Termiticidal activity of lectins from Myracrodruon urundeuva against Nasutitermes corniger and its mechanisms

The isolation of lectins from Myracrodruon urundeuva bark (MuBL) and heartwood (MuHL) as well as the termiticidal activity of MuHL against Nasutitermes corniger has already been described. This work reports on the purification of a leaf lectin (MuLL) and the characterization of MuBL, MuHL, and MuLL; also described are the resistance of hemagglutinating activity of the three lectins to trypsin activity from N. corniger gut and the termiticidal activity on N. corniger of MuBL (LC₅₀ of 0.974 mg ml⁻¹ on workers and 0.787 mg ml⁻¹ on soldiers) and MuLL (LC₅₀ of 0.374 mg ml⁻¹ on workers and 0.432 mg ml⁻¹ on soldiers). The antibacterial effect of MuBL, MuHL, and MuLL on bacteria from gut of N. corniger was also investigated and lectins showed similar bacteriostatic activity (MIC of 62.5 ??g ml⁻¹ for workers and 125 ??g ml⁻¹ for soldiers). MuBL and MuHL were more efficient bactericidal agents on bacteria in the workers’ gut (MBC of 125 ??g ml⁻¹) than MuLL (MBC of 250 ??g ml⁻¹) and similar bactericidal activity was detected on bacteria in the gut of soldiers (MBC of 250 ??g ml⁻¹). The termiticidal activity of M. urundeuva lectins can be explained by the chitin-binding property, resistance to termite digestive enzyme, and the antibacterial effect on symbiotic bacteria of N. corniger gut.     

Antibiofilm and antifungal activities of medium-chain fatty acids against Candida albicans via mimicking of the quorum-sensing molecule farnesol

Candida biofilms are tolerant to conventional antifungal therapeutics and the host immune system. The transition of yeast cells to hyphae is considered a key step in C. albicans biofilm development, and this transition is inhibited by the quorum-sensing molecule farnesol. We hypothesized that fatty acids mimicking farnesol might influence hyphal and biofilm formation by C. albicans. Among 31 saturated and unsaturated fatty acids, six medium-chain saturated fatty acids, that is, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid and lauric acid, effectively inhibited C. albicans biofilm formation by more than 75% at 2 µg ml⁻¹ with MICs in the range 100–200 µg ml⁻¹. These six fatty acids at 2 µg ml⁻¹ and farnesol at 100 µg ml⁻¹ inhibited hyphal growth and cell aggregation. The addition of fatty acids to C. albicans cultures decreased the productions of farnesol and sterols. Furthermore, down-regulation of several hyphal and biofilm-related genes caused by heptanoic or nonanoic acid closely resembled the changes caused by farnesol. In addition, nonanoic acid, the most effective compound diminished C. albicans virulence in a Caenorhabditis elegans model. Our results suggest that medium-chain fatty acids inhibit more effectively hyphal growth and biofilm formation than farnesol.     

Smoke-saturated Water and Karrikinolide Modulate Germination,Growth, Photosynthesis and Nutritional Values of Carrot (Daucus carota L.)

Plant-derived smoke is a positive regulator of seed germination and growth with regard to many plant species. Of the several compounds present in plant-derived smoke, karrikinolide or KAR₁ (3-methyl-2H-furo[2,3-c]pyran-2-one) is considered to be the major active growth-promoting compound. To test the efficacy of smoke-saturated water (SSW) and KAR₁ on carrot (Daucus carota L.), two separate pot experiments were simultaneously conducted in the same environmental conditions. SSW and KAR₁ treatments were applied to the plants in the form of aqueous solutions of variable concentrations. Prior to sowing, seeds were soaked in the solutions of SSW (25.8 µg L⁻¹_, 51.6 µg L⁻¹,103.2 µg L⁻¹ and 258.0 µg L⁻¹) and KAR₁ (0.015 µg L⁻¹, 0.150 µg L⁻¹, 1.501 µg L⁻¹ and 15.013 µg L⁻¹). Percent seed germination, vegetative growth, photosynthesis and nutritional values were the major parameters through which the plant response to the applied treatments was investigated. The results obtained indicated a significant improvement in all the plant attributes studied. In general, SSW (51.6 µg L⁻¹) and KAR₁ (1.501 µg L⁻¹) proved optimum treatments for most the parameters. As compared to the control, 51.6 µg L⁻¹ of SSW and 1.501 µg L⁻¹ of KAR₁ increased the percent seed germination by 58.0% and 54.4%, respectively. Over the control, the values of plant height and net photosynthetic rate were enhanced by 33.9% and 40.9%, respectively, due to 51.6 µg L⁻¹ of SSW, while the values of these parameters were increased by 25.2% and 34.0%, respectively, due to 1.501 µg L⁻¹ of KAR₁. In comparison with the control, treatment 51.6 µg L⁻¹ of SSW increased the contents of β-carotene and ascorbic acid by 32.7% and 37.9%, respectively, while the treatment 1.501 µg L⁻¹ M of KAR₁ enhanced these contents by 42.0% and 48.4%, respectively. This study provides an insight into an affordable and feasible method of crop improvement.

     

Effect of lectins from Opuntia ficus indica cladodes and Moringa oleifera seeds on survival of Nasutitermes corniger

Biodegradation by termites is a serious problem for wood and crop industries worldwide, and new environmentally friendly alternatives for termite control have been developed. This work investigated the effects of crude and purified preparations containing lectins from Opuntia ficus indica cladodes (OfiL) and Moringa oleifera seeds (WSMoL and cMoL) on Nasutitermes corniger workers and soldiers. Purified OfiL was more active than cladode extracts, showing a stronger termiticidal activity against workers (LC₅₀ of 0.116 mg ml⁻¹) than against soldiers. OfiL was active against soldiers only at 1.5 mg ml⁻¹. All preparations containing WSMoL and cMoL were active only at concentrations of 1.0 and 1.5 mg ml⁻¹. The tested preparations did not exert repellent activity against N. corniger. OfiL was able to kill workers and therefore is potentially a new tool for N. corniger control; as a consequence, this lectin could disturb organization, structure, and maintenance of termite colonies.     

Antimicrobial activity and cytotoxicity trait of a bioactive peptide purified from Lactococcus garvieae subsp. bovis BSN307T

A bioactive peptide of 8595 Da was purified from the cell free supernatant of Lactococcus garvieae subsp. bovis BSN307^T. MALDI MS/MS peptide mapping and the data base search displayed no significant similarity to any reported antimicrobial peptide of LAB. This peptide at a dose concentration of 200 µg ml⁻¹ inhibited the growth of both Gram-positive and Gram-negative bacteria by 58–89% and a dose of 500 µg ml⁻¹ scavenged 50% of DPPH-free radicals generated. Interestingly, cytotoxicity assay demonstrated that 17 µg ml⁻¹ of peptide selectively inhibited 50% proliferation of mammalian cancer cell lines HeLa and MCF-7 whereas normal H9c2 cells remained unaffected. Fluorescent microscopic analysis after DAPI nuclear staining of HeLa cells showed characteristics of apoptosis and activation of caspase-3 was ascertained by caspase-3 fluorescence assay.     

Purified Cladonia verticillaris lichen lectin: Insecticidal activity on Nasutitermes corniger (Isoptera: Termitidae)

Cladonia verticillaris lichen lectin (ClaveLL) was isolated through Sephadex G-100 gel filtration chromatography and characterized as a pure lectin through ÄKTA-FPLC and HPLC systems. The lichen extract (LE), protein fraction (F₁) and ClaveLL were assayed to evaluate their potential insecticidal and/or repellence activities on termite Nasutitermes corniger. LE, F₁ and ClaveLL were evaluated for hemagglutinating activity (HA), protein concentration and presence of secondary metabolites; preparations and active ClaveLL, free of secondary metabolites, were able to induce termite mortality. ClaveLL LC₅₀ values after 10 days for workers and soldiers were 0.196 and 0.5 mg ml^?1, respectively. C. verticillaris preparations are potential tools for researches involving control of termites (or other insects) of economic interest to wooden industry or agriculture as well as preservation of plant species that are targets of termites or other plagues.     

In vitro assays on the susceptibility of four species of nematophagous fungi to anthelmintics and chemical fungicides/antifungal drug

Using nematophagous fungi for the biological control of animal parasitic nematodes will become one of the most promising strategies in the search for alternative chemical drugs. The purpose of this study was to check the in vitro activity of four anthelmintics, four chemical fungicides and two antifungal drugs on the spore germination of nematophagous fungi: Duddingtonia flagrans (SF170), Arthrobotrys oligospora (447), Arthrobotrys superba (435) and Arthrobotrys sp. (PS011). A modified 24-well cell culture plate assay was conducted to evaluate the susceptibility of nematophagous fungi against drugs tested by calculating the effective middle concentrations (EC₅₀) of each tested drug to inhibit the germination of fungal spores. EC₅₀ ranged between 0·7 and 47·2 μg ml⁻¹ for fenbendazole, thiabendazole and ivermectin, except levamisole (546·5–4057·8 μg ml⁻¹). EC₅₀ of tested fungicides was 0·6–2·3 μg ml⁻¹ for carbendazim, 55·9–247·4 μg ml⁻¹ for metalaxyl, 24·4–45·2 μg ml⁻¹ for difenoconazole, and 555·9–1438·3 μg ml⁻¹ for pentachloronitrobenzene (PCNB). EC₅₀ of two antifungal drugs was 0·03–3·4 μg ml⁻¹ for amphotericin B and 0·3–10·9 μg ml⁻¹ for ketoconazole. The results showed that 10 tested drugs, except for levamisole and PCNB, had in vitro inhibitory effects on nematophagous fungi. The chlamydospores of D. flagrans had the highest sensitivity to nine tested drugs, except for ketoconazole.     

Dependence of the higher termite, Nasutitermes exitiosus and the lower termite, Coptotermes lacteus on their gut flora

The importance of the gut microorganisms in the termites Nasutitermes exitiosus and Coptotermes lacteus was investigated by feeding them with antibiotics. With N. exitiosus, antibiotics which killed both the bacteria and the spirochaetes (ampicillin, kanamycin, chloramphenicol, erythromycin, cephaloridine, tetracycline) reduced the life span of the termite from 250 days to about 13 days, whereas antibiotics which had little effect on the flora (penicillin, methicillin) did not greatly reduce the life span of the termite. The essential role of the spirochaetes in N. exitiosus was shown by feeding metronidazole, or exposing the termites to pure oxygen. Both treatments killed the spirochaetes, but not the bacteria, resulting in a life span for the termite of 13–22 days. Acid fuchsin did not kill the spirochaetes. Fungi were not essential for N. exitiosus. In C. lacteus all treatments, except that with acid fuchsin, killed the protozoa, thereby reducing the life span of the termite from 69 days to 6–29 days.     

Repellency and toxicity of a CO2-derived cedarwood oil on hard tick species (Ixodidae)

The repellency and toxicity of a CO₂-derived cedarwood oil (CWO) was evaluated against actively questing unfed nymphs of four species of hard ticks: Amblyomma americanum (L.), Dermacentor variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille). Using a vertical climb bioassay for repellency, nymphs of these species avoided a CWO-treated filter paper in proportional responses to treatment concentrations. At 60 min of exposure, I. scapularis nymphs were most sensitive with 50% repellency concentration (RC₅₀) of 19.8 µg cm^?2, compared with RC₅₀ of 30.8, 83.8 and 89.6 µg cm^?2 for R. sanguineus, D. variabilis and A. americanum, respectively. Bioassays determined the lethal concentration for 50% (LC₅₀) and 90% (LC₉₀) mortality of nymphs exposed to CWO in treated vials after 24- and 48-h exposure. After 24 h exposure, the LC₅₀ values were 1.25, 3.45 and 1.42 µg cm^?2 and LC₉₀ values were 2.39, 7.59 and 4.14 µg cm^?2 for D. variabilis, I. scapularis and R. sanguineus, respectively, but had minimal effect on A. americanum. After 48 h exposure, the LC₅₀ values were 4.14, 0.78, 0.79 and 0.52 µg cm^?2, and LC₉₀ values were 8.06, 1.48, 1.54 and 1.22 µg cm^?2 for A. americanum, D. variabilis, I. scapularis and R. sanguineus, respectively. The repellency of CWO on tick species decreased with time. The repellency and toxicity bioassays demonstrated concentration-dependent responses of tick nymphs to the oil, indicating the potential of the CO₂-derived cedarwood oil be developed as an eco-friendly repellent and/or acaricide.

     

Nanoparticles combined with cefixime as an effective synergistic strategy against Salmonella enterica typhi

Enteric fever caused by Salmonella typhi has been the most crucial health issue in rural people, especially in Southeast Asia and Africa. Another disease, Salmonellosis, caused by a large group of bacteria of the genus Salmonella, cause substantial economic loss resulting from mortality and morbidity. Higher concentration and repeated use of antibiotics to treat these diseases will likely develop antibiotic resistance among the microbes. The nanoparticle has good penetration power and can kill microbes. Combining two strategies by using nanoparticles with antibiotics kills microbes and reduces the chances of the development of antibiotics resistance. Silver, Nickel, Copper, and Zinc oxide Nanoparticles were chemically synthesized and characterized in this study. Silver nanoparticles at a concentration of 10 µg/ml inhibit all the strains under study.In comparison, silver nanoparticles (16.90 µg/ml), Nickel nanoparticles (83 µg ml^?1), Copper nanoparticles (249 µg ml^?1), and Zinc oxide (1614 µg ml^?1) along with 50 µg/ml cefixime gave maximum zone of inhibition of 35 mm, 19 mm, 31 mm and 23 mm respectively. The antimicrobial assay showed that silver nanoparticles presented good antibacterial performance against all multi-drug-resistant pathogenic Salmonella sp alone as well as in combinations. The present study proved that silver nanoparticles at the lowest concentration along with cefixime could be a possible alternative to control the multi-drug-resistant pathogens.     

Performance of polymyxin B agar-based tests among carbapenem-resistant Enterobacterales

Therapeutic options for infections caused by Carbapenem-resistant Enterobacterales (CRE) are restricted and include polymyxins-centred schemes. Evaluation of in vitro susceptibility is difficult and time consuming. Agar-based methodologies are an alternative to broth microdilution (BMD) and we aimed to evaluate the accuracy of those methods among Enterobacterales. A total of 137 non-duplicated CRE were subjected to polymyxin B BMD, agar screening test (Mueller Hinton plates containing 3 µg ml⁻¹ of polymyxin B) and agar dilution (antibiotic serially diluted 0·25–64 µg ml⁻¹). CRE of 42·3% were resistant to polymyxin B (MICs range: 0·25–>64 µg ml⁻¹) and 16·8% presented borderline MICs. Sensitivity, specificity, PPV and NPV were 86·2, 98·7, 98 and 90·7% for screening test and 86·2, 97·5, 96·1 and 90·6% for agar dilution. ME was 0·73 and 1·5% for screening and agar dilution respectively; VME was 5·8% for both techniques. In general, agar-based methods had a good performance. As far as we know, this is the first study to propose an agar screening test using polymyxin B instead of colistin.     

Anomalies in the enumeration of starved bacteria on culture media containing nalidic acid and tetracycline

Culturable counts of antibiotic resistant, genetically engineeredPseudomonas fluorescens were determined on antibiotic-containing plate count agar during starvation in water. Prior to starvation, colony counts obtained on all media separated into two groups. The mean of the colony counts on plate count agar with or without tetracycline (4.9 × 10⁶ ml⁻¹) was significantly higher than the mean colony counts on plate count agar containing either nalidixic acid or nalidixic acid plus tetraclycline (2.5×10⁶ ml⁻¹). After 20 days of starvation the highest mean colony counts continued to be obtained on plate count agar (7.2 × 10⁶ ml⁻¹) with slightly, but significantly, lower counts obtained on plate count agar containing either nalidixic acid (5.6 × 10⁶ ml⁻¹) or tetraclycline (1.5×10⁶ ml⁻¹). A combination of nalidixic acid and tetracycline in plate count agar, however, dramatically reduced colony counts (8.3 × 10² ml⁻¹) after this starvation period. The addition of catalase to plate count agar containing nalidixic acid and tetracycline negated the effect caused by this combination of antibiotics. When colony counts obtained over the entire 20 day incubation were considered, the addition of MgSO₄ to plate count agar containing nalidixic acid and tetracycline resulted in a significant increase in colony counts. Other combinations of antibiotics, nalidixic acid+carbenicillin, nalidixic acid+kanamycin, streptomycin+tetracycline, streptomycin+carbenicillin, rifampicin+tetracycline, rifampicin+carbenicillin, and rifampicin+kanamycin, did not inhibit colony formation of starved cells. Antibiotic resistant strains ofP. putida andEscherichia coli also displayed sensitivity to the combination of nalidixic acid and tetracycline in plate count agar after starvation.     

Subinhibitory concentrations of nalidixic acid alter bacterial physiology and induce anthropogenic resistance in a commensal strain of Escherichia coli in vitro

The human gut houses a complex group of bacterial genera, including both opportunistic pathogens and commensal micro-organisms. These are regularly exposed to antibiotics, and their subinhibitory concentrations play a pivotal role in shaping the microbial responses. This study was aimed to investigate the effects exerted by sub-MICs of nalidixic acid (NA) on the growth rate, bacterial motility, biofilm formation and expression of outer membrane proteins (OMPs) in a commensal strain of E. coli. The NA-sensitive strain was sequentially passaged under sub-MICs of NA. E-test was used to determine the MIC values of NA. Results indicated significant changes in the growth profile of commensal E. coli upon exposure to NA at sub-MICs. Differential expression of OMPs was observed in cells treated with sub-MICs of NA. Bacterial motility was reduced under 1/2 MIC of NA. Interestingly, successive passaging under 1/2 MIC of NA led to the emergence of resistant E. coli with an increased MIC value of 64 µg ml⁻¹ in just 24 days. The NA-resistant variant was confirmed by comparing its 16S rRNA sequence to that of the sensitive commensal strain. Mutations in the Quinolone Resistance-Determining Regions (QRDRs) of chromosomal gyrA, and Topoisomerase IV-encoding parC genes were detected in NA-resistant E. coli. Our results demonstrate how antibiotics play an important role as signalling molecules or elicitors in driving the pathogenicity of commensal bacteria in vitro.     

Efficacy of karanjin and phorbol ester fraction against termites (Odontotermes obesus)

The non-edible oil seeds of Jatropha curcas (physic nut) and Pongamia pinnata (karanja) contain some toxic components (phorbol esters in J. curcas and karanjin in P. pinnata), which may be used as biopesticides. In this study, the active components of J. curcas and P. pinnata oil were extracted and their efficacy against the termites Odontotermes obesus (Rambur), was tested. The phorbol ester fraction of J. curcas and karanjin of P. pinnata oil were found to be effective against termites. A mortality rate of 100% was achieved in 6 h with karanjin and in 12 h with phorbol ester fraction. The LC₅₀ levels of karanjin and phorbol esters fractions were 0.038 and 0.071 g ml⁻¹, respectively, after 24 h at a 95% (0.05) confidence limit.     

Insights into collateral susceptibility and collateral resistance in Acinetobacter baumannii during antimicrobial adaptation

The susceptibility of Acinetobacter baumannii exposed to primary antibiotic can be either increased or decreased when exposed to secondary antibiotic. This study was designed to assess the relative fitness, collateral susceptibility and collateral resistance of polymyxin B- (PMB-) adapted A. baumannii to ciprofloxacin (CIP), meropenem (MER), PMB, tetracycline (TET) and tobramycin (TOB). Strains of wild-type A. baumannii KACC 12454 (AB^KACC), wild-type A. baumannii CCARM 12088 (AB^CCARM), PMB-adapted AB^KACC, PMB-adapted AB^CCARM, stabilized AB^KACC and stabilized AB^CCARM were used in this study. Compared to the wild-type AB^KACC, the MICs of PMB were increased from 2 to 128 μg ml⁻¹ against PMB-adapted AB^KACC, while MICs of CIP, MER, TET and TOB were decreased from 2 to 1 μg ml⁻¹, 16 to 1 μg ml⁻¹, 16 to 2 μg ml⁻¹ and 64 to 16 μg ml⁻¹, respectively. The PMB-adapted AB^CCARM was resistant to CIP (32 μg ml⁻¹) and PMB (64 μg ml⁻¹) compared to the wild-type AB^CCARM. The resistance of stabilized AB^KACC and AB^CCARM to all antibiotics was lost after antibiotic-free culture in the exception of CIP and TET. The susceptibilities of wild-type, PMB-adapted and stabilized AB^KACC and AB^CCARM to CIP, MER, PMB, TET and TOB were increased in the presence of β-lactamase and efflux pump inhibitors. The high levels of relative fitness were observed for stabilized AB^KACC, PMB-adapted AB^CCARM and stabilized AB^CCARM. The stabilized AB^KACC and PMB-adapted AB^CCARM were highly heteroresistance to PMB and TET, respectively. The PMB-adapted AB^KACC and AB^CCARM showed various antibiotic patterns, known as collateral susceptibility and collateral resistance. The results provide useful information for designing effective antibiotic regimens that can enhance the antibiotic activity against A. baumannii infections.     

Purification and characterization of four key enzymes from a feather-degrading Bacillus subtilis from the gut of tarantula Chilobrachys guangxiensis

A feather-degrading bacterium was isolated from the gut of the tarantula Chilobrachys guangxiensis, and was classified as Bacillus subtilis (named Bacillus subtilis CH-1) according to both the phenotypic characteristics and 16S rRNA profile. The improved culture conditions for feather-degrading were 10.0 g l⁻¹ mannitol, 10.0 g l⁻¹ tryptone, 0.1 g l⁻¹ MgCl₂, 0.4 g l⁻¹ KH₂PO₄, 0.3 g l⁻¹ K₂HPO₄, 0.5 g l⁻¹ NaCl, and 2.0 g l⁻¹ intact feather, with pH 8.5 and 37 °C. In the optimized medium, the intact black feather was completely degraded by Bacillus subtilis CH-1 in 24 h. Furthermore, four kinds of enzymes which include extracellular protease Vpr, peptidase T, γ-glutamyl transpeptidase and glyoxalmethylglyoxal reductase were identified as having principal roles. Simultaneously, the relationship between the disulfide bond reducing activity (DRT) and the keratinase activity (KT) in B. subtilis CH-1 fermentation system was discussed. This is the first report for a feather-degrading enteric bacterium from tarantula. The identification of the enzymes shines a light on further understanding the molecular mechanism of feather-degrading by microbes.     

Cellulolytic enzyme production from agricultural residues for biofuel purpose on circular economy approach

This study evaluated the production of cellulolytic enzymes from different agricultural residues. The crude enzyme extract produced was characterized and applied for saccharification of some agricultural residues. Maximum cellulolytic activities were obtained using soybean hulls. All enzymatic activities were highly stable at 40 °C at a pH range of 4.5–5.5. For stability at low temperatures, the enzyme extract was stored at freezing temperature and cooling for about 290 days without major loss of activity. The K_m values found for total cellulase (FPase), endoglucanase (CMCase), and xylanase were 19.73 mg ml⁻¹, 0.65 mg ml⁻¹, and 22.64 mg ml⁻¹, respectively, and V_max values were 0.82 mol min⁻¹ mg⁻¹, 0.62 mol min⁻¹ mg⁻¹, and 104.17 mol min⁻¹ mg⁻¹ to cellulose, carboxymethyl cellulose, and xylan, respectively. In the saccharification tests, the total amount of total reducing sugars (TRS) released from 1 g of soybean hulls catalyzed by the enzymes present in the crude enzyme extract was 0.16 g g⁻¹ dry substrate.

     

Interstrains comparison of the antimicrobial effect and mode of action of a Vietnamese Cinnamomum cassia essential oil from leaves and its principal component against Listeria monocytogenes

The antibacterial activity of a Cinnamomum cassia essential oil (EO) and of its main component trans-cinnamaldehyde (90% w/w) was examined against five Listeria monocytogenes strains. The minimal inhibitory concentrations (MICs) of C. cassia EO against the five L. monocytogenes strains were identical (250 µg ml⁻¹), while the minimal bactericidal concentrations (MBCs) ranged between 800 and 1200 µg ml⁻¹. In order to study if this EO and trans-cinnamaldehyde altered the five strains at the membrane level, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured in presence of different concentrations (1/2MIC, MIC, 2MIC) of these antibacterial agents. A concentration-dependent increase of fluorescence anisotropy of DPH in their presence reflecting a rigidification of the membrane was observed for the five strains. This modification of the membrane fluidity was associated with a perturbation of the selective membrane permeability, as a perturbation of the gradient between intracellular and extracellular pH was also observed.     

Development and characterization of a carvacrol nanoemulsion and evaluation of its antimicrobial activity against selected food-related pathogens

Carvacrol has been recognized as an efficient growth inhibitor of food pathogens. However, carvacrol oil is poorly water-soluble and can be oxidized, decomposed or evaporated when exposed to the air, light, or heat. To overcome these limitations, a carvacrol nanoemulsion was developed and its antimicrobial activity against food pathogens evaluated in this study. The nanoemulsion containing 3% carvacrol oil, 9% surfactants (HLB 11) and 88% water, presented good stability over a period of 90 days. In general, the carvacrol nanoemulsion (MIC: 256 µg ml⁻¹ for E. coli and Salmonella spp., 128 µg ml⁻¹ for Staphylococcus aureus and Pseudomonas aeruginosa) exhibited improved antimicrobial activity compared to the free oil. The carvacrol nanoemulsion additionally displayed bactericidal activity against Escherichia coli, P. aeruginosa and Salmonella spp. Therefore, the results of this study indicated that carvacrol oil nanoemulsions can potentially be incorporated into food formulations, wherein their efficacy for the prevention and control of microbial growth could be evaluated.     

Methane Oxidation in Termite Hindguts: Absence of Evidence and Evidence of Absence

A steep oxygen gradient and the presence of methane render the hindgut internal periphery of termites a potential habitat for aerobic methane-oxidizing bacteria. However, methane emissions of various termites increased, if at all, only slightly when termites were exposed to an anoxic (nitrogen) atmosphere, and ¹⁴CH₄ added to the air headspace over live termites was not converted to ¹⁴CO₂. Evidence for the absence of methane oxidation in living termites was corroborated by the failure to detect pmoA, the marker gene for particulate methane monooxygenase, in hindgut DNA extracts of all termites investigated. This adds robustness to our concept of the degradation network in the termite hindgut and eliminates the gut itself as a potential sink of this important greenhouse gas.