Characterizing the Shearing Stresses within the CDC Biofilm Reactor Using Computational Fluid Dynamics

Using Bio-inline Reactor to Evaluate Sanitizer Efficacy in Removing Dual-species Biofilms Formed by Escherichia coli O157:H7 and Listeria monocytogenes

The efficacy of a sanitizer in biofilm removal may be influenced by a combination of factors such as sanitizer exposure time and concentration, bacterial species, surface topography, and shear stresses. We employed an inline biofilm reactor to investigate the interactions of these variables on biofilm removal with chlorine. The CDC bioreactor was used to grow E. coli O157:H7 and L. monocytogenes biofilms as a single species or with Ralstonia insidiosa as a dual-species biofilm on stainless steel, PTFE, and EPDM coupons at shear stresses 0.368 and 2.462 N/m2 for 48 hours. Coupons were retrieved from a CDC bioreactor and placed in an inline biofilm reactor and 100, 200, or 500 ppm of chlorine was supplied for 1- and 4 min. Bacterial populations in the biofilms were quantified pre- and posttreatment by plating on selective media. After chlorine treatment, reduction (Log CFU/cm2) in pathogen populations obtained from three replicates was analyzed for statistical significance. A 1-min chlorine treatment (500 ppm), on dual-species E. coli O157:H7 biofilms grown at high shear stress of 2.462 N/m2 resulted in significant E. coli O157:H7 reductions on SS 316L (2.79 log CFU/cm2) and PTFE (1.76 log CFU/cm2). Similar trend was also observed for biofilm removal after a 4-min chlorine treatment. Single species E. coli O157:H7 biofilms exhibited higher resistance to chlorine when biofilms were developed at high shear stress. The effect of chlorine in L. monocytogenes removal from dual-species biofilms was dependent primarily on the shear stress at which they were formed rather than the surface topography of materials. Besides surface topography, shear stresses at which biofilms were formed also influenced the effect of sanitizer. The removal of E. coli O157:H7 biofilms from EPDM material may require critical interventions due to difficulty in removing this pathogen. The inline biofilm reactor is a novel tool to evaluate the efficacy of a sanitizer in bacterial biofilm removal.

Coupon position does not affect Pseudomonas aeruginosa and Staphylococcus aureus biofilm densities in the CDC biofilm reactor

The CDC Biofilm Reactor method is the standard biofilm growth protocol for the validation of US Environmental Protection Agency biofilm label claims. However, no studies have determined the effect of coupon orientation within the reactor on biofilm growth. If positional effects have a statistically significant impact on biofilm density, they should be accounted for in the experimental design. Here, we isolate and quantify biofilms from each possible coupon surface in the reactor to quantitatively determine the positional effects in the CDC Biofilm Reactor. The results showed no statistically significant differences in viable cell density across different orientations and vertical positions in the reactor. Pseudomonas aeruginosa log densities were statistically equivalent among all coupon heights and orientations. While the Staphylococcus aureus cell growth showed no statistically significant differences, the densities were not statistically equivalent among all coupon heights and orientations due to the variability in the data. Structural differences were observed between biofilms on the high-shear baffle side of the reactor compared to the lower shear glass side of the reactor. Further studies are required to determine whether biofilm susceptibility to antimicrobials differs based on structural differences attributed to orientation.

The Infected Polypropylene Mesh: When Does Biofilm Form and Which Antiseptic Solution Most Effectively Removes It?

BACKGROUND

Polypropylene (PPE) mesh is commonly utilized to reconstruct catastrophic extensor mechanism disruptions in revision total knee arthroplasty. Unfortunately, these procedures are associated with a high rate of periprosthetic joint infection. The purpose of the current study was to: 1) visualize and quantify the progression of bacterial biofilm growth on PPE-mesh; and 2) determine which antiseptic solutions effectively remove viable bacteria.

METHODS

Knitted PPE mesh samples were cultured with either methicillin-sensitive Staphylococcus aureus (MSSA) or Escherichia coli (E. coli) for 7 days, with regular quantification of colony forming units (CFUs) and visualization using scanning electron microscopy to identify maturity. Immature (24 hour) and mature (72 hour) biofilm was treated with one of 5 commercial antiseptics for 3 minutes. A 0.05% chlorhexidine gluconate, a surfactant-based formulation of ethanol, acetic acid, sodium acetate, benzalkonium chloride, diluted povidone-iodine (0.35%), undiluted (10%) povidone-iodine, and 1:1 combination of 10% povidone-iodine and 3% hydrogen peroxide. A 3-log reduction in CFUs compared to saline was considered clinically meaningful.

RESULTS

The CFU counts plateaued, indicating maturity, at 72 hours for both MSSA and E. coli. The scanning electron microscopy confirmed confluent biofilm formation after 72 hours. The 10% povidone-iodine was clinically effective against all MSSA biofilms and immature E. coli biofilms. The 10% povidone-iodine with hydrogen peroxide was effective in all conditions. Only 10% povidone iodine formulations produced significantly (P < .0083) reduced CFU counts against mature biofilms.

CONCLUSIONS

Bacteria rapidly form biofilm on PPE mesh. Mesh contamination can be catastrophic, and clinicians should consider utilizing an antiseptic solution at the conclusion of mesh implantation. Undiluted povidone-iodine with hydrogen peroxide should be considered when attempting to salvage infected PPE mesh.

Biofilm formation of the food spoiler Brochothrix thermosphacta on different industrial surface materials using a biofilm reactor

Brochothrix thermosphacta is considered as a major food spoiler bacteria. This study evaluates biofilm formation by B. thermosphacta CD337(2) - a strong biofilm producer strain - on three food industry materials (polycarbonate (PC), polystyrene (PS), and stainless steel (SS)). Biofilms were continuously grown under flow at 25 °C in BHI broth in a modified CDC biofilm reactor. Bacterial cells were enumerated by plate counting, and biofilm spatial organization was deciphered by combining confocal laser scanning microscopy and image analysis. The biofilms had the same growth kinetics on all three materials and reach 8log CFU/cm2 as maximal concentration. Highly structured biofilms were observed on PC and PS, but less structured ones on SS. This difference was confirmed by structural quantification analysis using the image analysis software tool BiofilmQ. Biofilm on SS show less roughness, density, thickness and volume. The biofilm 3D structure seemed to be related to the coupon topography and roughness. The materials used in this study do not affect biofilm growth. However, their roughness and topography affect the biofilm architecture, which could influence biofilm behaviour.

Relationships between composite roughness and Streptococcus mutans biofilm depth under shear in vitro

OBJECTIVE

To investigate the effect of substrate, surface roughness, and hydraulic residence time (HRT) on Streptococcus mutans biofilms growing on dental composites under conditions relevant to the oral cavity.

METHODS

Dental composites were prepared with varying amounts of polishing and incubated in a CDC bioreactor with an approximate shear of 0.4 Pa. S. mutans biofilms developed in the bioreactors fed sucrose or glucose and at 10-h or 40-h HRT for one week. Biofilms were characterized by confocal laser microscopy (CLM). Composite surface roughness was characterized by optical profilometry, and pre- and post-incubation composite surface fine structure and elemental composition were determined using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS).

RESULTS

Polishing had a significant impact on surface roughness, varying by a factor of 15 between the polished samples and the unpolished control. S. mutans biofilms grew statistically significantly thicker on the unpolished composites. Biofilm thickness was greater at shorter 10-h HRT compared to 40-h HRT. In most cases, biofilm thickness was not statistically significantly greater in sucrose-fed bioreactors than in glucose-fed bioreactors. SEM-EDS analysis did not identify any significant change in elemental composition after aging.

CONCLUSIONS

Accurate characterization of oral cavity biofilms must consider shear forces and the use of techniques that minimize alteration of the biofilm structure. Under shear, surface smoothness is the most important factor determining S. mutans biofilm thickness followed by HRT, while sucrose presence did not result in significantly greater biofilm thickness.

CLINICAL SIGNIFICANCE

The obvious patterns of S. mutans growth along sub-micron scale grooving created by the polishing process suggested that initial biofilm attachment occurred in the shear-protected grooves. These results suggest that fine polishing may help prevent the initial formation of S. mutans biofilms compared to unpolished/coarse polished composites.

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.