Mohammed Bakkali

Chemical composition and antimicrobial activity of essential oils of Thymus algeriensis, Eucalyptus globulus and Rosmarinus officinalis from Morocco

BACKGROUND The present study reports on the antimicrobial activity and chemical composition of the essential oils (EOs) of Thymus algeriensis, Eucalyptus globulus and Rosmarinus officinalis from Morocco. RESULTS The composition of these species was analysed by GC-MS, and 65 components were identified. Eucalyptus globulus EO showed a great similarity with EOs from other regions, with 1,8-cineole (79.85%) the major component. Also rich in this constituent was Rosmarinus officinalis (43.99%). However, the chemical profile of Thymus algeriensis was rather different, and for the first time such a high content of borneol (23.48%) has been described in this EO. The antimicrobial activity of these species has also been studied against seven pathogenic and spoiling bacteria of significant importance. According to the results, Thymus algeriensis showed the best bacteriostatic and bactericidal effect, followed by Eucalyptus globulus and Rosmarinus officinalis. CONCLUSIONS As far as we know this is the first time that minimum inhibitory and bactericidal concentration values have been reported for Eucalyptus globulus EO. Our data support the possible use of this EO as well as Thymus algeriensis EO, as potential natural agents in preservatives for food and pharmaceutical products.

Chemical composition and antioxidant properties of Laurus nobilis L. and Myrtus communis L. essential oils from Morocco and evaluation of their antimicrobial activity acting alone or in combined processes for food preservation

BACKGROUND This study describes the antioxidant and antimicrobial activity of Laurus nobilis L. and Myrtus communis L. essential oils (EOs). This is the first report of the synergistic antimicrobial effect of these EOs in combination with physical food preservation treatments. RESULTS EOs obtained by steam distillation from aerial parts of Laurus nobilis and Myrtus communis were analysed by using gas chromatography-mass spectrometry. The main compounds were 1,8-cineole and 2-carene (L. nobilis EO); and myrtenyl acetate, 1,8-cineole and α-pinene (M. communis EO). L. nobilis EO showed higher antioxidant activity than M. communis EO in three complementary antioxidant tests. Although antimicrobial activity tests demonstrated the effectiveness of L. nobilis EO and the lack of bactericidal effect of M. communis EO, synergistic lethal effects were observed when combining each EO (0.2 µL mL(-1)) with mild heat (54°C for 10 min) or high hydrostatic pressure (175-400 MPa for 20 min). In contrast, combination of EOs with pulsed electric fields (30 kV cm(-1) for 25 pulses) showed no additional effects. CONCLUSION This study shows the great potential of these EOs in combined treatments with mild heat and high hydrostatic pressure to obtain a higher inactivation of foodborne pathogens, which might help in the design of safe processes applied at low intensity.

Effect of Thymus vulgaris and Origanum compactum essential oils on the shelf life of fresh goat cheese

We have carried out our study on the chemical composition and antimicrobial activity of Thymus vulgaris and Origanum compactum essential oils that were harvested in the northeast of Morocco. Carvacrol was the major component in the two investigated essential oils. A high antimicrobial activity has been shown on all tested bacterial strains. The effect of the incorporation of these two essential oils at concentrations of 0.05% and 0.1% on physicochemical, microbiological and sensorial characteristics of goat fresh cheese stored at 8°C has also been studied. No significant differences have been showed between control and aromatized cheeses with respect to pH, titrable acidity, dry matter, lactic acid bacteria and aerobic mesophylic flora. However, coliforms were completely inhibited by the presence of both essential oils from the first storage day. Shelf life estimation has been determined by the reparameterized Gompertz equation by monitoring the growth of molds and yeasts. Origanum compactum essential oil was more effective on extending the shelf life of fresh goat cheese than Thymus vulgaris essential oil. Nevertheless, the aromatized cheese with Thymus vulgaris essential oil was the most appreciated by the tasting panel.

Characterization of bottom ash from two hospital waste incinerators in Rabat, Morocco

The uncontrolled disposal of bottom ash generated by the incineration units of hazardous and infected wastes in developed countries are the main cause of significant damage, such as contamination of the soil, as well as surface and underground waters, which may put both the environment and public health at risk. In Morocco, little information is available on the chemical properties of the resulting ashes. In this study, 16 hospital waste ash samples were collected from the incinerators of the two main hospitals in Rabat: Ibn Sina and Cheikh Zayd. A series of tests was conducted, including particle size distribution, mineralogical and chemical composition, and heavy metal leaching behaviour. The results showed that the samples were composed mainly of P2O5 (18%), SiO2 (17%), Na2O (16%), CaO (14%) and SO3 (10%). Moreover, chemical analysis clearly demonstrated that medical waste (MW) contains large amounts of waste generated by domestic activities in the hospital, with a lack of sorting system in the monitoring of MW. Furthermore, the ashes contained high concentrations of heavy metals such as zinc, lead, chromium and nickel with a vast range of 0.5–25071 mg/kg. Leaching tests showed that the extracted amounts of all the heavy metals were lower, with concentrations < 2.85 mg/kg. Comparison of the corresponding heavy metal concentrations with the limit values set by the Council Decision 2003/33/EC allowed us to conclude that bottom ashes meet the waste acceptance criteria regarding these heavy metals.

Effect of Essential Oils on Cell Viability, Membrane Integrity and Membrane Fluidity of Listeria innocua and Escherichia coli

Abstract Listeria innocua LRGIA 01 and Escherichia coli CECT 471 cells were exposed to five essential oils (EOs) at different concentrations to determine their minimal inhibitory concentrations and minimal bactericidal concentrations. Since bacterial membranes are considered as a target of antimicrobial EOs, the membrane fluidity and integrity of bacteria were monitored respectively after 280 minutes or 24 hours exposure to Laurus nobilis or Satureja calamintha EOs. Measuring fluorescence anisotropy of two probes revealed that these two EOs rigidified the surface of membrane but increased the fluidity of its core. Application of the Live/Dead® BacLightTM kit after 24 hours contact with EOs at their MIC at the bacterial optimal temperature allowed observing that they damaged the membranes of bacteria and the persistence of Viable But Non Culturable (VBNC) bacteria. These observations should both be taken into account when considering addition of EOs to control the growth of certain important food-borne pathogenic bacteria.

Simultaneous P-Solubilizing and Biocontrol Activity of Rhizobacteria Isolated from Rice Rhizosphere Soil

Application of beneficial rhizobacteria as plant biofertilizers and biocontrol agents may be a promising alternative to chemical control. To perform this aim, the present work is an evaluation of three phosphate-solubilizing Aeromonas strains isolated from the rhizosphere of rice. These selected rhizobacteria were checked for quantitative assay of tricalcium phosphate (TCP) solubilization and P concentrations were between 119.56 and 165.85 mg l−1. Then, they were evaluated for extracellular hydrolytic enzymes production (chitinase, cellulase, amylase, lipase, and protease). The results showed that they were all able to hydrolyze different substrates apart from carboxymethyl cellulose. These test bacteria were checked in vitro as well for antagonism ability against six fungal phytopathogens, Colletotrichum acutatum, Verticillium dahliae, Phytophthora cinnamomi, Phytophthora cactorum, Botryotinia fuckheliana, and Fusarium oxysporum, and also against five phytopathogenic bacteria, Pseudomonas savastanoi, Clavibacter michiganensis, Ralstonia solanacearum, Erwinia amylovora, and Pseudomonas syringae. GT70 was the only isolate that showed antifungal effect against two fungi, V. dahliae and P. cactorum. For antibacterial activities, the best inhibition was obtained in the presence of GT70 and PT29 against R. Solanacearum. Finally, these bacteria were used for rice inoculation substituting soluble P by TCP. The results demonstrated significant increases in plant length and dry matter, especially in the presence of both strains GT70 and PT29 after 30 days under controlled conditions. However, more evaluation of these isolates under field conditions is needed before recommending them as biofertilizers.

The role of fish in the diet of swordfish ( Xiphias gladius ) in the Strait of Gibraltar

To study the diet of the swordfish ( Xiphias gladius ) in the Strait of Gibraltar, a total of 176 stomachs were examined from the Moroccan artisanal fishery targeting this species, from April to September 2015. The frequency of occurrence (FO), percentage in number and in weight of prey as well as the per cent index of relative importance of prey (%IRI) were calculated to assess the diet preferences of swordfish in relation to its body size, sex and month. Our findings confirm the opportunistic feeding behaviour of swordfish. The prey items consist primarily of fish (54.6% in number and 82.7% in weight), followed by cephalopod (43.36% in number and 17.25% in weight). The Atlantic horse mackerel ( Trachurus trachurus ) and the southern shortfin squid ( Illex coindetii ) are the most important prey, with a % IRI of 47.54 and 35.04%, respectively. The results revealed that there are no significant differences in the diet preferences among sexes and size classes. However, diet composition varied significantly among months. A significant correlation was found between the body length of predator and prey size. The remarkable decrease in the fullness index (fi) from June to August suggests that swordfish were in a spawning condition, with reduced feeding.

Gelatin-Based Edible Coating Combined with Mentha pulegium Essential Oil as Bioactive Packaging for Strawberries

The effect of gelatin-based edible coating incorporated with Mentha pulegium essential oil (MEO) on physicochemical (pH, titratable acidity (TA), weight loss, total soluble solids (TSS), and total phenolic content (TPC)), microbiological (total aerobic mesophilic flora (TAMF) and yeasts and moulds (YM)), and sensorial (color and firmness) characteristics of strawberries stored under refrigeration was studied. Strawberries were coated with gelatin alone (4%) and/or gelatin combined with two concentrations (0.5 and 1%) of MEO and stored at 4°C for 13 days. Gelatin coating and MEO combination significantly inhibited total flora and moulds and yeasts with comparison to control (uncoated strawberries) and had better hygienic quality at the end of storage. The effect was MEO concentration dependent. Our results also showed that the bioactive coating used in this investigation slowed down changes in pH, TA, weight loss, TSS, firmness, TPC, and color of strawberries. Gelatin coating incorporated with MEO at 1% protected at least 60% of strawberries from deterioration after 13 days of storage and could be used as bioactive packaging to prolong the shelf life and an alternative of pesticides use.

Screening for Lotus creticus growth promoting rhizobacteria under greenhouse conditions

Utilization of plant growth promoting rhizobacteria (PGPR) is now gradually increasing in agriculture and offers an attractive way to replace chemical fertilizers, pesticides, and supplements. This study was conducted with a view to isolate bacteria from the rhizosphere of the legume Lotus creticus ( L. creticus ) and to assess their plant growth promoting functional potentialities. A total of 113 rhizobacteria was isolated from the rhizosphere of L. creticus and were tested for their capacity of solubilizing tricalcium phosphate (TCP) on Pikovskaya (PVK) solid medium. Out of 29 phosphate solubilizing bacteria (PSB), 5 isolates were selected for their solubilization diameters (between 0.6 and 1.5 cm). These isolates were characterized for plant growth promoting (PGP) traits. The results showed that the highest concentration of indole acetic acid (IAA) was produced by LCR33 (19.08 ± 0.96 mg L -1 ). All 5 isolates could produce hydrogen cyanide (HCN), siderophores, ammonia and amino-cyclopropane carboxylate (ACC) deaminase. The isolates were evaluated for TCP solubilizing quantitative assay in PVK liquid medium. The concentrations of solubilized P were between 43.34±0.18 mg L -1 and 173.57±0.77 mg L -1 . This solubilization was accompanied by a pH decrease of the culture media from 7 to 4.06. Furthermore, the 5 selected PSB were tested in vitro for antagonism against phytopathogenic fungus Fusarium oxysporum . In fact, all the PSB, were capable of inhibiting its growth and the highest percentages of inhibition were obtained for LCP27 and LCR33 (48.15±0.99% and 40.74±0.45%). Also, the effect of these 2 PSB on growth of L. creticus plants was investigated under greenhouse conditions. Significant increases were obtained for shoot and root length and dry and fresh matter production of plants as compared to the uninoculated control. These PSB could be recommended as biofertilizers for contributing to the rehabilitation of degraded soils.

Arbuscular Mycorrhization and Growth Promotion of Peanut (Arachis hypogaea L.) After Inoculation with PGPR

Because of their potential to increase plant nutrition and yield, the use of some microorganisms in low-input agriculture and forestry has been addressed for successful agroecological investigations. A pot experiment was conducted to study the effects of some plant growth-promoting rhizobacteria (PGPR) on arbuscular mycorrhizal fungi (AMF) and growth of KP29’s peanut variety grown in the northwest of Morocco. Seeds were inoculated with three Pseudomonas (PP22, GP70, and GR1) and two Aeromonas strains (PR29 and GR70). Then, they were grown in two unsterilized soils collected from subsistence farmers’ fields of Laaouamra and Moulay Bousselham. Plant harvesting was made after 60 days of cultivation under growth chamber conditions, and the roots were removed and rinsed carefully. Results showed positive and negative effects of these rhizobacteria on growth and mycorrhization of peanut. Pseudomonad strains gave the greatest plant nutrient content (N, P, and K) and growth parameters. Also, bacterial inoculation had a positive impact on peanut mycorrhization by enhancing arbuscular abundance. Highest stimulation was noticed with pseudomonad strains on both soils. In addition, PR29 exhibited maximum values of mycorrhizal colonization on the soil of Laaouamra. However, the magnitude effect of inoculation on plant growth and mycorrhizal infection varied according to the origin of soils. On the other hand, only PP22 stimulated nodules formation on the soil of Laaouamra. In conclusion, this study reveals that GP70, GR1, and PP22 can enhance growth, yield, and nutrient uptake of peanut. They can also enhance biological nitrogen fixation and mineral uptake in combination with AMF.