# Antibiotic Resistance in Seawater Samples from East Coast of Spain
## 4 Discussion
This reflects the general resistance to \(\beta\)-lactams worldwide, with varying rates of resistance to other antibiotics depending on various factors such as geographical location. This fact also demonstrates the ability of antimicrobial resistance to distribute homogeneously in seawater. Nine percent of the _E. coli_ strains showed multidrug resistance, and again, the \(\beta\)-lactam family was present in all of the resistance profiles. Comparing these data with those of other studies, we see very different percentages of multidrug resistance. In a study carried out on the coast of Sicily, [63] found levels of multidrug resistance in their isolates ranging from 7% (against five antibiotics) to 14% (against four antibiotics). Similar results were obtained in isolates from Brazil beaches with multi-resistance levels ranging from 0 to 8.3% [64]. This supports the idea that the majority of multidrug-resistant ARBs are not of environmental origin but rather originate in places of high selective pressure, such as hospitals or highly contaminated ecosystems. The levels found in each geographical area are very consistent with the antibiotic use policies in these areas [65]. The enterococci in our study showed a low level of resistance (23%) compared with other studies conducted on Mediterranean beaches, for example, in Italy, with 38% of resistant strains [66], in Morocco (ca. 65%) [57], or in Tunisia, where this resistance is as high as 75% [67]. In our study, only strains resistant to tetracycline (20%) and daptomycin (3%) were obtained, with the latter being a rarely used drug. However, it is important to note that daptomycin is used as a last line of therapy, especially in vancomycin-resistant enterococcal infections [68]; therefore, the emergence of daptomycin-resistant enterococci is of concern in healthcare settings. No multidrug-resistant _Enterococcus_ spp. isolates were found. These data are encouraging as antibiotic-resistant enterococci found in coastal marine waters are often closely related to human clinical isolates, probably originating from urban wastewater [69, 70]. PCR assays revealed that _bla_TEM was the most frequently detected gene in the analyzed seawater samples. These results were in line with other studies in the Mediterranean, where this gene was detected in almost all samples [56, 63, 71], confirming that \(\beta\)-lactam antibiotic resistance genes were widely distributed in seawater samples, detecting it in fishes and wild marine species [72]. In a macro study carried out on water samples from oceans around the world, the authors found a high abundance of ARGs encoding resistance to \(\beta\)-lactam antibiotics, probably due to the high use of these antibiotics, as stated by the WHO [73, 74]. The presence of the _qnr_S, _sul_I, and _tetW_ genes was also comparable with the results of some other works that attested to their prevalence in coastal environments [75, 76], but this contrasts with the absence confirmed in other coastal waters, such as Sicily [63]. This observed variability in the presence and abundance of ARGs was highly dependent on antibiotic usage patterns, which was a key factor for the generation and propagation of ARGs [77]. Once again, the _bla_TEM gene was the most frequently detected gene in both _E. coli_ (92.9%) and _Enterococcus_ spp. isolates (40%). The remaining genes showed more variable percentages, with the exception of _sul_I in _E. coli_ isolates, which also stood out with identical percentages to _bla_TEM. Other studies have demonstrated that _bla_TEM, _tet_, and _sul_ genes are ubiquitous in _E. coli_ isolates from estuarine and marine environments [32, 36, 78, 79]. In the present study, the frequency with which ARGs were detected was higher in _E. coli_ isolates than in direct water samples. These results contrast with those found in other types of water, such as the study carried out by [PERSON] et al. [24] in water from ditches that flow into the sea, specifically in the region of Valencia Norte.