Abdelwaheb Chatti

Effects of static magnetic fields on growth and membrane lipid composition of Salmonella typhimurium wild-type and dam mutant strains

This study was carried out to explore the adaptive mechanisms of S. typhimurium particularly, the implication of the Dam methyltransferase in the remodelling of membrane lipid composition to overcome magnetic field stress. With this aim, we focused our analyses on the increase in viable numbers and membrane lipid modifications of S. typhimurium wild-type and dam mutant cells exposed for 10h to static magnetic fields (SMF; 200 mT). For the wild-type strain, exposure to SMF induced a significant decrease (p<0.05) of CFU at 6h, followed by an increase between 8 and 10h. Growth of the dam mutant was significantly affected (p<0.05) after 6h and no recovery was observed until 10h, highlighting a different behavior of SMF stressed wild-type and dam mutant strains. SMF significantly affected the phospholipid proportions in the two strains. The most affected were those of the acidic phospholipids, cardiolipins (CL). In the dam strain the phospholipid response to SMF followed a globally similar trend as in the wild-type with however lower effects, leading mainly to an unusual accumulation of CL. This would in part explain the different behavior of the wild-type and the dam strain. Results showed a significant increase of membrane cyclic fatty acids Cyc17 and Cyc19 in the wild-type strain but only the Cyc17 in the dam strain and a meaningful increase of the total unsaturated fatty acids (UFAs) to total saturated fatty acids (SFAs) ratios of the exposed cells compared to controls from 3 to 9h (p<0.05) for both strains. The net increase of the total UFAs to total SFAs ratios seemed to result mainly from the increase of (C18:1) proportion (p<0.05) and to a lower extent from that of (C16:1) (p<0.05). These modifications of cyclic and unsaturated fatty acid proportions constitute an adaptive response to SMF stress in S. typhimurium wild-type and dam mutants to maintain an optimum level of membrane fluidity under SMF.

Changes in Membrane Fatty Acid Composition of Pseudomonas aeruginosa in Response to UV-C Radiations

The changes in lipid composition enable the micro-organisms to maintain membrane functions in the face of environmental fluctuations. The relationship between membrane fatty acid composition and UV-C stress was determined for mid-exponential phase and stationary phase Pseudomonas aeruginosa. The total lipids were obtained by dichloromethane/methanol (3:1) and were quantified by GC. The TLC analysis of phospholipids showed the presence of three major fractions phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. Significant modifications, as manifested by an increase of UFA, were obtained. Interestingly, this microorganism showed a remarkable capacity for recovery from the stressful effects of UV-C.

Static magnetic field increases the sensitivity of Salmonella to gentamicin

The present study was carried out to evaluate the effects of static magnetic field (SMF) on antibiotic sensitivity of Salmonella enterica subsp. enterica serovar Hadar. We have evaluated antibiotic susceptibility using the disc diffusion method following exposure to SMF. Our results showed that exposure to a 200-mT SMF static magnetic field increased the efficiency (p < 0.01) of gentamicin against Salmonella Hadar but did not affect the diameter of the inhibition zone of some other antibiotics actives on Enterobacteria: penicillin, oxacillin, cephalotin, neomycin, amikacin, tetracyclin, erythromycin, spiramycin, chloramphenicol, nalidixic acid and vancomycin.

Effects of hydrogen peroxide on the motility, catalase and superoxide dismutase of dam and/or seqA mutant of Salmonella typhimurium.

In addition to their role in the virulence attenuation of Salmonella and other pathogens, dam or seqA genes increase the sensitivity towards hydrogen peroxide. The aim of our study is to investigate the effect of H2O2 on the motility, the catalase and superoxide dismutase activities of dam and/or seqA mutants of Salmonella typhimurium. Our findings showed significant differences of the effects of H2O2 on the motility between wild type strain and all of mutants. Hydrogen peroxide changes SOD isoenzyme profile of these mutants by disappearance of Fe-SOD. Concerning the catalase, an increase of its activity was observed in the wild type, dam and seqA mutant. However, H2O2 decreases the activity of this enzyme in the double mutant strain. We can suggest that the dam gene, together with seqA, play a protective role in the oxidative stress response of Salmonella typhimurium.

Effects of dam and/or seqA Mutations on the Fatty Acid and Phospholipid Membrane Composition of Salmonella enterica Serovar Typhimurium

We examined the phospholipids (Phls) and the membrane fatty acid (FA) composition in Salmonella enterica serovar Typhimurium dam and/or seqA mutants. Phosphatidylglycerol, phosphatidylethanolamine (PE), and cardiolipin (CL) are the major Phls present in all the strains and accounted for greater than 95% of the total lipid phosphorus. Phosphatidic acid and phosphatidylserine are the minor ones. The seqA mutant showed a decrease in PE and an increase in CL and phosphatidylglycerol proportion compared with the wild-type strain. The same changes were observed with the seqA dam double mutant. However, the dam mutation caused an unusual accumulation of CL with a significant decrease in the PE content, compared with the isogenic wild-type strain. FA composition of the total lipids and the different fractions containing Phls have been determined. The major saturated FAs (SFAs) and unsaturated FAs (UFAs) found were C(14:0), C(16:0) and C(16:1w7), C(18:1w9), respectively. Cyclic FAs, cyc(17:0) and cyc(19:0), were also present in appreciable amounts. Moreover, dam and/or seqA mutations caused a decrease in UFA/SFA ratio and there was a progressive reduction in the content of C(16:1w7) and C(18:1w9), going through the order seqA, dam/seqA, and dam mutants. This decrease in UFA content was compensated for in all strains by an increase in the corresponding C(17-) and C(19-) cyclic FAs. So these UFAs were converted to their cyclopropane derivatives, which resulted in a low UFA/SFA ratio. SeqA and Dam proteins might regulate FA biosynthesis and Phls composition of Salmonella enterica serovar Typhimurium.

Acid resistance of Salmonella isolated from animals, food and wastewater in Tunisia.

Ann Saudi Med 27(3) May-June 2007 www.saudiannals.net 195 Salmonella are important foodborne pathogens that infect a variety of hosts and cause a broad spectrum of diseases. During the past few dec cades, there has been an increase in salmonellosis worldwide. This can largely be attributed to an increase in transmission of broad hostcrange organisms to huc mans from infected food and water.1 However, it is well demonstrated that Salmonella can disseminate and surc vive in various environmental niches for long periods of time. They are pervasive in nature and may contaminate animals, vegetables, water and especially food during its production and distribution.2 The spread and dissemination of these enteric pathoc gens were accompanied by an important increase in rec sistance to antibiotics all over the world.3,4 Therefore, these bacteria are developing a crosscresistance to antic biotics often used in therapy or as additives.5c7 The occ currence of multiplecantibioticcresistant Salmonella was reported in many developed and noncdeveloped counc tries and continues to cause major health problems.8c 12 Therefore, the use of antibiotics must be restricted to reduce the selection and spread of multicresistant strains. This urgent need to replace antibiotics has prompted researchers to try to find other alternatives. Consequently, many compounds and chemicals, such as organic acids, were tested for their antimicrobial activities. Organic acids have long been used both for prec serving foods and in livestock production for disease prevention or as growthcpromoting feed additives.13c19 It has thus been demonstrated that organic acids have an antimicrobial activity which is pH dependent.13 Salmonella, as enteric pathogens, encounter a low pH value in the environment, especially during its tranc sit in the host. These bacteria must face this barrier to replicate and proliferate in the hosts. The study of acid resistance in previous research showed that some strains of E. coli are able to survive at very low pH valc ues, but stop growing at pH values less than 4.4.20c22 Acid resistance of Salmonella isolated from animals, food and wastewater in Tunisia

Effect of Temperature and Gamma Radiation on Salmonella Hadar Biofilm Production on Different Food Contact Surfaces

Salmonella is a pathogen transmitted by foods and it is one of the most important target bacteria in food irradiation studies. Few works were carried out on the effectiveness of gamma radiation against biofilms formed by this bacterium. Salmonella can form a biofilm on different material surfaces. The physicochemical properties of surfaces and environmental factors influence the adhesion of this pathogen. The present study investigated the effect of gamma radiation (1 and 2 kGy) and temperature (28°C and 37°C) on the development of Salmonella Hadar biofilm on polyvinyl chloride (PVC), glass, cellophane paper (CELLO), and polystyrene (POLY). The obtained results indicated that biofilm production is surface and temperature dependent. In addition, biofilm formation decreased significantly after gamma irradiation at either 1 or 2 kGy doses. However, the agfD and adrA genes expression did not demonstrate significant decrease. This work highlighted that gamma radiation treatment could reduce the biofilm formation of Salmonella enterica serovar Hadar on different food contact surfaces.

Effects of UV-C Radiation on Viability, Outer Membrane Proteins and Lipopolysaccharides of Shigella

The annual incidence of shigellosis throughout the world is estimated at 164.7 million cases and 1.1 million of those infected die with 69% of all deaths involving children less than 5 years old.

UV-C Adaptation of Shigella: Morphological, Outer Membrane Proteins, Secreted Proteins, and Lipopolysaccharides Effects

Water UV disinfection remains extremely important, particularly in developing countries where drinking and reclaimed crop irrigation water may spread devastating infectious diseases. Enteric bacterial pathogens, among which Shigella, are possible contaminants of drinking and bathing water and foods. To study the effect of UV light on Shigella, four strains were exposed to different doses in a laboratory-made irradiation device, given that the ultraviolet radiation degree of inactivation is directly related to the UV dose applied to water. Our results showed that the UV-C rays are effective against all the tested Shigella strains. However, UV-C doses appeared as determinant factors for Shigella eradication. On the other hand, Shigella-survived strains changed their outer membrane protein profiles, secreted proteins, and lipopolysaccharides. Also, as shown by electron microscopy transmission, morphological alterations were manifested by an internal cytoplasm disorganized and membrane envelope breaks. Taken together, the focus of interest of our study is to know the adaptive mechanism of UV-C resistance of Shigella strains.

Role of Sod Gene in Response to Static Magnetic Fields in Pseudomonas aeruginosa

The protective role of superoxide dismutase (SOD) against non-ionizing radiation such as static electromagnetic field (200 mT) has been studied in wild-type and mutant strain of Pseudomonas aeruginosa lacking cytosolic Mn-SOD (sodM), Fe-SOD (sodB), or both SODs (sodMB). Our results showed that inactivation of sodM and/or sodB genes increases the sensitivity of P. aeruginosa toward stress induced by the static magnetic field (200 mT). Furthermore, our results showed an enhancement of SOD, catalase, and peroxidases after exposure to the magnetic field. However, wild-type cells maintained significantly higher activities of antioxidant enzymes than mutant strains. The malondialdehyde produced by the oxidative degradation of unsaturated lipids and fatty acids showed significant increase in mutant strains compared to the wild-type. The overall results showed that the SOD has a protective role against a stress induced by static electromagnetic field in P. aeruginosa.