纳米银的制备及其复乳的体外抑菌活性

用(2-乙基己基)磺基琥珀酸钠(AOT)/肉豆蔻酸异丙酯/水微乳体系制备无毒、无刺激性的纳米银,通过透射电子显微镜(TEM)、紫外-可见吸收光谱(UV-vis)对其进行了表征。结果表明,纳米银呈球状、粒径分布均匀,平均粒径30nm。体外抑菌结果显示,纳米银复乳对金黄色葡萄球菌、大肠杆菌、无乳链球菌的最小抑菌质量浓度分别为50、100、50μg/L。     

Incorporation of Membrane Proteins Into Bicontinuous Microemulsions Through Winsor-III System-Based Extraction

The membrane proteins (MP) α-synuclein (ASYN) and bacteriorhodopsin (BR) were readily incorporated into bicontinuous microemulsions (BμEs) formed by two microemulsion systems: water/heptane/Aerosol-OT (AOT)/CK-2,13 and water/dodecane/sodium dodecyl sulfate (SDS)/1-pentanol. (CK-2,13 is an alkyl ethoxylate possessing two alkyl tail groups of carbon chain length 2 and 13 and an average degree of ethoxylation of 5.6.) MP were encapsulated in BμEs through preparation of Winsor-III systems at optimal salinity, with the anionic surfactants AOT and SDS providing the driving force for extraction. Dissolution of ASYN in BμEs greatly increased the former's α-helicity, similar to ASYN's behavior in the presence of biomembranes, while BμE- and vesicle-encapsulated BR possessed similar secondary structure. Small-angle neutron scattering (SANS) results clearly demonstrated the direct interaction of MP with the surfactants, resulting in a decrease of surface area per volume for surfactant monolayers due to decreased surfactant efficiency. The SANS signal for ASYN was isolated through the use of neutron contrast matching for the surfactants through partial deuteration of water and oil, one of the first reports of contrast matching for BμEs in the literature. The SANS results of the contrast-matched sample reflected similar aggregation for ASYN in BμEs as was reported previously for vesicles and SDS solution. This study demonstrates the potential use of BμEs as MP host systems for conducting biochemical reactions such as the conversion of sunlight into adenosine triphosphate by BR and studying the fundamental behavior of MP, such as the role of ASYN dysfunction in Parkinson's disease, as well as for isolation and purification of MP via Winsor-III-based extraction.     

AOT-磷脂反胶团体系萃取蛋白质的研究

研究了PC/AOT和PE/AOT混合体系在有机溶剂中形成反胶团的性质及其萃取蛋白质的性能,并解决了反胶团萃取中有磷脂存在时的蛋白质浓度的分析问题.研究结果表明,在AOT体系中加入磷脂能使胶团尺寸变大,且加入PE能提高血红蛋白和枯草杆菌a—淀粉酶的萃取率,加入PC则常使萃取性能变差.因此,在反胶团萃取蛋白质时,影响萃取的主要因素不仅是胶团的大小,还有胶团与蛋白质之间的相互作用.     

云南薄荷精油的化学成分及其抗菌活性研究

采用GC/MS法对云南薄荷精油挥发性成分进行鉴定,检测出49个成分,鉴定了其中44个成分.薄荷精油主要化学成分为薄荷醇、薄荷酮、苧烯、1,8-桉叶素、胡椒酮、大根香叶烯D、乙酸薄荷酯等.试验研究了薄荷精油对大肠杆菌、金黄葡萄球菌、烟曲霉菌、白念珠菌的抗菌活性.结果显示精油对大肠杆菌、金黄葡萄球菌、白念珠菌有明显的抗菌活...     

Research on the preparation and antibacterial properties of 2‐N‐thiosemicarbazide‐6‐O‐hydroxypropyl chitosan membranes with iodine

The 2‐N‐thiosemicarbazide‐6‐O‐hydroxypropyl chitosan (ATU‐HPCS) was prepared by chitosan grafted hydroxypropyl and thiosemicarbazide through the method of “amino protection‐graft‐deprotection,” while the ATU‐HPCS gel membranes were obtained from gelatin and polyvinyl pyrrolidone as additives, and the ATU‐HPCS membranes with iodine (ATU‐HPCS‐I₂‐M) were prepared by adding the ethanol solution of iodine in the ATU‐HPCS gel membranes. The ATU‐HPCS‐I₂‐M were characterized to evaluate their potential applications as antibacterial materials. The iodine releasing rule of ATU‐HPCS‐I₂‐M showed a sustained‐release effect of iodine, the maximum emission was approximately 0.80%. The inhibition zone diameters of ATU‐HPCS‐I₂‐M against Staphylococcus aureus (as Gram‐positive bacteria) and Escherichia coli (as Gram‐negative bacteria) were both greater than 15 mm, it demonstrated significant antibacterial activity compared with the ATU‐HPCS gel membranes. The double effects of the biocompatibility of chitosan and the sustained‐release of iodine provided an ideal healing environment for wound surface. These properties have made ATU‐HPCS‐I₂‐M highly potential as a novel natural macromolecule antimicrobial material preventing the bacteria from burns, surgery wounds, etc. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40535.     

Pharmacological Assessment of the Medicinal Potential of Acacia mearnsii De Wild.: Antimicrobial and Toxicity Activities

Acacia mearnsii De Wild. (Fabaceae) is a medicinal plant used in the treatment of microbial infections in South Africa without scientific validation of its bioactivity and toxicity. The antimicrobial activity of the crude acetone extract was evaluated by both agar diffusion and macrobroth dilution methods while its cytotoxicity effect was assessed with brine shrimp lethality assay. The study showed that both bacterial and fungal isolates were highly inhibited by the crude extract. The MIC values for the gram-positive bacteria (78.1-312.5) μg/mL, gram-negative bacteria (39.1-625) μg/mL and fungal isolates (625-5000) μg/mL differ significantly. The bacteria were more susceptible than the fungal strains tested. The antibiosis determination showed that the extract was more (75%) bactericidal than bacteriostatic (25%) and more fungicidal (66.67%) than fungistatic (33.33%). The cytotoxic activity of the extract was observed between 31.25 μg/mL and 500 μg/mL and the LC(50) value (112.36 μg/mL) indicates that the extract was nontoxic in the brine shrimp lethality assay (LC(50) > 100 μg/mL). These results support the use of A. mearnsii in traditional medicine for treatment of microbial infections. The extract exhibiting significant broad spectrum antimicrobial activity and nontoxic effects has potential to yield active antimicrobial compounds.     

Ultrasmall silver nanoparticles loaded in alginate–hyaluronic acid hybrid hydrogels for treating infected wounds

Nowadays, silver nanoparticles are in the limelight to control infection during wound healing process, and a vast variety of antimicrobial dressings based on colloidal silver have been marketed to fight wound invasion of pathogen bacteria, which represents one of the main adverse effects limiting the repair process. Here we propose a biofunctional hydrogel based on alginate (ALG) and hyaluronic acid (HA) embedding ultrasmall silver nanoparticles (usSN, <1?nm) as antimicrobial component. The hydrogels were fabricated in different size by a straightforward internal gelation method using CaCO₃ and glucono-δ-lactone. To follow usSN release from the hydrogels in aqueous media, catalytic activity of usSN-loaded hydrogels was evaluated. Results suggested that catalytic activity was low in intact hydrogels and high when hydrogels dissolved, which suggests that usSN firmly interact with polymer chains and are available in the medium depending on the extent of hydrogel degradation. HA-containing hydrogels showed faster dissolution in simulated physiological conditions and higher antibiofouling properties as compared to hydrogels made only of ALG. Free usSN were not toxic toward human mesenchymal stem cells (Ad-MSCs), previously isolated from subcutaneous adipose tissue biopsies, up to 50?µg/mL. At this concentration, viability of Ad-MSCs was unaffected whereas their motility was significantly higher as compared to control (p<0.01) for both free usSN and hydrogel integrating. Antimicrobial activity on clinical isolates of both Gram-positive and Gram-negative bacteria demonstrated that usSN at 50?µg/mL were able to kill all the bacteria tested after 24 and 48?h of contact time. In the case of hydrogels, a matrix effect was found and bacterial killing was significant only at 24?h and dependent on bacterial strain, being Gram-negative bacteria more susceptible. These results clearly indicate that usSN interaction with polymer network and exposure time can strongly affect usSN antimicrobial profile in the hydrogel and, in turn, timing of hydrogel change at injured site in a clinical setting. On the whole, ALG/HA hydrogels integrating usSN can be considered a suitable option to fabricate biofunctional dressings for hospitalized patients and worth of further in vivo investigation.     

Antibacterial finishing of polyester/cotton blend fabrics using neem (Azadirachta indica): A natural bioactive agent

The study focused on the development of biofunctional polyester/cotton blend fabric using a natural product. An antimicrobial agent extracted from the seeds of Neem tree (Azadirachta indica) was used for imparting antibacterial property to the blend fabric. Resin and catalyst concentrations were optimized to get the maximum crosslinking in the fabric blends using glyoxal/glycol as a crosslinking agent. The optimized concentrations were used to treat the fabric with the antimicrobial agent along with the crosslinking agent. Quantitative analysis was carried out to measure the antimicrobial activity against Gram‐positive and Gram‐negative bacteria. The results showed that the treated fabrics inhibited the growth of Gram‐positive bacteria (Bacillus subtilis) by more than 90% as compared to the control sample. Antimicrobial activity against Gram‐ positive bacteria was retained up to five machine washes and decreased thereafter. The antibacterial activity was higher against Gram‐positive bacteria as compared to Gram‐ negative bacteria (Proteus vulgaris). The treated fabrics also showed improved crease recovery property although the tensile property showed a marginal decrease. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Flash photolysis investigation on primary processes of the sensitized polymerization of vinylmonomers. III. Photoreactions of benzoin compounds and stationary polymerization experiments

Benzoin (B), benzoinacetate (BA), benzoinmethylether (BME) and benzoinisopropylether (BIPE) were irradiated at room temperature in benzene solution in the presence of styrene (St), methyl methacrylate (MMA), vinylacetate (VAc) or acrylonitrile (AN). Flash photolysis experiments at λ=347 nm yielded (a) rate constants k_q (in 1 mol^-1s^-1) of the reaction between excited sensitizers and monomers: 8·10⁹ (B/St), 5·10⁸ (B/MMA), 5·10⁹ (BA/St), 8·10⁸ (BA/MMA); (b) rate constants K^R.+M (in 1mol^-1 s^-1) of the reaction between sensitizer radicals and monomers: about 1.5·10⁵ (BME/St, BME/VAc, BA/VAc, B/VAc), 9· 10⁴ (BME/MMA), 2·10⁴ (BME/AN). The reaction R·+M caused in certain cases (B/St, B/VAc, BME/St) the formation of an additional optical absorption after the flash. Stationary irradiations at λ>320 nm of monomer solutions (5mol/1) showed that BA is least effective. Rates of polymerization increased in the series BA<B<BIPE<BME. For the systems containing St or MMA it was found that ?_i=_i+0.6α_R (?_i=quantum yield for the initiation of kinetic chains, α_R =fraction of triplets converted to radicals). The fraction of radicals starting kinetic chains is ca. 0.3 in these cases.     

Polymerization of acrylamide in single-phase in-verse dispersion systems at high volume fractions of dispersed phase

The preparation of single-phase inverse microemulsions of toluene/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water/acrylamide (AAm) is described and their properties prior to polymerization (macro and microviscosity as a function of volume fraction Φ_aw of the dispersed aqueous (water + acrylamide) phase, of the [to-luene]/[AOT] molar ratio and of the acrylamide/water mass ratio) were studied. The polymerization of acrylamide in dispersion systems was initiated by the oilsoluble initiator dibenzoyl peroxide at 60°C. The polymerization rate of acrylamide for a given [toluene]/[AOT] molar ratio and AAm/water mass ratio monotonically decreases beyond a Φ_aw value of 20%. The polymer particle size in polymerized systems as well as the molecular mass of polymer in the polymer particles increase on increasing the acrylamide concentration in the aqueous phase and/or the Φ_aw values of the dispersion system. On increasing the surfactant AOT concentration both polymer particle size and polymer molecular mass decrease for a given set of other relevant parameters of the dispersion system (i.e. [toluene]/[AOT] and AAm/water ratios). The polymerized inverse dispersion system can be converted to an oil-in-water dispersion by addition of water.     

Synthesis and characterization of quaternary ammonium PEGDA dendritic copolymer networks for water disinfection

Quaternary ammonium compounds are some of the most widely used antimicrobial agents for various medical applications due to their low toxicity and broad spectrum antimicrobial activity. Various generations of poly(ethyleneglycol)diacrylate (PEGDA) based dendrimers were synthesized by Michael addition reaction of PEGDA with ethylene diamine and diethyl amine. The percentage yield of different generation of dendrimers were 70%, 66%, 60%, and 85% for G1.0 (=), G1.5 (NH₂), G2.0 (=), and G2.5 (=, NEt₂), respectively. Synthesized dendrimers were also copolymerized with ethyleneglycol dimethacrylate by free radical bulk polymerization at room temperature using ammonium persulphate/N,N,N′,N′‐tetramethyl ethylenediamine as a redox initiator system to form dendritic copolymer networks. These networks were quaternized with hydrochloric acid by continuously refluxing at 40°C for 6 h. Dendrimers and quaternized dendritic copolymer networks were characterized by ¹HNMR, FTIR, Differential scanning calorimetry, Thermogravimetric analysis, Scanning electron microscope, swelling, and leaching studies. Synthesized quaternary ammonium dendritic copolymer networks were found to be biostable and insoluble in water and capable of killing both Gram‐positive and Gram‐negative bacteria when contaminated water was treated with them. It was also observed that antimicrobial efficiency of dendritic copolymer networks increases with the increase in nitrogen atoms in the copolymer. The dendritic copolymer network with 16 quaternary ammonium groups (G2.5 (=, NEt₂): EGDMA QHCl) were highly efficient to disinfect 10 mL bacterial solution of 2000 cfu/mL within 2 min even at a very low concentration of 0.005 g/mL. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

季铵盐改性蒙脱土的抗菌活性及抗菌机理

采用离子交换法将不同季钱盐插层到钠基蒙脱土中制备了改性蒙脱土.改性蒙脱土对革兰氏阳性菌(S.aereus)和革兰氏阴性菌(E coli)均有很强的抗菌作用,并且随着季铵盐在蒙脱土中的质量分数增加其抗菌活性增强.不同季铵盐改性蒙脱土的抗菌活性不同,其中双季铵盐改性蒙脱土的抗菌活性最好,对S.aereus和E coli的最小抑菌浓度分别为6.25 mg/L和12.5 mg/L.用扫描电镜对与细菌接触不同时间后的改性蒙脱土进行观察,结果表明:细菌先吸附到改性蒙脱土的表面,然后慢慢的变形死亡.同时,对在0.9%的生理盐水中浸泡不同时间后的改性蒙脱土进行X射线衍射和热重分析.结果表明:随着浸泡时间的增加,蒙脱土中的有机物质量分数及层间距均逐渐减少,说明季铵盐能从蒙脱土的层间解吸出来,并进入溶液中直接杀死细菌.因而,改性蒙脱土的抗菌活性是吸附与释放到溶液中的季铵盐离子协同作用的结果.     

A colorimetric determination of fatty acids as a new assay of lipases in reverse micelles

A new simple spectrophotometric method is described for the determination of the free fatty acid content in triglyceride oils or other lipophilic samples. The method utilizes phenol red as fatty acid indicator, which is solubilized phenol red as fatty acid indicator, which is solubilized in reverse micelles formed by AOT [sodiumbis(2-ethylhexyl) sulfosuccinate] in isooctane. Fatty acid determinations in vegetable oils can be carried out rapidly with oil samples of less than 100 mg. The acid value of three different oils tested agreed quite well with the acid value obtained for the same samples with another colorimetric determination using cupric acetate. The method can be extended to a continuous determination of fatty acids which are released during the initial stage of a lipase catalyzed hydrolysis of triglyceride substrates in reverse micelles. This new sensitive lipase assay has been applied for a lipase ofPseudomonas bacteria with lipase concentrations as low as 0.1 μg/ml. Using trioctanoylglycerol as substrate in 50 mM AOT/isooctane with w_o=[H₂O]/[AOT]=11.1 (pH 9.0), the apparent overall Michaelis-Menten constant (K_m′app,ov) is 27 mM and the turnover number (k_cat) 44 sec⁻¹.     

Applicability of the Brønsted Relation to Reactions of the Hydrated Electron

The hydrated electron, e^?_aq, reacts with Brønsted acids, BH⁺, to yield H atoms through a process of proton transfer For a series of Brønsted acids of charge types 1+, 0 and 1?, the rate constant, k, is related to the acid dissociation constant K according to k/p = GA(qK/p)^α, where α = 0.42. Some acids give rate constants deviating from this relation. These are shown to be ambident reagents with e^?_aq, one pathway obeying the Brønsted relation, while the other may be nucleophilic addition of e^?_aq to a reaction center in B. Thus —k(e^?_aq), the rate of disappearance of e^?_aq may be greater than +k(H), the rate of formation of H atoms. To account for the results, a molecular model for the structure of e^?_aq forming a hydrated anion is favored. Its reaction with H⁺_aq is discussed, accounting for recent observations on the rate of the reaction e^?_aq + H⁺_aq → H_aq, which in our view corresponds to proton transfer to fully ordered hydrated electrons, rather than electron addition to H⁺_aq.     

Development of an Experimental Ex Vivo Wound Model to Evaluate Antimicrobial Efficacy of Topical Formulations

Wound infections are considered a major cause for wound-associated morbidity. There is a high demand for alternative, robust, and affordable methods that can provide relatable and reproducible results when testing topical treatments, both in research and in the pharmaceutical industry. Here we present an ex vivo wound infection model using porcine skin and a burn wounding method, allowing for the efficacy evaluation of topical antimicrobial formulations. Utilizing this model, we demonstrate the potential of topical treatments after infecting the wounds with clinically significant bacteria, P. aeruginosa and S. aureus. We show that the method is compatible with several analytical tools used to analyze infection and antimicrobial effects. Both bacterial strains successfully infected the wound surface, as well as deeper regions of the tissue. Quantification of viable bacteria on the wound surface and in the tissue, longitudinal measurements of bioluminescence, fluorescence microscopy, and scanning electron microscopy were used to confirm the effects of antibacterial treatments. Furthermore, we show that biofilms are formed on the wound surface, indicating that the demonstrated method mirrors typical in vivo infections.     

巨尾桉单宁的提取分离及其抗菌抗氧化性能

采用超声波辅助法提取了巨尾桉叶中的单宁,大孔树脂吸附法纯化了粗提物,考察了提取物对8种常见菌种的抑制作用和对H2O2、DPPH.和.OH的清除作用。结果表明,巨尾桉单宁的提取得率为4.01%;经树脂分离纯化后单宁质量分数达到53.12%;巨尾桉单宁对除大肠杆菌外的供试菌种均有较强的抑制作用,纯化后的单宁对金黄色葡萄球菌、酵母菌和痢疾杆菌的最低抑菌质量浓度(MIC)均为1.0 g/L,对蜡状芽孢杆菌和沙门氏菌的抑制作用优于阳性对照物;粗提物、纯化物在质量浓度为0.50 g/L时对H2O2有最大清除率,分别为80.00%、89.12%,其IC50分别为0.11、0.12 g/L;抗坏血酸、粗提物和纯化物均在质量浓度为1.50 g/L时对DPPH.有最大清除率,分别为98.43%、88.97%和92.21%。在清除.OH体系中,粗提物、纯化物均在质量浓度为4.00 g/L时有最大清除率,分别为87.52%和94.32%,各试样对.OH的清除能力依次为抗坏血酸>纯化物>粗提物。     

Design,Synthesis, Antibacterial,Antifungal and Anticancer Evaluations of Novel β-Pinene Quaternary Ammonium Salts

β-pinene is a monoterpene isolated from turpentine oil and numerous other plants’ essential oils, which has a broad spectrum of biological activities. In the current work, six novel β-pinene quaternary ammonium (β-PQA) salts were synthesized and evaluated in vitro for their antifungal, antibacterial and anticancer activities. The in vitro assay results revealed that compounds 4a and 4b presented remarkable antimicrobial activity against the tested fungi and bacteria. In particular, compound 4a showed excellent activities against F. oxysporum f.sp. niveum, P. nicotianae var.nicotianae, R. solani, D. pinea and Fusicoccumaesculi, with EC₅₀ values of 4.50, 10.92, 9.45, 10.82 and 6.34 μg/mL, respectively. Moreover, compound 4a showed the best antibacterial action against E. coli, P. aeruginosa, S. aureus and B. subtilis, with MIC at 2.5, 0.625, 1.25 and 1.25 μg/mL, respectively. The anticancer activity results demonstrated that compounds 4a, 4b, 4c and 4f exhibited remarkable activity against HCT-116 and MCF-7 cell lines, with IC₅₀ values ranged from 1.10 to 25.54 μM. Notably, the compound 4c displayed the strongest cytotoxicity against HCT-116 and MCF-7 cell lines, with the IC₅₀ values of 1.10 and 2.46 μM, respectively. Furthermore, preliminary antimicrobial mechanistic studies revealed that compound 4a might cause mycelium abnormalities of microbial, cell membrane permeability changes and inhibition of the activity of ATP. Altogether, these findings open interesting perspectives to the application of β-PQA salts as a novel leading structure for the development of effective antimicrobial and anticancer agents.     

Comparative Antimicrobial Activity of Hp404 Peptide and Its Analogs against Acinetobacter baumannii

An amphipathic α-helical peptide, Hp1404, was isolated from the venomous gland of the scorpion Heterometrus petersii. Hp1404 exhibits antimicrobial activity against methicillin-resistant Staphylococcus aureus but is cytotoxic. In this study, we designed antimicrobial peptides by substituting amino acids at the 14 C-terminal residues of Hp1404 to reduce toxicity and improve antibacterial activity. The analog peptides, which had an amphipathic α-helical structure, were active against gram-positive and gram-negative bacteria, particularly multidrug-resistant Acinetobacter baumannii, and showed lower cytotoxicity than Hp1404. N-phenyl-1-naphthylamine uptake and DisC₃-5 assays demonstrated that the peptides kill bacteria by effectively permeating the outer and cytoplasmic membranes. Additionally, the analog peptides inhibited biofilm formation largely than Hp1404 at low concentrations. These results suggest that the analog peptides of Hp1404 can be used as therapeutic agents against A. baumannii infection.     

Influence of Ce3+ Substitution on Antimicrobial and Antibiofilm Properties of ZnCexFe2−xO4 Nanoparticles (X = 0.0, 0.02, 0.04, 0.06, and 0.08) Conjugated with Ebselen and Its Role Subsidised with γ-Radiation in Mitigating Human TNBC and Colorectal Adenocarcinoma Proliferation In Vitro

Cancers are a major challenge to health worldwide. Spinel ferrites have attracted attention due to their broad theranostic applications. This study aimed at investigating the antimicrobial, antibiofilm, and anticancer activities of ebselen (Eb) and cerium-nanoparticles (Ce-NPs) in the form of ZnCe_xFe_2−XO₄ on human breast and colon cancer cell lines. Bioassays of the cytotoxic concentrations of Eb and ZnCe_xFe_2−XO₄, oxidative stress and inflammatory milieu, autophagy, apoptosis, related signalling effectors, the distribution of cells through the cell-cycle phases, and the percentage of cells with apoptosis were evaluated in cancer cell lines. Additionally, the antimicrobial and antibiofilm potential have been investigated against different pathogenic microbes. The ZOI, and MIC results indicated that ZnCe_xFe_2−XO₄; X = 0.06 specimen reduced the activity of a wide range of bacteria and unicellular fungi at low concentration including P. aeruginosa (9.5 mm; 6.250 µg/mL), S. aureus (13.2 mm; 0.390 µg/mL), and Candida albicans (13.5 mm; 0.195 µg/mL). Reaction mechanism determination indicated that after ZnCe_xFe_2−xO₄; X = 0.06 treatment, morphological differences in S. aureus were apparent with complete lysis of bacterial cells, a concomitant decrease in the viable number, and the growth of biofilm was inhibited. The combination of Eb with ZFO or ZnCe_xFe_2−XO₄ with γ-radiation exposure showed marked anti-proliferative efficacy in both cell lines, through modulating the oxidant/antioxidant machinery imbalance, restoring the fine-tuning of redox status, and promoting an anti-inflammatory milieu to prevent cancer progression, which may be a valuable therapeutic approach to cancer therapy and as a promising antimicrobial agent to reduce the pathogenic potential of the invading microbes.