figure 4 : The rise of the Enterococcus: beyond vancomycin resistance : Nature Reviews Microbiology". www.nature.com. Retrieved 2015-06-09.
- Meziane-Cherif, Djalal; Saul, Frederick A.; Haouz, Ahmed; Courvalin, Patrice (2012). "Structural and Functional Characterization of VanG d-Ala:d-Ser Ligase Associated with Vancomycin Resistance in Enterococcus faecalis♦". The Journal of Biological Chemistry 287 (45): 37583–37592. doi:10.1074/jbc.M112.405522. ISSN 0021-9258. PMC 3488035. PMID 22969085.
- Coates, Anthony R. M. (2012-08-31). Antibiotic Resistance. Springer Science & Business Media. ISBN 9783642289507.
- McKinnell, James A.; Kunz, Danielle F.; Chamot, Eric; Patel, Mukesh; Shirley, Rhett M.; Moser, Stephen A.; Baddley, John W.; Pappas, Peter G.; Miller, Loren G. (2012). "Association of Vancomycin-Resistant Enterococcus Bacteremia and Ceftriaxone Usage". Infection control and hospital epidemiology : the official journal of the Society of Hospital Epidemiologists of America 33 (7). doi:10.1086/666331. ISSN 0899-823X. PMC 3879097. PMID 22669234.
- Phoenix, David A.; Harris, Frederick; Dennison, Sarah R. (2014-08-25). Novel Antimicrobial Agents and Strategies. John Wiley & Sons. ISBN 9783527676156.
- Balli, Eleni P.; Venetis, Chris A.; Miyakis, Spiros (2014). "Systematic Review and Meta-Analysis of Linezolid versus Daptomycin for Treatment of Vancomycin-Resistant Enterococcal Bacteremia". Antimicrobial Agents and Chemotherapy 58 (2): 734–739. doi:10.1128/AAC.01289-13. ISSN 0066-4804. PMID 24247127.
- Rastall, Bob; Gibson, Glenn (2006-05-01). Prebiotics: Development and Application. John Wiley & Sons. ISBN 9780470023143.