Phenotypic and genotypic antibiotic resistance of dominant bacterial isolates from cultured Whiteleg shrimp, Penaeus vannamei

Mary Ann Gito; Kyla Kris De la Cruz; Ivanne Pearl Guillermo; Diana Paguntalan; Carmelo del Castillo; Stephanie Pimentel; Christopher Marlowe Caipang

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Mary Ann Gito Graduate School, University of the Philippines Visayas, Iloilo City, Iloilo 5000, Philippines.
Kyla Kris De la Cruz Graduate School, University of the Philippines Visayas, Iloilo City, Iloilo 5000, Philippines.
Ivanne Pearl Guillermo Department of Biology, College of Liberal Arts, Sciences, and Education, University of San Agustin, Iloilo City, Iloilo 5000, Philippines.
Diana Paguntalan Division of Biological Sciences, College of Arts and Sciences, University of the Philippines Visayas, Miagao, Iloilo 5023, Philippines.
Carmelo del Castillo Institute of Aquaculture, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Miagao, Iloilo 5023, Philippines.
Stephanie Pimentel Fisheries and Food Research Development Center, Capiz State University, Roxas City 5800, Philippines.
Christopher Marlowe Caipang
cmacaipang@yahoo.com
Graduate School, University of the Philippines Visayas, Iloilo City, Iloilo 5000, Philippines.

Vol. 14: Accepted Articles

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July 9, 2026

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Antibiotic resistance in aquaculture poses significant threats to aquatic animal health and may contribute to the spread of antimicrobial resistance in the environment and human populations. This study characterized the phenotypic and genotypic antibiotic resistance profiles of dominant bacterial isolates recovered from cultured whiteleg shrimp (Penaeus vannamei) obtained from shrimp farms in Iloilo, Philippines. A total of 150 shrimp samples were processed for bacterial isolation, and dominant isolates were screened for multidrug resistance (MDR) using the Kirby–Bauer disk diffusion method. Based on the antibiotic resistance index (ARI), nine MDR isolates were selected for further analysis. Phenotypic susceptibility testing showed that all MDR isolates were resistant to ampicillin and rifampin. Resistance to ciprofloxacin (55.5%), erythromycin (44.4%), tetracycline (22.2%), chloramphenicol (11.1%), and streptomycin (11.1%) was also observed. Polymerase chain reaction (PCR) detected antibiotic resistance genes associated with chloramphenicol, tetracycline, and quinolone resistance, namely catB (44.4%), tetE (22.2%), and gyrA (11.1%), respectively. Discrepancies between phenotypic resistance patterns and detected resistance genes were observed, indicating phenotypic–genotypic discordance. These findings suggest that additional mechanisms beyond the targeted genes may influence the expression of resistance. The study highlights the complexity of antimicrobial resistance in aquaculture and underscores the value of integrating phenotypic and molecular approaches for effective surveillance and management.

Gito, M. A., De la Cruz, K. K., Guillermo, I. P., Paguntalan, D., del Castillo, C., Pimentel, S., & Caipang, C. M. (2026). Phenotypic and genotypic antibiotic resistance of dominant bacterial isolates from cultured Whiteleg shrimp, Penaeus vannamei. International Journal of Aquatic Biology, 14. Retrieved from http://ij-aquaticbiology.com/index.php/ijab/article/view/2919

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