Orientador: Marcelo Menossi Teixeira, Aluisio de Souza Pinheiro / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-08T01:46:04Z (GMT). No. of bitstreams: 1 Duarte_RodrigoDrummondCouto_D.pdf: 10481872 bytes, checksum: b2571c6b4e34ab56accd3eade31da7dd (MD5) Previous issue date: 2006 / Resumo: Arranjos de DNA são uma poderosa técnica de monitoramento da expressão gênica em larga escala. No entanto, a grande quantidade de dados gerados com esse tipo de experimento requer um tratamento estatístico adequado às suas características. Uma aplicação importante dos arranjos de DNA é a identificação de genes diferencialmente expressos em diferentes amostras de RNA. Essa seleção demanda testes estatísticos apurados, capazes de distinguir, entre o grande número de genes usualmente presentes nos arranjos, aqueles cuja expressão é significativamente diferenciada. Neste trabalho nós desenvolvemos algoritmos para a análise estatística dos dados provenientes de arranjos de DNA, eficientes em lidar com os problemas usuais nesse tipo de dados, como o número limitado de réplicas. Aplicados a dados simulados, os algoritmos desenvolvidos mostraram-se competitivos com outros métodos de análises descritos na literatura, superando-os em algumas situações. A aplicação desses algoritmos foi também demonstrada em um experimento voltado à identificação de genes de cana-deaçúcar diferencialmente expressos em resposta a deficiência de fosfato. O fósforo é um macronutriente essencial, captado pelas plantas principalmente na forma de fosfato inorgânico (Pi). A deficiência de fosfato é freqüente na natureza, especialmente nos solos ácidos das regiões tropicais e subtropicais. Devido a grande importância econômica da cana-de-açúcar, a identificação de genes diferencialmente expressos em resposta à deficiência de fosfato nesta espécie é de grande interesse científico e agronômico. Algoritmos de agrupamento foram também aplicados aos dados de expressão obtidos no experimento, identificando padrões de expressão gênica nos diferentes estágios da resposta da cana a esse estresse e proporcionando assim uma caracterização adicional da mesma. Futuramente, os resultados desse trabalho podem conduzir ao desenvolvimento de linhagens de cana-de-açúcar com melhor desempenho em solos pobres de fosfato, o que seria de extremo interesse agronômico / Abstract: DNA arrays are a powerful technique for monitoring gene expression in large scale. However, the great amount of data generated by this kind of experiment requires a statistical treatment adequate to its characteristics. An important application of DNA arrays is the identification of differentially expressed genes in different RNA samples. This selection demands refined statistical tests, able of distinguish among the great number of genes usually present in the arrays those which expression is significantly different. In this work, we have developed algorithms for the analysis of DNA array data, efficient in handling the usual problems in this kind of data, as the limited number of replicates. When applied to data simulations the developed algorithms showed to be competitive with other methods of analysis described in the literature and widely used, overperforming them in some situations. The application of these algorithms was also demonstrated in an experiment devoted to the identification of sugarcane genes differentially expressed in response to phosphate deficiency. Phosphorous is an essential macronutrient, absorbed by plants mostly in the form of inorganic phosphate (Pi). The phosphate deficiency is frequent in the nature, especially in the acid soils of tropical and subtropical areas. Because of the great economical importance of sugarcane, the identification of genes that are differentially expressed in response to phosphate deficiency in this species is of great scientific and agronomic interest. Clustering algorithms were also applied to the expression data obtained in the experiment, identifying patterns of gene expression in the different stages of the sugarcane response to the stress, thus providing an additional characterization of it. In the future, the results of this work can lead to the development of sugarcane cultivars that have better performance in phosphate deficient soils, what would be of great agronomic interest / Doutorado / Bioinformatica / Doutor em Genetica e Biologia Molecular

Orientadores: Marcelo Menossi Teixeira, Eugenio Cesar Ulian / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-09T08:36:41Z (GMT). No. of bitstreams: 1 Camargo_SandraRodriguesde_D.pdf: 3039020 bytes, checksum: 14d2f6b74500161c7e839b7d6776dd47 (MD5) Previous issue date: 2007 / Resumo: A cana-de-açúcar é uma cultura de grande importância social e econômica para o Brasil. Além da produção de açúcar, que coloca o país como o maior produtor mundial, a cana-de-açúcar tem alcançado grande destaque na produção de energia renovável e pouco poluente, o etanol. Devido ao rápido crescimento das áreas cultivadas e do aumento no número de indústrias processadoras da cana-de-açúcar, milhares de novos empregos têm sido gerados no Brasil. Por se tratar de uma cultura tão importante para a sociedade e economia brasileira, a cana-de-açúcar vem ganhando cada vez mais destaque e atenção das instituições de pesquisa públicas e privadas. Grande parte da pesquisa e experimentação desenvolvida atualmente para esta cultura visa o desenvolvimento de variedades mais adaptadas às condições edafoclimáticas do Brasil e mais resistentes e tolerantes contra pragas e doenças. Outro importante campo de estudo que tem sido bastante focado no momento é a compreensão dos mecanismos bioquímicos da síntese de sacarose com a finalidade de aumentar a produção deste açúcar e conseqüentemente de etanol. O desenvolvimento de um sistema genético capaz de modificar o metabolismo da planta, através de um estímulo artificial, pode ser muito útil no aumento da produtividade e qualidade ou na redução dos custos envolvidos com a produção de cana-de-açúcar. Esta tecnologia poderá contribuir significativamente para um avanço ainda maior da cana-de açúcar no país. A partir desta premissa, o presente estudo buscou identificar e caracterizar um sistema de indução de expressão gênica disparado pela aplicação externa de etanol em folhas de cana-de-açúcar. Para isso, fazendo uso da técnica de macroarranjos de cDNA, analisamos a expressão gênica de 3.575 ESTs, isolados de folhas de cana-de-açúcar, em resposta a aplicação de etanol. Setenta ESTs apresentaram padrão de expressão alterado pelo etanol. Dentre estes, foram identificados ESTs que codificavam para proteínas relacionadas ao processo de transcrição e tradução e estresse abiótico. Muitos genes cuja função ainda permanece desconhecida também foram identificados nesta análise. Dos 70 ESTs identificados, 48 tiveram expressão induzida pela aplicação de etanol. A partir dos ESTs selecionados como induzidos pelo tratamento com etanol, foi possível selecionar o gene ERD (early responsive dehydration) como candidato para identificação e caracterização da sua seqüência promotora. O EST do gene ERD apresentou um perfil de expressão interessante, com expressão basal baixa durante os tratamentos controle e indução da expressão após a primeira hora de tratamento com etanol. Estudos realizados com várias espécies de plantas demonstram que o sistema alc é um sistema eficiente de expressão gênica baseado na indução por etanol. A partir desta informação, desenvolvemos um vetor de expressão contendo o promotor alcA regulando a expressão do gene repórter da ß-glucuronidase e em seqüência, o promotor constitutivo Ubi-1 de milho controlando a expressão do gene alcR, um fator de transcrição indispensável para a ativação do sistema. Posteriormente, esta construção foi utilizada para transformação genética de plantas de cana-de-açúcar que no momento estão sendo selecionadas e analisadas quanto a introgressão estável do cassete gênico. Outra etapa do presente estudo foi realizada com o gene SsNAC23, já descrito como induzido por estresse de frio, estresse hídrico e herbivoria. Neste trabalho foi demonstrado que SsNAC23 também é induzido pela aplicação de etanol nas folhas de cana-de- açúcar logo após uma hora de exposição ao agente indutor. Concluindo, os resultados obtidos neste trabalho contribuem para elucidar questões importantes do processo de regulação da expressão gênica induzida por etanol, além da validação de um processo útil para aplicação na agricultura. A partir dos dados gerados nas análises de macroarranjos de cDNA foi possível ainda, validar um novo método de quantificação do erro estatístico resultante das análises realizadas no programa SOM (Self Organizing Maps) / Abstract: The sugarcane is a very important crop in Brazil, the biggest producer of the World. Besides sugar, the sugarcane is also used to produce ethanol, a very important renewable source of energy in Brazil. Nowadays this crop is responsible for generation of thousands of job positions directly and indirectly linked to the sugar and ethanol industry and market. Since the sugarcane is getting an important role in the Brazil economy, Brazilians researchers are focusing a lot of work in this crop to breed new varieties with improved traits and better adaptation to stressing environmental, such as cold, poor and acid soils, and attack of pests and diseases. Other important field of study is the improvement of sucrose content to increase the efficiency of ethanol production. The development of a genetic system triggered by an external stimulus and able to modify the plant metabolism may be very useful to improve productivity and quality, besides the cost reduction of sugarcane production. This technology might permit Brazil to increase the expansion of this crop without degrading the environmental. Therefore, the aim of this work was the identification of an efficient system of gene expression induced by ethanol. The technique of cDNA array was used to check the expression of 3,575 ESTs isolated from sugarcane leaves previously treated with ethanol. Seventy ESTs showed expression profile altered by ethanol. Among these ESTs with altered expression we have identified sequences encoding proteins involved with transcription and translation and genes previously reported as responsive to abiotic and biotic stresses. Forty eight of the 70 ESTs with altered expression were up-regulated by ethanol. The SsNAC23, a gene induced by cold, dry and insect attack, was also responsive to ethanol in this study. The expression of SsNAC23 in sugarcane leaves was increased after one hour of exposition to ethanol. The expression analysis of genes induced by ethanol in arrays filters allowed us select a candidate gene whose promoter region will be identified and studied. The gene chosen was the ERD, Early Responsive to Dehydration, whose expression profile was the absence of expression under control treatment and high induction after one hour of ethanol application. Previous works have showed that the genetic system based in ethanol induction, also known as alc system, can be very useful in crops. This system was tested in several plant species and the results were very promising. Therefore, one of the goals of this work was the production of genetic altered sugarcane plants with the alc system. For that, we have developed an expression cassette using the alcA promoter regulating the expression of the ß -glucuronidase, used as a reporter gene, and the constitutive promoter Ubi-1 from maize controlling the expression of the gene alcR, a transcriptor factor essential to ctivation of the alc system. The transformed sugarcanes are being analysed and selected to construct introgression. The results obtained in this work will contribute to understanding of gene expression regulation using an external and chemical inductor as well as provide new insights to the development of new approaches of gene expression control in sugarcane. Besides that, the array data was also used to validate a new statistical method of error estimation by using the SOM software / Doutorado / Genetica Vegetal e Melhoramento / Doutor em Genetica e Biologia Molecular

Staphylococcus aureus kann bei etwa 25% der gesunden Normalbevölkerung nachgewiesen werden, ohne Symptome zu verursachen. Dieser Keim ist jedoch auch einer der wichtigsten Erreger bei Osteomyelitis und Infektionen von orthopädischen Implantaten wie z. B. von künstlichen Knie- oder Hüftgelenken. Diese Infektionen führen meist zu aufwendigen und risikobehafteten operativen Eingriffen sowie zu einer langfristigen Antibiotikagabe. In der vorliegenden Arbeit sollten S. aureus-Isolate charakterisiert werden, die aus Osteomyelitisherden oder infizierten orthopädischen Implantaten gewonnen wurden. Ziel war es, die Isolate daraufhin zu untersuchen, ob bestimmte Stämme dominieren und ob das Vorhandensein bestimmter Virulenzfaktoren mit einem besonderen Risiko für solche Infektionen korreliert. Für diese Untersuchungen wurden DNA-Arrays eingesetzt, welche es ermöglichen, alle relevanten Virulenzfaktoren in einem Experiment nachzuweisen, einen „genetischen Fingerabdruck“ zu erheben und die Isolate so Verwandtschaftsgruppen (klonalen Komplexen, CC) zuzuordnen. Insgesamt wurden 119 klinische Isolate charakterisiert. Sie gehörten zu 20 verschiedenen klonalen Komplexen. CC8 (19,3%), CC45 (17,7%) und CC30 (12,6%) dominierten. MRSA waren selten nachweisbar. Die sieben MRSA-Isolate gehörten zu den lokal dominierenden Stämmen (Rhein-Hessen, Süddeutscher, Barnimer und Berliner Epidemiestamm sowie Europäischer caMRSA-Klon). Die Populationsstruktur der klinischen Isolate und die Häufigkeiten der untersuchten Virulenz- und Adhäsionsfaktoren entsprachen weitestgehend Isolaten von asymptomatischen Trägern, die in einer früheren Studie bestimmt wurden (Molecular epidemiology of Staphylococcus aureus in asymptomatic carriers; Monecke, Lüdicke, Slickers, Ehricht; Eur J Clin Microbiol Infect Dis. 2009). Es konnte kein molekularer Marker identifiziert werden, der allein für eine Risikostratifizierung eingesetzt werden kann. Das Gen für Staphylokinase (sak) war jedoch bei den klinischen Isolaten (90,8%) häufiger nachzuweisen als in Isolaten von asymptomatischen Trägern (71,6%). Einige andere Gene traten ebenfalls bei Patienten häufiger auf, aber waren insgesamt zu selten, um bei Osteomyelitis und Implantatinfektionen eine signifikante Rolle zu spielen. Ein Beispiel dafür war das Panton-Valentine Leukozidin, das in 0,7% der Isolate von asymptomatischen Trägern und in 3,4% der Patientenisolate gefunden wurde. CC15 war bei Isolaten von asymptomatischen Trägern häufiger vertreten (16.8%) als bei Patientenisolaten (5.9%). Da alle CC15-Isolate sak-negativ waren, könnte auch diese Beobachtung als Indiz für einen Zusammenhang zwischen dem Vorhandensein von Staphylokinase und Invasivität gewertet werden. CC45 war bei Patientenisolaten (17,7%) häufiger als bei den asymptomatischen Trägern (9,0%) vorhanden. Es konnte jedoch kein CC45-spezifischer Faktor identifiziert werden, der mit einer höheren Virulenz im Zusammenhang stehen könnte. Des Weiteren sollte untersucht werden, ob S. aureus in infizierten orthopädischen Implantaten endogenen Ursprungs ist. Bei 23 Patienten mit Infektionen von Knie- oder Hüfttotalendoprothesen konnten parallel Nasenabstriche genommen und untersucht werden. Fünfzehn von ihnen (65,2%) waren Träger von S. aureus und bei neun (39,1%) waren die Isolate aus Nasenabstrichen und den infizierten Endoprothesen identisch. Dies weist darauf hin, daß Träger von S. aureus ein erhöhtes Risiko haben, Infektionen von Knie- oder Hüfttotalendoprothesen zu erleiden und daß ein großer Teil dieser Infektionen endogenen Ursprungs ist. Deshalb sollten Patienten vor Implantation von Knie- oder Hüfttotalendoprothesen auf Trägerschaft von S. aureus untersucht werden. Falls S. aureus nachgewiesen wird, sollte dieser Keim generell präoperativ eradiziert werden, um das Risiko endogener Infektionen zu verringern. Eine prospektive Studie zu diesem Thema wird empfohlen. / Staphylococcus aureus is asymptomatically carried by approximately 25% of a normal population. It is also one of the most important causes of osteomyelitis and infections of orthopedic implants such as total hip or knee replacements. Such infections usually lead to complicated and risky surgical procedures as well as to long-term antibiotic treatment. In the present work, S. aureus isolates from osteomyelitis or implant infections were to be characterised. The aim of the study was to prove whether certain strains were overrepresented among patient isolates, and whether the presence of certain virulence factors might correlate with these infections. DNA arrays where used which facilitate to screen for all relevant virulence factors within a single experiment and which allow typing by obtaining a genetic fingerprint of the examined isolate. By this method, it was also possible to assign isolates to phylogenetic clusters, so-called clonal complexes. 119 clinical isolates were characterised in this way. They belonged to 20 different clonal complexes (CC). CC8 (19.3%), CC45 (17.7%) and CC30 (12.6%) dominated. MRSA were rarely detected. The seven MRSA isolates belonged to locally predominant epidemic strains (ST5-MRSA-II, ST228-MRSA-I, ST22-MRSA-IV, ST45-MRSA-IV and ST80-MRSA-IV). The population structure of the clinical isolates and the relative abundances of the examined virulence and adhesion factors corresponded largely to isolates from asymptomatic carriers, which has been examined in an earlier study (Molecular epidemiology of Staphylococcus aureus in asymptomatic carriers; Monecke, Lüdicke, Slickers, Ehricht; Eur J Clin Microbiol Infect Dis. 2009). No molecular maker was detected which could alone be used for risk assessment. The gene for staphylokinase (sak) was clearly more common among clinical isolates (90.8%) than in isolates from asymptomatic carriers (71.6%). Some other genes were also found to be more common in patient isolates, but were very rare so that a significant role in bone and implant infection appeared to be unlikely. An example is Panton-Valentine leukocidin, which was detected in 3.4% of patient isolates and 0.7% of carrier isolates. CC15 was more commonly detected among healthy carriers (16.8%), than among patients (5.9%). Since all CC15 isolates were negative for sak, this also might be related to a possible role of staphylokinase in pathogenesis of invasive disease. CC45 was more abundant in patient samples (17.7%) than in swabs of healthy carriers (9.0%). However, it was not possible to identify a CC45-specific factor which might have been related to a higher virulence. Another aim of the study was to investigate whether S. aureus from orthopaedic implant infections were of endogenous origin. For 23 patients with S. aureus infections of total knee or hip prosthetics, it was possible to obtain nasal swabs in order to detect and type possible S. aureus carriage strains. Fifteen of them (65.2%) carried S. aureus. In nine patients (39.1%), isolates from nasal swabs and foci of infection were identical. This indicates that carriers of S. aureus are at risk of developing infections of total knee or hip prosthetics, and that a considerable proportion of these infections are of endogenous origin. Therefore, patients should generally be screened for S. aureus carriage prior to joint replacement. In case of detection, S. aureus should be eradicated in order to decrease the risk of endogenous infection. A prospective study is recommended.

Staphylococcus aureus kann bei etwa 25% der gesunden Normalbevölkerung nachgewiesen werden, ohne Symptome zu verursachen. Dieser Keim ist jedoch auch einer der wichtigsten Erreger bei Osteomyelitis und Infektionen von orthopädischen Implantaten wie z. B. von künstlichen Knie- oder Hüftgelenken. Diese Infektionen führen meist zu aufwendigen und risikobehafteten operativen Eingriffen sowie zu einer langfristigen Antibiotikagabe. In der vorliegenden Arbeit sollten S. aureus-Isolate charakterisiert werden, die aus Osteomyelitisherden oder infizierten orthopädischen Implantaten gewonnen wurden. Ziel war es, die Isolate daraufhin zu untersuchen, ob bestimmte Stämme dominieren und ob das Vorhandensein bestimmter Virulenzfaktoren mit einem besonderen Risiko für solche Infektionen korreliert. Für diese Untersuchungen wurden DNA-Arrays eingesetzt, welche es ermöglichen, alle relevanten Virulenzfaktoren in einem Experiment nachzuweisen, einen „genetischen Fingerabdruck“ zu erheben und die Isolate so Verwandtschaftsgruppen (klonalen Komplexen, CC) zuzuordnen. Insgesamt wurden 119 klinische Isolate charakterisiert. Sie gehörten zu 20 verschiedenen klonalen Komplexen. CC8 (19,3%), CC45 (17,7%) und CC30 (12,6%) dominierten. MRSA waren selten nachweisbar. Die sieben MRSA-Isolate gehörten zu den lokal dominierenden Stämmen (Rhein-Hessen, Süddeutscher, Barnimer und Berliner Epidemiestamm sowie Europäischer caMRSA-Klon). Die Populationsstruktur der klinischen Isolate und die Häufigkeiten der untersuchten Virulenz- und Adhäsionsfaktoren entsprachen weitestgehend Isolaten von asymptomatischen Trägern, die in einer früheren Studie bestimmt wurden (Molecular epidemiology of Staphylococcus aureus in asymptomatic carriers; Monecke, Lüdicke, Slickers, Ehricht; Eur J Clin Microbiol Infect Dis. 2009). Es konnte kein molekularer Marker identifiziert werden, der allein für eine Risikostratifizierung eingesetzt werden kann. Das Gen für Staphylokinase (sak) war jedoch bei den klinischen Isolaten (90,8%) häufiger nachzuweisen als in Isolaten von asymptomatischen Trägern (71,6%). Einige andere Gene traten ebenfalls bei Patienten häufiger auf, aber waren insgesamt zu selten, um bei Osteomyelitis und Implantatinfektionen eine signifikante Rolle zu spielen. Ein Beispiel dafür war das Panton-Valentine Leukozidin, das in 0,7% der Isolate von asymptomatischen Trägern und in 3,4% der Patientenisolate gefunden wurde. CC15 war bei Isolaten von asymptomatischen Trägern häufiger vertreten (16.8%) als bei Patientenisolaten (5.9%). Da alle CC15-Isolate sak-negativ waren, könnte auch diese Beobachtung als Indiz für einen Zusammenhang zwischen dem Vorhandensein von Staphylokinase und Invasivität gewertet werden. CC45 war bei Patientenisolaten (17,7%) häufiger als bei den asymptomatischen Trägern (9,0%) vorhanden. Es konnte jedoch kein CC45-spezifischer Faktor identifiziert werden, der mit einer höheren Virulenz im Zusammenhang stehen könnte. Des Weiteren sollte untersucht werden, ob S. aureus in infizierten orthopädischen Implantaten endogenen Ursprungs ist. Bei 23 Patienten mit Infektionen von Knie- oder Hüfttotalendoprothesen konnten parallel Nasenabstriche genommen und untersucht werden. Fünfzehn von ihnen (65,2%) waren Träger von S. aureus und bei neun (39,1%) waren die Isolate aus Nasenabstrichen und den infizierten Endoprothesen identisch. Dies weist darauf hin, daß Träger von S. aureus ein erhöhtes Risiko haben, Infektionen von Knie- oder Hüfttotalendoprothesen zu erleiden und daß ein großer Teil dieser Infektionen endogenen Ursprungs ist. Deshalb sollten Patienten vor Implantation von Knie- oder Hüfttotalendoprothesen auf Trägerschaft von S. aureus untersucht werden. Falls S. aureus nachgewiesen wird, sollte dieser Keim generell präoperativ eradiziert werden, um das Risiko endogener Infektionen zu verringern. Eine prospektive Studie zu diesem Thema wird empfohlen. / Staphylococcus aureus is asymptomatically carried by approximately 25% of a normal population. It is also one of the most important causes of osteomyelitis and infections of orthopedic implants such as total hip or knee replacements. Such infections usually lead to complicated and risky surgical procedures as well as to long-term antibiotic treatment. In the present work, S. aureus isolates from osteomyelitis or implant infections were to be characterised. The aim of the study was to prove whether certain strains were overrepresented among patient isolates, and whether the presence of certain virulence factors might correlate with these infections. DNA arrays where used which facilitate to screen for all relevant virulence factors within a single experiment and which allow typing by obtaining a genetic fingerprint of the examined isolate. By this method, it was also possible to assign isolates to phylogenetic clusters, so-called clonal complexes. 119 clinical isolates were characterised in this way. They belonged to 20 different clonal complexes (CC). CC8 (19.3%), CC45 (17.7%) and CC30 (12.6%) dominated. MRSA were rarely detected. The seven MRSA isolates belonged to locally predominant epidemic strains (ST5-MRSA-II, ST228-MRSA-I, ST22-MRSA-IV, ST45-MRSA-IV and ST80-MRSA-IV). The population structure of the clinical isolates and the relative abundances of the examined virulence and adhesion factors corresponded largely to isolates from asymptomatic carriers, which has been examined in an earlier study (Molecular epidemiology of Staphylococcus aureus in asymptomatic carriers; Monecke, Lüdicke, Slickers, Ehricht; Eur J Clin Microbiol Infect Dis. 2009). No molecular maker was detected which could alone be used for risk assessment. The gene for staphylokinase (sak) was clearly more common among clinical isolates (90.8%) than in isolates from asymptomatic carriers (71.6%). Some other genes were also found to be more common in patient isolates, but were very rare so that a significant role in bone and implant infection appeared to be unlikely. An example is Panton-Valentine leukocidin, which was detected in 3.4% of patient isolates and 0.7% of carrier isolates. CC15 was more commonly detected among healthy carriers (16.8%), than among patients (5.9%). Since all CC15 isolates were negative for sak, this also might be related to a possible role of staphylokinase in pathogenesis of invasive disease. CC45 was more abundant in patient samples (17.7%) than in swabs of healthy carriers (9.0%). However, it was not possible to identify a CC45-specific factor which might have been related to a higher virulence. Another aim of the study was to investigate whether S. aureus from orthopaedic implant infections were of endogenous origin. For 23 patients with S. aureus infections of total knee or hip prosthetics, it was possible to obtain nasal swabs in order to detect and type possible S. aureus carriage strains. Fifteen of them (65.2%) carried S. aureus. In nine patients (39.1%), isolates from nasal swabs and foci of infection were identical. This indicates that carriers of S. aureus are at risk of developing infections of total knee or hip prosthetics, and that a considerable proportion of these infections are of endogenous origin. Therefore, patients should generally be screened for S. aureus carriage prior to joint replacement. In case of detection, S. aureus should be eradicated in order to decrease the risk of endogenous infection. A prospective study is recommended.