MIC versus MBEC to determine the antibiotic sensitivity of Staphylococcus aureus in peritoneal dialysis peritonitis

Microbiome and Otic Quinolone Levels Following Tympanoplasty Assessed by Gelatin Sponge Analysis

OBJECTIVE

To determine if absorbable gelatin sponge (AGS) can be used to assess the posttympanoplasty microbiome and otic antibiotic exposure.

STUDY DESIGN

Prospective.

SETTING

Tertiary hospital.

METHODS

Patients undergoing tympanoplasty were prospectively enrolled. Intraoperatively, AGS was applied to the medial ear canal/tympanic membrane (TM) for 1 minute after canal incision, then saved for analysis. Ear canals were packed with AGS at the end of surgery. Otic ofloxacin was administered until the first postoperative visit, when AGS was collected. Microbial presence was assessed by culture. Ofloxacin levels were assessed by liquid-chromatography mass-spectrometry.

RESULTS

Fifty-three patients were included. AGS was collected in 92.9% of patients seen within 21 days compared to 70.8% of those seen at 22 to 35 days. At surgery, AGS yielded bacteria and fungi in 81% and 11%, respectively, including Staphylococcus species (55%) and Pseudomonas species (25%). Postoperatively, AGS yielded bacteria in 71% and fungi in 21% at the meatus, (staphylococci 57% and pseudomonas 25%). TM samples yielded bacteria in 69%, fungi in 6%, staphylococci in 53%, and pseudomonas in 19%. Ofloxacin concentration at the meatus was 248 μg/mL (95% confidence interval [CI]: 119-377) and at the TM was 126 μg/mL (95% CI: 58-194). Ofloxacin-resistant colonies were found in 75% of patients.

CONCLUSION

Analysis of AGS is a viable technique for noninvasively studying healing metrics posttympanoplasty, including the microbiome and otic antibiotic exposure. Despite exposure to a high concentration of quinolones, the tympanoplasty wound is far from sterile, which may impact healing outcomes.

Host-derived protease promotes aggregation of Staphylococcus aureus by cleaving the surface protein SasG

Staphylococcus aureus is one of the leading causes of hospital-acquired infections, many of which begin following attachment and accumulation on indwelling medical devices or diseased tissue. These infections are often linked to the establishment of biofilms, but another often overlooked key characteristic allowing S. aureus to establish persistent infection is the formation of planktonic aggregates. Such aggregates are physiologically similar to biofilms and protect pathogens from innate immune clearance and increase antibiotic tolerance. The cell-wall-associated protein SasG has been implicated in biofilm formation via mechanisms of intercellular aggregation but the mechanism in the context of disease is largely unknown. We have previously shown that the expression of cell-wall-anchored proteins involved in biofilm formation is controlled by the ArlRS-MgrA regulatory cascade. In this work, we demonstrate that the ArlRS two-component system controls aggregation, by repressing the expression of sasG by activation of the global regulator MgrA. We also demonstrate that SasG must be proteolytically processed by a non-staphylococcal protease to induce aggregation and that strains expressing functional full-length sasG aggregate significantly upon proteolysis by a mucosal-derived host protease found in human saliva. We used fractionation and N-terminal sequencing to demonstrate that human trypsin within saliva cleaves within the A domain of SasG to expose the B domain and induce aggregation. Finally, we demonstrated that SasG is involved in virulence during mouse lung infection. Together, our data point to SasG, its processing by host proteases, and SasG-driven aggregation as important elements of S. aureus adaptation to the host environment.IMPORTANCEHere, we demonstrate that the Staphylococcus aureus surface protein SasG is important for cell-cell aggregation in the presence of host proteases. We show that the ArlRS two-component regulatory system controls SasG levels through the cytoplasmic regulator MgrA. We identified human trypsin as the dominant protease triggering SasG-dependent aggregation and demonstrated that SasG is important for S. aureus lung infection. The discovery that host proteases can induce S. aureus aggregation contributes to our understanding of how this pathogen establishes persistent infections. The observations in this study demonstrate the need to strengthen our knowledge of S. aureus surface adhesin function and processing, regulation of adhesin expression, and the mechanisms that promote biofilm formation to develop strategies for preventing chronic infections.

Persistent peritonitis in peritoneal dialysis: a comphrenesive review of recurrent, relapsing, refractory, and repeat peritonitis

Peritonitis is a major cause of morbidity and technique failure in patients receiving peritoneal dialysis. Complicated peritonitis that manifests as multiple or unresolving episodes is classified as refractory, recurrent, relapsing, or repeat peritonitis, and often possesses higher risk of technique failure and mortality as well as lower complete cure rates than primary or uncomplicated episodes. While these peritonitis subtypes affect a considerable portion of PD patients, details regarding their epidemiology, pathogenesis, diagnosis, clinical sequelae, and management have not yet been fully elucidated. Improved clinical awareness and understanding of complicated peritonitis subtypes is crucial to ensure optimal management for these patients; thus, we consolidate and report the pertinent findings of recent literature on these four entities.

Antimicrobial Treatment of Staphylococcus aureus Biofilms

Staphylococcus aureus is a microorganism frequently associated with implant-related infections, owing to its ability to produce biofilms. These infections are difficult to treat because antimicrobials must cross the biofilm to effectively inhibit bacterial growth. Although some antibiotics can penetrate the biofilm and reduce the bacterial load, it is important to understand that the results of routine sensitivity tests are not always valid for interpreting the activity of different drugs. In this review, a broad discussion on the genes involved in biofilm formation, quorum sensing, and antimicrobial activity in monotherapy and combination therapy is presented that should benefit researchers engaged in optimizing the treatment of infections associated with S. aureus biofilms.

Innovations in Therapeutic Improvement of the Cutaneous Microbiome in Children with Atopic Dermatitis

Biofilm is the dominant form of skin microbiota organization that provides adhesion and preservation of microorganisms in the skin micro-environment. It is necessary to ensure epidermal barrier function and local immunomodulation. Staphylococcus aureus becomes the major colonizer of skin lesions in case of atopic dermatitis exacerbation, and it also can form the biofilms. S. aureus growth and biofilm formation due to other microbial commensals on the skin of patients with atopic dermatitis leads to chronic output of pro-inflammatory cytokines and later to abnormalities in healthy skin microbiome. The role of microbial biofilm in human’s health makes the skin microbiota an attractive target for therapeutic intervention in various skin diseases.

The Medium Composition Impacts Staphylococcus aureus Biofilm Formation and Susceptibility to Antibiotics Applied in the Treatment of Bone Infections

The biofilm-associated infections of bones are life-threatening diseases, requiring application of dedicated antibiotics in order to counteract the tissue damage and spread of microorganisms. The in vitro analyses on biofilm formation and susceptibility to antibiotics are frequently carried out using methods that do not reflect conditions at the site of infection. To evaluate the influence of nutrient accessibility on Staphylococcus aureus biofilm development in vitro, a cohesive set of analyses in three different compositional media was performed. Next, the efficacy of four antibiotics used in bone infection treatment, including gentamycin, ciprofloxacin, levofloxacin, and vancomycin, against staphylococcal biofilm, was also assessed. The results show a significant reduction in the ability of biofilm to grow in a medium containing elements occurring in the serum, which also translated into the diversified changes in the efficacy of used antibiotics, compared to the setting in which conventional media were applied. The differences indicate the need for implementation of adequate in vitro models that closely mimic the infection site. The results of the present research may be considered an essential step toward the development of in vitro analyses aiming to accurately indicate the most suitable antibiotic to be applied against biofilm-related infections of bones.

Estimation of Minimum Biofilm Eradication Concentration (MBEC) on In Vivo Biofilm on Orthopedic Implants in a Rodent Femoral Infection Model

The formation of a biofilm on the implant surface is a major cause of intractable implant-associated infection. To investigate the antibiotic concentration needed to eradicate the bacteria inside a biofilm, the minimum biofilm eradication concentration (MBEC) has been used, mostly against in vitro biofilms on plastic surfaces. To produce a more clinically relevant environment, an MBEC assay against biofilms on stainless-steel implants formed in a rat femoral infection model was developed. The rats were implanted with stainless steel screws contaminated by two Staphylococcus aureus strains (UAMS-1, methicillin-sensitive Staphylococcus aureus; USA300LAC, methicillin-resistant Staphylococcus aureus) and euthanized on days 3 and 14. Implants were harvested, washed, and incubated with various concentrations (64–4096 μg/mL) of gentamicin (GM), vancomycin (VA), or cefazolin (CZ) with or without an accompanying systemic treatment dose of VA (20 μg/mL) or rifampicin (RF) (1.5 μg/mL) for 24 h. The implant was vortexed and sonicated, the biofilm was removed, and the implant was re-incubated to determine bacterial recovery. MBEC on the removed biofilm and implant was defined as in vivo MBEC and in vivo implant MBEC, respectively, and the concentrations of 100% and 60% eradication were defined as MBEC₁₀₀ and MBEC₆₀, respectively. As for in vivo MBEC, MBEC₁₀₀ of GM was 256–1024 μg/mL, but that of VA and CZ ranged from 2048–4096 μg/mL. Surprisingly, the in vivo implant MBEC was much higher, ranging from 2048 μg/mL to more than 4096 μg/mL. The addition of RF, not VA, as a secondary antibiotic was effective, and MBEC₆₀ on day 3 USA300LAC biofilm was reduced from 1024 μg/mL with GM alone to 128 μg/mL in combination with RF and the MBEC₆₀ on day 14 USA300LAC biofilm was reduced from 2048 μg/mL in GM alone to 256 μg/mL in combination with RF. In conclusion, a novel MBEC assay for in vivo biofilms on orthopedic implants was developed. GM was the most effective against both methicillin-sensitive and methicillin-resistant Staphylococcus aureus, in in vivo biofilms, and the addition of a systemic concentration of RF reduced MBEC of GM. Early initiation of treatment is desired because the required concentration of antibiotics increases with biofilm maturation.

Antibacterial and Antibiofilm Potency of XF Drugs, Impact of Photodynamic Activation and Synergy With Antibiotics

With increasing incidence of antimicrobial resistance, there is an urgent need for novel and effective antibacterials. Destiny Pharma plc have developed a series of porphyrin-based XF drugs, some with dual mechanisms of antibacterial action. An innate mechanism acts through binding to the outer bacterial membrane and a separate, light-activated, photodynamic (PD) mechanism, acts via the generation of reactive oxygen species. This study aimed to assess the innate and PD associated antibacterial activity of XF drugs against planktonic bacteria, their biofilms and combinational effects with conventional antibiotics. Minimum inhibitory concentrations (MICs) were determined for 3 XF drugs against 114 bacterial isolates. MICs for XF-73 and XF-70 were determined (± PD). DPD-207 was designed to not exhibit PD action due to its structure. XF-drugs (± PD) were further assessed for synergy with conventional antibiotics (using a checkerboard assay) and antibiofilm activity against susceptible strains. XF drugs were innately active against all tested Gram-positive isolates. PD action significantly increased bacterial susceptibility to XF-73 and XF-70 for all Gram-positive isolates. Generally, the XF drugs exhibited higher MICs against Gram-negative isolates, however PD significantly enhanced potency, particularly for XF-70. XF-73 and XF-70 exhibited synergy with ertapenem against a methicillin resistant Staphylococcus aureus (MRSA) strain (± PD) and XF-73 with polymyxin B (± PD) against Pseudomonas aeruginosa. No antagonism was seen between the XF drugs and any of the 5 antibiotics tested. The antibiofilm effect of XF drugs was also observed for all Staphylococcus isolates tested. Generally, PD did not enhance activity for other bacterial isolates tested with the exception of XF-73 against Acinetobacter baumannii biofilms. XF drugs exhibited significant antimicrobial activity against Gram-positive bacteria, with PD enhancement of bacterial susceptibility. Additionally, XF drugs displayed synergy with conventional antibiotics and demonstrated antibiofilm effects.

Hybrid donor-acceptor polymer nanoparticles and combination antibiotic for mitigation of pathogenic bacteria and biofilms

Biofilms pose a significant clinical problem in skin and soft tissue infections. Their resistance to antibiotics has spurred investigations into alternative treatments, such as nanoparticle-mediated photothermal ablation. Non-toxic Hybrid Donor- Acceptor (DA) Polymer nanoParticles (H-DAPPs) were developed for fluorescence imaging (using poly(3-hexylthiophene-2,5 diyl) (P3HT)) and rapid, near-infrared photothermal ablation (NIR- PTA) (using poly[4,4-bis(2-ethylhexyl)-cyclopenta[2,1-b;3,4-b']dithiophene-2,6-diyl-alt-2,1,3-benzoselenadiazole-4,7-diyl] (PCPDTBSe)). H-DAPPs were evaluated alone, and in combination with antibiotics, against planktonic S. aureus and S. pyogenes, and S. aureus biofilms. H-DAPPs NIR-PTA (15-700 μg/ mL) can generate rapid temperature changes of 27.6-73.1 °C, which can eradicate planktonic bacterial populations and reduce biofilm bacterial viability by more than 4- log (> 99.99%) with exposure to 60 s of 800 nm light. Reductions were confirmed via confocal analysis, which suggested that H-DAPPs PTA caused bacterial inactivation within the biofilms, but did not significantly reduce biofilm polysaccharides. SEM imaging revealed structural changes in biofilms after H-DAPPs PTA. S. aureus biofilms challenged with 100 μg/mL of H-DAPPs (H-DAPPs-100) to induce an average temperature of 55.1 °C, and the minimum biofilm eradication concentration (MBEC) of clindamycin, resulted in up to ~3- log decrease in bacterial viability compared to untreated biofilms and those administered H-DAPPs-100 PTA only, and up to ~2- log compared to biofilms administered only clindamycin. This study demonstrates that polymer nanoparticle PTA can mitigate biofilm infection and may improve antimicrobial efficacy.

Experimental infection of Asian house geckos with Enterococcus lacertideformus demonstrates multiple disease transmission routes and the in-vivo efficacy of antibiotics

The disease caused by Enterococcus lacertideformus is multisystemic and ultimately fatal. Since its emergence, the bacterium has significantly impacted the captive breeding programs of the extinct in the wild Christmas Island Lister's gecko (Lepidodactylus listeri) and blue-tailed skink (Cryptoblepharus egeriae). The bacterium's pathogenicity, inability to grow in-vitro, and occurrence beyond the confines of Christmas Island necessitated the development of an experimental infection and treatment model. Asian house geckos (Hemidactylus frenatus) were challenged with a single dose of E. lacertideformus inoculum either by mouth, application to mucosal abrasion or skin laceration, subcutaneous injection, coelomic injection, or via co-housing with an infected gecko. Five healthy geckos acted as controls. Each transmission route resulted in disease in at least 40% (n = 2) geckos, expanding to 100% (n = 5) when E. lacertideformus was applied to skin laceration and mucosal abrasion groups. Incubation periods post-infection ranged between 54 and 102 days. To determine the efficacy of antibiotic treatment, infected geckos were divided into six groups (enrofloxacin 10 mg/kg, per os (PO), every 24 h (q24), amoxicillin-clavulanic acid 10 mg/kg, PO, q24, enrofloxacin 10 mg/kg combined with amoxicillin-clavulanic acid 10 mg/kg, PO, q24, rifampicin 15 mg/kg, PO, q24, clarithromycin 15 mg/kg, PO, q24, and untreated controls) for 21 days. Response to treatment was assessed by the change in lesion size, bacterial dissemination, and histological evidence of a host immune response. Irrespective of the antibiotic given, histology revealed that geckos inoculated by skin laceration were observed to have more extensive disease spread throughout the animal's body compared to other inoculation routes. The reduction in the average surface area of gross lesions was 83.6% for geckos treated with enrofloxacin, followed by the combination therapy amoxicillin-clavulanic acid and enrofloxacin (62.4%), amoxicillin-clavulanic acid (58.2%), rifampicin (45.5%), and clarithromycin (26.5%). Lesions in geckos untreated with antibiotics increased in size between 100 and 300%. In summary, enrofloxacin and amoxicillin-clavulanic acid show promising properties for the treatment of E. lacertideformus infection in geckos. The Asian house gecko E. lacertideformus infection model therefore provides foundational findings for the development of effective therapeutic treatment protocols aimed at conserving the health of infected and at-risk reptiles.

In Vitro Antimicrobial Susceptibility Testing of Biofilm-Growing Bacteria: Current and Emerging Methods

The antibiotic susceptibility of bacterial pathogens is typically determined based on planktonic cells, as recommended by several international guidelines. However, most of chronic infections - such as those established in wounds, cystic fibrosis lung, and onto indwelling devices - are associated to the formation of biofilms, communities of clustered bacteria attached onto a surface, abiotic or biotic, and embedded in an extracellular matrix produced by the bacteria and complexed with molecules from the host. Sessile microorganisms show significantly increased tolerance/resistance to antibiotics compared with planktonic counterparts. Consequently, antibiotic concentrations used in standard antimicrobial susceptibility tests, although effective against planktonic bacteria in vitro, are not predictive of the concentrations required to eradicate biofilm-related infections, thus leading to treatment failure, chronicization and removal of material in patients with indwelling medical devices.Meeting the need for the in vitro evaluation of biofilm susceptibility to antibiotics, here we reviewed several methods proposed in literature highlighting their advantages and limitations to guide scientists towards an appropriate choice.

Silver Sulfadiazine Eradicates Antibiotic-Tolerant Staphylococcus aureus and Pseudomonas aeruginosa Biofilms in Patients with Infected Diabetic Foot Ulcers

Infections are among the most frequent and challenging events in diabetic foot ulcers (DFUs). Pathogenic bacteria growing in biofilms within host tissue are highly tolerant to environmental and chemical agents, including antibiotics. The present study was aimed at assessing the use of silver sulfadiazine (SSD) for wound healing and infection control in 16 patients with DFUs harboring biofilm-growing Staphylococcus aureus and Pseudomonas aeruginosa. All patients received a treatment based on a dressing protocol including disinfection, cleansing, application of SSD, and application of nonadherent gauze, followed by sterile gauze and tibio-breech bandage, in preparation for toilet surgery after 30 days of treatment. Clinical parameters were analyzed by the T.I.M.E. classification system. In addition, the activity of SSD against biofilm-growing S. aureus and P. aeruginosa isolates was assessed in vitro. A total of 16 patients with S. aureus and P. aeruginosa infected DFUs were included in the study. Clinical data showed a statistically significant (p < 0.002) improvement of patients’ DFUs after 30 days of treatment with SSD with significant amelioration of all the parameters analyzed. Notably, after 30 days of treatment, resolution of infection was observed in all DFUs. In vitro analysis showed that both S. aureus and P. aeruginosa isolates developed complex and highly structured biofilms. Antibiotic susceptibility profiles indicated that biofilm cultures were significantly (p ≤ 0.002) more tolerant to all tested antimicrobials than their planktonic counterparts. However, SSD was found to be effective against fully developed biofilms of both S. aureus and P. aeruginosa at concentrations below those normally used in clinical preparations (10 mg/mL). These results strongly suggest that the topical administration of SSD may represent an effective alternative to conventional antibiotics for the successful treatment of DFUs infected by biofilm-growing S. aureus and P. aeruginosa.

Aeromonas hydrophila RIT668 and Citrobacter portucalensis RIT669-Potential Zoonotic Pathogens Isolated from Spotted Turtles

Antimicrobial resistance (AMR) is one of the biggest challenges of the 21st century, and biofilm formation enables bacteria to resist antibiotic at much higher concentrations than planktonic cells. Earlier, we showed that the Gram-negative Aeromonas hydrophila RIT668 and Citrobacter portucalensis RIT669 (closely related to C. freundii NBRC 12681) from infected spotted turtles (Clemmys guttata), formed biofilms and upregulated toxin expression on plastic surfaces, and were predicted to possess multiple antibiotic resistance genes. Here, we show that they each resist several antibiotics in the planktonic phase, but were susceptible to neomycin, and high concentrations of tetracycline and cotrimoxazole. The susceptibility of their biofilms to neomycin and cotrimoxazole was tested using the Calgary device. For A. hydrophila, the minimum inhibitory concentration (MIC) = 500-1000, and the minimum biofilm eradication concentration (MBEC) > 1000 μg/mL, using cotrimoxazole, and MIC = 32.3-62.5, and MBEC > 1000 μg/mL, using neomycin. For C. freundii MIC = 7.8-15.6, and, MBEC > 1000 μg/mL, using cotrimoxazole, and MIC = 7.8, and MBEC > 1000 μg/mL, using neomycin. Both A. hydrophila and C. portucalensis activated an acyl homoserine lactone (AHL) dependent biosensor, suggesting that quorum sensing could mediate biofilm formation. Their multidrug resistance in the planktonic form, and weak biofilm eradication even with neomycin and cotrimoxazole, indicate that A. hydrophila and C. portucalensis are potential zoonotic pathogens, with risks for patients living with implants.

Overview of Quantitative Methodologies to Understand Antimicrobial Resistance via Minimum Inhibitory Concentration

Simple Summary

An emerging threat to human and food animal health is the development of antimicrobial resistance in bacteria associated with food animals. One of the primary tools for assessing resistance levels and monitoring for changes in expressed resistance is the use of minimum inhibitory concentration tests, which expose bacterial isolates to a series of dilutions of an antimicrobial agent to identify the lowest concentration of the antimicrobial that effectively prevents bacterial growth. These tests produce a minimum inhibitory value that falls within a range of concentrations instead of an exact value, a process known as censoring. Analysis of censored data is complex and careful consideration of methods of analysis is necessary. The use of regression methods such as logistic regression that divide the data into two or three categories is relatively easy to implement but may not detect important changes in the distributions of data that occur within the categories. Models that do not simplify the data may be more complex but may detect potentially relevant changes missed when the data is categorized. As a result, the analysis of minimum inhibitory concentration data requires careful consideration to identify the appropriate model for the purpose of the study.

Abstract

The development of antimicrobial resistance (AMR) represents a significant threat to humans and food animals. The use of antimicrobials in human and veterinary medicine may select for resistant bacteria, resulting in increased levels of AMR in these populations. As the threat presented by AMR increases, it becomes critically important to find methods for effectively interpreting minimum inhibitory concentration (MIC) tests. Currently, a wide array of techniques for analyzing these data can be found in the literature, but few guidelines for choosing among them exist. Here, we examine several quantitative techniques for analyzing the results of MIC tests and discuss and summarize various ways to model MIC data. The goal of this review is to propose important considerations for appropriate model selection given the purpose and context of the study. Approaches reviewed include mixture models, logistic regression, cumulative logistic regression, and accelerated failure time–frailty models. Important considerations in model selection include the objective of the study (e.g., modeling MIC creep vs. clinical resistance), degree of censoring in the data (e.g., heavily left/right censored vs. primarily interval censored), and consistency of testing parameters (e.g., same range of concentrations tested for a given antibiotic).

Biofilm Formation and Antibiotic Resistance Phenotype of Helicobacter pylori Clinical Isolates

We evaluated biofilm formation of clinical Helicobacter pylori isolates from Indonesia and its relation to antibiotic resistance. We determined the minimum inhibition concentration (MIC) of amoxicillin, clarithromycin, levofloxacin, metronidazole and tetracycline by the Etest to measure the planktonic susceptibility of 101 H. pylori strains. Biofilms were quantified by the crystal violet method. The minimum biofilm eradication concentration (MBEC) was obtained by measuring the survival of bacteria in a biofilm after exposure to antibiotics. The majority of the strains formed a biofilm (93.1% (94/101)), including weak (75.5%) and strong (24.5%) biofilm-formers. Planktonic resistant and sensitive strains produced relatively equal amounts of biofilms. The resistance proportion, shown by the MBEC measurement, was higher in the strong biofilm group for all antibiotics compared to the weak biofilm group, especially for clarithromycin (p = 0.002). Several cases showed sensitivity by the MIC measurement, but resistance according to the MBEC measurements (amoxicillin, 47.6%; tetracycline, 57.1%; clarithromycin, 19.0%; levofloxacin, 38.1%; and metronidazole 38.1%). Thus, biofilm formation may increase the survival of H. pylori and its resistance to antibiotics. Biofilm-related antibiotic resistance should be evaluated with antibiotic susceptibility.

Evaluation of the ability of linezolid and tedizolid to eradicate intraosteoblastic and biofilm-embedded Staphylococcus aureus in the bone and joint infection setting

OBJECTIVES

Prolonged use of linezolid for bone and joint infection (BJI) is limited by its long-term toxicity. The better safety profile of tedizolid, a recently developed oxazolidinone, could offer an alternative. However, its efficacy against biofilm-embedded and intracellular Staphylococcus aureus, the two main bacterial reservoirs associated with BJI chronicity, is unknown.

METHODS

Using three S. aureus strains (6850 and two clinical BJI isolates), linezolid and tedizolid were compared regarding their ability: (i) to target the S. aureus intracellular reservoir in an in vitro model of osteoblast infection, using three concentrations increasing from the bone concentration reached with standard therapeutic doses (Cbone = 2.5 × MIC; Cplasm = 10 × MIC; Cmax = 40 × MIC); (ii) to eradicate mature biofilm [minimal biofilm eradication concentration (MBEC)]; and (iii) to prevent biofilm formation [biofilm MIC (bMIC) and confocal microscopy].

RESULTS

Linezolid and tedizolid weakly reduced the intracellular inoculum of S. aureus in a strain-dependent manner despite the similar MICs for the tested strains, but improved cell viability even in the absence of an intracellular bactericidal effect. Conversely, linezolid and tedizolid were ineffective in eradicating mature biofilm formed in vitro, with MBEC >2000 and >675 mg/L, respectively. bMICs of tedizolid were 4-fold lower than those of linezolid for all strains.

CONCLUSIONS

Linezolid and tedizolid alone are not optimal candidates to target bacterial phenotypes associated with chronic forms of BJI. Despite weak intracellular activity, they both reduce infection-related cytotoxicity, suggesting a role in modulating intracellular expression of staphylococcal virulence factors. Although inactive against biofilm-embedded S. aureus, both-but particularly tedizolid-are able to prevent biofilm formation.

Pharmacokinetic profile of enrofloxacin and its metabolite ciprofloxacin in Asian house geckos (Hemidactylus frenatus) after single-dose oral administration of enrofloxacin

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were determined following oral administration in 21 Asian house geckos (Hemidactylus frenatus) at a dose of 10 mg/kg. Changes in enrofloxacin and ciprofloxacin plasma concentrations were quantified at regular intervals over 72 h (1, 2, 6, 12, 24, 48, and 72 h). Samples were analysed by high-pressure liquid chromatography (HPLC) and the enrofloxacin pharmacokinetic data underwent a two-compartment analysis. Due to the limited ciprofloxacin plasma concentrations above the lower limit of quantification (LLOQ), the ciprofloxacin data underwent non-compartment analysis and the half-life was determined by the Lineweaver-Burke plot and analysis. The enrofloxacin and ciprofloxacin mean half-lives (t _½) were 0.95 h (α) / 24.36 h (β), and 11.06 h respectively, area under the curve (AUC_0-24h) were 60.56 and 3.14 µg/mL*h, respectively, maximum concentrations (C _max) were 12.31 and 0.24 µg/mL, respectively, and time required to reach the C _max (T _max) were 1 and 2 h respectively. Enrofloxacin was minimally converted to the active metabolite ciprofloxacin, with ciprofloxacin concentrations contributing only 4.91% of the total fluoroquinolone concentrations (AUC_0-24h). Based on the pharmacokinetic indices when using susceptibility breakpoints when determined at mammalian body temperature it is predicted that single oral administration of enrofloxacin (10 mg/kg) would result in plasma concentrations effective against susceptible bacterial species inhibited by an enrofloxacin MIC ≤ 0.5 µg/mL in vitro, but additional studies will be required to determine its efficacy in vivo.

Review of Antibiotic Dosing with Peritonitis in APD

Peritonitis is the leading cause of transfer from peritoneal dialysis (PD) to hemodialysis (HD). It is also the leading cause of hospitalization of PD patients. The usual treatment of peritonitis for automated PD (APD) patients consists of antibiotics given once daily in the long dwell. However, the once-daily antibiotic dosing recommendations are based primarily on studies with continuous ambulatory PD (CAPD) regimens. Published studies on antibiotic dosing in APD are very limited. We will review the scant literature on this topic. It is possible that extrapolating once-daily dosing from CAPD to APD may lead to underdosing. There is a need for further pharmacokinetic studies of antibiotic dosing in APD.

Biosurfactants of Lactobacillus helveticus for biodiversity inhibit the biofilm formation of Staphylococcus aureus and cell invasion

Aim: This study aimed to evaluate the differences of biosurfactants produced by two Lactobacillus helveticus strains against the biofilm formation of Staphylococcus aureus in vitro and in vivo. Materials & methods: Scanning electron microscopy, Real time-quantitative PCR (RT-qPCR) and cell assay were used to analyze the inhibiting effect of biosurfactants against biofilm formation. Results & conclusion: Results showed that the biosurfactants have anti-adhesive and inhibiting effects on biofilm formation in vivo and in vitro. The biofilm-formative genes and autoinducer-2 signaling regulated these characteristics, and the biosurfactant L. helveticus 27170 is better than that of 27058. Host cell adhesion and invasion results indicated that the biosurfactants L. helveticus prevented the S. aureus invading the host cell, which may be a new strategy to eliminate biofilms.

The Adaptive Morphology of Bacillus subtilis Biofilms: A Defense Mechanism against Bacterial Starvation

Biofilms are commonly defined as accumulations of microbes, embedded in a self-secreted, polysaccharide-rich extra-cellular matrix. This study aimed to characterize specific morphological changes that occur in Bacillus subtilis biofilms under nutrient-limiting growth conditions. Under varying levels of nutrient depletion, colony-type biofilms were found to exhibit different rates of spatial expansion and green fluorescent protein production. Specifically, colony-type biofilms grown on media with decreased lysogeny broth content exhibited increased spatial expansion and more stable GFP production over the entire growth period. By modeling the surface morphology of colony-type biofilms using confocal and multiphoton microscopy, we analyzed the appearance of distinctive folds or "wrinkles" that form as a result of lysogeny broth content reduction in the solid agar growth media. When subjected to varying nutritional conditions, the channel-like folds were shown to alter their morphology; growth on nutrient-depleted media was found to trigger the formation of large and straight wrinkles connecting the colony core to its periphery. To test a possible functional role of the formed channels, a fluorescent analogue of glucose was used to demonstrate preferential native uptake of the molecules into the channels' interiors which supports their possible role in the transport of molecules throughout biofilm structures.

The future of biofilm research - Report on the '2019 Biofilm Bash'

In May 2019, 29 scientists with expertise in various subdisciplines of biofilm research got together in Leavenworth (WA, USA) at an event designated as the ‘2019 Biofilm Bash’. The goal of this informal two-day meeting was first to identify gaps in our knowledge, and then to come up with ways how the biofilm community can fill these gaps. The meeting was organized around six questions that covered the most important items brought forward by the organizers and participants. The outcome of these discussions is summarized in the present paper. We are aware that these views represent a small subset of our field, and that inevitably we will have inadvertently overlooked important developing research areas and ideas. We are nevertheless hopeful that this report will stimulate discussions and help create new ways of how we can advance our field.

Microbial biofilm correlates with an increased antibiotic tolerance and poor therapeutic outcome in infective endocarditis

BACKGROUND

Infective endocarditis (IE) is associated with high rates of mortality. Prolonged treatments with high-dose intravenous antibiotics often fail to eradicate the infection, frequently leading to high-risk surgical intervention. By providing a mechanism of antibiotic tolerance, which escapes conventional antibiotic susceptibility profiling, microbial biofilm represents a key diagnostic and therapeutic challenge for clinicians. This study aims at assessing a rapid biofilm identification assay and a targeted antimicrobial susceptibility profile of biofilm-growing bacteria in patients with IE, which were unresponsive to antibiotic therapy.

RESULTS

Staphylococcus aureus was the most common isolate (50%), followed by Enterococcus faecalis (25%) and Streptococcus gallolyticus (25%). All microbial isolates were found to be capable of producing large, structured biofilms in vitro. As expected, antibiotic treatment either administered on the basis of antibiogram or chosen empirically among those considered first-line antibiotics for IE, including ceftriaxone, daptomycin, tigecycline and vancomycin, was not effective at eradicating biofilm-growing bacteria. Conversely, antimicrobial susceptibility profile of biofilm-growing bacteria indicated that teicoplanin, oxacillin and fusidic acid were most effective against S. aureus biofilm, while ampicillin was the most active against S. gallolyticus and E. faecalis biofilm, respectively.

CONCLUSIONS

This study indicates that biofilm-producing bacteria, from surgically treated IE, display a high tolerance to antibiotics, which is undetected by conventional antibiograms. The rapid identification and antimicrobial tolerance profiling of biofilm-growing bacteria in IE can provide key information for both antimicrobial therapy and prevention strategies.

Unexpected synergistic and antagonistic antibiotic activity against Staphylococcus biofilms

Objectives

To evaluate putative anti-staphylococcal biofilm antibiotic combinations used in the management of periprosthetic joint infections (PJIs).

Methods

Using the dissolvable bead biofilm assay, the minimum biofilm eradication concentration (MBEC) was determined for the most commonly used antimicrobial agents and combination regimens against staphylococcal PJIs. The established fractional inhibitory concentration (FIC) index was modified to create the fractional biofilm eradication concentration (FBEC) index to evaluate synergism or antagonism between antibiotics.

Results

Only gentamicin (MBEC 64 mg/L) and daptomycin (MBEC 64 mg/L) were observed to be effective antistaphylococcal agents at clinically achievable concentrations. Supplementation of gentamicin with daptomycin, vancomycin or ciprofloxacin resulted in a similar or lower MBEC than gentamicin alone (FBEC index 0.25-2). Conversely, when rifampicin, clindamycin or linezolid was added to gentamicin, there was an increase in the MBEC of gentamicin relative to its use as a monotherapy (FBEC index 8-32).

Conclusions

This study found that gentamicin and daptomycin were the only effective single-agent antibiotics against established Staphylococcus biofilms. Interestingly the addition of a bacteriostatic antibiotic was found to antagonize the ability of gentamicin to eradicate Staphylococcus biofilms.

Staphylococcus aureus and the Cutaneous Microbiota Biofilms in the Pathogenesis of Atopic Dermatitis

Biofilm is the dominant mode of growth of the skin microbiota, which promotes adhesion and persistence in the cutaneous microenvironment, thus contributing to the epidermal barrier function and local immune modulation. In turn, the local immune microenvironment plays a part in shaping the skin microbiota composition. Atopic dermatitis (AD) is an immune disorder characterized by a marked dysbiosis, with a sharp decline of microbial diversity. During AD flares biofilm-growing Staphylococcus aureus emerges as the major colonizer in the skin lesions, in strict association with disease severity. The chronic production of inflammatory cytokines in the skin of AD individuals concurs at supporting S. aureus biofilm overgrowth at the expense of other microbial commensals, subverting the composition of the healthy skin microbiome. The close relationship between the host and microbial biofilm resident in the skin has profound implications on human health, making skin microbiota an attractive target for the therapeutic management of different skin disorders.

Large variations in clinical antibiotic activity against Staphylococcus aureus biofilms of periprosthetic joint infection isolates

Staphylococcus aureus biofilms have a high tolerance to antibiotics, making the treatment of periprosthetic joint infection (PJI) challenging. From a clinical perspective, bacteria from surgical specimens are cultured in a planktonic state to determine antibiotic sensitivity. However, S. aureus exists primarily as established biofilms in PJI. To address this dichotomy, we developed a prospective registry of total knee and hip arthroplasty PJI S. aureus isolates to quantify the activity of clinically important antibiotics against isolates grown as biofilms. S. aureus planktonic minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were assessed using clinical laboratory standard index assays for 10 antibiotics (cefazolin, clindamycin, vancomycin, rifampin, linezolid, nafcillin, gentamicin, trimethoprim/sulfamethoxazole, doxycycline, and daptomycin). Mature biofilms of each strain were grown in vitro, after which biofilm MIC (MBIC) and biofilm MBC (MBBC) were determined. Overall, isolates grown as biofilms displayed larger variations in antibiotic MICs as compared to planktonic MIC values. Only rifampin, doxycycline, and daptomycin had measurable biofilm MIC values across all S. aureus isolates tested. Biofilm MBC observations complemented biofilm MIC observations; rifampin, doxycycline, and daptomycin were the only antibiotics with measurable biofilm MBC values. 90% of S. aureus biofilms could be killed by rifampin, 50% by doxycycline, and only 15% by daptomycin. Biofilm formation increased bacterial antibiotic tolerance nonspecifically across all antibiotics, in both MSSA and MRSA samples. Rifampin and doxycycline were the most effective antibiotics at killing established S. aureus biofilms. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1604-1609, 2019.

The biofilm eradication activity of acetic acid in the management of periprosthetic joint infection

Objectives

Periprosthetic joint infection following joint arthroplasty surgery is one of the most feared complications. The key to successful revision surgery for periprosthetic joint infections, regardless of treatment strategy, is a thorough deep debridement. In an attempt to limit antimicrobial and disinfectant use, there has been increasing interest in the use of acetic acid as an adjunct to debridement in the management of periprosthetic joint infections. However, its effectiveness in the eradication of established biofilms following clinically relevant treatment times has not been established. Using an in vitro biofilm model, this study aimed to establish the minimum biofilm eradication concentration (MBEC) of acetic acid following a clinically relevant treatment time.

Materials and Methods

Using a methicillin-sensitive Staphylococcus aureus (MSSA) reference strain and the dissolvable bead assay, biofilms were challenged by 0% to 20% acetic acid (pH 4.7) for ten minutes, 20 minutes, 180 minutes, and 24 hours.

Results

The MBEC of acetic acid was found to be: 15%, 11%, 3.2%, and 0.8% following a ten-minute, 20-minute, 180-minute, and 24-hour treatment, respectively.

Conclusion

This study found that the MBEC of acetic acid following a 10- or 20-minute treatment time exceeded its safety threshold, making these concentrations unsuitable as a topical debridement adjunct. However, a clinically acceptable concentration (5%) was still found to eliminate 96.1% of biofilm-associated MSSA following a 20-minute treatment time.

Cite this article: S. T. J. Tsang, P. J. Gwynne, M. P. Gallagher, A. H. R. W. Simpson. The biofilm eradication activity of acetic acid in the management of periprosthetic joint infection. Bone Joint Res 2018;7:517–523. DOI: 10.1302/2046-3758.78.BJR-2018-0045.R1

Inflammatory cytokines and biofilm production sustain Staphylococcus aureus outgrowth and persistence: a pivotal interplay in the pathogenesis of Atopic Dermatitis

Individuals with Atopic dermatitis (AD) are highly susceptible to Staphylococcus aureus colonization. However, the mechanisms driving this process as well as the impact of S. aureus in AD pathogenesis are still incompletely understood. In this study, we analysed the role of biofilm in sustaining S. aureus chronic persistence and its impact on AD severity. Further we explored whether key inflammatory cytokines overexpressed in AD might provide a selective advantage to S. aureus. Results show that the strength of biofilm production by S. aureus correlated with the severity of the skin lesion, being significantly higher (P < 0.01) in patients with a more severe form of the disease as compared to those individuals with mild AD. Additionally, interleukin (IL)-β and interferon γ (IFN-γ), but not interleukin (IL)-6, induced a concentration-dependent increase of S. aureus growth. This effect was not observed with coagulase-negative staphylococci isolated from the skin of AD patients. These findings indicate that inflammatory cytokines such as IL1-β and IFN-γ, can selectively promote S. aureus outgrowth, thus subverting the composition of the healthy skin microbiome. Moreover, biofilm production by S. aureus plays a relevant role in further supporting chronic colonization and disease severity, while providing an increased tolerance to antimicrobials.

Lipase-Catalyzed Synthesis of Sucrose Monolaurate and Its Antibacterial Property and Mode of Action against Four Pathogenic Bacteria

The aim of this work was to evaluate the antibacterial activities and mode of action of sucrose monolaurate (SML) with a desirable purity, synthesized by Lipozyme TL IM-mediated transesterification in the novel ionic liquid, against four pathogenic bacteria including L. monocytogenes, B. subtilis, S. aureus, and E. coli. The antibacterial activity was determined by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and the time⁻kill assay. SML showed varying antibacterial activity against tested bacteria with MICs and MBCs of 2.5 and 20 mM for L. monocytogenes, 2.5 and 20 mM for B. subtilis, 10 and 40 mM for S. aureus, respectively. No dramatic inhibition was observed for E. coli at 80 mM SML. Mechanism of bacterial inactivation caused by SML was revealed through comprehensive factors including cell morphology, cellular lysis, membrane permeability, K⁺ leakage, zeta potential, intracellular enzyme, and DNA assay. Results demonstrated that bacterial inactivation against Gram-positive bacteria was primarily induced by the pronounced damage to the cell membrane integrity. SML may interact with cytoplasmic membrane to disturb the regulation system of peptidoglycan hydrolase activities to degrade the peptidoglycan layer and form a hole in the layer. Then, the inside cytoplasmic membrane was blown out due to turgor pressure and the cytoplasmic materials inside leaked out. Leakage of intracellular enzyme to the supernatants implied that the cell membrane permeability was compromised. Consequently, the release of K⁺ from the cytosol lead to the alterations of the zeta potential of cells, which would disturb the subcellular localization of some proteins, and thereby causing bacterial inactivation. Moreover, remarkable interaction with DNA was also observed. SML at sub-MIC inhibited biofilm formation by these bacteria.

The dissolvable bead: A novel in vitro biofilm model for evaluating antimicrobial resistance

In vitro biofilm assays are a vital first step in the assessment of therapeutic effectiveness. Current biofilm models have been found to be limited by throughput, reproducibility, and cost. We present a novel in vitro biofilm model, utilising a sodium alginate substratum for surface biofilm colony formation, which can be readily dissolved for accurate evaluation of viable organisms. The dissolving bead biofilm assay was evaluated using a range of clinically relevant strains. The reproducibility and responsiveness of the assay to an antimicrobial challenge was assessed using standardised methods. Cryo-scanning electron microscopy was used to image biofilm colonies. Biofilms were grown for 20h prior to testing. The model provides a reproducible and responsive assay to clinically-relevant antimicrobial challenges, as defined by established guidelines. Moreover cryo-scanning electron microscopy demonstrates that biofilm formation is localised exclusively to the alginate bead surface. Our results suggest that this simple model provides a robust and adaptable assay for the investigation of bacterial biofilms.

Streptokinase Treatment Reverses Biofilm-Associated Antibiotic Resistance in Staphylococcus aureus

Biofilms formed by Staphylococcus aureus is a serious complication to the use of medical implants. A central part of the pathogenesis relies on S. aureus’ ability to adhere to host extracellular matrix proteins, which adsorb to medical implants and stimulate biofilm formation. Being coagulase positive, S. aureus furthermore induces formation of fibrin fibers from fibrinogen in the blood. Consequently, we hypothesized that fibrin is a key component of the extracellular matrix of S. aureus biofilms under in vivo conditions, and that the recalcitrance of biofilm infections can be overcome by combining antibiotic treatment with a fibrinolytic drug. We quantified S. aureus USA300 biofilms grown on peg-lids in brain heart infusion (BHI) broth with 0%–50% human plasma. Young (2 h) and mature (24 h) biofilms were then treated with streptokinase to determine if this lead to dispersal. Then, the minimal biofilm eradication concentration (MBEC) of 24 h old biofilms was measured for vancomycin and daptomycin alone or in combination with 10 µg/mL rifampicin in the presence or absence of streptokinase in the antibiotic treatment step. Finally, biofilms were visualized by confocal laser scanning microscopy. Addition of human plasma stimulated biofilm formation in BHI in a dose-dependent manner, and biofilms could be partially dispersed by streptokinase. The biofilms could be eradicated with physiologically relevant concentrations of streptokinase in combination with rifampicin and vancomycin or daptomycin, which are commonly used antibiotics for treatment of S. aureus infections. Fibronolytic drugs have been used to treat thromboembolic events for decades, and our findings suggest that their use against biofilm infections has the potential to improve the efficacy of antibiotics in treatment of S. aureus biofilm infections.

Biofilm Antimicrobial Susceptibility Increases With Antimicrobial Exposure Time

BACKGROUND

The antimicrobial concentration required to kill all the bacteria in a biofilm, known as the minimum biofilm eradication concentration (MBEC), is typically determined in vitro by exposing the biofilm to serial concentrations of antimicrobials for 24 hours or less. Local delivery is expected to cause high local levels for longer than 24 hours. It is unknown if longer antimicrobial exposures require the same concentration to eradicate bacteria in biofilm. Questions/purposes Does MBEC change with increased antimicrobial exposure time?

METHODS

Biofilms were grown for 24 hours using five pathogens (methicillin-sensitive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa) and then exposed to four antimicrobials regimens: tobramycin, vancomycin, and tobramycin combined with vancomycin in 3:1 and 1:1 ratios by weight in concentrations of 62.5, 125, 250, 500, 1000, 2000, 4000, and 8000 μg/mL for three durations, 1, 3, and 5 days, in triplicate. MBEC was measured as the lowest concentration that killed all bacteria in the biofilm determined by 21-day subculture.

RESULTS

MBEC was lower when antimicrobial exposure time was longer. For the staphylococcus species, the MBEC was lower when exposure time was 5 days than 1 day in 11 of 12 antimicrobial/microorganism pairs. The MBEC range for these 11 pairs on Day 1 was 4000 to > 8000 μg/mL and on Day 5 was < 250 to 8000 μg/mL. MBEC for tobramycin/P. aeruginosa was 2000 μg/mL on Day 1 and ≤ 250 μg/mL on Day 5, and for E. coli, 125 μg/mL on Day 1 and ≤ 62.5 on Day 5.

CONCLUSIONS

Although antimicrobial susceptibility was lower for longer exposure times in the microorganisms we studied, confirmation is required for other pathogens. Clinical Relevance One-day MBEC assays may overestimate the local antimicrobial levels needed to kill organisms in biofilm if local levels are sustained at MBEC or above for longer than 24 hours. Future studies are needed to confirm that antimicrobial levels achieved clinically from local delivery are above the MBEC at relevant time points and to confirm that MBEC for in vitro microorganisms accurately represents MBEC of in vivo organisms in an clinical infection.

Effect of Mono and Di-rhamnolipids on Biofilms Pre-formed by Bacillus subtilis BBK006

Different microbial inhibition strategies based on the planktonic bacterial physiology have been known to have limited efficacy on the growth of biofilms communities. This problem can be exacerbated by the emergence of increasingly resistant clinical strains. Biosurfactants have merited renewed interest in both clinical and hygienic sectors due to their potential to disperse microbial biofilms. In this work, we explore the aspects of Bacillus subtilis BBK006 biofilms and examine the contribution of biologically derived surface-active agents (rhamnolipids) to the disruption or inhibition of microbial biofilms produced by Bacillus subtilis BBK006. The ability of mono-rhamnolipids (Rha-C10-C10) produced by Pseudomonas aeruginosa ATCC 9027 and the di-rhamnolipids (Rha-Rha-C14-C14) produced by Burkholderia thailandensis E264, and phosphate-buffered saline to disrupt biofilm of Bacillus subtilis BBK006 was evaluated. The biofilm produced by Bacillus subtilis BBK006 was more sensitive to the di-rhamnolipids (0.4 g/L) produced by Burkholderia thailandensis than the mono-rhamnolipids (0.4 g/L) produced by Pseudomonas aeruginosa ATCC 9027. Rhamnolipids are biologically produced compounds safe for human use. This makes them ideal candidates for use in new generations of bacterial dispersal agents and useful for use as adjuvants for existing microbial suppression or eradication strategies.

An immunological assay for identification of potential biofilm-associated antigens of Staphylococcus aureus

Attachment of bacterial pathogens to the niche tissue in the host is the first step in biofilm formation leading to colonization and establishment of infection in the host. While the most common method used for determining the potential role of a bacterial antigen in biofilm formation has been demonstration of loss of this property using specific knockout mutants, it is an expensive and a laborious procedure. This study describes an alternative immunological assay for identification of attachment antigens of Staphylococcus aureus, potentially important in the development of an effective vaccine against infections caused by this pathogen. The method is based upon the concept of inhibition of attachment of S. aureus to PEGs coated with virulence antigen-specific antibodies. Antibodies used for validation of this assay were specific for ClfA, FnBPA, SdrD, PNAG and α-toxin, accredited biofilm-associated antigens of S. aureus.

Prevention and treatment of Staphylococcus aureus biofilms

S. aureus colonizes both artificial and tissue surfaces in humans causing chronic persistent infections that are difficult to cure. It is a notorious pathogen due to its antibiotic recalcitrance and phenotypic adaptability, both of which are facilitated by its ability to develop biofilms. S. aureus biofilms challenge conventional anti-infective approaches, most notably antibiotic therapy. Therefore there is an unmet need to develop and include parallel approaches that target S. aureus biofilm infections. This review discusses two broad anti-infective strategies: (1) preventative approaches (anti-biofilm surface coatings, the inclusion of biofilm-specific vaccine antigens); and (2) approaches aimed at eradicating established S. aureus biofilms, particularly those associated with implant infections. Advances in understanding the distinct nature of S. aureus biofilm development and pathogenesis have led to growing optimism in S. aureus biofilm targeted anti-infective strategies. Further research is needed however, to see the successful administration and validation of these approaches to the diverse types of infections caused by S. aureus biofilms from multiple clinical strains.

Difficult peritonitis cases in children undergoing chronic peritoneal dialysis: relapsing, repeat, recurrent and zoonotic episodes

Despite technological improvements in dialysis connectology and dialysis technique, peritonitis remains the most common and most significant complication of peritoneal dialysis (PD) in children. Most children undergoing chronic PD experience none or only one peritonitis episode, while others have multiple episodes or episodes secondary to unusual organisms. Knowledge of potential risk factors and likely patient outcome is imperative if treatment is to be optimized. In this review we will, in turn, describe episodes of peritonitis that are characterized as either relapsing, recurrent, repeat or zoonosis-related to highlight the clinical issues that are commonly encountered by clinicians treating these infections.

Corneal Biofilms: From Planktonic to Microcolony Formation in an Experimental Keratitis Infection with Pseudomonas Aeruginosa

PURPOSE

Microbial biofilms commonly comprise part of the infectious scenario, complicating the therapeutic approach. The purpose of this study was to determine in a mouse model of corneal infection if mature biofilms formed and to visualize the stages of biofilm formation.

METHODS

A bacterial keratitis model was established using Pseudomonas aeruginosa ATCC 9027 (1 × 10(8) CFU/ml) to infect the cornea of C57BL/6 black mouse. Eyes were examined post-infection (PI) on days 1, 2, 3, 5, and 7, and imaged by slit lamp microscopy, and light, confocal, and electron microscopy to identify the stages of biofilm formation and the time of appearance.

RESULTS

On PI day 1, Gram staining showed rod-shaped bacteria adherent on the corneal surface. On PI days 2 and 3, bacteria were seen within webs of extracellular polymeric substance (EPS) and glycocalyx secretion, imaged by confocal microscopy. Scanning electron microscopy demonstrated microcolonies of active infectious cells bound with thick fibrous material. Transmission electron microscopy substantiated the formation of classical biofilm architecture with P. aeruginosa densely packed within the extracellular polymeric substances on PI days 5 and 7.

CONCLUSION

Direct visual evidence showed that biofilms routinely developed on the biotic surface of the mouse cornea. The mouse model can be used to develop new approaches to deal therapeutically with biofilms in corneal infections.

Sophorolipid biosurfactants: Possible uses as antibacterial and antibiofilm agent

Biosurfactants are amphipathic, surface-active molecules of microbial origin which accumulate at interfaces reducing interfacial tension and leading to the formation of aggregated micellular structures in solution. Some biosurfactants have been reported to have antimicrobial properties, the ability to prevent adhesion and to disrupt biofilm formation. We investigated antimicrobial properties and biofilm disruption using sophorolipids at different concentrations. Growth of Gram negative Cupriavidus necator ATCC 17699 and Gram positive Bacillus subtilis BBK006 were inhibited by sophorolipids at concentrations of 5% v/v with a bactericidal effect. Sophorolipids (5% v/v) were also able to disrupt biofilms formed by single and mixed cultures of B. subtilis BBK006 and Staphylococcus aureus ATCC 9144 under static and flow conditions, as was observed by scanning electron microscopy. The results indicated that sophorolipids may be promising compounds for use in biomedical application as adjuvants to other antimicrobial against some pathogens through inhibition of growth and/or biofilm disruption.

Material properties of biofilms-a review of methods for understanding permeability and mechanics

Microorganisms can form biofilms, which are multicellular communities surrounded by a hydrated extracellular matrix of polymers. Central properties of the biofilm are governed by this extracellular matrix, which provides mechanical stability to the 3D biofilm structure, regulates the ability of the biofilm to adhere to surfaces, and determines the ability of the biofilm to adsorb gases, solutes, and foreign cells. Despite their critical relevance for understanding and eliminating of biofilms, the materials properties of the extracellular matrix are understudied. Here, we offer the reader a guide to current technologies that can be utilized to specifically assess the permeability and mechanical properties of the biofilm matrix and its interacting components. In particular, we highlight technological advances in instrumentation and interactions between multiple disciplines that have broadened the spectrum of methods available to conduct these studies. We review pioneering work that furthers our understanding of the material properties of biofilms.

Biofilm formation by clinical isolates and its relevance to clinical infections

Reports of biofilms have increased exponentially in the scientific literature over the past two decades, yet the vast majority of these are basic science investigations with limited clinical relevance. Biofilm studies involving clinical isolates are most often surveys of isolate collections, but suffer from lack of standardization in methodologies for producing and assessing biofilms. In contrast, more informative clinical studies correlating biofilm formation to patient data have infrequently been reported. In this chapter, biofilm surveys of clinical isolates of aerobic and anaerobic bacteria, mycobacteria, and Candida are reviewed, as well as those pertaining to the unique situation of cystic fibrosis. In addition, the influence of host components on in vitro biofilm formation, as well as published studies documenting the clinical impact of biofilms in human infections, are presented.

Local gentamicin delivery from resorbable viscous hydrogels is therapeutically effective

BACKGROUND

Local delivery can achieve the high antimicrobial concentrations necessary to kill biofilm-related microbes. Degradation times for resorbable carriers are too long. Hydrogels (gels of hydrophilic polymer in water) can degrade faster but release antimicrobials too quickly. We previously developed hydrogels based on the copolymer poly(N-isopropylacrylamide-co-dimethyl-γ-butyrolactone acrylate-co-Jeffamine® M-1000 acrylamide) (PNDJ) with delivery times of several days with complete degradation in less than 6 weeks.

QUESTIONS/PURPOSES

We asked: (1) What is the elution profile of gentamicin from PNDJ hydrogels? (2) Is gentamicin released from gentamicin-loaded PNDJ (G-PNDJ) hydrogel effective for treatment of orthopaedic infection? (3) Does local gentamicin delivery from G-PNDJ hydrogel cause renal dysfunction?

METHODS

(1) Two formulations of G-PNDJ, lower dose (1.61 wt%) and higher dose (3.14 wt%), five samples each, were eluted in buffered saline under infinite sink conditions. (2) Infections were induced in 16 New Zealand White rabbits by inserting a Kirschner wire in a devascularized radius segment and inoculating with 7.5×10(6) colony-forming units Staphylococcus aureus. At 3 weeks, débridement was performed and a new Kirschner wire was placed in the dead space. Treatment was randomized to higher-dose G-PNDJ or no hydrogel. No systemic antimicrobials were used. Positive culture and acute inflammation on histology were used to determine the presence of infection 4 weeks postdébridement. (3) 3.14 wt% G-PNDJ, 0.75, 1.5, or 3.0 mL, was injected subcutaneously in nine Sprague-Dawley rats, three of each dose. Serum gentamicin, blood urea nitrogen, and creatinine were measured on Days 1, 3, 7, 14, and 28.

RESULTS

(1) Gentamicin release was sustained over 7 days with the higher-dose formulation release profile similar to release from high-dose antimicrobial-loaded bone cement. (2) Four weeks postdébridement, infection was present in eight of eight no-hydrogel rabbits but zero of eight rabbits treated with G-PNDJ hydrogel (p<0.001). (3) Blood urea nitrogen and creatinine were transiently elevated (p<0.05) only for the two of three rats receiving the 3.0-mL dose on Days 3 and 7.

CONCLUSIONS

Gentamicin is delivered from PNDJ hydrogel with low systemic exposure and decreased treatment failure for orthopaedic infection. Transient renal dysfunction occurs at high doses. Biodistribution and toxicity testing are needed for G-PNDJ to be clinically usable.

CLINICAL RELEVANCE

Resorbable viscous hydrogels for local antimicrobial delivery may improve outcomes for one-stage management of implant infections when uncemented reconstructions are performed.

Update on the challenging role of biofilms in peritoneal dialysis

Biofilms are commonly associated with an increased risk of patient infection. In peritoneal dialysis (PD), catheter associated infection, especially peritonitis, remains a clinically relevant problem. Although the presence of a biofilm is recognized in relapsing, repeat, and catheter-related peritonitis, it remains poorly characterized. In this review, an update on the role of biofilms in PD infections is presented. The emerging concept that host cells and tissue associated biofilms, in addition to the biofilms on the catheters themselves, contribute to the recalcitrance of infections is discussed. Furthermore, the evidence of biofilms on PD catheters, their developmental stages, and the possible influence of the PD environment are reviewed. The focus is given to ex vivo and in vitro studies that contribute to the elucidation of the interplay between host, microbial, and dialysis factors. The key issues that are still to be answered and the challenges to clinical practice are discussed.

(+)-Dehydroabietic acid, an abietane-type diterpene, inhibits Staphylococcus aureus biofilms in vitro

Potent drugs are desperately needed to counteract bacterial biofilm infections, especially those caused by gram-positive organisms, such as Staphylococcus aureus. Moreover, anti-biofilm compounds/agents that can be used as chemical tools are also needed for basic in vitro or in vivo studies aimed at exploring biofilms behavior and functionability. In this contribution, a collection of naturally-occurring abietane-type diterpenes and their derivatives was tested against S. aureus biofilms using a platform consisting of two phenotypic assays that have been previously published by our group. Three active compounds were identified: nordehydroabietylamine (1), (+)-dehydroabietic acid (2) and (+)-dehydroabietylamine (3) that prevented biofilm formation in the low micromolar range, and unlike typical antibiotics, only 2 to 4-fold higher concentrations were needed to significantly reduce viability and biomass of existing biofilms. Compound 2, (+)-dehydroabietic acid, was the most selective towards biofilm bacteria, achieving high killing efficacy (based on log Reduction values) and it was best tolerated by three different mammalian cell lines. Since (+)-dehydroabietic acid is an easily available compound, it holds great potential to be used as a molecular probe in biofilms-related studies as well as to serve as inspirational chemical model for the development of potent drug candidates.

Surface modification of silicone for biomedical applications requiring long-term antibacterial, antifouling, and hemocompatible properties

Silicone has been used for peritoneal dialysis (PD) catheters for several decades. However, bacteria, platelets, proteins, and other biomolecules tend to adhere to its hydrophobic surface, which may lead to PD outflow failure, serious infection, or even death. In this work, a cross-linked poly(poly(ethylene glycol) dimethacrylate) (P(PEGDMA)) polymer layer was covalently grafted on medical-grade silicone surface to improve its antibacterial and antifouling properties. The P(PEGDMA)-grafted silicone (Silicone-g-P(PEGDMA)) substrate reduced the adhesion of Staphylococcus aureus , Escherichia coli , and Staphylococcus epidermidis , as well as 3T3 fibroblast cells by ≥90%. The antibacterial and antifouling properties were preserved after the modified substrate was aged for 30 days in phosphate buffer saline. Further immobilization of a polysulfobetaine polymer, poly((2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide) (P(DMAPS)), on the Silicone-g-P(PEGDMA) substrate via thiol-ene click reaction leads to enhanced antifouling efficacy and improved hemocompatibility with the preservation of the antibacterial property. Compared to pristine silicone, the so-obtained Silicone-g-P(PEGDMA)-P(DMAPS) substrate reduced the absorption of bovine serum albumin and bovine plasma fibrinogen by ≥80%. It also reduced the number of adherent platelets by ≥90% and significantly prolonged plasma recalcification time. The results indicate that surface grafting with P(PEGDMA) and P(DMAPS) can be potentially useful for the modification of silicone-based PD catheters for long-term applications.

Peritoneal dialysis associated infections: An update on diagnosis and management

Peritoneal dialysis (PD) is associated with a high risk of infection of the peritoneum, subcutaneous tunnel and catheter exit site. Although quality standards demand an infection rate < 0.67 episodes/patient/year on dialysis, the reported overall rate of PD associated infection is 0.24-1.66 episodes/patient/year. It is estimated that for every 0.5-per-year increase in peritonitis rate, the risk of death increases by 4% and 18% of the episodes resulted in removal of the PD catheter and 3.5% resulted in death. Improved diagnosis, increased awareness of causative agents in addition to other measures will facilitate prompt management of PD associated infection and salvage of PD modality. The aims of this review are to determine the magnitude of the infection problem, identify possible risk factors and provide an update on the diagnosis and management of PD associated infection. Gram-positive cocci such as Staphylococcus epidermidis, other coagulase negative staphylococcoci, and Staphylococcus aureus (S. aureus) are the most frequent aetiological agents of PD-associated peritonitis worldwide. Empiric antibiotic therapy must cover both gram-positive and gram-negative organisms. However, use of systemic vancomycin and ciprofloxacin administration for example, is a simple and efficient first-line protocol antibiotic therapy for PD peritonitis - success rate of 77%. However, for fungal PD peritonitis, it is now standard practice to remove PD catheters in addition to antifungal treatment for a minimum of 3 wk and subsequent transfer to hemodialysis. To prevent PD associated infections, prophylactic antibiotic administration before catheter placement, adequate patient training, exit-site care, and treatment for S. aureus nasal carriage should be employed. Mupirocin treatment can reduce the risk of exit site infection by 46% but it cannot decrease the risk of peritonitis due to all organisms.