Characterization of a modified rotating disk reactor for the cultivation of Staphylococcus epidermidis biofilm

Challenges and current advances in in vitro biofilm characterization

Biofilms are structured communities of bacterial cells encased in a self-produced polymeric matrix, which develop over time and exhibit temporal responses to stimuli from internal biological processes or external environmental changes. They can be detrimental, threatening public health and causing economic loss, while they also play beneficial roles in ecosystem health, biotechnology processes, and industrial settings. Biofilms express extreme heterogeneity in their physical properties and structural composition, resulting in critical challenges in understanding them comprehensively. The lack of detailed knowledge of biofilms and their phenotypes has deterred significant progress in developing strategies to control their negative impacts and take advantage of their beneficial applications. A range of in vitro models and characterization tools have been developed and used to study biofilm growth and, specifically, to investigate the impact of environmental and growth factors on their development. This review article discusses the existing knowledge of biofilm properties and explains how external factors, such as flow condition, surface, interface, and host factor, may impact biofilm growth. The limitations of current tools, techniques, and in vitro models that are currently used for biofilms are also presented.

An overview of various methods for in vitro biofilm formation: a review

Biofilms are widely present in the natural environment and are difficult to remove as they are a survival strategy of microorganisms. Thus, the importance of studying biofilms is being increasingly recognized in food, medical, dental, and water quality-related industries. While research on biofilm detection methods is actively progressing, research on biofilm formation is not progressing rapidly. Moreover, there are few standardized methods because biofilm formation is affected by various factors. However, comprehensive knowledge of biofilm formation is essential to select a suitable method for research purposes. To better understand the various in vitro biofilm formation methods, the principles and characteristics of each method are explained in this review by dividing the methods into static and dynamic systems. In addition, the applications of biofilm research based on various assays are also discussed.

An adaptable microreactor to investigate the influence of interfaces on Pseudomonas aeruginosa biofilm growth

Abstract

Biofilms are ubiquitous and notoriously difficult to eradicate and control, complicating human infections and industrial and agricultural biofouling. However, most of the study had used the biofilm model that attached to solid surface and developed in liquid submerged environments which generally have neglected the impact of interfaces. In our study, a reusable dual-chamber microreactor with interchangeable porous membranes was developed to establish multiple growth interfaces for biofilm culture and test. Protocol for culturing Pseudomonas aeruginosa (PAO1) on the air–liquid interface (ALI) and liquid–liquid interface (LLI) under static environmental conditions for 48 h was optimized using this novel device. This study shows that LLI model biofilms are more susceptible to physical disruption compared to ALI model biofilm. SEM images revealed a unique “dome-shaped” microcolonies morphological feature, which is more distinct on ALI biofilms than LLI. Furthermore, the study showed that ALI and LLI biofilms produced a similar amount of extracellular polymeric substances (EPS). As differences in biofilm structure and properties may lead to different outcomes when using the same eradication approaches, the antimicrobial effect of an antibiotic, ciprofloxacin (CIP), was chosen to test the susceptibility of a 48-h-old P. aeruginosa biofilms grown on ALI and LLI. Our results show that the minimum biofilm eradication concentration (MBEC) of 6-h CIP exposure for ALI and LLI biofilms is significantly different, which are 400 μg/mL and 200 μg/mL, respectively. These results highlight the importance of growth interface when developing more targeted biofilm management strategies, and our novel device provides a promising tool that enables manipulation of realistic biofilm growth.

Key points

• A novel dual-chamber microreactor device that enables the establishment of different interfaces for biofilm culture has been developed.

• ALI model biofilms and LLI model biofilms show differences in resistance to physical disruption and antibiotic susceptibility.

Operational culture conditions determinate benzalkonium chloride resistance in L. monocytogenes-E. coli dual species biofilms

Biofilms pose a serious challenge to the food industry. Higher resistance of biofilms to any external stimuli is a major hindrance for their eradication. In this study, we compared the growth dynamics and benzalkonium chloride (BAC) resistance of dual species Listeria monocytogenes-Escherichia coli 48 h biofilms formed on stainless steel (SS) coupons surfaces under batch and fed-batch cultures. Differences between both operational culture conditions were evaluated in terms of total viable adhered cells (TVAC) in the coupons during 48 h of the mixed-culture and of reduction of viable adhered cells (RVAC) obtained after BAC-treatment of a 48 h biofilm of L. monocytogenes-E. coli formed under both culture conditions. Additionally, epifluorescence microscopy (EFM) and confocal scanning microscopy (CLSM) permitted to visualize the 2D and 3D biofilms structure, respectively. Observed results showed an increase in the TVAC of both strains during biofilm development, being the number of E. coli adhered cells higher than L. monocytogenes in both experimental systems (p < 0.05). Additionally, the number of both strains were higher approximately 2.0 log CFU/coupon in batch conditions compared to fed-batch system (p < 0.05). On the contrary, significantly higher resistance to BAC was observed in biofilms formed under fed-batch conditions. Furthermore, in batch system both strains had a similar reduction level of approximately 2.0 log CFU/coupon, while significantly higher resistance of E. coli compared to L. monocytogenes (reduction level of 0.69 and 1.72 log CFU/coupon, respectively) (p < 0.05) was observed in fed-batch system. Microscopic image visualization corroborated these results and showed higher complexity of 2D and 3D structures in dual species biofilms formed in batch cultures. Overall, we can conclude that the complexity of the biofilm structure does not always imply higher resistance to external stimuli, and highlights the need to mimic industrial operational conditions in the experimental systems in order to better assess the risk associated to the presence of pathogenic bacterial biofilms.

A Selection of Platforms to Evaluate Surface Adhesion and Biofilm Formation in Controlled Hydrodynamic Conditions

The early colonization of surfaces and subsequent biofilm development have severe impacts in environmental, industrial, and biomedical settings since they entail high costs and health risks. To develop more effective biofilm control strategies, there is a need to obtain laboratory biofilms that resemble those found in natural or man-made settings. Since microbial adhesion and biofilm formation are strongly affected by hydrodynamics, the knowledge of flow characteristics in different marine, food processing, and medical device locations is essential. Once the hydrodynamic conditions are known, platforms for cell adhesion and biofilm formation should be selected and operated, in order to obtain reproducible biofilms that mimic those found in target scenarios. This review focuses on the most widely used platforms that enable the study of initial microbial adhesion and biofilm formation under controlled hydrodynamic conditions—modified Robbins devices, flow chambers, rotating biofilm devices, microplates, and microfluidic devices—and where numerical simulations have been used to define relevant flow characteristics, namely the shear stress and shear rate.

Current In Vitro Biofilm-Infected Chronic Wound Models for Developing New Treatment Possibilities

Significance: The prevalence of chronic wounds is increasing worldwide. The most recent estimates suggest that up to 2% of the population in the industrialized countries is affected. Recent Advances: During the past few decades, bacterial biofilms have been elucidated as one of the primary reasons why chronic wounds fail to heal. Critical Issues: There is a lack of direct causation and evidence of the role that biofilms play in persistent wounds, which complicates research on new treatment options, since it is still unknown which factors dominate. For this reason, several different in vitro wound models that mimic the biofilm infections observed in chronic wounds and other chronic infections have been created. These different models are, among other purposes, used to test a variety of wound care products. However, chronic wounds are highly complex, and several different factors must be taken into consideration along with the infection, including physiochemical and human-supplemented factors. Furthermore, the limitations of using in vitro models, such as the lack of a responsive immune system should always be given due consideration. Future Directions: Present understandings of all the elements and interactions that take place within chronic wounds are incomplete. As our insight of in vivo chronic wounds continues to expand, so too must the in vitro models used to mimic these infections evolve and adapt to new knowledge.

Adjunct use of mouth rinses with a sonic toothbrush accelerates the detachment of a Streptococcus mutans biofilm: an in vitro study

BACKGROUND

The aim of this in vitro study was to examine the possible enhancement of the biofilm peeling effect of a sonic toothbrush following the use of an antimicrobial mouth rinse.

METHODS

The biofilm at a noncontact site in the interdental area was treated by sound wave convection with the test solution or by immersion in the solution. The biofilm peeling effect was evaluated by determining the bacterial counts and performing morphological observations. A Streptococcus mutans biofilm was allowed to develop on composite resin discs by cultivation with stirring at 50 rpm for 72 h. The specimens were then placed in recesses located between plastic teeth and divided into an immersion group and a combination group. The immersion group was treated with phosphate buffer, chlorhexidine digluconate Peridex™ (CHX) mouth rinse or Listerine® Fresh Mint (EO) mouth rinse. The combination group was treated with CHX or EO and a sonic toothbrush.

RESULTS

The biofilm thickness was reduced by approximately one-half compared with the control group. The combination treatment produced a 1 log reduction in the number of bacteria compared to the EO immersion treatment. No significant difference was observed in the biofilm peeling effect of the immersion group compared to the control group.

CONCLUSIONS

The combined use of a sonic toothbrush and a mouth rinse enhanced the peeling of the biofilm that proliferates in places that are difficult to reach using mechanical stress.

Testing Anti-Biofilm Polymeric Surfaces: Where to Start?

Present day awareness of biofilm colonization on polymeric surfaces has prompted the scientific community to develop an ever-increasing number of new materials with anti-biofilm features. However, compared to the large amount of work put into discovering potent biofilm inhibitors, only a small number of papers deal with their validation, a critical step in the translation of research into practical applications. This is due to the lack of standardized testing methods and/or of well-controlled in vivo studies that show biofilm prevention on polymeric surfaces; furthermore, there has been little correlation with the reduced incidence of material deterioration. Here an overview of the most common methods for studying biofilms and for testing the anti-biofilm properties of new surfaces is provided.

Comparison of periodontitis-associated oral biofilm formation under dynamic and static conditions

Purpose

The purpose of this study was to compare the characteristics of single- and dual-species in vitro oral biofilms made by static and dynamic methods.

Methods

Hydroxyapatite (HA) disks, 12.7 mm in diameter and 3 mm thick, were coated with processed saliva for 4 hours. The disks were divided into a static method group and a dynamic method group. The disks treated with a static method were cultured in 12-well plates, and the disks in the dynamic method group were cultured in a Center for Disease Control and Prevention (CDC) biofilm reactor for 72 hours. In the single- and dual-species biofilms, Fusobacterium nucleatum and Porphyromonas gingivalis were used, and the amount of adhering bacteria, proportions of species, and bacterial reduction of chlorhexidine were examined. Bacterial adhesion was examined with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).

Results

Compared with the biofilms made using the static method, the biofilms made using the dynamic method had significantly lower amounts of adhering and looser bacterial accumulation in SEM and CLSM images. The proportion of P. gingivalis was higher in the dynamic method group than in the static method group; however, the difference was not statistically significant. Furthermore, the biofilm thickness and bacterial reduction by chlorhexidine showed no significant differences between the 2 methods.

Conclusions

When used to reproduce periodontal biofilms composed of F. nucleatum and P. gingivalis, the dynamic method (CDC biofilm reactor) formed looser biofilms containing fewer bacteria than the well plate. However, this difference did not influence the thickness of the biofilms or the activity of chlorhexidine. Therefore, both methods are useful for mimicking periodontitis-associated oral biofilms.

Residual structure of Streptococcus mutans biofilm following complete disinfection favors secondary bacterial adhesion and biofilm re-development

Chemical disinfection of oral biofilms often leaves biofilm structures intact. This study aimed to examine whether the residual structure promotes secondary bacterial adhesion. Streptococcus mutans biofilms generated on resin-composite disks in a rotating disc reactor were disinfected completely with 70% isopropyl alcohol, and were again cultured in the same reactor after resupplying with the same bacterial solution. Specimens were subjected to fluorescence confocal laser scanning microscopy, viable cell counts and PCR-Invader assay in order to observe and quantify secondarily adhered cells. Fluorescence microscopic analysis, particularly after longitudinal cryosectioning, demonstrated stratified patterns of viable cells on the disinfected biofilm structure. Viable cell counts of test specimens were significantly higher than those of controls, and increased according to the amount of residual structure and culture period. Linear regression analysis exhibited a high correlation between viable and total cell counts. It was concluded that disinfected biofilm structures favored secondary bacterial adhesion.