Fethi Ben Abdallah

Detection by PCR of adhesins genes and slime production in clinical Staphylococcus aureus

The presence of the ica loci and adhesins genes in clinical Staphylococcus aureus strains were considered important factors of virulence. In this study, 46 strains of Staphylococcus aureus were isolated from auricular infection, and were investigated for slime production using Congo Red Agar method (CRA). In order to detect the adhesins genes (ica A, ica D, fnb A, cna, Clf A) Polymerase Chain Reaction was used. Qualitative biofilm production of S. aureus using CRA plates revealed that 56.5% of strains were slime producers. In addition 78.26% of strains were ica A and ica D positive. While the fnbA gene was present in 76.1% of isolated strains. Furthermore, 56.5% of strains have the cna gene and 30.4% were clfA positives. Overall this study confirms the presence of fnb A and ica A/ica D genes in the majority of studies S. aureus strains isolated from Staphylococcal sepsis. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preliminary safety assessment of Yarrowia lipolytica extracellular lipase : results of acute and 28-day repeated dose oral toxicity studies in rats

Interest in extracellular lipase sourced from the non conventional yeast Yarrowia lipolytica has increased over the last decade. The enzyme was recently suggested as a good candidate for pancreatic exocrine insufficiency treatment. However, there is still a lack of oral safety evaluation data. In this work, we conducted acute and 28-day repeated dose toxicity studies in rats. Both male and female rats were first orally treated with fungal lipase at either single or repeated doses. The results demonstrated that neither single dose nor chronic administration of lipase was associated with mortality or abnormalities in general conditions, behavior and growth. Except a decrease in urine pH and a dose-unrelated increase of triglycerides observed in males, chronic administration of lipase resulted in similar hematological, blood biochemical and urine parameters to those of untreated animals. Minor histopathological changes were observed in lungs and livers of treated and untreated animals but they were considered of no toxicological significance. This study provides, for the first time, safety data on Yarrowia lipolytica extracellular lipase that support its use as a pharmaceutical.

RT-PCR assays for in vivo expression ofVibrio alginolyticus virulence genes in cultured giltheadDicentrarchus labrax andSparus aurata

In this study, we investigated the pathogenic potency of twoVibrio alginolyticus strains isolated from cultured giltheadDicentrarchus labrax andSparus aurata, in Tunisia. The enzymatic activities of the extracellular products of the studied strains characterized with the API-ZYM system, revealed the existence of several activities. The 50% lethal doses levels were then determined, virulence levels ranged from 1.03×105 to 1.0×106 CFU/fish. In addition, we also searched for the presence of eightVibrio cholerae virulence genes:ctxA, zot, ace, toxR, toxS, toxRS, toxT, and Virulence Pathogenicity Island (VPI), in the genome of two isolated strains ofV. alginolitycus. Thein vivo expression oftoxR, toxS, VPI andace genes in both fish species, was tested by reverse transcriptase polymerase chain reaction. Indeed, we have noted that for each strain all the virulence genes selected were expressed in sea bream as well as in sea bass.

Outer membrane proteins and morphological alterations of Shigella spp. under starvation in seawater

In this study, we incubated four strains of Shigella in seawater microcosms (at room temperature and at 4°C) for eight months and we studied the alteration of their morphologic and outer membranes proteins. The starved cells showed an evolution to the filterable minicells state capable to pass membrane pore size 0.45 µm. In addition, the atomic force micrographs showed a reduction of the cells size and an evolution to coccoid-shapes. Outer membrane proteins patterns of stressed bacteria did not changed too much and these modifications were manifested by the appearance of one new band.

Biofilm formation, cell surface hydrophobicity, and fatty acids analysis of starved Salmonella enterica serovar Typhimurium in seawater.

Salmonella is an international foodborne pathogen widely disseminated in seawater that regularly causes large outbreaks of food poisoning. In this study, we have investigated the effect of starvation on the ability of Salmonella enterica serovar Typhimurium cells to adhere to polystyrene microplate and Hep2 cells in seawater microcosms after incubation for 3 years. Cell surface hydrophobicity was evaluated. Effect of stress on fatty acids composition was also established. Our results showed that after incubation in seawater, the ability of starved cells to adhere to polystyrene microplate was decreased significantly. However, the adhesion values to Hep2 cells have increased. In addition, cells surface hydrophobicity was decreased. The fatty acids composition of starved cells was modified.

Morphological changes of starvedSalmonella enterica serovar Agona cells in soil after resuscitation

In this study we investigated the morphological and biochemical changes ofSalmonella enterica serovar Agona incubated during 13 years in natural soil microcosm. After its resuscitation, the cells showed a biochemical profile completely inactive. These cells recuperated their initial characters after 6 months of incubation in Tryptic Soy broth. The scanning electron micrographs showed a reduction of the cells size and an evolution to coccoid-shapes. After 6 months of resuscitation,Salmonella enterica serovar Agona cells recuperated their original rod shape. The resuscitate cells ofSalmonella enterica serovar Agona were identified by multiplex PCR following the simultaneous amplification of thephoP, Hin andH-li genes.

Biofilm production, adherence and hydrophobicity of starved Shigella in seawater

In this work, we incubated four Shigella strains for one month at room temperature and at 4°C. Their adhesion capacity to KB cells, biofilm formation on microplate and surface hydrophobicity of starved cells were investigated. Our results showed that the stressed cells exhibited a remarkable increase in their hydrophobicity from 19 to 34 % and in their capacity to produce biofilm. Adherence assays to KB cells showed an increase in the number of adherent cells from 0.7 to 6.7% after one month of incubation in seawater. However, the percentage of invasion was decreased from 34 to 11% under stress condition.

Alterations of outer membrane proteins and virulence genes expression in gamma-irradiated Vibrio parahaemolyticus and Vibrio alginolyticus.

Gamma-irradiation technology sterilizes microorganisms and thereby prevents decay and improves the safety and shelf stability of food products. In this study we treated the foodborne pathogens Vibrio parahaemolyticus and Vibrio alginolyticus with gamma-irradiation (0.5 kGy) to evaluate their adaptative response. Outer membrane protein patterns of irradiated bacteria were found altered when analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. These modifications were manifested by the appearance and/or disappearance of bands as well as in the expression level of certain proteins. In addition, we searched for the presence of eight Vibrio cholerae virulence genes, toxR, toxS, toxRS, ctxA, zot, ace, toxT, and virulence pathogenicity island (VPI), in the genome of investigated strains. The expression of toxR, toxS, VPI, and ace genes in gamma-irradiated bacteria, studied by reverse transcriptase polymerase chain reaction, was altered. These variations were manifested by an increase and/or a decrease in the expression level of tested virulence genes.

Slime producing, heavy metals and antibiotics resistance in Aeromonas hydrophila isolated in Tunisia

Aeromonas hydrophila strains isolated from different naturally polluted environments (ten from wastewater, six from bay used for aquaculture, eight from sea coast water and six from fish) were subjected to 13 antibiotics, and to four heavy metals (Copper, Cobalt, Zinc and Mercury) by using agar diffusion and agar dilution methods, respectively. In addition, effect of heavy metals on slime production was also investigated. Results of the antibiotic resistance agreed with those of heavy metals resistance, however, treated wastewater and bay strains were much tolerant than seawater and fish bacteria. The range of metal concentrations that was tolerated in the liquid media yielded information on the tolerance levels of A. hydrophila to different tested concentrations of metals. Copper and zinc were the best tolerated metals. Mercury was the most toxic component for all bacteria. Almost all A. hydrophila produced slime and a small number of strains have changed their morphotype under the heavy metals concentration. Our results have shown that Tunisian aquatic biotopes have a significant proportion of antibiotic and heavy metal resistant to A. hydrophila.

Effect of combined long-term starvation and γ-irradiation on membrane fatty acids and cell surface hydrophobicity of Salmonella enterica serovar Typhimurium

This study was carried out to explore the adaptive mechanisms of Salmonella enterica serovar Typhimurium, in particular the implication of fatty acids (FA) in the remodeling of membrane lipid composition to overcome the combined effects of long-term starvation and γ-irradiation stresses. In addition, cell surface hydrophobicity was also evaluated. The bacterial strains (control and starved) were treated with a nonlethal γ-irradiation dose of 0.5 kGy and sublethal doses of 1 kGy. Gas chromatography analysis showed that the FA composition of starved and γ-irradiated cells was modified. However starvation combined with γ-irradiation induced more modifications in the FA composition than γ-irradiation or starvation alone. Indeed, the unsaturated FA-to-saturated FA ratio decreased significantly for both strains compared with γ-irradiated cells, as main consequence of the cyclic FA formation. Our results showed that starvation, irradiation, or combined stresses significantly influenced the hydrophobicity, and this may have affected the virulence state of Salmonella Typhimurium cells. This study represents one of the few to demonstrate the modifications on bacterial membrane as a cellular response to survive to the ionizing radiation combined with long-term starvation stress.