Adhesion and removal kinetics of Bacillus cereus biofilms on Ni-PTFE modified stainless steel

Biofilm control remains a challenge to food safety. A well-studied non-fouling coating involves codeposition of polytetrafluoroethylene (PTFE) during electroless plating. This coating has been reported to reduce foulant build-up during pasteurization, but opportunities remain in demonstrating its efficacy in inhibiting biofilm formation. Herein, the initial adhesion, biofilm formation, and removal kinetics of Bacillus cereus on Ni-PTFE-modified stainless steel (SS) are characterized. Coatings lowered the surface energy of SS and reduced biofilm formation by > 2 log CFU cm^?2. Characterization of the kinetics of biofilm removal during cleaning demonstrated improved cleanability on the Ni-PTFE coated steel. There was no evidence of biofilm after cleaning by either solution on the Ni-PTFE coated steel, whereas more than 3 log and 1 log CFU cm^?2 of bacteria remained on the native steel after cleaning with water and an alkaline cleaner, respectively. This work demonstrates the potential application of Ni-PTFE non-fouling coatings on SS to improve food safety by reducing biofilm formation and improving the cleaning efficiency of food processing equipment.     

Sessile Legionella pneumophila is able to grow on surfaces and generate structured monospecies biofilms

Currently, models for studying Legionella pneumophila biofilm formation rely on multi-species biofilms with low reproducibility or on growth in rich medium, where planktonic growth is unavoidable. The present study describes a new medium adapted to the growth of L. pneumophila monospecies biofilms in vitro. A microplate model was used to test several media. After incubation for 6 days in a specific biofilm broth not supporting planktonic growth, biofilms consisted of 5.36 ± 0.40 log (cfu cm^?2) or 5.34 ± 0.33 log (gu cm^?2). The adhered population remained stable for up to 3 weeks after initial inoculation. In situ confocal microscope observations revealed a typical biofilm structure, comprising cell clusters ranging up to ～300 μm in height. This model is adapted to growing monospecies L. pneumophila biofilms that are structurally different from biofilms formed in a rich medium. High reproducibility and the absence of other microbial species make this model useful for studying genes involved in biofilm formation.     

Biofilm formation by the yeast Rhodotorula mucilaginosa: process,repeatability and cell attachment in a continuous biofilm reactor

Yeast biofilms contribute to quality impairment of industrial processes and also play an important role in clinical infections. Little is known about biofilm formation and their treatment. The aim of this study was to establish a multi-layer yeast biofilm model using a modified 3.7 l bench-top bioreactor operated in continuous mode (D = 0.12 h^?1). The repeatability of biofilm formation was tested by comparing five bioprocesses with Rhodotorula mucilaginosa, a strain isolated from washing machines. The amount of biofilm formed after 6 days post inoculation was 83 μg cm^?2 protein, 197 μg cm^?2 polysaccharide and 6.9 × 10⁶ CFU cm^?2 on smooth polypropylene surfaces. Roughening the surface doubled the amount of biofilm but also increased its spatial variability. Plasma modification of polypropylene significantly reduced the hydrophobicity but did not enhance cell attachment. The biofilm formed on polypropylene coupons could be used for sanitation studies.     

Comparison of selected disinfectants efficiency against <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> biofilm formed on various surfaces

Listeria monocytogenes is a main etiological factor of listeriosis, spread mainly by food products. In recent years, an increasing number of patients with listeriosis and an augmentation in L. monocytogenes antibiotic resistance, e.g. to penicillin and ampicillin, has been reported. The aim of the study was to characterise the L. monocytogenes strains isolated from fish-processed food products. Species identification, based on the multiplex-PCR reaction, was performed, and the genetic similarity of the isolates was analysed with the RAPD technique. The strains, in the form of planktonic cells and a biofilm, were subjected to drug-susceptibility analysis, and the effect of disinfectants on the bacillus cells was evaluated. All of the analysed strains were of the Listeria monocytogenes species. Three genetically distant strains were detected, i.e. Lm I, Lm II and Lm III. Approximately 66.6% penicillin-resistant and 66.6% cotrimoxazole-resistant strains were found. No erythromycin-resistant strain was detected. The Lm II strain was simultaneously resistant to four antibiotics, i.e. penicillin, ampicillin, meropenem and cotrimoxazole. The strongest biofilm was formed on aluminium foil and the weakest on rubber. The tested disinfectant antibiofilm effectiveness was related to the type of surface. The most effective agent was paracetic acid and hydrogen peroxide (elimination rate 5.10–6.62 log CFU?×?cm^?2 and 5.70–7.39 log CFU?×?cm^?2 after 1- and 5-min exposure, respectively) and the least—sodium hydroxide (elimination rate 0.52–1.20 log CFU?×?cm^?2 and 0.98–1.81 log CFU?×?cm^?2 after 1- and 5-min exposure, respectively). Further studies on a greater number of L. monocytogenes strains are recommended.     

Listeria monocytogenes Can Form Biofilms in Tap Water and Enter Into the Viable but Non-Cultivable State

Listeria monocytogenes is a foodborne pathogen that can be transmitted through contaminated raw food or by ready-to-eat products that have been in contact with contaminated surfaces. Tap water (TW) is used to wash produce, as a processed food constituent and to wash processing surfaces and floors. The main aim of this work was to investigate the formation and survival of L. monocytogenes biofilms on stainless steel (SS) coupons in TW at 4, 22, 30 and 37 °C. For that, coupons with biofilm were visualised in situ while other coupons were scraped to quantify total cells by SYTO 9, cultivable numbers by plating onto brain heart infusion agar and viable numbers by the direct viable count method. Results showed that L. monocytogenes can form biofilms on SS surfaces in TW at any temperature, including at 4 °C. The number of total cells was similar for all the conditions tested while cultivable numbers varied between the level of detection (<8.3 CFU cm^?2) and 3.5?×?10⁵ CFU cm^?2, meaning between 7.0?×?10⁴ and 1.1?×?10⁷ cells cm^?2 have entered the viable but non-cultivable (VBNC) state. This work clearly demonstrates that L. monocytogenes can form biofilms in TW and that sessile cells can remain viable and cultivable in some conditions for at least the 48 h investigated. On the other hand, VBNC adaptation suggests that the pathogen can remain undetectable using traditional culture recovery techniques, which may give a false indication of processing surface hygiene status, leading to potential cross-contamination of food products.     

Kinetics of biofilm formation and desiccation survival of Listeria monocytogenes in single and dual species biofilms with Pseudomonas fluorescens,Serratia proteamaculans or Shewanella baltica on food-grade stainless steel surfaces

This study investigated the dynamics of static biofilm formation (100% RH, 15 °C, 48–72 h) and desiccation survival (43% RH, 15 °C, 21 days) of Listeria monocytogenes, in dual species biofilms with the common spoilage bacteria, Pseudomonas fluorescens, Serratia proteamaculans and Shewanella baltica, on the surface of food grade stainless steel. The Gram-negative bacteria reduced the maximum biofilm population of L. monocytogenes in dual species biofilms and increased its inactivation during desiccation. However, due to the higher desiccation resistance of Listeria relative to P. fluorescens and S. baltica, the pathogen survived in greater final numbers. In contrast, S. proteamaculans outcompeted the pathogen during the biofilm formation and exhibited similar desiccation survival, causing the N_{21 days} of Serratia to be ca 3 Log₁₀(CFU cm^?2) greater than that of Listeria in the dual species biofilm. Microscopy revealed biofilm morphologies with variable amounts of exopolymeric substance and the presence of separate microcolonies. Under these simulated food plant conditions, the fate of L. monocytogenes during formation of mixed biofilms and desiccation depended on the implicit characteristics of the co-cultured bacterium.     

Influence of biofilms on iron and manganese deposition in drinking water distribution systems

Although health risk due to discoloured water is minimal, such water continues to be the source of one of the major complaints received by most water utilities in Australia. Elevated levels of iron (Fe) and/or manganese (Mn) in bulk water are associated with discoloured water incidents. The accumulation of these two elements in distribution systems is believed to be one of the main causes for such elevated levels. An investigation into the contribution of pipe wall biofilms towards Fe and Mn deposition, and discoloured water events is reported in this study. Eight laboratory-scale reactors were operated to test four different conditions in duplicate. Four reactors were exposed to low Fe (0.05?mg?l^?1) and Mn (0.02?mg?l^?1) concentrations and the remaining four were exposed to a higher (0.3 and 0.4?mg?l^?1 for Fe and Mn, respectively) concentration. Two of the four reactors which received low and high Fe and Mn concentrations were chlorinated (3.0?mg?l^?1 of chlorine). The biological activity (measured in terms of ATP) on the glass rings in these reactors was very low (～1.5 ng cm^?2 ring). Higher concentrations of Fe and Mn in bulk water and active biofilms resulted in increased deposition of Fe and Mn on the glass rings. Moreover, with an increase in biological activity, an increase in Fe and Mn deposition was observed. The observations in the laboratory-scale experiments were in line with the results of field observations that were carried out using biofilm monitors. The field data additionally demonstrated the effect of seasons, where increased biofilm activities observed on pipe wall biofilms during late summer and early autumn were found to be associated with increased deposition of Fe and Mn. In contrast, during the cooler months, biofilm activities were a magnitude lower and the deposited metal concentrations were also significantly less (ie a drop of 68% for Fe and 86% for Mn). Based on the laboratory-scale investigations, detachment of pipe wall biofilms due to cell death or flow dynamics could release the entrapped Fe and Mn into the bulk water, which could lead to a discoloured water event. Hence, managing biofilm growth on drinking water pipelines should be considered by water utilities to minimize accumulation of Fe and Mn in distribution networks.     

Aggregatibacter actinomycetemcomitans biofilm killing by a targeted ciprofloxacin prodrug

A pH-sensitive ciprofloxacin prodrug was synthesized and targeted against biofilms of the periodontal pathogen Aggregatibacter actinomycetemcomitans (Aa). The dose required to reduce the viability of a mature biofilm of Aa by ～80% was in the range of ng?cm^?2 of colonized area (mean biofilm density 2.33?×?10⁹?cells?cm^?2). A mathematical model was formulated that predicts the temporal change in the concentration of ciprofloxacin in the Aa biofilm as the drug is released and diffuses into the bulk medium. The predictions of the model were consistent with the extent of killing obtained. The results demonstrate the feasibility of the strategy to induce mortality, and together with the mathematical model, provide the basis for design of targeted antimicrobial prodrugs for the topical treatment of oral infections such as periodontitis. The targeted prodrug approach offers the possibility of optimizing the dose of available antimicrobials in order to kill a chosen pathogen while leaving the commensal microbiota relatively undisturbed.     

Continuous flow system for biofilm formation using controlled concentrations of Pseudomonas putida from chicken carcass and coupled to electrochemical impedance detection

Abstract

Most studies dealing with monitoring the dynamics of biofilm formation use microbial suspensions at high concentrations. These conditions do not always represent food or water distribution systems. A continuous flow system capable of controlling the concentration of the microbial suspension stream from 10⁴ to 10⁶ CFU ml^?1 is reported. Pseudomonas putida biofilms formed using 100-fold, 1,000-fold or 10,000-fold diluted bacterial suspensions were monitored in-line by electrochemical impedance spectroscopy (EIS) and total plate counts. Randles equivalent circuit model and a modified Randles model with biofilm elements were used to fit the EIS data. In Randles equivalent circuit, the charge transfer resistance decreased as the biofilm formed. The log colony counts of the biofilm correlated to the charge transfer resistance. In the biofilm model, the biofilm resistance and the double layer capacitance decreased as the biofilm formed. The log colony counts of the biofilm correlated to the biofilm resistance.     

Multi-species biofilms defined from drinking water microorganisms provide increased protection against chlorine disinfection

A model biofilm, formed of multiple species from environmental drinking water, including opportunistic pathogens, was created to explore the tolerance of multi-species biofilms to chlorine levels typical of water-distribution systems. All species, when grown planktonically, were killed by concentrations of chlorine within the World Health Organization guidelines (0.2–5.0?mg?l^?1). Higher concentrations (1.6–40-fold) of chlorine were required to eradicate biofilm populations of these strains, ～70% of biofilms tested were not eradicated by 5.0?mg?l^?1 chlorine. Pathogenic bacteria within the model multi-species biofilms had an even more substantial increase in chlorine tolerance; on average ～700–1100?mg?l^?1 chlorine was required to eliminate pathogens from the biofilm, 50–300-fold higher than for biofilms comprising single species. Confocal laser scanning microscopy of biofilms showed distinct 3D structures and multiple cell morphologies and arrangements. Overall, this study showed a substantial increase in the chlorine tolerance of individual species with co-colonization in a multi-species biofilm that was far beyond that expected as a result of biofilm growth on its own.     

Antimicrobial mechanism and the effect of atmospheric pressure N2 plasma jet on the regeneration capacity of Staphylococcus aureus biofilm

Abstract

This study systematically assessed the inactivation mechanism on Staphylococcus aureus biofilms by a N₂ atmospheric-pressure plasma jet and the effect on the biofilm regeneration capacity from the bacteria which survived, and their progenies. The total bacterial populations were 7.18?±?0.34 log10 CFU ml^?1 in biofilms and these were effectively inactivated (>5.5-log10 CFU ml^?1) within 30?min of exposure. Meanwhile, >80% of the S. aureus biofilm cells lost their metabolic capacity. In comparison, ～20% of the plasma-treated bacteria entered a viable but non-culturable state. Moreover, the percentage of membrane-intact bacteria declined to ～30%. Scanning electron microscope images demonstrated cell shrinkage and deformation post-treatment. The total amount of intracellular reactive oxygen species was observed to have significantly increased in membrane-intact bacterial cells with increasing plasma dose. Notably, the N₂ plasma treatment could effectively inhibit the biofilm regeneration ability of the bacteria which survived, leading to a long-term phenotypic response and dose-dependent inactivation effect on S. aureus biofilms, in addition to the direct rapid bactericidal effect.     

Thermal mitigation of Pseudomonas aeruginosa biofilms

Bacterial biofilms infect 2–4% of medical devices upon implantation, resulting in multiple surgeries and increased recovery time due to the very great increase in antibiotic resistance in the biofilm phenotype. This work investigates the feasibility of thermal mitigation of biofilms at physiologically accessible temperatures. Pseudomonas aeruginosa biofilms were cultured to high bacterial density (1.7?×?10⁹ CFU cm^?2) and subjected to thermal shocks ranging from 50°C to 80°C for durations of 1–30 min. The decrease in viable bacteria was closely correlated with an Arrhenius temperature dependence and Weibull-style time dependence, demonstrating up to six orders of magnitude reduction in bacterial load. The bacterial load for films with more conventional initial bacterial densities dropped below quantifiable levels, indicating thermal mitigation as a viable approach to biofilm control.     

Cleaning and decontamination efficacy of wiping cloths and silver dihydrogen citrate on food contact surfaces

Aims: To test the efficacy of four wipe cloth types (cotton bar towel, nonwoven, microfibre and blended cellulose/cotton) with either quaternary ammonia cleaning solution or silver dihydrogen citrate (SDC) in cleaning food contact surfaces. Methods: Swab samples collected from untreated, cloth‐treated and cloth disinfectant‐treated surfaces were subjected to hygiene monitoring using adenosine triphosphate (ATP) bioluminescence and aerobic total plate counting (TPC) assays. Results: Adenosine triphosphate measurements taken after wiping the surfaces showed poor cleaning by nonwoven cloths (2·89 RLU 100 cm^?2) than the microfibre (2·30 RLU 100 cm^?2), cotton terry bar (2·26 RLU 100 cm^?2) and blended cellulose/cotton cloth types (2·20 RLU 100 cm^?2). The cellulose/cotton cloth showed highest log reduction in ATP‐B RLU values (95%) and CFU values (98·03%) when used in combination with SDC disinfectant. Conclusions: Cleaning effect of wiping cloths on food contact surfaces can be enhanced by dipping them in SDC disinfectant. ATP‐B measurements can be used for real‐time hygiene monitoring in public sector, and testing microbial contamination provides more reliable measure of cleanliness. Significance and Impact of the Study: Contaminated food contact surfaces need regular hygiene monitoring. This study could help to estimate and establish contamination thresholds for surfaces at public sector facilities and to base the effectiveness of cleaning methods.     

Colorimetric assay for biofilms in wet processing conditions

Controlling bacterial biofilms is necessary for food safety and industrial processing in clean room environments. Our goal was to develop a method to quantitatively measure biofilm produced by pathogens under wet poultry production and processing conditions. Stainless steel and glass coupons were incubated in aqueous media containing reduced nutrients and exposed to Listeria monocytogenes under static temperature and humidity conditions. Samples were measured separately by biofilm assay and viable cell density, and then confirmed by spectrophotometry and microscopy. The biofilm assay resulted in different t groupings from the cell density. The mean from the biofilm assay was 0.50, and the error% was 0.595. The mean of the log₁₀ density (cfu/cm²) was 5.90, and the standard deviation ranged from 0.127 to 0.438 on 24 coupons. The typical sequence of biofilm development, followed by microscopy of biofilm grown on glass coupons, exhibited a change from dispersed single cells to an all-over pattern of clumps with few dispersed cells. L. monocytogenes formed biofilms on all of the substrata tested. Bacterial counts from planktonic cultures at 24, 48, 72, and 144 h confirmed that L. monocytogenes remained viable throughout the experiment and reached equilibrium between 6 and 24 h. The cell density log₁₀/ml was 8.01, 8.03, 7.69, and 6.66, respectively; and the standard deviation ranged from 0.156 to 0.394. The data will be used to grow stable biofilms of Listeria spp. collected from the food processing environment for further study. This is the first use of the crystal violet assay for measurement of bacterial biofilms on stainless steel under these conditions. The methods tested are applicable to other bacteria and substrata.     

Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces

The aim of the present work was to explore possibilities of photocatalytic TiO₂ coating for reducing biofilms on non-living surfaces. The model organism, Deinococcus geothermalis, known to initiate growth of durable, colored biofilms on machine surfaces in the paper industry, was allowed to form biofilms on stainless steel, glass and TiO₂ film coated glass or titanium. Field emission electron microscopy revealed that the cells in the biofilm formed at 45°C under vigorous shaking were connected to the surface by means of numerous adhesion threads of 0.1--0.3 μm in length. Adjacent cells were connected to one another by threads of 0.5--1 μm in length. An ultrastructural analysis gave no indication for the involvement of amorphous extracellular materials (e.g., slime) in the biofilm. When biofilms on photocatalytic TiO₂ surfaces, submerged in water, were exposed to 20 W h m⁻² of 360 nm light, both kinds of adhesion threads were completely destroyed and the D. geothermalis cells were extensively removed (from >10⁷ down to below 10⁶ cells cm⁻²). TiO₂ films prepared by the sol-gel technique were slightly more effective than those prepared by the ALD technique. Doping of the TiO₂ with sulfur did not enhance its biofilm-destroying capacity. The results show that photocatalytic TiO₂ surfaces have potential as a self-cleaning technology for warm water using industries.     

Influence of surface copper content on Stenotrophomonas maltophilia biofilm control using chlorine and mechanical stress

Abstract

This work aimed to evaluate the action of materials with different copper content (0, 57, 96 and 100%) on biofilm formation and control by chlorination and mechanical stress. Stenotrophomonas maltophilia isolated from drinking water was used as a model microorganism and biofilms were developed in a rotating cylinder reactor using realism-based shear stress conditions. Biofilms were characterized phenotypically and exposed to three control strategies: 10?mg l^?1 of free chlorine for 10?min, an increased shear stress (a fluid velocity of 1.5?m s^?1 for 30s), and a combination of both treatments. These shock treatments were not effective in biofilm control. The benefits from the use of copper surfaces was found essentially in reducing the numbers of non-damaged cells. Copper materials demonstrated better performance in biofilm prevention than chlorine. In general, copper alloys may have a positive public health impact by reducing the number of non-damaged cells in the water delivered after chlorine exposure.     

Quantification of water and biomass in small colony variant PAO1 biofilms by confocal Raman microspectroscopy

The Raman spectra, water content, and biomass density of wild-type (WT) Pseudomonas aeruginosa PAO1, small colony variant (SCV) PAO1, and Pseudoalteromonas sp. NCIMB 2021 biofilms were compared in order to determine their variation with strain and species. Living, fully submerged biofilms were analyzed in situ by confocal Raman microspectroscopy for up to 2 weeks. Water to biomass ratios (W/BRs), which are the ratios of the O–H stretching vibration of water at 3,450 cm⁻¹ to the C–H stretching band characteristic of biomass at 2,950 cm⁻¹, were used to estimate the biomass density and cell density by comparison with W/BRs of protein solutions and bacterial suspensions, respectively, on calibration curves. The hydration within SCV biofilm colonies was extremely heterogeneous whereas W/BRs were generally constant in young WT biofilm colonies. The mean biomass in biofilm colonies of WT or colony cores of SCV was typically equivalent to 16% to 27% protein (w/v), but was 10% or less for NCIMB 2021. The corresponding cell densities were 7.5 to >10 × 10¹⁰ cfu mL⁻¹ for SCV, while the maximum cell density for NCIMB biofilms was 2.8 × 10¹⁰ cfu mL⁻¹.     

In vitro efficacy of bismuth thiols against biofilms formed by bacteria isolated from human chronic wounds

Aims: The purpose of this study was to evaluate the antimicrobial efficacy of thirteen bismuth thiol preparations for bactericidal activity against established biofilms formed by two bacteria isolated from human chronic wounds. Methods: Single species biofilms of a Pseudomonas aeruginosa or a methicillin‐resistant Staphylococcus aureus were grown in either colony biofilm or drip‐flow reactors systems. Biofilms were challenged with bismuth thiols, antibiotics or silver sulfadiazine, and log reductions were determined by plating for colony formation. Conclusions: Antibiotics were ineffective or inconsistent against biofilms of both bacterial species tested. None of the antibiotics tested were able to achieve >2 log reductions in both biofilm models. The 13 different bismuth thiols tested in this investigation achieved widely varying degrees of killing, even against the same micro‐organism in the same biofilm model. For each micro‐organism, the best bismuth thiol easily outperformed the best conventional antibiotic. Against P. aeruginosa biofilms, bismuth‐2,3‐dimercaptopropanol (BisBAL) at 40–80 μg ml^?1 achieved >7·7 mean log reduction for the two biofilm models. Against MRSA biofilms, bismuth‐1,3‐propanedithiol/bismuth‐2‐mercaptopyridine N‐oxide (BisBDT/PYR) achieved a 4·9 log reduction. Significance and Impact of the Study: Bismuth thiols are effective antimicrobial agents against biofilms formed by wound bacteria and merit further development as topical antiseptics for the suppression of biofilms in chronic wounds.     

Attachment of and Biofilm Formation by Enterobacter sakazakii on Stainless Steel and Enteral Feeding Tubes

Enterobacter sakazakii has been reported to form biofilms, but environmental conditions affecting attachment to and biofilm formation on abiotic surfaces have not been described. We did a study to determine the effects of temperature and nutrient availability on attachment and biofilm formation by E. sakazakii on stainless steel and enteral feeding tubes. Five strains grown to stationary phase in tryptic soy broth (TSB), infant formula broth (IFB), or lettuce juice broth (LJB) at 12 and 25°C were examined for the extent to which they attach to these materials. Higher populations attached at 25°C than at 12°C. Stainless steel coupons and enteral feeding tubes were immersed for 24 h at 4°C in phosphate-buffered saline suspensions (7 log CFU/ml) to facilitate the attachment of 5.33 to 5.51 and 5.03 to 5.12 log CFU/cm², respectively, before they were immersed in TSB, IFB, or LJB, followed by incubation at 12 or 25°C for up to 10 days. Biofilms were not produced at 12°C. The number of cells of test strains increased by 1.42 to 1.67 log CFU/cm² and 1.16 to 1.31 log CFU/cm² in biofilms formed on stainless steel and feeding tubes, respectively, immersed in IFB at 25°C; biofilms were not formed on TSB and LJB at 25°C, indicating that nutrient availability plays a major role in processes leading to biofilm formation on the surfaces of these inert materials. These observations emphasize the importance of temperature control in reconstituted infant formula preparation and storage areas in preventing attachment and biofilm formation by E. sakazakii.     

Sub-lethal concentrations of Muscari comosum bulb extract suppress adhesion and induce detachment of sessile yeast cells

The formation of yeast biofilm on food industry equipment can lead to serious hygiene problems and economic losses due to food spoilage and equipment impairment. This study explored the ability of a sub-lethal concentration of the bulb extract of Muscari comosum to modulate adhesion of Candida albicans and subsequent biofilm development by this fungus. The HPLC profile of the ethanolic bulb extract showed phenolic constituents, which were found to undergo Folin-Ciocalteu reagent reduction. Prior to the adhesion tests, it was shown that up to 4000 mg l^?1 of natural extract did not adversely affect fungal growth nor did it act as a carbon energy source for C. albicans. Mathematical models predicted that 4000 mg l^?1 and 700 mg l^?1 of bulb extract would cause more than 98% reduction in fungal coverage on abiotic surfaces, without killing the planktonic cells. When added to C. albicans biofilm, the natural extract was shown to induce the dispersion of sessile cells in a dose-dependent manner.