Assessment of resistance towards biocides following the attachment of micro-organisms to, and growth on, surfaces

Antiseptic Chitosan-Poly(hexamethylene) Biguanide Hydrogel for the Treatment of Infectious Wounds

Topical wound infections create the ideal conditions for microbial colonization and growth in terms of moisture, temperature, and nutrients. When they are not protected, numerous types of bacteria from the internal microbiota and the external environment may colonize them, creating a polymicrobial population. Treatment of these wounds often necessitates the use of antibiotics that may have systemic harmful effects. Unlike antibiotics, topical antiseptics exhibit a wider range of activity and reduced systemic toxicity and resistance. In order to address this issue, we developed an antiseptic Chitosan-Poly (hexamethylene) Biguanide (CS-PHMB) hydrogel. The prepared hydrogel was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). SEM images showed the smooth morphology and characteristic FTIR peaks of PHMB and confirmed the incorporation of the antiseptic into the chitosan (CS) hydrogel. A Water Vapor Permeation Rate study confirms the moisture retention ability of the CS-PHMB hydrogel. Rheological studies proved the gel strength and temperature stability. The prepared hydrogel inhibited the growth of S. aureus, P. aeruginosa, E. coli, methicillin-resistant Staphylococcus aureus (MRSA), and K. pneumoniae, which confirms its antibacterial properties. It also inhibited biofilm formation for S. aureus and E. coli. CS-PHMB hydrogel is also found to be hemo- and cytocompatible in nature. Thus, the developed CS-PHMB hydrogel is a very potent candidate to be used for treating infectious topical wounds with low systemic toxicity.

Prophylaxis of Ocular Infection in the Setting of Intraocular Surgery: Implications for Clinical Practice and Risk Management

In this review we discuss the role of intraocular surgery preoperative prophylaxis. The correct choice of antimicrobial drug is variable in each surgical setting, according to the available strengths of evidence, the anatomical district involved, and the type of procedure. In the ophthalmic surgical field, there has been a progressive shift from antibiotic formulations, which are known to cause antibiotic resistance, to a new class of antiseptic compounds, which proved to be effective not only against bacteria, but also against fungi, protozoa, and viruses. Among these, povidone-iodine (PVI) is a water-soluble polymer that can form a complex with iodine, and the perioperative application of PVI 5-10% eye drop for 3 min is the gold standard for infection prophylaxis. A new formulation of 0.6% PVI eye drop is a new option for infection prophylaxis in the days before surgery. Chlorhexidine is a biguanide compound, which is a valid alternative with a good safety and efficacy profile and is the antiseptic of choice in patients with iodine allergy. New compounds that are currently being studied include polyhexamethylene biguanide (PHMB), picloxydine, ozone, hypochlorous acid (HOCl), and Biosecur. PHMB is a biguanide polymer that was found to be more effective than PVI in in vitro studies for reducing microorganisms and extending the duration of antisepsis, but to date, there are no formulations available on the market for preoperative ocular surgery in which it is present as main ingredient. Ozone is a molecule with oxidizing effect, which showed interesting preliminary results but is not effective against virus, Staphylococcus aureus and Candida albicans. HOCl has a natural bactericidal propriety but its applicability to prophylaxis of ocular infection in the setting of ocular surgery is not established. Biosecur is a non-toxic organic alcohol-free compound that exhibited bactericidal and fungicidal effect versus all common microorganisms and is currently available as an ocular spray.

Fungal cell barriers and organelles are disrupted by polyhexamethylene biguanide (PHMB)

The similarities between fungal and mammalian cells pose inherent challenges for the development of treatments for fungal infections, due to drug crossover recognition of host drug targets by antifungal agents. Thus, there are a limited number of drug classes available for treatment. Treatment is further limited by the acquisition and dissemination of antifungal resistance which contributes to the urgent need of new therapies. Polyhexamethylene biguanide (PHMB) is a cationic antimicrobial polymer with bactericidal, parasiticidal and fungicidal activities. The antifungal mechanism of action appears to involve preferential mechanical disruption of microbial cell structures, offering an alternative to conventional antifungals. However, the antifungal mechanisms have been little studied. The aim of this study was to characterise PHMB's activities on selected yeast (Saccharomyces cerevisiae, Candida albicans) and filamentous fungal species (Fusarium oxysporum, Penicillium glabrum). Fungal membrane disruption, cell entry and intracellular localisation activities of PHMB were evaluated using viability probe entry and polymer localisation studies. We observed that PHMB initially permeabilises fungal cell membranes and then accumulates within the cytosol. Once in the cytosol, it disrupts the nuclear membrane, leading to DNA binding and fragmentation. The electrostatic interaction of PHMB with membranes suggests other intracellular organelles could be potential targets of its action. Overall, the results indicate multiple antifungal mechanisms, which may help to explain its broad-spectrum efficacy. A better understanding of PHMB's mechanism(s) of action may aid the development of improved antifungal treatment strategies.

Impact of benzalkonium chloride, benzethonium chloride and chloroxylenol on bacterial antimicrobial resistance

This review examined 3655 articles on benzalkonium chloride (BKC), benzethonium chloride (BZT) and chloroxylenol (CHO) aiming to understand their impact on antimicrobial resistance. Following the application of inclusion/exclusion criteria, only 230 articles were retained for analysis; 212 concerned BKC, with only 18 for CHO and BZT. Seventy-eight percent of studies used MIC to measure BKC efficacy. Very few studies defined the term 'resistance' and 85% of studies defined 'resistance' as <10-fold increase (40% as low as 2-fold) in MIC. Only a few in vitro studies reported on formulated products and when they did, products performed better. In vitro studies looking at the impact of BKC exposure on bacterial resistance used either a stepwise training protocol or exposure to constant BKC concentrations. In these, BKC exposure resulted in elevated MIC or/and MBC, often associated with efflux, and at time, a change in antibiotic susceptibility profile. The clinical relevance of these findings was, however, neither reported nor addressed. Of note, several studies reported that bacterial strains with an elevated MIC or MBC remained susceptible to the in-use BKC concentration. BKC exposure was shown to reduce bacterial diversity in complex microbial microcosms, although the clinical significance of such a change has not been established. The impact of BKC exposure on the dissemination of resistant genes (notably efflux) remains speculative, although it manifests that clinical, veterinary and food isolates with elevated BKC MIC carried multiple efflux pump genes. The correlation between BKC usage and gene carriage, maintenance and dissemination has also not been established. The lack of clinical interpretation and significance in these studies does not allow to establish with certainty the role of BKC on AMR in practice. The limited literature and BZT and CHO do not allow to conclude that these will impact negatively on emerging bacterial resistance in practice.

Antifungal Polymeric Materials and Nanocomposites

Rising global populations due to medicinal advancements increases the patient population susceptible to superficial and severe fungal infections. Fungi often implicated in these diseases includes the dermatophytes (Microsporum spp., Epidermophtyon spp., Trichophyton spp.) as well as species of the Candida spp., Aspergillosis spp. and Cryptococcus spp. genera. In addition, increasing global populations leads to increasing agricultural demands. Thus, fungal infections of preharvested crops and stored food by plant pathogens such as Magnaporthe oryzae and Fusarium oxysporum can have detrimental socioeconomic effects due to food insecurity. Current antifungal strategies are based mainly on small molecule antifungal drugs. However, these drugs are limited by poor solubility and bioavailability. Furthermore, antifungal resistance against these drugs are on the rise. Thus, antimicrobial polymers offer an alternative antifungal strategy. Antifungal polymers are characterised by cationic and hydrophobic regions where the cationic regions have been shown to interact with microbial phospholipids and membranes. These polymers can be synthetic or natural and demonstrate distinct antifungal mechanisms ranging from fungal cell membrane permeabilisation, cell membrane depolarisation or cell entry. Although the relative importance of such mechanisms is difficult to decipher. Due to the chemical properties of these polymers, they can be combined with other antimicrobial compounds including existing antifungal drugs, charcoals, lipids and metal ions to elicit synergistic effects. In some cases, antifungal polymers and nanocomposites show better antifungal effects or reduced toxicity compared to the widely used small molecule antifungal drugs. This review provides an overview of antimicrobial polymers and nanocomposites with antifungal activity and the current understanding of their antifungal mechanisms.

Visible Light-Activated Carbon Dots for Inhibiting Biofilm Formation and Inactivating Biofilm-Associated Bacterial Cells

This study aimed to address the significant problems of bacterial biofilms found in medical fields and many industries. It explores the potential of classic photoactive carbon dots (CDots), with 2,2′-(ethylenedioxy)bis (ethylamine) (EDA) for dot surface functionalization (thus, EDA-CDots) for their inhibitory effect on B. subtilis biofilm formation and the inactivation of B. subtilis cells within established biofilm. The EDA-CDots were synthesized by chemical functionalization of selected small carbon nanoparticles with EDA molecules in amidation reactions. The inhibitory efficacy of CDots with visible light against biofilm formation was dependent significantly on the time point when CDots were added; the earlier the CDots were added, the better the inhibitory effect on the biofilm formation. The evaluation of antibacterial action of light-activated EDA-CDots against planktonic B. subtilis cells versus the cells in biofilm indicate that CDots are highly effective for inactivating planktonic cells but barely inactivate cells in established biofilms. However, when coupling with chelating agents (e.g., EDTA) to target the biofilm architecture by breaking or weakening the EPS protection, much enhanced photoinactivation of biofilm-associated cells by CDots was achieved. The study demonstrates the potential of CDots to prevent the initiation of biofilm formation and to inhibit biofilm growth at an early stage. Strategic combination treatment could enhance the effectiveness of photoinactivation by CDots to biofilm-associated cells.

Ways to improve biocides for metalworking fluid

Metalworking fluids (MWF) are mainly emulsions of oil in water containing additives such as corrosion inhibitors, emulsifiers, defoamers, and biocides. Microbial contamination of MWF is almost systematic, and some of their constituents serve as nutrients for contaminating microorganisms. Biocides for MWF are protection products used to counter microbial contaminations and growth. Ideally, a biocide for MWF should have the following non-exhaustive criteria: have a broad-spectrum activity, be usable at low concentrations, be compatible with the formulation and the physical-chemical properties of MWF, be stable over time, retain its effectiveness in the presence of soiling, have no corrosive action on metals, present no danger to humans and the environment, be inexpensive. The future lies in the development of new molecules with biocidal activity corresponding to these ideal specifications, but in the meantime, it is possible to improve the performance of existing molecules currently on the market. Different strategies for potentiation of the activity of existing biocides are possible. The compatibility of the potentiation strategies with their use in metal working fluids is discussed.

Re-evaluation of polihexanide use in wound antisepsis in order to clarify ambiguities of two animal studies

OBJECTIVE

Due to classification of the agent polihexanide (PHMB) in category 2 'may cause cancer' by the Committee for Risk Assessment of the European Chemicals Agency in 2011, the users of wound antiseptics may be highly confused. In 2017, this statement was updated, defining PHMB up to 0.1% as a preservative safe in all cosmetic products. In the interest of patient safety, a scientific clarification of the potential carcinogenicity of PHMB is necessary.

METHODS

A multidisciplinary team (MDT) of microbiologists, surgeons, dermatologists and biochemists conducted a benefit-risk assessment to clarify the hazard of antiseptic use of PHMB.

RESULTS

In two animal studies, from which the assessment of a carcinogenic risk was derived, PHMB was administered orally over two years in extremely high concentrations far above the NO(A)EL (no-observed-(adverse-) effect level) in rats and mice. Feeding in the NO(A)EL range resulted in no abnormal effects. In one male in the highest dose group of 4000ppm PHMB, an adenocarcinoma was found, which the author attributed to chronic inflammation of the colon with systemic atypical exposure. The increasing incidence of hemangiosarcomas highly probably resulted from increased endothelial proliferation, triggered by the exceedingly high dosage fed, because PHMB is not genotoxic and there is no evidence for epigenetic effects.

DISCUSSION

It is well known that PHMB is not absorbed when applied topically. Considering the absence of genotoxicity and epigenetic effects together with the interpretation of the animal studies, it is the consensus of the multidisciplinary experts that a carcinogenic risk from PHMB-use for wound antisepsis can be ruled out.

CONCLUSION

On this basis and considering their effectiveness, tolerability and clinical evidence, the indications for PHMB based wound antiseptics are justified.

Polyhexamethylene Biguanide:Polyurethane Blend Nanofibrous Membranes for Wound Infection Control

Polyhexamethylene biguanide (PHMB) is a broad-spectrum antiseptic which avoids many efficacy and toxicity problems associated with antimicrobials, in particular, it has a low risk of loss of susceptibility due to acquired antimicrobial resistance. Despite such advantages, PHMB is not widely used in wound care, suggesting more research is required to take full advantage of PHMB’s properties. We hypothesised that a nanofibre morphology would provide a gradual release of PHMB, prolonging the antimicrobial effects within the therapeutic window. PHMB:polyurethane (PU) electrospun nanofibre membranes were prepared with increasing PHMB concentrations, and the effects on antimicrobial activities, mechanical properties and host cell toxicity were compared. Overall, PHMB:PU membranes displayed a burst release of PHMB during the first hour following PBS immersion (50.5–95.9% of total released), followed by a gradual release over 120 h (≤25 wt % PHMB). The membranes were hydrophilic (83.7–53.3°), gradually gaining hydrophobicity as PHMB was released. They displayed superior antimicrobial activity, which extended past the initial release period, retained PU hyperelasticity regardless of PHMB concentration (collective tensile modulus of 5–35% PHMB:PU membranes, 3.56 ± 0.97 MPa; ultimate strain, >200%) and displayed minimal human cell toxicity (<25 wt % PHMB). With further development, PHMB:PU electrospun membranes may provide improved wound dressings.

Visualization and Quantification of the Oral Hygiene Effects of Brushing, Dentifrice Use, and Brush Wear Using a Tooth Brushing Simulator

Approaches that reproduce dental hygiene regimens under controlled conditions have applications in preclinical research. We have applied standardized, reproducible brushing regimes to typodonts coated in simulated or biological plaques to assess the effects on tooth cleaning of toothbrush/dentifrice regimens. Replicated typodonts were coated with Occlude^TM or Glogerm^TM indicators to simulate plaque, and brushed reproducibly using a mechanical brushing simulator to compare the cleaning of occlusal surfaces before and after brushing with water or a dentifrice. An in vitro model using salivary inocula to cultivate oral biofilms on typodont surfaces was then developed to evaluate removal of disclosed plaque by new toothbrushes in comparison to toothbrushes with wear equivalent to 3 months of use. Analyses of typodonts brushed under controlled conditions significantly (p < 0.01) distinguished between brushed and unbrushed surfaces and between the use of water vs. dentifrice for the removal of simulated interproximal plaque (p < 0.05). New toothbrushes removed significantly (p < 0.05) more biological plaque from typodont surfaces than brushes that had been worn by repeated brushing. Through controlled and defined brushing of typodonts with simulated and biological plaques, the effectiveness of dental hygiene regimens was compared under reproducible conditions. Data indicate that the cleaning effectiveness of brushing was augmented by the addition of dentifrice and that new brushes were significantly more effective than brushes with substantial wear from previous use. Whilst we have focussed on the occlusal surfaces of molars and worn brushes, the method could be applied to a range of other tooth surfaces and oral hygiene regimens.

Hydrogen peroxide and sodium hypochlorite disinfectants are more effective against Staphylococcus aureus and Pseudomonas aeruginosa biofilms than quaternary ammonium compounds

Background

Antimicrobial disinfectants are used as primary treatment options against pathogens on surfaces in healthcare facilities to help prevent healthcare associated infections (HAIs). On many surfaces, pathogenic microorganisms exist as biofilms and form an extracellular matrix that protects them from the antimicrobial effects of disinfectants. Disinfectants are used as all-purpose antimicrobials though very few specifically make biofilm efficacy claims. The objective of this study was to evaluate the efficacy of eight registered disinfectants (six registered by the Environmental Protection Agency and two products registered in by the European Chemical Agency) with general bactericidal claims, but currently no biofilm efficacy claims, against Staphylococcus aureus ATTC-6538 and Pseudomonas aeruginosa ATCC-15442 biofilms. We hypothesized that hydrogen peroxide and sodium hypochlorite disinfectant products would be more effective than quaternary ammonium chlorides.

Methods

This study tested the bactericidal efficacy of eight registered disinfectant products against S. aureus ATCC-6538 and P. aeruginosa ATCC-15442 grown on glass coupons using a Center for Disease Control (CDC) biofilm reactor and EPA MLB SOP MB-19. Bactericidal efficacy was determined after treating coupons with disinfectants following standard EPA MLB SOP MB-20.

Results

Overall, sodium hypochlorite and hydrogen peroxide disinfectants had significantly higher bactericidal efficacies than quaternary ammonium chloride disinfectants. We also found that all tested disinfectants except for quaternary ammonium chloride disinfectants met and exceeded the EPA standard for bactericidal efficacy against biofilms.

Conclusion

In general, bactericidal efficacy against biofilms differed by active ingredient. The efficacies of sodium hypochlorite and hydrogen peroxide disinfectants did not vary between strains, but there were significant differences between strains treated with quaternary ammonium chloride disinfectants.

In vitro studies of the antibacterial activity of Copaifera spp. oleoresins, sodium hypochlorite, and peracetic acid against clinical and environmental isolates recovered from a hemodialysis unit

Background

Patients submitted to hemodialysis therapy are more susceptible to infection, especially to infection by Gram-positive bacteria. Various research works have attempted to discover new antimicrobial agents from plant extracts and other natural products.

Methods

The present study aimed to assess the antibacterial activities of Copaifera duckei, C. reticulata, and C. oblongifolia oleoresins; sodium hypochlorite; and peracetic acid against clinical and environmental isolates recovered from a Hemodialysis Unit. The Minimum Inhibitory Concentration and the Fractionated Inhibitory Concentration Index were determined; the ability of the tested compounds/extracts to inhibit biofilm formation was evaluated by calculating the MICB50 and IC50.

Results

C. duckei was the most efficient among the assayed Copaifera species, and its oleoresin was more effective than peracetic acid and sodium hypochlorite. Copaifera oleoresins and disinfectants did not act synergistically at any of the tested combinations. Certain of C. duckei oleoresin, peracetic acid, and sodium hypochlorite concentrations inhibited biofilm formation and eradicated 50% of the biofilm population.

Conclusion

C. duckei oleoresin is a potential candidate for disinfectant formulations. Based on these results and given the high incidence of multi-resistant bacteria in hemodialysis patients, it is imperative that new potential antibacterial agents like C. duckei oleoresin, which is active against Staphylococcus, be included in disinfectant formulations.

Time-Dependent Effects of Rifampicin on Staphylococcal Biofilms

Objective

To test the time-dependent effects of rifampicin on established biofilms of Staphylococcus epidermidis isolated from patients with cardiac implant infections and catheter-related bacteremia.

Methods

Biofilms were grown in microtiter plates for 24 hours, dyed and stained with crystal violet. The mean optical density (OD) was used for quantification. The OD ratio (ODr = OD of the treated biofilm/OD of the untreated biofilm) was used to measure changes in the thickness of the biofilms over the time. Biofilms were incubated with rifampicin (0.6 mg/mL) for 1, 5, 15, 30 and 60 minutes. Unstained biofilms were sonicated and plated on Columbia agar for time-kill curves.

Results

The incubation of the biofilms with rifampicin led to a significant reduction of the OD of the biofilms within 1 minute (ODr baseline: 1; ODr 1 min: 0.333 ± 0.131) (p<0.001). With regard to bacterial killing, rifampicin reduced the mean log count, but viable bacteria were still grown from biofilms in 13 out of 28 isolates despite MIC values < 0.01 mg/L.

Conclusions

In conclusion, our results confirm that rifampicin at a concentration of 1.2 mg/mL immediately reduces established biofilms formed by S. epidermidis although it is not bactericidal despite very low MICs at planktonic conditions.

Enhanced killing of Escherichia coli using a combination of polyhexamethylene biguanide hydrochloride and 1-bromo-3-chloro-5,5- dimethylimidazolidine-2,4-dione

The bactericidal activities of polyhexamethylene biguanide hydrochloride (PHMB), 1-bromo-3-chloro-5,5-dimethylimidazolidine-2,4-dione (BCDMH) and the combination of the two (designated as PB) were compared using Escherichia coli as the test organism. PB exhibited strong bactericidal activity: 10 mg/L PHMB combined with 8 mg/L BCDMH resulted in approximately 5.74 log10 reduction (LR), whereas 320 mg/L PHMB or 20 mg/L BCDMH was about 5.53 and 6.56 LR, respectively. Analyses using scanning electron microscopy, flow cytometry and atomic absorption spectroscopy indicated that PB, PHMB and BCDMH disrupted cell membranes and changed membrane structure and permeability, resulting in the leakage of intracellular soluble proteins and ions. PB exerted stronger effects on potassium and magnesium leakage, membrane potential and permeability than BCDMH did. PB caused less protein leakage than PHMB did. These results suggest that at a relatively low concentration, PB exhibited good bactericidal activity and physiological effect on E. coli.

Unexpected Like-Charge Self-Assembly of a Biguanide-Based Antimicrobial Polyelectrolyte

Polyelectrolyte chains dissolved in good solvent are expected to collapse in compact configurations in the presence of multivalent ions. Here, we show that a weakly charged, hydrophilic polyelectrolyte containing biguanide groups self-assembles in water also in the presence of monovalent counterions, even at low salt concentrations. The polymer assembles in a compact, ordered, hairpin-like shape that, with increasing the ionic strength of the solution, can collapse further in three- or five-folded structures. Neither water nor ions mediate the self-assembly which, instead, is driven by the like-charge pairing of the biguanide units. The thermodynamics of the self-assembly show that the self-association is enthalpically driven, is isodesmic (at least at low aggregation number), and is favored by increasing salt concentration. This unique self-assembly behavior may be linked to the well-known polymer's antimicrobial properties and could help in rationalizing its biological activity.

The antimicrobial polymer PHMB enters cells and selectively condenses bacterial chromosomes

To combat infection and antimicrobial resistance, it is helpful to elucidate drug mechanism(s) of action. Here we examined how the widely used antimicrobial polyhexamethylene biguanide (PHMB) kills bacteria selectively over host cells. Contrary to the accepted model of microbial membrane disruption by PHMB, we observed cell entry into a range of bacterial species, and treated bacteria displayed cell division arrest and chromosome condensation, suggesting DNA binding as an alternative antimicrobial mechanism. A DNA-level mechanism was confirmed by observations that PHMB formed nanoparticles when mixed with isolated bacterial chromosomal DNA and its effects on growth were suppressed by pairwise combination with the DNA binding ligand Hoechst 33258. PHMB also entered mammalian cells, but was trapped within endosomes and excluded from nuclei. Therefore, PHMB displays differential access to bacterial and mammalian cellular DNA and selectively binds and condenses bacterial chromosomes. Because acquired resistance to PHMB has not been reported, selective chromosome condensation provides an unanticipated paradigm for antimicrobial action that may not succumb to resistance.

Acid environments affect biofilm formation and gene expression in isolates of Salmonella enterica Typhimurium DT104

The aim of this study was to examine the survival and potential virulence of biofilm-forming Salmonella Typhimurium DT104 under mild acid conditions. Salmonella Typhimurium DT104 employs an acid tolerance response (ATR) allowing it to adapt to acidic environments. The threat that these acid adapted cells pose to food safety could be enhanced if they also produce biofilms in acidic conditions. The cells were acid-adapted by culturing them in 1% glucose and their ability to form biofilms on stainless steel and on the surface of Luria Bertani (LB) broth at pH7 and pH5 was examined. Plate counts were performed to examine cell survival. RNA was isolated from cells to examine changes in the expression of genes associated with virulence, invasion, biofilm formation and global gene regulation in response to acid stress. Of the 4 isolates that were examined only one (1481) that produced a rigid biofilm in LB broth at pH7 also formed this same structure at pH5. This indicated that the lactic acid severely impeded the biofilm producing capabilities of the other isolates examined under these conditions. Isolate 1481 also had higher expression of genes associated with virulence (hilA) and invasion (invA) with a 24.34-fold and 13.68-fold increase in relative gene expression respectively at pH5 compared to pH7. Although genes associated with biofilm formation had increased expression in response to acid stress for all the isolates this only resulted in the formation of a biofilm by isolate 1481. This suggests that in addition to the range of genes associated with biofilm production at neutral pH, there are genes whose protein products specifically aid in biofilm production in acidic environments. Furthermore, it highlights the potential for the use of lactic acid for the inhibition of Salmonella biofilms.

Effects of benzalkonium chloride on planktonic growth and biofilm formation by animal bacterial pathogens

BACKGROUND

Resistance toward quaternary ammonium compounds (QACs) is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as biofilm formation.

OBJECTIVES

In this study, the effects of benzalkonium chloride on planktonic growth and biofilm formation by some field isolates of animal bacterial pathogens were investigated.

MATERIALS AND METHODS

Forty clinical isolates of Escherichia coli, Salmonella serotypes, Staphylococcus aureus and Streptococcus agalactiae (10 isolates of each) were examined for effects of benzalkonium chloride on biofilm formation and planktonic growth using microtiter plates. For all the examined strains in the presence of benzalkonium chloride, biofilm development and planktonic growth were affected at the same concentrations of disinfectant.

RESULTS

The means of strains growth increase after the minimal inhibitory concentration (MIC) were significant in all the bacteria (except for E. coli in 1/32 and S. agalactiae in of 1/8 MIC). Biofilm formation increased with decrease of antiseptics concentration; a significant increase was found in all the samples. The most turbidity related to S. aureus and the least to Salmonella.

CONCLUSIONS

Bacterial resistance against quaternary ammonium compounds is increasing which can increase the bacterial biofilm formation.

Chlorhexidine digluconate effects on planktonic growth and biofilm formation in some field isolates of animal bacterial pathogens

Background:

To study chlorhexidine digluconate disinfectant effects on planktonic growth and biofilm formation in some bacterial field isolates from animals.

Objectives:

The current study investigated chlorhexidine digluconate effects on planktonic growth and biofilm formation in some field isolates of veterinary bacterial pathogens.

Materials and Methods:

Forty clinical isolates of Escherichia coli, Salmonella serotypes, Staphylococcus. aureus and Streptococcusagalactiae (10 isolates for each) were examined for chlorhexidine digluconate effects on biofilm formation and planktonic growth using microtiter plates. In all of the examined strains in the presence of chlorhexidine digluconate, biofilm development and planktonic growth were affected at the same concentrations of the disinfectant.

Results:

Chlorhexidine digluconate inhibited the planktonic growth of different bacterial species at sub-MICs. But they were able to induce biofilm development of the E. coli, Salmonella spp., S. aureus and Str. agalactiae strains.

Conclusions:

Bacterial resistance against chlorhexidine is increasing. Sub-MIC doses of chlorhexidine digluconate can stimulate the formation of biofilm strains.

Effectiveness of coating acrylic resin dentures on preventing Candida adhesion

PURPOSE

The aim of this study was to prevent the adhesion of C. albicans on acrylic resin dentures by modifying their surfaces.

MATERIALS AND METHODS

Ninety acrylic resin plates were divided into three groups. Group I: conventionally processed acrylic resin plates. Group II: plates painted with 2-Octyl Cyanoacrylate adhesive. Group III: plates painted with Adper Single Bond Adhesive. All specimens were immersed separately in containers filled with artificial saliva that contained C. albicans and then incubated for 11 days at 37°C. Three methods of evaluation were used to count the adhered Candida: direct culture, slide count, and serial dilutions.

RESULTS

C. albicans in 1/10, 1/10², and 1/10³ dilutions showed overgrowth in group I, while overgrowth was noted only with 1/10 dilution in group III. For group III, mean colony numbers of 123, 22, 3.4, and 0 were found for the 1/10², 1/10³, 1/10⁴, and 1/10⁵ dilutions, respectively. Regarding the slide counts, group I showed a mean fungal count of 166 compared to 40 for group III with 1/10 dilution, 21 compared to 9 with 1/10³ dilution, 8.6 compared to 0.7 with 1/10³ dilution, and 1.2 compared to 0 with 1/10⁴ dilution. No plates in group II showed any candidal colonies regardless of the method of evaluation (0%). These differences were statistically significant (p < 0.0001).

CONCLUSION

Coating the acrylic resin dentures with Adper Single Bond Adhesive was effective in reducing C. albicans adhesion to dentures, while coating with 2-Octyl Cyanoacrylate adhesive completely inhibited such adhesion.

Antimicrobial Pressure of Ciprofloxacin and Gentamicin on Biofilm Development by an Endoscope-Isolated Pseudomonas aeruginosa

This work aims at characterizing endoscope biofilm-isolated (PAI) and reference strain P. aeruginosa (PA) adhesion, biofilm formation and sensitivity to antibiotics. The recovery ability of the biofilm-growing bacteria subjected to intermittent antibiotic pressure (ciprofloxacin (CIP) and gentamicin (GM)), as well as the development of resistance towards antibiotics and benzalkonium chloride (BC), were also determined. The capacity of both strains to develop biofilms was greatly impaired in the presence of CIP and GM. Sanitization was not complete allowing biofilm recovery after the intermittent cycles of antibiotic pressure. The environmental pressure exerted by CIP and GM did not develop P. aeruginosa resistance to antibiotics nor cross-resistance towards BC. However, data highlighted that none of the antimicrobials led to complete biofilm eradication, allowing the recovery of the remaining adhered population possibly due to the selection of persister cells. This feature may lead to biofilm recalcitrance, reinforcement of bacterial attachment, and recolonization of other sites.

Clinical use of the antiseptic polihexanide for genital tract infections

BACKGROUND

In clinical practice, treatment of genital tract infections is based on administration of either antibiotics or antiseptics. While antibiotics may be applied systemically or topically, antiseptics may be applied only topically. In case of bacterial vaginosis (BV), antibiotic therapy may often be limited and side effects due to systemic administration may develop. Polihexanide (PHMB) is a promising option for the topical treatment of genital tract infections, in particular BV and vaginitis.

METHOD

A systematic search for publications on the use of PHMB for the treatment of genital infections in two electronic databases was performed. Titles, abstracts and citations were imported into a reference database. Duplicates were removed and two reviewers assessed each identified publication separately.

RESULTS

Among a total of 204 references, 3 prospective randomized trials were identified. Two trials treated BV infections with PHMB in comparison to clindamycin as antibiotic standard therapy with no significant differences either in safety or in efficacy. The third controlled trial investigated the clinical efficacy of PHMB compared to placebo in the treatment of human papilloma virus. Patients treated with PHMB daily for up to 16-weeks showed significantly higher (52%) clearance of genital warts as compared to patients treated with placebo (4%).

CONCLUSION

PHMB may be a clinically effective alternative for the treatment of BV and human papilloma virus. Although PHMB-based antiseptics are available since the late 90s, controlled trials to investigate its clinical potential for antiseptic treatment are scant. Clinical use of antiseptics for the treatment of infectious diseases should be explored and supported further.

Activity of disinfectants against foodborne pathogens in suspension and adhered to stainless steel surfaces

The purpose of this study was to investigate and compare the efficacy of various disinfectants on planktonic cells and biofilm cells of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli. Numbers of viable biofilm cells decreased after treatment with all tested disinfectants (iodine, biguanide, quaternary ammonium compounds, peracetic acid and sodium hypochlorite). Sodium hypochlorite was the most effective disinfectant against biofilm cells, while biguanide was the least effective. Scanning electron microscopy observations revealed that cells adhered on stainless steel surface after treatment with the disinfectants. No viable planktonic cells were observed after treatment with the same disinfectants. Based on our findings, we concluded that biofilm cells might be more resistant to disinfectants than plancktonic cells.

Microbicide activity of clove essential oil (Eugenia caryophyllata)

Clove essential oil, used as an antiseptic in oral infections, inhibits Gram-negative and Gram-positive bacteria as well as yeast. The influence of clove essential oil concentration, temperature and organic matter, in the antimicrobial activity of clove essential oil, was studied in this paper, through the determination of bacterial death kinetics. Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa were the microorganisms selected for a biological test. To determine the temperature effect, they were assayed at 21° and 37° C. The concentration coefficient was determined with 0.4%, and 0.2% of essential oil. The influence of the presence of organic matter was determined with 0.4% of essential oil. The results obtained demonstrated that Escherichia coli were more sensitive even though the essential oil exerted a satisfactory action in three cases. In the three microbial species, 0.4% of essential oil at 21° C have reduced the bacterial population in 5 logarithmic orders. Organic matter reduces the antibacterial activity even though the bactericide efficacy was not lost. Clove essential oil can be considered as a potential antimicrobial agent for external use.

Effectiveness of antibacterial copper additives in silicone implants

Staphylococcus epidermidis plays a major role in capsular contractures of silicone breast implants. This in vitro study evaluates the antibacterial effect of copper on S. epidermidis in silicone implants. Specimens of a silicone material used for breast augmentation (Cu0) and specimens coated with different copper concentrations (Cu1, Cu2) were artificially aged. Surface roughness and surface free energy were assessed. The specimens were incubated in an S. epidermidis suspension. We assessed the quantification and the viability of adhering bacteria by live/dead cell labeling with fluorescence microscopy. Additionally, inhibition of bacterial growth was evaluated by agar diffusion, broth culture, and quantitative culture of surface bacteria. No significant differences in surface roughness and surface free energy were found between Cu0, Cu1 and Cu2. Aging did not change surface characteristics and the extent of bacterial adhesion. Fluorescence microscopy showed that the quantity of bacteria on Cu0 was significantly higher than that on Cu1 and Cu2. The ratio of dead to total adhering bacteria was significantly lower on Cu0 than on Cu1 and Cu2, and tended to be higher for Cu2 than for Cu1. Quantitative culture showed equal trends. Copper additives seem to have anti-adherence and bactericidal effects on S. epidermidis in vitro.

Antimicrobial gauze as a dressing reduces pin site infection: a randomized controlled trial

BACKGROUND

Pin site infection is a common problem in external fixation. Plain gauze wetted with normal saline is commonly used for a pin site dressing owing to the simplicity and low cost. Evidence to support adding an antimicrobial agent in the dressing material is lacking.

QUESTIONS/PURPOSES

We compared the rate of pin tract infection using plain gauze and gauze impregnated with polyhexamethylene biguanide in patients undergoing limb lengthening procedures.

PATIENTS AND METHODS

We included 38 patients (40 limbs) undergoing limb lengthening or deformity correction using an external fixator between July 2009 and June 2010. There were 23 male patients and 15 female patients, with a mean age of 26.3 years (range, 5-68 years). The patients were randomized into two groups: a polyhexamethylene biguanide group (22 limbs) and a control group (18 limbs). The metal-skin interfaces were assessed by a researcher blinded to the type of gauze at 2, 4, 8, and 12 weeks after surgery for the pin site infection based on a predetermined grading system. There were a total of 483 metal-skin interfaces, with 1932 total observations. Infection rates were compared using the chi square test and relative risk with 95% confidence interval.

RESULTS

The infection rate was lower (χ(2) [1, n = 1932] = 23.00) and the risk for infection was lower (relative risk, 0.228; 95% confidence interval, 0.118, 0.443) for the polyhexamethylene biguanide group (n = 1068; 1.0%) than for the control group (n = 864; 4.5%).

CONCLUSIONS

Use of polyhexamethylene biguanide-impregnated gauze can reduce the risk of pin tract infection in external fixation.

LEVEL OF EVIDENCE

Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Comparative susceptibility of Salmonella Typhimurium biofilms of different ages to disinfectants

There is a general consensus that with increasing age a biofilm shows increased resistance to antimicrobials. In this study the susceptibility of 3-, 5- and 7-day-old Salmonella enterica serovar Typhimurium biofilms to disinfectants was evaluated. It was hypothesized that 7-day-old biofilms would be more resistant to disinfectants compared to 3- and 5-day-old biofilms. Biofilms were formed using the MBEC™ system and treated with six chemical disinfectants for 1 and 5 min. Four disinfectants at the highest concentration available showed 100% reduction in viable cells from all ages of biofilms after exposure for 5 min, and ethanol at 70% v/v was the least effective against biofilms, followed by chlorhexidine gluconate (CG). At the recommended user concentrations, only sodium hypochlorite showed 100% reduction in viable cells from all ages of biofilms. Benzalkonium chloride and CG were the least effective against biofilms, followed by quaternary ammonium compound which only showed 100% reduction in viable cells from 5-day-old biofilms. Overall, the results from this study do not display enhanced resistance in 7-day-old biofilms compared to 3- and 5-day-old biofilms. It is concluded that under the conditions of this study, the age of biofilm did not contribute to resistance towards disinfectants. Rather, the concentration of disinfectant and an increased contact time were both shown to play a role in successful sanitization.

Spatial and temporal patterns of biocide action against Staphylococcus epidermidis biofilms

The dynamic antimicrobial action of chlorine, a quaternary ammonium compound, glutaraldehyde, and nisin within biofilm cell clusters of Staphylococcus epidermidis was investigated using time-lapse confocal scanning laser microscopy. The technique allowed for the simultaneous imaging of changes in biofilm structure and disruption of cellular membrane integrity through the loss of an unbound fluorophore loaded into bacterial cells prior to antimicrobial challenge. Each of the four antimicrobial agents produced distinct spatial and temporal patterns of fluorescence loss. The antimicrobial action of chlorine was localized around the periphery of biofilm cell clusters. Chlorine was the only antimicrobial agent that caused any biofilm removal. Treatment with the quaternary ammonium compound caused membrane permeabilization that started at the periphery of cell clusters, then migrated steadily inward. A secondary pattern superimposed on the penetration dynamic suggested a subpopulation of less-susceptible cells. These bacteria lost fluorescence much more slowly than the majority of the population. Nisin caused a rapid and uniform loss of green fluorescence from all parts of the biofilm without any removal of biofilm. Glutaraldehyde caused no biofilm removal and also no loss of membrane integrity. Measurements of biocide penetration and action time at the center of cell clusters yielded 46 min for 10 mg liter(-1) chlorine, 21 min for 50 mg liter(-1) chlorine, 25 min for the quaternary ammonium compound, and 4 min for nisin. These results underscore the distinction between biofilm removal and killing and reinforce the critical role of biocide reactivity in determining the rate of biofilm penetration.

Chapter 4: In vitro biofilm models: an overview

Observing naturally occurring biofilms in situ or ex situ has revealed the wide distribution of sessile microbial communities. The ubiquity, variety and complexity of biofilms is now widely accepted by microbiologists. While they are associated with many beneficial functions such as nutrient cycling, bioremediation and colonization resistance, adverse effects including recalcitrance, their involvement in industrial fouling, contamination and infection have made biofilms a priority research topic. We know that most biofilms, other than within certain infections and laboratory flasks, are composed of multiple species and that there is arguably no unifying biofilm architecture. Biofilms do however share certain properties including the presence of gradients of nutrients, gasses and metabolic products, relatively increased cell density, deposition of extracellular polymeric substances and marked recalcitrance towards antimicrobial treatments. Much of our understanding of biofilm physiology and micro-ecology originates from experiments using in vitro biofilm models. Broadly speaking, such models may be used to replicate environmental conditions within the laboratory or to focus on selected variables such a growth rate or fluid flow, etc. This chapter provides an overview of some commonly used biofilm models including microtitre plate systems, flow cells, the constant depth film fermenter, annular reactors and the perfused biofilm fermenter. While perfused biofilm fermenters, in particular, enable growth rate to be controlled within thin, relatively homogenous, quasi steady-state biofilms through modulation of flow rate nutrient availability, other models provide representative modelling of in situ conditions where steady states may be uncommon.

Copper and quaternary ammonium cations exert synergistic bactericidal and antibiofilm activity against Pseudomonas aeruginosa

Biofilms are slimy aggregates of microbes that are likely responsible for many chronic infections as well as for contamination of clinical and industrial environments. Pseudomonas aeruginosa is a prevalent hospital pathogen that is well known for its ability to form biofilms that are recalcitrant to many different antimicrobial treatments. We have devised a high-throughput method for testing combinations of antimicrobials for synergistic activity against biofilms, including those formed by P. aeruginosa. This approach was used to look for changes in biofilm susceptibility to various biocides when these agents were combined with metal ions. This process identified that Cu(2+) works synergistically with quaternary ammonium compounds (QACs; specifically benzalkonium chloride, cetalkonium chloride, cetylpyridinium chloride, myristalkonium chloride, and Polycide) to kill P. aeruginosa biofilms. In some cases, adding Cu(2+) to QACs resulted in a 128-fold decrease in the biofilm minimum bactericidal concentration compared to that for single-agent treatments. In combination, these agents retained broad-spectrum antimicrobial activity that also eradicated biofilms of Escherichia coli, Staphylococcus aureus, Salmonella enterica serovar Cholerasuis, and Pseudomonas fluorescens. To investigate the mechanism of action, isothermal titration calorimetry was used to show that Cu(2+) and QACs do not interact in aqueous solutions, suggesting that each agent exerts microbiological toxicity through independent biochemical routes. Additionally, Cu(2+) and QACs, both alone and in combination, reduced the activity of nitrate reductases, which are enzymes that are important for normal biofilm growth. Collectively, the results of this study indicate that Cu(2+) and QACs are effective combinations of antimicrobials that may be used to kill bacterial biofilms.

Antibiofilm activity of sodium bicarbonate, sodium metaperiodate and SDS combination against dental unit waterline-associated bacteria and yeast

AIM

To determine the effect of sodium bicarbonate (SB), sodium metaperiodate (SMP) and sodium dodecyl sulfate (SDS) combination on biofilm formation and dispersal in dental unit waterline (DUWL)-associated bacteria and yeast.

METHODS AND RESULTS

The in vitro effect of SB, SMP and SDS alone and in combination on biofilm formation and dispersal in Pseudomonas aeruginosa, Klebsiella pneumoniae, Actinomyces naeslundii, and Candida albicans was investigated using a 96-well microtitre plate biofilm assay. The combination showed a broad-spectrum inhibitory effect on growth as well as biofilm formation of both gram-negative and gram-positive bacteria, and yeast. In addition, the SB + SMP + SDS combination was significantly more effective in dispersing biofilm than the individual compounds. The combination dispersed more than 90% of P. aeruginosa biofilm whereas the commercial products, Oxygenal 6, Sterilex Ultra, and PeraSafe showed no biofilm dispersal activity.

CONCLUSION

The composition comprising SB, SMP, and SDS was effective in inhibiting as well as dispersing biofilms in DUWL-associated bacteria and yeast.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that a composition comprising environmentally friendly and biologically safe compounds such as SB, SMP, and SDS has a potential application in reducing DUWL-associated acquired infections in dental clinics.

Disinfectant test against monoculture and mixed-culture biofilms composed of technological, spoilage and pathogenic bacteria: bactericidal effect of essential oil and hydrosol of Satureja thymbra and comparison with standard acid-base sanitizers

AIMS

To assess the antimicrobial action of three natural-derived products (essential oil, decoction and hydrosol of Satureja thymbra) against biofilms, composed of useful, spoilage and pathogenic bacteria (formed as monoculture or/and mixed-culture), and to compare their efficiency with three standard acid and alkaline chemical disinfectants.

METHODS AND RESULTS

Two acids (hydrochloric and lactic, pH 3), one alkali (sodium hydroxide, pH 11), the essential oil of S. thymbra (1% v/v) and the two by-products of the essential oil purification procedure (the decoction and the hydrosol fraction of essential oil, 100%), were tested against biofilms formed by five bacterial species, either as monospecies, or as mixed-culture of all species. The tested bacterial species were Staphylococcus simulans and Lactobacillus fermentum (useful technological bacteria), Pseudomonas putida (spoilage bacterium), Salmonella enterica and Listeria monocytogenes (pathogenic bacteria). Biofilms were left to be formed on stainless steel coupons for 5 days at 16 degrees C, before the application of disinfection treatments, for 60 and 180 min. The disinfection efficiency was evaluated by detaching the remaining viable biofilm cells and enumerating them by agar plating, as well as by automated conductance measurements (using Rapid Automated Bacterial Impedance Technique). Both these methods revealed that the essential oil and the hydrosol of S. thymbra exhibited a strong antimicrobial action against both monospecies and mixed-culture biofilms. Surprisingly, the efficiency of the other three acid-base disinfectants was not adequate, although a long antimicrobial treatment was applied (180 min).

CONCLUSIONS

The essential oil of S. thymbra (1%), as well as its hydrosol fraction (100%), presents sufficient bactericidal effect on bacterial biofilms formed on stainless steel.

SIGNIFICANCE AND IMPACT OF THE STUDY

Use of natural antimicrobial agents could provide alternative or supplemented ways for the disinfection of microbial-contaminated industrial surfaces.

The Listeria monocytogenes homolog of the Escherichia coli era gene is involved in adhesion to inert surfaces

Two transposon-insertional mutants of Listeria monocytogenes showing smaller viable surface-attached cell populations after disinfection with N,N-didecyl-N,N-dimethylammonium chloride were identified. In both mutants, transposon Tn917-lac was found to be inserted into the same gene, lmo1462, which is homologous to the essential Escherichia coli era gene. Both L. monocytogenes lmo1462-disrupted mutants displayed lower growth rates, as was also shown for several E. coli era mutants, and the lmo1462 gene was able to complement the growth defect of an E. coli era mutant. We showed that the disruption of lmo1462 decreased the ability of L. monocytogenes cells to adhere to stainless steel. Our results suggest that this era-like gene is involved in adhesion and contributes to the presence of L. monocytogenes on surfaces.

Influence of starvation, surface attachment and biofilm growth on the biocide susceptibility of the biodeteriogenic yeast Aureobasidium pullulans

AIM

To investigate the effect of starvation, surface attachment and growth in a biofilm on the susceptibility of Aureobasidium pullulans to the biocides 2-n-octyl-4-isothiazolin-3-one (OIT) and sodium hypochlorite (NaOCl).

METHODS AND RESULTS

Fluorescence loss from a green fluorescent protein (GFP)-transformed strain was used to monitor real-time loss in viability as previously described in situ in 96-well plates. Exponential phase, yeast-like (YL) cells were settled in the bottom of the wells as a low-density monolayer (LDM) and were susceptible to all biocide concentrations (25-100 mug ml(-1)). The exponential phase YL cells were either starved for 48 h in suspension or starved for 48 h as LDMs in the wells. Starvation in both cases led to a small reduction in susceptibility to the biocides. In contrast, 48-h biofilms grown in malt extract broth showed an apparent lack of susceptibility to 25 and 50 mug ml(-1) OIT and to 25-100 mug ml(-1) NaOCl. However, when the OIT concentration was increased to compensate for the higher cell density in the biofilm, the biofilms were found to be equally susceptible to the LDM.

CONCLUSIONS

Starvation of A. pullulans YL cells either in suspension or as attached LDM resulted in a decrease in susceptibility to low concentrations of both OIT and NaOCl while the apparent reduced susceptibility of mature biofilms was due to the increase in biofilm cell density rather than true biofilm resistance per se.

SIGNIFICANCE AND IMPACT OF THE STUDY

Monitoring fluorescence loss from the GFP-transformed strain of A. pullulans can be used as a fast and reliable method for monitoring cell death in real time as a response to biocide and antimicrobial challenge.