Editing Vancomycin-resistant Staphylococcus aureus (section)

==History==
Three classes of vancomycin-resistant ''S. aureus'' have emerged that differ in vancomycin [[minimum inhibitory concentration|susceptibilities]]: vancomycin-intermediate ''S. aureus'' (VISA), heterogeneous vancomycin-intermediate ''S. aureus'' (hVISA), and high-level vancomycin-resistant ''S. aureus'' (VRSA).<ref name="pmid17888634">{{cite journal |author=Appelbaum PC |title=Reduced glycopeptide susceptibility in methicillin-resistant ''Staphylococcus aureus'' (MRSA) |journal=Int. J. Antimicrob. Agents |volume=30 |issue=5 |pages=398–408 |date=November 2007 |pmid=17888634 |doi=10.1016/j.ijantimicag.2007.07.011 }}</ref>

===Vancomycin-intermediate ''S. aureus'' (VISA)===
Vancomycin-intermediate ''S. aureus'' (VISA) ({{IPAc-en|ˈ|v|iː|s|ə}} or {{IPAc-en|v|iː|aɪ|ɛ|s|eɪ}}) was first identified in [[Japan]] in 1996<ref>{{cite journal|last1=Hiramatsu|first1=K.|last2=Hanaki|first2=H.|last3=Ino|first3=T.|last4=Yabuta|first4=K.|last5=Oguri|first5=T.|last6=Tenover|first6=F. C.|date=1997-07-01|title=Methicillin-resistant Staphylococcus aureus clinical strain with reduced vancomycin susceptibility.|journal=Journal of Antimicrobial Chemotherapy|language=en|volume=40|issue=1|pages=135–136|doi=10.1093/jac/40.1.135|issn=0305-7453|pmid=9249217|doi-access=free}}</ref> and has since been found in hospitals elsewhere in [[Asia]], as well as in [[the United Kingdom]], [[France]], the [[United States|U.S.]], and [[Brazil]]. It is also termed GISA (glycopeptide-intermediate ''Staphylococcus aureus''), indicating resistance to all glycopeptide antibiotics. These bacterial strains present a thickening of the cell wall, which is believed to reduce the ability of vancomycin to diffuse into the division septum of the cell required for effective vancomycin treatment.<ref>{{cite journal |vauthors=Howden BP, Davies JK, Johnson PD, Stinear TP, Grayson ML |title=Reduced vancomycin susceptibility in ''Staphylococcus aureus'', including vancomycin-intermediate and heterogeneous vancomycin-intermediate strains: resistance mechanisms, laboratory detection, and clinical implications |journal=Clin. Microbiol. Rev. |date=Jan 2010 | volume=23 |issue=1 |pages=99–139 |doi=10.1128/CMR.00042-09 |pmid=20065327 |pmc=2806658 |url=}}</ref>
[[File:S aureus blood agar.jpg|thumb|''[[Staphylococcus aureus|S. aureus]]'' [[blood agar]]]]

===Vancomycin-resistant ''S. aureus'' (VRSA)===
High-level vancomycin resistance in ''S. aureus'' has rarely been reported.<ref name="pmid21109164">{{cite journal |author=Gould IM |title=VRSA-doomsday superbug or damp squib? |journal=Lancet Infect Dis |volume=10 |issue=12 |pages=816–8 |date=December 2010 |pmid=21109164 |doi=10.1016/S1473-3099(10)70259-0 }}</ref> ''[[In vitro]]'' and ''[[in vivo]]'' experiments reported in 1992 demonstrated that vancomycin resistance genes from ''[[Enterococcus faecalis]]'' could be transferred by [[horizontal gene transfer|gene transfer]] to ''S. aureus'', conferring high-level vancomycin resistance to ''S. aureus''.<ref>{{Cite book|title = Bacterial Toxins: Genetics, Cellular Biology and Practical Applications|url = https://books.google.com/books?id=FdAAAgAAQBAJ&q=vancomycin%2520resistance%2520genes%2520from%2520Enterococcus%2520faecalis%2520could%2520be%2520transferred%2520by%2520horizontal%2520gene%2520transfer%2520to%2520S.%2520aureus%252C%2520conferring%2520high-level%2520vancomycin%2520resistance%2520to%2520S.%2520aureus&pg=PA119|publisher = Horizon Scientific Press|date = 2013|isbn = 9781908230287|first = Thomas|last = Proft}}</ref> Until 2002 such a genetic transfer was not reported for wild ''S. aureus'' strains. In 2002, a VRSA strain ({{IPAc-en|ˈ|v|ɜr|s|ə}} or {{IPAc-en|v|iː|ɑr|ɛ|s|eɪ}}) was isolated from a patient in Michigan.<ref>{{Cite book|title = Antimicrobial Resistance in Bacteria|url = https://books.google.com/books?id=sQ7URquB4YcC&q=Vancomycin-resistant%2520S.%2520aureus%2520%2520%2520horizontal%2520gene%2520transfer&pg=PT45|publisher = Horizon Scientific Press|date = 2007|isbn = 9781904933243|first = Carlos F.|last = Amábile-Cuevas}}</ref> The isolate contained the ''mecA'' gene for [[methicillin-resistant Staphylococcus aureus|methicillin resistance]]. Vancomycin [[minimum inhibitory concentration|MICs]] of the VRSA isolate were consistent with the VanA phenotype of ''[[Enterococcus]]'' species, and the presence of the ''vanA'' gene was confirmed by [[polymerase chain reaction]]. The DNA sequence of the VRSA ''vanA'' gene was identical to that of a [[vancomycin-resistant Enterococcus|vancomycin-resistant strain of ''Enterococcus faecalis'']] recovered from the same catheter tip. The ''vanA'' gene was later found to be encoded within a [[transposon]] located on a [[plasmid]] carried by the VRSA isolate. This transposon, Tn''1546'', confers ''vanA''-type vancomycin resistance in enterococci.<ref name="pmid16323116">{{cite journal |author=Courvalin P |title=Vancomycin resistance in gram-positive cocci |journal=Clin. Infect. Dis. |volume=42 |pages=S25–34 |date=January 2006 |issue=Suppl 1 |pmid=16323116 |doi=10.1086/491711 |doi-access=free }}</ref>

As of 2019, 52 VRSA strains have been identified in the United States, India, Iran, Pakistan, Brazil, and Portugal.<ref>{{cite journal |last1=Cong |first1=Yanguang |last2=Yang |first2=Sijin |last3=Rao |first3=Xiancai |title=Vancomycin resistant Staphylococcus aureus infections: A review of case updating and clinical features |journal=J Adv Res |date=2020 |volume=21 |pages=169–176 |doi=10.1016/j.jare.2019.10.005 |pmid=32071785|pmc=7015472 }}</ref>

===Heterogeneous vancomycin-intermediate S. aureus (hVISA)===
The definition of hVISA according to Hiramatsu et al. is a strain of Staphylococcus aureus that gives resistance to vancomycin at a frequency of 10<sup>−6</sup> colonies or even higher.<ref>{{Cite book|title = Emerging Infections in Asia|url = https://books.google.com/books?id=5WKoOibILtkC&q=heterogeneous%2520vancomycin-intermediate%2520S.%2520aureus&pg=PA234|publisher = Springer Science & Business Media|date = 2008-04-11|isbn = 9780387757216|first1 = Yichen|last1 = Lu|first2 = Max|last2 = Essex|first3 = Bryan|last3 = Roberts}}</ref>