# Antibiotic Resistance in Seawater Samples from East Coast of Spain
## 3 Results
### Antibiotic-Resistant Gene Determination in Water Samples and Bacterial Isolates  
The presence of five antibiotic resistance genes in the 77 seawater samples was analyzed as described in the Section 2. Forty-four of the samples (57%) were positive for at least one of the genes. As shown in Table 4, the _bla_TEM gene was the most frequently detected gene (46.7%), followed by _qmt_S (32.5%) and _sul_I (23.4%); the _tet_W gene was detected in 17% of the samples, while _erm_B was only found to be present in one sample (Supplementary Materials Table S3). The statistical analysis only showed a significant relationship between the _tet_W gene and the region of Alicante (\(\chi^{2}\) = 10.384, \(p<0.05\)), and it was not detected in any of the samples from South Valencia. Combinations of two genes were detected in 24 seawater samples (31%), with the most abundant combinations being those containing the _bla_TEM gene. Three gene combinations were detected in nine samples (ca. 12%). Finally, four and five gene combinations were present in only one sample. A statistically significant dependence relationship was only detected between the _tet_W gene and the sampling zones of North Valencia and Alicante (\(\chi^{2}\) = 10,384, \(p<0.05\)) as this gene was not detected in any of the samples from South Valencia. The _bla_TEM gene, together with the _sul_I gene, was the most frequently detected gene, with each of them being found in 53 _E. coli_ strains (92.9%) (Table 5). They were followed in frequency by the _tet_W and _qmt_S genes, present in 40% and 36.8% of the samples, respectively. In contrast, the _erm_B gene was detected in only three isolates (5%) (Supplementary Materials Table S2). The statistical analysis showed no dependence relationship between the sampling area and the frequency of gene detection in _E. coli_ isolates (\(p>0.05\)). The analysis of genes in enterococci (Table 6) again showed that the _bla_TEM gene was the most abundant, with it being detected in 40% of the isolates. The percentages of the other genes ranged from 3.3% for _qmt_S and _tet_W to 6.6% for _erm_B. It should be noted that _sul_I was not detected (Supplementary Materials Table S5). The statistical analysis showed no relationship between the sampling area and the occurrence of genes in the isolates (\(p>0.05\)). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Zone**} & \multirow{2}{*}{**No. Samples**} & \multicolumn{6}{c}{**Number of Positive Samples**} \\ \cline{3-6}  & & _bla_TEM & _qmt_S & _erm_B & _sul_I & _tet_W \\ \hline NV & 21 & 6 & 5 & 0 & 3 & 5 \\ SV & 30 & 15 & 9 & 0 & 5 & 0 \\ A & 26 & 15 & 11 & 1 & 10 & 8 \\ \hline Total (\%) & 77 & 36 (46.7) & 25 (32.5) & 1 (1.2) & 18 (23.4) & 13 (16.9) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Presence of antibiotic resistance genes in water samples according to sampling zone. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Zone**} & \multirow{2}{*}{**No. Isolates**} & \multicolumn{6}{c}{**Number of Positive Isolates**} \\ \cline{3-6}  & & _bla_TEM & _qmt_S & _erm_B & _sul_I & _tet_W \\ \hline NV & 14 & 13 & 4 & 0 & 13 & 2 \\ SV & 23 & 21 & 11 & 1 & 21 & 11 \\ A & 20 & 19 & 6 & 2 & 19 & 10 \\ \hline Total (\%) & 57 & 53 (92.9) & 21 (36.8) & 3 (5.2) & 53 (92.9) & 23 (45.1) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Presence of antibiotic resistance genes in _E. coli_ isolates according to sampling zone. For most of the genes investigated, their presence was greater in the _E. coli_ isolates than in the directly analyzed waters (Figure 2). In North Valencia, the _bla_TEM and _suI_ genes were detected at significantly higher levels in the _E. coli_ isolates than in the seawater samples (\(\chi^{2}=13.988\), \(p=0.0002\) and \(\chi^{2}=20.896\), \(p=0.000\), respectively).