Project description:This project was designed to observe changes in proteins expression and toxicity proteins expression of Aeromonas hydrophila under normal and iron restriction conditions.
Project description:Antibiotic resistance (AMR) in aquatic bacteria affecting aquaculture has been a growing concern given the potential for mixing of bacterial populations in the aquatic environment and exposure to different pharmaceuticals from drugs used in aquaculture, as well as wastewater effluent and agricultural run-off. To better understand the mechanism for AMR in a common aquatic fish pathogen exposed to low dose antibiotics we monitored the genetic changes, as well as gene expression, in Aeromonas hydrophila as the bacteria was exposed to incremental doses of oxytetracycline (OTC), a commonly used drug in aquaculture. We were able to render all three isolates of our original A. hydrophila resistant to therapeutic levels of OTC (i.e. ≥100ppm). The relatively quick phenotypic adaptation (often less than 3 days) to different OTC concentrations was very similar across our replicates. Our whole genome sequencing data and transcriptome results suggested several genes underwent point mutations across all replicates. Further differential gene expression was observed and likely impacted several pathways which may explain the progressive resistance to OTC associated with incremental exposure to the drug. The specific mutations consistently identified in isolates exposed to OTC were on AHA_ 2785 (associated with an outer membrane protein), AHA_2910 (involved in the efflux pump mechanism), and AHA_0308 (associated with the small ribosomal subunit protein S10). The pathways involved in the differential gene expression included efflux- pump mechanisms, outer membrane proteins, and ribosomal protein OTC target. Our findings support the notion that AMR can occur via genetic regulation of several intrinsic mechanisms within a bacterial population. This finding could have implications in aquaculture where bacteria such as A. hydrophila can be exposed to varying levels of antibiotics during in-feed treatments.
Project description:The type III secretion system (T3SS) is an important virulence factor of Gram-negative bacteria, including the genus Aeromonas, a group of aquatic bacteria capable of both mutualistic and pathogenic interactions. Aeromonas species are increasingly recognized as opportunistic human pathogens. The type strain A. schubertii ATCC 43700 encodes two distinct T3SSs located in the Aeromonas pathogenicity islands 1 and 2, hereby designated as API1 and API2, respectively. This work investigates the role of API1 and API2 in A. schubertii-induced cytotoxicity and identifies novel type III secretion effectors. HeLa cell infections showed that API1, but not API2, is essential for cellular cytotoxicity resulting in both apoptotic and necrotic cell death. The ΔAPI1 mutant failed to induce cytotoxicity, whereas the wild-type (WT) and ΔAPI2 strains induced comparable cytotoxic effects. Proteomic analysis identified 7 candidate effectors secreted by the API1 injectisome under low-calcium conditions. These included two previously characterized effectors, AopH and AopO of A. salmonicida, and five novel effectors hereby named AopI, AopJ, AopL, AopT, and AopU, whose injection into host cells via API1 was validated using a split luciferase reporter system. Functional analysis revealed distinct roles for these effectors. AopL, homologous to the VopQ effector of Vibrio cholerae, accelerated caspase 3-independent necrosis, while AopI, homologous to ExoY of Pseudomonas aeruginosa, suppressed caspase activation and necrosis, indicating a pro-survival function. These results show the role of API1 injectisome in the cytotoxicity of A. schubertii and expand our understanding of T3SS-mediated host-pathogen interactions in Aeromonas species.