Amina Bakhrouf

Antioxidant properties of the essential oil of Eugenia caryophyllata and its antifungal activity against a large number of clinical Candida species.

Many essential oils are known to possess an antioxidant activity and antifungal properties and therefore they potentially act as antimycotic agents. Essential oil of clove (Eugenia caryophyllata) was isolated by hydrodistillation. The chemical composition of the essential oil was analysed by gas chromatography and gas chromatography/mass spectroscopy. The antioxidant effect of the tested oil was evaluated by measuring its 2,2‐diphenyl‐l‐1‐picrylhydrazil radical scavenging ability and the antiradical dose required to cause a 50% inhibition (IC50) was recorded. The antifungal activity of essential oils was evaluated against 53 human pathogenic yeasts using a disc paper diffusion method. Our results show that the major components present in the clove bund oil were eugenol (88.6%), eugenyl acetate (5.6%), β‐caryophyllene (1.4%) and 2‐heptanone (0.9%). The tested essential oil exhibited a very strong radical scavenging activity (IC50 = 0.2 μg ml−1) when compared with the synthetic antioxidant (tert‐butylated hydroxytoluene, IC50 = 11.5 μg ml−1). On the other hand, this species displayed an important antifungal effect against the tested strains. It is clear that clove oil shows powerful antifungal activity; and it can be used as an easily accessible source of natural antioxidants and in pharmaceutical applications.

Chemical composition and biological activities of Tunisian Cuminum cyminum L. essential oil: A high effectiveness against Vibrio spp. strains

Essential oil extracted by hydrodistillation from Tunisian variety of Cuminumcyminum was characterized by means of GC and GC-MS. Twenty-one components were identified and C. cyminum contained cuminlaldehyde (39.48%), gamma-terpinene (15.21%), O-cymene (11.82%), beta-pinene (11.13%), 2-caren-10-al (7.93%), trans-carveol (4.49%) and myrtenal (3.5%) as a major components. Moreover, C. cyminum oil exhibited higher antibacterial and antifungal activities with a high effectiveness against Vibrio spp. strains with a diameter of inhibition zones growth ranging from 11 to 23 mm and MIC and MBC values ranging from (0.078-0.31 mg/ml) to (0.31-1.25mg/ml), respectively. On the other hand, the cumin oil was investigated for its antioxidant activities using four different tests then compared with BHT. Results showed that cumin oil exhibit a higher activity in each antioxidant system with a special attention for beta-carotene bleaching test (IC(50): 20 microg/ml) and reducing power (EC(50): 11 microg/ml). In the light of these findings, we suggested that C. cyminum essential oil may be considered as an interesting source of antibacterial, antifungal and antioxidants components used as potent agents in food preservation and for therapeutic or nutraceutical industries.

Cell surface hydrophobicity, biofilm formation, adhesives properties and molecular detection of adhesins genes in Staphylococcus aureus associated to dental caries.

Staphylococcus aureus is an important pathogen that forms biofilm. In this study, 22 S. aureus have been isolated from the oral cavity of Tunisian children and investigated for slime production using Congo red agar method (CRA) and semi quantitative adherence assay. The hydrophobicity of strains was evaluated by the microbial adhesion to solvent (MATS) test. The adherence of S. aureus to Hep2 cells was examined by light microscopy. The genes implicated in adhesion (icaA, icaD, fnbA, cna, clfA) were detected. Polymerase chain reaction was used. The affinity to hexadecane was low proving a hydrophilic character of all the studied strains. Qualitative biofilm production revealed that 50% of strains were slime producers. The result of OD(570) showed that four strains isolated from the caries-active children were highly biofilm positive. In addition, 50% of strains were icaA and icaD positive. The fnbA gene was present in 59.1% of isolated strains. Furthermore, 54.5% of strains harboured the cna gene, 9.1% were clfA positive and 50% were hla positive. Quantitative adherence varied considerably among the tested strains. All strains showed adherence to Hep2 cells. However, the level of adhesion varied between strains as follows. Seven strains were defined as moderately adherent, nine as strongly adherent and six as weakly adherent. The percentage of infected cells ranged from 15+/-0.0376 (B374) to 96+/-0.019 (B295) and the total number of bacteria per 100 cells ranged from 15+/-5.1 (B374) to 1824+/-30.1 (B295).

Detection of macrolide and disinfectant resistance genes in clinical Staphylococcus aureus and coagulase-negative staphylococci

BackgroundStaphylococcus aureus and Coagulase-negative staphylococci (CoNS) are a major source of infections associated with indwelling medical devices. Many antiseptic agents are used in hygienic handwash to prevent nosocomial infections by Staphylococci. Our aim was to determine the antibiotic susceptibility and resistance to quaternary ammonium compound of 46 S. aureus strains and 71 CoNS.MethodsS. aureus (n = 46) isolated from auricular infection and CoNS (n = 71), 22 of the strains isolated from dialysis fluids and 49 of the strains isolated from needles cultures were investigated. Erythromycin resistance genes (erm A, erm B, erm C, msr A and mef) were analysed by multiplex PCR and disinfectant-resistant genes (qac A, qac B, and qac C) were studied by PCR-RFLP.ResultsThe frequency of erythromycin resistance genes in S. aureus was: erm A+ 7.7%, erm B+ 13.7%, erm C+ 6% and msr A+ 10.2%. In addition, the number of positive isolates in CoNS was respectively erm A+ (9.4%), erm B+ (11.1%), erm C+ (27.4%), and msr A+ (41%). The MIC analyses revealed that 88 isolates (74%) were resistant to quaternary ammonium compound-based disinfectant benzalkonium chloride (BC). 56% of the BC-resistant staphylococcus isolates have at least one of the three resistant disinfectants genes (qac A, qac B and qac C). Nine strains (7.7%) among the CoNS species and two S. aureus strains (2%) harboured the three-qac genes. In addition, the qac C were detected in 41 strains.ConclusionsMulti-resistant strains towards macrolide and disinfectant were recorded. The investigation of antibiotics and antiseptic-resistant CoNS may provide crucial information on the control of nosocomial infections.

Comparison of chemical composition and antimicrobial activities ofMentha longifolia L. ssp.longifolia essential oil from two Tunisian localities (Gabes and Sidi Bouzid)

This study was conceived to evaluate the difference in the chemical composition of the essential oil ofMentha longifolia ssp.longifolia from two ecotypes (Sidi Bouzid and Gabes) as well as the difference of the composition of the oils extracted from the leaves and stems. The antimicrobial activity was also tested against 16 human pathogenic microorganisms. The chemical composition of the hydrodistilled essential oils ofMentha longifolia ssp.longifolia were analysed by GC and GC/MS system. Remarkable differences were recorded between the percentages of the few constituents from leaves and stems and between plants from the two geographical provinces. The chemical analysis of the essential oil obtained from leaves and stems showed the presence of 34 compounds. The most important ones were consecutively: 1,8-cineole (5.6–10.8%), menthone (20.7–28.8%), terpineol-4 (3.1–4.9%), menthol (19.4–32.5%), pulegone (7.8–17.8%) and piperitone (2.2–3.3%). These major components occur in different amounts depending on the organs (leaves or stems) and the geographical origin of the plant. The antimicrobial activity of the essential oil was tested using the disc-diffusion assay and minimal inhibition concentration (MIC) values were estimated according to the microdilution method. The results showed that the essential oil ofMentha longifolia ssp.longifolia had great potential of antimicrobial activity against all 8 bacteria and 8 yeast species tested. The (MIC) for bacteria was ranging from 0.195 to 3.12 × 103 μg/ml.

Anti-cariogenic and anti-biofilms activity of Tunisian propolis extract and its potential protective effect against cancer cells proliferation

Propolis is a multifunctional substance used by bees to maintain the safety of their hives. It is worldwide used for its potential therapeutic effects. In this study, Tunisian propolis ethanol extract (EEP) was tested for their anti-cariogenic, anti-biofilms and antiproliferative effects of many cell lines. The Tunisian EEP was evaluated in vitro against 33 oral pathogens including streptococci and enterococci using broth microdilution method. The anti-biofilms activity of EEP was assessed via Crystal Violet staining and MTT assays. The Tunisian EEP antiproliferative effect was evaluated on normal (MRC-5) and cancer cell lines (HT-29, A549, Hep-2, raw 264.7, Vero) by the ability of the cells to metabolically reduce MTT to a formazan dye. Our results revealed that Tunisian EEP possessed excellent protective effects against cariogenic and biofilms activity of oral streptococci. Furthermore, EEP showed a strong antiproliferative potencies against all studied cancer cell lines as judged by IC50 and its value ranges from 15.7 ± 3.4 to 200 ± 22.2 μg mL⁻¹. These results suggest that EEP is able to inhibit cancer cell proliferation, cariogenic bacteria and oral biofilms formation. It could have a promising role in the future medicine and nutrition when used as antibiotic or food additive.

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)

Screening of antimicrobial activity of marine sponge extracts collected from Tunisian coast

The antibacterial activity of the ethyl acetate extracts of seven marine sponges collected from the Tunisian Mediterranean coast (Monastir) were tested against eight human pathogenic bacteria and six human pathogenic fungi using the agar disk diffusion method. The results show that 90% of the sponge extracts present significant activity against at least one bacterial strain. Extracts of the sponges Agelas oroides and Axinella damicornis appeared to be quite promising due to their capacity to inhibit the growth of Pseudomonas aeruginosa and gentamycin resistant strains of Listeria monocytogenese and Enterococcus feacalis as well as broad spectrum activity against all the other bacteria. The antifungal activity of these sponge extracts is not so promising, in fact only three among 9 sponge extracts show moderate capacity of growth inhibition against fungi strains. Agelas oroides which shows interesting antibacterial activity, has moderate activity against fungi strains tested in this study. Our results with antibacterial and antifungal activity in vitro open the way for complementary investigation in order to purify and identify active molecules.

In vitro effect of pH and ethanol on biofilm formation by clinicalica-positiveStaphylococcus epidermidis strains

Biofilm production is an important step in the pathogenesis ofStaphylococcus epidermidis associated biomaterial infections.Staphylococcus epidermidis strains isolated from dialysis fluid (n=9) and needle cultures (n=14) were phenotyped and genotyped for extracellular polysaccharide production and were examined for their ability to produce slime in a medium at various pH levels (3, 5, 7, 9 and 12) and with ethanol supplementation (0, 2, 5, 10 and 15%) using a semi-quantitative adherence assay. A total of 23 clinicalicaADBC positiveS. epidermidis, one reference strain (S. epidermidis CIP 106510) used as positive control, and oneicaADBC negative strain (E21) were investigated. Qualitative biofilm production analysis revealed that 15 of the 23icaADBC positive strains (65.21%) produced slime on Congo Red agar plates. Quantitative biofilm was determined by measuring the optical density at 570 nm (OD570). The results show that the slime production depended on the pH value of the medium and the ethanol concentration. At highly acidic (pH 3) and alkaline (pH 12) levels, the OD570 was lower, while at pH 7 the adhesion was moderate. In addition the cells adhered strongly with 2% ethanol than with the other concentrations. Our results suggest that pH and ethanol were stress factors that led toS. epidermidis biofilm formation and also play a possible role in the pathogenesis of biomaterial-related infections.

Antibacterial and resistance-modifying activities of thymoquinone against oral pathogens

BackgroundThe presence of resistant bacteria in the oral cavity can be the major cause of dental antibiotic prophylaxis failure. Multidrug efflux has been described for many organisms, including bacteria and fungi as part of their drugs resistance strategy. The discovery of a new efflux pump inhibitor could extend the useful lifetime of some antibiotics.MethodsIn this study, the MICs of thymoquinone (TQ), tetracycline and benzalkonium chloride (BC) were determined in absence and in presence of a sub-MIC doses of thymoquinone (1/2 MIC). In addition the 4,6-diamidino-2-phenylindole (DAPI) efflux assay was carried out to determine the effect of TQ on DAPI cells accumulation.ResultsTQ induced a selective antimicrobial activity. Its synergic effect resulted in at least a 4-fold potentiation of the tested antibiotics and antiseptic. In addition, TQ inhibited the DAPI efflux activity in a concentration-dependent manner. The rate of DAPI accumulation in clinical isolates was enhanced with TQ (0 to 200 μg/ml). There is also a decrease in loss of DAPI from bacteria in the presence of TQ. The concentration causing 50% of DAPI efflux inhibition after 15 minutes was approximately 59 μg/ml for Pseudomonas aeroginosa and 100 μg/ml and Staphylococcus aureus respectively.ConclusionsTQ possesses a selective antibacterial activity against oral bacteria. It is therefore suggested that TQ could be used as a source of natural products with resistance-modifying activity. Further investigation is needed to assess their clinical relevance.