Detection of Bacterial Internalization in Lettuce (Lactuca sativa) Leaves Grown in Aquaponic Systems with Nile Tilapia (Oreochromis niloticus) Under Microbial Challenge

Abstract

Aquaponic systems are increasingly recognized as sustainable technologies for integrated fish and vegetable production. However, concerns remain regarding the potential internalization of human pathogens into vegetables grown in these systems. This study assessed the risk of pathogen internalization in lettuce leaves grown in aquaponic systems with Nile tilapia challenged with <i>Escherichia coli</i> or <i>Vibrio cholerae</i>. The system comprised nine fish tanks, eighteen hydroponic pipes, and eighty-one lettuce plants, with tanks assigned to three treatments. Samples of water, fish gut, fish blood, and lettuce leaves were collected. Microbiological analyses included selective culture, biochemical assays, and molecular identification. Although colonies consistent with <i>E. coli</i> and <i>V. cholerae</i> were recovered on selective media, molecular sequencing identified other bacterial species, including <i>Aeromonas sp</i>., <i>Aeromonas caviae</i>, <i>Aeromonas veronii</i>, <i>Enterobacter hormaechei</i>, and <i>Citrobacter freundii.</i> The findings indicate that conventional culture-based methods may produce false-positive results and highlight the importance of molecular confirmation. Notably, pathogenic bacteria associated with tilapia were detected and appeared capable of disseminating through the system and internalizing into lettuce tissues. This result highlights the need for biosecurity measures, contamination monitoring, and the combined use of conventional and molecular diagnostic tools to ensure accurate pathogen detection and compliance with international food safety standards.