Effect of growth temperature, surface type and incubation time on the resistance of Staphylococcus aureus biofilms to disinfectants

The Hidden World Within: Microbial Dynamics in Root Canal Systems

Several hundred different microbial taxa have made the oral cavity their home because of their evolution in multiple species communities within the special ecosystem. On the other hand, the dental pulp or internal tissue of the tooth is a connective tissue that is physiologically sterile and where any microbial infiltration is a harmful indication. It causes the pulp tissue to become inflamed, which leads to the death of the pulp and diffuses infection with inflammation to the peri-radicular tissues. Comprehending the biology of biofilms, the microbial makeup, and the host's reaction to infections in the pathobiology of root canal infections has received a lot of attention throughout the last few decades. Such comprehensive knowledge is required to design preventive medicines as well as clinically effective treatment regimens. Surprisingly, clinical approaches have concentrated more on radiographically perfecting channel preparation than on debridement of these intricate root canal systems, despite the clear realization that root canal infections are biofilm mediated. Since the present comprehension of the microbial etiopathogenesis of apical periodontitis highlights the significance of focusing on procedures such as "canal cleaning" and chemo-mechanical disinfection, the exclusive purpose of endodontic therapy is mainly missed while discussing "canal shaping." We thoroughly examine the state of our knowledge of the composition and functional traits of the root canal microbiome in this review. We also go into the difficulties with root canal disinfection and the cutting-edge approaches that try to solve these difficulties. In conclusion, we present essential guidance for prospective research areas, underscoring their significance as crucial considerations in the field of frontiers in oral health.

Characteristics of Staphylococcus aureus biofilm matured in tryptic soy broth, low-fat milk, or whole milk samples along with inactivation by 405 nm light combined with folic acid

In the present study, the characteristics of Staphylococcus aureus biofilms matured in tryptic soy broth (TSB), low-fat milk, or whole milk samples were identified along with their resistance to 405 nm light with or without folic acid. Phenotypic properties of carbohydrate and protein contents in extracellular polymeric substance (EPS) of S. aureus biofilms matured in different conditions were identified. The carbohydrate content was higher in the biofilm matured in low-fat milk (1.27) than the samples matured in whole milk (0.58) and TSB (0.10). Protein content in the EPS of biofilm was higher in the sample matured in whole milk (6.59) than the samples matured in low-fat milk (3.24) and TSB (2.08). Moreover, the maturation condition had a significant effect on the membrane lipid composition of the biofilm, producing more unsaturated fatty acids in biofilm matured in milk samples. These changes in biofilm matured in milk samples increased the resistance of S. aureus to 405 nm light in the presence of folic acid (LFA). Additionally, transcriptomic analysis was conducted to identify the response of S. aureus biofilm to LFA treatment. Several genes related to DNA and protein protection from oxidative stress along with biofilm accumulation were overexpressed in the LFA-treated biofilms. These results indicate the maturation of S. aureus biofilm in various samples and the biofilms responses to bactericidal treatments.

Comparative Evaluation of the Antimicrobial Activity of NeoPutty MTA and Modified NeoPutty MTA: An In Vitro Study

Aim

Mineral trioxide aggregate (MTA) is a relatively new versatile dental material. MTA has many advantages as well as disadvantages. To reduce most of the drawbacks of MTA, a premixed bioceramic MTA, NeoPutty MTA, was introduced in 2020. In this study, we assessed the antimicrobial activity of the newer MTA, NeoPutty MTA. We modified NeoPutty MTA and compared both against Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli.

Materials and Methods

Using the agar diffusion method, NeoPutty MTA was tested for antibacterial activity against the above-mentioned microorganisms. A base layer of Petri plates was done using Muller-Hinton agar for S. aureus, E. coli, and P. aeruginosa and brain heart infusion agar for E. faecalis. A total of 32 plates were employed; the plates were divided randomly into four test groups having eight plates each, so microorganisms were tested eight times. Three cavities were made in agar and filled with freshly mixed materials after 24 h. A pour plate seeded the microorganisms. The plates were pre-incubated for 2 h at room temperature and incubated at 37°C for 24 h. An independent observer measured the inhibition zone diameters.

Results

NeoPutty MTA, when tested alone, did not show much antibacterial activity against E. faecalis, S. aureus, and E. coli but had significant antimicrobial activity against P. aeruginosa when used at different concentrations. Modified NeoPutty (NeoPutty with antibiotics added individually) showed significant antibacterial activity against these microorganisms, as seen by the zone of inhibition of these bacteria.

Conclusion

Modified NeoPutty with antibiotics has a better antimicrobial effect than NeoPutty MTA.

Biofilm formation under food-relevant conditions and sanitizers' tolerance of a Pseudomonas fluorescens group strain

AIMS

The aim of this study was to determine the biofilm-forming ability of a strain belonging to the Pseudomonas fluorescens group isolated from the dairy environment under food-relevant conditions. Moreover, the effects of commercial sanitizers against preformed biofilms were assessed both in terms of viability and structure.

METHODS AND RESULTS

The biofilms were formed on polystyrene, stainless steel (SS), and polytetrafluoroethylene (PTFE) in a wide range of temperatures (4-25°C) and were subjected to the action of 10 different sanitizers. The strain under study showed to be a strong biofilm-former regardless of temperature, particularly on polystyrene. The biofilms were mostly sensitive to chlorine and peracetic acid-based sanitizers. For some sanitizers (e.g. amphoteric), a relationship was observed between the material and the tolerance, while the temperature was not statistically significant. The formation of long-term biofilms on SS was also structurally affected by the temperature, showing microcolonies more irregular in shape and with lower cellularity at 4°C compared to 15°C, where the biofilm was more compact and with a high presence of EPS.

CONCLUSIONS

The strain belonging to the P. fluorescens group was shown to quickly adhere and form mature biofilm at temperatures and on materials relevant to the food sector; however, biofilms formed under different conditions were differently tolerant to disinfectants.

SIGNIFICANCE AND IMPACT OF THE STUDY

Findings from this study could provide a basis for developing targeted sanitation protocols in food plants.

Staphylococcus aureus Cell Wall Phenotypic Changes Associated with Biofilm Maturation and Water Availability: A Key Contributing Factor for Chlorine Resistance

Staphylococcus aureus biofilms are resistant to both antibiotics and disinfectants. As Staphylococci cell walls are an important defence mechanism, we sought to examine changes to the bacterial cell wall under different growth conditions. Cell walls of S. aureus grown as 3-day hydrated biofilm, 12-day hydrated biofilm, and 12-day dry surface biofilm (DSB) were compared to cell walls of planktonic organisms. Additionally, proteomic analysis using high-throughput tandem mass tag-based mass spectrometry was performed. Proteins involved in cell wall synthesis in biofilms were upregulated in comparison to planktonic growth. Bacterial cell wall width (measured by transmission electron microscopy) and peptidoglycan production (detected using a silkworm larva plasma system) increased with biofilm culture duration (p < 0.001) and dehydration (p = 0.002). Similarly, disinfectant tolerance was greatest in DSB, followed by 12-day hydrated biofilm and then 3-day biofilm, and it was least in the planktonic bacteria--suggesting that changes to the cell wall may be a key factor for S. aureus biofilm biocide resistance. Our findings shed light on possible new targets to combat biofilm-related infections and hospital dry surface biofilms.

Genetic and compositional analysis of biofilm formed by Staphylococcus aureus isolated from food contact surfaces

INTRODUCTION

Staphylococcus aureus is an important pathogen that can form biofilms on food contact surfaces (FCS) in the dairy industry, posing a serious food safety, and quality concern. Biofilm is a complex system, influenced by nutritional-related factors that regulate the synthesis of the components of the biofilm matrix. This study determines the prevalence of biofilm-associated genes and evaluates the development under different growth conditions and compositions of biofilms produced by S. aureus.

METHODS

Biofilms were developed in TSB, TSBG, TSBNaCl, and TSBGNaCl on stainless-steel (SS), with enumeration at 24 and 192 h visualized by epifluorescence and scanning electron microscopy (SEM). The composition of biofilms was determined using enzymatic and chemical treatments and confocal laser scanning microscopy (CLSM).

RESULTS AND DISCUSSION

A total of 84 S. aureus (SA1-SA84) strains were collected from 293 dairy industry FCS (FCS-stainless steel [n = 183] and FCS-polypropylene [n = 110]) for this study. The isolates harbored the genes sigB (66%), sar (53%), agrD (52%), clfB/clfA (38%), fnbA/fnbB (20%), and bap (9.5%). 99. In particular, the biofilm formed by bap-positive S. aureus onto SS showed a high cell density in all culture media at 192 h in comparison with the biofilms formed at 24 h (p < 0.05). Epifluorescence microscopy and SEM revealed the metabolically active cells and the different stages of biofilm formation. CLSM analysis detected extracellular polymeric of S. aureus biofilms on SS, such as eDNA, proteins, and polysaccharides. Finally, the level of detachment on being treated with DNase I (44.7%) and NaIO 4(42.4%) was greater in the biofilms developed in TSB compared to culture medium supplemented with NaCl at 24 h; however, there was no significant difference when the culture medium was supplemented with glucose. In addition, after treatment with proteinase K, there was a lower level of biomass detachment (17.7%) of the biofilm developed in TSBNaCl (p < 0.05 at 24 h) compared to that in TSB, TSBG, and TSBGNaCl (33.6, 36.9, and 37.8%, respectively). These results represent a deep insight into the composition of S. aureus biofilms present in the dairy industry, which promotes the development of more efficient composition-specific disinfection strategies.

A Plasma-Based Decontamination Process Reveals Potential for an in-Process Surface-Sanitation Method

Methods, which use an indirect plasma treatment for the inactivation of microorganisms in foods, claim a vastly growing field of research. This paper presents a method that uses plasma-processed air (PPA) as a sanitizer. In addition to a sanitation concept for the decontamination of produce in the value chain, the presented method offers a possible application as an “in-process” surface sanitation. PPA provides antimicrobial-potent species, which are predominantly reactive nitrogen species (RNS); this has an outstanding groove penetration property. In an experimental approach, surfaces, made from materials, which are frequently used for the construction of food-processing plants, were inoculated with different microorganisms. Listeria monocytogenes (ATCC 15313), Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 10538), Salmonella enterica subsp. enterica serovar Typhimurium (ATCC 43971), and Salmonella enterica subsp. enterica serovar Enteritidis (ATCC 13076) are all microorganisms that frequently appear in foods and possess the risk for cross-contamination from the plant to the produce or vice versa. The contaminated samples were treated for various treatment times (1–5 min) with PPA of different antimicrobial potencies. Subsequently, the microbial load on the specimens was determined and compared with the load of untreated samples. As a result, reduction factors (RF) up to several log10-steps were obtained. Although surface and the bacterial strain showed an influence on the RF, the major influence was seen by a prolongation of the treatment time and an increase in the potency of the PPA.

Effect of biofilm formation on different types of plastic shopping bags: Structural and physicochemical properties

Plastics and biofilms have a complicated relationship that has great interest. Bacterial cell attachment and biofilm formation is considered to cause health and environmental risks from plastic waste accumulation. In water, plastic waste could serve as a new substrate for bacteria. In our study, the attachment of Escherichia coli K12, to four types of plastic shopping bags (biodegradable polylactic acid and the non-biodegradable polypropylene, polyethylene and polyvinyl chloride) was investigated. The change in physicochemical phenomena of each plastic, such as reduced hydrophobicity and higher exopolysaccharide concentrations (total extractable protein and carbohydrate) resulted in increased biofilm content on the plastic surfaces. The bacterial colonization of different plastic surfaces controls the ionic strength of the nutrition sources. The adhesion of Escherichia coli K12 cells on the surfaces were revealed by SEM images. The finding shows that increases surface roughness, besides favor for adhesion of bacterial cells due to hydrophobicity leading to a rapid attachment of Escherichia coli K12 on the surfaces. In addition, we used Derjaguin-Landau-Verwey-Overbeek theory to predict the attachment of Escherichia coli K12, which gave result of adhesion due to the high energy barrier. This present study added to our knowledge of the possible consequences of plastics acting as a new habitat for microbes in different aquatic condition.

Present status and future directions - microbiology of endodontic infections

Apical periodontitis has a microbial aetiology and is one of the most common inflammatory diseases that affect humans. Fungi, archaea and viruses have been found in association with apical periodontitis, but bacteria are by far the most prevalent and dominant microorganisms in endodontic infections. Bacterial infection of the root canal system only occurs when the pulp is necrotic or was removed for previous treatment. In some specific cases, including acute and chronic abscesses, the bacterial infection may reach the periradicular tissues. Intracanal bacteria are usually observed as sessile multispecies communities (biofilms) attached to the dentinal root canal walls. Infection in the main root canal lumen can spread to other areas of the root canal system. Although more than 500 bacterial species have been detected in endodontic infections, a selected group of 20 to 30 species are most frequently detected and may be considered as the core microbiome. There is a high interindividual variability in the endodontic microbiome in terms of species composition and relative abundance. Obligate anaerobic species are more abundant in the intraradicular bacterial communities of teeth with primary apical periodontitis, while both anaerobes and facultatives dominate the communities in post-treatment apical periodontitis. Bacterial interactions play an essential role in determining the overall virulence of the community, which has been regarded as the unit of pathogenicity of apical periodontitis. This article reviews the microbiologic aspects of endodontic infections and provides perspectives for future research and directions in the field.

Investigation on biofilm formation activity of Enterococcus faecium under various physiological conditions and possible application in bioremediation of tannery effluent

Treatment of tannery effluent (TE) using bacterial biofilm is a trending approach in the current scenario, due to greater survival and adaptation in stress conditions. The present study is concerned with the characterization of biofilm-forming bacterium Enterococcus faecium from tannery sludge and the investigation of their activity under different physiological conditions. Biofilm formation by E. faecium was strongly affected by variable physiological conditions. The optimum conditions were pH 7.5, temperature 28 °C, incubation time up to 96 h, glucose 1%, yeast extract 0.1-0.5%, NaCl 0.1-0.5%, tannery effluent-TE up to 50% v/v and Cd, Cr (VI) and Ni from 0.25 to 0.5 mM. Further, E. faecium treated TE was less phytotoxic on the fenugreek plant than the TE treated by non-biofilm forming isolate. The toxicity of TE could be reduced by the potentially biofilm-forming bacteria, which may be used in the bioremediation process.

Inhibition of Biofilm Formation of Foodborne Staphylococcus aureus by the Citrus Flavonoid Naringenin

Taking into consideration the importance of biofilms in food deterioration and the potential risks of antiseptic compounds, antimicrobial agents that naturally occurring are a more acceptable choice for preventing biofilm formation and in attempts to improve antibacterial effects and efficacy. Citrus flavonoids possess a variety of biological activities, including antimicrobial properties. Therefore, the anti-biofilm formation properties of the citrus flavonoid naringenin on the Staphylococcus aureus ATCC 6538 (S. aureus) were investigated using subminimum inhibitory concentrations (sub-MICs) of 5~60 mg/L. The results were confirmed using laser and scanning electron microscopy techniques, which revealed that the thick coating of S. aureus biofilms became thinner and finally separated into individual colonies when exposed to naringenin. The decreased biofilm formation of S. aureus cells may be due to a decrease in cell surface hydrophobicity and exopolysaccharide production, which is involved in the adherence or maturation of biofilms. Moreover, transcriptional results show that there was a downregulation in the expression of biofilm-related genes and alternative sigma factor sigB induced by naringenin. This work provides insight into the anti-biofilm mechanism of naringenin in S. aureus and suggests the possibility of naringenin being used in the industrial food industry for the prevention of biofilm formation.

Staphylococcus aureus Responds to Physiologically Relevant Temperature Changes by Altering Its Global Transcript and Protein Profile

Staphylococcus aureus is an opportunistic pathogen that colonizes the anterior nares of 30 to 50% of the population. Colonization is most often asymptomatic; however, self-inoculation can give rise to potentially fatal infections of the deeper tissues and blood. Like all bacteria, S. aureus can sense and respond to environmental cues and modify gene expression to adapt to specific environmental conditions. The transition of S. aureus from the nares to the deeper tissues and blood is accompanied by changes in environmental conditions, such as nutrient availability, pH, and temperature. In this study, we perform transcriptomics and proteomics on S. aureus cultures growing at three physiologically relevant temperatures, 34°C (nares), 37°C (body), and 40°C (pyrexia), to determine if small scale, biologically meaningful alterations in temperature impact S. aureus gene expression. Results show that small but definite temperature changes elicit a large-scale restructuring of the S. aureus transcriptome and proteome in a manner that, most often, inversely correlates with increasing temperature. We also provide evidence that a large majority of these changes are modulated at the posttranscriptional level, possibly by sRNA regulatory elements. Phenotypic analyses were also performed to demonstrate that these changes have physiological relevance. Finally, we investigate the impact of temperature-dependent alterations in gene expression on S. aureus pathogenesis and demonstrate decreased intracellular invasion of S. aureus grown at 34°C. Collectively, our results demonstrate that small but biologically meaningful alterations in temperature influence S. aureus gene expression, a process that is likely a major contributor to the transition from a commensal to pathogen.

IMPORTANCE Enteric bacterial pathogens, like Escherichia coli, are known to experience large temperature differences as they are transmitted through the fecal oral route. This change in temperature has been demonstrated to influence bacterial gene expression and facilitate infection. Staphylococcus aureus is a human-associated pathogen that can live as a commensal on the skin and nares or cause invasive infections of the deeper tissues and blood. Factors influencing S. aureus nasal colonization are not fully understood; however, individuals colonized with S. aureus are at increased risk of invasive infections through self-inoculation. The transition of S. aureus from the nose (colonization) to the body (infection) is accompanied by a modest but definite temperature increase, from 34°C to 37°C. In this study, we investigate whether these host-associated small temperature changes can influence S. aureus gene expression. Results show widespread changes in the bacterial transcriptome and proteome at three physiologically relevant temperatures (34°C, 37°C, and 40°C).

Microencapsulation of benzalkonium chloride enhanced its antibacterial and antibiofilm activities against Listeria monocytogenes and Escherichia coli

AIMS

In this study, benzalkonium chloride (BAC) microcapsules were developed for surface disinfection purpose and were evaluated against Listeria monocytogenes and Escherichia coli biofilms.

METHODS AND RESULTS

Microcapsules were prepared with two different strategies: uncomplexed BAC-microcapsules (UBM) containing BAC and maltodextrins, and complexed BAC-microcapsules (CBM) containing BAC complexed by pectin and maltodextrins. The minimum inhibitory concentrations (MICs) of free and microencapsulated BAC were investigated against two food pathogens: L. monocytogenes and E. coli. The antibiofilm activities of UBM and CBM against L. monocytogenes and E. coli biofilms formed on stainless steel at 37°C were evaluated and compared to BAC used under its free form. MICs of encapsulated BAC were up to fourfold lower than those of free BAC. The UBM and CBM showed higher antibiofilm effect when compared to the free BAC.

CONCLUSIONS

Overall, results demonstrated that microencapsulation enhanced the antibacterial activity of BAC against L. monocytogenes and E. coli biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of such BAC microcapsule-based delivery systems can improve surface disinfection procedures and reduce the required BAC concentrations and the related cytotoxicity of this antimicrobial compound.

Anti-biofilm activity of dodecyltrimethylammonium chloride microcapsules against Salmonella enterica serovar Enteritidis and Staphylococcus aureus

Dodecyltrimethylammonium chloride (DTAC) was trapped into maltodextrins/pectin spray dried microcapsules to improve its activity against Salmonella enteritidis and Staphylococcus aureus biofilms. Two different microcapsules were prepared: uncomplexed DTAC-microcapsules (UDM), containing DTAC and maltodextrins; and complexed DTAC-microcapsules (CDM) containing DTAC complexed with pectin and maltodextrins. The minimum inhibitory concentrations (MIC) of both free and microencapsulated DTAC were investigated against S. Enteritidis and S. aureus. The MICs of DTAC were significantly lower when encapsulated. CDM treatment resulted in a 2 and 3.2 log reduction in S. aureus and S. Enteritidis biofilm culturable biomass, respectively. Microencapsulation reduced the cytotoxicity of DTAC by up to 32-fold. Free DTAC and CDM targeted the cell membrane resulting in the leakage of the intracellular molecules and subsequent cell death. The development of DTAC microcapsules reduced the amount of DTAC required to maintain the high standards of cleanliness and hygiene required in the food processing industries.

Thermal and non-thermal treatment effects on Staphylococcus aureus biofilms formed at different temperatures and maturation periods

The objective of this study was to investigate the effect of temperature and maturation period on the resistance of Staphylococcus aureus biofilms to thermal and non-thermal treatments. First, biofilm development was compared at three different temperatures (15, 25, and 37°C) for 5 days. The cell population at 15 and 25°C remained relatively consistent approximately at 6.3 log CFU/cm², whereas 37°C resulted in the highest cell population on day 1 (7.6 log CFU/cm²) followed by a continual decline. Then, biofilm resistance to steam and sodium hypochlorite (NaOCl) treatments was evaluated. Obtained results highlighted that biofilms had different resistance to both treatments depending on development conditions. Specifically, steam treatment of 10 s eliminated 4.1 log CFU/cm² of the biofilm formed at 25°C for 5 days. The same treatment inactivated over 5 log population of biofilms developed in other temperature and maturation period conditions. Treatment with NaOCl reduced approximately 1 log CFU/cm² of biofilm cells developed at 25°C for 5 days. However, inactivation was found to be over 2 log CFU/cm² under other development conditions. An extracellular polymeric substances (EPS) quantification using 96-well plates and stainless steel coupons was conducted. In the 96-well plate experiment, it was found that the highest amount of polysaccharide was secreted at 25°C (p < 0.05), while total biomass and protein contents were greatest at 37°C (p < 0.05). No significant difference in EPS content was observed for stainless steel, but the results displayed a similar trend to the 96-well plate. In particular, biofilms developed at 25°C tended to secret the highest amount of polysaccharide, which aligned with the current literature. This finding indicated that polysaccharide was the main contribution to the enhanced resistance of S. aureus biofilms. Overall, it was shown that biofilms formed at 25°C for 5 days exhibited the greatest resistance to thermal and nonthermal treatments due to the elevated exopolysaccharide secretion. This study demonstrates that temperature and maturation period significantly affect the resistance of S. aureus biofilms to thermal and non-thermal treatments.

Novel eradication methods for Staphylococcus aureus biofilm in poultry farms and abattoirs using disinfectants loaded onto silver and copper nanoparticles

Recent developments in the nanotechnology field have created opportunities to design new biomaterials for Staphylococcus aureus biofilm eradication. These biomaterials including disinfectant-loaded nanoparticles could overcome the limitations of conventional disinfectants. The objective of this study was to assess the biocidal activity of five commercial disinfectants (DC&R®, VirkonS®, TH4++, Tek-Trol, and peracetic acid) alone and as with silver and copper nanocomposites on S. aureus biofilm at different concentrations and exposure times. Consequently, 227 samples were collected from two broiler farms, two-layer farms, and three abattoirs at El-Dakahlia Province, Egypt, during summer 2018. The samples were collected from birds as well as the surrounding environment. S. aureus strains were isolated and biofilm producers were phenotypically evaluated by Congo red agar (CRA) test. Besides, 4 biofilm-associated genes including bap, fnbA, cna, and ebps were genotypically detected by PCR technology. Out of 227 collected samples, 141 (62.1%) strains were identified as S. aureus, while 127 strains (90.1%) were S. aureus biofilm producers for all examined samples except for hand swabs of abattoir workers. The prevalence of fnbA and bap genes was 79.5% (101/127) and 20.5% (26/127), respectively but, no strains harbored cna or ebps genes. Tested nanocomposites were prepared using an aqueous solution of metal salts such as copper sulfate and silver nitrate and added to the same amount of disinfectant solution. The obtained nanocomposites were characterized by transmission electron microscopy (TEM) and zeta potential which showed spherical and elongated particles and with a surface charge of disinfectants-silver and copper nanocomposites-of 2.92 and 3.43 mV, respectively. Complete eradication of S. aureus biofilm was observed after treatment with disinfectants loaded onto silver (AgNPs) and copper (CuNPs) nanoparticles in varying concentrations as well as at different exposure times in comparing to disinfectants alone. Our results exhibited the potential applications of disinfectant nanocomposites in complete eradication of S. aureus biofilm in farms and abattoirs without developing of disinfectant resistant bacteria.

Pseudomonas aeruginosa Biofilm Removal from Two Kinds of Granite Commonly Found in Catering Kitchen

The biofilm formation on the surfaces which are in direct contact with food products might lead to their contamination and, consequently, present serious health problems for the consumers. The goals of the present work were to study P. aeruginosa biofilm formation on two granites and to investigate the efficiency of sodium hypochlorite (NaCLO) against the same biofilm formed on these substrata using the plate count method (PCM) and epifluorescence microscopy (EP). More biofilm cells adhered to Rosa Porrino than Gris Pinhel, and the PCM method indicated that NaCLO was efficient against the biofilm installed on the Gris Pinhel at the concentration of 1.5% after 15 min of treatment, while it was not efficient against the one installed on the Rosa Porrino. By contrast, the EP showed that the biofilm persists on two granites after NaCLO treatment, at different concentrations and contact times. In addition, the surface properties of granites such as mineral composition, roughness, and physicochemical properties were determined by X-ray diffraction (XRD), scanning electron microscopy coupled with electron diffraction spectroscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared (FTIR), atomic force microscopy (AFM), and contact angle measurement (CAM), respectively. The results revealed that Gris Pinhel is hydrophilic with a high roughness value and Rosa Porrino is hydrophobic with low roughness, while both of them contain the quartz, feldspar, and mica as the main dominant compositions.

Artificial dry surface biofilm models for testing the efficacy of cleaning and disinfection

Dry surface biofilms (DSB) harbouring pathogens are widespread in healthcare settings, are difficult to detect and are resistant to cleaning and disinfection interventions. Here, we describe a practical test protocol to palliate the lack of standard efficacy test methods for DSB. Staphylococcus aureus DSB were produced over a 12-day period, grown with or without the presence of organic matter, and their composition and viability were evaluated. Disinfectant treatment was conducted with a modified ASTM2967-15 test and reduction in viability, transferability and biofilm regrowth post-treatment were measured. Dry surface biofilms produced over a 12-day period had a similar carbohydrates, proteins and DNA content, regardless of the presence or absence of organic matter. The combination of sodium hypochlorite (1000 ppm) and a microfiber cloth was only effective against DSB in the absence of organic load. With the increasing concerns of the uncontrolled presence of DSB in healthcare settings, the development of effective intervention model in the presence of organic load is appropriate for the testing of biocidal products, while the use of three parameters, log₁₀ reduction, transferability and regrowth, provides an accurate and practical measurement of product efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: The widespread presence of biofilms on dry surfaces in healthcare settings has been recently documented. These dry surface biofilms (DSB) present an unprecedented challenge to cleaning and disinfection processes. Here, we describe a practical efficacy protocol based on an in vitro Staphylococcus aureus DSB model. The protocol measures reduction in viability, transferability and biofilm regrowth post-treatment to provide altogether a practical assessment of product efficacy against dry surface biofilms.

The oceans are changing: impact of ocean warming and acidification on biofouling communities

Climate change (CC) is driving modification of the chemical and physical properties of estuaries and oceans with profound consequences for species and ecosystems. Numerous studies investigate CC effects from species to ecosystem levels, but little is known of the impacts on biofilm communities and on bioactive molecules such as cues, adhesives and enzymes. CC is induced by anthropogenic activity increasing greenhouse emissions leading to rises in air and water temperatures, ocean acidification, sea level rise and changes in ocean gyres and rainfall patterns. These environmental changes are resulting in alterations within marine communities and changes in species ranges and composition. This review provides insights and synthesis of knowledge about the effect of elevated temperature and ocean acidification on microfouling communities and bioactive molecules. The existing studies suggest that CC will impact production of bioactive compounds as well as the growth and composition of biofouling communities. Undoubtedly, with CC fouling management will became an even greater challenge.

Behavior of Foodborne Pathogens Listeria monocytogenes and Staphylococcus aureus in Mixed-Species Biofilms Exposed to Biocides

In nature and man-made environments, microorganisms reside in mixed-species biofilms, in which the growth and metabolism of an organism are different from these behaviors in single-species biofilms. Pathogenic microorganisms may be protected against adverse treatments in mixed-species biofilms, leading to health risk for humans. Here, we developed two mixed five-species biofilms that included one or the other of the foodborne pathogens Listeria monocytogenes and Staphylococcus aureus The five species, including the pathogen, were isolated from a single food-processing environmental sample, thus mimicking the environmental community. In mature mixed five-species biofilms on stainless steel, the two pathogens remained at a constant level of ∼105 CFU/cm2 The mixed five-species biofilms as well as the pathogens in monospecies biofilms were exposed to biocides to determine any pathogen-protective effect of the mixed biofilm. Both pathogens and their associate microbial communities were reduced by peracetic acid treatments. S. aureus decreased by 4.6 log cycles in monospecies biofilms, but the pathogen was protected in the five-species biofilm and decreased by only 1.1 log cycles. Sessile cells of L. monocytogenes were affected to the same extent when in a monobiofilm or as a member of the mixed-species biofilm, decreasing by 3 log cycles when exposed to 0.0375% peracetic acid. When the pathogen was exchanged in each associated microbial community, S. aureus was eradicated, while there was no significant effect of the biocide on L. monocytogenes or the mixed community. This indicates that particular members or associations in the community offered the protective effect. Further studies are needed to clarify the mechanisms of biocide protection and to identify the species playing the protective role in microbial communities of biofilms.IMPORTANCE This study demonstrates that foodborne pathogens can be established in mixed-species biofilms and that this can protect them from biocide action. The protection is not due to specific characteristics of the pathogen, here S. aureus and L. monocytogenes, but likely caused by specific members or associations in the mixed-species biofilm. Biocide treatment and resistance are a challenge for many industries, and biocide efficacy should be tested on microorganisms growing in biofilms, preferably mixed systems, mimicking the application environment.

Transcriptome analysis of silver nanoparticles treated Staphylococcus aureus reveals potential targets for biofilm inhibition

The biofilms of Staphylococcus aureus on the implanted materials and chronic wounds are life-threatening and are a substantial financial burden on the healthcare system. Silver nanoparticles (SNP), known for their multi-level physiological effects in planktonic cells could be a promising agent in the treatment of biofilm-related infections also. To gain insight into the effects of SNP on various physiological processes in biofilms we studied the transcriptome of Staphylococcus aureus ATCC 29213. To distinguish between 'nanoparticles-specific' and 'ion-specific' effect of silver, we performed a comparative analysis of the functional genes in response to Ag⁺. As compared to untreated biofilms, 21% (i.e. 629 genes) and 28.5% (i. e. 830 genes) of the total functional coding genes were differentially regulated upon exposure to SNP and Ag⁺. Genes encoding capsular polysaccharides, intercellular adhesion, virulence were downregulated in SNP and Ag⁺ treated biofilms. Genes involved in carbohydrate, protein metabolism including DNA and RNA synthesis, oxidative stress etc. were differentially expressed. Further, activation of efflux pumps and multidrug export proteins was observed, which clearly indicates the presence of metal stress resistance determinants in S. aureus. Silver blocked the integration of mobile genetic elements in S. aureus genome. Our study points out quorum sensing and virulence determinants as possible targets for inhibition of biofilms possibly with/without existing antibiotics. However, further studies on these aspects are warranted. Scanning electron microscopy (SEM) and confocal microscopy revealed changes in biofilm morphology, architecture and thickness in presence of silver nanoparticles and ionic silver, substantiating the transcriptome data.

Susceptibility patterns and the role of extracellular DNA in Staphylococcus epidermidis biofilm resistance to physico-chemical stress exposure

Background

Over 65% of human infections are ascribed to bacterial biofilms that are often highly resistant to antibiotics and host immunity. Staphylococcus epidermidis is the predominant cause of recurrent nosocomial and biofilm-related infections. However, the susceptibility patterns of S. epidermidis biofilms to physico-chemical stress induced by commonly recommended disinfectants [(heat, sodium chloride (NaCl), sodium hypochlorite (NaOCl) and hydrogen peroxide (H₂O₂)] in domestic and human healthcare settings remains largely unknown. Further, the molecular mechanisms of bacterial biofilms resistance to the physico-chemical stresses remain unclear. Growing evidence demonstrates that extracellular DNA (eDNA) protects bacterial biofilms against antibiotics. However, the role of eDNA as a potential mechanism underlying S. epidermidis biofilms resistance to physico-chemical stress exposure is yet to be understood. Therefore, this study aimed to evaluate the susceptibility patterns of and eDNA release by S. epidermidis biofilm and planktonic cells to physico-chemical stress exposure.

Results

S. epidermidis biofilms exposed to physico-chemical stress conditions commonly recommended for disinfection [heat (60 °C), 1.72 M NaCl, solution containing 150 μL of waterguard (0.178 M NaOCl) in 1 L of water or 1.77 M H₂O₂] for 30 and 60 min exhibited lower log reductions of CFU/mL than the corresponding planktonic cells (p < 0.0001). The eDNA released by sub-lethal heat (50 °C)-treated S. epidermidis biofilm and planktonic cells was not statistically different (p = 0.8501). However, 50 °C-treated S. epidermidis biofilm cells released significantly increased eDNA than the untreated controls (p = 0.0098). The eDNA released by 0.8 M NaCl-treated S. epidermidis biofilm and planktonic cells was not significantly different (p = 0.9697). Conversely, 5 mM NaOCl-treated S. epidermidis biofilms exhibited significantly increased eDNA release than the corresponding planktonic cells (p = 0.0015). Further, the 50 μM H₂O₂-treated S. epidermidis biofilms released significantly more eDNA than the corresponding planktonic cells (p = 0.021).

Conclusions

S. epidermidis biofilms were less susceptible to physico-chemical stress induced by the four commonly recommended disinfectants than the analogous planktonic cells. Further, S. epidermidis biofilms enhanced eDNA release in response to the sub-lethal heat and oxidative stress exposure than the corresponding planktonic cells suggesting a role of eDNA in biofilms resistance to the physico-chemical stresses.

Roles of pyruvate dehydrogenase and branched-chain α-keto acid dehydrogenase in branched-chain membrane fatty acid levels and associated functions in Staphylococcus aureus

PURPOSE

Membrane fluidity to a large extent is governed by the presence of branched-chain fatty acids (BCFAs). Branched-chain α-keto acid dehydrogenase (BKD) is the key enzyme in BCFA synthesis. A Staphylococcus aureus BKD-deficient strain still produced substantial levels of BCFAs. Pyruvate dehydrogenase (PDH) with structural similarity to BKD has been speculated to contribute to BCFAs in S. aureus.

METHODOLOGY

This study was carried out using BKD-, PDH- and BKD : PDH-deficient derivatives of methicillin-resistant S. aureus strain JE2. Differences in growth kinetics were evaluated spectrophotometrically, membrane BCFAs using gas chromatography and membrane fluidity by fluorescence polarization. Carotenoid levels were estimated by measuring A465 of methanol extracts from 48 h cultures. MIC values were determined by broth microdilution.Results/Key findings. BCFAs made up 50 % of membrane fatty acids in wild-type but only 31 % in the BKD-deficient mutant. BCFA level was ~80 % in the PDH-deficient strain and 38 % in the BKD : PDH-deficient strain. BKD-deficient mutant showed decreased membrane fluidity, the PDH-deficient mutant showed increased membrane fluidity. The BKD- and PDH-deficient strains grew slower and the BKD : PDH-deficient strain grew slowest at 37 °C. However at 20 °C, the BKD- and BKD : PDH-deficient strains grew only a little followed by autolysis of these cells. The BKD-deficient strain produced higher levels of staphyloxanthin. The PDH-deficient and BKD : PDH-deficient strains produced very little staphyloxanthin. The BKD-deficient strain showed increased susceptibility to daptomycin.

CONCLUSION

The BCFA composition of the cell membrane in S. aureus seems to significantly impact cell growth, membrane fluidity and resistance to daptomycin.

Effect of incubation duration, growth temperature, and abiotic surface type on cell surface properties, adhesion and pathogenicity of biofilm-detached Staphylococcus aureus cells

The goal of this study was to investigate the effect of growth conditions such as the temperature (20, 30 and 37 °C), incubation duration (24 and 48 h) and surface type (stainless steel and polycarbonate) on the cell surface physicochemical properties and adhesion to abiotic surfaces of biofilm-detached and planktonic Staphylococcus aureus cells. This study tested also the hypothesis that S. aureus planktonic cells exhibit distinct pathogenic properties compared with their sessile counterparts. The results showed that the changes of the growth conditions promoted changes in the zeta potential, hydrophobicity, electron donor/acceptor character of the studied cell populations. Biofilm-detached cells showed a greater adhesion to stainless steel and polycarbonate compared with planktonic cells. Compared with planktonic cells, sessile ones showed higher cytotoxic effect against HeLa cells, DNase activity, and siderophore levels. The higher cytotoxic effect and production of DNase and siderophore increased with the increase of temperature and duration of incubations. Based on the obtained data, the S. aureus biofilm-detached cells were found to be distinct in many physiological properties compared with their planktonic counterparts.

Impact of temperature on Marinobacter hydrocarbonoclasticus SP17 morphology and biofilm structure during growth on alkanes

Alkanes are widespread pollutants found in soil, freshwater and marine environments. Marinobacter hydrocarbonoclasticus (Mh) strain SP17 is a marine bacterium able to use many hydrophobic organic compounds, including alkanes, through the production of biofilms that allow their poor solubility to be overcome. This study pointed out that temperature is an environmental factor that strongly affects the biofilm formation and morphology of Mh on the model alkanes, hexadecane and paraffin. We showed that Mh biofilm formation and accumulation of intracytoplasmic inclusions are higher on solid alkanes (hexadecane at 10 °C and paraffin at 10 °C and 30 °C) than on liquid alkane (hexadecane at 30 °C) or soluble substrate (lactate at both temperatures). We also found that Mh produces more extracellular polymeric substances at 30 °C than at 10 °C on alkanes and none on lactate. We observed that bacterial length is significantly higher at 10 °C than at 30 °C on lactate and hexadecane. On paraffin, at 30 °C, the cell morphology is markedly altered by large rounded or irregularly shaped cytoplasmic inclusions. Altogether, the results showed that Mh is able to adapt and use alkanes as a carbon source, even at low temperature.

Respiratory pathogens mediate the association between lung function and temperature in cystic fibrosis

INTRODUCTION

Mean annual ambient temperature is a replicated environmental modifier of cystic fibrosis (CF) lung disease with warmer temperatures being associated with lower lung function. The mechanism of this relationship is not completely understood. However, Pseudomonas aeruginosa, a pathogen that infects the lungs of CF individuals and decreases lung function, also has a higher prevalence in individuals living in warmer climates. We therefore investigated the extent to which respiratory pathogens mediated the association between temperature and lung function.

METHODS

Thirteen respiratory pathogens observed on CF respiratory cultures were assessed in multistep fashion using clustered linear and logistic regression to determine if any mediated the association between temperature and lung function. Analysis was performed in the CF Twin-Sibling Study (n=1730; primary population); key findings were then evaluated in the U.S. CF Foundation Data Registry (n=15,174; replication population).

RESULTS

In the primary population, three respiratory pathogens (P. aeruginosa, mucoid P. aeruginosa, and methicillin-resistant Staphylococcus aureus) mediated the association between temperature and lung function. P. aeruginosa accounted for 19% of the association (p=0.003), mucoid P. aeruginosa for 31% (p=0.001), and MRSA for 13% (p=0.023). The same three pathogens mediated association in the replication population (7%, p<0.001; 7%, p=0.002; and 4%, (p=0.002), respectively).

CONCLUSIONS

Three important respiratory pathogens in CF mediate the association between lower lung function and warmer temperatures. These findings have implications for understanding regional variations in clinical outcomes, and interpreting results of epidemiologic studies and clinical trials that encompass regions with different ambient temperatures.

Optimization of culture conditions for Gardnerella vaginalis biofilm formation

Bacterial vaginosis is the leading vaginal disorder in women in reproductive age. Although bacterial vaginosis is related with presence of a biofilm composed predominantly by Gardnerella vaginalis, there has not been a detailed information addressing the environmental conditions that influence the biofilm formation of this bacterial species. Here, we evaluated the influence of some common culture conditions on G. vaginalis biofilm formation, namely inoculum concentration, incubation period, feeding conditions and culture medium composition. Our results showed that culture conditions strongly influenced G. vaginalis biofilm formation and that biofilm formation was enhanced when starting the culture with a higher inoculum, using a fed-batch system and supplementing the growth medium with maltose.

Impact of growth temperature and surface type on the resistance of Pseudomonas aeruginosa and Staphylococcus aureus biofilms to disinfectants

Biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus on food-contact-surfaces represents a significant risk for the public health. In this context, the present study investigates the relationship between the environmental conditions of biofilm formation and the resistance to disinfectants. Therefore, a static biofilm reactor, called NEC-Biofilm System, was established in order to study the effect of growth temperature (20, 30 and 37°C), and of the surface type (stainless steel and polycarbonate), on biofilm resistance to disinfectants. These conditions were selected to mimic the biofilm formation on abiotic surfaces of food processing industries. The antibiofilm assays were performed on biofilms grown during 24 h. The results showed that the growth temperature influenced significantly the biofilm resistance to disinfectants. These data also revealed that the growth temperature has a significant effect on the biofilm structure of both bacteria. Furthermore, the increase of the biofilm growth temperature increased significantly the algD transcript level in sessile P. aeruginosa cells, whereas the icaA one was not affected in S. aureus cells. Overall, our findings show that the biofilm structure and matrix cannot fully explain the biofilm resistance to disinfectant agents. Nevertheless, it underlines the intimate link between environmental conditions, commonly met in food sectors, and the biofilm resistance to disinfectants.

Effect of temperature on the release of carvacrol and cinnamaldehyde incorporated into polymeric systems to control growth and biofilms of Escherichia coli and Staphylococcus aureus

This study assessed the effect of temperature on the release of essential oil components incorporated by melt compounding into polymeric films. Specifically, polyethylene-co-vinylacetate (EVA) films containing carvacrol (CAR) and cinnamaldehyde (ALD), alone and in combination, were prepared and their surface and mechanical properties and antibacterial and anti-biofilm activity against Escherichia coli and Staphylococcus aureus were evaluated. The addition of ALD and CAR did not provoke variation in the surface morphology of EVA and allowed their delivery. At 37°C, films containing CAR, ALD or their combination (25+75%) were found to have the strongest bactericidal effect, whereas at lower temperatures a lower killing rate was observed. There was no clear evidence of the influence of temperature on the anti-biofilm activity of the essential oil component-based polymeric films. The biomass formed on EVA containing ALD, CAR or their combination (25+75) was significantly lower (60-80% reduction) than that formed on the EVA control at both 37° and 22°C.

Effect of culture conditions on the resistance of Pseudomonas aeruginosa biofilms to disinfecting agents

The relationship between the environmental conditions of biofilm formation and resistance to disinfectants was studied. Anti-biofilm assays were performed against biofilms grown at 20, 30 and 37°C on stainless steel and polycarbonate, over 24 and 48 h. A rise in growth temperature increased the resistance of 24 h biofilms to disinfectants containing didecyldimethylammonium chloride and decreased it to a disinfectant containing alkyldimethylbenzylammonium chloride. The increase in growth temperature coupled with an incubation time of 24 h promoted increases in both matrix production and the membrane rigidity of sessile cells. An increase in incubation time also increased both matrix production and the membrane rigidity of sessile cells. Such phenomena resulted in an increased resistance to disinfectants of biofilms grown at 20 and 30°C. The resistance of 48 h biofilms to disinfectants decreased with an increase in growth temperature despite the increase in matrix production and the membrane rigidity of sessile cells.

Phenotype and expression profile analysis of Staphylococcus aureus biofilms and planktonic cells in response to licochalcone A

Staphylococcus aureus is one of the most important pathogens in humans and animals. The formation of biofilm by S. aureus is considered an important mechanism of antimicrobial resistance. Therefore, finding effective drugs against the biofilm produced by S. aureus has been a high priority. Licochalcone A (LAA), a natural plant product, was reported to have antibacterial activities and showed good activity against all 21 tested strains of S. aureus biofilm and planktonic cells. To detect the possible molecular mechanism of LAA against S. aureus biofilm or planktonic cells, Affymetrix GeneChips were used to determine the global comparative transcription of S. aureus biofilm and planktonic cells triggered by treatment with sub-bactericidal and sub-inhibitory concentrations of LAA, respectively. LAA significantly altered (greater than a 2- or less than -2-fold change) the expression of 693 genes in planktonic cells and 817 genes in biofilm. The levels of genes encoding autolysis-associated proteins, cell wall proteins, pathogenic factors, protein synthesis genes, and enzymes involved in capsule synthesis were significantly altered in LAA-treated S. aureus. Furthermore, some differences observed in the microarray analysis were verified by real-time RT-PCR. To our knowledge, this is the first observation of phenotype and expression profiles of S. aureus biofilm and planktonic cells in response to LAA treatment.

Identification of lactobacilli with inhibitory effect on biofilm formation by pathogenic bacteria on stainless steel surfaces

Two hundred and thirty individual clones of microorganisms were recovered from milk tanks and milking machine surfaces at two distinct farms (Bejaja City, Algeria). Of these clones, 130 were identified as lactic acid bacteria (LAB). In addition Escherichia coli, Salmonella, Staphylococcus aureus and Pseudomonas aeruginosa species were identified in the remaining 100 isolates-spoilage isolate. These isolates were assayed for ability to form biofilms. S. aureus, Lactobacillus brevis strains LB1F2, LB14F1 and LB15F1, and Lactobacillus pentosus strains LB2F2 and LB3F2 were identified as the best biofilm formers. Besides, these LAB isolates were able to produce proteinaceous substances with antagonism against the aforementioned spoilage isolates, when grown in MRS or TSB-YE media. During the screening, L. pentosus LB3F2 exhibited the highest antibacterial activity when grown in TSB-YE medium at 30 °C. Additionally, L. pentosus LB3F2 was able to strongly hamper the adhesion of S. aureus SA3 on abiotic surfaces as polystyrene and stainless steel slides. LAB isolates did not show any hemolytic activity and all of them were sensitive to different families of antibiotic tested. It should be pointed out that LB3F2 isolate was not cytotoxic on the intestinal cells but could stimulate their metabolic activity. This report unveiled the potential of LB1F2, LB14F1, LB15F1, LB2F2, and LB3F2 isolates to be used as natural barrier or competitive exclusion organism in the food processing sector as well as a positive biofilm forming bacteria.

Biofilm formation and persistence on abiotic surfaces in the context of food and medical environments

The biofilm formation on abiotic surfaces in food and medical sectors constitutes a great public health concerns. In fact, biofilms present a persistent source for pathogens, such as Pseudomonas aeruginosa and Staphylococcus aureus, which lead to severe infections such as foodborne and nosocomial infections. Such biofilms are also a source of material deterioration and failure. The environmental conditions, commonly met in food and medical area, seem also to enhance the biofilm formation and their resistance to disinfectant agents. In this regard, this review highlights the effect of environmental conditions on bacterial adhesion and biofilm formation on abiotic surfaces in the context of food and medical environment. It also describes the current and emergent strategies used to study the biofilm formation and its eradication. The mechanisms of biofilm resistance to commercialized disinfectants are also discussed, since this phenomenon remains unclear to date.