Nadia Skali Senhaji

Effects of NaCl and mannitol induced stress on sugarcane (Saccharum sp.) callus cultures

The effects of NaCl and mannitol iso-osmotic stresses on calli issued from sugarcane cultivars (cvs.) R570, CP59-73 and NCo310 were investigated in relation to callus growth, water content, ion and proline concentrations. Callus growth and water content decreased under both stresses with the highest reduction under mannitol-induced osmotic stress. The ion concentration was drastically affected after exposure to NaCl and mannitol. Salt stress induced an increase in Na+ and Cl− accumulation and a decrease in K+ and Ca2+ concentrations. Under mannitol-induced osmotic stress, K+ and Ca2+ concentrations decreased significantly while Na+ and Cl− concentrations remained unchanged. Free proline accumulation occurred under both stresses and was more marked in stress-sensitive cv. than in stress-resistant one. Our results indicated that the physiological mechanisms operating at the plant cell level in response to salt- and osmotic-induced stress in sugarcane cvs. are different. Among the cvs., we concluded that the stress resistance is closely related to the maintain of an adequate water status and a high level of K+ and Ca2+ under both stresses and a low level of Na+ concentration in the presence of NaCl. Thus, sugarcane (Saccharum sp.) can be regarded as a Na+ excluder. We also provided evidence that proline accumulation is a stress-sensitive trait rather than a stress resistance marker.

Antibacterial Activity of Extracts of Myrtus communis Against Food-Borne Pathogenic and Spoilage Bacteria

The following study was conducted to investigate the efficacy of several leaf and berry extracts against a range of food-borne pathogens and food spoilage bacteria. The methanol, ethanol, and ethyl acetate extracts of Myrtus communis leaves and berries were examined for in vitro antibacterial activity. The methanolic leaf extract of M. communis, which was seen to have antibacterial activity against Listeria monocytogenes CECT 4032 and Pseudomonas aeruginosa IH, was further investigated to determine the effect of the extract on viable counts of bacteria using the bacterial cell-death time. Most of the extracts showed relatively high antibacterial activity against most of the tested microorganisms. None of the extracts was active against Escherichia coli K12. The results obtained confirm the antibacterial potential of the extracts of M. communis.

Antimicrobial activities of the bacteriocin-like substances produced by lactic acid bacteria isolated from Moroccan dromedary milk

A total of 450 different colonies, isolated from 25 samples of dromedary milk collected from Laâyoune region of Morocco, were tested for antimicrobial compounds production. Out of these, 30 were determined to be lactic acid bacteria (LAB) and able to inhibit the growth of the indicator strain Listeria innocua CECT 4030. Seven isolates were selected by the large and clear zones of inhibition when tested by the agar well diffusion assay. They were classified by phenotypic and biochemical analysis as two Enterococcus durans (E204 and E214), two Lactococcus lactis (R75 and R76), one Enterococcus faecium R111, one Lactococcus cremoris R112 and one Enterococcus avium R122. Their antimicrobial compounds were detected in cell-free culture supernatant fluids under conditions that eliminate acid and hydrogen peroxide inhibition. The antimicrobial activity was altered after treatment with trypsin, -chymotrypsin, pepsin or papain which confirms the proteinaceous nature of the inhibition. It was heat stable even at autoclaving temperature (121°C for 15 min) and also active over a wide pH range (2 to 10). This fact suggests that bacteriocin-like produced by the seven LAB strains may find application as biopreservatives in food products. Key words: Dromedary milk, lactic acid bacteria, bacteriocin-like substances, antimicrobial activity.

Growth of Enterococcus durans E204 producing bacteriocin-like substance in MRS Broth: Description of the growth and quantification of the bacteriocin-like substance

Bacteriocin-like substance E204 is an antimicrobial compound produced by Enterococcus durans E204 isolated from camel milk of Morocco that shows a broad spectrum of inhibitory activity against taxonomically related microorganisms. It is sensitive to digestive proteases. In the first study, de Man, Regosa and Sharpe (MRS) broth was inoculated by E204 strain, incubated for 30°C at 200 rpm and monitored by checking dry cell weight, nutrients consumption, lactic acid and bacteriocin-like productions. The maximum biomass (2.3 g/l) and antimicrobial activity (32 AUml -1 ) were obtained at 12 h of incubation. No increase in the production of bacteriocin-like was recorded after the exponential phase. In the other hand, the quantification of the antimicrobial activity was carried out by a photometric assay on culture tubes based on the determination of the ID50 dose causing 50% growth inhibition of Enterococcus faecium 410 CECT in 6 h of incubation. The highest bacteriocin-like titre (279.71 BUml -1 ) was obtained at acidic pH (3.5) and at 70°C after 10 min of incubation. Key words : Enterococcus durans, bacteriocin-like, MRS broth, nutrients consumption, quantification.