Antibiotics are a group of substances potentially harmful to the environment. They can play a role in bacterial resistance transfer among pathogenic and non-pathogenic bacteria. In this experiment three representatives of medically important chemotherapeutics, confi rmed to be present in high concentrations in wastewater treatment plants with HPLC analysis were used: erythromycin, sulfamethoxazole and trimethoprim. Erythromycin concentration in activated sludge was not higher than 20 ng L , respectively in winter and summer. Due to a wide variety of PCR-detectable resistance mechanisms towards these substances, the most common found in literature was chosen. For erythromycin: erm and mef genes, for sulfamethoxazole: sul1, sul2, sul3 genes, in the case of trimethoprim resistance dhfrA1 and dhfr14 were used in this study. The presence of resistance genes were analyzed in pure strains isolated from activated sludge and in the activated sludge sample itself. The research revealed that the value of minimal inhibitory concentration (MIC) did not correspond with the expected presence of more than one resistance mechanisms. Most of the isolates possessed only one of the genes responsible for a particular chemotherapeutic resistance. It was confi rmed that it is possible to monitor the presence of resistance genes directly in activated sludge using PCR. Due to the limited isolates number used in the experiment these results should be regarded as preliminary.
Microbial community and physiochemical processes were monitored by means of denaturing gradient gel electrophoresis (PCR-DGGE) in two sequencing batch reactors (SBRs) running for partial nitritationanammox and differing in the feeding phase durations (6 h 40 min for SBR1 and 40 min for SBR2). Both SBRs were treated with reject water with a high ammonia concentration (>600 mg 3 4 NH /dm ) for over 370 days. The aim of the experiment was to present the influence of this parameter on total bacterial and anammox bacterial community structure. Molecular analysis revealed that a drastic decrease in influent ammonia concentration to the studied communities caused a change of genotypic structure in their composition. The difference in the reactors working scheme can be the reason for divergence in the community structure though having no drastic influence on its performance and biodiversity level. Feeding time has stronger influence on the genotypic composition of the total bacterial community than on anammox biocenosis.
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