DDI - Teses de doutoramento
Permanent URI for this collection
Browse
Browsing DDI - Teses de doutoramento by advisor "Caniça, Manuela"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Assessing antibiotic resistance in Gram negative bacteria from animals and the wider environmentPublication . Jones-Dias, Daniela; Caniça, Manuela; Nogueira, IsabelThe alarming increase in the levels of antibiotic resistant bacteria in clinical practice launched the call for a broader understanding of this event. This Ph.D. thesis aimed to unravel the main mobile antibiotic resistance determinants circulating in Gram negative bacteria from non-human sources, showing the contribution of mobile genetic elements for the overall process. The susceptibility and molecular epidemiological studies performed on different collections of bacterial isolates showed the predominance of multidrug resistant Escherichia coli in animals of different origins, soil and vegetables. E. coli and other species of Gram negative bacteria were related with carriage of diverse antibiotic resistance genes [e.g. blaCTX-M-1, blaCTX-M-15, blaCMY-2, blaGES-11, qnrS1, aac(6’)-Ib-cr, strAB, tet, drfA, aadA, mcr-1] that were associated with a transferable genetic support. Indeed, an assortment of mobile genetic elements (e.g. IncI1 and IncF plasmids, ISEcp1 insertion sequences, Tn402 and Tn7 transposons and class 1, 2 and 3 integrons) was detected in the genetic proximity of those antibiotic resistance genes, suggesting their profound involvement, not only in interspecies dispersion, but also in the movement of the genes within the cell. Specific genomic investigation of two Enterobactericeae isolates and the proteomic study of a third, underscored the potential of massive omic approaches to study antibiotic resistance as a global process. One of the key findings released from these studies is that antibiotic resistance is not only linked to virulence and pathogenicity, but can also be connected to core bacterial metabolic processes. The results obtained throughout this thesis extend our knowledge on the distribution of mobile antibiotic resistance genes in animals, environment and, ultimately, in the food chain. If the gathered results increased our concerns towards the current distribution of antibiotic resistant bacteria, they can also be an encouragement to address this problem at a global scale.
- Decrypting the diversity of microbiome in aquaculturePublication . Salgueiro, Vanessa; Caniça, Manuela; Manageiro, Vera; Nogueira, IsabelAquaculture can play an important role in reducing the overexploitation of natural re- sources and feeding the world’s growing population. However, the use of e.g., antibiotics in aquaculture can favor the development of resistant bacteria and jeopardize the safety of its products. Thus, this Ph.D. thesis aimed to contribute to the deciphering of aquaculture’s mi- crobiome and resistome, as well as to the understanding of the role of mobile genetic elements (MGE) in the dissemination of resistance genes in these environments. Several approaches were used, to obtain the results that most reflect the microbiome and resistome of seabream and bivalve mollusks from aquaculture. All microbiomes studied were very diverse, encompassing commensal and pathogenic bacteria from seabream and bivalve mollusks (e.g., Aeromonas,Kocuria, Pseudomonas and Vibrio genera), as well as bacteria important in human medicine (e.g., Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae). Twenty-one new se- quence types were described in Aeromonas spp., Citrobacter sp., Enterobacter spp., Shewanella spp., Staphylococcus sp. and Vibrio spp. Decreased susceptibilities to phenicols, oxytetracy- cline, β-lactams (namely carbapenems), quinolones, glycopeptides, mupirocin, erythromycin, and colistin were found. The resistome also revealed a great diversity of genes in all samples studied associated with antibiotics (e.g., blaTEM-1B, mecA, sul2, mcr-9.1), disinfectants (e.g.,formA-type), and heavy metals (e.g., sil) resistance. Twenty-five different genes related with increased virulence were also detected. Thirteen new β-lactams resistance genes were identi- fied (e.g., blaCTX-M-246, blaFOX-18, and blaOXA-958) and 35 other resistance genes, namely for antibi- otics (e.g., mcr-9 and qnrD2), heavy metals (e.g., emrA and mdtE) and disinfectants ( sitABCD- type), and virulence factors (e.g., astA and hlyF) were here described for the first time associated with aquaculture. Our results suggest that some of these resistance genes (e.g., erm(T)-type,qnrB19, catA1-type, tet(A), dfrA-type, aph(6)-Id, qacE∆ 1 and merA) are being disseminated by MGE such as plasmids, class 1 integrons, and Tn As1. These findings not only expand our knowledge about aquaculture’s microbiome and resistome, but also provide the necessary xiv information to implement the most suitable measures to control antibiotic resistance in aqua- culture environments.
- Dynamics of β-lactamases in Gram-negative bacteriaPublication . Manageiro, Vera; Caniça, Manuela; Caeiro, Maria Filomenaβ-Lactamase production is the most important resistance mechanism among Gram-negative bacteria. The overall aim of this PhD thesis was to contribute to the knowledge of molecular epidemiology of β-lactamases and to the understanding of their diversity in a structural-functional level. To accomplish this aim, several studies with different approaches were performed. The emergence of β-lactamase-producing isolates, as well as the appearance of new epidemic clones, is of great concern. The studies presented in the first chapter of results, have clearly shown that specific extended-spectrum β-lactamase (ESBL)-, plasmid-mediated AmpC β-lactamase (PMAβ)- and carbapenem-hydrolyzing class D β-lactamase (CHDL)-producing clones are able to persist in clinical settings for long periods, resulting in a complex β-lactamase endemic situation. A high diversity of β-lactamases was encountered, specifically: CTX-M family which is the most prevalent ESBL, and PMAβ (e.g., DHA-1, CMY-2, CMY-39, MIR-1, MIR-3, FOX-5 and the novel CMY-46 and CMY-50), both in Enterobacteriaceae, as well as CHDLs OXA-23 and OXA-24/40 in Acinetobacter baumannii. The results obtained in this thesis also highlight different strategies for bacterial spread of resistance that can occur through either clonal spread or horizontal gene transfer of mobile genetic elements. In the second chapter of results, structure/function correlation of five novel clinical important β-lactamases, namely three inhibitor-resistant SHV (SHV-72, SHV-84 and SHV-107), one ESBL (SHV-55) and one parental SHV (SHV-99), are presented. One of the key findings we can infer from results is that the conserved motif Lys234-Thr/Ser235-Gly236, present in class A β-lactamases, is a hot-spot for β-lactamase inhibition, meaning that new compounds can be designed to address this structural feature. In summary, the work performed in this thesis allows the elucidation on the dynamics of β-lactamases in Gram-negative bacteria, in Portugal. Molecular characterization together with biochemical data is essential for understanding the emergence of new resistance mechanisms and their spread.