Abdelkarim Mahdhi

Effect of dietary supplementation of probiotics and palm fruits extracts on the antioxidant enzyme gene expression in the mucosae of gilthead seabream (Sparus aurata L.)

Antioxidant activity is particularly important, since oxidation is an unavoidable reaction in all living bodies. At present, natural antioxidants to be used on food as an alternative to synthetic ones are being sought. Gilthead seabream (Sparus aurata L.) specimens were fed for 4 weeks with diets enriched with bacterial probiotics (Shewanella putrefaciens Pdp11 and Bacillus sp), single or in combination with Tunisian dates palm fruit extracts. The expression of the main antioxidant enzyme genes (superoxide dismutase, catalase and glutathione reductase) in the mucosae (gut, skin and gill) was evaluated after 2 and 4 weeks. Previously, free radical scavenging and several antioxidant assays were developed to know the antioxidant properties present on the palm fruits extracts. The results demonstrated that experimental diets alter the expression of the studied antioxidant genes, primarily in the gill and skin. Furthermore, the tested probiotics and mainly, the aqueous date palm fruits extracts had significant antioxidant properties based on their protective effect against the levels of intracellular reactive oxygen species, especially when administering during 4 weeks. For this reason, probiotics and date palm fruit extracts may serve as good natural antioxidants and could potentially be considered as a functional food ingredient for fish in farms.

Effects of dietary administration of fenugreek seeds, alone or in combination with probiotics, on growth performance parameters, humoral immune response and gene expression of gilthead seabream (Sparus aurata L.)

ABSTRACT The use of immunostimulants is considered a promising preventive practice that may help to maintain animal welfare and a healthy environment, while increasing production and providing higher profits. The purpose of this study was to evaluate the effects on gilthead seabream (Sparus aurata L.) of the dietary administration of fenugreek (Trigonella foenum graecum) seeds, alone or combined with one of the following probiotic strains: Bacillus licheniformis (TSB27), Lactobacillus plantarum or Bacillus subtilis (B46). Gilthead seabream were fed a control or one of the supplemented diets for 3 weeks. The effects of these supplemented diets on growth performance parameters and the humoral immune response (natural haemolytic complement, peroxidase, total IgM levels, proteases and antiproteases activities) were evaluated after 2 and 3 weeks of feeding. Simultaneously, the expression levels of some immune‐relevant genes (igm, tcr‐&bgr;, csfr1 and bd) were measured in the head‐kidney. Interestingly, all probiotic supplemented diets increased seabream growth rates, especially the B. licheniformis supplemented diet. Generally, humoral immune parameters were enhanced by the dietary supplementation at the different time points measured. The results showed a significant increases in the immune parameters, principally in fish fed only fenugreek or fenugreek combined with B. subtilis. Furthermore, real time qPCR revealed that dietary supplementation significantly enhances the expression of immune‐associated genes in the head‐kidney, particularly igm gene expression. These results suggest that fenugreek alone or combined with one of the probiotic strains mentioned enhances the immune response of gilthead seabream, a species with one of the highest rates of production in marine aquaculture. HIGHLIGHTSInnate immune response was enhanced by the fenugreek dietary supplementation.Humoral immune parameters were stimulates mainly by fenugreek + B. subtilis diet.Supplemented diets induced an important up‐regulation of igm gene expression.Fenugreek and probiotic tested could be considered as a good aqua feed supplements.The use of immunostimulants is a promising alternative to maintain animal welfare.

Using mixture design to construct consortia of potential probiotic Bacillus strains to protect gnotobiotic Artemia against pathogenic Vibrio

Abstract To evaluate the potential probiotic effect of three Bacillus strains on the survival and growth of an Artemia culture and to obtain the optimal formulation of pure cultures of the bacilli, challenge tests were performed with the pathogenic bacterium Vibrio alginolyticus (S1) using mixture design. According to molecular analyses involving amplified ribosomal DNA restriction analysis (ARDRA), these bacteria corresponded to Bacillus subtilus, Bacillus cereus and Bacillus coagulans. An antimicrobial susceptibility and antagonism assay revealed that these strains were susceptible to most antimicrobial drugs and have an inhibitory effect against tested pathogenic Vibrio. Furthermore, the investigated Bacillus strains were fairly adhesive to polystyrene, with values ranging from 0.10 to 0.32 at 595 nm. Statistical analysis demonstrated that Bacillus strains enhance protection against pathogens, have no impact on survival, but improve the growth of larvae, for which the highest growth rate was obtained when the mixture composition was 32% B. subtilus, 68% B. cereus and no B. coagulans.

Quality and antioxidant response of gilthead seabream (Sparus aurata L.) to dietary supplements of fenugreek (Trigonella foenum graecum) alone or combined with probiotic strains

Abstract The present study was conducted to determine the potential effect of the dietary intake of fenugreek (Trigonella foenum graecum) seeds alone or in combination with Bacillus licheniformis, Lactobacillus plantarum or B. subtilis on gilthead seabream quality and antioxidant response after 2 and 3 weeks of experimental feeding. The results showed that the supplements did not affect the percentage of the fatty acid profiles of muscle, demonstrating that all the additives tested can be administrated without any negative effect on biochemical composition and quality of gilthead seabream. The quantification of thiobarbituric acid reactive substances in muscle demonstrated the significant beneficial effect of the experimental diets compared with the control one. Besides, an increase in superoxide dismutase and catalase in liver was recorded after 3 weeks of administration of experimental diets. Furthermore, real time qPCR revealed that dietary supplementation with FEBS significantly enhances the expression of scavenging enzymes, such as cat and gr genes in the liver after 3 weeks. The findings suggest that the administration of fenugreek supplement alone or combined with probiotic strains could be considered as a good source of natural antioxidants and as a functional aquafeed ingredient for gilthead seabream. HighlightsAntioxidant status of seabream after dietary fenugreek + probiotics was evaluated.Supplemented diets did not affect the fatty acid profiles of the muscle.Experimental diets showed antioxidant properties (decreased the TBARS in muscle).SOD and CAT were enhanced after fed experimental diets for 3 weeks.Fenugreek + probiotics up‐regulated liver antioxidant‐related gene expression.

Survival and retention of the probiotic properties of Bacillus sp. strains under marine stress starvation conditions and their potential use as a probiotic in Artemia culture

The probiotic properties of Bacillus strains isolated from Artemia culture and the effect of marine stress on viability and survival were investigated, as well as the changes occurring in their properties. Analyses showed that these bacteria corresponded to the genus Bacillus sp. Antagonism and adherence assays revealed that Bacillus strains have an inhibitory effect against tested pathogenic bacteria and are fairly adherent. Normal and starved cells showed different enzymatic profiles. Challenge tests performed with Artemia larvae provided evidence that the tested Bacillus strains were neither pathogenic nor toxic to the host and conferred protection for Artemia culture against pathogens. The tested strains maintained their viability and their probiotic properties during the period of study. The results suggest that the tested strains have suffered changes allowing them to survive in seawater in the absence of nutrients and outside their natural host, identifying them as potential probiotic candidates for Artemia culture.

Use of mixture design to construct a consortium of date palm (Phoenix dactylifera L.) fruit extract and potentially probiotic Bacillus strain to confer protection against vibriosis in Artemia culture

BACKGROUND To find a biological control treatment applicable to shrimp hatcheries, the influence of the dietary administration of a consortium of two date palm (Phoenix dactylifera L.) fruit extracts and potentially probiotic Bacillus strain on Artemia culture was studied. Challenge tests were performed with virulent Vibrio alginolyticus to assess the protective effects of Deglet Nour and Degla fruit extracts alone or in conjunction with potentially probiotic Bacillus strain. RESULTS Under the conducted bioassays, where Deglet Nour and Degla fruit extracts were used singly or in association with potentially probiotic Bacillus strain, the survival and growth rates of Artemia nauplii were improved. Nauplii protection against virulent Vibrio strain was highest using a feed comprising 2.7% Deglet Nour/97.3% Deglat extract and no Bacillus bacteria. CONCLUSION The present findings provide evidence that the use of palm fruit extracts singly or in conjunction with potentially probiotic Bacillus strain has tremendous potential as a biocontrol treatment for Artemia culture, particularly with regard to improving culture conditions and the ability to inhibit bacterial pathogens under in vivo conditions.

Adhesion, invasion, cytotoxic effect and cytokine production in response to atypical Salmonella Typhimurium infection

Pathogenic bacteria such as Salmonella have the ability to respond to a wide variety of environmental stimuli. These responses allow them to survive and withstand insults both of an external location as well as within the host. The aim of this study was to investigate the effect of preadaptation in stressful conditions encountered in seawater microcosms for different periods of time on Salmonella Typhimurium survival, antibiotic susceptibility and interactions with Caco-2 cells. These results showed that the number of bacterial cells depends from the periods of stress in culture medium, highlighting the importance of using the right culture medium for the enumeration of stressed bacteria. The antibiotic resistance of starved cells was modified and their exposure to stressful conditions in seawater during 12 months significantly increased adhesion, invasion and cytotoxic activities on Caco-2 cells. Moreover, cellular cytokines IL-6 and IL-8 secretions were up-regulated. Present results seem to suggest that the preadaptation of S. Typhimurium in seawater microcosms affect the cultural characters by the appearance of the atypical cells that may play a critical role in the intestinal infection and in the systemic spread of the disease. These findings are very important to understand bacterial responses to changing conditions and explain the persistence of these atypical in eukaryotic cells.

Determination of biological characteristics of Tunisian Artemia salina populations

In this study, Artemia salina cysts collected from four Tunisian hypersaline environments were characterized using biometrical, biological and biochemical descriptors. Biometrical analysis revealed that the mean diameter value ranged from 220.25 to 237.76 μm, for the untreated cysts, from 199 to 224.52 μm for decapsulated cysts and that the chorion thickness ranged from 6.62 to 10.58 μm. 48 h after hatching, Artemia from Sebkha El Meleh, Sebha Moknine, Sfax saltworks and Sahline saltworks presented a hatching percentage of 52.7%, 53.75%, 70.16% and 43.74%, respectively. The length of the freshly hatched instar I nauplii varied from 429 to 449.34 μm. The fatty acids profile showed that the n-3 series was strongly dominant in the samples collected from Sebkha Moknine and Sfax saltworks, representing a percentage ranging from 17.92% to 22.45% of the total fatty acids. The data collected in this study can be useful to add new information on biological and biochemical characterization of Artemia strains present in Tunisia. On the basis of fatty acid profile, the Artemia strains collected from Sahline saltworks, Sfax saltworks and Sebkha El Meleh can be as classified as “marine” type, and that from Sebha of Moknine as “freshwater” type.

Change in physiological cellular state of halophilic Bacillus sp. under long marine stress starvation conditions

The aim of this study is to give insight about the effect of long marine stress starvation conditions in the physiological responses of three potential halophilic probiotic Bacillus isolates isolated from Artemia culture. Bacteria were cultured in sterilized seawater and incubated at ambient temperature for one year. The obtained results showed that the isolates viability was maintained during the studied period. Compared to normal cells, starved cells increased their adhesive ability and cell surface hydrophobicity. Our data demonstrated that the tested isolates maintained their enzymatic profile in non-starvation conditions and under stress conditions they expressed enzymes like esterase lipase (C8), amylase, lipase, and caseinase. The present finding suggests that the tested strains have developed strategies that allow them to overcome stressful conditions in the absence of nutrients and makes them as a potential candidate probiotics.