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To better understand food safety risks, functional genomic analysis was conducted to identify undescribed antibiotic resistance genes in fish samples from an aquaculture fish farm in Ohio. A fosmid genomic library from pooled DNA of antibioticresistant isolates was used to screen for resistance genes against tetracycline (Tet). A new Tet-resistant determinant designated as tet47 was identified, with the original hosts being Providenciaspp. from fish intestine. The new gene was also found to confer Tet resistance in Escherichia coli.Fish and byproducts were shown to be possible carriers that may disseminate new, functional, and potentially transmissible antibiotic resistance determinants through food, feed, and environmental contacts.

Rapid and specific detection of viable Listeria monocytogenescells, particularly in processed foods, is a major challenge in the food industry. To assess the suitability of using RNA-based detection methods to detect viable cells, several sets of PCR primers and florescent probes were designed targeting the 16S rRNA, internalin A, and ribosomal protein L4 genes. One-step real-time reverse transcriptase (RT) PCR assays were conducted using RNAs extracted from control and heat-treated L. monocytogenessamples. The cycle threshold values were significantly higher in heat-treated cells than in controls. However, realtime RT-PCR amplification signals were still detected even in samples stored at room temperature for 24 h after lethal treatments, and the intensity of the signals was correlated with the cell population. The 16S rRNA molecules were the most stable of the three targets evaluated, and the impact on detection efficacy of the relative positions of the PCR primers within the target genes was limited under the experimental conditions. These results suggest that real-time RT-PCR assays have advantages over conventional PCR assays for assessing viable L. monocytogenescells, but the results are affected by the stability of the RNA molecules targeted. These findings could have a major impact on interpretation of RNA-based detection data and gene expression studies.

Several virulence factors are involved in Listeria monocytogenespathogenicity. L. monocytogenesinternalins, particularly internalin A, are required for bacterial adhesion to and invasion of human intestinal epithelial cells. The expression of inter-nalins is thus related to virulence. Identification of conditions involved in regulating the expression of L. monocytogenesvirulence factors is essential for developing targeted strategies to control listeriosis incidence and improving therapeutic approaches. The primary aim of this study was to develop a quantitative real-time reverse transcriptase PCR platform to study the impact of environmental factors on L. monocytogenesScott A virulence factor expression, particularly in potentially complex ecosystems. A Taqman PCR–based, rapid quantitative gene expression evaluation method was established with the L. monocytogenesribosomal protein L4 encoding gene used as an internal standard. Our data suggest that inlAexpression is influenced by food composition and temperature, indicating that certain food processing or storage conditions, such as the use of lactic and acetic acids at common storage temperatures, could affect the expression of L. monocytogenesvirulence factor.