Bacterial biofilms in food processing environments: a review of recent developments in chemical and biological control

Sources of propionic acid bacteria contamination in the milking parlor environment on Alpine Dairy Farms

High quality raw milk is an important prerequisite for the production of long ripened raw milk cheeses. This implies not only the absence of pathogenic microorganisms in raw milk, but also low levels of spoilage bacteria, including dairy propionic acid bacteria (dPAB), that can cause blowing and sensory defects in cheese, resulting in severe economic losses for producers. Raw milk contamination with dPAB has been primarily associated with improperly cleaned milking systems, but they have been detected in feed, soil, feces and on the teat skin. The objective of this study was to identify potential sources of raw milk contamination with dPAB in the barn and milking parlor environments. We also wanted to know more about the prevalence of the dPAB species in these environments and the levels of contamination. For this purpose, 16 small scale Alpine dairy farms were visited in August 2022: samples were taken from the barn environment (e.g., swab samples, air, feed, bedding), the milking system (swab samples, residual cleaning water, cleaning sponges, milk filters) and milk samples were collected at various sampling points along the milking system. Samples were analyzed for dPAB contamination, and results showed contamination at multiple sampling locations. We observed potential adverse effects of improperly set cleaning parameters of the milking system, as well as of farm specific practices. In addition, we identified cleaning water residues as an important source of contamination. Based on these findings, we propose potential mitigation strategies to reduce the risk of raw milk contamination with cheese spoilage bacteria, thereby contributing to a more sustainable food production.

Controlling of foodborne pathogen biofilms on stainless steel by bacteriophages: A systematic review and meta-analysis

This study investigates the potential of using bacteriophages to control foodborne pathogen biofilms on stainless steel surfaces in the food industry. Biofilm-forming bacteria can attach to stainless steel surfaces, rendering them difficult to eradicate even after a thorough cleaning and sanitizing procedures. Bacteriophages have been proposed as a possible solution, as they can penetrate biofilms and destroy bacterial cells within, reducing the number of viable bacteria and preventing the growth and spread of biofilms. This systematic review and meta-analysis evaluates the potential of bacteriophages against different biofilm-forming foodborne bacteria, including Cronobacter sakazakii, Escherichia coli, Staphylococcus aureus, Pseudomonas fluorescens, Pseudomonas aeruginosa and Listeria monocytogenes. Bacteriophage treatment generally causes a significant average reduction of 38 % in biofilm formation of foodborne pathogens on stainless steel. Subgroup analyses revealed that phages are more efficient in long-duration treatment. Also, applying a cocktail of phages is 1.26-fold more effective than applying individual phages. Phages at concentrations exceeding 107 PFU/ml are significantly more efficacious in eradicating bacteria within a biofilm. The antibacterial phage activity decreases substantially by 3.54-fold when applied at 4 °C compared to temperatures above 25 °C. This analysis suggests that bacteriophages can be a promising solution for controlling biofilms in the food industry.

Natural phenolic compounds: Antimicrobial properties, antimicrobial mechanisms, and potential utilization in the preservation of aquatic products

Natural antibacterials have stood out in the last decade due to the growing demand for reducing chemical preservatives in food. In particular, natural phenolic compounds are secondary metabolites produced by plants for numerous functions including antimicrobial defence. Polyphenol has significant antimicrobial activity, but its antimicrobial properties are affected by the cell structure difference of bacteria, the concentration, type, and extraction method of polyphenol, and the treatment time of bacteria exposed to polyphenol. Therefore, this paper analyzed the antibacterial activity and mechanism of polyphenol as an antimicrobial agent. However, there remained significant considerations, including the interaction of polyphenols and food matrix, environmental temperature, and the effect of color and odor of some polyphenols on sensory properties of aquatic products, and the additive amount of polyphenols. On this basis, the application strategies of polyphenols as the antimicrobial agent in aquatic products preservation were reviewed.

A combined treatment of Proteinase K and biosynthesized ZnO-NPs for eradication of dairy biofilm of sporeformers

Biofilms of sporeformers found in the dairy industry are the major contaminants during processing, as they withstand heat and chemical treatment that are used to control microbes. The present work is aimed to remove these resistant forms of bacterial community (biofilm) present in dairy production lines using ecofriendly agents based on proteinase K (Prot-K) coupled with Zinc oxide nanoparticles (ZnO-NPs). Some metal/metal oxide (Ag, CuO and ZnO) NPs were prepared microbially, and ZnO-NPs were characterized as the most effective ones among them. The produced ZnO-NPs were 15-25 nm in size with spherical shape, and FTIR analysis confirmed the presence of proteins and alkanes surrounding particles as capping agents. Application of Prot-K for eradication (removal) of a model biofilm of mixed sporeformers on food-grade stainless steel resulted in an 83% reduction in the absorbance of crystal violet-stained biofilm. When Prot-K was mixed with the biosynthesized NPs ZnO_G240, the reduction increased to 99.19%. This finding could contribute to an efficient cleaning approach combined with CIP to remove the recalcitrant biofilms in dairy production lines.

Additive Nanosecond Laser-Induced Forward Transfer of High Antibacterial Metal Nanoparticle Dose onto Foodborne Bacterial Biofilms

Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the transfer distance effects on the antibacterial activity regarding biofilms of Gram-negative and Gram-positive food bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Listeria monocytogenes, Salmonella spp.) indicated the optimal operation regimes of the versatile modality. LIFT-induced nanoparticle penetration into a biofilm was studied by energy-dispersion X-ray spectroscopy, which demonstrated that nanoparticles remained predominantly on the surface of the biofilm.

Sophorolipids—Bio-Based Antimicrobial Formulating Agents for Applications in Food and Health

Sophorolipids are well-known glycolipid biosurfactants, produced mainly by non-pathogenic yeast species such as Candida bombicola with high yield. Its unique environmental compatibility and high biodegradable properties have made them a focus in the present review for their promising applications in diverse areas. This study aims to examine current research trends of sophorolipids and evaluate their applications in food and health. A literature search was conducted using different research databases including PubMed, ScienceDirect, EBSCOhost, and Wiley Online Library to identify studies on the fundamental mechanisms of sophorolipids and their applications in food and health. Studies have shown that various structural forms of sophorolipids exhibit different biological and physicochemical properties. Sophorolipids represent one of the most attractive biosurfactants in the industry due to their antimicrobial action against both Gram-positive and Gram-negative microorganisms for applications in food and health sectors. In this review, we have provided an overview on the fundamental properties of sophorolipids and detailed analysis of their applications in diverse areas such as food, agriculture, pharmaceutical, cosmetic, anticancer, and antimicrobial activities.

Effect of atmospheric cold plasma (ACP) on chlorine adapted Salmonella enterica on spring onion

One of the main drawbacks of chlorine disinfectants is the emergence of chlorine adapted (CA) or resistant microbial cells. This research aimed to investigate the effect of chlorine adaptation on resistance of Salmonella enterica upon atmospheric cold plasma (ACP) application at different voltages (6, 8, and 11 kV) and times (5, 10, and 15 min). Due to higher conversion efficiency and reduced dielectric barrier discharge (DBD) power consumption, this method was used for cold plasma generation in this study. A higher lethality effect was observed from a higher voltage and longest times (11 kV-15 min) on CA S. enterica than non-CA (p<0.05). Still, it induced higher percentages of injured cells in CA (58.77%) than non-CA (0.61%) (p<0.05). The highest ACP effect on the inactivation of the indigenous natural flora of onion leaves was observed at the lowest voltage (p<0.05). More than 3 log CFU/g reduction (p<0.05) was observed at 6 kV after 5 and 10 min. ACP reduced CA and non-CA S. enterica cells on onion leaf surface to a lower extent than pure treated cells in broth media. Nevertheless similar to broth media, a high percentage of injury (61.03%) was induced on CA cells at higher voltage (11 kV-10 min) compared to non-CA (2.15%) (p<0.05). Biofilm results revealed ACP application (6 kV-5 min) reduced average ODs in CA and non-CA cells (p<0.05). Chlorine adaptation and ACP treatment influenced the antibiotic resistance pattern according to applied voltage, time, and antibiotic type. The finding showed despite highest lethality of high voltages and long times (11 kV-15 min), given the high percentages of injured cells, lower voltages may offer acceptable inactivation of pathogenic bacteria with lower injury induction. In conclusion, ACP has the potential ability to eliminate CA cells of S. enterica, which is predominant in fresh-cut vegetable outbreaks.

In Vitro Preformed Biofilms of Bacillus safensis Inhibit the Adhesion and Subsequent Development of Listeria monocytogenes on Stainless-Steel Surfaces

Listeria monocytogenes continues to be one of the most important public health challenges for the meat sector. Many attempts have been made to establish the most efficient cleaning and disinfection protocols, but there is still the need for the sector to develop plans with different lines of action. In this regard, an interesting strategy could be based on the control of this type of foodborne pathogen through the resident microbiota naturally established on the surfaces. A potential inhibitor, Bacillus safensis, was found in a previous study that screened the interaction between the resident microbiota and L. monocytogenes in an Iberian pig processing plant. The aim of the present study was to evaluate the effect of preformed biofilms of Bacillus safensis on the adhesion and implantation of 22 strains of L. monocytogenes. Mature preformed B. safensis biofilms can inhibit adhesion and the biofilm formation of multiple L. monocytogenes strains, eliminating the pathogen by a currently unidentified mechanism. Due to the non-enterotoxigenic properties of B. safensis, its presence on certain meat industry surfaces should be favored and it could represent a new way to fight against the persistence of L. monocytogenes in accordance with other bacterial inhibitors and hygiene operations.

Inactivation of Bacteria Using Bioactive Nanoparticles and Alternating Magnetic Fields

Foodborne pathogens are frequently associated with risks and outbreaks of many diseases; therefore, food safety and processing remain a priority to control and minimize these risks. In this work, nisin-loaded magnetic nanoparticles were used and activated by alternating 10 and 125 mT (peak to peak) magnetic fields (AMFs) for biocontrol of bacteria Listeria innocua, a suitable model to study the inactivation of common foodborne pathogen L. monocytogenes. It was shown that L. innocua features high resistance to nisin-based bioactive nanoparticles, however, application of AMFs (15 and 30 min exposure) significantly potentiates the treatment resulting in considerable log reduction of viable cells. The morphological changes and the resulting cellular damage, which was induced by the synergistic treatment, was confirmed using scanning electron microscopy. The thermal effects were also estimated in the study. The results are useful for the development of new methods for treatment of the drug-resistant foodborne pathogens to minimize the risks of invasive infections. The proposed methodology is a contactless alternative to the currently established pulsed-electric field-based treatment in food processing.

Innovative Control of Biofilms on Stainless Steel Surfaces Using Electrolyzed Water in the Dairy Industry

Biofilms on food-contact surfaces can lead to recurrent contamination. This work aimed to study the biofilm formation process on stainless steel plates used in the dairy industry: 304 surface finish 2B and electropolished; and the effect of a cleaning and disinfection process using alkaline (AEW) and neutral (NEW) electrolyzed water. Milk fouling during heat processing can lead to type A or B deposits, which were analyzed for composition, surface energy, thickness, and roughness, while the role of raw milk microbiota on biofilm development was investigated. Bacteria, yeasts, and lactic acid bacteria were detected using EUB-338, PF2, and Str-493 probes, respectively, whereas Lis-637 probe detected Listeria sp. The genetic complexity and diversity of biofilms varied according to biofilm maturation day, as evaluated by 16S rRNA gene sequence, denaturing gradient gel electrophoresis, and fluorescence in situ hybridization microscopy. From analysis of the experimental designs, a cleaning stage of 50 mg/L NaOH of AEW at 30 °C for 10 min, followed by disinfection using 50 mg/L total available chlorine of NEW at 20 °C for 5 min is a sustainable alternative process to prevent biofilm formation. Fluorescence microscopy was used to visualize the effectiveness of this process.

The Influence of Surface Topography and Wettability on Escherichia coli Removal from Polymeric Materials in the Presence of a Blood Conditioning Film

The reduction of biofouling and the reduction of cross-contamination in the food industry are important aspects of safety management systems. Polymeric surfaces are used extensively throughout the food production industry and therefore ensuring that effective cleaning regimes are conducted is vital. Throughout this study, the influence of the surface characteristics of three different polymeric surfaces, polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA) and polyethylene terephthalate (PET), on the removal of Escherichia coli using a wipe clean method utilising 3% sodium hypochlorite was determined. The PTFE surfaces were the roughest and demonstrated the least wettable surface (118.8°), followed by the PMMA (75.2°) and PET surfaces (53.9°). Following cleaning with a 3% sodium hypochlorite solution, bacteria were completely removed from the PTFE surfaces, whilst the PMMA and PET surfaces still had high numbers of bacteria recovered (1.2 × 107 CFU/mL and 6.3 × 107 CFU/mL, respectively). When bacterial suspensions were applied to the surfaces in the presence of a blood conditioning film, cleaning with sodium hypochlorite demonstrated that no bacteria were recovered from the PMMA surface. However, on both the PTFE and PET surfaces, bacteria were recovered at lower concentrations (2.0 × 102 CFU/mL and 1.3 × 103 CFU/mL, respectively). ATP bioluminescence results demonstrated significantly different ATP concentrations on the surfaces when soiled (PTFE: 132 relative light units (RLU), PMMA: 80 RLU and PET: 99 RLU). Following cleaning, both in the presence and absence of a blood conditioning film, all the surfaces were considered clean, producing ATP concentrations in the range of 0-2 RLU. The results generated in this study demonstrated that the presence of a blood conditioning film significantly altered the removal of bacteria from the polymeric surfaces following a standard cleaning regime. Conditioning films which represent the environment where the surface is intended to be used should be a vital part of the test regime to ensure an effective disinfection process.

Resistance of pathogenic biofilms on glass fiber filters formed under different conditions

This study investigated the survivals of two pathogens (Escherichia coli O157:H7 and Staphylococcus aureus) in different adhered forms on glass fiber filters (GFFs) at 43 and 68% relative humidity (RH). Efficacies of chemical sanitizers at reducing pathogenic biofilms on GFFs were also evaluated. Inoculated GFFs were incubated at 28 °C in TSB (type I), on TSA (type II), or on TSA under 100% RH (type III) to produce biofilms. When GFFs were incubated at 43 or 68% RH for 7 days, type III biofilms were less than 2 log₁₀ CFU/filter reduction whereas type I and type II biofilms were 4-6 log₁₀ CFU/filter reduction. Additionally, type III biofilms were highly resistant to sanitizing treatment compared than other biofilms (type I and II). Therefore, the method to produce biofilms used in this study could be used to produce highly resistance pathogenic biofilms in the laboratory for related experiments.

Strain variability in biofilm formation: A food safety and quality perspective

The inherent differences in microbial behavior among identically treated strains of the same microbial species, referred to as "strain variability", are regarded as an important source of variability in microbiological studies. Biofilms are defined as the structured multicellular communities with complex architecture that enable microorganisms to grow adhered to abiotic or living surfaces and constitute a fundamental aspect of microbial ecology. The research studies assessing the strain variability in biofilm formation are relatively few compared to the ones evaluating other aspects of microbial behavior such as virulence, growth and stress resistance. Among the available research data on intra-species variability in biofilm formation, compiled and discussed in the present review, most of them refer to foodborne pathogens as compared to spoilage microorganisms. Molecular and physiological aspects of biofilm formation potentially related to strain-specific responses, as well as information on the characterization and quantitative description of this type of biological variability are presented and discussed. Despite the considerable amount of available information on the strain variability in biofilm formation, there are certain data gaps and still-existing challenges that future research should cover and address. Current and future advances in systems biology and omics technologies are expected to aid significantly in the explanation of phenotypic strain variability, including biofilm formation variability, allowing for its integration in microbiological risk assessment.

Carvacrol encapsulation into nanostructures: Characterization and antimicrobial activity against foodborne pathogens adhered to stainless steel

Carvacrol is a natural antimicrobial capable of inhibiting several microorganisms. The encapsulation of this compound may increase its stability, water solubility and provide controlled release. In this study, carvacrol encapsulated into nanoliposomes (NLC) and polymeric Eudragit® nanocapsules (NCC) was tested against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella spp. adhered to stainless steel. NLC showed an average diameter of 270.8 nm, zeta potential of +8.64 mV, and encapsulation efficiency of 98%. Minimum Bactericidal Concentration (MBC) of NLC was 3.53 mg/mL against Salmonella and 5.30 mg/mL against the other bacteria. NCC presented an average diameter of 159.3 nm, zeta potential of +44.8 mV, and encapsulation efficiency of 97%. MBC of NCC was 4.42 mg/mL against E. coli and 3.31 mg/mL against the other bacteria. After 2 h incubation with NCC at carvacrol concentration equivalent to ½ MBC, viable counts of Salmonella and E. coli were below the detection limit (1.69 CFU/mL). The population of L. monocytogenes and S. aureus was reduced by 2 log CFU/mL in 6 h. Afterwards, pools of each bacterium were separately adhered to stainless steel coupons (initial population 6.5 CFU/cm²). Salmonella and E. coli were inhibited below the detection limit using the NCC at concentration equivalent to MBC, while L. monocytogenes and S. aureus were reduced by 4 log CFU/cm² and 3.5 log CFU/cm², respectively. Although free carvacrol presented better results than encapsulated one in all tests performed, using encapsulated carvacrol could be more interesting for food applications by masking the strong aroma of the compound, in addition to a controlled release of carvacrol. The results suggest that NCC have potential for use in food contact surfaces in order to avoid bacterial adhesion and subsequent biofilm formation.

Quantitative and Compositional Study of Monospecies Biofilms of Spoilage Microorganisms in the Meat Industry and Their Interaction in the Development of Multispecies Biofilms

Food spoilage is a serious problem in the food industry, since it leads to significant economic losses. One of its main causes is the cross-contamination of food products from industrial surfaces. Three spoilage bacterial species which are highly present in meat and the gastrointestinal tract of chickens were selected: Pseudomonas fragi, Leuconostoc gasicomitatum, and Lactobacillus reuteri. The dual aim was to determine their ability to form monospecies biofilms and to examine how they interact when they coexist together. To do so, mature monospecies biofilms were produced statically for seven days at a temperature of 30 °C. L. gasicomitatum was also used to investigate the behavior of P. fragi and L. reuteri in the formation of multispecies biofilms. The structure and composition of the monospecies biofilms were evaluated by direct epifluorescence microscopy, and the multispecies biofilms were evaluated by plate counting. Both L. gasicomitatum and L. reuteri were able to form biofilms, with counts of approximately 7 Log CFU/cm2 and a defined structure. However, P. fragi obtained counts to the order of 4 Log CFU/cm2, which is significantly different from the previous species (P < 0.05), and it had no network of cell conglomerates. The content of the L. gasicomitatum and L. reuteri biofilm matrices were 70-80% protein, unlike P. fragi, which presented a higher polysaccharide content (P < 0.05). In the multispecies biofilms, the presence of P. fragi did not affect the growth of L. gasicomitatum, which remained at between 5.76 to 6.1 Log CFU/cm2. However, L. reuteri was able to displace L. gasicomitatum growth after 24 h of coexisting in a mixed biofilm, presenting differences in counts of approximately 2 Log CFU/cm2. The study of the biofilms constructed by food industry resident microbiota can help to understand the ecological relations that exist between species, characterize them, and propose strategies to eliminate them. The name of genes and species should be written in italic.

Antimicrobial and antifouling polymeric coating mitigates persistence of Pseudomonas aeruginosa biofilm

Food wasted due to food spoilage remains a global challenge to the environmental sustainability and security of food supply. In food manufacturing, post-processing contamination of food can occur due to persistent bacterial biofilms, which can be resistant to conventional cleaning and sanitization. The objective was to characterize the efficacy of a polymeric coating in reducing Pseudomonas aeruginosa biofilm establishment and facilitating its removal. Viable cell density of a 48 h biofilm was reduced by 2.10 log cfu cm^-2 on the coated surface, compared to native polypropylene. Confocal laser scanning and electron microscopy indicated reductions in mature biofilm viability and thickness on the coated material. The antifouling coating improved cleanability, with ∼2.5 log cfu cm^-2 of viable cells remaining after 105 min cleaning by water at 65 °C, compared to 4.5 log cfu cm^-2 remaining on native polypropylene. Such coatings may reduce the persistence of biofilms in food processing environments, in support of reducing food spoilage and waste.

High voltage atmospheric cold air plasma control of bacterial biofilms on fresh produce

Atmospheric cold plasma (ACP) offers great potential for decontamination of food borne pathogens. This study examined the antimicrobial efficacy of ACP against a range of pathogens of concern to fresh produce comparing planktonic cultures, monoculture biofilms (Escherichia coli, Salmonella enterica, Listeria monocytogenes, Pseudomonas fluorescens) and mixed culture biofilms (Listeria monocytogenes and Pseudomonas fluorescens). Biotic and abiotic surfaces commonly occurring in the fresh food industry were investigated. Microorganisms showed varying susceptibility to ACP treatment depending on target and process factors. Bacterial biofilm populations treated with high voltage (80 kV) ACP were reduced significantly (p < 0.05) in both mono- and mixed species biofilms after 60 s of treatment and yielded non-detectable levels after extending treatment time to 120 s. However, an extended time was required to reduce the challenge mixed culture biofilm of L. monocytogenes and P. fluorescens inoculated on lettuce, which was dependent on biofilm formation conditions and substrate. Contained treatment for 120 s reduced L. monocytogenes and P. fluorescens inoculated as mixed cultures on lettuce (p < 0.05) by 2.2 and 4.2 Log10 CFU/ml respectively. When biofilms were grown at 4 °C on lettuce, there was an increased resistance to ACP treatment by comparison with biofilm grown at temperature abuse conditions of 15 °C. Similarly, L. monocytogenes and P. fluorescens exposed to cold stress (4 °C) for 1 h demonstrated increased tolerance to ACP treatment compared to non-stressed cells. These finding demonstrates that bacterial form, mono versus mixed challenges as well as environmental stress conditions play an important role in ACP inactivation efficacy.

Control of Listeria innocua Biofilms on Food Contact Surfaces with Slightly Acidic Electrolyzed Water and the Risk of Biofilm Cells Transfer to Duck Meat

Biofilm formation on food contact surfaces is a potential hazard leading to cross-contamination during food processing. We investigated Listeria innocua biofilm formation on various food contact surfaces and compared the washing effect of slightly acidic electrolyzed water (SAEW) at 30, 50, 70, and 120 ppm with that of 200 ppm of sodium hypochlorite (NaClO) on biofilm cells. The risk of L. innocua biofilm transfer and growth on food at retail markets was also investigated. The viability of biofilms that formed on food contact surfaces and then transferred cells to duck meat was confirmed by fluorescence microscopy. L. innocua biofilm formation was greatest on rubber, followed by polypropylene, glass, and stainless steel. Regardless of sanitizer type, washing removed biofilms from polypropylene and stainless steel better than from rubber and glass. Among the various SAEW concentrations, washing with 70 ppm of SAEW for 5 min significantly reduced L. innocua biofilms on food contact surfaces during food processing. Efficiency of transfer of L. innocua biofilm cells was the highest on polypropylene and lowest on stainless steel. The transferred biofilm cells grew to the maximum population density, and the lag time of transferred biofilm cells was longer than that of planktonic cells. The biofilm cells that transferred to duck meat coexisted with live, injured, and dead cells, which indicates that effective washing is essential to remove biofilm on food contact surfaces during food processing to reduce the risk of foodborne disease outbreaks.

Antibacterial, antibiofilm and antiquorum sensing effects of Thymus daenensis and Satureja hortensis essential oils against Staphylococcus aureus isolates

AIMS

The present study was conducted to investigate the effects of Thymus daenensis and Satureja hortensis essential oils (EOs) on the planktonic growth, biofilm formation and quorum sensing (QS) of some Staphylococcus aureus isolates (strong biofilm producers).

METHODS AND RESULTS

Minimum inhibitory concentration (MIC) of the EOs, inhibition of biofilm formation as well as disruption of preformed Staph. aureus biofilms were assessed. The antibiofilm activity of the EOs was determined using microtitre plate test (MtP) and scanning electron microscope (SEM). The QS inhibitory activity was also examined on the pregrown biofilms by gene expression analysis using quantitative real-time RT-polymerase chain reaction (PCR) of hld gene (RNAIII transcript). Moreover, tetrazolium-based colorimetric assay (MTT) was performed to detect cytotoxic effects of these EOs on the Vero cell line. Finally, the major components of the tested EOs were determined using Gas Chromatography-Mass Spectrometry (GC-MS). The MICs of T. daenensis and S. hortensis EOs against planktonic cells of the isolates were 0·0625 and 0·125 μl ml^-1 respectively. The minimum bactericidal concentrations for both of the EOs was 0·125 μl ml^-1 . The MtP test showed a significant inhibitory effect of the EOs on the biofilm formation and disruption at sub-MIC concentrations. These results were confirmed by SEM. Real-time PCR revealed a significant down-regulation of hld gene following treatment with MIC/2 concentration of S. hortensis EO. GC-MS analysis showed that carvacrol, terpinene and thymol were the major components of the applied EOs.

CONCLUSIONS

As selected EOs did not show significant cytotoxic effects even up to tenfold of MIC concentration, the applied EOs seem to be good candidates for preventing of biofilm formation of Staph. aureus cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study introduced T. daenensis and S. hortensis EOs as new antibiofilm, and S. hortensis EO as anti-QS herbal agents with natural origin against Staph. aureus.

Enhancement of photobactericidal activity of chlorin-e6-cellulose nanocrystals by covalent attachment of polymyxin B

Following light irradiation, a new nanomaterial, elaborated from CNCs, chlorin-e6 and polymyxin B, demonstrated efficiency against Gram-negative bacteria (Escherichia coli,Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus,Staphylococcus epidermidis).

Current status in biotechnological production and applications of glycolipid biosurfactants

Biosurfactants are natural compounds with surface activity and emulsifying properties produced by several types of microorganisms and have been considered an interesting alternative to synthetic surfactants. Glycolipids are promising biosurfactants, due to low toxicity, biodegradability, and chemical stability in different conditions and also because they have many biological activities, allowing wide applications in different fields. In this review, we addressed general information about families of glycolipids, rhamnolipids, sophorolipids, mannosylerythritol lipids, and trehalose lipids, describing their chemical and surface characteristics, recent studies using alternative substrates, and new strategies to improve of production, beyond their specificities. We focus in providing recent developments and trends in biotechnological process and medical and industrial applications.