الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
The genus Aeromonas comprises 36 Gram-negative bacterial species which mostly act as opportunistic microorganisms. These bacteria are distributed naturally in diverse aquatic ecosystems, where they are easily isolated from animals such as fish and crustaceans. A capacity for adaptation also makes Aeromonas able to colonize terrestrial environments and their inhabitants, so these microorganisms can be identified from different sources, such as soils, plants, fruits, vegetables, birds, reptiles, amphibians, among others.
Infectious processes usually develop in immunocompromised humans; in fish and other marine animals, this process occurs under conditions of stress. Such events are most often associated with incorrect practices in aquaculture. Aeromonas has element diverse ranges and denominated virulence factors, which promote adhesion, colonization, and invasion into host cells. These virulence factors, such as membrane components, enzymes, and toxins, for example, are differentially expressed among species, making some strains more virulent than others. Due to their diversity, no single virulence factor was considered a determinant in the infectious process generated by these microorganisms.
Aeromonas spp. could be isolated and biochemically identified using conventional methods. Also, molecular assays are necessary to correctly identify this microorganism and study genetic factors related to its virulence. The aims of this study are to clarify the incidence and importance of Aeromonas spp. and its virulence genes in fish meat and canned fish products, which are important aspects for food hygiene and public health. In addition to that, application of some essential oils (cinnamon, clove, garlic, thyme, and onion) on tilapia fish fillets stored at 4oC, to stand for their antimicrobial effect against Aeromonas spp. and improving the keeping quality of fish meat fillets at storage temperature.
180 samples of fish meat and canned fish were randomly collected as the following; Nile tilapia, catfish, mugil, shrimps, canned tuna, and canned salmon (30 of each) to study the prevalence of Aeromonas spp. with special reference A. hydrophila and its virulent genes in the examined samples. The study showed that the mean values of Aeromonas counts were 0.28±0.03×102, 0.5±0.15×102, 0.158 ± 0.04×102, and 0.037±0.01×102 cfu/g for, Nile tilapia, catfish, mugil, and shrimp samples, respectively. The study revealed that Aeromonas species were isolated in 60 of 180 examined samples with a percentage of 33.3%, they could be divided into 7 species: A. hydrophila, A. caviae, A. media, A. shubertii, A. sobria, A. veronii bv sobria, and A. veronii bv veronii were found at a percentage of 7.8%, 5%, 2.8%, 7.2%, 5%, 2.8%, 2.8%, respectively. A. hydrophila, represented 14/60 (23%) of the isolated strains, were subjected to PCR test, and 12 (85.7 %) were confirmed using 16S rRNA gene. Virulence genes such as Aerolysin (AHA) gene was detected in 5 (41.6 %) of the tested strains. While the heat-stable enterotoxin (AST) gene was not detected. The effect of some essential oils (Eos) was evaluated using agar well diffusion assay and for the evaluation of the minimum inhibitory concentrations (MICs) of the tested Eos, a Resazurin microtiter plate assay was used. An experimental study was carried out to evaluate the efficacy of these Eos against A. hydrophila that was artificially inoculated into Nile tilapia fish fillets during storage at 4oC. Cinnamon, clove, and garlic showed a significant reduction in A. hydrophila counts compared to control samples, while thyme and onion Eos had lower effects. Cinnamon, clove, and garlic could be recommended as a natural antimicrobial for the preservation of fish products as they significantly improved the sensory and organoleptic parameters, including color, odor, texture, and pH values of the examined fish fillets, and could increase the shelf life for 2-3 days compared with control.
Aeromonas spp. is a potential biological hazard in fish meat and canned fish, as a foodborne pathogen, besides their role in fish spoilage. It could be concluded that Aeromonas spp. was isolated from various kinds of fish meat and owned some virulent genes to produce enterotoxins which may be a public health hazard to consumers. Application of cinnamon, clove, and garlic essential oils effectively inhibited the growth of A. hydrophilla and extended the shelf-life of tilapia fish fillets by 2-3 days compared to the control.