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As the prevalence of type 2 diabetes has increased globally, so has the need to further investigate the disorder’s underlying features and a potential target for treatment. Drosophila melanogaster has proven to be an excellent model organism to study type 2 diabetes (T2D). To see whether it can serve as a model organism to identify the treatment of T2D, a type 2 diabetes like model were created in Drosophila through high sugar diet (HSD). The aim of the study was to investigate the therapeutic effects of six different probiotic bacteria strains on T2D characteristics markers. Longevity, size, and weight measurement were performed. Followed by verification of HSD effects on these phenotypes. It was demonstrated that probiotics could improve weight and lifespan. Treatment using probiotics showed statistically increased body weight in both 3rd instar larvae and adult flies (p-value <0.05). There was no statistically significant difference in length between any of the groups including controls (p-value 0.25). However, the triglyceride assay showed a slightly significant difference between control low sugar diet and few of the treatment groups (L. paracasei with p-value 0.037, and L. acidophilus with p-value 0.025) fed larvae/adult flies, and there was no statistically significant difference between controls (high and low sugar diets), and probiotics treatment groups (L. plantarum, B. animalis and B. breve) fed larvae/adult flies with a p-value >0.05. To investigate the effect on gene expression of four genes (FASNCG3523, FASNCG3524, FASNCG17374 & dsREBP) important in lipid metabolism, qPCR was performed using the Taqman method. All probiotic treatment groups had significantly decreased gene expression of FASN compared to the control groups. Findings of this study suggest that Drosophila melanogaster can be utilized as a model organism to study T2D and that further studies concerning the effects of probiotic treatment in Drosophila are required to fully understand the interactions and mechanism of action.

Bacteria communicate with their hosts in part via surface, secreted and transmembrane proteins (collectively the secretome) resulting in probiotic (beneficial) or pathogenic (harmful) outcomes to the host. Therapeutic benefits of probiotic bacteria have been shown previously, but the molecular mechanisms and the health-promoting effector components involved are still being elucidated. Some evidence suggests that probiotic bacteria can competitively adhere to intestinal mucus and displace pathogens. The adherence of probiotic bacteria to human intestinal mucus and cells appears to be mediated, at least in part, by secretome proteins. Secretome proteins-encoding open reading frames can be identified in bacterial genome sequences using bioinformatics. However, functional analysis of the translated secretome is possible only if many secretome proteins are expressed and purified individually. Phage display technology offers a very efficient way to purify and functionally characterise proteins by displaying them on the surface of the bacteriophage. While a phage display system for cloning secretome proteins has been previously reported it is not efficient for enrichment and display of Gram-positive secretome proteins. In this study a new phage display system has been developed and applied in direct selection, identification, expression and purification of Gram-positive Lactobacillus rhamnosus strain HN001 secretome proteins. The new phage display system is based on the requirement of a signal sequence for assembly of sarcosyl-resistant filamentous phage virions. Using this system 89 secretome open reading frames were identified from a library of only 106 clones, performing at least 20-fold more efficiently than the previously reported enrichment method. Seven of the identified secretome proteins are unique for L. rhamnosus HN001. A L. rhamnosus HN001 shot-gun phage display library was also constructed to capture proteins that mediate adhesion or aggregation, initial steps in establishing host-microbe contact or forming multicellular aggregates, both of which may lead to beneficial effects – colonisation of the gastro-intestinal tract and exclusion of pathogens. In search for proteins involved in adhesion, a L. rhamnosus HN001 shot-gun phage display library was screened against the human extracellular matrix component fibronectin commonly used as binding target by bacteria that colonise diverse tissues. This screen selected, instead of a fibronectin-binding protein, a protein that binds to avidin, used to immobilise biotinylated fibronectin. Affinity screening of the shot-gun library for binding to L. rhamnosus HN001 cells identified a secretome protein, Lrh33, as an HN001-cell surface binding protein. This protein contains two bacterial immunoglobulin-like domains type 3. Analysis of phage-displayed nested deletions of Lrh33 determined that the proximal (N-terminal) immunoglobulin-like domain is not sufficient for binding; only the constructs displaying both domains demonstrated binding to HN001. Lrh33 does not have any similarity to previously identified Lactobacillus-binding proteins and no match in the NCBI database (at a cutoff value of > e-13), hence it represents potentially a new type of bacterial auto-aggregation protein.

In this study, strains of probiotic bacteria have been selected for tolerance to low pH, bile, sucrose, oxygen in media and low storage temperatures. Lactobacillus acidophilus 2401 and Bifidobacterium infantis 1912 were selected as strains able to survive in these conditions. These two strains were then offered further protection from the adverse conditions of food processing and storage by microencapsulation in a calcium alginate and starch gel matrix. Encapsulation in calcium alginate increases survival in yoghurt. In cheddar cheese the free L. acidophilus 2401 and B. infantis 1912 cells survived better than the encapsulated cells, probably due to the dense nature of the cheddar cheese matrix combined with the encapsulation restricting the flow of the nutrients and metabolites between the outside environment and the cells. In ice cream survival was high, probably due to the high fat and solids nature of the ice cream combined with the low storage temperature. The trial results of the laboratory scale production was consistent with the survival results for yoghurt and cheddar cheese. Incorporation of encapsulated probiotic bacteria into ice cream and cheddar cheese was acceptable by sensory standards and largely unnoticeable in comparison with the same foods without capsules. The capsules were visible and able to be felt on the tongue when eaten in yoghurt causing the product to be disliked by the panellists. / Master of Science (Hons)

Probiotic bacteria are live microorganisms, which manifest health benefits in humans. The goal of this work was to characterize rheological properties of probiotic bacteria (Lactobacillus reuteri) formulation in which maltodextrin and sucrose used as excipients. To fulfil the goal, first, thermal, structural and rheological properties of maltodextrin, sucrose solutions and probiotic bacteria slurry were investigated. Probiotic bacteria formulations were prepared by adding probiotic bacteria slurry to maltodextrin and sucrose solutions at different mass fractions. Finally, rheological properties of probiotic bacteria formulations were evaluated. From TGA, the water content of PB slurry including intracellular water found 81%. In DLS, three different types of aggregations of maltodextrin were observed and characteristic size of Probiotic bacteria found 1μm. The optical microscopy results indicate that at the liquid - air interface and in dehydrated state the bacteria are birefringent and arranged in an ordered fashion resembling a nematic phase. Most of the MD, SU and MD+SU solutions show Newtonian behaviour. MD and SU solutions show strong increase of viscosity with increasing concentration. This dependence can be described by using the Spurlin–Martin–Tennent’s model. The viscosities of MD+SU solutions increase with increasing proportion of maltodextrin. The oscillation data of MD and MD+SU solutions can be described by Maxwell model. The viscosities of MD, SU, MD+SU mixed solutions decrease with increasing temperature. This temperature dependency can be described by Arrhenius model of viscosity. At very high concentrations of MD, a deviation from this behaviour is observed. The probiotic bacteria slurry shows shear thinning behaviour at low shear stress and Newtonian behaviour at higher stresses. All probiotic formulations in which probiotic bacteria dispersed in maltodextrin and sucrose solutions show Newtonian behaviour. The viscosities of maltodextrin solutions and MD+SU mixed solutions decrease by addition of probiotic bacteria whereas mixed effects of probiotic bacteria addition on the viscosity of sucrose solutions were observed. The viscosity of probiotic bacteria slurry decreases with increasing temperature, although deviations from this behavior are seen at certain conditions.

The goal of this work was a study the influence of food and beverages on the viability and growth of probiotic bacteria. The influence of food and beverages was tested on monocultures of Lactobacillus acidophilus, Bifidobacterium breve and mixed culture of probiotic microorganisms. In the experimental part, probiotic cultures were incubated in selected foods and beverages. After that they were tested in a model conditions of digestive tract. In some probiotic cultures, growth of viable cells during incubation in the digestive tract was observed. The increase of probiotic cells was showed predominantly in foods that contained higher levels of sugars and fats or a suitable combination. Their increase was up to four times in some cases. Based on the results, mixed probiotic cultures aren’t surprisingly exhibited better survival and maintain sufficient amount of viable cells even during the digestive process. Moreover, probiotic microorganisms could be recommended to consumption during meals better than just with a beverage.

The discovery of antibiotics have revolutionized modern medicine, facilitating the treatment of a variety of bacterial infections, enabled surgeries otherwise impossible to perform and increased life expectancy in all countries. However, the rapid development of resistance among microorganisms and the increasing numbers of clinical outbreaks caused by multiresistant bacteria have accelerated the need for new alternatives to antibiotics. Probiotic bacteria armed with defense systems have been studied as potential substitutes of antibiotics. These probiotic competitors can still contribute to the spread of resistance genes among microorganisms through horizontal gene transfer. The aim of this study was to investigate whether constructed CRISPR-Cas9 systems have the potential to protect probiotic bacteria against horizontal transfer of antibiotic resistance genes. Transformation, transduction and conjugation assays in strains carrying or not carrying a plasmid-bourne CRISPR-Cas9 system were performed in order to compare the frequencies of transfer of the most common resistance genes. The transformation and transduction assays demonstrated that the constructed CRISPR-Cas9 system entails a decrease in efficiency of transfer for targeted resistance genes. Moreover, it can be concluded that potentially increasing Cas9 levels by reducing its degradation results in increased prevention of horizontal gene transfer through transformation and transduction. Finally, we state that the CRISPRCas9 system does not result in protection against antibiotic resistance genes entering the cells through conjugation.

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-03-04T16:25:51Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Roger Dissertação Mestrado 2014_ versão Final biblioteca_ Entregue_.pdf: 1359994 bytes, checksum: ce3bbcf3906e6cb72bdfea9a7b7e7d06 (MD5) / Made available in DSpace on 2016-03-04T16:25:51Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Roger Dissertação Mestrado 2014_ versão Final biblioteca_ Entregue_.pdf: 1359994 bytes, checksum: ce3bbcf3906e6cb72bdfea9a7b7e7d06 (MD5) Previous issue date: 2014-02-20 / CAPES / CNPq / FINEP / O gênero Shewanella é um representante da classe das Gammaproteobactérias, família Shewanellaceae, compondo um grupo de bactérias gram-negativas, móveis, baciliforme, oxidase positiva, comumente encontrada em ambiente marinho e isolada do trato digestivo de animais aquáticos. Devido a suas características vem sendo amplamente testado como probiótico na carcinicultura. Estes têm sido utilizados na aquicultura para o controle biológico, aumento da taxa de conversão alimentar e sistema imune dos camarões. Este estudo teve por objetivo identificar potenciais bactérias probióticas retiradas do hepatopâncreas e estômago do camarão cultivado em sistema heterotrófico, avaliar as relações filogenéticas das cepas com o gênero Shewanella e caracteriza-las através de análisesmorfológicas, bioquímicas, produção de biofilme e antibiograma. A partir do cultivo heterotrófico de Litopenaeus vannamei, foram selecionadas as cepasIPA-S.51, IPA-S.111 e IPA-S.252para identificação através do sequenciamento parcial do gene 16S rRNA e comparados ao GenBank – NCBI e RDP - Seqmatch. As cepas foram alinhadas a 45 espécies do gênero Shewanella e avaliadas filogeneticamente utilizando os métodos Neighbor-Joining, Máxima Verossimilhança e Inferência Bayesiana. Quanto àsanálises morfológicas foram avaliadas parâmetros de acordo com a similaridade a padrões estabelecidos. Os testes bioquímicos foram realizados com o auxílio dos kits BACTRAY I, BACTRAY II e BACTRAY III (Labroclin®), totalizando 30 testes bioquímicos. A avaliação da capacidade de formação de biofilme foi realizada segundo Christensen e colaboradores. No antibiograma as cepas bacterianas foram submetidas a 13 antibióticos distintos segundo à técnica de Kirby e Bauer, com três repetições. O sequenciamento das cepas revelou alta similaridade a espécie Shewanella algae, utilizando o GenBank e o RDP-seqmath. A Inferência Bayesiana apresentou maior aporte estatístico e fidelidade dentre os métodos analisados. A Shewanella upenei apresentou alta similaridade as cepas estudadas, assim como a S. algae. As análises filogenéticas não descartam a hipótese de novas espécies para IPA-S.51, IPA-S.111 e IPAS. 252. As cepas estudadas foram sensíveis aos antibióticos Ampicilina/Subactan, Ofloxacina e Tetraciclina. A caracterização fenotípica fortalece a hipótese de especiação para as cepas testadas. Portanto, a capacidade de formação de biofilme, adicionada ao alto potencial enzimático e antagonismo a patógenos, característico do gênero Shewanella, tornam estas cepas potenciais probióticos para carcinicultura. / The genus Shewanella is one representant of Gammoproteobacteria class, family Shewanellaceae, being part of gram-negative bacteria group, mobile, bacilliform, oxidasepositive, commonly found on marine environments and isolated from the digestive tract of aquatic animals. Due to its characteristics, some tests as probiotics are being carried out in carciniculture. They are being used on aquaculture for biological control, augmentations on feed conversion rates and immune system of shrimps. This study has as objective identify potentials probiotics bacteria found in the hepatopancreas and stomach of shrimps cultivated on heterotrophic based system, evaluating the strain phylogenetic relationships with Shewanella genus and characterizing them through morphological and biochemical analysis, biofilm production and antibiogram. The strains IPA-S.51, IPA-S.111 e IPA-S.252 were selected from the heterotrophic cultivation of Litopenaeus vannamei, identified through partial 16S rRNA sequencing and compared to GenBank – NCBI and RDP - Seqmatch.The strains were aligned to 45 species of Shewanella genus and phylogenetically evaluated using Neighbor-Joining,Maximum-Likelihood estimation and Bayesian Inference.Regarding the morphological analysis parameters were evaluated according with established standard similarities. The biochemical tests were conducted with the assistance of BACTRAY I, BACTRAY II and BACTRAY III (Labroclin®) kits, totalizing 30 biochemical tests.The Biofilm capacity evaluation was made according Christensen et al. Regarding the antibiogram, the bacterial strains had undergone 13 distinct antibiotics according Kirby and Bauer, with three repetitions. The strains sequencing showed high similarity to Shewanella algae species, using GenBank and RDP-seqmath.The Bayesian inference displayed higher statistic contribution e fidelity among the other methods.The Shewanella upenei showed high similarity to the strains in study also as Shewanella algae.The phylogenetic analysis does not exclude the hypothesis of IPA-S.51, IPA-S.111 e IPA-S.252 being new species.The strains studied were sensitives to the antibiotics Ampicillin/Sulbactam, Ofloxacin, Tetracyclin. The phenotypic characterization of the strains supports the hypothesis of speciation. Thus, the capacity of biofilm formation plus the high enzymatic potential and antagonism interactions to pathogens, characteristics found in the Shewanella genus, make these strains potential probiotics to carciniculture.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-03-16T15:01:11Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) CAROLINA KROPNICZKI GOUVEIA - DISSERTAÇÃO.pdf: 1168935 bytes, checksum: ec9fc0cb4665cb4641bd7162f5449c56 (MD5) / Made available in DSpace on 2016-03-16T15:01:11Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) CAROLINA KROPNICZKI GOUVEIA - DISSERTAÇÃO.pdf: 1168935 bytes, checksum: ec9fc0cb4665cb4641bd7162f5449c56 (MD5) Previous issue date: 2012 / A produção de camarões marinhos na região Nordeste do Brasil vem crescendo principalmente pela introdução da espécie Litopenaeus vannamei. Adicionadas à dieta ou diretamente na água, as bactérias probióticas têm sido utilizadas para controle biológico e aumento da digestibilidade alimentar e do sistema imune dos animais, elevando a lucratividade dos empreendimentos dedicados à carcinicultura. A influência de enzimas exógenas de bactérias na digestão dos camarões não está bem elucidada e ainda existe uma grande lacuna no que diz respeito a aspectos nutricionais tanto dos microrganismos, quanto dos animais cultivados. Dessa forma, objetivou-se avaliar as atividades proteolítica e amilolítica de cepas bacterianas isoladas do hepatopâncreas e estômago do L. vannamei e identificar as bactérias produtoras destas enzimas pelo sequenciamento do gene 16S rRNA. Para estudo do ambiente em tanques heterotróficos experimentais utilizando dois probióticos comerciais (HP1 e HP2) e em tanques controles heterotrófico (Het) e autotrófico (Aut), amostras de água foram tomadas ao final do experimento para contagem de bactérias heterotróficas, autotróficas e víbrios por plaqueamento em meios específicos. As médias de população bacteriana foram submetidas à análise de variância (ANOVA) complementada pelo teste de Tukey (p<0,05). Dos órgãos das amostras de camarão (n=3) foram retirados os materiais internos para isolamento das cepas bacterianas e seleção in vitro pela capacidade de produção de enzimas digestivas. Uma cepa de Bacillus subtilis (ATCC 6633) foi utilizada como testemunha na identificação utilizando os inicializadores universais para o domínio bactéria fD1 (Forward) e rD1 (Reverse). A população de bactérias heterotróficas foi mais representativa quando comparada às de autotróficas e víbrios, e o experimento Het atingiu a maior média (1,91x107 UFC/mL). As menores cargas de víbrios foram encontradas nos tanques experimentais HP1 e HP2 com médias de 2,46x104 e 2,00x104 UFC/mL, respectivamente. De 64 cepas isoladas, 11 possuíram índices enzimáticos satisfatórios (IE ≥ 2,0) para a produção de protease e amilase. Os amplicons após sequenciamento do DNA apresentaram tamanho maior que 1,4Kb e homologia com o GenBank e RDP, identificando bactérias como Bacillus subtilis e Shewanella algae. O incremento da população heterotrófica está relacionado à adição de melaço como fonte de carbono no sistema de cultivo e nos experimentos com os probióticos comerciais, a carga vibrionácea foi reduzida. A técnica de sequenciamento do gene 16S rRNA utilizando os primers fD1 e rD1 foi eficiente na caracterização bacteriana a nível de espécie e até subespécie, revelando a presença de bactérias com potencial para utilização como probiótico. / The marine shrimps cash crop in the Northeast region of Brazil is raising due to the introduction of Litopenaus vannamei. The probiotics bacteria added in the diet or directly in the water have been used for biological control and augmentations in the alimental digestibility and in the immune system, increasing the profits of enterprises related to carciniculture. The influence of bacterial exogenic enzymes on shrimp digestion is not clear and still has a gap concerning the nutrition aspects of shrimps and microorganisms. Therefore, this study had as objective the evaluations of proteolytic and amylolytic activities of bacterial strains isolated from hepatopancreas and stomach of L. vannamei and identify the bacteria responsible for enzymes production by sequencing the 16S rRNA gene. For environmental study in heterotrophic tanks using two commercial probiotics (HP1 e HP2) and in heterotrophic (Het) and autotrophic (Aut) control tanks, water samples were collected at the end of the experiment in order to count the autotrophic and heterotrophic bacteria and vibrio by plating in specific media. The means of bacterial population were submitted to variance analysis (ANOVA) and complemented by Tukey’s test (p<0.05). Internal materials were extracted from shrimp organs samples (n=3) in order to isolate the bacterial strains and “in vitro” selection due to its capacity to produce digestive enzymes. One strain of Bacillus subtilis (ATCC 6633) was used as witness on the identification using the universal primers fD1 (Forward) e rD1 (Reverse). The population of heterotrophic bacteria was more representative compared with autotrophic and vibrio population and the Het experiment presented the greatest mean (1,91x107 CFU.mL-1). The minor loads of vibrio were found in the experimental tanks HP1 and HP2 with means 2,46x104 e 2,00x104 CFU.mL-1 respectively. From sixty four strains, only eleven showed satisfactory enzymatic index (EI ≥ 2.0) to protease and amylase production. The amplicons after the DNA sequencing showed sizes bigger than 1,4Kb and homology with GenBank e RDP, identifying bacteria as Bacillus subtilis and Shewanella algae. The increment of heterotrophic population is related with the addition of molasses as carbon source in the crop system and the vibrio load were reduced in the experiments with commercial probiotics. The sequencing technique of 16S rRNA gene using fD1 and rD1 were efficient in the characterization of bacteria at the level of species and even at the level of subspecies, revealing the presence of bacteria with potential use as probiotic.

Os antibióticos têm sido utilizados como aditivos na alimentação animal para aumentar o desempenho e manter a saúde dos animais, como suínos e frangos, destinadas à produção de alimentos de origem animal. No entanto, desde 2006, a Comunidade Europeia proibiu o uso de antibióticos para esse proposito devido ao desenvolvimento de resistência bacteriana aos antibióticos. Como resultado, várias alternativas foram estudadas e propostas para substituir os antibióticos utilizados na alimentação animal. Os óleos essenciais têm recebido considerável atenção devido às suas propriedades antimicrobianas. Portanto, o objetivo do presente trabalho foi avaliar in vitro a atividade antibacteriana dos óleos essenciais contra a microbiota patogênica e probiótica de ocorrência no trato gastrointestinal de suínos e aves, destinadas à produção de alimentos de origem animal. A atividade antibacteriana seletiva, a qual, significou uma alta atividade antibacteriana contra bactérias patogênicas e reduzida ou nenhuma atividade sobre bactérias probióticas, foi avaliada como característica fundamental dos óleos essenciais com alto desempenho. Esta característica foi avaliada nos óleos essenciais usados individualmente e em combinações binarias. Inicialmente, no Capítulo 2, uma triagem de vinte e oito óleos essenciais (OEs) através do método de difusão em disco mostrou que Eucalyptusglobulus, E. exserta, Pimenta pseudocaryophylllus, Orange Oil Phase Essence, e CitrusTerpens (Os dois últimos OEs foram subprodutos do processamento da laranja para obtenção de suco) tiveram uma atividade antibacteriana seletiva sobre a bactéria patogênica Salmonella Enteritidis e a bactéria probiótica Lactobacillus plantarum. Numa fase posterior, esses cinco óleos foram avaliados individualmente e em misturas binárias, contra cinco bactérias patogênicas e três bactérias probióticas. Os melhores resultados foram observados quando os OEs foram avaliados isoladamente e não em misturas. Assim, Orange Oil Phase Essence e Citrus Terpens destacaram-se por ter a melhor atividade antibacteriana seletiva contra essas bactérias. No Capítulo 3, uma análise mais detalhada da atividade antibacteriana dos óleos essenciais foi realizada utilizando Orange Oil Phase Essence e a mistura composta pelos óleos de E. globulus e P. pseudocaryophyllus. Estes dois óleos foram selecionados com base nos resultados do Capitulo 2 e da disponibilidade de OEs em nosso estoque. Ambos, óleo e a mistura foram avaliados sobre a bactéria patogênica mais resistente, E. faecalis, e a bactéria probiótica menos resistente L. rhamnosus, como observado no Capitulo 2. A avaliação da Concentração Inibitória Mínima e Concentração Bactericida Mínima do Orange Oil Phase Essence e da mistura mostrou que não tiveram um efeito antibacteriano seletivo sobre E. faecalis e L. rhamnosus. Finalmente, no Capitulo 4, foi avaliada a atividade antibacteriana individual e combinada dos óleos de E. globulus e P. pseudocaryophyllus sobre E. faecalis e L. rhmanosus. Os resultados mostraram que a combinação destes dois OEs, avaliadas pelo método checkerboard, não potencializou a atividade antibacteriana seletiva dos dois OEs. Portanto, observou-se que o óleo de E. globulus isoladamente apresentou a melhor atividade antibacteriana seletiva contra E. faecalis e L. rhamnosus. Em conclusão, este trabalho permitiu identificar óleos essenciais com perfil antibacteriano seletivo para eles serem possíveis alternativas botânicas aos antibióticos utilizados na alimentação animal. / Antibiotics have been used in animal feed to maintain health and increase performance, as in the case of pigs and poultry intended for food production of animal origin. However, since 2006 the European Community has banned the use of antibiotics for this purpose due to the emergence and increase of antibiotic-resistant bacteria. As a result, several alternatives have been studied and proposed to substitute antibiotics used in animal feed. Essential oils have received considerable attention due to their antimicrobial properties. Therefore, the objective of this work was to evaluate in vitro the antibacterial activity of essential oils against pathogenic and probiotic bacteria that occur in the gastrointestinal tract of swine and poultry, intended for food production of animal origin. The selective antibacterial activity, which means high antibacterial activity on pathogenic bacteria and reduced or no activity on probiotic bacteria, was evaluated as a fundamental feature of the highest-performance essential oils. This feature was evaluated in essential oils used individually and in binary combinations. Initially, in Chapter 2, the screening of twenty-eight essential oils (EOs) by disk diffusion method showed that Eucalyptus globulus, E. exserta, Pimenta pseudocaryophylllus, Orange Oil Phase Essence, and Citrus Terpens (the last two EOs were by-products of orange juice production) had a selective antibacterial activity against the pathogenic Salmonella Enteritidis and probiotic Lactobacillus plantarum. At a later stage those five oils were evaluated, individually and in binary blends, against five pathogenic bacteria and three probiotic bacteria. Better results were observed when the EOs were checked alone and not in blends. Orange Oil Phase Essence and Citrus Terpens stood out for having the two best selective antibacterial activities against those bacteria. In Chapter 3, a more detailed analysis of essential oil antibacterial activities was perfomed using Orange Oil Phase Essence and the blend composed of E. globulus and P. pseudocaryophyllus. These two oils were selected based on the results of Chapter 2 and from the availability of our EO stock. Both oil and blend were checked on the most resistant pathogenic bacterium, E. faecalis, and on the less resistant probiotic bacterium of the Lactobacillus genus, L. rhamnosus, as observed in Chapter 2. The evaluation of Minimal Inhibitory Concentration and Minimal Bactericidal Concentration for Orange Oil Phase Essence and the blend showed that there was not a selective antibacterial effect against E. faecalis and L. rhamnosus. Finally, in Chapter 4, the individual and combined antibacterial activities of E. globulus and P. pseudocaryophyllus essential oils on E. faecalis and L. rhmanosus were evaluated. The results showed that the combination of two EOs evaluated by checkerboard method did not potentiate the selective antibacterial activity of the two EOs. Therefore, it was observed that the E. globulus essential oil alone had the best selective antibacterial activity against E. faecalis and L. rhamnosus. In conclusion, this work enabled the identification of essential oils with selective antibacterial profile that can become possible botanical alternatives to antibiotics used in animal feed.