Abstract
Acquisition and dissemination of genes coding for antibiotic resistance in bacteria is a global phenomenon that has occurred in the last 50 years, mostly due to selective pressure, and likely the result of extensive use of antibiotics in humans and animals.1,2,3 The most common antibiotic resistance reported is to β-lactams. Of utmost importance and of public health concern, is the resistance acquired through plasmids, which may contain genes encoding enzymes such as β-lactamases (ESBL).4 Antibiotic resistance in bacteria and genes associated with resistance, have been increasingly considered as environmental contaminants of ecological concern.5,6 Thus, the presence of resistance genes in bacteria identified in wildlife species is potentially an important tool for estimating the degree of environmental contamination.6-9 The California sea lion (Zalophus californianus californianus) is a resident of the Gulf of California and the North Pacific and could potentially be used as sentinel for environment alterations. The aim of this study was to identify antibiotic resistant bacteria from sea lions in the Gulf of California and the Pacific Coast of Baja California. From 2011 to 2013, a total of 123 samples from rectal swabs and feces were obtained from 9 rookeries in these two locations. Bacterial identification and antimicrobial minimum inhibitory concentration (MIC) were performed using the VITEK 2 system (bioMérieux, France). The bla-SHV, bla-TEM and bla-CTX-M beta-lactamases genes were detected by PCR. A total of 147 bacterial isolates were obtained, with 35 isolates from both locations showing resistance to a variety of antibiotics as follows: ampicillin (12 strains), nitrofurantoin (11 strains), cefazolin, ampicillin/sulbactam (10 strains), and cefoxitin (8 strains), aztreonam and trimethroprim/sulfamethoxazole (5 strains). From the Pacific Coast isolates, we identified β-lactamases genes sequences congruent to blaSHV-33 in Klebsiella oxytoca and Klebsiella pneumoniae strains; blaTEM-1 in three strains (K. pneumoniae, Yokenella regensburgei and Serratia marcescens), KPC-1 in Edwardsiella tarda strain. Considering these results, it is likely that Pacific rookeries and the adjacent coastal water are more commonly affected by the anthropogenic activities than other areas in the Gulf of California, and that the sea lion population may serve as a sentinel for antibiotic resistance as an environmental pollutant and contaminant. To the author's knowledge, this is the first study to report these findings in Mexico and in the California sea lion population of the Gulf of California and the North Pacific coast.
Acknowledgment
This study was supported by Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT) grants IN221314 and IN229111, UNAM. Rosalía Avalos received CONACyT (Mexican National Council for Science and Technology) Scholarship No. 201527. We thank the monitoring personal of the Área de Protección de Flora y Fauna Islas del Golfo de California, Baja California-CONANP (Carlos Godínez, Hugo Moreno Prado, Rito Vale Navarro, Eduardo Guillén Díaz, and Joel Prieto Ceseña), Africam Safari Zoo (MVZ. Osvaldo Rey Martinez Gonzalez), Exportadora de Sal SA de CV., and Liliana Suárez, Octavio López, Jesús Sotomayor and María Fernanda Ramírez, for their assistance in field work.
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