Quantitative analysis of Staphylococcus epidermidis biofilm on the surface of biomaterial

Associations of motility and auto-aggregation with biofilm-formation capacity levels in Clostridioidesdifficile

Clostridioides difficile (C. difficile) is responsible for one of the most common nosocomial infections worldwide. This work assessed associations between biofilm-formation capacity levels of C. difficile and cell viability, motility, flagella, motility and auto-aggregation in 118 clinical isolates. Biofilm production was assessed by the crystal violet method. Cell viability was determined by BacTiter-Glo™ Microbial Cell Viability Assay and live-imaging microscopy. Expression levels of LuxS, Cwp84, Spo0A, PilA, and FliC were measured by real-time PCR. Motility was visually assessed in agar tubes. Auto-aggregation levels were determined by OD600 measurements. Out of 118 isolates, 66 (56 %) were biofilm producers, with most being strong or moderate producers. Cell viability, motility and auto-aggregation positively correlated with biofilm-production capacity (p = 0.0001, p = 0.036 and p < 0.0001, respectively). Positive associations were found between pilA, fliC and luxS expression levels and biofilm-production capacity (p = 0.04, p = 0.01, p = 0.036, respectively). This is the first report of associations between biofilm-formation capacity and cell viability, pilA, fliC, and luxS gene expression, auto-aggregation and motility. These correlations should be further explored to expand knowledge on the regulation of C. difficile biofilm formation, and pathogenesis, which will have notable implications on treatment options.

Wetting and Imbibition Characteristics of Pseudomonas fluorescens Biofilms Grown on Stainless Steel

This study aims to provide insights into biofilm resistance associated with their structural properties acquired during formation and development. On this account, the wetting and imbibition behavior of dehydrated Pseudomonas fluorescens biofilms grown on stainless steel electropolished substrates is thoroughly examined at different biofilm ages. A polar liquid (water) and a non-polar liquid (diiodomethane) are employed as wetting agents in the form of sessile droplets. A mathematical model is applied to appraise the wetting and imbibition performance of biofilms incorporating the evaporation of sessile droplets. The present results show that the examined biofilms are hydrophilic. The progressive growth of biofilms leads to a gradual increase of substrate surface coverage─up to full coverage─accompanied by a gradual decrease of biofilm surface roughness. It is noteworthy that just after 24 h of biofilm growth, the surface roughness increases about 6.7 times the roughness of the clean stainless steel surface. It is further found that the imbibition of liquid in the biofilm matrix is restricted only to the biofilm region under the sessile droplet. The lack of further capillary imbibition into the biofilm structure, beyond the droplet deposition region, implies that the biofilm matrix is not in the form of an extended network of interconnected micro/nanopores. All in all, the present results indicate a resilient biofilm structure to biocide penetration despite its hydrophilic nature.

Highly variable effect of sonication to dislodge biofilm-embedded Staphylococcus epidermidis directly quantified by epifluorescence microscopy: an in vitro model study

BACKGROUND

In cases of prosthetic joint infections, culture of sonication fluid can supplement culture of harvested tissue samples for correct microbial diagnosis. However, discrepant results regarding the increased sensitivity of sonication have been reported in several studies. To what degree bacteria embedded in biofilm are dislodged during the sonication process has to our knowledge not been fully elucidated. In the present in vitro study, we have evaluated the effect of sonication as a method to dislodge biofilm by quantitative microscopy.

METHODS

We used a standard biofilm method to cover small steel plates with biofilm forming Staphylococcus epidermidis ATCC 35984 and carried out the sonication procedure according to clinical practice. By comparing area covered with biofilm before and after sonication with epifluorescence microscopy, the effect of sonication on biofilm removal was quantified. Two series of experiments were made, one with 24-h biofilm formation and another with 72-h biofilm formation. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to confirm whether bacteria were present after sonication. In addition, quantitative bacteriology of sonication fluid was performed.

RESULTS

Epifluorescence microscopy enabled visualization of biofilm before and after sonication. CLSM and SEM confirmed coccoid cells on the surface after sonication. Biofilm was dislodged in a highly variable manner.

CONCLUSION

There is an unexpected high variation seen in the ability of sonication to dislodge biofilm-embedded S. epidermidis in this in vitro model.

Staphylococcus epidermidis Biofilms Have a High Tolerance to Antibiotics in Periprosthetic Joint Infection

Both Staphylococcus aureus and Staphylococcus epidermidis are commonly associated with periprosthetic joint infections (PJIs). The treatment of PJI can be challenging because biofilms are assumed to have an increased intolerance to antibiotics. This makes the treatment of PJI challenging from a clinical perspective. Although S. aureus has been previously demonstrated to have increased biofilm antibiotic tolerance, this has not been well established with Staphylococcus epidermidis. A prospective registry of PJI S. epidermidis isolates was developed. The efficacy of clinically relevant antibiotics was quantified against these isolates. S. epidermidis planktonic minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were collected using clinical laboratory standard index (CLSI) assays for eight antibiotics (doxycycline, vancomycin, daptomycin, clindamycin, rifampin, nafcillin, and trimethoprim/sulfamethoxazole). Mature biofilms were grown in vitro, after which minimum biofilm inhibitory concentration (MBIC) and minimum biofilm bactericidal concentration (MBBC) were quantified. Only rifampin and doxycycline had a measurable MBIC across all tested isolates. Based on MBBC, 64% of S. epidermidis biofilms could be eliminated by rifampin, whereas only 18% by doxycycline. S. epidermidis biofilm was observed to have a high tolerance to antibiotics as compared to planktonic culture. Isolate biofilm antibiotic tolerance varied to a larger degree than was seen in planktonic cultures.

Establishment of an in vivo rat model for chronic musculoskeletal implant infection

Background

The aim of the study was to establish an experimental chronic musculoskeletal infection model in vivo characterized by (a) a small bacterial inoculum, (b) no general or local signs of infection, (c) several parallels (implants) in each animal and finally (d) a model that is technically easy to perform.

Methods

Bone xenografts with steel plates were implanted intramuscularly in rats. To the xenografts, different inocula of Staphylococcus aureus and two strains of Staphylococcus epidermidis were added. The animals were observed for different time periods before the removal of the xenografts. The xenografts and steel plates were subjected to quantitative bacterial culture after sonication. Additional steel plates were subjected to scanning electron microscopy (SEM) for visualization of biofilm formation.

Results

Inoculation of bone grafts with S. aureus did produce a pyogenic infection in all animals. A chronic infection was established in rats where the bone grafts were inoculated with S. epidermidis. A bacterial inoculum of 100 colony-forming units (CFU) of S. epidermidis was adequate as a minimum infective dose. During a period of up until 42 days, the animals infected with S. epidermidis had no general or local signs of infection. According to the results of the quantitative bacterial culture of sonicate fluid and SEM, a biofilm was developed on all implants.

Conclusion

In the present in vivo model, a very small bacterial inoculum succeeded in establishing a chronic musculoskeletal implant infection where a biofilm was formed on the implants. The experimental model is easy to perform and allows several implants in each animal. The model could be useful for the study of biofilm formation in vivo on different implants and different surfaces.

Bioluminescence assay for cell viability

Theoretical aspects of the adenosine triphosphate bioluminescence assay based on the use of the firefly luciferin-luciferase system are considered, as well as its application for assessing cell viability in microbiology, sanitation, medicine, and ecology. Various approaches for the analysis of individual or mixed cultures of microorganisms are presented, and capabilities of the method for investigation of biological processes in live cells including necrosis, apoptosis, as well as for investigation of the dynamics of metabolism are described.

Non-Equilibrium Plasma Processing for the Preparation of Antibacterial Surfaces

Non-equilibrium plasmas offer several strategies for developing antibacterial surfaces that are able to repel and/or to kill bacteria. Due to the variety of devices, implants, and materials in general, as well as of bacteria and applications, plasma assisted antibacterial strategies need to be tailored to each specific surface. Nano-composite coatings containing inorganic (metals and metal oxides) or organic (drugs and biomolecules) compounds can be deposited in one step, and used as drug delivery systems. On the other hand, functional coatings can be plasma-deposited and used to bind antibacterial molecules, for synthesizing surfaces with long lasting antibacterial activity. In addition, non-fouling coatings can be produced to inhibit the adhesion of bacteria and reduce the formation of biofilm. This paper reviews plasma-based strategies aimed to reduce bacterial attachment and proliferation on biomedical materials and devices, but also onto materials used in other fields. Most of the activities described have been developed in the lab of the authors.

Copaifera langsdorffii oleoresin and its isolated compounds: antibacterial effect and antiproliferative activity in cancer cell lines

BACKGROUND

Natural products display numerous therapeutic properties (e.g., antibacterial activity), providing the population with countless benefits. Therefore, the search for novel biologically active, naturally occurring compounds is extremely important. The present paper describes the antibacterial action of the Copaifera langsdorffii oleoresin and ten compounds isolated from this oleoresin against multiresistant bacteria; it also reports the antiproliferative activity of the Copaifera langsdorffii oleoresin and (-)-copalic acid.

METHODS

MICs and MBCs were used to determine the antibacterial activity. Time-kill curve assays provided the time that was necessary for the bacteria to die. The Minimum Inhbitory Concentration of Biofilm (CIMB50) of the compounds that displayed the best results was calculated. Cytotoxicity was measured by using the XTT assay.

RESULTS

The diterpene (-)-copalic acid was the most active antibacterial and afforded promising Minimum Inhibitory Concentration (MIC) values for most of the tested strains. Determination of the bactericidal kinetics against some bacteria revealed that the bactericidal effect emerged within six hours of incubation for Streptococcus pneumoniae. Concerning the antibiofilm action of this diterpene, its MICB50 was twofold larger than its CBM against S. capitis and S. pneumoniae. The XTT assay helped to evaluate the cytotoxic effect; results are expressed as IC50. The most pronounced antiproliferative effect arose in tumor cell lines treated with (-)-copalic acid; the lowest IC50 value was found for the human glioblastoma cell line.

CONCLUSIONS

The diterpene (-)-copalic acid is a potential lead for the development of new selective antimicrobial agents to treat infections caused by Gram-positive multiresistant microorganisms, in both the sessile and planktonic mode. This diterpene is also a good candidate to develop anticancer drugs.

Antimicrobial efficacy of combined clarithromycin plus daptomycin against biofilms-formed methicillin-resistant Staphylococcus aureus on titanium medical devices

In vitro efficacy of combined eradication therapy with clarithromycin and daptomycin against biofilm-formed methicillin-resistant Staphylococcus aureus on the orthopedic titanium devices was evaluated. The bactericidal effect of this antibiotic was investigated by a re-culture test, the scanning electron microscopy, and fluorescence microscopy using a double-staining dyes. Clarithromycin decreased the amount to half in 24 h. Although MRSA biofilms were not eradicated with clarithromycin or daptomycin alone, clarithromycin combined with daptomycin was useful to sterilize titanium devices within 72 h. This in vitro study showed that combined treatment with clarithromycin plus daptomycin is useful to eradicate staphylococcal biofilms formed on orthopedic devices.

Biofilm-forming Staphylococcus epidermidis expressing vancomycin resistance early after adhesion to a metal surface

We investigated biofilm formation and time of vancomycin (VCM) resistance expression after adhesion to a metal surface in Staphylococcus epidermidis. Biofilm-forming Staphylococcus epidermidis with a VCM MIC of 1 μg/mL was used. The bacteria were made to adhere to a stainless steel washer and treated with VCM at different times and concentrations. VCM was administered 0, 2, 4, and 8 hours after adhesion. The amount of biofilm formed was evaluated based on the biofilm coverage rates (BCRs) before and after VCM administration, bacterial viability in biofilm was visually observed using the fluorescence staining method, and the viable bacterial count in biofilm was measured. The VCM concentration required to decrease BCR significantly compared with that of VCM-untreated bacteria was 4 μg/mL, even in the 0 hr group. In the 4 and 8 hr groups, VCM could not inhibit biofilm growth even at 1,024 μg/mL. In the 8 hr group, viable bacteria remained in biofilm at a count of 10⁴ CFU even at a high VCM concentration (1,024 μg/mL). It was suggested that biofilm-forming Staphylococcus epidermidis expresses resistance to VCM early after adhesion to a metal surface. Resistance increased over time after adhesion as the biofilm formed, and strong resistance was expressed 4–8 hours after adhesion.

Early staphylococcal biofilm formation on solid orthopaedic implant materials: in vitro study

Biofilms forming on the surface of biomaterials can cause intractable implant-related infections. Bacterial adherence and early biofilm formation are influenced by the type of biomaterial used and the physical characteristics of implant surface. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis, the main pathogen in implant-related infections, to form biofilms on the surface of the solid orthopaedic biomaterials, oxidized zirconium-niobium alloy, cobalt-chromium-molybdenum alloy (Co-Cr-Mo), titanium alloy (Ti-6Al-4V), commercially pure titanium (cp-Ti) and stainless steel. A bacterial suspension of Staphylococcus epidermidis strain RP62A (ATCC35984) was added to the surface of specimens and incubated. The stained biofilms were imaged with a digital optical microscope and the biofilm coverage rate (BCR) was calculated. The total amount of biofilm was determined with the crystal violet assay and the number of viable cells in the biofilm was counted using the plate count method. The BCR of all the biomaterials rose in proportion to culture duration. After culturing for 2-4 hours, the BCR was similar for all materials. However, after culturing for 6 hours, the BCR for Co-Cr-Mo alloy was significantly lower than for Ti-6Al-4V, cp-Ti and stainless steel (P<0.05). The absorbance value determined in the crystal violet assay and the number of viable cells on Co-Cr-Mo were not significantly lower than for the other materials (P>0.05). These results suggest that surface properties, such as hydrophobicity or the low surface free energy of Co-Cr-Mo, may have some influence in inhibiting or delaying the two-dimensional expansion of biofilm on surfaces with a similar degree of smoothness.

Effect of surface roughness of biomaterials on Staphylococcus epidermidis adhesion

Background

Implant-related infections are caused by adhesion of bacteria to the surface of biomaterials. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis (ATCC35984) to adhere to the surface of solid biomaterials at different levels of roughness below 30 nm Ra and investigated the minimum level of roughness required to promote bacterial adhesion on five kinds of biomaterials: oxidized zirconium-niobium alloy (Oxinium), cobalt-chromium-molybdenum alloy (Co-Cr-Mo), titanium alloy (Ti-6Al-4 V), commercially pure titanium (Cp-Ti) and stainless steel (SUS316L), samples of which were categorized into a fine group and a coarse group according to surface roughness. The test specimens were physically analyzed and the viable bacterial density of the adhered bacteria was quantitatively determined (n = 20).

Results

The amount of bacteria that adhered to the biomaterials in the coarse group was higher than those in the fine group. Oxinium, Ti-6Al-4 V and SUS316L in particular demonstrated statistically significant differences between the two groups (P < 0.05). Of the materials, the Co-Cr-Mo specimens exhibited significantly lower amounts of adhered bacteria than the Ti-6Al-4 V, Cp-Ti and SUS316L specimens in the fine group. Similarly, the Co-Cr-Mo specimens in the coarse group exhibited significantly lower values than the other four materials.

Conclusions

These results suggest that minimum level of roughness affecting initial bacterial adherence activity differs according to the type of biomaterial used, and that even a surface roughness of below 30 nm Ra in Oxinium, Ti-6Al-4 V and SUS316L can promote bacterial adhesion. Relative hydrophobic Co-Cr-Mo surfaces were less susceptible to bacterial adherence.

Infection with spinal instrumentation: Review of pathogenesis, diagnosis, prevention, and management

Background:

Instrumentation has become an integral component in the management of various spinal pathologies. The rate of infection varies from 2% to 20% of all instrumented spinal procedures. Every occurrence produces patient morbidity, which may adversely affect long-term outcome and increases health care costs.

Methods:

A comprehensive review of the literature from 1990 to 2012 was performed utilizing PubMed and several key words: Infection, spine, instrumentation, implant, management, and biofilms. Articles that provided a current review of the pathogenesis, diagnosis, prevention, and management of instrumented spinal infections over the years were reviewed.

Results:

There are multiple risk factors for postoperative spinal infections. Infections in the setting of instrumentation are more difficult to diagnose and treat due to biofilm. Infections may be early or delayed. C Reactive Protein (CRP) and Magnetic Resonance Imaging (MRI) are important diagnostic tools. Optimal results are obtained with surgical debridement followed by parenteral antibiotics. Removal or replacement of hardware should be considered in delayed infections.

Conclusions:

An improved understanding of the role of biofilm and the development of newer spinal implants has provided insight in the pathogenesis and management of infected spinal implants. This literature review highlights the mechanism, pathogenesis, prevention, and management of infection after spinal instrumentation. It is important to accurately identify and treat postoperative spinal infections. The treatment is often multimodal and prolonged.

Adherence ability of Staphylococcus epidermidis on prosthetic biomaterials: an in vitro study

Bacterial adhesion to the surface of biomaterials is an essential step in the pathogenesis of implant-related infections. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis to adhere to the surface of solid biomaterials, including oxidized zirconium-niobium alloy (Oxinium), cobalt-chromium-molybdenum alloy, titanium alloy, commercially pure titanium, and stainless steel, and performed a biomaterial-to-biomaterial comparison. The test specimens were physically analyzed to quantitatively determine the viable adherent density of the S. epidermidis strain RP62A (American Type Culture Collection [ATCC] 35984). Field emission scanning electron microscope and laser microscope examination revealed a featureless, smooth surface in all specimens (average roughness <10 nm). The amounts of S. epidermidis that adhered to the biomaterial were significantly lower for Oxinium and the cobalt-chromium-molybdenum alloy than for commercially pure titanium. These results suggest that Oxinium and cobalt-chromium-molybdenum alloy are less susceptible to bacterial adherence and are less inclined to infection than other materials of a similar degree of smoothness.

Quantitative analysis of biofilm formed on vascular prostheses by Staphylococcus epidermidis with different ica and aap genetic status

OBJECTIVES

This study aims to examine biofilm formed on vascular prostheses by Staphylococcus epidermidis with different ica and aap genetic status, and to evaluate the effect of antibiotic-modified prostheses on bacterial colonization.

METHODS

Biofilm formation was determined using fluorescence microscopy imaging. Quantitative analysis was conducted using the biofilm coverage ratio (BCR) calculations.

RESULTS

Our investigations prove that the BCR method with fluorescent dye enabled an accurate assessment of biofilm coverage and comparison of the obtained results. The ica+ aap+ strains formed a biofilm on all of the examined vascular prostheses. Uni-Graft(®) modified with covalently immobilized amikacin was effective in preventing bacterial adherence.

CONCLUSIONS

Molecular biology techniques combined with phenotype studies give a broad insight into biofilm formation mechanisms. On the other hand, fluorescence microscopy imaging along with BCR calculations are reliable and simple tools to quantitatively estimate biofilm formation, as well as the effectiveness of antimicrobial prosthesis modification.

Chip-calorimetric monitoring of biofilm eradication with antibiotics provides mechanistic information

Increased antibiotic resistance of pathogenic bacteria dwelling in biofilm structures has motivated the development of various monitoring tools specifically designed for biofilm investigations. In this study, the potential of the recently emerging chip calorimetry for this purpose was analysed. The activity of biofilms of Pseudomonas putida PaW340 was monitored chip-calorimetrically and compared with counts of colony forming units (CFU), bioluminescence-based ATP measurements, and quantitative confocal laser scanning microscopy (CLSM). The biofilms were treated with antibiotics differing in their mechanisms of action (bactericidal kanamycin vs. bacteriostatic tetracycline) and referenced to untreated biofilms. For untreated biofilms, all methods gave comparable results. Calorimetric killing curves, however, reflecting metabolic responses to biofilm eradication non-invasively in real time, differed from those obtained with the established methods. For instance, heat signals increased right after addition of the antibiotics. This transient increase of activity was not detected by the other methods, since only calorimetry delivers specific information about the catabolic part of the metabolism. In case of the bactericidal antibiotic, CFU misleadingly indicated successful biofilm eradication, whereas calorimetry revealed enduring activity. Our results show that calorimetry holds promise to provide valuable mechanistic information, thereby complementing other methods of biofilm analysis.

Preservation of spinal instrumentation after development of postoperative bacterial infections in patients undergoing spinal arthrodesis

STUDY DESIGN

This is a retrospective review.

OBJECTIVE

The purpose of this study is to evaluate the efficacy of medical and surgical management of postoperative infections after the placement of spinal instrumentation in the context of retaining the instrumentation.

SUMMARY OF BACKGROUND DATA

The implementation of spinal instrumentation for the treatment of various spinal conditions is associated with a risk of developing a postoperative wound infection. An aggressive medical and surgical approach is necessary for eradication of subfascial infections and treatment is often performed with the guidance of infectious diseases consultants. These medical specialists frequently recommend removal of the implanted spinal instrumentation due to the concern for the potential of persistent microbial infection resulting from the formation of bacteria harboring biofilm on the indwelling spinal hardware.

METHODS

Of 854 consecutive patients who had undergone spinal instrumentation by the senior author, 17 patients were identified who developed postoperative infections, 16 of which were treated by the senior author.

RESULTS

All patients underwent surgical debridement and received antimicrobial therapy in consultation with the infectious diseases consultants. Spinal instrumentation was preserved in all cases. Two patients had clinical and radiologic evidence of nonunion and later underwent a staged instrumentation revision procedure. Eradication of the infection was successful in all patients. The mean follow-up period was 2.1 years (range, 12 mo to 4.5 y).

CONCLUSIONS

A combination of aggressive surgical debridement with microbial-guided pharmacotherapy enabled infection cure in all patients with postoperative bacterial infections after spinal instrumentation. Adjunct measures including the use of wound vacuum devices and long-term suppressive antimicrobial therapy were also used in high-risk patients. These results show that postoperative bacterial infections in the setting of spinal instrumentation can be successfully treated without removing titanium alloy instrumentation.

Antimicrobial peptide incorporated poly(2-hydroxyethyl methacrylate) hydrogels for the prevention of Staphylococcus epidermidis-associated biomaterial infections

The effectiveness of the antimicrobial peptide maximin-4, the ultrashort peptide H-Orn-Orn-Trp-Trp-NH(2), and the lipopeptide C(12)-Orn-Orn-Trp-Trp-NH(2) in preventing adherence of pathogens to a candidate biomaterial were tested utilizing both matrix- and immersion-loaded poly(2-hydroxyethyl methacrylate) (poly(HEMA)) hydrogels. Antiadherent properties correlated to both the concentration released and the relative antimicrobial concentrations of each compound against Staphylococcus epidermidis ATCC 35984, at each time point. Immersion-loaded samples containing C(12)-Orn-Orn-Trp-Trp-NH(2) exhibited the lowest adherence profile for all peptides studied over 1, 4, and 24 h. The results outlined in this article show that antimicrobial peptides have the potential to serve as an important weapon against biomaterial associated infections.

Evaluation of antimicrobial effects of novel implant materials by testing the prevention of biofilm formation using a simple small scale medium-throughput growth inhibition assay

Staphylococcal colonization of implants is a serious complication of orthopaedic surgery. Anti-infectious modification of implant surfaces may serve to prevent bacterial colonization. The authors set out to develop an in vitro test system for the analysis of prevention of biofilm formation by Staphylococcus epidermidis and Staphylococcus aureus on implant materials. Biofilm growth was monitored over 10 days on titanium disks in order to develop appropriate test parameters. Bacterial cell counts following ultrasonic treatment of the colonized samples were compared with scanning electron microscope images of the specimens. Copper ion containing surfaces (ie copper [Cu] and inter-metallic Ti-Cu films) were used for growth inhibition assays: copper ion releasing specimens led to reduced bacterial numbers in biofilms and decreased bacterial persistence in the model used. The assay used represents an inexpensive and quick in vitro screen for the antibacterial effects of novel implant surface materials.

Casbane diterpene as a promising natural antimicrobial agent against biofilm-associated infections

Croton nepetaefolius is a native plant from northeastern Brazil that belongs to the Euphorbiaceae family. The biological action of this plant has been extensively explored, being the secondary metabolites responsible for its properties alkaloids, diterpenes, and triterpenes. This study aimed to evaluate the ability of casbane diterpene (CD), isolated from the ethanolic extract of C. nepetaefolius, to inhibit microbial growth and biofilm formation of several clinical relevant species (bacteria and yeasts). It was found that CD possessed biocidal and biostatic activity against the majority of the species screened, with minimal active concentrations ranging between 125 and 500 µg/mL. In addition, it was observed that biofilm formation was inhibited even when the planktonic growth was not significantly affected. In conclusion, CD showed potential to be a natural tool for the treatment of diseases caused by different infectious microorganisms.

Quaternized chitosan inhibits icaA transcription and biofilm formation by Staphylococcus on a titanium surface

Our previous study (Z. X. Peng et al., Carbohydr. Polym. 81:275-283, 2010) demonstrated that water-soluble quaternary ammonium salts, which are produced by the reaction of chitosan with glycidyl trimethylammonium chloride, provide chitosan derivatives with enhanced antibacterial ability. Because biofilm formation is believed to comprise the key step in the development of orthopedic implant-related infections, we further evaluated the efficacy of hydroxypropyltrimethyl ammonium chloride chitosan (HACC) with different degrees of substitution (DS; referred to as HACC 6%, 18%, and 44%) in preventing biofilm formation on a titanium surface. We used a tissue culture plate method to quantify the biomass of Staphylococcus epidermidis and Staphylococcus aureus biofilms and found that HACC, especially HACC 18% and 44%, significantly inhibited biofilm formation compared to the untreated control, even at concentrations far below their MICs (P < 0.05). Scanning electron microscopy showed that inhibition of biofilm formation on titanium increased dramatically with increased DS and HACC concentrations. Confocal laser scanning microscopy indicated that growth of a preexisting biofilm on titanium was inhibited by concentrations of HACC 18% and 44% below their minimum biofilm eradication concentrations. We also demonstrated that HACC inhibited the expression of icaA, which mediates the production of extracellular polysaccharides, both in new biofilms and in preexisting biofilms on titanium. Our results indicate that HACC may serve as a new antibacterial agent to inhibit biofilm formation and prevent orthopedic implant-related infections.