الفهرس 
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Abstract
The MPN of coliform bacteria, isolation and identification of bacteria from Nile River water of Egypt at two different locations and the detection of tet genes among the identified bacterial isolates using PCR reaction has been studied.
According to the MPN water samples that were collected from the two different locations were containing high number of bacteria (0.9x102 - 0.17 x102 CFU/100ml). The isolated bacteria were tested for its sensitivity against two different concentrations of tetracycline. Only 31 resistance bacteria were selected to be identified according to biochemical characterization and the 16S rDNA sequence techniques.
According to morphological and biochemical characterization and 16S rDNA encoding genes, selected bacterial isolates were identified. Most resistant bacterial isolates were belonging to the family Enterobacteriaceae: (38.7 %) were Klebsiella sp., (25.8 %) were Kluyvera sp., (16.1 %) were Escherichia coli, (12.9 %) were Enterobacter sp., (3.2 %) were Atlantibacter hermannii and (3.2 %) was non-enteric isolate, Aeromonas hydrophila which belong to family Aeromonadaceae.
The obtained 16S rDNA sequences of the bacterial isolates which are reported in this study were BLASTn on NCBI database to find the best matched and then the gene sequences were submitted to the NCBI under accession no. (MH266225-MH266252), accession no.MH423704-MH423705) and (accession No.MH469556).
The phylogenetic tree of the 16S rDNA revealed that all resistant bacterial isolates were distinct from other reference sequences from NCBI.
Tetracycline resistant genes were detected in the selected 31 bacterial isolates. Six tet resistance determinants tet A, B, C, D, M and O were tested, as tet A, B, C and D represent the efflux pump mechanism while tet M and O represent the ribosomal protection protein mechanism only three determinants tet A, D and M were detected. Three determinants were detected tet A, D and M.
To identity the genes, the partial nucleotide sequences of tet genes detected in the present study and published sequences were found to be nearly identical to the entries for the different tet genes. Nucleotide sequence of tet genes for the 29 identified isolates has been deposited in the NCBI GenBank under different accession numbers.
Among the 31 identified bacterial isolates 29 bacteria were harbored tet genes, two isolates did not detect any type of the tested tet genes. Gene of tet A was carried by 44.8 % of the identified bacteria, tet D gene was carried by 79 %, while tet M gene were carried by 13.7 % of identified bacteria.
Among the 31 identified bacteria combination of tet genes has been detected, the majority (72.4%) harbored a single tet gene A or D or M, some bacteria (17.2%) harbored two different tet genes A and D while (10.3 %) of bacteria harbored three different tet genes A and D and M in the same strains. Based on the bioinformatics tools the patterns revealed that the detected genes tet A, D and M were generally grouped into 2 clusters: cluster I mainly including tet A and D gene and cluster II mainly including tet M gene.