Bacterial Shrimp Disease in Iraqi Marine Waters

A sample of 116 shrimps Metapenaeus affinis (H. Milne-Edwards, 1837) were collected from local fish markets in Basrah Province, Southern Iraq. Height, weight, and pathological signs of the shrimps were recorded. Both morphological and biochemical examination by VITEK identification system were undertaken. Pathological infections were seen on the cuticle of abdominal segments in addition to a severe infection in uropod (tail segment), rostrum and pleopods (walking legs). Results of biochemical identification showed the presence of Aeromonas sobria and A. salmonicida from the infected organs and this study is considered as the first record of this bacterial infection in shrimps in Iraq.

Isolation of Aeromonas sobria JC18 from milkfish (Chanos chanos) intestine with proteolytic and cellulolytic activities for fish probiotic

Attention on the probiotic application for the improvement of fish resident intestinal microbiota has risen in the last decades. It is demonstrated that probiotics may function not only by direct inhibition of pathogenic bacteria or manipulation of enzymatic digestion of feed but also by modulation of immunity in fish. In the present study, we aimed to isolate the autochthonous microbiota of marine fish intestines as probiotic candidates based on cellulolytic and proteolytic activity. Bacteria were isolated and purified on a cellulose agar with 24h of incubation. A total of 18 bacterial strains were purified and stored in -80°C. Phenotypic screening based on the antibiotic resistance, antagonistic activity against pathogenic bacteria, resistance to an acidic environment, and ability of colonization in fish intestine found a selected strain, namely JC18. Infection test, molecular and phenotypic characterizations revealed that the JC18 isolate was a non-pathogenic Aeromonas sobria. It is hence revealed that the milkfish intestine is a potent source of proteolytic bacteria for fish probiotic screening.

Characterization and Antimicrobial Resistance of Environmental and Clinical Aeromonas Species Isolated from Fresh Water Ornamental Fish and Associated Farming Environment in Sri Lanka

The aims of this study were to characterize and investigate antimicrobial susceptibility and presence of integrons in 161 Aeromonas spp. isolated from ornamental freshwater fish farming environment, apparently healthy and diseased fish. Phylogenetic analyses of the gyrB gene sequences identified Aeromonas veronii as the most abundant species (75.8%) followed by Aeromonas hydrophila (9.3%), Aeromonas caviae (5%), Aeromonas jandaei (4.3%), Aeromonas dhakensis (3.7%), Aeromonas sobria (0.6%), Aeromonas media (0.6%), and Aeromonas popoffii (0.6%). Susceptibility to thirteen antimicrobials was determined and antimicrobial resistance frequencies were: amoxicillin (92.5%), enrofloxacin (67.1%), nalidixic acid (63.4%), erythromycin (26.1%), tetracycline (23.6%), imipenem (18%), trimethoprim-sulfamethoxazole (16.8%), and gentamicin (16.8%). Multi-drug resistance (MDR) was widespread among the isolates (51.6%, 83/161) with 51.6% (63/122) A. veronii isolates being MDR. In addition, 68.3% of isolates had multiple antibiotic resistance (MAR) indexes higher than 0.2, suggesting that they originated from a high-risk source of contamination where antimicrobials are often used. In all, 21.7% isolates carried class 1 integrons, with 97.1% having gene cassettes, while there were 12 isolates carrying class 2 integron gene cassettes. Our findings highlight that the aquatic environment and ornamental fish act as reservoirs of multidrug resistant Aeromonas spp. and underline the need for a judicious use of antimicrobials and timely surveillance of antimicrobial resistance (AMR) in aquaculture.

Effects of Selenium-enriched Bacillus Subtilis on Growth Inflammatory and Intestinal Microbes of Common Carp Induced by Mercury

Mercury (Hg) is a global pollutant that affects the health of humans and ecosystems. Selenium (Se) is an essential trace element for many organisms including humans. Bacillus subtilis is widely distributed in nature, is one of the main probiotics used in aquaculture, and has a certain adsorption effect on heavy metals. The interaction between Hg and Se was rigorously studied, especially due to the observation of the protective effect of Se on Hg toxicity. The common carp was exposed to Hg (0.03 mg/L), and 105 cfu/g Se-rich B. subtilis was added to the feed. After 30 days of feeding, samples were taken to evaluate the growth performance, serological response, inflammatory response, and intestinal microbial changes. In this study, when fish were exposed to Hg, the growth performance of the Se-rich B. subtilis plus 0.03 mg/L Hg fish group was lower than that of the control group and higher than 0.03 mg/L Hg; The levels of LZM and IgM decreased, but after supplementation with Se-rich B. subtilis, the levels of LZM and IgM increased; Hg treatment significantly up-regulated the mRNA expression of IL-1β, IL-8, TNF-α and NF-κB P65, but down-regulated the mRNA expression of IL-10, TGF-β and IkBα. However, compared with the Hg group, the Se-rich B. subtilis plus Hg group can significantly increase the mRNA expression levels of IL-1β, IL-8, TNF-α and NF-κB P65, but reduce the regulation of IL-10, TGF-β and IkBα expression. At the genus level, the abundance of Aeromonas in the intestines of common carp in the Hg treatment group increased, and Se-rich B. subtilis could reduce the abundance of Aeromonas (pathogenic bacteria). Through the analysis of the species, we found that the Hg group was mainly composed of Aeromonas sobria and Aeromonas hydrophila. However, in the Se-rich B. subtilis treatment group, we found that Aeromonas sobria was significantly less than the Hg group. Because Aeromonas (pathogenic bacteria) is harmful to the fish, it can induce inflammation in the fish and make the fish sick. Through microbiological analysis, it is found that Se-rich B. subtilis improves Hg-induced intestinal microbial changes, alleviates the abundance of Aeromonas, and alleviates the inflammation of the fish.

Myo-Inositol Restores Tilapia’s Ability Against Infection by Aeromonas sobria in Higher Water Temperature

Bacterial infection presents severe challenge to tilapia farming, which is largely influenced by water temperature. However, how water temperature determines tilapias’ survival to infection is not well understood. Here, we address this issue from the perspective of metabolic state. Tilapias were more susceptible to Aeromonas sobria infection at 33°C than at 18°C, which is associated with differential metabolism of the fish. Compared to the metabolome of tilapia at 18°C, the metabolome at 33°C was characterized with increased an tricarboxylic acid cycle and a reduced level of myo-inositol which represent the most impactful pathway and crucial biomarker, respectively. These alterations were accompanied with the elevated transcriptional level of 10 innate immune genes with infection time, where il-1b, il-6, il-8, and il-10 exhibited a higher expression at 33°C than at 18°C and was attenuated by exogenous myo-inositol in both groups. Interestingly, exogenous myo-inositol inactivated the elevated TCA cycle via inhibiting the enzymatic activity of succinate dehydrogenase and malate dehydrogenase. Thus, tilapias showed a higher survival ability at 33°C. Our study reveals a previously unknown relationship among water temperature, metabolic state, and innate immunity and establishes a novel approach to eliminate bacterial pathogens in tilapia at higher water temperature.