Gentamicin improves the activities of daptomycin and vancomycin against Enterococcus faecalis in vitro and in an experimental foreign-body infection model

An in vitro study on the efficacy of hydrogen peroxide mediated high-power photodynamic therapy affecting Enterococcus faecalis biofilm formation and dispersal

OBJECTIVE

Biofilms are involved in failure of root canal treatment due to their high resistance to antimicrobial agents, which make their removal as a big challenge. The present study aims at utilizing hydrogen peroxide (HP) plus high frequency laser reinforced antimicrobial photodynamic therapy (a-PDT) as a complementary therapy against Enterococcus faecalis (E. faecalis) at planktonic and biofilm stages.

MATERIALS AND METHODS

E. faecalis at planktonic and biofilm stages was treated with the photosensitizer HP, followed by no irradiation or irradiation with a power of 2.5 W (ʎ = 980 nm). The cell viability, anti-biofilm, anti-metabolic potential, and temperature changes were evaluated.

RESULTS

The combination of HP and 980 nm diode laser intensely boosted antibacterial and anti-biofilm efficacy compared with either component alone, affirming HP reinforcement as a bacteriostatic agent. The maximum effect on biofilm occurs in 5.25% sodium hypochlorite (NaOCl) group. During laser irradiations, the mean of temperature changes remains below 5.6 °C.

CONCLUSIONS

It could be concluded that the HP could improve anti-biofilm efficacy as a photosensitizer in a-PDT.

Antibacterial potential of riboflavin mediated blue diode laser photodynamic inactivation against Enterococcus faecalis: A laboratory investigation

OBJECTIVES

This study aimed to evaluate the inactivation potency of riboflavin-mediated blue diode laser photodynamic inactivation (PDI) against Enterococcus faecalis at planktonic and biofilm stages and also investigated its effect on the tooth color change.

MATERIALS AND METHODS

The antibacterial and antibiofilm activities of riboflavin mediated PDI against E. faecalis were investigated. The numbers of colony-forming units (CFUs)/mL were calculated. Teeth discoloration were evaluated using the CIE L*a*b* based color difference (ΔE).

RESULTS

Antibacterial analysis indicated that the blue diode laser irradiation at 12, 18, 24, and 30 J/cm² alone and different concentrations of riboflavin solution (6.25 to 100 μM) reduced the number of CFU/mL of E. faecalis, but the reduction was not statistically significant (P > 0.05). Depending on the riboflavin concentration and the light dose, there can be as much as a 1-log effect on CFU/mL. In addition, E. faecalis biofilm was more affected with 30 J/cm² irradiation dosage and 100 μM riboflavin than other groups. Meanwhile, bacterial suspensions treated with 5.25% sodium hypochlorite (NaOCl) showed maximum biofilm inhibition and colony number reduction, compared with the control. The teeth exhibited clinically acceptable color change after riboflavin treatment at concentration ranging from 6.25 to 50 μM (ΔE < 3.7).

CONCLUSIONS

The riboflavin mediated PDI process is somewhat less effective than NaOCl but perhaps less toxic to tissues. It might be feasible to repeat the riboflavin + light treatment to further promote efficacy.

Daptomycin synergistic properties from in vitro and in vivo studies: a systematic review

INTRODUCTION

Daptomycin is a bactericidal lipopeptide antibiotic approved for the treatment of systemic infections (i.e. skin and soft tissue infections, bloodstream infections, infective endocarditis) caused by Gram-positive cocci. It is often prescribed in association with a partner drug to increase its bactericidal effect and to prevent the emergence of resistant strains during treatment; however, its synergistic properties are still under evaluation.

METHODS

We performed a systematic review to offer clinicians an updated overview of daptomycin synergistic properties from in vitro and in vivo studies. Moreover, we reported all in vitro and in vivo data evaluating daptomycin in combination with other antibiotic agents, subdivided by antibiotic classes, and a summary graph presenting the most favourable combinations at a glance.

RESULTS

A total of 92 studies and 1087 isolates (723 Staphylococcus aureus, 68 Staphylococcus epidermidis, 179 Enterococcus faecium, 105 Enterococcus faecalis, 12 Enterococcus durans) were included. Synergism accounted for 30.9% of total interactions, while indifferent effect was the most frequently observed interaction (41.9%). Antagonistic effect accounted for 0.7% of total interactions. The highest synergistic rates against S. aureus were observed with daptomycin in combination with fosfomycin (55.6%). For S. epidermidis and Enterococcus spp., the most effective combinations were daptomycin plus ceftobiprole (50%) and daptomycin plus fosfomycin (63.6%) or rifampicin (62.8%), respectively.

FUTURE PERSPECTIVES

We believe this systematic review could be useful for the future updates of guidelines on systemic infections where daptomycin plays a key role.

In Vitro Evaluation of Five Newly Isolated Bacteriophages against E. faecalis Biofilm for Their Potential Use against Post-Treatment Apical Periodontitis

State-of-the-art treatment of root canal infection includes the use of mechanical debridement and chemical agents. This disinfection method is limited, and microorganisms can remain in the canal system. Enterococcus faecalis appears with a high prevalence in secondary and persistent root canal infections and can be linked to endodontic treatment failure due to its various resistance mechanisms. Here, we evaluated the activity of newly isolated bacteriophages against clinical isolates of E. faecalis (including one vancomycin- and gentamicin-resistant strain) as a single treatment or in combination with gentamicin and vancomycin. For the resistant strain, daptomycin and fosfomycin were tested. Sixteen E. faecalis strains were used to screen for the presence of bacteriophages in sewage. Five different bacteriophages were characterized in terms of virion morphology, host range and killing-kinetics against each E. faecalis host strain. To investigate the antibiofilm effect of antibiotic and phages, E. faecalis biofilm was grown on porous glass beads and treated with different antibiotic concentrations and with isolated bacteriophages alone or in staggered combinations. A strong biofilm reduction was observed when phages were combined with antibiotic, where combinations with gentamicin showed a better outcome compared to vancomycin. Regarding the resistant strain, daptomycin had a superior antibiofilm effect than fosfomycin.

Mutations in respiratory complex I promote antibiotic persistence through alterations in intracellular acidity and protein synthesis

Antibiotic persistence describes the presence of phenotypic variants within an isogenic bacterial population that are transiently tolerant to antibiotic treatment. Perturbations of metabolic homeostasis can promote antibiotic persistence, but the precise mechanisms are not well understood. Here, we use laboratory evolution, population-wide sequencing and biochemical characterizations to identify mutations in respiratory complex I and discover how they promote persistence in Escherichia coli. We show that persistence-inducing perturbations of metabolic homeostasis are associated with cytoplasmic acidification. Such cytoplasmic acidification is further strengthened by compromised proton pumping in the complex I mutants. While RpoS regulon activation induces persistence in the wild type, the aggravated cytoplasmic acidification in the complex I mutants leads to increased persistence via global shutdown of protein synthesis. Thus, we propose that cytoplasmic acidification, amplified by a compromised complex I, can act as a signaling hub for perturbed metabolic homeostasis in antibiotic persisters.

Bugs on Drugs: A Drosophila melanogaster Gut Model to Study In Vivo Antibiotic Tolerance of E. coli

With an antibiotic crisis upon us, we need to boost antibiotic development and improve antibiotics’ efficacy. Crucial is knowing how to efficiently kill bacteria, especially in more complex in vivo conditions. Indeed, many bacteria harbor antibiotic-tolerant persisters, variants that survive exposure to our most potent antibiotics and catalyze resistance development. However, persistence is often only studied in vitro as we lack flexible in vivo models. Here, I explored the potential of using Drosophila melanogaster as a model for antimicrobial research, combining methods in Drosophila with microbiology techniques: assessing fly development and feeding, generating germ-free or bacteria-associated Drosophila and in situ microscopy. Adult flies tolerate antibiotics at high doses, although germ-free larvae show impaired development. Orally presented E. coli associates with Drosophila and mostly resides in the crop. E. coli shows an overall high antibiotic tolerance in vivo potentially resulting from heterogeneity in growth rates. The hipA7 high-persistence mutant displays an increased antibiotic survival while the expected low persistence of ΔrelAΔspoT and ΔrpoS mutants cannot be confirmed in vivo. In conclusion, a Drosophila model for in vivo antibiotic tolerance research shows high potential and offers a flexible system to test findings from in vitro assays in a broader, more complex condition.

Difficult to treat: are there organism-dependent differences and overall risk factors in success rates for two-stage knee revision?

OBJECTIVES

Failure after two-stage procedure for periprosthetic joint infection (PJI) is a rare, but devastating complication. Some authors assume a correlation of underlying organisms and recurrence rate. Methicillin-resistant Staphylococci (MRS) and other organisms (quinolone-resistant Gram-negative bacteria, rifampicin-resistant Staphylococcus, Enterococcus, and Candida) are meant to be "difficult to treat" (DTT) with an inferior outcome for two-stage revision. In addition to the type of bacteria, some more risk factors seem to be present. The aim of this study was (1) to detect a difference of reinfection rates between reinfection-causing groups of bacteria ["difficult to treat" (DTT), "easy to treat" (ETT) and methicillin-resistant staphylococci (MRS)] after a two-stage procedure, and (2) find overall risk factors for reinfection in a standardized long (spacer insertion for at least 6 weeks) two-stage procedure for periprosthetic knee infection.

METHODS

One hundred and thirty-seven two-stage revisions for periprosthetic knee infection were performed at one tertiary referral center. Finally, 96 patients could be included for analyses. Possible risk factors (comorbidities, prior surgery, etc.) and the types of organisms were documented. Quinolone-resistant Gram-negative bacteria, rifampicin-resistant Staphylococcus, Enterococcus, and Candida were classified as "difficult to treat" (DTT). Methicillin-resistant Staphylococci were summarized as "MRS", all other organism are summarized as "easy to treat" (ETT). Statistical analyses included univariate analysis (t test, Fisher's exact test, Chi square test) and logistic regression analysis.

RESULTS

There were no statistical significant differences in recurrent infection rates between organism groups (DTT vs. ETT, p = 0.674; DTT vs. MRS, p = 0.705; ETT vs. MRS, p = 0.537). Risk factors seem to be "need of revision after first stage" (p = 0.019, OR 5.62) or completed second stage (p = 0.000, OR 29.07), numbers of surgeries (p = 0.028) and alcohol abuse (p = 0.019, OR 5.62).

CONCLUSIONS

Revision needed during or after a two-stage exchange, numbers of surgeries and alcohol abuse are risk factors for recurrence, a different recurrence rates between organism-groups cannot be shown. The absence of significant differences in recurrence rates points to the importance of the individuality of each periprosthetic infection case: a reduction of necessary surgeries (with a thorough debridement, appropriate antibiotic addition to spacers) and the control of comorbidities (alcohol abuse) appear to be essential components of a two-stage exchange.

Microcalorimetric detection of staphylococcal biofilm growth on various prosthetic biomaterials after exposure to daptomycin

Primary aim of this in vitro study was to test the efficacy of daptomycin to eradicate staphylococcal biofilms on various orthopedic implant materials. Secondary aim was to quantitatively estimate the formation of staphylococcal biofilm. We tested six clinically important biomaterials: Cobalt chrome, pure titanium, grid-blasted titanium, porous plasma-coated titanium with/without hydroxyapatite, and polyethylene. Biofilms of S. aureus and S. epidermidis were formed on the samples and thereafter exposed to daptomycin. Samples were subsequently sonicated in order to detect dislodged biofilm bacteria and transferred to a microcalorimeter for real-time measurement of growth-related heat flow. Minimal biofilm eradication concentration (MBEC) was determined as the lowest concentration of daptomycin required to eradicate biofilm bacteria on the sample. Median MBEC of S. aureus biofilm on smooth metallic surfaces was lower than the rough metallic surfaces. In experiments with S. epidermidis, no pattern was seen in relation to the surface roughness. Regarding the quantitative estimation of staphylococcal biofilm formation on the sample, we found a significantly higher amount of biofilm growth on the rough surfaces than the smooth samples and polyethylene. In conclusion, the presented study showed that daptomycin could eradicate S. aureus biofilm at lower concentrations on the smooth surfaces compared to the rough surfaces, as well as polyethylene. In experiments with daptomycin against S. epidermidis biofilms, no pattern was seen in relation to the surface roughness. Furthermore, we demonstrated a faster detection of staphylococcal heat flow due to higher biofilm quantity on the rough surfaces compared to smooth samples and polyethylene. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2809-2816, 2018.

Prevention of High-Level Daptomycin-Resistance Emergence In Vitro in Streptococcus mitis-oralis by Using Combination Antimicrobial Strategies

Among the viridans group streptococci, S. mitis-oralis strains are frequently resistant to multiple β-lactams and tolerant to vancomycin (VAN). This scenario has led to the proposed clinical use of newer agents, like daptomycin (DAP) for such S. mitis-oralis strains. However, recent recognition of the rapid and durable emergence of high-level DAP-resistance (DAP-R; DAP MICs > 256 µg/ml) induced by DAP exposures in vitro and in vivo has dampened enthusiasm for such approaches. In this study, we evaluated a broad range of DAP combination regimens in vitro for their capacity to prevent emergence of high-level DAP-R in a prototype S. mitis-oralis strain (351) during serial passage experiments, including DAP + either gentamicin (GEN), rifampin (RIF), trimethoprim-sulfamethoxazole (TMP-SMX), imipenem (IMP), ceftaroline (CPT), tedizolid (TDZ), or linezolid (LDZ). In addition, we assessed selected DAP combination regimens for their ability to exert either an early bactericidal impact and/or synergistically kill the S. mitis-oralis study strain. During serial passage, three of the eight antibiotic combinations (DAP + GEN, CPT, or TMP- SMX) exhibited significantly reduced DAP MICs (≈ by 8-40 fold) vs serial exposure in DAP alone (DAP MICs > 256 µg/ml). In addition, combinations of DAP + GEN and DAP + CPT were both bactericidal and synergistic in early time-kill curve interactions.

Evaluation of daptomycin combinations with cephalosporins or gentamicin against Streptococcus mitis group strains in an in vitro model of simulated endocardial vegetations (SEVs)

Objectives

Among viridans group streptococcal infective endocarditis (IE), the Streptococcus mitis group is the most common aetiological organism. Treatment of IE caused by the S. mitis group is challenging due to the high frequency of β-lactam resistance, drug allergy and intolerability of mainstay antimicrobial agents such as vancomycin or gentamicin. Daptomycin has been suggested as an alternative therapeutic option in these scenarios based on its excellent susceptibility profile against S. mitis group strains . However, the propensity of many S. mitis group strains to rapidly evolve stable, high-level daptomycin resistance potentially limits this approach.

Methods

We evaluated the activity of 6 mg/kg/day daptomycin alone or in combination with gentamicin, ceftriaxone or ceftaroline against two daptomycin-susceptible S. mitis group strains over 96 h in a pharmacokinetic/pharmacodynamic model of simulated endocardial vegetations.

Results

Daptomycin alone was not bactericidal and high-level daptomycin resistance evolved at 96 h in both organisms. Combinations of daptomycin + ceftriaxone and daptomycin + ceftaroline demonstrated enhanced killing activity compared with each antibiotic alone and prevented emergence of daptomycin resistance at 96 h. Use of gentamicin as an adjunctive agent neither improved the efficacy of daptomycin nor prevented the development of daptomycin resistance.

Conclusions

Addition of ceftriaxone or ceftaroline to daptomycin improves the bactericidal activity against S. mitis group strains and prevents daptomycin resistance emergence. Further investigation with combinations of daptomycin and β-lactams in a large number of strains is warranted to fully elucidate the clinical implications of such combinations for treatment of S. mitis group IE.

Probing the Mechanism of LAL-32, a Gold Nanoparticle-Based Antibiotic Discovered through Small Molecule Variable Ligand Display

The unrelenting rise of antimicrobial-resistant bacteria has necessitated the search for novel antibiotic solutions. Herein we describe further mechanistic studies on a 2.0-nm-diameter gold nanoparticle-based antibiotic (designated LAL-32). This antibiotic exhibits bactericidal activity against the Gram-negative bacterium Escherichia coli at 1.0 μM, a concentration significantly lower than several clinically available antibiotics (such as ampicillin and gentamicin), and acute treatment with LAL-32 does not give rise to spontaneous resistant mutants. LAL-32 treatment inhibits cellular division, daughter cell separation, and twin-arginine translocation (Tat) pathway dependent shuttling of proteins to the periplasm. Furthermore, we have found that the cedA gene imparts increased resistance to LAL-32, and shown that an E. coli cedA transposon mutant exhibits increased susceptibility to LAL-32. Taken together, these studies further implicate cell division pathways as the target for this nanoparticle-based antibiotic and demonstrate that there may be inherently higher barriers for resistance evolution against nanoscale antibiotics in comparison to their small molecule counterparts.

Management of infections associated with neurosurgical implanted devices

INTRODUCTION

Neurosurgical devices are increasingly used. With it, neurosurgical device-related infections gain relevance. As biofilms are involved in implant-associated infections the diagnosis and treatment is challenging and requires specific anti-biofilm concepts and management algorithms. Areas covered: The literature concerning the management of neurosurgical device-associated infections is scarce and heterogeneous treatment concepts are discussed, but no standardized diagnostic and treatment procedures exist. Therefore, we emphasize extrapolating management strategies predominantly from orthopedic device-associated infections, where the concept is better established and clinically validated. This review covers infections associated with craniotomy fixation devices, cranioplasties, external ventricular and lumbar drainages, internal shunts and neurostimulators. Expert commentary: Sonication of the removed implants significantly improves microbiological diagnosis. A combined surgical and antimicrobial management is crucial for successful treatment: appropriate surgical intervention is combined with prolonged anti-biofilm therapy of usually 12 weeks. In selected patients, new treatment algorithms enable cure of neurosurgical device-associated infections without implant removal or with a one-stage implant exchange, considerably improving the quality of patient lives.

Reduced ability to detect surface-related biofilm bacteria after antibiotic exposure under in vitro conditions

Background and purpose - Antibiotic treatment of patients before specimen collection reduces the ability to detect organisms by culture. We investigated the suppressive effect of antibiotics on the growth of non-adherent, planktonic, and surface-related biofilm bacteria in vitro by using sonication and microcalorimetry methods. Patients and methods - Biofilms of Staphylococcus aureus, S. epidermidis, Escherichia coli, and Propionibacterium acnes were formed on porous glass beads and exposed for 24 h to antibiotic concentrations from 1 to 1,024 times the minimal inhibitory concentration (MIC) of vancomycin, daptomycin, rifampin, flucloxacillin, or ciprofloxacin. The beads were then sonicated to dislodge biofilm, followed by culture and measurement of growth-related heat flow by microcalorimetry of the resulting sonication fluid. Results - Vancomycin did not inhibit the heat flow of staphylococci and P. acnes at concentrations ≤1,024 μg/mL, whereas flucloxacillin at >128 μg/mL inhibited S. aureus. Daptomycin inhibited heat flow of S. aureus, S. epidermidis, and P. acnes at lower concentrations (32-128 times MIC, p < 0.001). Rifampin showed inconsistent results in staphylococci due to random emergence of resistance, which was observed at concentrations ≤1,024 times MIC (i.e. 8 μg/mL). Ciprofloxacin inhibited heat flow of E. coli at ≥4 times MIC (i.e. ≥ 0.06 μg/mL). Interpretation - Whereas time-dependent antibiotics (i.e. vancomycin and flucloxacillin) showed only weak growth suppression, concentration-dependent drugs (i.e. daptomycin and ciprofloxacin) had a strong suppressive effect on bacterial growth and reduced the ability to detect planktonic and biofilm bacteria. Exposure to rifampin rapidly caused emergence of resistance. Our findings indicate that preoperative administration of antibiotics may have heterogeneous effects on the ability to detect biofilm bacteria.

Sub-lethal doses of photodynamic therapy affect biofilm formation ability and metabolic activity of Enterococcus faecalis

BACKGROUND

During photodynamic therapy (PDT) in the treatment of a primary endodontic infection, it is extremely likely that microorganisms would be exposed to sub-lethal doses of PDT (sPDT). Although sPDT cannot kill microorganisms, it can considerably influence microbial virulence. This study was conducted to characterize the effect of sPDT using toluidine blue O (TBO), methylene blue (MB), and indocyanine green (ICG) on biofilm formation ability and metabolic activity of Enterococcus faecalis.

METHODS

The antimetabolic and antibiofilm potential of ICG-, TBO-, and MB-sPDT against E. faecalis was analyzed at sub-lethal doses (1/2-1/64 minimum inhibitory concentration) using the XTT reduction assay, crystal violet assay, and scanning electron microscopy.

RESULTS

Higher doses of sPDT adversely affected biofilm formation ability and metabolic activity. ICG-, TBO-, and MB-PDT at a maximum sub-lethal dose markedly reduced the formation of biofilm up to 42.8%, 22.6%, and 19.5%, respectively. ICG-, TBO-, and MB-sPDT showed a marked reduction in bacterial metabolic activity by 98%, 94%, and 82%, respectively. ICG-PDT showed a stronger inhibitory effect on biofilm formation in E. faecalis than MB- and TBO-PDT at sub-lethal levels. Interestingly, a gradual increase in metabolic activity and biofilm formation upon exposure to a lower dose of test sPDT were observed.

CONCLUSION

sPDT showed dual effect on biofilm formation ability and metabolic activity of E. faecalis. High doses revealed antimetabolic and antibiofilm potential activity, whereas lower doses had conflicting results. Hence, when PDT is prescribed in clinical settings, the dose of PDT used in vivo should be taken into consideration.

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.

New in vitro and in vivo models to evaluate antibiotic efficacy in Staphylococcus aureus prosthetic vascular graft infection

OBJECTIVE

Prosthetic vascular graft infection (PVGI) is an emerging disease, mostly caused by staphylococci, with limited data regarding efficacy of current antistaphylococcal agents. We aimed to assess the efficacy of different antibiotic regimens.

METHODS

Six different strains of MSSA and MRSA were used. We compared results of minimal biofilm inhibitory and eradicating concentrations (MBICs and MBECs) obtained with a Calgary Biofilm Pin Lid Device (CBPD) with those yielded by an original Dacron(®)-related minimal inhibitory and eradicating concentration measure model. We then used a murine model of Staphylococcus aureus vascular prosthetic material infection to evaluate efficacy of different antibiotic regimens: vancomycin and daptomycin combined or not with rifampicin for MRSA and the same groups with cloxacillin and cloxacillin combined with rifampicin for MSSA.

RESULTS

We demonstrated that classical measures of MBICs and MBECs obtained with a CPBD could overestimate the decrease in antibiotic susceptibility in material-related infections and that the nature of the support used might influence the measure of biofilm susceptibility, since results yielded by our Dacron(®)-related minimal eradicating assay were lower than those found with a plastic device. In our in vivo model, we showed that daptomycin was significantly more bactericidal than comparators for some strains of MRSA or MSSA but not for all. For the majority of strains, it was as efficient as comparators. The addition of rifampicin to daptomycin did not enhance daptomycin efficacy.

CONCLUSIONS

Despite the heterogeneity of results according to bacterial strains, these innovative models represent an option to better evaluate the in vitro efficacy of antibiotics on Dacron(®)-related biofilm S. aureus infections, and to screen different antibiotic regimens in a mouse model of PVGIs.

Combination antibiotic therapy for the treatment of infective endocarditis due to enterococci

INTRODUCTION

Enterococci are common causes of infective endocarditis (IE) in both health care and community-based setting. Enterococcal IE requires bactericidal therapy for an optimal outcome. For decades, cell-wall-active antimicrobial agents (penicillins or vancomycin) in combination with aminoglycosides were the cornerstone of the treatment; however, the emergence of antibiotic resistance has significantly reduced the efficacy of these regimens.

MATERIALS AND METHODS

Data for this review were identified by searches of MEDLINE and references from relevant articles on antibiotic combination regimens for the treatment of enterococcal IE. Abstracts presented in scientific conferences were not searched for.

CONCLUSION

New effective and safe combination treatments, including double-β-lactam and daptomycin/β-lactam combination, are proving useful for the management of IE due to enterococci.

Biofilms in periprosthetic orthopedic infections

As the number of total joint arthroplasty and internal fixation procedures continues to rise, the threat of infection following surgery has significant clinical implications. These infections may have highly morbid consequences to patients, who often endure additional surgeries and lengthy exposures to systemic antibiotics, neither of which are guaranteed to resolve the infection. Of particular concern is the threat of bacterial biofilm development, since biofilm-mediated infections are difficult to diagnose and effective treatments are lacking. Developing therapeutic strategies have targeted mechanisms of biofilm formation and the means by which these bacteria communicate with each other to take on specialized roles such as persister cells within the biofilm. In addition, prevention of infection through novel coatings for prostheses and the local delivery of high concentrations of antibiotics by absorbable carriers has shown promise in laboratory and animal studies. Biofilm development, especially in an arthoplasty environment, and future diagnostic and treatment options are discussed.

Medical treatment of prosthetic vascular graft infections: Review of the literature and proposals of a Working Group

More than 400000 vascular grafts are inserted annually in the USA. Graft insertion is complicated by infection in 0.5-4% of cases. Vascular graft infections (VGIs) are becoming one of the most frequent prosthesis-related infections and are associated with considerable mortality, ranging from 10 to 25% within 30 days following the diagnosis. Treatment of VGI is based on urgent surgical removal of the infected graft followed by prolonged antibiotherapy. Data regarding the best antibiotherapy to use are lacking since no well designed trial to study antimicrobial treatment of VGI exists. Moreover, since VGIs demonstrate very specific pathophysiology, guidelines on other material-related infections or infective endocarditis treatment cannot be entirely applied to VGI. A French multidisciplinary group gathering infectious diseases specialists, anaesthesiologists, intensivists, microbiologists, radiologists and vascular surgeons was created to review the literature dealing with VGI and to make some proposals regarding empirical and documented antibiotic therapy for these infections. This article reveals these proposals.

Ozonated saline shows activity against planktonic and biofilm growing Staphylococcus aureus in vitro: a potential irrigant for infected wounds

Infections associated with deep wounds require extensive surgical and medical care. New adjunctive treatments are required to aid in the eradication of the bacterial biofilms found on infected wounds and, in particular, any underlying hardware. Ozone has been used as a safe and efficient disinfectant in water treatment plants for many years. The purpose of this study is to investigate the anti-biofilm potential of ozonated saline against biofilms of Staphylococcus aureus, a microorganism commonly implicated in wound infections. A custom-made bacterial biofilm bioreactor was used to grow S. aureus biofilms on discs of medical grade titanium alloy. An ozone generator was connected in-line and biofilms and planktonic bacteria were exposed to ozone in saline. Cytotoxicity was assessed against primary ovine osteoblasts in the same system. In tests against planktonic S. aureus, a 99% reduction in bacterial numbers was detected within 15 minutes of exposure. S. aureus biofilms were significantly more resistant to ozone, although complete eradication of the biofilm was eventually achieved within 5 hours. Ozonated saline was not found to be cytotoxic to primary ovine osteoblasts. Ozonated saline may be suitable as an adjuvant therapy to treat patients as an instillation fluid for wound irrigation and sterilisation.

A modified chronic infection model for testing treatment of Staphylococcus aureus biofilms on implants

Bacterial biofilms causing implant-associated osteomyelitis is a severe complication with limited antimicrobial therapy options. We designed an animal model, in which implant associated osteomyelitis arise from a Staphylococcus aureus biofilm on a tibia implant. Two bioluminescently engineered (luxA-E transformed), strains of S. aureus were utilized, Xen29 and Xen31. Biofilm formation was assessed with epifluorescence microscopy. Quantitative measurements were performed day 4, 6, 8, 11 and 15 post-surgery. Bacteria were extracted from the biofilm by sonication and the bacterial load quantified by culturing. Biofilm formation was evident from day 6 post-implantation. Mean bacterial load from implants was ∼1×10(4) CFU/implant, while mean bacterial load from infected tibias were 1×10(6) CFU/bone. Bioluminesence imaging revealed decreasing activity throughout the 15-day observation period, with signal intensity for both strains reaching that of the negative control by day 15 while there was no significant reduction in bacterial load. The model is suitable for testing antimicrobial treatment options for implant associated OM, as treatment efficacy on both biofilm and viable counts can be assessed.

Clinical presentation and treatment of orthopaedic implant-associated infection

Orthopaedic implants are highly susceptible to infection. The aims of treatment of infection associated with internal fixation devices are fracture consolidation and prevention of chronic osteomyelitis. Complete biofilm eradication is not the primary goal, as remaining adherent microorganisms can be removed with the device after fracture consolidation. By contrast, in periprosthetic joint infection (PJI), biofilm elimination is required. Surgical treatment of PJI includes debridement with retention, one- or two-stage exchange and removal without reimplantation. In addition, prolonged antibiotic treatment, preferably with an agent that is effective against biofilm bacteria, is required. Rifampicin is an example of an antibiotic with these properties against staphylococci. However, to avoid the emergence of resistance, rifampicin must always be combined with another antimicrobial agent. With this novel treatment approach, orthopaedic implant-associated infection is likely to be eradicated in up to 80-90% of patients. Because most antibiotics have a limited effect against biofilm infections, novel prophylactic and therapeutic options are needed. Surface coating with antimicrobial peptides that reduce bacterial attachment and biofilm formation can potentially prevent implant-associated infection. In addition, quorum-sensing inhibitors are a novel therapeutic option against biofilm infections.

High activity of Fosfomycin and Rifampin against methicillin-resistant staphylococcus aureus biofilm in vitro and in an experimental foreign-body infection model

Increasing antimicrobial resistance reduces treatment options for implant-associated infections caused by methicillin-resistant Staphylococcus aureus (MRSA). We evaluated the activity of fosfomycin alone and in combination with vancomycin, daptomycin, rifampin, and tigecycline against MRSA (ATCC 43300) in a foreign-body (implantable cage) infection model. The MICs of the individual agents were as follows: fosfomycin, 1 μg/ml; daptomycin, 0.125 μg/ml; vancomycin, 1 μg/ml; rifampin, 0.04 μg/ml; and tigecycline, 0.125 μg/ml. Microcalorimetry showed synergistic activity of fosfomycin and rifampin at subinhibitory concentrations against planktonic and biofilm MRSA. In time-kill curves, fosfomycin exhibited time-dependent activity against MRSA with a reduction of 2.5 log10 CFU/ml at 128 × the MIC. In the animal model, planktonic bacteria in cage fluid were reduced by <1 log10 CFU/ml with fosfomycin and tigecycline, 1.7 log10 with daptomycin, 2.2 log10 with fosfomycin-tigecycline and fosfomycin-vancomycin, 3.8 log10 with fosfomycin-daptomycin, and >6.0 log10 with daptomycin-rifampin and fosfomycin-rifampin. Daptomycin-rifampin cured 67% of cage-associated infections and fosfomycin-rifampin cured 83%, whereas all single drugs (fosfomycin, daptomycin, and tigecycline) and rifampin-free fosfomycin combinations showed no cure of MRSA cage-associated infections. No emergence of fosfomycin resistance was observed in animals; however, a 4-fold increase in fosfomycin MIC (from 2 to 16 μg/ml) occurred in the fosfomycin-vancomycin group. In summary, the highest eradication of MRSA cage-associated infections was achieved with fosfomycin in combination with rifampin (83%). Fosfomycin may be used in combination with rifampin against MRSA implant-associated infections, but it cannot replace rifampin as an antibiofilm agent.

Activities of fluconazole, caspofungin, anidulafungin, and amphotericin B on planktonic and biofilm Candida species determined by microcalorimetry

We investigated the activities of fluconazole, caspofungin, anidulafungin, and amphotericin B against Candida species in planktonic form and biofilms using a highly sensitive assay measuring growth-related heat production (microcalorimetry). C. albicans, C. glabrata, C. krusei, and C. parapsilosis were tested, and MICs were determined by the broth microdilution method. The antifungal activities were determined by isothermal microcalorimetry at 37°C in RPMI 1640. For planktonic Candida, heat flow was measured in the presence of antifungal dilutions for 24 h. Candida biofilm was formed on porous glass beads for 24 h and exposed to serial dilutions of antifungals for 24 h, and heat flow was measured for 48 h. The minimum heat inhibitory concentration (MHIC) was defined as the lowest antifungal concentration reducing the heat flow peak by ≥50% (≥90% for amphotericin B) at 24 h for planktonic Candida and at 48 h for Candida biofilms (measured also at 24 h). Fluconazole (planktonic MHICs, 0.25 to >512 μg/ml) and amphotericin B (planktonic MHICs, 0.25 to 1 μg/ml) showed higher MHICs than anidulafungin (planktonic MHICs, 0.015 to 0.5 μg/ml) and caspofungin (planktonic MHICs, 0.125 to 0.5 μg/ml). Against Candida species in biofilms, fluconazole's activity was reduced by >1,000-fold compared to its activity against the planktonic counterparts, whereas echinocandins and amphotericin B mainly preserved their activities. Fluconazole induced growth of planktonic C. krusei at sub-MICs. At high concentrations of caspofungin (>4 μg/ml), paradoxical growth of planktonic C. albicans and C. glabrata was observed. Microcalorimetry enabled real-time evaluation of antifungal activities against planktonic and biofilm Candida organisms. It can be used in the future to evaluate new antifungals and antifungal combinations and to study resistant strains.

An in vitro study on the effects of nisin on the antibacterial activities of 18 antibiotics against Enterococcus faecalis

Enterococcus faecalis rank among the leading causes of nosocomial infections worldwide and possesses both intrinsic and acquired resistance to a variety of antibiotics. Development of new antibiotics is limited, and pathogens continually generate new antibiotic resistance. Many researchers aim to identify strategies to effectively kill this drug-resistant pathogen. Here, we evaluated the effect of the antimicrobial peptide nisin on the antibacterial activities of 18 antibiotics against E. faecalis. The MIC and MBC results showed that the antibacterial activities of 18 antibiotics against E. faecalis OG1RF, ATCC 29212, and strain E were significantly improved in the presence of 200 U/ml nisin. Statistically significant differences were observed between the results with and without 200 U/ml nisin at the same concentrations of penicillin or chloramphenicol (p<0.05). The checkerboard assay showed that the combination of nisin and penicillin or chloramphenicol had a synergetic effect against the three tested E. faecalis strains. The transmission electron microscope images showed that E. faecalis was not obviously destroyed by penicillin or chloramphenicol alone but was severely disrupted by either antibiotic in combination with nisin. Furthermore, assessing biofilms by a confocal laser scanning microscope showed that penicillin, ciprofloxacin, and chloramphenicol all showed stronger antibiofilm actions in combination with nisin than when these antibiotics were administered alone. Therefore, nisin can significantly improve the antibacterial and antibiofilm activities of many antibiotics, and certain antibiotics in combination with nisin have considerable potential for use as inhibitors of this drug-resistant pathogen.

Activities of fosfomycin and rifampin on planktonic and adherent Enterococcus faecalis strains in an experimental foreign-body infection model

Enterococcal implant-associated infections are difficult to treat because antibiotics generally lack activity against enterococcal biofilms. We investigated fosfomycin, rifampin, and their combinations against planktonic and adherent Enterococcus faecalis (ATCC 19433) in vitro and in a foreign-body infection model. The MIC/MBClog values were 32/>512 μg/ml for fosfomycin, 4/>64 μg/ml for rifampin, 1/2 μg/ml for ampicillin, 2/>256 μg/ml for linezolid, 16/32 μg/ml for gentamicin, 1/>64 μg/ml for vancomycin, and 1/5 μg/ml for daptomycin. In time-kill studies, fosfomycin was bactericidal at 8× and 16× MIC, but regrowth of resistant strains occurred after 24 h. With the exception of gentamicin, no complete inhibition of growth-related heat production was observed with other antimicrobials on early (3 h) or mature (24 h) biofilms. In the animal model, fosfomycin alone or in combination with daptomycin reduced planktonic counts by ≈4 log10 CFU/ml below the levels before treatment. Fosfomycin cleared planktonic bacteria from 74% of cage fluids (i.e., no growth in aspirated fluid) and eradicated biofilm bacteria from 43% of cages (i.e., no growth from removed cages). In combination with gentamicin, fosfomycin cleared 77% and cured 58% of cages; in combination with vancomycin, fosfomycin cleared 33% and cured 18% of cages; in combination with daptomycin, fosfomycin cleared 75% and cured 17% of cages. Rifampin showed no activity on planktonic or adherent E. faecalis, whereas in combination with daptomycin it cured 17% and with fosfomycin it cured 25% of cages. Emergence of fosfomycin resistance was not observed in vivo. In conclusion, fosfomycin showed activity against planktonic and adherent E. faecalis. Its role against enterococcal biofilms should be further investigated, especially in combination with rifampin and/or daptomycin treatment.

Antibiotic Resistance in Enterococcus faecalis Isolated from Hospitalized Patients

Background and aims

Enterococci are Gram-positive cocci that often occur in pairs (diplococci) or short chains. Be-side developing high level of antibiotic resistance, these bacteria can cause wide range of disease in human, thus to help provide an effective treatment for infections caused by this genus, this study was conceived to provide information on Enterococcus faecalis Antibiotic resistance to widely used antibiotics in hospitalized patients.

Materials and methods

Disk diffusion agar and Broth dilution methods were used to perform Antibiogram test on isolated Enterococcus faecalis. Culture medium used for Disk diffusion agar test was Muller Hinton agar, and for Broth dilution methods, Muller Hinton broth culture medium was utilized. In disk diffusion agar method, different commercial antibiotics disks produced by Pharmaceutical companies were used. Microsoft Excel software was used to perform statistical analysis.

Results

Based on antibiograms of 105 cases, a high resistance to Synercid, Nalidixic acid, Oxacillin and Teofilin was de-tected whereas the lowest resistance observed in Nitrofurantoin, Vancomycin, Linezolid and Teicoplanin antibiotics.

Conclusion

According to the results, Teicoplanin, Vancomycin, Linezolid and Nitrofurantoin are recommended against E. faecalis species.

Daptomycin: the role of high-dose and combination therapy for Gram-positive infections

Daptomycin, a cyclic lipopeptide with rapid bactericidal activity, is approved at doses of 4 mg/kg and 6 mg/kg for the treatment of its respective indications [i.e. complicated skin and soft-tissue infections (cSSTIs) caused by Gram-positive bacteria; and Staphylococcus aureus bacteraemia associated with right-sided infective endocarditis (RIE) or cSSTIs, or RIE due to S. aureus]. Higher doses and combination therapy strategies have been investigated in some difficult-to-treat infections in order to: enhance clinical success rates; treat pathogens that may be non-susceptible to standard doses; and minimise the risk of resistance development in patients, particularly those who may need an extended treatment duration, who may have had suboptimal surgical management and/or who may have not responded to prior antibiotic therapy. Although clinical trial data of daptomycin doses >6 mg/kg and of daptomycin in combination with other antibiotics are limited, clinical experience reported to date suggests that daptomycin is effective and well tolerated at higher doses and in combination. In this review, the rationale both for high-dose and combination therapy strategies with daptomycin is explored and the available evidence is presented by indication and evaluated from a clinical perspective. Safety and efficacy are discussed from prospective and retrospective clinical studies, together with case reports for a variety of infections, including bacteraemia, endocarditis, cSSTIs and osteomyelitis, and expert recommendations are provided in summary of the evidence. The use of high-dose daptomycin, alone or in combination, may be useful for difficult-to-treat Gram-positive infections and further evaluation of these strategies is warranted.

What Is New in the Understanding of Non Healing Wounds Epidemiology, Pathophysiology, and Therapies

Chronic wounds are a growing socioeconomic problem in the western world. Knowledge on recalcitrant wounds relies on in vitro studies or clinical observations, and there is emerging evidence on the clinical impact of bacterial biofilm on skin healing. Chronic wounds are locked in the inflammatory state of wound healing, and there are multiple explanations for this arrest with the theory of exaggerated proteolysis as the most commonly accepted. Previously, there has not been enough focus on the different etiologies of chronic wounds compared to acute, healing wounds. There is an urgent need to group chronic wounds by its cause when searching for possible diagnostic or therapeutic targets. Good wound management should therefore consist of recognition of basic wound etiology, irrigation, and debridement in order to reduce microbial and necrotic load, frequently changed dressings, and appropriate antimicrobial and antibiofilm strategies based on precise diagnosis. Representative sampling is required for diagnosis and antimicrobial treatment of wounds. The present review aims at describing the impact of biofilm infections on wounds in relation to diagnosing, treatment strategies, including experimentally adjuvant approaches and animal models.

Activities of fosfomycin, tigecycline, colistin, and gentamicin against extended-spectrum-β-lactamase-producing Escherichia coli in a foreign-body infection model

Limited antimicrobial agents are available for the treatment of implant-associated infections caused by fluoroquinolone-resistant Gram-negative bacilli. We compared the activities of fosfomycin, tigecycline, colistin, and gentamicin (alone and in combination) against a CTX-M15-producing strain of Escherichia coli (Bj HDE-1) in vitro and in a foreign-body infection model. The MIC and the minimal bactericidal concentration in logarithmic phase (MBC(log)) and stationary phase (MBC(stat)) were 0.12, 0.12, and 8 μg/ml for fosfomycin, 0.25, 32, and 32 μg/ml for tigecycline, 0.25, 0.5, and 2 μg/ml for colistin, and 2, 8, and 16 μg/ml for gentamicin, respectively. In time-kill studies, colistin showed concentration-dependent activity, but regrowth occurred after 24 h. Fosfomycin demonstrated rapid bactericidal activity at the MIC, and no regrowth occurred. Synergistic activity between fosfomycin and colistin in vitro was observed, with no detectable bacterial counts after 6 h. In animal studies, fosfomycin reduced planktonic counts by 4 log(10) CFU/ml, whereas in combination with colistin, tigecycline, or gentamicin, it reduced counts by >6 log(10) CFU/ml. Fosfomycin was the only single agent which was able to eradicate E. coli biofilms (cure rate, 17% of implanted, infected cages). In combination, colistin plus tigecycline (50%) and fosfomycin plus gentamicin (42%) cured significantly more infected cages than colistin plus gentamicin (33%) or fosfomycin plus tigecycline (25%) (P < 0.05). The combination of fosfomycin plus colistin showed the highest cure rate (67%), which was significantly better than that of fosfomycin alone (P < 0.05). In conclusion, the combination of fosfomycin plus colistin is a promising treatment option for implant-associated infections caused by fluoroquinolone-resistant Gram-negative bacilli.

The diagnostic protocol for evaluation of periprosthetic joint infection

Infection is becoming the most important as well as the most devastating mechanism of prosthetic joint failure. The incidence is increasing because the absolute number of patients operated is increasing and because more often very sick, debilitated and immunocompromised patients are operated. The trend reveals a further increase in the years to come. Diagnosis may be very easy in case of high grade processes, but also extremely difficult in some other instances. Misdiagnosing infection leads to repeated early failures that are distressing for patients as well as surgeons. To avoid failures related to misdiagnosed prosthetic joint infections a step-wise algorithm of action is proposed and the diagnostic strength of the steps discussed. The key point is to select potential candidates to define the probability of an ongoing infection and then to select the tools to strengthen the suspicion. Further procedures are based on the analysis of the pseudo-synovial fluid obtained by aspiration. Diagnostic conclusions form the basis for treatment decisions.

Intrinsic and acquired resistance mechanisms in enterococcus

Enterococci have the potential for resistance to virtually all clinically useful antibiotics. Their emergence as important nosocomial pathogens has coincided with increased expression of antimicrobial resistance by members of the genus. The mechanisms underlying antibiotic resistance in enterococci may be intrinsic to the species or acquired through mutation of intrinsic genes or horizontal exchange of genetic material encoding resistance determinants. This paper reviews the antibiotic resistance mechanisms in Enterococcus faecium and Enterococcus faecalis and discusses treatment options.

Pathogenesis and treatment concepts of orthopaedic biofilm infections

Implant-associated infection is caused by surface-adhering bacteria persisting as biofilm. Periprosthetic joint infection is difficult to diagnose and treat. The high susceptibility of implanted devices to infection is because of a locally acquired host defense defect, and persistence is mainly because of the rapid formation of a biofilm resistant to host defense and antimicrobial agents. Successful treatment of periprosthetic joint infection requires the optimal surgical procedure combined with long-term antimicrobial therapy directed against surface-adhering microorganisms. Surgical treatment according to an algorithm has been validated in several observational studies. The role of rifampin against device-associated staphylococcal infection has been evaluated in an animal model, in observational studies and in a controlled trial. Given the limited efficacy of traditional antibiotics in implant-associated infections, novel strategies such as coating of the device, vaccination against biofilms, and quorum-sensing inhibitors are promising future options for prevention and treatment.

Role of rifampin against Propionibacterium acnes biofilm in vitro and in an experimental foreign-body infection model

Propionibacterium acnes is an important cause of orthopedic-implant-associated infections, for which the optimal treatment has not yet been determined. We investigated the activity of rifampin, alone and in combination, against planktonic and biofilm P. acnes in vitro and in a foreign-body infection model. The MIC and the minimal bactericidal concentration (MBC) were 0.007 and 4 μg/ml for rifampin, 1 and 4 μg/ml for daptomycin, 1 and 8 μg/ml for vancomycin, 1 and 2 μg/ml for levofloxacin, 0.03 and 16 μg/ml for penicillin G, 0.125 and 512 μg/ml for clindamycin, and 0.25 and 32 μg/ml for ceftriaxone. The P. acnes minimal biofilm eradication concentration (MBEC) was 16 μg/ml for rifampin; 32 μg/ml for penicillin G; 64 μg/ml for daptomycin and ceftriaxone; and ≥128 μg/ml for levofloxacin, vancomycin, and clindamycin. In the animal model, implants were infected by injection of 10⁹ CFU P. acnes in cages. Antimicrobial activity on P. acnes was investigated in the cage fluid (planktonic form) and on explanted cages (biofilm form). The cure rates were 4% for daptomycin, 17% for vancomycin, 0% for levofloxacin, and 36% for rifampin. Rifampin cured 63% of the infected cages in combination with daptomycin, 46% with vancomycin, and 25% with levofloxacin. While all tested antimicrobials showed good activity against planktonic P. acnes, for eradication of biofilms, rifampin was needed. In combination with rifampin, daptomycin showed higher cure rates than with vancomycin in this foreign-body infection model.