No / Gram-positive bacterial lipoproteins are a functionally diverse and important class of peripheral membrane proteins. Recent advances in molecular biology and the availability of whole genome sequence data have overturned many long-held assumptions about the export and processing of these proteins, most notably the recent discovery that not all lipoproteins are exported as unfolded substrates through the general secretion pathway. Here, we review recent discoveries concerning the export and processing of these proteins, their role in virulence in Gram-positive bacteria and their potential as vaccine candidates or targets for new antimicrobials. / Biotechnology and Biological Sciences Research Council (grant numbers F009224/1, F009429/1, EGH16082), the Medical Research Council (MRC), the Commission of the European Community (grant LSHG-CT-2004–005257) and The Royal Society.

Yes / Highly branched poly(N-isopropylacrylamide) (HB-PNIPAM), functionalized with vancomycin at the chain ends, acted as a bacterial adhesive and was incorporated into polyurethane foams to form semi-interpenetrating networks. The poly(N-isopropylacrylamide) was labelled with a solvatochromic dye, Nile red. It was found that the thermal response of the polymer was dependent on architecture and temperature dependent color changes were observed within the foam. The foams had open pore structures and the presence of the HB-PNIPAM substantially reduced the shrinkage of the foam as the temperature was increased upto 20 °C. The foams were selectively adhesive for Staphylococcus aureus (Gram-positive bacteria) compared to Pseudomonas aeruginosa (Gram-negative bacteria) and the presence of S. aureus was indicated by increased fluorescence intensity (590 to 800 nm).

Yes / Highly branched poly(N-isopropyl acrylamide) additives chain end functionalised with vancomycin have been designed to agglutinate and report on targetted Gram-positive strains of bacteria (S. aureus). These branched systems selectively desolvate with temperature or binding interactions depending on their chain architecture. We have prepared samples with three different degrees of branching which have incorporated Nile red acrylate as a low concentration of co-monomer to report upon their solution properties. A linear analogue polymer functionalised with vancomycin along the chain instead of the termini is presented as a control which does not bind to targeted bacteria. These samples were analysed by diffusion NMR spectrometry (DOSY), calorimetry, fluorescence lifetime measurements, optical microscopy and scanning electron microscopy to gain a full understanding of their solution properties. The branched polymers are shown conclusively to have a core-shell structure, where the chain ends are expressed from the desolvated globule even above the lower critical solution temperature – as demonstrated by NMR measurements. The level of desolvation is critically dependent on the degree of branching, and as a result we have found intermediate structures provide optimal body temperature bacterial sensing as a consequence of the Nile red reporting dye. / To support initial polymer synthesis work SR has received funding from UK/Smith and Nephew Ltd (UK) (TSB 103988) and MRC (MR/N501888/2). Funding for further analytical work by TS was funded by the Royal Society of Chemistry (E21- 8346952505). Furthermore Translate MedTech (Higher Education Funding Council England, 2016-2018) funding paid for research student Mariya Kalinichenko to fund electron microscopy studies. The authors acknowledge support provided by the internal seed fund of University of Bradford High Performance Computing Service in the completion of this work.

Rhodococcus fascians is a Gram-positive phytopathogenic bacterium which induces the development of leafy galls, local amplifications of multiple buds, on most infected plants. This process is linked to the production of phytohormones along with the presence of essential virulence-associated genes like the plasmid loci att and fas and the chromosomal gene vicA. However, the presence of these genes is not sufficient to ensure the infection phenotype development, indicating that other genes play a role in R. fascians pathogenicity. In this work, we studied the metabolic modifications occurring when the bacterium interacts with its host using a proteomic approach. A comparison between virulent and avirulent strains showed variations in the expression of catalases. In the virulent strain, besides the transitory induction of the att locus expression, the bacterium changes its metabolism from the Krebs cycle to the glyoxylate shunt, a process which is frequently observed in bacteria confronted to a hostile environment. The expression of the shunt-specific enzyme isocitrate lyase increased, while expression of fumarate hydratase and pyruvate dehydrogenase decreased. Hence, we focused on the link between the glyoxylate shunt and virulence. A screening of a R. fascians mutant library based on the capacity of bacteria to use acetate as the sole carbon source, a metabolic pathway depending on the glyoxylate shunt, resulted in the identification of a new gene essential for R. fascians pathogenicity. This gene encodes a glycosyl transferase, an enzyme known to be involved in the bacterial cell wall biosynthesis but possibly also implicated in cytokinin secretion. A mutant in this gene harboured an altered colony phenotype and could not induce malformations on infected plants. Accordingly, our results were integrated in the leafy gall pathology model recently presented by Stes et al. (2011). Finally, the several questions that are raised by this work, allowed us to suggest further research perspectives in order to unveil a little more of the R. fascians mysterious ways to interact with the plant./Rhodococcus fascians est une bactérie Gram-positive phytopathogène qui induit le développement de galles feuillées, des amplifications locales de multiples bourgeons, sur la plupart des plantes infectées. Ce processus est lié à la production de phytohormones ainsi qu’à la présence de gènes essentiels associés à la virulence tels que les loci plasmidiques att et fas et le gène chromosomique vicA. Cependant, la présence de ces gènes ne suffit pas à garantir le développement du phénotype d’infection, indiquant que d’autres gènes jouent un rôle dans la pathogénicité de R. fascians. Dans ce travail, nous avons étudié les modifications métaboliques qui se produisent lorsque la bactérie interagit avec son hôte par une approche protéomique. Une comparaison entre les souches virulente et avirulente a mis en évidence des variations d’expression au niveau des catalases. Dans la souche virulente, outre l’induction transitoire de l’expression du locus att, la bactérie change son métabolisme pour passer du cycle de Krebs au shunt du glyoxylate, un processus fréquemment observé chez les bactéries confrontées à un environnement hostile. L’expression de l’isocitrate lyase, enzyme spécifique au shunt, augmente, tandis que celle de la fumarate hydratase et de la pyruvate déhydrogénase diminue. Nous nous sommes donc intéressés au lien entre le shunt du glyoxylate et la virulence. Le screening d’une banque de mutants de R. fascians basé sur la capacité de la bactérie à utiliser l’acétate comme seule source de carbone, une voie métabolique dépendant du shunt du glyoxylate, a permis d’identifier un nouveau gène essentiel pour la pathogénicité de R. fascians. Ce gène code pour une glycosyl transferase, une enzyme impliquée dans la biosynthèse de la paroi bactérienne mais également dans la sécrétion des cytokinines. Un mutant dans ce gène présente un phénotype de colonie altéré et ne peut induire de malformations chez les plantes infectées. Finalement, nos résultats et les pistes d’interprétations que nous avons émisent nous permettent de compléter le modèle de l’interaction R. fascians-plante proposé récemment par Stes et al. (2011). Des perspectives de recherches visant une meilleure compréhension de ce pathosystème sont proposées. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

MSc (Microbiology) / Department of Microbiology / See the attached abstract below

Les quatre étapes principales d'infection des bactéries par leurs virus sont (i) la reconnaissance spécifique de la cellule hôte et l'entrée du génome dans le cytoplasme,(ii) la réplication du génome viral, (iii) l'assemblage des particules virales, et (iv) leur relâchement, menant dans la plupart des cas à la lyse de la cellule. Bien que la description des étapes individuelles du cycle viral a été relativement bien établie, les détails de comment d'ADN viral chemine du virion jusqu’au cytoplasme de la bactérie hôte et de comment l'environnement cellulaire participe au processus restent mal compris.La première étape de l’infection est la reconnaissance d’un récepteur à la surface de la bactérie hôte par la machinerie d’adsorption du phage. Les barrières que l’agent infectieux doit franchir par la suite sont la membrane externe de la bactérie Gram-negative, la paroi cellulaire et la membrane cytoplasmique. Ceci implique une dégradation localisée de la paroi et le cheminement de l’ADN à travers un pore dans la membrane. L‘ADN linéaire se circularise normalement dans le cytoplasme et il est répliqué par la suite. On a utilisé le bactériophage SPP1 qui infecte la bactérie Gram-positive Bacillus subtilis comme modèle d’étude pour disséquer ces différentes étapes clés pour le démarrage de l’infection virale. Dans ce travail de thèse les conditions d’infection et d’acquisition de données pour suivre en temps réel la dépolarisation de la membrane cellulaire de B. subtilis lors de l’infection par SPP1 ont été mis au point. Il est montré que le démarrage de l’infection déclenche une dépolarisation très rapide de la membrane cytoplasmique.Le potentiel de membrane n’est plus rétablit pendant toute la durée du cycle d'infection. Ce changement du potentiel de membrane au début de l’infection dépend de la présence du récepteur YueB. L’amplitude de la dépolarisation dépend du nombre de particules virales infectieuses présentes et de la concentration du récepteur YueB à la surface de la bactérie hôte. L’interaction du phage avec le récepteur YueB conduit à l’interaction irréversible et à l'éjection de l’ADN de SPP1. Pour établir si c’est l’interaction avec YueB ou le début de l’entrée de l’ADN qui conduit à la dépolarisation de la membrane on a utilisé des phages SPP1 éclates par EDTA qui adsorbent normalement à B. subtilis mais qui n’avaient plus leur ADN. Les résultats obtenus ont montré que la dépolarisation requiert l’interaction du virus intacte avec le récepteur YueB. Des concentrations sous-millimolaire de Ca2+ sont nécessaires et suffisantes pour SPP1 liaison réversible à l'enveloppe d'hôte et donc de déclencher la dépolarisation.La cinétique d’entrée de l’ADN du bactériophage SPP1 dans la bactérie Bacillus subtilis a été suivie en temps réel par microscopie de fluorescence. On a mis au point une méthode de microscopie pour visualiser des particules virales marquées avec des «quantum dots» ce qui permit de démontrer que ces particules se fixent préférentiellement aux pôles des bacilli. L’immuno-marquage du récepteur de SPP1,la protéine YueB, a montré que celle-ci a une organisation ponctuée à la surface de B.subtilis et se concentre particulièrement aux extrémités de la bactérie. Cette localisation particulière du phage sur la surface de la cellule hôte corrèle avec l’observation que l’ADN viral rentre dans le cytoplasme (<2 min) et se réplique dans des foci situés dans la plupart des cas à proximité des pôles de B. subtilis. L’étude spatio-temporelle de l’interaction de SPP1 avec son hôte Gram-positive montre que le virus cible des régions spécifiques de la bactérie pour son entrée et pour sa réplication. Transfert d'ADN dans le cytoplasme dépend des concentrations millimolaires de Ca2+. Un modèle décrivant les événements précoces de l'infection bactériophage SPP1 est présenté. / The four main steps of bacterial viruses (bacteriophages) lytic infection are (i) specific recognition and genome entry into the host bacterium, (ii) replication of the viral genome, (iii) assembly of viral particles, and (iv) their release, leading in most cases to cell lysis. Although the course of individual steps of the viral infection cycle has been relatively well established, the details of how viral DNA transits from the virion to the host cytoplasm and of how the cellular environment catalyzes and possibly organizes the entire process remain poorly understood.Tailed bacteriophages are by far the most abundant viruses that infect Eubacteria. The first event in their infection is recognition of a receptor on the surface of host bacterium by the phage adsorption machinery. The barriers that the infectious particle overcomes subsequently are the cell wall and the cytoplasmic membrane of bacteria. This implies a localized degradation of the wall and the flow of its double stranded DNA (dsDNA) through a hydrophilic pore in the membrane. The lineards DNA molecule is most frequently circularized in the cytoplasm followed by its replication. In this study we used bacteriophage SPP1 that infects the Gram-positive bacterium Bacillus subtilis as a model system to dissect the different steps leading to transfer of the phage genome from the viral capsid to the host cell cytoplasm.normally to B. subtilis but do not trigger depolarization of the CM. Attachment of intact SPP1 particles is thus required for phage-induced depolarization.The beginning of B. subtilis infection by bacteriophage SPP1 was followed inspace and time. The position of SPP1 binding at the cell surface was imaged by fluorescence microscopy using virus particles labeled with "quantum dots". We found that SPP1 reversible adsorption occurs preferentially at the cell poles. This initial binding facilitates irreversible adsorption to the SPP1 phage receptor protein YueB,which is encoded by a putative type VII secretion system gene cluster.Immunostaining and YueB – GFP fusion showed that the phage receptor protein YueB is found over the entire cell surface. It concentrates at the bacterial poles too,and displays a punctate distribution over the sidewalls. The dynamics of SPP1 DNA entry and replication was visualised in real time by assaying specific binding of a fluorescent protein to tandem sequences present in the SPP1 genome. During infection, most of the infecting phages DNA entered and replicated near the bacterial poles in a defined focus. Therefore, SPP1 assembles a replication factory at a specific location in the host cell cytoplasm. DNA delivery to the cytoplasm depends on millimolar concentrations of Ca2+ allowing uncoupling it from the precedent steps of SPP1 adsorption to the cell envelope and CM depolarization that require only micromolar amounts of this divalent cation. A model describing the early events of bacteriophage SPP1 infection is presented.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 112-144).

Orientadores: Arnaldo Yoshiteru Kuaye, Izildinha Moreno / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-08T11:59:55Z (GMT). No. of bitstreams: 1 Nascimento_MaristeladaSilvado_D.pdf: 987996 bytes, checksum: b40b83ce1cfdfd6fe5e6d3a67301de6d (MD5) Previous issue date: 2007 / Resumo: A biopreservação é uma técnica utilizada para estender a vida útil e aumentar a segurança dos alimentos por meio do emprego de microbiota protetora e/ou seus peptídeos antimicrobianos. O objetivo deste trabalho foi avaliar a atividade antimicrobiana de culturas produtoras de bacteriocinas sobre alguns patógenos Gram-positivos de ocorrência comum em produtos lácteos. As culturas bacteriocinogênicas Lactococcus lactis subsp. Lactis ATCC 11454, Lactobacillus plantarum ALC 01 e Enterococcus faecium FAIR-E 198 apresentaram comportamento distinto em relação à produção de bacteriocinas quando inoculadas em caldo MRS e em leite desnatado reconstituído (LDR) a 10%. Na avaliação do espectro de ação antimicrobiano pelo método de difusão em ágar por inoculação em poços, as bacteriocinas produzidas por Lb. plantarum ALC 01 e E. faecium FAIR-E 198 apresentaram atividade inibitória apenas sobre as linhagens de Listeria monocytogenes, já a nisina produzida por Lc. lactis subsp. lactis ATCC 11454 demonstrou espectro de ação mais amplo, porém com menor atividade que as demais culturas bacteriocinogênicas. Na avaliação da compatibilidade de desenvolvimento associativo com fermentos lácticos comerciais, somente Lc. lactis subsp. lactis ATCC 11454 apresentou atividade (halo de 6mm) sobre as linhagens constituintes de ambos os fermentos lácticos avaliados. A determinação da atividade acidificante foi realizada em LDR 10% após 8 e 24h de incubação a 35ºC; a adição de 0,1% e de 0,5% das culturas bacteriocinogênicas não afetou significativamente a capacidade de acidificação dos fermentos lácticos. Além disso, observou-se que o desenvolvimento associativo dos fermentos lácticos com Lb. Plantarum ALC 01 e E. faecium FAIR-E 198, em ambas as concentrações, proporcionou significativo aumento da atividade das bacteriocinas destas culturas, enquanto que a atividade da nisina de Lc. lactis subsp. lactis ATCC 11454 foi suprimida. A atividade de aminopeptidases foi determinada após desenvolvimento das culturas lácticas em caldo MRS, Lb. Plantarum ALC 01 apresentou as maiores atividades. Também foi analisado o comportamento de patógenos Gram-positivos durante desenvolvimento associativo com as culturas produtoras de bacteriocinas e fermento láctico em LDR 10% a 35ºC por 48h. Lb. plantarum ALC 01 e E. faecium FAIR-E 198 não influenciaram significativamente o desenvolvimento de Bacillus cereus K1-B041 e de Staphylococcus aureus ATCC 27154 durante as primeiras 24h de incubação a 35ºC, contudo apresentaram forte ação inibitória sobre L monocytogenes Scott A. Já Lc. lactis subsp. lactis ATCC 11454 afetou o desenvolvimento de todos os patógenos apenas durante as primeiras 12h de incubação. O fermento láctico demonstrou significativa ação inibitória sobre B. cereus K1-B041 (>7,37 log UFC/ml) e L monocytogenes Scott A (>6,26 log UFC/ml). Em queijo Minas Frescal, não foi observada diferença significativa entre a ação das culturas bacteriocinogênicas e o fermento láctico sobre L. monocytogenes Scott A e S. aureus ATCC 27154. B. cereus K1-B041 demonstrou susceptibilidade a Lb. plantarum ALC 01 e E. faecium FAIR-E 198 após 7 dias. Pelo método de diluição crítica não foi detectada atividade de bacteriocina nos queijos durante os 21 dias de estocagem a 8 ± 1ºC. A adição das culturas produtoras de bacteriocinas como adjuntas ao queijo Minas Frescal não promoveu alteração no pH e na acidez, contudo Lb. plantarum ALC 01 e E. faecium FAIR-E 198 promoveram aumento da proteólise primária e secundária. Embora os resultados obtidos demonstrem que as culturas bacteriocinogênicas avaliadas não possam ser empregadas como único método de conservação, estas podem atuar em sinergia com outros fatores para aumentar a eficiência no controle de patógenos Gram-positivos, especialmente L. monocytogenes, em produtos lácteos fermentados / Abstract: The biopreservation system, such as bacteriocinogenic lactic bacteria cultures and/or their bacteriocins, have received increasing attention and new approaches to control pathogenic and spoilage microorganisms have been developed. The purpose of this study was to evaluate the action of bacteriocin-producing cultures (Lactococcus lactis subsp. lactis ATCC 11454, Lactobacillus plantarum ALC 01 and Enterococcus faecium FAIR-E 198) on some Gram-positive pathogens in different culture media and dairy products. The bacteriocin production was influenced by the media. The antimicrobial activity of these cultures was evaluated by agar-well diffusion assay. The bacteriocins produced by Lb. plantarum ALC 01 and E. faecium FAIR-E 198 presented inhibitory activity on Listeria monocytogenes alone, on the other hand, the nisin produced by Lc. lactis subsp. Lactis ATCC 11454 demonstrated wide action spectrum, albeit with lower activity. In compatibility of associative development evaluation with the commercial starter culture, only Lc. lactis subsp. lactis ATCC 11454 presented activity on the starter culture. The acidifier activity determination was carried out in skimmed milk after 8h and 24h of incubation at 35ºC. The addition of 0.1% and 0.5% of the bacteriocinogenic cultures did not affect the production of lactic acid by the starter culture. The associative development of the starter culture with Lb. plantarum ALC 01 and E. faecium FAIR-E 198 provided significant increase in bacteriocin activity of these cultures, while the activity of Lc. Lactis subsp. lactis ATCC 11454 nisin was suppressed. The aminopeptidase activity was determined after cellular lise of the lactic cultures previously grown in MRS broth. Lb plantarum ALC 01 presented the largest activity. Moreover, the behavior of Gram-positive pathogens was analyzed during co-culture with the bacteriocin-producing bacteria and with the starter culture in skimmed milk. Lb. plantarum ALC 01 and E. faecium FAIR-E 198 did not influence the development of Bacillus cereus K1-B041 and of Staphylococcus aureus ATCC 27154 during the first 24h of incubation at 35ºC. They presented strong inhibition on L. monocytogenes Scott A. Lc. lactis subsp. lactis ATCC 11454 affected the development of the pathogens studied during the first 12h of incubation. The starter culture demonstrated good inhibition of B. cereus K1-B041 (>7.37 log UFC/ml) and L monocytogenes Scott A (>6.26 log UFC/ml). In Minas Frescal cheese, significant difference was not observed between the action of the bacteriocinogenic cultures and the starter culture on L. monocytogenes Scott A and S. aureus ATCC 27154. B. cereus K1- B041 demonstrated susceptibility to Lb. plantarum ALC 01 and E. faecium FAIR-E 198 after 7 days. Bacteriocin activity was not detected in the cheeses during 21 days at 8 ± 1ºC. The addition of the bacteriocin-producing bacteria as an adjunct culture to the Minas Frescal cheese did not promote alteration in the pH and in the acidity, however Lb. plantarum ALC 01 and E. faecium FAIR-E 198 promoted an increase of the cheese proteolysis. Although the obtained results demonstrated that bacteriocinogenic cultures cannot be used as only method of conservation, these can be used as an additional barrier to optimize the control of Gram-positive pathogens, especially L. monocytogenes, in dairy products / Doutorado / Doutor em Tecnologia de Alimentos

L’hème est une molécule essentielle à de nombreuses fonctions bactériennes. Cependant, cette molécule génère des radicaux libres qui lui confèrent des propriétés toxiques. Nous avons caractérisé les mécanismes de l’homéostasie de l’hème impliquant le transporteur d’efflux HrtBA. Chez L. lactis nous avons démontré que HrtBA empêche l’accumulation membranaire et intracellulaire d’hème exogène par un mécanisme ménaquinone dépendant. HrtBA est aussi présent chez de nombreux pathogènes. Chez S. agalactiae, la transcription de HrtBA est régulée par un système à deux composants HssRS. Le senseur HssS reconnait l’hème exogène internalisé. Pour élucider le rôle de l’hème de l’hôte dans la virulence de S. agalactiae, un modèle d’infection systémique chez la souris utilisant la luminescence (lux) et l’imagerie in vivo (IVIS) a été mis en place. Le suivi de la luminescence de bactéries hypersensibles à l’hème (ΔhrtBA) montre que l’hème de l’hôte est toxique et que la capacité de S. agalactiae à assurer son homéostasie est déterminante pour ’linfection. De manière similaire, en montrant que le métabolisme respiratoire est indispensable pour l’infection (ΔcydA), S. agalactiae dépend donc de sa capacité à acquérir l’hème de l’hôte pour être infectieuse. En utilisant le promoteur de HrtBA couplé à l’opéron lux, nous avons étudié la capacité de S. agalactiae à détecter et acquérir l’hème in vivo au cours de l’infection. Nos résultats montrent que l’hème de l’hôte est particulièrement biodisponible dans le foie. Au contraire dans le cerveau, l’hème n’est pas détecté par la bactérie. Nos résultats démontrent que l’hème de l’hôte est un paramètre important des capacités d’adaptation de S. agalactiae à son hôte lors de l’infection. Bloquer HrtBA ou le senseur d’hème HssS pourrait constituer une cible pour la recherche antibiotique chez S. agalactiae ou d’autres pathogènes. Enfin, nous avons démontré chez E. faecalis que l’expression de HrtBA est aussi dépendante d’un système à deux composants. Nous avons utilisé la même stratégie que pour S. agalactiae pour créer un senseur d’hème spécifique qui a permis de démontrer pour la première fois que E. faecalis rencontre et utilise l’hème du tractus digestif. / Heme is a redox-reactive molecule with essential function in bacterial metabolism. However, this molecule generates reactive oxygen species responsible for its toxicity. We characterized the mechanism of heme homeostasis involving the efflux transporter HrtBA. In L. lactis, we demonstrated that HrtBA prevents from membrane and intracellular accumulation of internalized exogenous heme thanks to a menaquinone dependent mechanism. HrtBA is also present in several pathogens. In S. agalactiae, the transcription of HrtBA is regulated by a two-component system HssRS. The HssS sensor recognizes internalized exogenous heme. To clarify the role of heme of the host in the virulence of S. agalactiae, a systemic infection model in mice using luminescence (lux) and in vivo imaging (IVIS) has been set up. The monitoring of luminescence generated by heme hypersensitive (ΔhrtBA) bacteria shows that heme of host is toxic and that the capability of S. agalactiae to control heme homeostasis is crucial for infection. In the same way, by demonstrating that respiratory metabolism is crucial for infection (ΔcydA), we demonstrated that S. agalactiae depends on its capacity to acquire the heme of the host to become infectious. By using the HrtBA promoter coupled with lux operon, we studied the capacity of S. agalactiae to detect and to acquire heme in vivo during the infection. Our results show that host heme is especially biodisponible in the liver. On the contrary, heme is not detected by bacteria in the brain. Our results prove that heme of the host is an important parameter for the adaptation of S. agalactiae to its host during infection. Blocking HrtBA or heme sensor HssS could so be a target for antibiotic research against S. agalactiae and other pathogens. Finally, we show in E. faecalis that HrtBA expression also depends on a two-component system. We used the same strategy as in S. agalactiae to create a specific heme sensor that allowed us to demonstrate for the first time that E. faecalis meets and uses heme in the digestive tract.

Antibiotic resistance in multidrug resistant bacteria cause high mortality rates worldwide, where there has been over 1,000,000 deaths reported as of the year 2019. Antibiotics were thought to be the cure for fighting infectious diseases and preventing further spreading of infection. This became a major problem due to bacteria evolving and developing mechanisms for resistance. The purpose of this review was to see if there are differences in the resistance mechanism of gram negative and gram positive bacteria, focusing mainly on the six most common multidrug resistant pathogenic bacteria; Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecium, Acinetobacter baumannii, Klebsiella pneumoniae and Streptococcus pneumoniae. The results show that there is a difference in the resistance mechanism between gram positive and gram negative multidrug resistant bacteria. The difference in resistant mechanisms is due to the cell wall compositions of gram negative and gram positive bacteria. The main difference as to why the gram negative bacteria have more resistance is due to the outer membrane. Antibiotics have a hard time to diffuse through and into the cell, that is they can easily decrease their outer membrane permeability. Gram positive bacteria lack an outer membrane which makes them become more susceptible to antibiotics. The most common antibiotic resistance mechanisms in gram negative bacteria are outer membrane mechanisms such as lipid A and lipopolysaccharide modification as well as mutations in porin channels. On the other hand, the most common resistance mechanisms for gram positive bacteria are point mutations especially in penicillin binding proteins as well mutations in the rpoB gene. One important gram positive bacteria is Methicillin resistant Staphylococcus aureus, which developed a new mechanism against antibiotics, a missense mutation and mutation on the promoter region in penicillin binding protein 4. Recently new research has come forward showing that N-chlorotaurine (NCT) inhibits resistance in both gram positive and gram negative multidrug resistant bacteria. The research on NCT is still fairly new and only time will tell if this method of inhibiting resistance will be used in the future. This review highlights the importance and concern of multidrug resistance bacteria, especially due to bacteria being able to rapidly evolve when antibiotics are used incorrectly. It is important to understand the differences in resistance between gram negative and gram positive bacteria and how resistance spreads. This knowledge can be used to develop antibiotics that treat infections. It is however still a challenge to overcome resistance in multidrug resistant bacteria due to evolutionary adaptation especially through horizontal gene transfer, where resistant bacteria can adapt to changing conditions. / Antibiotikaresistens hos multiresistenta gramnegativa och grampositiva bakterier orsakar hög dödlighet över hela världen, där det har rapporterats över 1,000,000 dödsfall för år 2019. Antibiotika ansågs vara botemedlet för att bekämpa infektionssjukdomar och förhindra ytterligare spridning av infektioner. Detta blev ett stort problem på grund av att bakterier utvecklades mekanismer för resistens, vilket gör att de kan överleva när de behandlas med antibiotika. Syftet med denna studien är att se om det finns skillnader i resistensmekanismener för gramnegativa och grampositiva bakterier, med fokus på de sex vanligaste multiresistenta bakterierna; Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecium, Acinetobacter baumannii, Klebsiella pneumoniae och Streptococcus pneumoniae. Resultaten visar att det finns en skillnad i resistensmekanismen mellan grampositiva och gramnegativa multiresistenta bakterier. Skillnaden i resistenta mekanismer beror på cellväggssammansättningen av gramnegativa och grampositiva bakterier. Den största skillnaden till varför de gramnegativa bakterierna har mer resistens beror på det yttre membranet. Antibiotika har svårt att penetrera genom och in i cellen genom att minska deras yttre membranpermeabilitet. Grampositiva bakterier saknar ett yttre membran som gör att de blir mer mottagliga för antibiotika. De vanligaste antibiotikaresistensmekanismerna hos gramnegativa bakterier är yttre membranmekanismer som lipid A och lipopolysackaridmodifiering samt mutationer i porinkanaler. De vanligaste resistensmekanismerna för grampositiva bakterier är punktmutationer, särskilt i penicillinbindande proteiner samt mutationer i rpoB genen. En viktig grampositiv bakterie är Meticillin-resistent Staphylococcus aureus, som utvecklade en ny mekanism mot antibiotika, en missense-mutation och mutation på promotorregionen i penicillinbindande protein 4. Nyligen har ny forskning kommit fram som visar att N-klorotaurin (NCT) hämmar resistens i både grampositiva och gramnegativa multiresistenta bakterier. Forskningen om NCT är fortfarande ny och bara tiden kommer att utvisa om denna metod för att hämma resistens kommer att användas i framtiden. Den här studien belyser vikten och oron för multidresistena bakterier, särskilt på grund av att bakterier snabbt kan utveckla antibiotikaresistens när antibiotika används på fel sätt. Det är viktigt att förstå skillnaderna i resistens mellan gramnegativa och grampositiva bakterier och hur resistens sprids inom resistenta bakterier. Denna kunskap kan användas för att utveckla antibiotika som behandlar infektioner orsakade av både gramnegativa och grampositiva bakterier. Det är fortfarande en utmaning att övervinna resistens hos multiresistenta bakterier på grund av evolutionär anpassning särskilt genom horisontell genöverföring, där resistenta bakterier kan anpassa sig till förändrande förhållanden.