In vitro determination of the antibiotic susceptibility of biofilm-forming Pseudomonas aeruginosa and Staphylococcus aureus: possible role of proteolytic activity and membrane lipopolysaccharide

Antimicrobial activities of spirooxindolopyrrolidine tethered dicarbonitrile heterocycles against multidrug resistant nosocomial pathogens

BACKGROUND

Microbial infections together with rising drug resistance pose a threat to immunocompromised individual. In this perspective, compounds with spirooxindolopyrrolidine play a significant role in research on antimicrobial drug delivery research owing to their various pharmaceutical activities. Spiroheterocyclic compounds are present in number of medications as active motif due to their exceptional structural properties which enable for easy interaction with the protein of the biological target. Inspired by this biological precedent encouraged to synthesize a new class of dispirooxindole fused pyrrolidine heterocycles via a three-component cycloaddition strategy.

MATERIALS AND METHODS

The new class of structurally intriguing spirooxindolopyrrolidines were synthesized through three component cycloaddition process and the structure of products were assigned through spectroscopic analysis. The newly synthesized compounds were assessed for their antimicrobial sensitivity test with standard Kirby Bauer method with common drugs.

RESULTS

The structurally unexplored hybrid heterocycles fused spirooxindolopyrrolidine exhibited excellent antimicrobial activity against the common nosocomial microbial pathogens. Of four compounds, the compound bearing a chlorine atom on the aryl ring (4a) exhibited significant antimicrobial activity (zone of inhibition: 9.00 ± 1.00-17.00 ± 0.35 mm and MIC: 16.00-256.00 μg/mL) against selected nosocomial infection causing microbial pathogens. Hence, the compound 4a has been considered as an effective drug of interest in therapeutic field for compacting infectious diseases causing pathogens.

CONCLUSION

With an aim of developing more effective and economically more affordable antimicrobial leads with a unique mechanism of action, we have designed and synthesized structurally diverse spirooxindolopyrrolidine tethered hybrids that has been assayed against multidrug resistant nosocomial pathogens. The regioisomer having chloro substituted on the phenyl ring showed potent activity when compared to standard drug. Future studies are required to explicate the pharmacological properties of new hybrid heterocycles that have been synthesized in our laboratory for the novel therapeutic development.

Discovery and structure-activity relationships of the quinolinequinones: Promising antimicrobial agents and mode of action evaluation

In our pursuit of developing the novel, potent, and selective antimicrobial agents, we managed to obtain the quinolinequinone for their antimicrobial profile with minimal inhibitory concentrations (MICs) determined against a panel of seven bacterial strains (three gram-positive and four gram-negative bacteria) and three fungi. The structure-activity relationship (SAR) for the quinolinequinone class of antimicrobials was determined. Interestingly, QQ1, QQ4, QQ6-9, QQ12, and QQ13 displayed equal antibacterial potential against S. aureus (MIC = 1.22 mg/L), respectively, to the standard positive control Cefuroxime-Na. QQ10 had the best inhibitory activity with the MIC value of 1.22 mg/L (fourfold more potent compared to reference standard Clotrimazole) against Candida albicans. On the other hand, while QQ10 is not too effective against gram-positive bacteria as much as the other analogs, QQ10 was the most effective quinolinequinones against fungi. Selected quinolinequinones were further evaluated for the mode of action, using in vitro antibiofilm activity, bactericidal activity by using time-kill curve assay, antibiofilm activity, and potential antimicrobial activity against each of 32 clinically obtained resistant strains of Gram-positive Bacteria. The results also revealed that the QQ14 had specific antifungal activity against fungi in particular C. albicans. Our results clearly showed that quinolinequinones are much more active in the inhibition of the biofilm attachment process than the inhibition of mature biofilm formation. Thus, as treatment options are narrowing for Methicillin-resistant Staphylococcus spp., Vancomycin-resistant Staphylococcus spp. daily, the quinolinequinones reported herein display promise as the lead candidates for further clinical applications against serious infections.

Exploration of brominated Plastoquinone analogs: Discovery and structure-activity relationships of small antimicrobial lead molecules

In the fight with the antimicrobial resistance, our continuous effort to find quinone analogs with higher inhibitory activity has previously led us to the promising Plastoquinone analogs. The 1,4-quinone moiety substituted with alkoxy substituent(s) plays an important role in the field of antimicrobial and anticancer drug discovery and development. Thus, an extensive series of 1,4-quinones, substituted in different positions with a variety of alkoxy substituents, has been designed, synthesized, and evaluated for their antimicrobial activity. Here, we describe the synthesis of brominated Plastoquinone analogs (BrPQ1-15) based on the dimethyl-1,4-quinone scaffold by employing two different paths. We also present here the in vitro antimicrobial activity of these analogs (BrPQ1-15) against a panel of pathogenic organisms. These studies resulted in several new selective antibacterial inhibitors and gave valuable insights into the structure-activity relationships. Among all the analogs studied, two analogs BrPQ1 with a methoxy substituent and BrPQ14 with a cyclic dioxy stand out as the most promising antibacterial molecules against Staphylococcus aureus and Staphylococcus epidermidis. Afterwards, two analogs were selected for a further investigation for biofilm evaluation. Finally, molecular docking studies for BrPQ1 and BrPQ14 with probable target S. aureus PNPase (5XEX) and predictive ADMET studies were also carried out.

Characterization of Ciprofloxacin Resistance Levels: Implications for Ototopical Therapy

HYPOTHESIS

Ciprofloxacin-resistant pathogens are inhibited by high concentrations of ciprofloxacin found in commercially-available ototopical solutions.

BACKGROUND

Ciprofloxacin-resistant pathogens in otitis media are currently treated with ototopical ciprofloxacin suspensions. This is done irrespective of laboratory-reported ciprofloxacin susceptibility, under the assumption that the high concentration of ciprofloxacin applied topically is sufficient to overcome antimicrobial resistance.

METHODS

We evaluated 34 ciprofloxacin-resistant isolates consisting of Staphylococcus aureus, Pseudomonas aeruginosa, Corynebacterium spp., and Turicella otitidis. Ciprofloxacin minimum inhibitory concentration (MIC) assays and clinical ototopical solution minimum bactericidal concentration (CMBC) assays were performed.

RESULTS

Amongst the ciprofloxacin-resistant isolates, ciprofloxacin MICs ranged from 8 to 256 mcg/ml (mean: 87.1 mcg/ml) and CMBCs ranged from 23.4 to 1500 mcg/ml (mean: 237.0 mcg/ml). There were no significant differences with respect to MIC in comparing P. aeruginosa versus Corynebacterium spp. (mean: 53.3 versus 55.2, p = 0.86), S. aureus versus P. aeruginosa (mean: 128.0 versus 53.3, p = 0.34), and S. aureus versus Corynebacterium spp. (mean: 128.0 versus 55.2, p = 0.09). The correlation between ciprofloxacin MIC and CMBC was poor (Pearson's r = -0.08, p = 0.75).

CONCLUSIONS

Ciprofloxacin-resistant pathogens commonly recovered from otitis media exhibit highly variable ciprofloxacin MIC and CMBC levels. Ciprofloxacin was able to inhibit growth in all isolates tested at MIC levels less than or equal to 256 mcg/ml; however, CMBC's up to 1500 mcg/ml were observed within that same group. The clinical relevance of these in vitro MICs is unclear due in part to higher bactericidal concentrations (CMBC) in several strains. Our results suggest that treatment failures may be due to a combination of factors rather than high-level resistance alone.

Modulating photochemical reactions in Langmuir monolayers of Escherichia coli lipid extract with the binding mechanisms of eosin decyl ester and toluidine blue-O photosensitizers

Photodynamic damage to the cell envelope can inactivate microorganisms and may be applied to combat super-resistance phenomenon, empowered by the indiscriminate use of antibiotics. Efficiency in microbial inactivation is dependent on the incorporation of photosensitizers (PS) into the bacterial membranes to trigger oxidation reactions under illumination. Herein, Langmuir monolayers of Escherichia coli lipid extract were built to determine the binding mechanisms and oxidation outcomes induced by eosin decyl ester (EosDEC) and toluidine blue-O (TBO) PSs. Surface-pressure isotherms of the E. coli monolayers were expanded upon EosDEC and TBO, suggesting incorporation of both PSs. Fourier-transform infrared spectroscopy (FTIR) of Langmuir-Schaefer (LS) films reveled that the EosDEC and TBO binding mechanisms are dominated by electrostatic interactions with the anionic polar groups, with limited penetration into the chains. Light-irradiation reduced the relative area of E. coli monolayer on TBO, indicating an increased loss of material to the subphase owing to the chain cleavage, generated by contact-dependent reactions with excited states of TBO. In contrast, the increased relative area of E. coli monolayers containing EosDEC suggests lipid hydroperoxidation, which is PS contact-independent. Even considering a small chain penetration, the saturated EosDEC may have partitioned towards saturated reach domains, avoiding direct contact with membrane unsaturations.

Bacterial Biofilm Formation Using PCL/Curcumin Electrospun Fibers and Its Potential Use for Biotechnological Applications

Electrospun nanofibers are used for many applications due to their large surface area, mechanical properties, and bioactivity. Bacterial biofilms are the cause of numerous problems in biomedical devices and in the food industry. On the other hand, these bacterial biofilms can produce interesting metabolites. Hence, the objective of this study is to evaluate the efficiency of poly (Ɛ- caprolactone)/Curcumin (PCL/CUR) nanofibers to promote bacterial biofilm formation. These scaffolds were characterized by scanning electron microscopy (SEM), which showed homogeneous fibers with diameters between 441-557 nm; thermogravimetric analysis and differential scanning calorimetry (TGA and DSC) demonstrated high temperature resilience with degradation temperatures over >350 °C; FTIR and ¹H-NMR serve as evidence of CUR incorporation in the PCL fibers. PCL/CUR scaffolds successfully promoted the formation of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa biofilms. These results will be valuable in the study of controlled harvesting of pathogenic biofilms as well as in metabolites production for biotechnological purposes.

Bioactive glass S53P4 eradicates Staphylococcus aureus in biofilm/planktonic states in vitro

Background: Increasing antimicrobial resistance to antibiotics is a substantial health threat. Bioactive glass S53P4 (BAG) has an antimicrobial effect that can reduce the use of antibiotics. The aim of this study was to evaluate the antimicrobial efficacy of BAG in vitro on staphylococci in biofilm and in planktonic form. Secondary aims were to investigate whether supernatant fluid primed from BAG retains the antibacterial capacity and if ciprofloxacin enhances the effect.Methods: BAG-S53P4 granules, <45 µm, primed in tryptic soy broth (TSB) were investigated with granules present in TSB (100 mg/mL) and after removal of granules (100, 200, and 400 mg/mL). The efficacy of BAG to eradicate Staphylococcus aureus biofilm in vitro was tested using 10 different clinical strains and 1 reference strain in three test systems: the biofilm-oriented antiseptic test based on metabolic activity, the biofilm bactericidal test based on culturing surviving bacteria, and confocal laser scanning microscopy (CLSM) combined with LIVE/DEAD staining.Results: Exposure to 48 h primed BAG granules (100 mg/mL) produced bactericidal effects in 11/11 strains (p = 0.001), and CLSM showed reduction of viable bacteria in biofilm (p = 0.001). Supernatant primed 14 days, 400 mg/mL, reduced metabolic activity (p < 0.001), showed bactericidal effects for 11/11 strains (p = 0.001), and CLSM showed fewer viable bacteria (p = 0.001). The supernatant primed for 48 h, or in concentrations lower than 400 mg/mL at 14 days, did not completely eradicate biofilm.Conclusion: Direct exposure to BAG granules, or primed supernatant fluid, effectively eradicated S. aureus in biofilm. The anti-biofilm effect is time- and concentration-dependent. When BAG had reached its full antimicrobial effect, ciprofloxacin had no additional effect.

Chlorinated plastoquinone analogs that inhibit Staphylococcus epidermidis and Candida albicans growth

Infectious diseases are the significant global health problem because of drug resistance to most classes of antimicrobials. Interest is growing in the development of new antimicrobials in pharmaceutical discovery. For that reason, the urgency for scientists to find and/or develop new important molecules is needed. Many natural active molecules that exhibit various biological activities have been isolated from the nature. For the present research, a new selected set of aminobenzoquinones, denoted as plastoquinone analogs (PQ1-24), was employed for their in vitro antimicrobial potential in a panel of seven bacterial strains (three Gram-positive and four Gram-negative bacteria) and three fungi. The results revealed PQ analogs with specific activity against bacteria including Staphylococcus epidermidis and pathogenic fungi, including Candida albicans. PQ8 containing methoxy group at the ortho position on the phenylamino moiety exhibited the highest growth inhibition against S. epidermidis with a minimum inhibitory concentration of 9.76 μg/mL. The antifungal profile of all PQ analogs indicated that five analogs (while PQ1, PQ8, PQ9, PQ11, and PQ18 were effective against Candida albicans, PQ1 and PQ18 were effective against Candida tropicalis) have potent antifungal activity. Selected analogs, PQ1 and PQ18, were studied for biofilm evaluation and time-kill kinetic study for better understanding.

In Vitro Comparison of Antibacterial and Antibiofilm Activities of Selected Fluoroquinolones against Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus

An in vitro overview of the inhibitory effects of selected fluoroquinolones against planktonic and biofilm cells of the methicillin-resistant Staphylococcus aureus (MRSA) strain American type culture collection (ATCC) 43300 and the Pseudomonas aeruginosa strain ATCC 27853 was carried out. Biofilm cells of both strains were less susceptible to the selected antibiotics than their planktonic counterparts. In addition, certain antibiotics were more effective against biofilm cells, while others performed better on the planktonic cells. Against P. aeruginosa, ciprofloxacin was the most potent on both planktonic and biofilm cells, whereas ofloxacin was the least potent on both biofilm and planktonic cells. Moxifloxacin and gatifloxacin were the most potent against both planktonic and biofilm MRSA bacteria, however, not in the same order of activity. Norfloxacin was the least active when tested against both planktonic and biofilm cells. The results of this work are expected to provide insight into the efficacy of various fluoroquinolones against MRSA and Pseudomonas aeruginosa biofilms. This study could form the basis for future clinical studies that could recommend special guidelines for the management of infections that are likely to involve bacteria in their biofilm state.

Identification of Anti-staphylococcal and Anti-biofilm Compounds by Repurposing the Medicines for Malaria Venture Pathogen Box

There has been an alarming increase in infections caused by antimicrobial-resistant pathogens. These infections are responsible for more than half a million deaths globally each year. Staphylococcus aureus is one of the deadliest bacterial pathogen responsible for nosocomial and community acquired infections. The open-access Pathogen Box (PBox) provides a potential platform to identify new treatment options against antibiotic-resistant bacteria by repurposing it. In this study, we have screened the PBox library comprised of ~400 compounds to identify novel anti-staphylococcal compounds. in vitro antimicrobial screening using S. aureus isolates, ATCC 29213 (methicillin-sensitive) and ATCC 700699 (methicillin-resistant) revealed 13 compounds which showed highly potent antibacterial activity against both planktonic and biofilm state. The 13 compounds were not found cytotoxic to mouse macrophage cell line, RAW264.7. Out of the 13 compounds, only MMV687251 and MMV676477 revealed structural similarity with vancomycin by comparing their atomic pair fingerprints using Tanimoto coefficient method. The structural similarities may indicate similar mode of action like vancomycin for the two compounds. Our result showed that PBox compounds offer a promising lead for the development of new anti-staphylococcal treatment options.

Drug resistance of oral bacteria to new antibacterial dental monomer dimethylaminohexadecyl methacrylate

Only two reports exist on drug-resistance of quaternary ammonium monomers against oral bacteria; both studies tested planktonic bacteria for 10 passages, and neither study tested biofilms or resins. The objectives of this study were to investigate the drug-resistance of Streptococcus mutans, Streptococcus sanguinis and Streptococcus gordonii against dimethylaminohexadecyl methacrylate (DMAHDM), and to evaluate biofilms on resins with repeated exposures for 20 passages for the first time. DMAHDM, dimethylaminododecyl methacrylate (DMADDM) and chlorhexidine (CHX) were tested with planktonic bacteria. Biofilms were grown on a resin containing 3% DMAHDM. Minimum-inhibitory concentrations were measured. To detect drug-resistance, the survived bacteria from the previous passage were used as inoculum for the next passage for repeated exposures. S. gordonii developed drug-resistance against DMADDM and CHX, but not against DMAHDM. Biofilm colony-forming units (CFU) on DMAHDM-resin was reduced by 3–4 log; there was no difference from passages 1 to 20 (p > 0.1). No drug-resistance to DMAHDM was detected for all three bacterial species. In conclusion, this study showed that DMAHDM induced no drug-resistance, and DMAHDM-resin reduced biofilm CFU by 3–4 log, with no significant change from 1 to 20 passages. DMAHDM with potent antibacterial activities and no drug-resistance is promising for dental applications.

Changes in the lipopolysaccharide of Proteus mirabilis 9B-m (O11a) clinical strain in response to planktonic or biofilm type of growth

The impact of planktonic and biofilm lifestyles of the clinical isolate Proteus mirabilis 9B-m on its lipopolysaccharide (O-polysaccharide, core region, and lipid A) was evaluated. Proteus mirabilis bacteria are able to form biofilm and lipopolysaccharide is one of the factors involved in the biofilm formation. Lipopolysaccharide was isolated from planktonic and biofilm cells of the investigated strain and analyzed by SDS–PAGE with silver staining, Western blotting and ELISA, as well as NMR and matrix-assisted laser desorption ionization time-of-flight mass spectrometry techniques. Chemical and NMR spectroscopic analyses revealed that the structure of the O-polysaccharide of P. mirabilis 9B-m strain did not depend on the form of cell growth, but the full-length chains of the O-antigen were reduced when bacteria grew in biofilm. The study also revealed structural modifications of the core region in the lipopolysaccharide of biofilm-associated cells—peaks assigned to compounds absent in cells from the planktonic culture and not previously detected in any of the known Proteus core oligosaccharides. No differences in the lipid A structure were observed. In summary, our study demonstrated for the first time that changes in the lifestyle of P. mirabilis bacteria leads to the modifications of their important virulence factor—lipopolysaccharide.

Challenges in Application of Langmuir Monolayer Studies To Determine the Mechanisms of Bactericidal Activity of Ruthenium Complexes

The effects induced by antibiotics on the bacterial membrane may be correlated with their bactericidal activity, and such molecular-level interactions can be probed with Langmuir monolayers representing the cell membrane. In this study, we investigated the interaction between [Ru(mcbtz)₂(PPh₃)₂] (RuBTZ, mcbtz = 2-mercaptobenzothiazoline) and [Ru(mctz)₂(PPh₃)₂] (RuCTZ, mctz = 2-mercaptothiazoline) with Langmuir monolayers of a lipid extract of Escherichia coli, an extract of lipopolysaccharides (LPSs), and a zwitterionic phospholipid, dioleoylphosphatidyl choline (DOPC). RuBTZ and RuCTZ had little effects on DOPC, which is consistent with their negligible toxicity toward mammalian cells that may be approximated by a zwitterionic monolayer. Also little were their effects on LPSs. In contrast, RuBTZ and RuCTZ induced expansion in the surface pressure isotherms and decreased the compressional modulus of the E. coli lipid extract. While the more hydrophobic RuBTZ seemed to affect the hydrophobic tails of the E. coli extract monolayer to a larger extent, according to polarization modulation infrared reflection absorption spectroscopy results, evidence of a stronger RuBTZ interaction could not be confirmed unequivocally. Therefore, the interaction with the E. coli cell membrane cannot be directly correlated with the observed higher bactericidal activity of RuBTZ, in comparison to that of RuCTZ. This appears to be a case in which Langmuir monolayer studies do not suffice to determine the mechanisms responsible for the bactericidal activity.

Defeating Bacterial Resistance and Preventing Mammalian Cells Toxicity Through Rational Design of Antibiotic-Functionalized Nanoparticles

The rational synthesis of alternative materials is highly demanding due to the outbreak of infectious diseases and resistance to antibiotics. Herein, we report a tailored nanoantibiotic synthesis protocol where the antibiotic binding was optimized on the silver-silica core-shell nanoparticles surface to maximize biological responses. The obtained silver nanoparticles coated with mesoporous silica functionalized with ampicillin presented remarkable antimicrobial effects against susceptible and antibiotic-resistant Escherichia coli. In addition, these structures were not cell-death inducers and different steps of the mitotic cell cycle (prophase, anaphase and metaphase) were clearly identified. The superior biological results were attributed to a proper and tailored synthesis strategy.

Drug treatments for prosthetic joint infections in the era of multidrug resistance

INTRODUCTION

Despite many advances, the management of prosthetic joint infection is still a complex issue. Moreover, in recent years the problem of antimicrobial resistance has emerged as an important challenge.

AREAS COVERED

We analysed recent advances in different aspects of prosthetic joint infections. The importance of biofilms needs to be considered for antibiotic selection because, when embedded in these structures, bacteria acquire resistant behaviour. Moreover, the presence of resistance mechanisms in some species of organisms increases the difficulty of management. In this sense, the growing importance of methicillin-resistant staphylococci, multidrug-resistant Enterobacteriaceae or Pseudomonas aeruginosa is of increasing concern. Together with these organisms, others with constitutive resistance against most antibiotics (like Enterococcus sp., mycobacteria or fungi) represent a similar problem for selection of therapy. Research into new materials that can be used as drug carriers opens a new field for management of these infections and will likely come to the front line in the coming years.

EXPERT OPINION

Individualised therapies should carefully consider the aetiology, pathogenesis and antimicrobial susceptibility. Satisfactory clinical outcome could be further fostered by enhancing the multidisciplinary approach, with better collaboration in the antibiotic selection and the surgical management.

Optimization and Evaluation of a Chitosan/Hydroxypropyl Methylcellulose Hydrogel Containing Toluidine Blue O for Antimicrobial Photodynamic Inactivation

Photodynamic inactivation (PDI) combined with chitosan has been shown as a promising antimicrobial approach. The purpose of this study was to develop a chitosan hydrogel containing hydroxypropyl methylcellulose (HPMC), chitosan and toluidine blue O (TBO) to improve the bactericidal efficacy for topical application in clinics. The PDI efficacy of hydrogel was examined in vitro against the biofilms of Staphylococcusaureus (S. aureus) and Pseudomonasaeruginosa (P. aeruginosa). Confocal scanning laser microscopy (CSLM) was performed to investigate the penetration level of TBO into viable S. aureus biofilms. Incorporation of HMPC could increase the physicochemical properties of chitosan hydrogel including the hardness, viscosity as well as bioadhesion; however, higher HMPC concentration also resulted in reduced antimicrobial effect. CSLM analysis further demonstrated that higher HPMC concentration constrained TBO diffusion into the biofilm. The incubation of biofilm and hydrogel was further performed at an angle of 90 degrees. After light irradiation, compared to the mixture of TBO and chitosan, the hydrogel treated sample showed increased PDI efficacy indicated that incorporation of HPMC did improve antimicrobial effect. Finally, the bactericidal efficacy could be significantly augmented by prolonged retention of hydrogel in the biofilm as well as in the animal model of rat skin burn wounds after light irradiation.

Sub-MIC of antibiotics induced biofilm formation of Pseudomonas aeruginosa in the presence of chlorhexidine

Public health is facing a new challenge due to the alarming increase in bacterial resistance to most of the conventional antibacterial agents. It has been found that only minor cell damage is caused when exposed to sub-lethal levels of antimicrobial. Biofilms can play an important role in producing resistance, which is developed to reservoirs of pathogens in the hospital and cannot be easily removed. The aim of this study was to test whether the sub-lethal dose of antibiotics can induce biofilm formation of P. aeruginosa following incubating in the presence and absence of chlorhexidine. Standard antibiotic-micro broth 96-flat well plates were used for determination of MIC and biofilm assay. The adherence degree of biofilm was determined by estimation of OD _{630 nm} values using ELISA reader. The mean 22 isolates of P. aeruginosa growing in culture with presence and absence of chlorhexidine, could exhibited the significant (p < 0.001) proportion of adherence followed incubation in sub minimal inhibitory concentrations (Sub-MIC) of cefotaxim, amoxicillin, and azithromycin in comparison with control (antibiotic-free broth), while the sub-MIC of ciprofloxacin revealed significant inhibition of biofilm. Conclusion: Incubating the isolates of P. aeruginosa to sub-MIC of antibiotics exhibited induction of biofilm in the presence of chlorhexidine.

Efficacy of combined vancomycin and fosfomycin against methicillin-resistant Staphylococcus aureus in biofilms in vivo

Infection by methicillin-resistant Staphylococcus aureus (MRSA) is a life-threatening condition, and formation of biofilms can lead to treatment failure in a clinical setting. The aim of this study was to demonstrate the in vivo bactericidal effects of a combination of vancomycin (VAN) and fosfomycin (FOS) against MRSA in a rat carboxymethyl cellulose-pouch biofilm model. The results of the time-kill assay showed that the combination therapy was capable of killing at low minimal inhibitory concentrations (MIC) (½ × MIC VAN +1 × MIC FOS and 1 × MIC VAN + 1 × MIC FOS). In the in vivo study, a synergistically bactericidal effect was observed when using the combination therapy on MRSA embedded in the mature biofilm model. In comparison with the untreated control group and the groups receiving either VAN or FOS alone, the rats treated with combination therapy had lower MRSA colony counts in exudates from the pouch, lower white blood cell and neutrophil counts, and C-reactive protein (CRP) in peripheral blood. Furthermore, histological analysis of the pouch wall indicated combination therapy resulted in disappearance of biofilm-like structures, marked decrease in necrosis, and formation of granular tissue. In conclusion, the combination of VAN with FOS had a synergistic bactericidal effect on chronic MRSA infection embedded in biofilm, providing an alternative approach to treating this condition.

Screening the mechanical stability of Escherichia coli biofilms through exposure to external, hydrodynamic shear forces

The desire to attain a deeper understanding of the fundamental aspects governing the mechanical properties of biofilms has become more prominent in recent years. This has largely been due to the realization that these sessile microbial communities often withstand environments where hydrodynamic turbulence and shearing forces are considerable. In the present study, Escherichia coli K-12 was used as a model system to develop a laboratory technique that can be used to quickly screen the mechanical integrity or stability of laboratory cultivated bacterial biofilms when exposed to such external, hydrodynamic shear forces. The screening method utilizes a custom-built, automated water jetting apparatus to generate and precisely apply a pressurized stream of water directly to biofilms cultured in multi-well plates. An optimized set of water jetting parameters was determined to resolve subtle to moderate differences in the mechanical stability of isogenic strains of E. coli K-12 as a function of percent biofilm removal. Mutations in both flagella biosynthesis (fliA) and acetate metabolism (ackA and ackA pta) were shown to impair the mechanical integrity of 24-h biofilms, while a "housekeeping" strain deficient in arginine metabolism (argD) exhibited a mechanical stability profile comparable to the parent strain.

Cerium oxide and iron oxide nanoparticles abolish the antibacterial activity of ciprofloxacin against gram positive and gram negative biofilm bacteria

Metal oxide nanoparticles have been suggested as good candidates for the development of antibacterial agents. Cerium oxide (CeO2) and iron oxide (Fe2O3) nanoparticles have been utilized in a number of biomedical applications. Here, the antibacterial activity of CeO2 and Fe2O3 nanoparticles were evaluated on a panel of gram positive and gram negative bacteria in both the planktonic and biofilm cultures. Additionally, the effect of combining CeO2 and Fe2O3 nanoparticles with the broad spectrum antibiotic ciprofloxacin on tested bacteria was investigated. Thus, minimum inhibitory concentrations (MICs) of CeO2 and Fe2O3 nanoparticles that are required to inhibit bacterial planktonic growth and bacterial biofilm, were evaluated, and were compared to the MICs of the broad spectrum antibiotic ciprofloxacin alone or in the presence of CeO2 and Fe2O3 nanoparticles. Results of this study show that both CeO2 and Fe2O3 nanoparticles fail to inhibit bacterial growth and biofilm biomass for all the bacterial strains tested. Moreover, adding CeO2 or Fe2O3 nanoparticles to the broad spectrum antibiotic ciprofloxacin almost abolished its antibacterial activity. Results of this study suggest that CeO2 and Fe2O3 nanoparticles are not good candidates as antibacterial agents, and they could interfere with the activity of important antibiotics.