The emergence of β-lactamase-mediated antibiotic resistance is one of the biggest threats in modern times. Combined with the discovery void of new forms of antibiotics, this sets the course toward a future where the efficacy of present-day health care will be jeopardized. To hinder the spread of β-lactamase-mediated antibiotic resistance, the development of the drug class β-lactamase inhibitors has been prioritized. The foremost candidate for development of this drug class, that has wide-spectrum inhibition of β-lactamases, is the clinically available avibactam of the diazabicyclooctane-scaffold (i.e., DBO-scaffold). However, the clinical applications of this inhibitor have been limited against one of the more rapidly spreading β-lactamases; OXA-48. In order to bolster the drug development of β-lactamase inhibitors of the DBO-scaffold, with good inhibitory activity toward OXA-48, DBO-ligands with different structure elements were analyzed for stability of the Michaelis Complex in the OXA-48 binding site using molecular dynamic simulations. The results indicate that elongation of the chain to the anionic group of the ligand combined with the addition of a methyl group to the DBO-ring was stabilizing for the productive position between the backbone hydrogens of Y211 and S70. The binding affinity was also estimated using the Linear Interaction Energy method, and an offset parameter of γ ≈ -19 kcal/mol was found and could represent the entropic differences of a flexible ligand-protein system. The results of this study may also indicate that the ligand stability of the Michaelis Complex is of minor consequence to the inhibition mechanism as a whole compared to the reaction rate.

No description available.

No description available.

Mounting concerns about drug-resistant pathogenic bacteria have rekindled the interest in bacteriophages (bacterial viruses). As bacteria’s natural predators, bacteriophages offer a critical advantage over antibiotics, namely that they can be highly specific. This means that phage therapeutics can be designed to destroy only the infectious agent(s), without causing any harm to our microbiota. However, the potential secondary effects on the balance of microbiota through bacteriophage-induced genome evolution remains as one of the critical apprehensions regarding phage therapy. There exists a significant gap in knowledge regarding the direct and indirect effect of phage therapeutics on the microbiota. The aim of this thesis was to: (1) establish an in vivo model for investigation of the evolutionary dynamics and co-evolution of therapeutic phage and its corresponding host bacterium in the gut; (2) determine if phage therapy can affect the composition of the gut microbiota, (3) observe the differences of phage-resistant bacteria mutants evolved in vivo in comparison to those evolved in vitro. We used germ-free mice colonized with a consortium of eight known bacteria, known as the altered Schaedler flora (ASF). The colonizing strain of choice (mock infection) was a non-pathogenic strain E. coli K-12 (JM83) known to co-colonize the ASF model, which was challenged in vivo with T7 phage (strictly lytic). We compared the composition of the gut microbiota with that of mice not subject to phage therapy. Furthermore, the resistant mutants evolved in vivo and in vitro were characterized in terms of growth fitness and motility. / Thesis / Master of Applied Science (MASc) / Bacteriophages are viruses that infect bacteria. After their discovery in 1917, bacteriophages were a primary cure against infectious disease for 25 years, before being completely overshadowed by antibiotics. With the rise of antibiotic resistance, bacteriophages are being explored again for their antibacterial activity. One of the critical apprehensions regarding bacteriophage therapy is the possible perturbations to our microbiota. We set out to explore this concern using a simplified microbiome model, namely germ-free mice inoculated with only 8 bacteria plus a mock infection challenged with bacteriophage. We monitored this model for 9 weeks and isolated a collection of phage-resistant bacterial mutants from the mouse gut that developed post phage challenge, maintaining the community of mock infection inside the gut. A single dose of lytic phage challenge effectively decreased the mock infection without causing any extreme long-term perturbations to the gut microbiota.

[ES] Las bacterias resistentes a múltiples antibióticos, como el Enterococo resistente a vancomicina (ERV), son un problema creciente en los pacientes hospitalizados, por lo que se necesita estrategias alternativas para combatir estos patógenos. Las infecciones causadas por ERV suelen comenzar con la colonización del tracto intestinal, un paso crucial que se afectado por la presencia de la microbiota. Sin embargo, los antibióticos alteran la microbiota y esto promueve la colonización de ERV. Una vez que el patógeno ha colonizado el intestino, alcanza niveles muy altos pudiendo diseminar a otros órganos y pacientes. A pesar de su importancia, se sabe muy poco sobre los genes que codifica para colonizar el intestino y sobre el mecanismo por el cual la microbiota suprime su colonización intestinal, siendo los dos objetivos principales. En primer lugar hemos utilizado una metodología previamente descrita (Zhang et al., 2017, BMC Genomics), basada en la generación de una librería de mutantes por transposición junto a secuenciación masiva, con el fin de identificar los genes codificados por ERV necesarios para la colonización del intestino en ratones. Además, hemos realizado análisis metatranscriptómicos para identificar aquellos genes más expresados. El análisis ha identificado genes cuya interrupción reduce significativamente la colonización intestinal en el intestino grueso. Los genes que más afectaron a la colonización codifican proteínas relacionadas con la absorción o el transporte de diversos nutrientes como los carbohidratos (subunidad EIIAB del transportador PTS de manosa, el regulador transcripcional de la familia LacI, ácido N-acetilmurámico 6-fosfato eterasa) o iones (proteína transportadora dependiente de ATP (ABC) y proteínas del grupo [Fe-S]). El papel de estos genes en la colonización se ha confirmado mediante experimentos de mutagénesis directa y de competición con la cepa salvaje. Además, estos genes afectan a la colonización intestinal con diferentes antibióticos (clindamicina y vancomicina). Para identificar el mecanismo molecular por el cual cada gen afecta a la colonización, hemos realizado experimentos in vitro y ex vivo además del análisis transcriptómico. Los experimentos in vitro confirman que las proteínas del grupo [Fe-S] están involucradas en el transporte iones de hierro, principalmente Fe3+. Por otra parte, los genes de la subunidad EIIAB del transportador de manosa y del ácido N-acetilmurámico 6-fosfato eterasa son necesarios para la utilización de la manosa y el ácido N-acetilmurámico, respectivamente, azúcares que suelen estar presentes en el intestino. También confirmamos que el regulador transcripcional de la familia LacI es un represor que afecta a proteínas transportadoras ABC, probablemente implicadas en la absorción de carbohidratos. Además, algunos de estos genes están codificados principalmente por cepas clínicas de E. faecium y en menor medida por cepas comensales. En segundo lugar, estudiamos los mecanismos de protección de un consorcio de cinco bacterias comensales, que anteriormente se había demostrado que disminuían la colonización intestinal por ERV en ratones. Mediante transcriptómica, metabolómica y los ensayos in vivo observamos que el consorcio bacteriano inhibe el crecimiento de ERV mediante la reducción de nutrientes, concretamente fructosa. Por último, el análisis ARN-Seq in vivo de cada aislado en combinación con los ensayos ex vivo e in vivo demostraron que una sola bacteria (Olsenella sp.) proporciona protección. En conjunto, los resultados obtenidos han identificado la función de genes específicos requeridos por ERV para colonizar el intestino. Además, hemos identificado un mecanismo mediante el cual la microbiota confiere protección. Estos resultados podrían conducir a nuevos enfoques terapéuticos para prevenir las infecciones causadas por este patógeno multiresistente a los antibióticos. / [CA] Els bacteris resistents a múltiples antibiòtics, com el Enterococo resistent a vancomicina (ERV), són un problema creixent en els pacients hospitalitzats, que són resistents a la majoria d'antibiòtics disponibles per la qual cosa es necessita estratègies alternatives per a combatre aquests patògens. Les infeccions causades per ERV solen començar amb la colonització del tracte intestinal, un pas crucial que es veu afectat per la presència de la microbiota. No obstant això, els antibiòtics alteren la microbiota i això promou la colonització de ERV. Una vegada que el patogen ha colonitzat l'intestí, aconsegueix nivells molt alts podent disseminar a altres òrgans i pacients. Malgrat la seua importància, se sap molt poc sobre els gens que codifica ERV per a colonitzar l'intestí i sobre el mecanisme pel qual la microbiota suprimeix la seua colonització intestinal. En primer lloc hem utilitzat una metodologia prèviament descrita (Zhang et al., 2017, BMC Genomics), basada en la generació d'una llibreria de mutants per transposició junt amb seqüenciació massiva, amb la finalitat d'identificar els gens codificats per ERV necessaris per a la colonització de l'intestí en ratolins. A més a més, hem realitzat anàlisi metatranscriptòmics per a identificar aquells gens més expressats. L'anàlisi ha identificat gens quina interrupció redueix significativament la colonització intestinal en l'intestí gros. Els gens que més van afectar la colonització codifiquen proteïnes relacionades amb l'absorció o el transport de diversos nutrients com els carbohidrats (subunitat EIIAB del transportador PTS de manosa, el regulador transcripcional de la família LacI, àcid N-acetilmuràmic 6-fosfat eterasa) o ions (proteïna transportadora dependent d'ATP (ABC) i proteïnes del grup [Fe-S]). El paper d'aquests gens en la colonització s'ha confirmat mitjançant experiments de mutagènesis directa i de competició amb el cep salvatge. A més, aquests gens afecten la colonització intestinal amb diferents antibiòtics (clindamicina i vancomicina). Per a identificar el mecanisme molecular pel qual cada gen afecta a la colonització, hem realitzat experiments in vitro i ex viu a més de l'anàlisi transcriptòmic. Els experiments in vitro confirmen que les proteïnes del grup [Fe-S] estan involucrades en el transport d'ions de ferro, principalment Fe3+. D'altra banda, els gens de la subunitat EIIAB del transportador PTS de manosa i de l'àcid N-acetilmuràmic 6-fosfat eterasa són necessaris per a la utilització de la manosa i l'àcid N-acetilmuràmic, respectivament, sucres que solen estar presents en l'intestí. També confirmem que el regulador transcripcional de la família LacI és un repressor que afecta proteïnes transportadores ABC, probablement implicades en l'absorció de carbohidrats. A més a més, alguns d'aquests gens estan codificats principalment per ceps clínics de E. faecium i en menor mesura per ceps comensals. En segon lloc, estudiem els mecanismes de protecció d'un consorci de cinc bacteris comensals, que adès s'havia demostrat que disminuïen la colonització intestinal per ERV en ratolins. Amb l'ús de transcriptòmica, metabolòmica i els assajos in vivo observem que el consorci bacterià inhibeix el creixement de ERV mitjançant la reducció de nutrients, concretament fructosa. Finalment, l'anàlisi ARN-Seq in vivo de cada aïllat en combinació amb els assajos ex viu i in vivo van demostrar que un sol bacteri (Olsenella sp.) proporciona protecció. En conjunt, els resultats obtinguts han identificat la funció de gens específics requerits per ERV per a colonitzar l'intestí. A més, hem identificat un mecanisme mitjançant el qual la microbiota confereix protecció. Aquests resultats podrien conduir a nous enfocaments terapèutics per a previndre les infeccions causades per aquest patogen multiresistent als antibiòtics. / [EN] Multidrug-resistant bacteria, such as vancomycin-resistant-Enterococcus (VRE), are an increasing problem in hospitalized patients. Some VRE strains can be resistant to most available antibiotics, thus, alternative strategies to antibiotics are urgently needed to combat these challenging pathogens. Infections caused by VRE frequently start by colonization of the intestinal tract, a crucial step that is impaired by the presence of the intestinal microbiota. Administration of antibiotics disrupts the microbiota, which promotes VRE intestinal colonization. Once VRE has colonized the gut, it reaches very high levels, which promotes its dissemination to other organs and its transfer to other patients. Despite the relevance of VRE gut colonization, very little is known about the genes encoded by this pathogen to colonize the gut and about the mechanisms by which the microbiota suppresses VRE gut colonization. In this thesis, we have utilized a previously described methodology (Zhang et al., 2017, BMC Genomics), based on the generation of a transposon mutant library coupled with high-throughput sequencing, in order to identify VRE encoded genes required for colonization of the mouse intestinal tract. In addition, we have performed metatranscriptomic analysis in mice to identify VRE genes specifically expressed in the gut. Our analysis has identified genes whose disruption significantly reduces VRE gut colonization in the large intestine. The genes that most affected VRE gut colonization encoded for proteins related to the uptake or transport of diverse nutrients such as carbohydrates (PTS mannose transporter subunit EIIAB, LacI family DNA-binding transcriptional regulator, N-acetylmuramic acid 6-phosphate etherase) or ions (phosphate ABC transporter ATP-binding protein and proteins from [Fe-S] cluster). The role of these genes in gut colonization has been confirmed through targeted mutagenesis and competition experiments against a wild type strain. Moreover, these genes affect gut colonization under different antibiotic treatments (clindamycin and vancomycin). To elucidate the mechanism by which each gene influences gut colonization, we have performed in vitro and ex vivo experiments besides transcriptomic analysis. In vitro experiments confirm that proteins from [Fe-S] cluster are involved in the transport of different forms of iron ions, mostly Fe3+. On the other hand, the PTS mannose transporter subunit EIIAB and N-acetylmuramic acid 6-phosphate etherase genes are required for the utilization of mannose and N-acetyl-muramic acid, respectively, sugars that are usually present in the intestinal environment. We have also confirmed that LacI family DNA-binding transcriptional regulator is a repressor that affects the expression of genes encoding for an ABC transporter probably involved in the uptake of carbohydrates. Furthermore, we have confirmed that some of these genes are encoded mainly by E. faecium clinical strains but not or to a lower extent by commensal strains. Secondly, we studied the mechanisms of protection of a consortium of five commensals bacteria, previously shown to restrict VRE gut colonization in mice. Functional transcriptomics in combination with targeted metabolomics and in vivo assays performed in this thesis indicated that the bacterial consortium inhibits VRE growth through nutrient depletion, specifically by reducing the levels of fructose. Finally, in vivo RNA-Seq analysis of each bacterial isolate of the consortium in combination with ex vivo and in vivo assays demonstrated that a single bacterium (Olsenella sp.) could recapitulate the protective effect. Altogether, the results obtained have identified the function of specific genes required by VRE to colonize the gut. In addition, we have identified a specific mechanism by which the microbiota confers protection against VRE colonization. These results could lead to novel therapeutic approaches to prevent infections caused by this pathogen. / Flor Duro, A. (2021). Characterization of Genes and Functions Required by Multidrug-resistant Enterococci to Colonize the Intestine [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/166494

Introduktion: Antibiotikaresistens är ett allvarligt och komplext folkhälsoproblem. WHO uppmanar genom initiativet One health att antibiotikaresistens behöver ses holistiskt och att tvärdisciplinära lösningar krävs. AI och maskininlärning bedöms ha stor potential att användas inom beslutsstöd för att begränsa antibiotikaresistensen. För att AI ska våga användas och implementeras bör den vara tillförlitlig, vilket innebär att hänsyn till etiska aspekter bör tas under hela systemens livscykel. Trots förhoppningar kring AI:s potential är forskningsfältet ungt och det beskrivs svårigheter med att utföra systematiska litteraturstudier. Det kan därför finnas behov av studier av kartläggande karaktär. Syfte: Syftet var att kartlägga rådande kunskapsläge kring hur artificiell intelligens kan användas som beslutsstöd i arbetet med att begränsa antibiotikaresistens. Metod: En kvalitativ scoping review med en induktiv tematisk analys. Resultat: Maskininlärning, såsom AI, användes för att utveckla beslutsstöd tänkta att implementeras i klinisk miljö. De hade i regel som avsikt att på olika sätt och i olika grad förutse viktiga aspekter i ett vårdförlopp som kan hjälpa vårdpersonal att välja en individanpassad antibiotikabehandling. Förhoppningarna med tekniken motiverades med en rad olika teoretiska nyttor, men de reala nyttorna kunde i regel inte konstateras inom ramen för studierna. Slutsats: För att konstatera och kunna fördela nyttan krävs vidare forskning som tar hänsyn till etisk AI. / Introduction: Antibiotic resistance is a serious and complex public health issue. Through the One Health initiative, WHO calls for a holistic approach to antibiotic resistance and for interdisciplinary solutions. AI and machine learning are considered to have great potential for use in decision support to limit antibiotic resistance. For AI to be used and implemented, it should be reliable, which means that ethical aspects should be considered throughout the life cycle of the systems. Despite hopes for the potential of AI, the research field is young and difficulties are present in conducting systematic literature studies. There may therefore be a need for studies of a mapping nature. Purpose: The purpose was to map the current state of knowledge on how artificial intelligence can be used as decision support in the efforts to limit antibiotic resistance. Method: A qualitative scoping review with an inductive thematic analysis. Results: Machine learning, such as AI, was used to develop decision support intended to be implemented in clinical settings. They generally aimed to predict important aspects of the course of care that could help healthcare professionals choose an individualized antibiotic treatment. The potential of the technology is justified by a variety of theoretical benefits, but the real benefits could not be ascertained in the context of the studies. Conclusion: Further research is needed to establish and distribute the benefits while also considering ethical AI.

Anthropogenic activities generate waste products that pollute the environment with bacteria and heavy metals. This research assessed pollution of the Kahwa River, Bukavu Town, DRC with cadmium and lead (HMs) and bacterial enteropathogens. A survey of businesses, households and healthcare facilities showed general use of the river to remove effluent and waste. Indicator organisms were cultured at over 200 cfu/100 ml showing faecal contamination of the river water. Antibiotic resistance was shown by enteropathogenic Vibrio cholerae and Salmonella typhi to ampicillin and cotrimoxazole with some sensitivity shown to ciprofloxacin. River water contained HMs at around 40 times the World Health Organisation limit for drinking water. The bacteria, particularly from river sediment, tolerated HMs up to a concentration of 1.5 mg/ml. The presence in the Kahwa River of antibiotic-resistant pathogens showing tolerance to HMs has serious public health implications / Environmental Management / M.Sc. (Environmental management)

L'augmentation et la dissémination de la résistance aux antibiotiques chez les bactéries à gram-negatif, particulièrement les Entérobactéries, les bactéries du genre Pseudomonas et Acinetobacter, représentent un problème majeur de santé publique au niveau mondial. Les infections nosocomiales causées par les bactéries multi-résistantes (BMR) ont conduit non seulement à une augmentation de la mortalité, de la morbidité, et du coût de traitement, mais aussi continuent de mettre en danger la vie des patients surtout immunodéprimés en milieu hospitalier. Bien entendu, l'utilisation abusive et non contrôlée des antibiotiques a grandement contribué à la large diffusion des déterminants de la résistance; cependant, des études récentes ont démontré que ces déterminants de la résistance pouvaient émerger à partir de sources anciennes et/ou environnementales. Ainsi, face à cette préoccupation mondiale, plusieurs études ont été rapportées avec des recommandations importantes de conduire des études épidémiologiques, moléculaires, et génomiques afin de contrôler la diffusion et l'augmentation de la résistance aux antibiotiques. De plus, durant ces 10 dernières années, nous avons assisté à l'emergence et au développement de nouvelles technologies de séquençage à haut débit coïncidant avec une augmentation exponentielle du nombre de genomes bactériens séquencés. / The increase and spread of multidrug-resistant (MDR) gram-negative bacteria especially Enterobacteriaceae, Pseudomonas, and Acinetobacter (E.P.A) species have become a major concern worldwide. The hospital-acquired infections caused by MDR bacteria have led not only to an increase in mortality, morbidity, and cost of treatment, but also continue to endanger the life of patients, especially those immunocompromised. Although the frequent misuse of antibiotic drug has greatly contributed to worldwide dissemination and resistance to antibiotics; recent studies have shown that these resistance determinants could emerge from ancient or environmental sources. Front of this worldwide concern, several studies have been reported with significant recommendations to conduct molecular epidemiology, and genomic studies, in order to control the increase and the dissemination of the antibiotic resistance. Moreover, during these last 10 years, we are witnessing the emergence and development of new technologies of high throughput sequencing and coinciding with an exponential increase of number of bacterial genomes sequenced today. Therefore, it is in this context that the project of this thesis was conducted with three essential objectives: (i) the genome sequencing of clinical MDR bacteria, the analysis and the identification of the mechanisms and the genetic determinants of antimicrobial resistance (ii) the achievement of molecular epidemiology studies from clinical MDR bacteria responsible of outbreak (iii) the development and implementation of molecular tools for monitoring and diagnosis of potential MDR bacteria.

A presença de antibióticos no ecossistema representa um sério risco à saúde humana e animal em virtude do desenvolvimento crescente de resistência bacteriana. Uma vez que a maioria dos antibióticos é persistente à degradação biológica, os processos oxidativos avançados são apontados como uma das tecnologias mais efetivas para decompor esses compostos em águas residuárias. A bacitracina zíncica (Bc-Zn) é um potente antibiótico constituído por uma mistura complexa de peptídeos não-biodegradáveis, conjugados ao zinco. Apesar de ser um antibiótico amplamente consumido na medicina humana e animal, é preocupante a escassez de estudos que investigam sua degradação e destino ambiental. O presente trabalho analisou a degradação da Bc-Zn através dos processos de fotólise direta e UV/H2O2 em diferentes condições de radiação UVC e concentração inicial de H2O2. Os parâmetros cinéticos rendimento quântico da fotólise, constantes cinéticas de pseudo-primeira ordem e constante cinéticas de segunda ordem foram satisfatoriamente estimados pela modelagem do sistema fotoquímico experimental. Os resultados revelaram que a fotólise direta permitiu degradar todos os congêneres da mistura de Bc-Zn nas maiores doses de radiação UVC empregadas. No entanto, não houve remoção de TOC após 120 minutos de irradiação. A adição de H2O2 acelerou substancialmente a fotodegradação do antibiótico, apresentando constantes cinéticas de pseudo-primeira ordem uma ordem de grandeza superiores às obtidas por fotólise direta. Além disso, remoção considerável de até 71% do TOC foi alcançada. A análise estatística demonstrou que a radiação UV foi um fator bem mais significativo para a fotodegradação da Bc-Zn em relação à concentração inicial de H2O2, sendo as melhores condições do processo alcançadas para a maior taxa específica de emissão de fótons (1,11×10-5 Einstein L-1 s-1). Ensaios biológicos com soluções tratadas por fotólise direta e UV/H2O2 indicaram remoção completa da atividade antimicrobiana residual, ainda que os produtos da fotodegradação tenham se mostrado não-biodegradáveis. Análises de toxicidade indicaram que o metal zinco presente no antibiótico é responsável pela a toxicidade no micro-organismo-teste Vibrio fischeri. Estudos adicionais devem ser realizados para identificar os sub-produtos formados, bem como para investigar a degradação da Bc-Zn em efluentes industriais reais. / The presence of antibiotics in ecosystems represents a serious risk to human and animal health, caused by the increase in bacterial resistance. Since most antibiotics resist to biological degradation, advanced oxidation processes are pointed out as the most effective technologies for degrading these compounds in wastewater. Zinc bacitracin (Bc-Zn) is a potent antibiotic with a complex mixture of non-biodegradable peptides conjugated to zinc. Despite being a widely used antibiotic in human and animal medicine, the scarcity of studies dealing with its degradation and environmental fate is a matter of concern. In this work, Bc-Zn degradation by direct photolysis and the UV/H2O2 process was investigated for different UVC radiation conditions and initial H2O2 concentrations. Kinetic parameters, namely the photolysis quantum yield, pseudo-first order kinetic constants and second-order kinetic constants, were satisfactorily estimated from experimental data by modeling the photochemical system. The results showed that all the congeners of the Bc-Zn mixture were photolyzed at the highest UVC doses applied, while no TOC removal was observed after 120 minutes of irradiation. The addition of H2O2 substantially accelerated Bc-Zn photodegradation, with pseudo-first order kinetic constants of one order of magnitude higher than those observed under direct photolysis. In addition, a remarkable removal of up to 71% of TOC was achieved. Statistical analyses showed that UV radiation had a much more important effect on Bc-Zn photodegradation in comparison with initial H2O2 concentration, with the best process conditions achieved for the highest specific photon emission rate (1.11×10-5 Einstein L-1 s-1). Biological assays carried out with the solutions treated by direct photolysis and UV/H2O2 revealed no residual antimicrobial activity, though photodegradation products remained non-biodegradable. In addition, toxicity analyses indicated that the zinc metal present in the antibiotic is responsible for the toxic effect on the test microorganism Vibrio fischeri. Finally, further studies should be performed to identify the by-products formed and to investigate Bc-Zn degradation in real industrial wastewater.

A presença de antibióticos no ecossistema representa um sério risco à saúde humana e animal em virtude do desenvolvimento crescente de resistência bacteriana. Uma vez que a maioria dos antibióticos é persistente à degradação biológica, os processos oxidativos avançados são apontados como uma das tecnologias mais efetivas para decompor esses compostos em águas residuárias. A bacitracina zíncica (Bc-Zn) é um potente antibiótico constituído por uma mistura complexa de peptídeos não-biodegradáveis, conjugados ao zinco. Apesar de ser um antibiótico amplamente consumido na medicina humana e animal, é preocupante a escassez de estudos que investigam sua degradação e destino ambiental. O presente trabalho analisou a degradação da Bc-Zn através dos processos de fotólise direta e UV/H2O2 em diferentes condições de radiação UVC e concentração inicial de H2O2. Os parâmetros cinéticos rendimento quântico da fotólise, constantes cinéticas de pseudo-primeira ordem e constante cinéticas de segunda ordem foram satisfatoriamente estimados pela modelagem do sistema fotoquímico experimental. Os resultados revelaram que a fotólise direta permitiu degradar todos os congêneres da mistura de Bc-Zn nas maiores doses de radiação UVC empregadas. No entanto, não houve remoção de TOC após 120 minutos de irradiação. A adição de H2O2 acelerou substancialmente a fotodegradação do antibiótico, apresentando constantes cinéticas de pseudo-primeira ordem uma ordem de grandeza superiores às obtidas por fotólise direta. Além disso, remoção considerável de até 71% do TOC foi alcançada. A análise estatística demonstrou que a radiação UV foi um fator bem mais significativo para a fotodegradação da Bc-Zn em relação à concentração inicial de H2O2, sendo as melhores condições do processo alcançadas para a maior taxa específica de emissão de fótons (1,11×10-5 Einstein L-1 s-1). Ensaios biológicos com soluções tratadas por fotólise direta e UV/H2O2 indicaram remoção completa da atividade antimicrobiana residual, ainda que os produtos da fotodegradação tenham se mostrado não-biodegradáveis. Análises de toxicidade indicaram que o metal zinco presente no antibiótico é responsável pela a toxicidade no micro-organismo-teste Vibrio fischeri. Estudos adicionais devem ser realizados para identificar os sub-produtos formados, bem como para investigar a degradação da Bc-Zn em efluentes industriais reais. / The presence of antibiotics in ecosystems represents a serious risk to human and animal health, caused by the increase in bacterial resistance. Since most antibiotics resist to biological degradation, advanced oxidation processes are pointed out as the most effective technologies for degrading these compounds in wastewater. Zinc bacitracin (Bc-Zn) is a potent antibiotic with a complex mixture of non-biodegradable peptides conjugated to zinc. Despite being a widely used antibiotic in human and animal medicine, the scarcity of studies dealing with its degradation and environmental fate is a matter of concern. In this work, Bc-Zn degradation by direct photolysis and the UV/H2O2 process was investigated for different UVC radiation conditions and initial H2O2 concentrations. Kinetic parameters, namely the photolysis quantum yield, pseudo-first order kinetic constants and second-order kinetic constants, were satisfactorily estimated from experimental data by modeling the photochemical system. The results showed that all the congeners of the Bc-Zn mixture were photolyzed at the highest UVC doses applied, while no TOC removal was observed after 120 minutes of irradiation. The addition of H2O2 substantially accelerated Bc-Zn photodegradation, with pseudo-first order kinetic constants of one order of magnitude higher than those observed under direct photolysis. In addition, a remarkable removal of up to 71% of TOC was achieved. Statistical analyses showed that UV radiation had a much more important effect on Bc-Zn photodegradation in comparison with initial H2O2 concentration, with the best process conditions achieved for the highest specific photon emission rate (1.11×10-5 Einstein L-1 s-1). Biological assays carried out with the solutions treated by direct photolysis and UV/H2O2 revealed no residual antimicrobial activity, though photodegradation products remained non-biodegradable. In addition, toxicity analyses indicated that the zinc metal present in the antibiotic is responsible for the toxic effect on the test microorganism Vibrio fischeri. Finally, further studies should be performed to identify the by-products formed and to investigate Bc-Zn degradation in real industrial wastewater.