Antimicrobial activity of a food-grade fully dilutable microemulsion against Escherichia coli and Staphylococcus aureus

Microemulsions are colloidal nanodispersions of oil and water stabilized by an interfacial film of surfactant molecules, typically in conjunction with a cosurfactant. There is a limited number of reports in the literature on microemulsion use for antimicrobial purposes. The physicochemical characterization of a food-grade fully dilutable microemulsion system with glycerol monolaurate (GML) as oil, organic acids as cosurfactant, Tween 80 as surfactant, and the antimicrobial activities against Escherichia coli and Staphylococcus aureus have been studied in this paper. The influence of organic acids on oil solubilization was clearly reflected in the phase behavior of these systems. Propionic acid demonstrated the greatest capability to improve the oil solubilization among the tested linear and nonlinear chain organic acids and contributed to the formation of U-type microemulsion systems. One microemulsion formulation with an average particle size of 8 nm was selected, the composition is GML/propionic acid/Tween 80/water = 3:9:8:12. The kinetics of killing experiments demonstrated that the undiluted microemulsion caused a complete loss of viability of E. coli or S. aureus cells in 1 min and still had effective bactericidal effects even when diluted, more than 99% viable E. coli cells were killed within 15 min and a complete loss of viability was achieved at 45 min while more than 99% viable S. aureus cells were killed within 30 min and a complete loss of viability was achieved at 60 min in the presence of the 10-fold diluted microemulsion. The fast killing kinetics of the ten-fold serial dilutions of microemulsions were in good agreement with the mode of action studies, indicating that the interaction between the antimicrobial microemulsions and bacterial membranes significantly decreased the bacterial cell surface hydrophobicity and induced the quick release of 260 nm absorbing materials. This work suggests the potential use of food-grade fully dilutable microemulsions for antimicrobial purposes in beverages or seafood products.     

In vitro and in vivo antifungal activity of a water-dilutable cassia oil microemulsion against Geotrichum citri-aurantii

BACKGROUND: Recently, food‐grade microemulsions have been of increasing interest to researchers and have shown great potential in industrial applications. In this study a food‐grade water‐dilutable microemulsion system with cassia oil as oil, ethanol as cosurfactant, Tween 20 as surfactant and water was developed and its antifungal activity in vitro and in vivo against Geotrichum citri‐aurantii was assessed. RESULTS: The phase diagram results confirmed the feasibility of forming a water‐dilutable microemulsion based on cassia oil. One microemulsion formulation, cassia oil/ethanol/Tween 20 = 1:3:6 (w/w/w), was selected with the capability to undergo full dilution with water. The average particle size was 6.3 nm. The in vitro antifungal experiments showed that the microemulsion inhibited fungal growth on solid medium and prevented arthroconidium germination in liquid medium and that cassia oil had stronger activity when encapsulated in the microemulsion. The in vivo antifungal experiments indicated that the water‐dilutable microemulsion was effective in preventing postharvest diseases of citrus fruits caused by G. citri‐aurantii. CONCLUSION: The results of this study suggest a promising utilisation of water‐dilutable microemulsions based on essential oils for the control of postharvest diseases. Copyright © 2012 Society of Chemical Industry     

聚甘油单月桂酸酯-油酸微乳体系的构建及其性能

为构建安全高效的微乳体系,提高姜黄素的溶解度,拓展微乳液及姜黄素在食品中的应用,制备具有较高姜黄素溶解度、可无限稀释的食品级微乳液。以油酸和不同聚合度的聚甘油单月桂酸酯、不同碳链长的醇为原料,通过对拟三元相图的分析,筛选表面活性剂和助表面活性剂,研究表面活性剂与助表面活性剂质量比（Km）、水相pH值和NaCl浓度对微乳体系相行为的影响,用电导率法分析微乳液的结构,用激光粒度仪和透射电镜测定观察微乳液滴的粒径、微观形貌。结果表明,以质量比为2∶1的六聚和十聚甘油单月桂酸酯复配为表面活性剂,以乙醇为助表面活性剂,Km=1/2,制备的微乳液效果最好,微乳区域面积占比最大,微乳液滴呈均一球形,粒径在10～100?nm之间。非中性的水相、NaCl的加入均会导致微乳区域面积占比的减小和最小可稀释比的增大。当表面活性剂与油相质量比为9∶1时,能够形成可无限稀释微乳体系,该体系结构在含水量小于45%时为W/O型,继续增加含水量,体系结构逐渐转变为双连续型,含水量超过60%时为O/W型。姜黄素微乳化不影响姜黄素生物活性,且姜黄素的溶解度可达4.87?mg/mL,可有效地解决姜黄素溶解性差、稀释性差的问题,说明微乳液是姜黄素的优良载体。     

Solubilisation of soybean oil in microemulsions using various surfactants

Microemulsions are transparent, isotropic solutions of oil, water and surfactant (and possibly cosurfactant) which are thermodynamically stable, and have been much studied in terms of pharmaceutical and cosmetic applications. However, the application of microemulsions in foods has been limited both due to toxic or irritant nature of ionic surfactants and the difficulty of solubilising large triglycerides. Three surfactants, food-grade ethoxylated mono- and diglycerides (EMD) and phospholipids, and non-food-grade polyoxyethylene oleyl ether (POE) were examined for their ability to form microemulsions using soybean oil, and their areas of formation expressed on phase diagrams. Microemulsions prepared with EMD and phospholipids required the presence of a short-chain alcohol for formation. Both oil/water (o/w) and water/oil (w/o) microemulsions could be formed using EMD, and the microemulsion area of the phase diagram increased on addition of sucrose and increase in temperature. Depending on sucrose and ethanol concentrations, microemulsions formed with EMD were found to retain their integrity at temperatures below which they formed. Microemulsions could be formed using phospholipids, but only at high surfactant concentration and in the presence of a short-chain alcohol. O/w microemulsions containing 10% oil (w/w) were prepared with POE at surfactant concentrations of >20% (w/w). Dynamic light scattering of microemulsion samples diluted with water indicated particle radii of 6.5 nm. Freeze-fracture SEM showed the structures to be of a droplet type, however, this was more evident at higher surfactant/oil concentrations. The results indicated that it is possible to formulate microemulsions at low EMD and POE surfactant concentration. These microemulsions systems may potentially be used for encapsulation of oil-soluble bioactives, e.g. α-tocopherol, in food systems.     

橄榄油微乳体系的相行为及影响因素研究

本文以大豆卵磷脂和司盘80(Span80)复配为表面活性剂,乙醇为助表面活性剂,构建橄榄油微乳体系。采用拟三元相图法,考察亲水亲油平衡值(HLB值)、表面活性剂与助表面活性剂的比值(Km值)、盐浓度等因素对微乳体系相行为的影响,并通过电导率、负染透射电镜等方法研究微乳体系的结构,以优化体系配方、考察微乳液的形成规律。结果表明:大豆卵磷脂与Span80以质量比为3:1复配为混合表面活性剂,并与助表面活性剂无水乙醇按质量比(Km值)为2:1混合,所形成的大豆卵磷脂/Span80/乙醇/橄榄油/水微乳区域面积最大;甘油或少量盐离子的加入,可以在一定程度上增大微乳单相区的面积,但当盐浓度(C_NaCl)大于4 mol/L时,微乳区域面积明显减小;在大豆卵磷脂/Span80/橄榄油/乙醇/甘油/水微乳体系中,当水相(w_水/w_甘油=1:1)含量大于22 wt%时,体系逐渐由W/O型转变为双连续型结构。当水相含量超过30 wt%,体系则发生相分离。此研究为橄榄油微乳液的制备及应用提供理论和技术支持。     

Optimizing the use of garlic oil as antimicrobial agent on fresh-cut tomato through a controlled release system

Encapsulation of garlic oil (GO) in β-cyclodextrin (β-CD) was undertaken to generate a release system of antimicrobial volatiles and tested on microbial growth and sensory quality of fresh-cut tomato. GO volatile profile was characterized by gas chromatography mass spectrometry and to demonstrate the disadvantages of applying free GO to fresh-cut tomato, the effect of different free oil treatments (0, 50, 100, and 200 μg/100 g) on microbial growth and sensorial quality was tested. The effect of GO capsules (0, 0.25, 0.5, and 1 g/100 g) on microbial growth and sensory quality of tomato was also investigated. Allyl disulfide was the most abundant GO compound identified. The release of volatiles from GO: β-CD capsules (12: 88 [w/w] ratio) was evaluated at 100% relative humidity (RH). Close to 70% of GO volatiles were released from capsules when exposed to 100% RH during 5 wk. The most effective antimicrobial concentrations of free oil (100 and 200 μg/100 g) applied to tomatoes did not present acceptable sensory quality for panelists. Tomato was affected by the highest concentration of GO capsules applied, showing the lowest microbial growth and the highest sensory quality. In this context, successful encapsulation in β-CD could stimulate further interest in the use of GO for the control of microbial growth in fresh-cut tomato. PRACTICAL APPLICATION: The present study demonstrated that relative humidity in-package of fresh-cut tomatoes can be used as a trigger to release antimicrobial garlic oil volatiles from β-cyclodextrin capsules, reducing microbial growth and the sensory effect of the treatment caused by the free garlic oil. In this context, successful encapsulation in β-cyclodextrin could stimulate further interest in the use of garlic oil for the control of microbial growth in fresh-cut tomatoes.     

丁香油的微乳液研究

研究了盐(NaCl)对于香油微乳液体系相态的影响,结果表明,随NaCl浓度的增加,体系由2相态(O/W型微乳液-丁香油)经3相态、4相态、3相态再转变成2相态(W/O型微乳液-水)。电导实验结果表明用正丁醇做助表面活性剂时,体系发生电导渗透(6.0ml水),在含水量为18.0ml时完全相反转(即由W/O型转变为O/W型),并可以获得较为稳定的O/W型丁香油微乳液。     

Antimicrobial,Rheological, and Thermal Properties of Plasticized Polylactide Films Incorporated with Essential Oils to Inhibit Staphylococcus aureus and Campylobacter jejuni

Polylactide (PLA) is the most mature biobased and biodegradable polymer. Due to its inherent brittleness, the polymer cannot be used as a packaging material without plasticizer. An attempt was made to develop antimicrobial plasticized PLA film by incorporating polyethylene glycol (PEG) and 3 essential oils (EO), namely cinnamon, garlic, and clove by solvent casting method. Physical, thermal, and rheological properties of those films were evaluated for practical applications whereas the antimicrobial properties were tested against Staphylococcus aureus and Campylobacter jejuni—pathogens related to poultry industry. Both PEG and EOs led to the formation of flexible PLA/PEG/EO films with significant drop in the glass transition temperature (T_g), and mechanical property. Time–temperature superposition (TTS) principle was employed to melt rheology of EO‐based films at selected temperature, and rheological moduli superimposed well in an extended frequency range. Among EOs, cinnamon and clove oil–based films (PLA/PEG/CIN and PLA/PEG/CLO) exhibited a complete zone of inhibition against C. jejuni at the maximum concentration (1.6 mL per 2 g PLA/PEG blend) whereas the garlic oil–based film (PLA/PEG/GAR) had the lowest activity.     

Characteristics of microcapsule of red ginger (Zingiber officinale var. Rubrum) essential oil produced from different Arabic gum ratios on antimicrobial activity toward Escherichia coli and Staphylococcus aureus

Essential oil has antimicrobial activity. Encapsulation of essential oil might affect its antimicrobial activity. The present study was aimed to study the characteristic of red ginger essential oil microcapsule obtained from varying Arabic gum ratios on the growth inhibition of E. coli dan S. aureus. Red ginger essential oil from steam distillation was coated using Arabic gum with ratio 1:3, 1:4, 1:5 (w/b). The 1:3 (v/w) ratio of red ginger essential oil and Arabic gum showed the best microcapsule characteristics with average inhibition diameter zones 5.67 mm for E. coli and 6.67 mm for S. aureus, and reduction of bacterial count for E. coli 1.8 log CFU/g and S. aureus 2.3 log CFU/g, yield of microcapsule 51.54%, water activity 0.207, water content 3.57%, solubility 97.46%, surface oil 0.08%, and particle size 258.2 µm. The major component of red ginger essential oil was ar-curcumene, zingiberen, β-bisabolene, β-sesquiphellandrene, and camphene.     

凉粉草精油微乳液抗氧化和抗A375细胞增殖活性

本实验以凉粉草为原料,通过水蒸气蒸馏法提取得到凉粉草精油,并运用气相色谱-质谱联用仪进行组成分析,依据峰面积计算得到相对含量较高的组分为香树烯（25.53%）、β-石竹烯（19.31%）、异石竹烯（11.30%）、甲位葎草烯（8.30%）、佛术烯（7.62%）。通过伪三元相图筛选得到以吐温60为表面活性剂,乙醇为助表面活性剂,表面活性剂与助表面活性剂质量比（Km）为2∶1,混合表面活性剂与油相的质量比（Smix）为8∶2的凉粉草精油微乳液,且该微乳液经100、200 倍稀释后仍保持稳定。凉粉草精油经微乳液包埋后的抗氧化活性得到不同程度的提高,其1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）自由基清除能力略有提升,氧自由基吸收能力（oxygen radical absorbance capacity,ORAC）和过氧自由基清除能力（peroxyl radical scavenging capacity,PSC）分别提升为原来的2.6 倍和8.4 倍。此外,微乳液包埋同样提高了凉粉草精油对人恶性黑色素瘤细胞A375的增殖抑制作用,凉粉草精油微乳化后的半数效应质量浓度约为原来的1/5。综上,微乳液包埋较好地提升了凉粉草精油在水环境的抗氧化和抗A375细胞增殖活性,为凉粉草资源的高值化开发与利用提供了理论依据。     

鱼油微乳液的制备与特性研究

目的制备鱼油微乳液并研究其特性。方法采用食用大豆油和丙三醇作为鱼油的油相溶剂,失水山梨醇油酸酯聚氧乙烯醚(Tween 80)和乳糖(9:1,w/w)为表面活性剂相,制备了O/W型鱼油微乳液。拟三元相图法考察了盐度和pH对微乳液区的影响,测定了鱼油微乳的电导率变化和粒径大小,研究了微乳液的流变特性。结果该鱼油微乳液具有较好的耐酸性和耐盐性,平均粒径在10～100 nm之间,稳定性良好。流变特性研究表明表面活性剂相和油相质量比为9∶1,含水量80%(w/w)的鱼油微乳液具有剪切变稀的流变行为,属于拟塑性流体。结论鱼油微乳液制备简便,稳定性良好,是包封鱼油的新方法。     

Antimicrobia activity of garlic (Allium sativum L.) and holy basil (Ocimum sanctum L.) essential oils applied by liquid vs. vapour phases

Antimicrobial activity of garlic (Allium sativum L.) and holy basil (Ocimum sanctum L.) essential oils (GEO and HBEO, respectively) was evaluated in liquid vs. vapour phases. Diallyl disulphide and diallyl trisulphide in GEO while eugenol, caryophyllene and methyl eugenol in HBEO were predominant active compounds. Individually, GEO was highly effective in the vapour phase, showing the greatest antimicrobial activity (P ≤ 0.05) against Bacillus cereus and Staphylococcus aureus with complete inhibition, followed by Salmonella typhimurium and Pseudomonas fluorescens, but had no effect on Escherichia coli, Lactobacillus plantarum or Listeria monocytogenes. The combined GEO:HBEO (a 1:1 ratio) at 30 μL demonstrated inhibitive activity against all bacteria tested with complete inhibition against B. cereus and S. aureus. Minimum bactericidal concentration (MBC) of the combined oil was <0.4% v/v, except for P. fluorescens requiring a higher MBC (1.5%, v/v). This study demonstrated potential of the combined GEO:HBEO to be used for food preservation applications.     

棕榈仁油/甘油/吐温/水体系中的微乳化作用研究

分别以吐温-20、吐温-40、吐温-60、吐温-80和吐温-85为表面活性剂,甘油为助表面活性剂,在相同的条件下,制作了棕榈仁油/甘油/吐温/水四组分体系的拟三元相图.讨论了助表面活性剂(醇)与表面活性剂的质量比(Km)及不同表面活性剂对混合体系微乳化作用的影响.结果表明,所研究的各体系中,以吐温-60所形成的微乳状液区最大.     

Thyme Oil Encapsulated in Halloysite Nanotubes for Antimicrobial Packaging System

An antimicrobial capsule releasing thyme oil was developed using modified halloysite nanotubes (HNTs). In order to increase the pore volume, HNTs were treated with 5.0 mol/L NaOH solution, which resulted in the encapsulation of more thyme oil molecules inside the HNTs. The morphology of the raw HNTs and NaOH‐treated HNTs (N‐HNTs) was characterized using transmission electron microscopy and nitrogen adsorption‐desorption analysis. The loading capacity increased from 180.7 ± 12.7 to 256.4 ± 16.7 mg thyme oil/g HNT after the NaOH treatment. The aerial release characteristics of thyme oil from both the HNT capsules were investigated in a closed‐package atmosphere system at 4, 25, and 40 °C. The antimicrobial activity of the capsule against Escherichia coli O157:H7 was determined using the vapor phase assay. Moreover, the antimicrobial effects of the capsule against E. coli O157:H7, total mesophilic aerobic bacteria (MAB), and molds and yeasts (MY) on the surfaces of cherry tomatoes were investigated at 4 and 25 °C for 5 d. When the cherry tomatoes were exposed to the thyme oil‐loaded N‐HNT capsule, the number of E. coli O157:H7, MAB, and MY significantly reduced during storage.     

Chemical Composition and Antioxidative Activity of Echinophora platyloba DC. Essential Oil,and Its Interaction with Natural Antimicrobials against Food‐Borne Pathogens and Spoilage Organisms

Abstract: This study was undertaken to determine the chemical composition and antioxidative capacity of Echinophora platyloba DC. essential oil, and its antimicrobial potency against Listeria monocytogenes, Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Salmonella typhimurium, Escherichia coli O157:H7, Pseudomonas aeruginosa, Candida albicans, Candida tropicalis, Rhodotorula rubra, and Rhodotorula mucilaginosa. The essential oil was analyzed by GC and GC‐MS; and evaluated for its antioxidative and antimicrobial (singly or in combination with chitosan, nisin, monolaurin, or amphotericin B) activity. Thirty‐three components were characterized representing 95.69% of the total oil composition in which thymol, trans‐ocimene, carvacrol, and (E)‐sesqui‐lavandulol were the major constituents. The oil exhibited high scavenging (IC₅₀: 49.7 ± 2.3 μg/mL) and relative antioxidative activity (RAA%: 85.21 ± 0.4) in 1,1‐diphenyl‐2‐picrylhydrazyl radicals and β‐carotene/linoleic acid bleaching assays, respectively. The oil showed antimicrobial activity against L. monocytogenes, B. cereus, B. subtilis, S. aureus, S. typhimurium, E. coli O157:H7, P. aeruginosa, C. albicans, C. tropicalis, R. Rubra, and R. mucilaginosa. Moreover, R. mucilaginosa and P. aeruginosa were the most susceptible and most resistant organisms, respectively. Regarding the checkerboard data, 47 fractional inhibitory concentration index (FICIs) (≤0.5) indicated synergistic, whereas 7 FICIs (>0.5 to 1) indicated additive effect. Consequently, E. platyloba DC. essential oil could be used as a recommended natural antioxidant and antimicrobial substance for food preservation.     

Antibacterial PVP/cinnamon essential oil nanofibers by emulsion electrospinning

This study presents the production of antibacterial Polyvinylpyrrolidone/cinnamon essential oil (PVP/CEO) nanofibers by oil-in-water emulsion electrospinning, with solution properties such as GC-MS, conductivity, viscosity, and characterization using SEM (fiber morphology), FT-IR (chemical structure), UV-vis (release properties of CEO). In addition, the antimicrobial properties of the nanofibers are also investigated by the disc diffusion method (antimicrobial properties) using Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. According to the results, the viscosity values increase with the addition of surfactant and with increased CEO concentration, but the conductivity increases until PVP1 then has decrease tendency. As concerns the fiber properties, the average fiber diameter increased with surfactant addition and CEO concentration except for PVP4. Also, the spinnability and fiber smoothness were enhanced significantly with surfactant and CEO. FT-IR analysis results verified the existence of CEO and PVP in the structure of the nanofibers. The absorbance values increased with the CEO concentration except for PVP4. Lastly, the antimicrobial results showed that 2, 3, and 4 wt% CEO concentration values are suitable for good antibacterial properties, while there is no zone formation with 1 wt% CEO concentration of PVP nanofibers. It is another important result that the antibacterial activity increases with the size of the nanofibrous material.     

ENHANCEMENT OF ANTIMICROBIAL ACTIVITIES BY THE FOOD-GRADE MONOLAURIN MICROEMULSION SYSTEM

Monolaurin (M) is a potential natural antimicrobial agent used in foods. It is considered to have an antimicrobial activity against gram-positive bacteria. A monolaurin microemulsion (MME) system inhibited the growth of Bacillus subtilis, Escherichia coli, Aspergillus niger and Penicillium digitatum . Microemulsions (MEs) are transparent, isotropic solutions of oil, surfactant, cosurfactant and water, which are thermodynamically stable and have been much studied in terms of pharmaceutical and cosmetic applications. The growth of B. subtilis was inhibited more strongly by MME than by M. A similar pattern was observed for E. coli, A. niger and P. digitatum , although an enhanced inhibition by MME system over that obtained in comparable M alone was not observed.

PRACTICAL APPLICATIONS

Monolaurin is considered to have an antimicrobial activity against gram-positive bacteria but not against gram-negative bacteria. A monolaurin microemulsion system inhibited the growth of Bacillus subtilis , Escherichia coli , Aspergillus niger and Penicillium digitatum , and will be regarded as a "natural" antimicrobial preservative.     

Antimicrobial effect of food-grade GML microemulsions against Staphylococcus aureus

Food-grade GML (Glycerol Monolaurate, the glycerol monoester of lauric acid) microemulsions based on multi-component mixtures and enhanced antimicrobial effects have been studied. The compositions included water, GML, several surfactants (ethoxylated sorbitan esters, sucrose esters), alcohols (pentanol and dodecanol), salt (potassium sorbate). The influence of surfactants, alcohols and salt on the phase behavior is discussed in this paper. Four improved formulations of microemulsion systems with large O/W regions have been obtained and demonstrated the enhanced antimicrobial activities against Staphylococcus aureus, compared to Glycerol Monolaurate. Subsequently, one formulation with the highest antimicrobial activity was further studied with respect to the influence of each component on the antimicrobial effect. The results showed that among all the components, GML had the significantly highest (P < 0.01) inhibition ratio 63.52% and played a dominating role in the antimicrobial activities. Therefore, it was concluded that food-grade GML microemulsions had enhanced antimicrobial activities against S. aureus, with a major contribution of GML.     

Formulation of a cosurfactant-free O/W microemulsion using nonionic surfactant mixtures

ABSTRACT:  A cosurfactant-free O/W microemulsion composed of oil, a mixture of hydrophilic and hydrophobic surfactants, and water has been developed using food-grade components as a nutrient delivery system. We started our investigation to monitor the phase behavior of this system based on a hydrophilic surfactant (Tween 80). From a phase diagram, the weight ratio of 5.4:33.8:60.8 = oil:surfactant:water was selected as a combination ratio for the O/W microemulsion system. We also investigated the combination effect of different hydrophobic surfactants to Tween 80 on microemulsion formation. Use of hydrophobic surfactants with Tween 80 produced smaller droplets than Tween 80 alone. Rheological studies showed that all microemulsions followed shear-thinning behavior. The turbidity of microemulsions did not change after accelerated stability tests, indicating that this microemulsion system was stable under the given harsh conditions. When docosahexaenoic acid (DHA) oil was applied to this microemulsion system, the particle size and the turbidity were not significantly changed. Dilution with a different aqueous medium, either water or acidic fluid, did not significantly change the microemulsion turbidity. DHA oil incorporated in microemulsion showed higher oxidation stability than free DHA oil.     

Atomic force microscopy study of the antimicrobial activity of aqueous garlic versus ampicillin against Escherichia coli and Staphylococcus aureus

BACKGROUND: In this study the effects of ampicillin and aqueous garlic extract on Escherichia coli (ATCC 9637) and Staphylococcus aureus (ATCC 25923) were compared. Atomic force microscopy (AFM) was used to study the possible mechanisms of membrane disruption. RESULTS: Ampicillin disrupted the cell membrane of E. coli, inducing pores and cell leakage. Aqueous garlic extract also induced leakage from the cell membrane in E. coli, but no pores were observed. The trend in Young's modulus for E. coli was E_native ≈ E_age > E_amp. In contrast, S. aureus incubated with low ampicillin (≤50µg mL^?1) and garlic (≤50 mg mL^?1) concentrations showed no significant changes in surface morphology compared with the untreated bacterium. The trend in Young's modulus for S. aureus was E_native ≈ E_age ≈ E_amp. CONCLUSION: The trend E_native ≈ E_age for E. coli and S. aureus supports the hypothesis that the compounds in garlic show intracellular activity. This proof‐of‐concept study of the aqueous crude isolate of garlic points to the feasibility of further AFM investigations to compare the antimicrobial properties of various pure thiosulfinate isolates found in garlic. Copyright © 2009 Society of Chemical Industry