MICROBIAL SURFACE-ACTIVE SUBSTANCES AS ANTIADHESIVE AGENTS

Surfactants synthesized by microorganisms (MS) are widely used in different branches of industry. The applying of microbial surfactants in biology and medicine as an alternative to synthetic disinfectants or drugs is promising due to their antimicrobial and antiadhesive properties. MS are amphiphilous compounds that lower the surface and interfacial tension in liquids. Due to the advantages of MS over their synthetic analogues (biodegradability, lack of toxicity, stability of physicochemical properties in a wide range of temperatures and pH), as well as their unique biological properties, these substances keep attracting more and more interest [1]. Thus MS have already been tried and shown promise in petroleum production and mining, in chemical and food industries, in agriculture, and in nature-friendly technologies for environmental remediation [2]. In 2011, a review of practical applying of MS for biology and medicine [3] analyzed their antimicrobial (antiviral, antibacterial and antifungal) and anti-adhesive activities, as well as the possibility of using these products of microbial synthesis for therapeutic purposes. In 2014, Mulligan et al. published a monograph [4] summarizing the information on microbial biosurfactants, including their anti-adhesive properties. Since 1990s, microbial biosurfactants have been massively studied as alternatives for the preparations that disrupt biofilms on various materials used in medicine and in food industry. Microorganisms colonizing surfaces are known to be a fairly dangerous phenomenon, resulting in spoilage of food and facilitating the spread of infectious diseases. Many studies proved the possibility of using inorganic (for example, silver [5]) and other chemical substances (ellagic acid, esculetin, fisetin [6]) to prevent adhesion, antibiotics and bacteriophage therapy [7] to fight various infections. However, emergence of resistance of microorganisms to antibiotics and other biocides, and the high costs of methods of adhesion prevention and biofilm disruption stimulated the search of new substances with necessary properties. Compared to accepted anti-adhesive agents, MS have a range of advantages [1–4]: – they do not pollute the environment, since they are biodegradable; – they do not induce allergic reactions, because are non-toxic;; – because they are can be used in various environmental conditions due to stable physicochemical properties; – their highly specific mechanisms of action prevent the emergence of resistant microorganisms. UDC 759.873.088.5:661.185 http://dx.doi.org/10.15407/biotech9.03.007

Surfactants synthesized by microorganisms (MS) are widely used in different branches of industry. The applying of microbial surfactants in biology and medicine as an alternative to synthetic disinfectants or drugs is promising due to their antimicrobial and antiadhesive properties.
MS are amphiphilous compounds that lower the surface and interfacial tension in liquids. Due to the advantages of MS over their synthetic analogues (biodegradability, lack of toxicity, stability of physicochemical properties in a wide range of temperatures and pH), as well as their unique biological properties, these substances keep attracting more and more interest [1]. Thus MS have already been tried and shown promise in petroleum production and mining, in chemical and food industries, in agriculture, and in nature-friendly technologies for environmental remediation [2].
In 2011, a review of practical applying of MS for biology and medicine [3] analyzed their antimicrobial (antiviral, antibacterial and antifungal) and anti-adhesive activities, as well as the possibility of using these products of microbial synthesis for therapeutic purposes. In 2014, Mulligan et al. published a monograph [4] summarizing the information on microbial biosurfactants, including their anti-adhesive properties.
Since 1990s, microbial biosurfactants have been massively studied as alternatives for the preparations that disrupt biofilms on various materials used in medicine and in food industry. Microorganisms colonizing surfaces are known to be a fairly dangerous phenomenon, resulting in spoilage of food and facilitating the spread of infectious diseases. Many studies proved the possibility of using inorganic (for example, silver [5]) and other chemical substances (ellagic acid, esculetin, fisetin [6]) to prevent adhesion, antibiotics and bacteriophage therapy [7] to fight various infections. However, emergence of resistance of microorganisms to antibiotics and other biocides, and the high costs of methods of adhesion prevention and biofilm disruption stimulated the search of new substances with necessary properties.
Compared to accepted anti-adhesive agents, MS have a range of advantages [1][2][3][4]: -they do not pollute the environment, since they are biodegradable; -they do not induce allergic reactions, because are non-toxic;; -because they are can be used in various environmental conditions due to stable physicochemical properties; -their highly specific mechanisms of action prevent the emergence of resistant microorganisms.
The aim of this review is to summarize the current reports on anti-adhesive potential of biosurfactants, synthesized by different groups of microorganisms, and on their ability to disrupt biofilms on abiotic and biotic surfaces.

A n t i -a d h e s i v e p r o p e r t i e s o f surfactants synthesized by bacteria of Pseudomonas genus
Rhamnolipids. First reports of these surfactants come from as early as 1940-es [8]. The rhamnolipids consist of one or two rhamnose molecules bound to one, two (seldom three) molecules of hydroxyaliphatic acids. Depending on the number of the carbohydrate molecules and fatty acids they are usually classified as mono-rhamno-mono-lipids, monorhamno-di-lipids, di-rhamno-mono-lipids and di-rhamno-di-lipids. Over 60 homologues of rhamnolipids are synthesized by bacteria of Pseudomonas genus (Pseudomonas chlororaphis, Pseudomonas alcaligenes, Pseudomonas putida, Pseudomonas stutzeri, etc.), yet the main producers are strains of Pseudomonas aeruginosa [4,[9][10][11].
Despite the long history of research, biological properties of rhamnolipids started not that long ago. Thus, in 2001, Abalos et al. found the antifungal action of seven homologues of rhamnolipids of P. aeruginosa АТ10, which in low concentrations (16-32 μg/ml) inhibited the growth of Aspergillus, Penicillium and Aureobasidium fungi, as well as the phytopathogenic Botrytis and Rhizoctonia [12]. In 2003, antimicrobial action of rhamnolipids of P. aeruginosa 47T2 NCBIM 40044 was published [13]. Thus, minimal inhibitory concentrations (MIC) of these surfactants against some bacteria of genera Serratia, Enterobacter, Klebsiella, and Staphylococcus were 0.5-32 μg/ml. Studies [12,13] inspired the following research directed at the possibility of using microbial surfactants as antimicrobial agents [14][15][16]. After several years (in 2005) it was established that besides the antimicrobial action, rhamnolipids of P. aeruginosa PAO1 alsopossess anti-adhesive properties [17]. It was found that the surfactants prevented biofilm formation by Bordetella bronchiseptica ТК-4 on glass and silicon surfaces. Data on antimicrobial and anti-adhesive action of surfactants produced by Pseudomonas representatives are summarized in reviews [10,11,18]. We provide results which were not included in those works.
The effect of rhamnolipids on attachment of microorganisms to various surfaces. Rodrigues et al. [19] studied anti-adhesive properties of rhamnolipids of P. aeruginosa DS10-129 and established that the number of the attached bacterial (Staphylococcus epidermidis GB 9/6, Staphylococcus aureus GB 2/1, Streptococcus salivarius GB 24/9, Rothia dentocariosa GBJ 52/2B) and yeast (Candida tropicalis GB 9/9, Candida albicans GBJ 13/4A, C. tropicalis GB 9/9) cells decreased to 40 and 30% respectively if the silicon was pretreated by a surfactant preparation at 4 mg/ml. Also, Janek et al. [20] demonstrated the influence of di-rhamnolipids and phosphatidylethanolamines synthesized by Pseudomonas putida BD2 on the attachment of microorganisms to polystirol, which is the material of most medical prostheses. Wrocław hospitals were used. If the polystirol was pretreated with di-rhamnolipids (0.5 mg/ ml), the amount of the attached bacterial and yeast cells decreased to 21-57 and 10-11%, respectively. Phosphatidylethanolamines were less efficient anti-adhesive agents: their presence inhibited the adhesion of bacteria and yeasts only to 77 and 21%, respectively [20]. The authors of [21] established the efficiency of using rhamnolipids of P. aeruginosa LCD12 to prevent the attachment of cells of Bacillus subtilis RI6, E. coli PJ3, S. aureus FD5, S. epidermidis LK8 to a polystirol surface. Adhesion of test cultures was 50-80% if the wells of microplate were pre-treated with surfactant of LCD12 strain at the concentration of 8-64 μg/ml [21].
The role of rhamnolipids in biofilm destruction. The research of the last years is notable for having not only established not only the anti-adhesive properties of rhamnolipids but also their role in biofilm destruction on medical materials. Since S. aureus cause various infectious diseases, Gomesa and Nitschke [22] studied the effect of rhamnolipids of P. aeruginosa S5 on the destruction of biofilm of this pathogen. Experiments showed that as soon as two hours later, rhamnolipids caused biofilm destruction by 40-55% (depending on the surfactant concentration), and after twelve hours exposure, by 70-80%. In [21], Das [23] studied the ability of rhamnolipids of P. aeruginosa HG3 to destroy the biofilm of yeast Yarrowia lipolytica NCIM 3589. Their contribution is rather important since it had been established that Y. lipolytica is an opportunistic microorganism, able to cause invasive candidiasis in patients who are fed parenterally [24]. Thus, Dusane et al. [23] showed that an hour after the biofilm on a polystirol surface was treated with preparations of P. aeruginosa HG3 surfactants (3.0-100 mg/ml) the degree of its destruction was 40-50%, and after three hours, in the presence of 6-12 mg/ml rhamnolipids it reached 75%. Singh et al. studied the ability of di-rhamnolipids of P. aeruginosa DSVP20 to destroy the structure formed by yeast C. albicans GH103 on polystirol [25]. Before that [26], it was established that these microorganisms easily colonize surfaces of prostheses (larynx, knee, heart valves), implants (especially breast), endotracheal tubes, leading to the infection spreading throughout the organism. In the experiment they used a solution of the surfactant, obtained by extracting it from the supernatant of the cultural liquid of P. aeruginosa DSVP20 with ethyl acetate. The efficiency of the destruction process for the biofilm of C. albicans GH103 in the wells of a microplate depended on the concentration of di-rhamnolipids (0.04-5.0 mg/ml) and exposure [25]. Thus, experiments showed that 50-60% yeast cells remained in the biofilm on polystirol surface two hours after treatment with surfactant (0.16-0.62 mg/ml) produced by DSVP20 strain. However, at higher concentrations of P. aeruginosa DSVP20 surfactant, after twelve hours the biofilm was practically totally destroyed (Table 1). Turbhekar et al. [27] established the ability of P. aeruginosa RT rhamnolipids to destroy the biofilm of C. albicans BT107. A single hour after the surface was treated with the surfactant preparation, the degree of destruction of BT107 strain biofilm on the polystirol surface was, on average, 52%, and after three hours of exposure at the surfactant concentration of 25-100 mg/ ml it reached 70%.
An overview of data on anti-adhesive properties of rhamnolipids, synthesized by oorganisms of Pseudomonas genus and their role in biofilm destruction on medical materials are shown in Table 2.
Lipopeptides. In early 1990-es [28] it was established that bacteria of Pseudomonas genus are able to produce not only rhamnolipids, but also lipopeptides. Lipopeptides consist of a lipid part connected with a short linear or cyclical oligopeptide. They differ by the length and composition of the lipid residue, the type, number and configuration of the amino acids in the peptide [4,29]. The [4] and [29] provide the generalized information about the lipopeptide producers among the bacteria of Pseudomonas, pathways of surfactant synthesis, their antimicrobial and antifungal properties, practical use. However, these reviews mostly lack info on the anti-adhesive properties of lipopeptides of the bacteria of Pseudomonas genus. Until quite recently, anti-adhesive properties were studied only for glycolipids of Pseudomonas sp., but in 2010, Raaijmakers et al. [30] established that lipopeptides viscosin and massetolide А, synthesized by P. fuorescens НТ7, disrupted the process of plastic surface colonization by P. aeruginosa PAO1. Unfortunately, the article doesn't state at which concentration they applied the lipopeptides.

Bacteria of Bacillus genus as producers of lipopeptides with anti-adhesive properties
Of the most studied lipopeptide producers, one can name the genus Bacillus, in particular strains of B. subtilis. These lipopeptides are divided into three families of cyclical compounds: surfactin, iturin and fengicin, differing by the position, length and isomers of fatty acids in their molecules [4,29,34]. The ability of B. subtilis AMS-H2O-1 to synthesize surfactin was first established in 1968 [32], and in 1977 B. subtilis DS-104 was found to produce iturin [33]. The reports [29,34] and [4] provide summaries on most producers of lipopeptides, cultivation conditions and media, and practical applications. The first reports on the antimicrobial action of B. subtilis OKB105 surfactin go back to 1997. Vollenbroich et al. showed that the lipopeptide of OKB105 strain (0.032 mg/ml) could inhibit the growth of Mycoplasma hyorhinis and Mycoplasma orale, Note: -not reported.

Reviews
able to cause infectious diseases of the urinary tract [35,36].
In 2001, the surfactin produced by B. sub tilis HT73 was for the first time shown to prevent attaching Salmonella enterica SJW1103 cells to polystirol and silicon [37]. It was established that the lipopeptide (5-50 μg/ml) lowered the number of the test culture cells attached to polystirol surface by 60-85%. These authors also established the efficiency of using the lipopeptide of the strain HT73 (100 μg/ml) for the total destruction of the biofilms of S. enterica SJW1103, E. coli TH5, P. mirabilis GI7 on urethral catheters. The data on biologic properties of the lipopeptides of bacteria Bacillus genus are given in [29,34]. Let us consider the results on anti-adhesive properties which were not included in those reviews.

The effect of lipopeptides on the attachment of microorganisms to different surfaces
Zeraik and Nitschke [38] found the ability of surfactin, synthesized by B. subtilis LB5a, to prevent attaching to polystirol cells of S. aureus ATCC 25923, Listeria monocytogenes ATCC 19112 and Micrococcus luteus ATCC 4698 surface. Lipopeptide (10 mg/ml) of the strain LB5a decreased adhesion of the studied cells by 63-66%. The authors compared the efficiency of using surfactin of B. subtilis LB5a (10 mg/ml) and rhamnolipids of P. aeruginosa LВ1 (40 mg/ml) as anti-adhesive preparations. Studies showed that lipopeptides of strain LB5a are more efficient anti-adhesive agents: adhesion of bacteria to the polystirol surface when treated with the rhamnolipids of strain LВ1 was 2-3 times higher, then in the presence of surfactin.
Rivardo et al. [39]  The ability of strain Bacillus cereus NK1 to synthesize lipopeptides with expressed surface activity has also been investigated [40]. The authors found that these surfactants are able to prevent formation of biofilms of P. aeruginosa НР1 and S. epidermidis РІ5 on plastic. At 15 mg/ ml, the preparations of surfactants inhibited by 55-65% adhesion on abiotic surface both P. aeruginosa НР1 and S. epidermidis РІ5. In the study [41] they showed that lipopeptides of B. subtilis AC7 are efficient against the formation of biofilm of C. albicans OD1. Thus, if the silicon surface of the urethral catheters was treated with preparations of surfactants of AC7 (20-200 μg/ml), the number of adherent cells of C. albicans OD1 dropped by more than 70%.
In 2013, Ajesh et al. [42] isolated strain B. cereus AK1, capable of synthesizing a lipopeptide which by its chemical composition was different from surfactin and iturin. It was proposed to be called kannurin. The authors managed to find the ability of kannurin (0.25-512 μg/ml) to prevent the attachment of yeasts C. albicans LK3 and Cryptococcus neoformans ВМ8 to silicon surface. Thus, when the material was treated with surfactant preparations (2-64 μg/ml), the adhesion of test cultures reduced by 25-75%.

The role of lipopeptides in the destruction of biofilms
Recent years showed increasing attention the researchers pay to the search of new lipopeptide surfactants capable not only of biofilm formation prevention but also of destroying those already established on medical materials, since microorganisms in their structure there are resistant practically to all known antimicrobial preparations [43]. Sriram et al. [40] studied the ability of lipopeptides of B. cereus NK1 to destroy formed biofilms of P. aeruginosa НР1 and S. epidermidis РІ5 on polystirol surface. Experiments showed that as soon as two hours later, lipopeptides (5.0-15.0 mg/ml) disrupted the biofilm on average by 25-55% (Table 3).
The highest level of P. aeruginosa НР1 and S. epidermidis РІ5 biofilm destruction (54-58%) was reached by using maximal ( [44]. The report inspired Rautela et al. [45], who studied the ability of lipopeptides of B. amyloliquefaciens AR2 to disrupt already formed on polystirol biofilms of the yeasts C. albicans (MTCC 1637, MTCC 4748 and MTCC 183). After three hours of treating the surface with lipopeptides of B. amyloliquefaciens AR2 (1-6 mg/ml) they observed destruction of biofilms on it. The most efficient (up to 80%) was the process of biofilm destruction by surfactants at the concentration of 6 mg/ml. The researchers found that if the polystirol surface was treated with lipopeptides at lower concentration (1-4 mg/ml), the exposure necessary to destroy the biofilm, was longer (6-12 hours). Table 4 summarizes data on anti-adhesive properties of lipopeptides of representatives of the genus Bacillus and their role in the destruction of biofilms on medical materials. Therefore, data prove the efficiency of using lipopeptides of the genus Bacillus as anti-adhesive agents [35][36][37][38][39][40][41][42][43][44][45]. If the surfaces were treated with preparations of lipopeptides (0.002-15.0 mg/ml), microbe adhesion decreased by more than 60%. The experiments showed that lipopeptides (0.025-15.0 mg/ml) are also able to practically utterly (80-90%) destroy biofilms formed on polystirol.

Surfactants of Lactobacillus genus bacteria as anti-adhesive agents
Data on surfactants, synthesized by representatives of the genus Lactobacillus, are scarce. Initial research appeared in 1990-es [46,47]. In 1993, Blomberg et al. [46] found the ability of bacteria of the genus Lactobacillus (Lactobacillus crispatus 152, Lactobacillus fermentum 104R, Lactobacillus murinus C39 and others) to produce substances, able to prevent adhesion of cells of E. coli K88. In time (1996), it was established that these substances have high content of proteins, polysaccharides, phosphates. Nowadays, there is still next to nothing on the chemical composition of the surfactants synthesized by bacteria of the genus Lactobacillus [47][48][49]. The established ability of L. fermentum B54 and Lactobacillus acidophilus RC14 to produce surfactants which at 20 mg/ml prevented adhesion of E. faecalis 1131 on glass surfaces: after 4 hours, the amount of adherent cells did not exceed 30-33% [47]. Studying biological properties of surface-active substances of the representatives of the genus Lactobacillus is an urgent task, since they are the most suitable anti-adhesive agents for medicine due to lack of pathogenicity. Unfortunately, by now there are but few single data points suggesting the ability of these surfactants to prevent microbial colonization of various surfaces. Below we give an overview of latest years' research on antiadhesive potential of surfactants synthesized by bacteria of the genus Lactobacillus.

The effect of surface-active substances on the adhesion of microorganisms to various surfaces
As the authors of [48] report, the surfactants of Lactobacillus paracasei ssp. paracasei A20 are able to prevent adhesion of some microorganisms to plastic. So, if plastic was treated with surfactant preparations (3-50 mg/ml), the amount of adherent cells of E. coli E-8 and P. aeruginosa L-7 was 11 and 21%,   [45] authors of [52] established that it was possible to prevent colonization of FKJ347 urethral catheters by Proteus mirabilis, if the catheters were treated with surfactants of strain L. acidophilus GF4. The experiments showed that if the surfactant was used at a much lower concentration of 1-10 μg/ml, the number of the adherent cells was as low as 20-30%.

The role of surface-active substances in biofilm destruction
One of the problems of bladder catheterization in medical practice is the organ's easy colonizability by microorganisms which are able to cause infectious diseases. One of the pathogens is P. mirabilis, which is able to hydrolyze urine using its own urease [53]. A consequence of this is the sedimentation of magnesium phosphate and calcium phosphate on the inside of the catheter, which blocks the urine flow from the bladder.
Conglomerates of cells and salts are formed, which later on leads to biofilm formation. Abd Ulkareem Ali [52] studied the efficiency of using preparations of surfactants of strain L. acidophilus GF4 to destroy the biofilm of P. mirabilis, formed on urethral catheters, and to prevent the formation of a new one. The first round of experiments established that 45 clinical isolates of the bacteria (94% of the studied) formed biofilms. Later experiments showed that surfactants of L. acidophilus GF4 (6 μg/ml) caused 50% destruction of P. mirabilis FKJ347 biofilm, formed on plate wells. In [51] they showed that the surfactants, synthesized by Lactobacillus sp. CV8LAC, at the concentration of 17.5-800 μg/ml destroyed on polystirol surface the biofilm of С. аlbicans CA-2894 and С. аlbicans DSMZ 11225. It was found that at the concentration of 800 μg/ml, the degree of the destruction of yeast biofilm reached 70%. These are the first studies which  [54] show that surfactants of L. аcidophilus showed high ability to disrupt the structure of biofilms on biotic surface. A continuation of the work by Fracchia et al. [51] was the study by Simone et al. [54], which established the ability of surfactants (10-1 000 mkg/ml) of L. аcidophilus ATCC 4356 to destroy biofilms of the yeast Candida. At the concentration of the surfactant of 100 μg/ml they observed the destruction of the biofilm С. аlbicans SDC284 by 55%. Generalized data on anti-adhesive properties of the surfactants, synthesized by representatives of the genus Lactobacillus, and their role in the destruction of biofilms are presented in Table 5. Analysis shows that using surfactants, synthesized by bacteria of the genus Lactobacillus as antiadhesive agents and to destroy biofilms is efficient [46][47][48][49][50][51][52][53][54]. Treating abiotic and biotic materials with surfactants (0.003-50.0 mg/ml) was accompanied by decrease of adhesion of microorganisms to 30-80%. However, currently there are only single reports of the anti-adhesive properties of the surfactants of the bacteriae of the genus Lactobacillus.

Fungi as producers of surfactants with antiadhesive properties
In the beginning of the ХХІ century, there was a marked increase in the research of surfactants produced by organisms belonging to the genera Саndida and Pseudozyma. It is explained by the ability of fungi to produce, on cheap substrates, substantially higher concentrations of surfactants compared to bacteria, which is economically profitable [55]. In 1970-80-ies, Candida bogoriensis FT6-1 was first found to synthesize sophorolipids, which contain disaccharide sophorose, linked by glycosidic bond to the penultimate atom of the carbon chain of the fatty acid С16-С19, however the research of biological properties of fungal surfactants started later [56][57][58]. In 2001, Golubev et al. [57] showed that glycolipids of Pseudozyma fusiformata VKM Y-282 have an antifungal activity [57]. By their chemical composition these glycolipids are mannosyl erythritol lipids, which as the basic structure have 4-O--D-mannopyranosyl meso-erythritol, linked with fatty acid and/ or acetyl groups. In their further studies, the authors established the ability of glycolipids of the strain VKM Y-282 to inhibit the growth of fungi of the genera Cryptococcus, Filobasidiella, Candida and Saccharomyces at low concentrations (0.13-1.6 mg/ml) [58]. First studies of the anti-adhesive properties of fungi occurred in 2011 [59,60]. Luna et al. [59] found the ability of sophorolipid lunasan, synthesized by Candida sphaerica UCP0995, at 10 mg/ml to lower adhesion to plastic of the bacteria of the genus Lactobacillus (Lactobacillus casei G43 -by 90%, Lactobacillus reuteri 104R -55%), Staphylococcus (S. aureus S27 -90%, S. epidermidis GB -22%), Streptococcus (Streptococcus oralis J22 -91%, Streptococcus mutans HG985 -50%) and P. aeruginosa CS34 -by 90%. An influential article of Rufino et al. [60], shows anti-adhesive properties of rufisan -a sophorolipid produced by C. lipolytica UCP0988. If polystirol surface is treated with a preparation of the surfactant of the strain UCP 0988 at the concentration of 0.75 mg/l, the number of adherent cells of Streptococcus agalactiae LNM103, L. сasei G43, S. mutans NS27 and S. aureus H75 are 80-90%; Streptococcus sanguis 12, S. oralis J22 and S. mutans HG985 -60-75%, and P. aeruginosa Р351 -49%. Under conditions of increased concentration of rufisan (12 mg/l), decreased (by 20-50%) adhesion of the cells of E. сoli NH471, S. epidermidis B41 and C. albicans ТР31 has also been observed. The articles [11,[61][62][63] provide an overview of data on surfactant producers among fungi, optimal conditions of their biosynthesis and their biological properties. Let us review the data on anti-adhesives which were left out of these reviews.

The influence of fungal surfactants on microorganism adhesion to various surfaces
Padmapriya and Suganthi [64] established the ability of surfactants synthesized by C. tropicalis CTY 25H and C. albicans FGY 25H to prevent attachment of cells of P. aeruginosa JC92, K. рneumoniae GH107, E. coli ATCC 20743, P. mirabilis РJ502, S. aureus ATCC 25923, C. albicans HY103 and bacteriae belonging to genera Citrobacter and Bacillus, isolated from hospitals of Coimbatore (India), to urethral catheters. The surfactants were obtained by twice extracting supernatant of the cultural liquid of C. tropicalis CTY 25H and C. albicans FGY 25H with dichloromethane. According to the data of infrared spectroscopy, these surfactants contain alkenes, hydroxyl, carbonyl, aromatic nitro-and amino residues. More efficient for prevention of test cultures' adhesion were surfactants of C. tropicalis CTY 25H (0.1-1.0 mg/ml): if the catheters were treated so, the number of adherent cells of P. aeruginosa JC92, K. рneumoniae GH107 and E. coli ATCC 20743 was 50-60%, P. mirabilis РJ502 and S. aureus ATCC 25923 -15-20%, C. albicans HY103, and of bacteria of the genera Citrobacter and Bacillus -5-12%. Using surfactant preparations of C. albicans FGY 25H (0.2-1.5 mg/ml) lead to higher cell adhesion (15-90%). The authors of [65] studied the ability of the surfactants of Trichosporon montevideense CLOA72 to prevent adhesion of yeast C. albicans CC to plastic. Thus, under treatment with surfactant (4-16 mg/ml), the amount of test culture cells adherent to plastic was as low as 10-25%. The authors showed that using lower (0.5-2.5 mg/ml) concentrations of surfactants of T. montevideense CLOA72 is less efficient: the adhesion of C. albicans CC cells reached 95%. They note that surfactants synthesized by T. montevideense CLOA72 are glycolipids but their chemical composition isn't stated.

The role of surface-active substances of fungi in the destruction of biofilms
We managed to find only a single report [66] describing the ability of surfactants of S. cerevisiae D1, D2 and D3 strains (0.1-1.0 mg/ml) to destroy bacterial and yeast biofilms on polystirol. It was established that the most efficient were the preparations of S. cerevisiae D3 surfactants (0.1-0.2 mg/ml), in the presence of which the observed destruction of C. albicans СА107 biofilm was by 10-20%. The surfactants of S. cerevisiae D3 at the concentration of 0.1 mg/ml caused the destruction of B. subtilis BТ37 biofilm by 30%. A comparison of S. cerevisiae D3 surfactants with sodium dodecyl sulphate (SDS), which is widely used as a component of disinfectants, showed that at higher (up to 1.0 mg/ml) concentrations of SDS the biofilm of C. albicans СА107 is destructed by 30% and B. subtilis BТ37 -by 40% [66]. There are, however, no data on the chemical composition of S. cerevisiae D3 surfactants. Therefore, the results support the notion that fungal surfactants (Table 6) are a fairly efficient agent preventing adhesion of microbial cells [59][60][61][62][63][64][65]. If materials were treated with surfactants (0.00075-16.0 mg/ml), adhesion of microorganisms did not, on average, exceed 40-90%. Currently, fungal surfactants are little researched as to their ability to destroy microbial biofilms.

Anti-adhesive potential of the surfactants of Аcinetobacter calcoaceticus ІМВ В-7241, Nocardia vaccinni IMB B-7405 and Rhodococcus erythropolis IMB Ac-5017
Earlier, in the Department of Biotechnology and Microbiology of the National University of Food Technologies the oil-oxidizing bacteria were isolated from the oil polluted samples of soil, identified as Rhodococcus erythropolis ЕК-1, Acinetobacter calcoaceticus К-4 and Nocardia vaccinii К-8 [67] and registered in the Microorganisms Depositary of the Institute of Microbiology and Virology the National Academy of Sciences of Ukraine under the numbers IMV Ac-5017, IMV B-7241and IMV В-7405 respectively. We found they were able to produce surfactants on hydrophilic and hydrophobic substrates [68][69][70]. By their chemical nature surfactants of R. erythropolis ІМV Ас-5017 are a complex of glyco-, phospho-and neutral lipids with compounds of polysaccharide-protein nature, surfactants of A. calcoaceticus ІМV В-7241 and N. vaccinii ІМV В-7405 are complexes of glyco-, aminoand neutral lipids. Glycolipids of all strains are represented by trehalosomycolates [11].
Later, the ability of the surfactants of А. calcoaceticus ІМV В-7241, synthesized on ethanol, glycerol and n-hexadecane to destroy formed bacterial biofilms, was also studied. The data provided in Table 7 suggest that regardless of the nature of the carbon source (ethanol, glycerol, n-hexadecane) and the degree of purification (supernatant, surfactant solution), all surfactants at the concentrations of 0.04-1.28 mg/ml destroyed the biofilm of S. aureus BMC-1 by 21-88%, and the destruction increased with the increase in surfactant concentration. The highest degree of biofilm destruction of the S. aureus BMC-1 (88%) was obtained with 1.28 mg/ml solution of surfactant synthesized on n-hexadecane. At the concentration of 0.04 mg/ml we already observed destruction of the biofilm of the test culture by 54 and 58%, respectively. Further research showed that unlike of S. aureus BMC-1, biofilm of B. subtilis BT-2 and E. сoli ІЕМ-1 were more efficiently destroyed by surfactants (0.04-1.28 mg/ml) synthesized on ethanol. Thus, the maximal degree of biofilm destruction of test cultures after treatment with surfactant solution (1.28 mg/ml) was 86 and 53%, respectively. Surfactants synthesized by strain ІМV В-7241 were more efficient destructors of bacterial biofilms compared to rhamnolipids of P. aeruginosa LBI and surfactin of B. subtilis RT7 [72], which supports the possibility of using them as novel disinfectants to eliminate bacterial biofilms.
The analyzed literature of the recent years concerning anti-adhesive properties of surfactants synthesized by various groups of microorganisms and their role in the destruction of bacterial biofilms on biotic and abiotic surfaces, demonstrated the possibility to use these products of microbial synthesis to develop novel efficient disinfectants. Comparative analysis of the well-known microbial surfactants is given in Table 8. These data show that microbial surfactants have their own advantages and disadvantages. A substantial advantage of microbial surfactants is the fact that synthesis of some of these compounds (rhamnolipids of the bacteria belonging to the genus Pseudomonas, sophorolipids of the yeast Саndida and surfactants of A. calcoaceticus ІМV В-7241) is possible on the waste of food industry (fried vegetable oil, soap stock) and biodiesel production (technical glycerol). Notably, most currently known microbial surfactants have high antiadhesive properties towards a wide range of test cultures at fairly low concentrations. As to most disadvantages of microbial surfactants as anti-adhesive agents, eliminating them is only a question of time and optimization of bio-surfactant synthesis using both intensification of the production technologies and improvement of strains by genetic and metabolic engineering.   Low (<18%) yield of product from substrate; producers are opportunistic pathogens [11,[59][60][61][62][63][64][65] A complex of aminoand glycolipids Acinetobacter calcoaceticus ІМВ В-7241 Synthesis on waste (fried vegetable oil, glycerol); high anti-adhesive potential at low surfactant concentrations Low anti-adhesive potential towards fungi [69,70,71]