Etiolofia, epidemiologia e progn��stico das pneumonias associadas �� ventila����o mec��nica em um hospital de ensino, com ��nfase no estudo molecular e virul��ncia de Staphylococcus aureus

Coordena����o de Aperfei��oamento de Pessoal de N��vel Superior (CAPES)

Proteomic and peptidomic study of proteolysis in quarter milk after infusion with lipoteichoic acid from Staphylococcus aureus

Mastitic milk is associated with increased bovine protease activity, such as that from plasmin and somatic cell enzymes, which cause proteolysis of the caseins and may reduce cheese yield and quality. The aim of this work was to characterize the peptide profile resulting from proteolysis in a model mastitis system and to identify the proteases responsible. One quarter of each of 2 cows (A and B) was infused with lipoteichoic acid from Staphylococcus aureus. The somatic cell counts of the infused quarters reached a peak 6h after infusion, whereas plasmin activity of those quarters also increased, reaching a peak after 48 and 12h for cow A and B, respectively. Urea-polyacrylamide gel electrophoretograms of milk samples of cow A and B obtained at different time points after infusion and incubated for up to 7 d showed almost full hydrolysis of beta- and alpha(S1)-casein during incubation of milk samples at peak somatic cell counts, with that of beta-casein being faster than that of alpha(S1)-casein. Two-dimensional gel electrophoretograms of milk 6h after infusion with the toxin confirmed hydrolysis of beta- and alpha(S1)-casein and the appearance of lower-molecular-weight products. Peptides were subsequently separated by reversed-phase HPLC and handmade nanoscale C(18) columns, and identified by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry. Twenty different peptides were identified and shown to originate from alpha(s1)- and beta-casein. Plasmin, cathepsin B and D, elastase, and amino- and carboxypeptidases were suggested as possible responsible proteases based on the peptide cleavage sites. The presumptive activity of amino- and carboxypeptidases is surprising and may indicate the activity of cathepsin H, which has not been reported in milk previously.

Genome sequencing unveils a novel sea enterotoxin-carrying PVL phage in staphylococcus aureus ST772 from India

Staphylococcus aureus is a major human pathogen, first recognized as a leading cause of hospital-acquired infections. Community-associated S. aureus (CA-SA) pose a greater threat due to increase in severity of infection and disease among children and healthy adults. CA-SA strains in India are genetically diverse, among which is the sequence type (ST) 772, which has now spread to Australia, Europe and Japan. Towards understanding the genetic characteristics of ST772, we obtained draft genome sequences of five relevant clinical isolates and studied the properties of their PVL-carrying prophages, whose presence is a defining hallmark of CA-SA. We show that this is a novel prophage, which carries the structural genes of the hlb-carrying prophage and includes the sea enterotoxin. This architecture probably emerged early within the ST772 lineage, at least in India. The sea gene, unique to ST772 PVL, despite having promoter sequence characteristics typical of low expression, appears to be highly expressed during early phase of growth in laboratory conditions. We speculate that this might be a consequence of its novel sequence context. The crippled nature of the hlb-converting prophage in ST772. suggests that widespread mobility of the sea enterotoxin might be a selective force behind its `transfer' to the PVL prophage. Wild type ST772 strains induced strong proliferative responses as well as high cytotoxic activity against neutrophils, likely mediated by superantigen SEA and the PVL toxin respectively. Both proliferation and cytotoxicity were markedly reduced in a cured ST772 strain indicating the impact of the phage on virulence. The presence of SEA alongside he genes for the immune system-modulating PVL toxin may contribute to the success and virulence of ST772.

Staphylococcus aureus resistente �� meticilina (MRSA): tipifica����o do cassete cromoss��mico SCCmec e resist��ncia a antimicrobianos em pacientes com fibrose c��stica assistidos em dois centros no Rio de Janeiro

A infec����o pulmonar de etiologia bacteriana �� um dos principais problemas que levam a morbi-mortalidade na fibrose c��stica (FC). Staphylococcus aureus se destaca como um dos micro-organismos mais frequentes e com um agravante para a terap��utica quando se apresentam resistentes �� oxacilina (MRSA). Amostras MRSA podem ser classificadas tanto genotipicamente quanto fenotipicamente em MRSA adquiridas na comunidade (CA-MRSA) ou adquiridas no hospital (HA-MRSA). Fenotipicamente, essa classifica����o �� muito controversa, podendo se basear em crit��rios epidemiol��gicos ou ainda pelo perfil de susceptibilidade aos antimicrobianos. Por outro lado, a classifica����o genot��pica consiste na determina����o dos cassetes cromoss��micos (SCCmec), local de inser����o do gene mecA (que confere resist��ncia a meticilina). Atualmente s��o reconhecidos 11 tipos de SCCmec, sendo os de tipo I ao III e VIII relacionados ao gen��tipo HA-MRSA e IV ao XI ao gen��tipo CA-MRSA. Classicamente CA-MRSA �� capaz de produzir a toxina Panton-Valentine leukocidin (PVL), codificada pelos genes luk-S e luk-F que est�� associada �� pneumonia necrotizante e infec����es de tecidos moles em pacientes com FC com quadros de exacerba����o pulmonar. No Brasil, raros s��o os trabalhos envolvendo caracteriza����o de SCCmec em amostras de pacientes com FC. Diante disso, este estudo teve como objetivo principal a caracteriza����o dos tipos de SCCmec e ainda a determina����o do perfil de susceptibilidade a antimicrobianos em uma popula����o de MRSA recuperada de pacientes com FC assistidos em dois centros de tratamento no Rio de Janeiro, Hospital Universit��rio Pedro Ernesto (HUPE) e Instituto Fernandes Figueira (IFF). Foram estudadas 108 amostras de MRSA isoladas do per��odo de 2008 a 2010, sendo 94 oriundas de 28 pacientes adultos atendidos no IFF e 14 de 2 pacientes adultos atendidos no HUPE. Foram encontradas altas taxas de resist��ncia para os antimicrobianos oxacilina, cefoxitina e eritromicina. Todas as amostras foram sens��veis �� vancomicina e a linezolida quando determinada as Concentra����es Inibit��rias M��nimas (CIM). Atrav��s da t��cnica de PCR foi poss��vel a tipifica����o dos SCCmec em 82,4% das amostras, sendo 64% destas compat��veis ao gen��tipo CA-MRSA. N��o houve diferen��a estat��stica nas taxas de susceptibilidade aos antimicrobianos entre as amostras CA-MRSA e HA-MRSA. Foram encontrados os SCCmec dos tipos I, III, IV e V, sendo os tipos I e IV os mais frequentes. O gene que codifica a toxina PVL foi encontrado em 34,2% das amostras e foi observado em amostras CA-MRSA e HA-MRSA. Nosso estudo se destaca por apresentar um alto percentual de amostras CA-MRSA e ainda por ser o primeiro do pa��s a detectar a presen��a do gene que codifica a toxina PVL em pacientes com FC. Al��m disso, de forma in��dita na literatura, encontramos o gene luk-S, em amostras classificadas como HA-MRSA em pacientes com FC. Os poucos estudos nacionais, bem como as diferen��as encontradas entre trabalhos, refletem a necessidade de conhecimento mais aprimorado do MRSA envolvido nas infec����es pulmonares dos pacientes com FC.

Epidemiologia molecular de Staphylococcus aureus resistentes �� meticilina (MRSA) isolados de pacientes com Fibrose C��stica

Staphylococcus aureus resistente �� meticilina (MRSA) �� um importante pat��geno pulmonar em pacientes com fibrose c��stica (FC). Caracteriza-se pela resist��ncia a todos os β-lact��micos, devido a presen��a do elemento gen��tico m��vel SCCmec o qual abriga o gene mecA. Al��m disso, �� reconhecido por v��rios fatores de virul��ncia o qual destacamos a toxina Panton-Valentine Leukocidin (PVL), uma citolisina formadora de poros na c��lula hospedeira, e por apresentar diversos clones epid��micos envolvidos em surtos hospitalares. O objetivo desse estudo foi caracterizar a epidemiologia de MRSA, isolados de pacientes com FC referente a dois centros de refer��ncia no Rio de Janeiro a partir da aplica����o de t��cnicas fenot��picas e genot��picas. Um total de 57 amostras de MRSA foi submetido ao teste de difus��o em ��gar para 11 antimicrobianos a fim de avaliar perfil de resist��ncia, com aplica����o da t��cnica da PCR foi tipificado o SCCmec e investigado a presen��a do gene LukS-PV respons��vel pela codifica����o da toxina PVL com intuito de estabelecer uma melhor caracteriza����o epidemiol��gica dos clones identificados pela t��cnica do MLST (Multilocus Sequence Typing). Os antimicrobianos n��o β-lact��micos apresentaram um percentual de resist��ncia abaixo de 50%, em que destacamos a eritromicina com o maior percentual 45,6% e quanto ao perfil de resist��ncia 24,6% foram multirresistentes. Com exce����o do SCCmec II, os outros tipos foram encontrados (I, III, IV e V) com os respectivos percentuais de 22,8% (n=13), 7,1% (n=4), 61,4% (n=35) e 3,5% (n=2) e apenas 5,3% (n=3) das amostras n��o foram caracterizadas, n��o h�� dados da preval��ncia do SCCmec IV. Vinte (35,1%) amostras apresentaram produtos de amplifica����o compat��vel com a presen��a do gene lukS, aproximadamente metade dessas amostras (55%) estava correlacionada ao SCCmec IV. Com a an��lise do MLST, obtivemos os STs 1 (n=1, 1,7%), 5 (n=28, 49,1%), 30 (n=11, 19,3%), 72 (n=1, 1,7%), 398 (n=1, 1,7%), 1635 (n=7, 12,3%), 1661 (n=2, 3,5%), 239 (n=5, 8,8%), e ainda identificamos um novo ST (2732) presente em 1 amostra. A partir de uma an��lise associativa entre o MLST e o SCCmec foi poss��vel observar a presen��a de linhagens caracter��sticas de clones epid��micos, como o UK-EMRSA-3 (ST5, SCCmec I), USA 800/pedi��trico (ST5, SCCmec IV), Oceania Southwest Pacific Clone - OSPC (ST30, SCCmec IV) e Brazilian Epidemic Clone - BEC (ST239, SCCmec III). Em conclus��o este estudo �� o primeiro a caracterizar linhagens epid��micas de MRSA nos centros de atendimento a pacientes com FC no Rio de Janeiro, sendo necess��rio um monitoramento constante a fim de evitar a dissemina����o desses clones.

Detection and quantification of staphylococcus aureus enterotoxin B in food product using isotopic dilution techniques and mass spectrometry

L���ent��rotoxine B staphylococcique (SEB) est une toxine ent��rique hautement r��sistante �� la chaleur et est responsable de plus de 50 % des cas d���intoxication d���origine alimentaire par une ent��rotoxine. L���objectif principal de ce projet de ma��trise est de d��velopper et valider une m��thode bas��e sur des nouvelles strat��gies analytiques permettant la d��tection et la quantification de SEB dans les matrices alimentaires. Une carte de peptides tryptiques a ��t�� produite et 3 peptides tryptiques sp��cifiques ont ��t�� s��lectionn��s pour servir de peptides t��moins �� partir des 9 fragments prot��olytiques identifi��s (couverture de 35 % de la s��quence). L���anhydride ac��tique et la forme deut��r��e furent utilis��s afin de synth��tiser des peptides standards marque��s avec un isotope l��ger et lourd. La combinaison de m��langes des deux isotopes �� des concentrations molaires diff��rentes fut utilis��e afin d�����tablir la lin��arit�� et les r��sultats ont d��montr�� que les mesures faites par dilution isotopique combin��e au CL-SM/SM respectaient les crit��res g��n��ralement reconnus d�����preuves biologiques avec des valeurs de pente pr��s de 1, des valeurs de R2 sup��rieure �� 0,98 et des coefficients de variation (CV%) inf��rieurs �� 8 %. La pr��cision et l���exactitude de la m��thode ont ��t�� ��valu��es �� l���aide d�����chantillons d���homog��nat de viande de poulet dans lesquels SEB a ��t�� introduite. SEB a ��t�� enrichie �� 0,2, 1 et 2 pmol/g. Les r��sultats analytiques r��v��lent que la m��thode procure une plage d���exactitude de 84,9 �� 91,1 %. Dans l���ensemble, les r��sultats pr��sent��s dans ce m��moire d��montrent que les m��thodes prot��omiques peuvent ��tre utilis��es efficacement pour d��tecter et quantifier SEB dans les matrices alimentaires. Mots cl��s : spectrom��trie de masse; marquage isotopique; prot��omique quantitative; ent��rotoxines

lncidence of enterotoxigenic Staphylococcus aureus in relation to the microbial safety of seafood

A detailed study was made on the microbial quality, with special reference to food safety, of the fish and fishery products in the retail trade in Cochin and around. Also, farmed molluscan shellfishes like mussels and oysters were investigated for the microbial quality including the presence of pathogenic bacteria. Special stress has been given to monitor the incidence of coagulase positive as well as coagulase negative Staphylococcus in these products and their relative incidence have been recorded.In the next part, the investigation was centered mainly on toxigenic S.aureus. This is because among the Gram positive toxigenic bacteria, the Saureus with potential to produce thermostable enterotoxins are more relavent in food safety conceming seafoods in comparison with the Gram-negative pathogens like Salmonella and V.cholerae.The incidence, toxigenic potential and conditions of toxin production by S.aureus have been investigated in detail. An attempt has also been made to relate the toxigenisis with the presence of the concerned toxigenic genes in the genomes of S. aureus strains.

Vergleichende Untersuchungen Methicillin-resistenter Staphylococcus aureus des Klinikums Kassel der Jahre 1999 bis 2004

Die vorliegende Arbeit liefert erstmals einen umfassenden ��berblick ��ber die molekulare Epidemiologie von Methicillin resistenten Staphylococcus aureus (MRSA) eines nordhessischen Krankenhauses inklusive seines Umfeldes und deren Entwicklung in einem Zeitraum von f��nf Jahren. Von besonderer Bedeutung ist, dass die MRSA-St��mme hierf��r nicht nur anhand ihrer SCCmec-Region (staphylococcal cassette chromosome) typisiert wurden, sondern eine weitergehende Charakterisierung auf Grund der Bestimmung des Vorkommens von Antibiotikaresistenz- und Toxingenen, sowie Plasmiden erfolgte. Dabei wurde ein neuer SCCmec-Typ entdeckt und charakterisiert und weitere noch unbekannte SCCmec-Elemente beschrieben. Bei der Charakterisierung der MRSA-Kollektive konnten bzgl. aller untersuchten Eigenschaften im Laufe der Zeit signifikante Ver��nderungen beobachtet werden. Am deutlichsten waren diese Unterschiede zwischen dem ��ltesten Kollektiv aus 1999 und allen nachfolgenden Kollektiven. Die Kollektive aus 2001, 2002, 2003 und 2004 zeigten untereinander gr����ere ��hnlichkeiten, aber dennoch gleichzeitig eine tendenziell divergente Entwicklung einzelner Eigenschaften. Besonders auffallend war das dominante Auftreten von SCCmecIV mit 63-87% der Isolate eines Kollektivs ab 2001, gegen��ber 16% in 1999. Weiterhin erfolgte eine markante Ver��nderung im Vorkommen einzelner Antibiotikaresistenzgene von 1999 bis 2004. So waren aacA-aphD und ermA bei MRSA aus 1999 mit 84% bzw. 90% deutlich h��ufiger als in allen Kollektiven der folgenden Jahre (aacA-aphD: max. 32%, ermA: max. 40%). Wohingegen ermC ein stets zunehmendes Vorkommen von 3% auf 67% ��ber den Untersuchungszeitraum zeigte. Unkontinuierliches aber statistisch relevant vermehrtes Auftreten von tetM konnte bei Isolaten aus 1999 (40%) und 2004 (74%) nachgewiesen werden. Auch bei Toxingenen zeigten sich deutliche Unterschiede in der zeitlichen Verteilung. Ab 2001 zeigten alle Isolate wesentlich h��here Anteile an sec, seg und sei verglichen mit den MRSA aus 1999. So konnte sec im Kollektiv aus 1999 gar nicht nachgewiesen werden, in denen der Folgejahre mit 54-77%. Die Werte f��r seg und sei stiegen von 48% bzw. 41% in 1999 kontinuierlich auf ��ber 90% in 2004. Die H��ufigkeit von MRSA sowohl mit mehreren Resistenzgenen als auch die mit mehreren Toxingenen nahm im Laufe der Zeit zu und korrelierte mit dem Vorkommen von Plasmiden. Bez��glich seiner Korrelation mit den vorkommenden Plasmiden zeigte SCCmecIV im Erhebungszeitraum besonders deutlich eine Ver��nderung. So nahm ��ber den Zeitraum der Beobachtung die Anzahl der St��mme die zus��tzlich zu einem gro��en Plasmid ein weiteres kleines Plasmid besa��en signifikant zu. Auch beim Vergleich der SCCmec-Typen der MRSA-Isolate konnten Unterschiede bzgl. aller weiteren untersuchten Eigenschaften dargestellt werden. So zeigten z.B. alle SCCmecIIIA das sea-Gen, w��hrend dies bei allen anderen in der vorliegenden Arbeit untersuchten SCCmec-Typen nur vereinzelt vorkam. SCCmecII-St��mme wiesen sowohl die meisten Antibiotikaresistenz- als auch Toxingene auf. Es wurde ferner gezeigt, dass St��mme mit vielen Resistenzgenen auch eine hohe Anzahl Toxingene besa��en und dies im Zusammenhang mit einem erh��hten Plasmidgehalt stehen k��nnte. Aus den MRSA-Kollektiven isolierte Plasmide konnten aufgrund von Restriktionsanalysen als verwandt zu ��-Laktamase-Plasmiden des Grundtyps pI524 und pI258 beschrieben werden. Der in vorliegender Arbeit gezeigte Zusammenhang zwischen der Anzahl von direct repeat units (dru) in der Hypervariablen Region (HVR) und dem SCCmec-Typ half den Unterschied zwischen SCCmecIV und SCCmecIVA, sowie die Sonderstellung des in vorliegender Arbeit erstmalig beschriebenen SCCmecIA/II darzustellen. Nicht alle Isolate konnten einem bekannten SCCmec-Typ zugeordnet werden, es handelt sich bei diesen Ausnahmen um weitere noch unbekannte und hier erstmalig beschriebene SCCmec-Typen. Aufgrund der vorliegenden Arbeit konnte ein neuer SCCmec-Typ definiert werden, namentlich der Typ SCCmecIA/II, der seit 1999 in der Region geh��uft vorkommt Die vorliegenden Untersuchungen zeigten somit, dass die Epidemiologie von MRSA der Region Nordhessen trotz bestehender Gemeinsamkeiten zur MRSA-Situation in ganz Deutschland auch Besonderheiten aufweist. Diese nun zu kennen kann einen Beitrag zur gezielten Verbesserung bisheriger Ma��nahmen zur Ausbreitungskontrolle von MRSA in der nordhessischen Region leisten.

Differential recognition of Staphylococcus aureus quorum-sensing signals depends on both extracellular loops 1 and 2 of the transmembrane sensor AgrC.

Virulence in Staphylococcus aureus is regulated via agr-dependent quorum sensing in which an autoinducing peptide (AIP) activates AgrC, a histidine protein kinase. AIPs are usually thiolactones containing seven to nine amino acid residues in which the thiol of the central cysteine is linked to the alpha-carboxyl of the C-terminal amino acid residue. The staphylococcal agr locus has diverged such that the AIPs of the four different S. aureus agr groups self-activate but cross-inhibit. Consequently, although the agr system is conserved among the staphylococci, it has undergone significant evolutionary divergence whereby to retain functionality, any changes in the AIP-encoding gene (agrD) that modifies AIP structure must be accompanied by corresponding changes in the AgrC receptor. Since AIP-1 and AIP-4 only differ by a single amino acid, we compared the transmembrane topology of AgrC1 and AgrC4 to identify amino acid residues involved in AIP recognition. As only two of the three predicted extracellular loops exhibited amino acid differences, site-specific mutagenesis was used to exchange the key AgrC1 and AgrC4 amino acid residues in each loop either singly or in combination. A novel lux-based agrP3 reporter gene fusion was constructed to evaluate the response of the mutated AgrC receptors. The data obtained revealed that while differential recognition of AIP-1 and AIP-4 depends primarily on three amino acid residues in loop 2, loop 1 is essential for receptor activation by the cognate AIP. Furthermore, a single mutation in the AgrC1 loop 2 resulted in conversion of (Ala5)AIP-1 from a potent antagonist to an activator, essentially resulting in the forced evolution of a new AIP group. Taken together, our data indicate that loop 2 constitutes the predicted hydrophobic pocket that binds the AIP thiolactone ring while the exocyclic amino acid tail interacts with loop 1 to facilitate receptor activation.

Produ����o de enterotoxinas e da toxina da s��ndrome do choque t��xico por cepas de Staphylococcus aureus isoladas na mastite bovina

A total of 72 strains of Staphylococcus aureus were examined for the production of staphylococcal enterotoxins (SE) A, B, C, D and toxic shock syndrome toxin (TSST-1). The strains were isolated from milk samples from cows with mastitis in dairy herds of S��o Paulo State, Brazil. Off 72 isolates, 38 (52.8%) produced SEA, 38 (52.8%) SEB, 32 (44.4%) SED, 28 (38.9%) SEC and 27 (37.5%) TSST-1. From the 72 strains, 66 (91.7%) produced, at least, one or more toxin, including TSST-1.

Peritoneal Dialysis-Related Peritonitis Due to Staphylococcus aureus: A Single-Center Experience over 15 Years

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA): molecular background, virulence, and relevance for public health

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Import��ncia do Staphylococcus aureus nas mastites subcl��nicas: pesquisa de enterotoxinas e toxina do choque t��xico, e a rela����o com a contagem de c��lulas som��ticas

O Staphylococcus aureus �� um dos principais agentes das mastites consideradas contagiosas, apresentando elevada incid��ncia na maioria dos rebanhos leiteiros em v��rios pa��ses. Al��m de perdas econ��micas �� importante salientar o aspecto de sa��de p��blica para cepas produtoras de enterotoxinas e da toxina do choque t��xico. A enterotoxina A, relacionada com maior ��nfase nos casos de toxinfec����es alimentares, pode ser veiculada pelo leite cru, pasteurizado e subprodutos l��cteos. A s��ndrome do choque t��xico �� determinada mais freq��entemente pela toxina do choque t��xico, por��m as enterotoxinas do tipo B e C tamb��m podem ser implicadas. O objetivo deste estudo foi verificar a ocorr��ncia de S.aureus produtores de enteroxinas e da toxina do choque t��xico em amostras de leite de animais com mastite subcl��nica, e correlacionar estes resultados com a contagem de c��lulas som��ticas; utilizando a t��cnica de celofane over agar para detec����o da TNAase, kit comercial para identifica����o das enterotxinas e contagem eletr��nica de c��lulas som��ticas. Avaliod]MORENO, B.[u-se 209 amostras de leite oriundas de vacas com mastite subcl��nica por S.aureus, e dentre estas, 209 (98,86%) produziram TNAse, nove amostras (4,39%) foram produtoras de enterotoxinas, sendo que uma (0,49%) dentre elas foi produtora de EED, tr��s (1,46%) de EEC, e tr��s (1,46%) de EEB. em uma amostra (0,49%), detectou-se concomitantemente EEA e EEB e em outra EEB e EEC. A toxina do choque t��xico n��o foi encontrada nas cepas avaliadas neste estudo, assim como n��o houve aumento estatisticamente significativo, na contagem de c��lulas som��ticas, das amostras de cepas produtoras de enteroxinas.

Determination of toxigenic capacity by reverse transcription polymerase chain reaction in coagulase-negative staphylococci and Staphylococcus aureus isolated from newborns in Brazil

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a burn unit from Brazil

Methicillin-resistant Staphylococcus aureus (MRSA) poses a threat for patients in burn units. Studies that mix epidemiological designs with molecular typing may contribute to the development of strategies for MRSA control. We conducted a study including: molecular characterization of Staphylococcal Chromosome Cassette mecA (SCCmec), strain typing with pulsed field gel electrophoresis (PFGE) and detection of virulence genes, altogether with a case-case-control study that assessed risk factors for MRSA and for methicillin-susceptible S. aureus (MSSA), using S. aureus negative patients as controls. Strains were collected from clinical and surveillance cultures from October 2006 through March 2009. MRSA was isolated from 96 patients. Most isolates (94.8%) harbored SCCmec type III. SCCmec type IV was identified in isolates from four patients. In only one case it could be epidemiologically characterized as community-associated. PFGE typing identified 36 coexisting MRSA clones. When compared to MSSA (38 isolates), MRSA isolates were more likely to harbor two virulence genes: tst and lukPV. Previous stay in other hospital and admission to Intensive Care Unit were independent risk factors for both MRSA and MSSA, while the number of burn wound excisions was significantly related with the former (OR = 6.80, 95%CI = 3.54-13.07). In conclusion, our study found polyclonal endemicity of MRSA in a burn unit, possibly related to importing of strains from other hospitals. Also, it pointed out to a role of surgical procedures in the dissemination of MRSA strains. �� 2013 Elsevier Ltd and ISBI. All rights reserved.