As fluorquinolonas são antimicrobianos frequentemente prescritos no Brasil e em outros países e utilizados no tratamento de diversos tipos de infecções, principalmente naquelas do trato urinário e gastrintestinal. A ação desses compostos ocorre devido a interação dos mesmos com a DNA-girase e a topoisomerase IV bacterianas. A DNA girase é codificada pelos genes gyrA e gyrB e a topoisomerase IV, pelos genes parE e parC. Estudos evidenciaram existir nesses genes regiões nas quais as mutações ocorrem de modo mais frequente, sendo esses sítios chamados de Quinolone Resistance Determining Regions (QRDR). Mutações nas QRDR levam a substituição de aminoácidos nas topoisomerases, diminuindo a afinidade destas enzimas pelas quinolonas, acarretando, portanto, em um fenótipo de resistência para essa classe de antimicrobianos. Este mecanismo de resistência mostrou-se um dos principais responsáveis pela resistência antimicrobiana para essa classe de antimicrobiano em isolados clínicos. Entretanto, outros mecanismos de resistência podem estar presentes, entre eles a aquisição de determinantes plasmidiais (qnrA, qnrB, qnrS, qepA, oqxA e oqxB). A maioria dos estudos foi realizada utilizando isolados bacterianos clínicos, contudo, pouco tem sido investigado sobre os mecanismos de resistência com bactérias de origem ambiental. Diante disso, o presente trabalho objetivou identificar os principais mecanismos de resistência às quinolonas em isolados bacterianos ambientais e os principais gêneros dessa microbiota que os albergam. Para tanto, 69 isolados bacterianos ambientais foram selecionados. Os principais gêneros bacterianos selecionados foram Stenotrophomonas, Achromobacter, Ochrobactrum e Escherichia para os quais foram pesquisados além dos genes Plasmid Mediated Quinolone Resistance (PMQR), mutações nos genes gyrA, gyrB, parE e parC e a tipagem plasmidial. No conjunto os resultados permitem evidenciar um padrão de mutações nos genes codificadores das topoisomerases semelhante ao observado em isolados bacterianos clínicos, atuando os genes PMQR de modo sinérgico na contribuição da elevação da concentração inibitória mínima (CIM) frente às fluorquinolonas. No entando, mecanismos adicionais que possam contribuir com os níveis de resistência não podem ser descartados, sobretudo sistemas de efluxo. A tipagem plasmidial evidenciou que a maioria dos isolados apresenta plasmídeos da família ColE-like. / Fluoroquinolones are antimicrobials frequently prescribed in Brazil and in other countries and used in the treatment of various types of infections, especially those of the urinary tract and gastrointestinal tract. The action of these compounds occurs due to their interaction with bacterial DNA-gyrase and topoisomerase IV. The DNA gyrase is encoded by the gyrA and gyrB genes and the topoisomerase IV, by the parE and parC genes. Studies have shown that there are regions in which the mutations occur more frequently, these sites being called QRDR (Quinolone Resistance Determining Regions). Mutations in QRDR lead to amino acid substitution in topoisomerases, reducing the affinity of these enzymes for the quinolones, thus leading to a resistance phenotype for this class of antimicrobials. This mechanism of resistance was shown to be one of the main factors responsible for antimicrobial resistance for this class of chemotherapy in clinical isolates. However, other mechanisms of resistance may be present, among them the acquisition of plasmid determinants (qnrA, qnrB, qnrS, qepA, oqxA and oqxB). Most studies were carried out using clinical bacterial isolates, however, little research has been done on the mechanisms. The present work aimed to identify the main mechanisms of resistance to quinolones in environmental bacterial isolates and the main genera of this microbiota that harbor them. For this purpose, 69 bacterial isolates were selected from environmental samples. The main bacterial genera selected were Stenotrophomonas, Achromobacter, Ochrobactrum and Escherichia for which the genes PMQR, gyrA, gyrB, parE and parC and the plasmid typing were investigated. The results pattern of mutations in the genes coding for topoisomerases are similar to that observed in clinical bacterial isolates, acting PMQR genes synergistically in the contribution of MIC elevation to fluoroquinolones. However, additional mechanisms that may contribute to resistance levels cannot be discarded, especially efflux systems. Plasmid typing evidenced that most of the isolates present plasmids from the ColE-like family

Biocides and antibiotics are commonly used in Irish agriculture. This could lead to accumulation at sublethal levels in water and resistance development. The risk of this has earlier been assessed as non-existent. However, resistant strains have been found in Irish farm waste water. Due to possible horizontal gene transfer between bacterial populations the risk may be higher. Antibiotic resistance mechanisms have worked against certain biocides and antibiotic resistant strains have in certain cases showed reduced biocidal susceptibility. The aim of this project was to characterise bacterial populations from Irish aquatic samples and investigate their susceptibility to agriculturally common biocides and relevant antibiotics. Isolates from Dublin Bay water samples (n=15) were characterised using basic techniques. Minimum inhibitory concentration (MIC) tests with a broth microdilution method were performed with eight biocides and complimentary minimum bactericidal concentration (MBC) tests. Antibiotic disc diffusions were performed with eight antibiotics. The samples contained gram-negative isolates (n=3), Staphylococcus aureus (n=1) and Bacillus spp. (n=8) isolates. All isolates were on average resistant towards methylated spirits and iodine at the 2% v/v starting concentration. MIC values for Tri Scrub and the generic biocide were high. All MBC values were on average higher than the corresponding MIC values. A significant amount of the Bacillus spp. isolates were resistant towards β-lactams. As there is statistical uncertainty around the results, further investigations are needed. In conclusion, a trend of both high MIC and MBC values while showing resistance towards the largest number of antibiotics could be seen in Bacillus spp. isolates.