# Antibiotic Resistance in Seawater Samples from East Coast of Spain
## 4 Discussion  
In recent decades, humanity has been confronted with the growing problem of the spread of antibiotic-resistant bacteria (ARB) and the difficulty of treating associated infections. The presence of these bacteria in coastal environments, as well as the presence of ARGs circulating freely in the water, represents a serious problem, especially for individuals who visit such areas for leisure purposes [46]. However, data on their presence and importance in the marine environment are still limited. To this end, 77 water samples from the coastal waters of Comunitat Valencia (eastern Spain) were analyzed using microbial and molecular methods, to determine the presence of ARB and ARGs. The main species studied included _E. coli_ and _Enterococcus_ sp., which were tested for resistance to 12-14 antibiotics. The detected levels of both microorganisms were within the range found in the compilation of several studies in marine waters worldwide encompassing four decades of research [47], ranging from 0.59 to 3.51 log\({}_{10}\) CFU/100 mL for _E. coli_ and 0.63 to 3.21 log\({}_{10}\) CFU/100 mL for _Enterococcus_ sp. In a macro study conducted in Spain between 2012 and 2015, covering 1392 beaches throughout the country, a mean of 1.4 log\({}_{10}\) CFU/100 mL for _E. coli_ and 1.32 log\({}_{10}\) CFU/100 mL for _Enterococcus_ sp. was found for the southern Mediterranean, where our samples were collected, with a national mean of 1.93 and 1.65 log\({}_{10}\) CFU/100 mL for each of the microorganisms [48]. Our values were within these averages, although we found some samples with _E. coli_ values of 4.4 log\({}_{10}\) CFU/100 mL and some samples of _Enterococcus_ sp. with values of 4.2 log\({}_{10}\) CFU/100 mL; both results were above acceptable levels and could have been due to the spillage of fecal matter due to problems with the Sewerage system at the location or run-off from rainfall. It should also be noted that these exceptionally polluted samples were taken in the summer, on beaches close to the city of Valencia, where not only members of the local population (Valencia and its metropolitan area comprise a population of around one and a half million inhabitants) but also many tourists bathed during this period. Some authors have already stated that beaches in urban environments, as in our case, are of lower quality than those in semi-urban or natural environments [49; 50; 51; 52], which is related to the number of people using the beaches, as well as the number of pets and birds, especially seagulls, that have access to them [53; 54; 55]. It is, therefore, difficult to determine the origin of this contamination. Figure 3: Comparison of ARG occurrence among the _Enterococcus_ sp. isolates and water from the different locations (NV: North Valencia; SV: South Valencia; A: Alicante). *: significant differences (\(p<0.05\)) between gene occurrence in water samples and in the _Enterococcus_ sp. isolates. The search for ARB was directed toward the detection of _E. coli_ and enterococci of fecal origin. Both microorganisms have been recognized as important actors in the spread of antibiotic resistance [56, 57]. The percentage of _E. coli_ strains resistant to at least one antibiotic (59.6%) was similar to that obtained in a study conducted on beaches in Brazil [58] and lower than that obtained in other studies in Portugal [56] or China [59], with percentages of up to 80% being observed. Ampicillin resistance was the most frequent observation, confirming that \(\beta\)-lactam resistance was the most prevalent form in the aquatic environment [60, 61]. Other antibiotics, such as ciprofloxacin, nalidixic acid, tetracycline, and sulfamethoxazole, were found to have resistance rates ranging from 14% to 18%. Similar findings were made by [PERSON] et al. [62] in a study conducted in Antarctica, an extreme location where the human presence is due to the establishment of scientific bases and where the removal of fecal contamination is very strictly controlled.