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Citrobacter freundii, Tilapia, Pseudomonas, Antimoicrobial Resistance


Tilapia is one of the most commonly eaten fish in the United States, yet little is known about the bacteria that it could carry. Because the vast majority of tilapia are raised and processed outside the United States, it is possible that there is less control of its bacterial content due to a higher chance of exposure to environments that could lead to the retention and/or introduction of pathogenic bacterial species. Therefore, it is important to determine if the tilapia sold commercially in the United States carry pathogenic bacteria that could pose a significant health risk to consumers. To address this issue, a study was initiated to find potential bacterial pathogens in locally-purchased tilapia. Of the bacteria that have been isolated so far, two were studied in greater depth, Citrobacter freundii and an isolate from the Pseudomonas genus. The goal was to identify the species of the Pseudomonas isolate and to start the process of determining if the isolates were resistant to antimicrobials and carried virulence factors. After finding conditions for running robust PCR reactions, DNA was isolated from the bacteria and used to amplify the 16S rRNA gene. This amplified gene from the Pseudomonas species was sequenced and the sequence was compared to the NCBI database. The results suggest that this isolate is either a strain of Pseudomonas lundensis or an entirely new species. In testing for antimicrobial resistance, both isolates were found to be resistant to Cefoxitin and Cefazolin. Additionally, C. freundii was resistant to Streptomycin and the Pseudomonas species was resistant to Ampicillin. Virulence factors, some of which are connected to antimicrobial-resistance genes, that have previously been found in C. freundii are a major focus of future research.

Content Notes

Research Report

First Advisor

John Weber



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