Ali Chokr

Antibacterial and antibiofilm activities of polysaccharides, essential oil, and fatty oil extracted from Laurus nobilis growing in Lebanon.

OBJECTIVE To evaluate the antibacterial activity of the extracts of Laurus nobilis against three Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212 and Staphylococcus epidermidis CIP 444) and two Gram-negative bacteria (Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853). Also, the antibiofilm activity has been investigated against the biofilm produced by Staphylococcus epidermidis CIP 444. MATERIALS The polysaccharides, essential oil, and fatty oils extracted from the plant were used in broth microdilution methods to study the minimal inhibitory concentration, and then the minimal bactericidal concentration was determined. RESULTS The results showed that alginate, fucoidan, fatty oils and essential oil have good antibacterial activities against the 5 bacterial strains, and a negligible biofilm eradication activity of fucoidan, laminaran, fatty oil, and essential oil was observed, but a promising biofilm eradication activity was obtained with alginate, which showed a reduced biofilm mass even at low concentration. CONCLUSIONS The extracts obtained have promising antibacterial capacities which need further investigation for them to be incorporated in medical or nutritional applications.

Design, synthesis and biological evaluation of potential antibacterial butyrolactones

Novel butyrolactone analogues were designed and synthesized based on the known lichen antibacterial compounds, lichesterinic acids (B-10 and B-11), by substituting different functional groups on the butyrolactone ring trying to enhance its activity. All synthesized butyrolactone analogues were evaluated for their in vitro antibacterial activity against Streptococcus gordonii. Among the derivatives, B-12 and B-13 had the lowest MIC of 9.38μg/mL where they have shown to be stronger bactericidals, by 2-3 times, than the reference antibiotic, doxycycline. These two compounds were then checked for their cytotoxicity against human gingival epithelial cell lines, Ca9-22, and macrophages, THP-1, by MTT and LDH assays which confirmed their safety against the tested cell lines. A preliminary study of the structure-activity relationships unveiled that the functional groups at the C4 position had an important influence on the antibacterial activity. An optimum length of the alkyl chain at the C5 position registered the best antibacterial inhibitory activity however as its length increased the bactericidal effect increased as well. This efficiency was attained by a carboxyl group substitution at the C4 position indicating the important dual role contributed by these two substituents which might be involved in their mechanism of action.

A comparative study of procedures for binding of aflatoxin M1 to Lactobacillus rhamnosus GG

Several strains of lactic acid bacteria (LAB), frequently used in food fermentation and preservation, have been reported to bind different types of toxins in liquid media. This study was carried out to investigate the effect of different concentrations of Lactobacillus rhamnosus GG (ATCC 53103) to bind aflatoxin M1 (AFM1) in liquid media. AFM1 binding was tested following repetitive washes or filtration procedures in combination with additional treatments such as heating, pipetting, and centrifugation. The mixture of L. rhamnosus GG and AFM1 was incubated for 18 h at 37 °C and the binding efficiency was determined by quantifying the unbound AFM1 using HPLC. The stability of the complexes viable bacteria-AFM1 and heat treated bacteria-AFM1 was tested. Depending on the bacterial concentration and procedure used, the percentages of bound AFM1 by L. rhamnosus GG varied from as low as undetectable to as high as 63%. The highest reduction in the level of unbound AFM1 was recorded for the five washes procedure that involved heating and pipetting. Results also showed that binding was partially reversible and AFM1 was released after repeated washes. These findings highlight the effect of different treatments on the binding of AFM1 to L. rhamnosus GG in liquid matrix.

Culture medium pH influence on Gluconacetobacter physiology: Cellulose production rate and yield enhancement in presence of multiple carbon sources

Gluconacetobacter genera are valued for bacterial cellulose (BC) and acetic acid production. BC is produced at optimal yields in classical microbiological media that are expensive for a large scale of production. In addition, BC usage for industrial purposes is limited due to low conversion rate into cellulose and to long incubation duration. In this paper, Gluconacetobacter isolated from apple vinegar was kinetically studied to evaluate cellulose production in presence of different carbon sources. Acetic and citric acid effect on Gluconacetobacter metabolism is clarified. It was shown that Gluconacetobacter uses glucose as a primary carbon source for cells growth and products formation. Acetic acid employment as a co-carbon source in Hestrin Schramm medium showed an increase of 17% in BC yield with a moderate decrease in the crystallite size of the resulting polymer.

Antibacterial activities of natural lichen compounds against Streptococcus gordonii and Porphyromonas gingivalis

The oral bacteria not only infect the mouth and reside there, but also travel through the blood and reach distant body organs. If left untreated, the dental biofilm that can cause destructive inflammation in the oral cavity may result in serious medical complications. In dental biofilm, Streptococcus gordonii, a primary oral colonizer, constitutes the platform on which late pathogenic colonizers like Porphyromonas gingivalis, the causative agent of periodontal diseases, will bind. The aim of this study was to determine the antibacterial activity of eleven natural lichen compounds belonging to different chemical families and spanning from linear into cyclic and aromatic structures to uncover new antibiotics which can fight against the oral bacteria. The compounds were screened by broth microdilution assay. Three compounds were shown to have promising antibacterial activities where the depsidone core with certain functional groups constituted the best compound, psoromic acid, with the lowest MICs=11.72 and 5.86μg/mL against S. gordonii and P. gingivalis, respectively. The compounds screened had promising antibacterial activity which might be attributed to some important functional groups as discussed in our study. The best compounds did not induce the death of gingival epithelial carcinoma cells (Ca9-22). These results introduce new compounds having potent antibacterial activities against oral pathogens causing serious medical complications.

Diversity Investigation of the Seaweeds Growing on the Lebanese Coast

By specialized underwater cameras we have filmed and collected samples of algae from the following sites along the Lebanese coast: Batroun, Barbara, Manara, Officer’s Military club, Saida, Sarafand, Tyre and Naqoura. We have identified ninety-four species of algae that grow along the Lebanese coast and we have established a collection sites map of these algal species. The identification of the samples was done in three steps: (1) Determine the largest group (green, brown and red algae) to which the sample belongs, then continue searching within the most likely group. (2) Seek off in the succession of morphological types which proposed that the sample is approaching. (3) Seek out using the illustrations and descriptions a satisfactory identification. It is worth noting that confirmation cannot be obtained in all cases unless a careful reading of the description is done. (4) We then proceeded to the classification of the collected seaweeds which are distributed as follows: Rhodophyta forty one species, Ochrophyta twenty two species, Chlorophyta twenty six species and Cyanobacteria five species. (5) Synthesis: The present study allowed us to establish a primary infrastructure regarding the distribution of the Lebanese seaweeds. Such findings represent an important scientific support concerning the Mediterranean seaweeds, which provides a great assist in algal studies and all its applications. This screening of the Lebanese coastline shows a broad and significant algal distribution. The most common algal types among the identified ones are: Sargassum, Padina, Laurencia, Ulva, Corallina, Hypnea, Chondracanthus, Jania, Amphiroa, Pterocladia, Cladophera, Codium.

A novel technique for aflatoxin M1 detoxification using chitin or treated shrimp shells: in vitro effect of physical and kinetic parameters on the binding stability

This study aimed to investigate the ability of chitin and heat-treated shrimp shells to bind aflatoxin M1 (AFM1) in liquid matrix. Several concentrations of chitin or shrimp shells (grinded and ungrinded) were incubated in AFM1-contaminated phosphate-buffered saline (PBS) at different incubation times. The stability of the formed adsorbent-AFM1 complex was also tested in milk at different incubation times and temperatures. The unbound AFM1 was quantified by HPLC. Thereby, the percentages of the initial bounded AFM1 varied between 14.29 and 94.74%. Interestingly, in milk, an increase in incubation time coupled with a decrease in temperature affected positively the amount of bounded AFM1 to chitin and negatively those bounded to ungrinded shells. Results also revealed a partial reversibility in the binding of AFM1 to these adsorbents. These findings provided strong evidence on ability of chitin or shrimp shells by-product to bind AFM1 in milk and in PBS.

Screening for antibacterial and antibiofilm activities in Astragalus angulosus

Aim: In a search for finding novel therapeutic agents, extracts from an endemic Lebanese plant, Astragalus angulosus, were evaluated for their potential in-vitro antibacterial and antibiofilm activities against three Gram-positive bacterial strains; Staphylococcus epidermidis (CIP444), Staphylococcus aureus (ATCC25923), and Enterococcus faecalis (ATCC29212); in addition to two Gram-negative strains, Escherichia coli (ATCC35218) and Pseudomonas aeruginosa (ATCC27853). Materials and Methods: The plant was collected in April of 2013 and divided into several different portions, then its extracts were obtained by maceration using two different solvents. Extract analysis followed directly where microtiter broth dilution method was employed to assess antibacterial activity, while antibiofilm potential was tested using colorimetric method. Results: Whole plant ethanolic extract showed the highest bacteriostatic effect at a concentration of 12.78 mg/ml and also was the most versatile exerting its effect against 3 different strains. Other extracts also exhibited an effect but at higher concentrations and each against a single strain. Regarding antibiofilm activity, the majority of the extracts were able to eradicate >50% of S. epidermidis preformed biofilm, where the highest activity was obtained with flower fraction extracted in water, achieving 67.7% biofilm eradication at 0.2 mg/ml. Conclusions: This plant possesses a promising potential in regard to eradicating bacteria and their biofilms and it is the first contributing step of establishing a library for the endemic Lebanese plants in this domain.

A comparative study of antibodies against proteins extracted from staphylococcal biofilm for the diagnosis of orthopedic prosthesis–related infections in an animal model and in humans

Staphylococcus aureus and Staphylococcus epidermidis are the microorganisms most frequently seen in periprosthetic infections (PPI) with the capacity of forming biofilm. To find potential antigens for the diagnosis of PPI, the immunogenicity of protein components in biofilm from a model biofilm-positive strain (S. epidermidis RP62A) was investigated. A guinea pig animal model of PPI was developed and sera were obtained. Sera of patients with PPI and those of controls were also collected. Data generated with an enzyme-linked immunosorbent assay showed that there were significantly higher levels of anti-extracellular protein IgG in sera of infected animals than in controls. We also found significantly higher anti-extracellular protein IgG levels in infected patients, compared to the controls; however, receiver operating characteristic curves did not aid in diagnosing PPI.