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Transferable vancomycin resistance in a community-associated mrsa lineage

Transferable Vancomycin Resistance in a Community-Associated MRSA Lineage Flávia Rossi, M.D., Ph.D., Lorena Diaz, Ph.D., Aye Wollam, B.Sc., Diana Panesso, Ph.D., Yanjiao Zhou, Ph.D., Sandra Rincon, M.Sc., Apurva Narechania, M.A., Galen Xing, Thais S.R. Di Gioia, M.D., André Doi, M.D., Truc T. Tran, Pharm.D., Jinnethe Reyes, M.Sc., Jose M. Munita, M.D., Lina P. Carvajal, B.Sc., Alejandra Hernandez-Roldan, M.Sc., Denise Brandão, M.D., Inneke Marie van der Heijden, Ph.D., Barbara E. Murray, M.D., Paul J. Planet, M.D., Ph.D., George M. Weinstock, Ph.D., and Cesar A. Arias, M.D., Ph.D.
From the Department of Pathology, Divi- We report the case of a patient from Brazil with a bloodstream infection caused by sion of Microbiology of the Central Labo- a strain of methicillin-resistant Staphylococcus aureus (MRSA) that was susceptible to ratory (LIM 03) and Department of In-fectious Disease (LIM 54), Hospital das vancomycin (designated BR-VSSA) but that acquired the vanA gene cluster during Clínicas da Faculdade de Medicina da antibiotic therapy and became resistant to vancomycin (designated BR-VRSA). Both Universidade de São Paulo, São Paulo strains belong to the sequence type (ST) 8 community-associated genetic lineage (F.R., T.S.R.D.G., A.D., D.B., I.M.H.); Mo-lecular Genetics and Antimicrobial Resis- that carries the staphylococcal chromosomal cassette mec (SCCmec) type IVa and the tance Unit, Universidad El Bosque, Bogota S. aureus protein A gene (spa) type t292 and are phylogenetically related to MRSA (L.D., D.P., S.R., J.R., L.P.C., C.A.A.), and lineage USA300. A conjugative plasmid of 55,706 bp (pBRZ01) carrying the vanA Centro Internacional de Entrena miento e Investigaciones Medicas (CIDEIM), Cali cluster was identified and readily transferred to other staphylococci. The pBRZ01 (A.H.-R.) — both in Colombia; Clinica plasmid harbors DNA sequences that are typical of the plasmid-associated replica- Alemana de Santiago, Universidad del tion genes rep24 or rep21 described in community-associated MRSA strains from Desarrollo, Santiago, Chile (J.M.M.); the Department of Internal Medicine, Division Australia (pWBG745). The presence and dissemination of community-associated of Infectious Diseases (L.D., D.P., T.T.T., MRSA containing vanA could become a serious public health concern.
J.R., J.M.M., A.H.-R., B.E.M, C.A.A.), and the Department of Microbiology and Mo-lecular Genetics (B.E.M., C.A.A.), Univer-sity of Texas Medical School at Houston, and the University of Houston College of Since the description in 2002 of the vanA gene cluster in MRSA as the mechanism of high-level vancomycin resistance, 13 isolates have been re- Pharmacy (T.T.T.) — both in Houston; the Genome Institute, Washington University ported in the United States,1,2 with others reported in India3 and Iran.4 Entero­ at St. Louis, St. Louis (A.W., Y.Z., G.M.W.); coccus faecalis and E. faecium have been implicated as the donors of the vancomycin and Sackler Institute for Comparative Ge- resistance genes.5,6 The VRSA isolates were recovered from patients with soft-tissue nomics, American Museum of Natural His-tory (A.N., P.J.P.), and Division of Pediatric or skin infections, and multilocus sequence typing has shown that 12 U.S. VRSA iso-Infectious Diseases, Columbia University lates belong to clonal complex 5 (including ST5, ST85, ST231, and ST371)1 and that (G.X., P.J.P.) — both in New York. Ad- the 13th isolate belongs to clonal complex 30. Clonal complex 5 is the most widely dress reprint requests to Dr. Arias at the University of Texas Medical School, 6431 disseminated hospital-associated MRSA clonal complex in the United States, with pat-Fannin St., Rm. 2.112 MSB, Houston, TX terns designated as USA100 and USA800 on pulsed-field gel electrophoresis (PFGE).1 77030, or at [email protected].
Community-associated MRSA emerged during the 1990s and rapidly dissemi- This article was updated on April 17, 2014, nated across the United States, most often causing severe skin and soft-tissue in-at NEJM.org.
fections but on occasion causing life-threatening infections such as necrotizing pneumonia.7 Early variants of this community-associated MRSA were initially N Engl J Med 2014;370:1524-31.
DOI: 10.1056/NEJMoa1303359
traced to PFGE pattern USA400, but these variants were rapidly replaced by isolates Copyright 2014 Massachusetts Medical Society. within the genetic lineage designated USA300-ST8 (clonal complex 8). A variant of USA300-ST8 emerged in South America in 2005 (designated USA300 Latin n engl j med 370;16 nejm.org april The New England Journal of Medicine Downloaded from nejm.org at FIOCRUZ on April 24, 2014. For personal use only. No other uses without permission. Copyright 2014 Massachusetts Medical Society. All rights reserved. Transferable Vancomycin Resistance in MRSA Lineage American Variant [USA300-LV])8 and has spread recommendation of contact isolation. A sample rapidly, replacing the previously predominant from a rectal swab obtained 2 weeks after the clonal complex 5 hos pital-associated clone (known initial positive blood culture indicated coloniza- as the Chilean–Cordobes clone).9,10 Here we re- tion with vancomycin-resistant E. faecalis (VREF). port on the acquisition of the vanA gene cluster The fever diminished, and daptomycin was con- by an invasive bloodstream isolate of community- tinued for an additional 4 weeks. However, while associated MRSA lineage in a patient at a Brazilian the patient was receiving daptomycin, oral muco- sal lesions developed and his respiratory status and fever worsened. Blood cultures yielded Steno­ trophomonas maltophilia; treatment with levofloxa- cin was started and intravenous catheters were The patient was a 35-year-old man from São Paulo removed. Respiratory secretions yielded extended- with mycosis fungoides, cocaine addiction, and spectrum, beta-lactamase–producing Kleb siel a pneu­ diabetes mellitus. He was initially admitted to a moniae and carbapenem-resistant Acinetobacter bau­ psychiatric hospital in November 2011 for depres- mannii. Polymixin B sulfate was added to the sion and suicidal ideation. Leg cellulitis developed treatment regimen. Multisystem organ failure and was treated with cephalexin and topical gen- ensued, and blood cultures grew Candida albi­ tamicin. The patient was discharged with a pre- cans. Be cause of the patient's worsening status, scription for clindamycin but was readmitted in care was withdrawn in November 2012. The June 2012 because of worsening psychiatric symp- patient died while receiving meropenem, lin ez- toms and recurrent infections of the skin and soft olid, polymyxin B sulfate, and amphotericin B. tissues. Vancomycin and cefepime were adminis- (A summary of the patient's course is presented tered for 8 days; blood cultures obtained during in Fig. 1.) this period were sterile. The patient remained in the hospital to receive chemotherapy with gem- citabine, vinorelbine, and dexamethasone for my- cosis fungoides (skin cancer). In July 2012, while Bacterial Identification, Susceptibility
the patient remained in the hospital, fever recurred, Testing, and Molecular Typing
and treatment with vancomycin and piperacillin– S. aureus and VREF isolates recovered from the tazobactam was started. On July 16 and 24, blood patient's blood samples and rectal swabs, respec- cultures yielded MRSA isolates that were suscep- tively, were identified by means of a polymerase- tible to vancomycin, linezolid, and clindamycin chain-reaction (PCR) assay11,12 and 16S ribosomal (see Table S1 in the Supplementary Appendix, avail- RNA sequencing.13 Susceptibility was determined able with the full text of this article at NEJM.org). with the use of agar dilution and broth microdilu- Vancomycin was continued for 13 days (highest tion.14 To assess the genetic background of the vancomycin trough level, 8.7 μg per milliliter), isolates, PFGE was performed on two S. aureus iso- followed by treatment with teicoplanin for an ad- lates recovered from the patient's blood (BR-VSSA ditional 14 days.
and BR-VRSA) (Fig. 1); on representative MRSA A transthoracic echocardiogram showed no evi- isolates circulating in South American hospitals, dence of infective endocarditis. On August 15, including the Latin American variant (USA300- the day after teicoplanin was discontinued, fever LV) and Chilean–Cordobes clones; and on refer- recurred. Blood cultures were positive for two ence strains from the following pandemic clones: MRSA isolates, one of which was resistant to USA300 (NRS482),9 the Brazilian clone (F338), both vancomycin (minimal inhibitory concen- the Iberian clone (NRS385-USA500), the Pediat- tration, >32 μg per milliliter) and teicoplanin ric clone (NRS387-USA800), and the New York– (minimal inhibitory concentration, 32 μg per Japan clone (NRS382-USA100). Typing of BR-VRSA milliliter); the isolate was also resistant to eryth- was performed with the use of multilocus se- romycin, clin da mycin, ciprofloxacin, gentamicin, quence typing, SCCmec, and spa. PCR assays were and trimethoprim–sulfamethoxazole (Table S1 in used to detect the genes encoding Panton– the Supplementary Appendix).
Valentine leukocidin (PVL) and the arginine cata- Treatment with daptomycin was started, and bolic mobile element, which are often found in the patient was placed in a single room, with a MRSA USA300.9 n engl j med 370;16 nejm.org april The New England Journal of Medicine Downloaded from nejm.org at FIOCRUZ on April 24, 2014. For personal use only. No other uses without permission. Copyright 2014 Massachusetts Medical Society. All rights reserved. Plasmid Characterization and Bacterial
performed to classify plasmid replicons. The Biosafety Committee at the University of Texas– We assessed the transferability of resistance to Houston approved these experiments.
vancomycin by performing filter matings,15 us- ing BR-VRSA and the VREF isolate from the pa- Whole-Genome Sequencing and Phylogenetic
tient as donors and BR-VSSA, S. aureus RN4220, Analysis
S. aureus COL, and E. faecalis OG1RF as recipients BR-VSSA, BR-VRSA, and VREF isolates were evalu- (Table S2 in the Supplementary Appendix). A donor- ated by means of whole-genome sequencing with to-recipient ratio of 1:10 was used for mating ex- the use of the Illumina platform. Annotation and periments, as described previously.15 Selection was assembly were performed as previously described19; performed on brain–heart infusion (BHI) agar details are available at the National Center for supplemented with vancomycin and fusidic acid at Bio technology Information (GenBank Bioproject concentrations of 32 μg per milliliter and 25 μg numbers 205852 [for BR-VSSA], PRJNA183704 per milliliter, respectively. To determine whether [for BR-VRSA], and 205838 [for VREF]). Details of vanA was present on a plasmid, S1 nuclease di- genomic comparisons (including the identifica- gestion of total DNA, coupled with PFGE and hy- tion of single-nucleotide polymorphisms [SNPs]) bridization with a vanA probe, was performed.16,17 and phylogenetic analysis are described in the PCR assays targeting pSK41-like6 and Inc18-like Supplementary Appendix.
plasmids6 and the rep plasmid families18 were A Novel Transferable vanA Plasmid in BR-VRSA
Initial molecular characterization showed that BR-VRSA displayed a PFGE pattern that was in- distinguishable from that of BR-VSSA (Fig. 2A), sug- gesting that BR-VRSA was selected in vivo during the administration of glycopeptides and other anti- microbial drugs. Moreover, S1 nuclease digestion and hybridization showed that BR-VRSA contained a plasmid of approximately 55 kb (not present in BR-VSSA) that carried vanA and aac(6')–aph(2''), which encode enzymes that confer resistance to vancomycin and gentamicin, respectively (Fig. 2B). Growth rates were similar for both organisms (Fig. S1 in the Supplementary Appendix), suggest- ing that acquisition of the vanA plasmid did not Nov. 2011–
Feb. 2012
affect the in vitro fitness of the strain.
Filter-mating assays showed that the rate of transfer of vancomycin resistance from BR-VRSA Figure 1. The Patient's Clinical Course before and after Isolation
of the Vancomycin-Resistant Staphylococcus aureus.
(donor) to BR-VSSA (recipient) was 2.6×10−4 trans- The antibiotics used are depicted in colored rectangles, with beta-lactams conjugants per donor (Table S2 in the Supple- in blue (cephalexin, cefepime, and piperacillin–tazobactam), clindamycin in men tary Appendix). Rates of transfer to other green, glycopeptides in pink (vancomycin and teicoplanin), and daptomycin staphylococci (S. aureus RN4220-RF and COL) in yellow; the number in each rectangle corresponds to the number of days were 1.65×10−4 and 6×10−5, respectively (Table S2 of treatment with the antibiotic. The drugs are shown in the order in which in the Supplementary Appendix). Experiments they were added to therapy. Dosages were as follows: cephalexin, 500 mg every 6 hours, given orally; clindamycin, 450 mg every 8 hours, given orally; with S1 nuclease indicated that the plasmid con- cefepime, 1 g every 8 hours, given intravenously; piperacillin–tazobactam, taining vanA (designated pBRZ01; 55,706 bp) 3.375 g every 6 hours, given intravenously; vancomycin, 1 g every 12 hours, was the only large plasmid that was readily given intravenously; teicoplanin, 400 mg daily, given intravenously; and dapto- transferred to S. aureus during the mating experi- mycin, 6 mg per kilogram of total body weight daily, given intravenously. The ment (Fig. 2B). We were unable to transfer vanco- final days of hospitalization are not included. SSTI denotes skin and soft-tissue infection, BR-VSSA vancomycin-susceptible S. aureus, BR-VRSA vancomycin- mycin resistance to a laboratory strain of E. faeca­ resistant S. aureus, and VREF vancomycin-resistant Enterococcus faecalis.
lis (strain OG1RF), which suggests that the plasmid was not able to replicate in enterococci. n engl j med 370;16 nejm.org april The New England Journal of Medicine Downloaded from nejm.org at FIOCRUZ on April 24, 2014. For personal use only. No other uses without permission. Copyright 2014 Massachusetts Medical Society. All rights reserved.

Transferable Vancomycin Resistance in MRSA Lineage The transfer of vancomycin resistance from inverted repeat (Fig. S2 in the Supplementary Ap- VREF recovered from the patient's rectal swab pendix), was identified, with the insertion of two was also unsuccessful.
open reading frames encoding an enterococcal Analysis of the sequence of pBRZ01 (Fig. 2C) resolvase and transposase (from the Tn3 family), indicated that a Tn1546-like element underwent respectively (Fig. S2 in the Supplementary Ap pen- important DNA rearrangements (Fig. S2 in the dix). The sequence of the vanA cluster (including Supplementary Appendix). An insertion sequence 614 bp upstream and 222 bp downstream) har- (IS1216) was found at the 5' end of the Tn1546 bored by the VREF infecting the patient was variant, with a deletion of 3397 bp eliminating the identical to the sequence in BR-VRSA and was left inverted repeat, the gene encoding integrase also identical to the sequences from plasmids (open reading frame 1), and part of the gene en- pWZ7140 and pWZ909, previously identified in coding resolvase (open reading frame 2) (Fig. S2 E. faecalis.20 These findings support the view in the Supplementary Appendix). Downstream of that the vanA cluster has an enterococcal origin. vanZ, a deletion of 96 bp, including the right Genomic analysis (confirmed by means of PCR A Smal Digestion PFGE
B S1 Nuclease Digestion and Hybridization with VanA
C BR-VRSA Plasmid pBRZ01
Vancomycin resistance conferred by the vanA cluster Aminoglycoside resistance conferred by acc(6')–aph(2'') DNA replication, cell division, conjugation machinery Transposases and resolvases Hypothetical proteins Figure 2. Results of Pulsed-Field Gel Electrophoresis (PFGE), S1 Nuclease Digestion of Total DNA, Hybridization,
and Plasmid Annotation.
Panel A shows the results of SmaI digestion of total DNA followed by PFGE. Lane M shows the lambda ladder (with
the molecular sizes in kilobases shown at left); lane 1, BR-VSSA; lane 2, BR-VRSA (donor); lane 3, transconjugant
number 1 Staphylococcus aureus RN4220-RF; lane 4, transconjugant number 2 S. aureus RN4220-RF; lane 5, S. aureus
RN4220-RF (recipient); and lane 6, vancomycin-resistant Enterococcus faecalis (vanA). Panel B shows the results of S1
digestion of the total DNA of staphylococcal strains and vancomycin-resistant E. faecalis followed by PFGE (at left) and
hybridization with a VanA probe (at right). In the results at left, lane 1 shows BR-VSSA; lane 2, BR-VRSA (donor);
lane 3, transconjugant number 1 S. aureus RN4220-RF; lane 4, transconjugant number 2 S. aureus RN4220-RF; lane 5,
S. aureus RN4220RF (recipient); lane 6, vancomycin-resistant E. faecalis; and lane M the lambda ladder. In the results at
right, the white and red arrows highlight the positive signal for vanA hybridization in staphylococcal and enterococcal
strains, respectively. Panel C shows a schematic representation of the annotation of the BR-VRSA plasmid pBRZ01.
n engl j med 370;16 nejm.org april The New England Journal of Medicine Downloaded from nejm.org at FIOCRUZ on April 24, 2014. For personal use only. No other uses without permission. Copyright 2014 Massachusetts Medical Society. All rights reserved. assay) of VREF indicated that the repR gene score of q>20) differentiating the two strains, (typical of Inc18 type plasmids previously associ- whereas a comparison of each of these strains ated with transfer of the vanA cluster into clonal with the USA300 strain TCH1516 showed a dif- complex 5 S. aureus) and the traA gene (required ference of 1637 SNPs (965 core SNPs) for BR-VSSA for plasmid transfer)6 were absent, which supports and 1757 SNPs (1005 core SNPs) for BR-VRSA, the absence of transferability of the enterococcal suggesting that BR-VSSA is more similar to the plasmid and further indicating that VREF was progenitor of BR-VRSA. (The SNP score is a mea- not the direct donor of vanA genes to BR-VRSA. sure of the number of reads from a sequencing Comparison of pBRZ01 with pWBG745 that agree with regard to a particular SNP.) (38,204 bp), a plasmid identified in community- associated MRSA isolates from remote areas of Australia (clonal complex 5), showed 99% iden- tity across 21,164 nucleotides.21 In addition, a The acquisition of high-level vancomycin resis- sequence analysis indicated that the plasmid tance by S. aureus has been deemed a major clini- containing vanA is not related to the pSK41-like cal and epidemiologic threat. However, since the staphylococcal or Inc18-like enterococcal plasmids first characterization of a strain of VRSA in the previously associated with vanA-carrying plasmids United States,5,23 only a few other isolates have from VRSA isolates identified in the United States been reported. All the VRSA isolates from the and belonging to clonal complex 5.1,6 Instead, the United States described to date have been isolated vanA plasmid harbors sequences that are typical from infections of the skin and soft-tissue or of the recently designated rep24 family18 or rep21 from colonizers of the skin. This case documents family22 found in pWBG745. (Other genetic de- a bloodstream infection caused by a VRSA strain terminants conferring antibiotic resistance that in a patient with a serious skin condition that are present in the BR-VRSA genome are shown probably predisposed the patient to bacterial in Table S3 in the Supplementary Appendix.) colonization. The patient was treated repeatedly with beta-lactams and glycopeptides, and our ST8 Community-Associated Genetic
analyses suggest that the MRSA isolate had also Background in BR-VRSA
acquired the vanA plasmid during therapy. The PFGE indicated that BR-VRSA is genetically re- genetic characterization and genomic analyses lated to MRSA USA300 (Fig. 3A), and multilocus also suggest that the vanA gene cluster present in sequence typing showed that BR-VRSA belongs BR-VRSA may have originated from an entero- to ST8 (as do USA300 and USA300-LV), harbors coccal donor. The DNA sequence of the vanA SCCmec type IVa, and is spa type t292. Unlike gene cluster (and partial flanking sequences) of USA300 and USA300-LV, BR-VRSA lacked genes BR-VRSA is identical to the sequence present in encoding PVL. Neither the arcA gene nor the en- the genome of VREF that was recovered from a tire arginine catabolic mobile element was swab of the patient's rectum, suggesting that present in BR-VRSA, as has also been noted for VREF may have been the donor. However, the MRSA strains belonging to the USA300-LV lin- presence of a different plasmid in this isolate and eage. BR-VRSA and BR-VSSA harbor an intact the absence of transferability of the vanA cluster bsa operon (for bacteriocin production) that is from VREF to staphylococci or enterococci suggest characteristic of community-associated MRSA; that acquisition occurred through different inter- VRSA strains from clonal complex 5 lack this mediaries. Indeed, the Tn1546-like element in operon.1 Whole-genome, SNP-based phylogenetic BR-VRSA was altered, indicating that po tentially analysis (performed with either the whole ge- important genetic rearrangements of Tn154624 nome [Fig. 3B] or the core genome [Fig. S3 in the had occurred. The presence of the insertion se- Supplementary Appendix]) showed that there is a quences flanking the vanA gene cluster (Fig. S2 in close relationship between BR-VSSA and BR-VRSA the Supplementary Appendix) may also provide the and between each of these variants and other truncated Tn1546-derived element with mobility.
ST8 genomes, including USA300 and USA300-LV. The results of our genomic and phylogenetic Genomic comparisons of BR-VSSA and BR-VRSA analyses (with more SNP changes detected on revealed only 288 SNPs (134 in the core genome) the branches leading to BR-VRSA than on those with a score indicating high quality (defined as a leading to BR-VSSA) suggest that BR-VRSA is n engl j med 370;16 nejm.org april The New England Journal of Medicine Downloaded from nejm.org at FIOCRUZ on April 24, 2014. For personal use only. No other uses without permission. Copyright 2014 Massachusetts Medical Society. All rights reserved.

Transferable Vancomycin Resistance in MRSA Lineage derived from BR-VSSA or a strain closely resem- Table S1 in the Supplementary Appendix) were bling BR-VSSA. However, since BR-VSSA did not gentamicin-resistant and vancomycin-susceptible, contain pBRZ01, the origin of this plasmid is and it is tempting to speculate that they may unknown. The two MRSA isolates recovered (but have been carriers of a version of pBRZ01 that then discarded) from the patient's blood before did not contain the vanA gene cluster.
the isolation of BR-VSSA and BR-VRSA (Fig. 1, and Apart from the type of infection, several factors A PFGE and Dendrogram of S. aureus Strains
USA300 (Nebraska) Percentage of Similarity
B Phylogenetic Tree
0.03 substitutions Figure 3. Phylogenetic Comparisons of BR-VRSA and BR-VSSA with Representatives of Other Methicillin-Resistant
Staphylococcus aureus (MRSA) Clones.
Panel A shows a dendrogram of the pandemic MRSA clones, BR-VRSA and BR-VSSA, generated with PFGE and the
use of GelCompar II software, version 6.5 (Applied Maths). Patterns were clustered by means of UPGMA (unweighted
pair group method with arithmetic mean), with the use of the Dice similarity coefficient and an optimization of 0.50%
and a tolerance of 1.0%. PFGE types, or clusters, were identified on the basis of a similarity of 75% or higher (indicated by
the vertical red line). ST denotes sequence type. The phylogenetic tree shown in Panel B is based on whole-genome
single-nucleotide polymorphisms (SNPs) and was generated with the use of the maximum-likelihood optimality
criterion. Branch lengths are proportional to the number of evolutionary changes (substitutions per site). All nodes
have 100% bootstrap support. Sequence types (STs) and clonal complexes (CCs) of the S. aureus strains are indicated.
n engl j med 370;16 nejm.org april The New England Journal of Medicine Downloaded from nejm.org at FIOCRUZ on April 24, 2014. For personal use only. No other uses without permission. Copyright 2014 Massachusetts Medical Society. All rights reserved. that may have important public health implications USA300 genetic lineage and capable of producing distinguish this case from previously reported severe, invasive bloodstream infections. This obser- cases of VRSA infection. First, this case is an ex- vation is supported by our finding that BR-VRSA, ample of the acquisition of a vanA gene cluster that unlike previously reported VRSA strains, harbors occurred independently of the hospital-associated an intact bsa operon,1 a genetic marker of com- MRSA clonal complex 5 lineage. The molecular and munity-associated MRSA strains.26 In addition, genomic data indicate that the genetic background characterization and sequencing of pBRZ01 indi- of the VRSA strain is closely related to community- cate that rep24 or rep21 family plasmids recently associated MRSA strains dis semi nat ed in several described in community-associated MRSA (belong- parts of the world (USA300 ST8 harboring SCCmec ing to clon al complex 5)21 in Australia have been type IVa). An ST8 community-associated variant of acquired by the MRSA ST8 genetic lineage and are the MRSA USA300 clone (USA300-LV), which has capable of capturing the vanA cluster on a trans- been reported in the northern part of South ferable plasmid. Finally, because USA300-like America,8,9,25 has almost replaced the common strains spread rapidly and replace other MRSA hospital-associated clone (ST5 Chilean–Cordobes lineages with such efficiency, our findings raise clone).9,10,25 However, the genetic background of the possibility that vancomycin resistance may be BR-VRSA differs from that of USA300-LV and from disseminated to MRSA clonal complex 8 isolates that of the prototypical USA300 in that it lacks the in both the hospital and the community.
genes encoding PVL, a genetic marker of commu- Supported by grants from the National Institute of Allergy and nity-associated MRSA strains. This difference sug- Infectious Diseases (R01 AI093749, to Dr. Arias) and the National gests that BR-VRSA is a novel variant of ST8 Institutes of Health (1U54 HG004968, to Dr. Weinstock).
Disclosure forms provided by the authors are available with community-associated MRSA, closely related to the the full text of this article at NEJM.org.
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