Reversible daptomycin tolerance of adherent staphylococci in an implant infection model

A lipoglycopeptide antibiotic for Gram-positive biofilm-related infections

Drug-resistant Gram-positive bacterial infections are still a substantial burden on the public health system, with two bacteria ( Staphylococcus aureus and Streptococcus pneumoniae ) accounting for over 1.5 million drug-resistant infections in the United States alone in 2017. In 2019, 250,000 deaths were attributed to these pathogens globally. We have developed a preclinical glycopeptide antibiotic, MCC5145, that has excellent potency (MIC 90 ≤ 0.06 μg/ml) against hundreds of isolates of methicillin-resistant S. aureus (MRSA) and other Gram-positive bacteria, with a greater than 1000-fold margin over mammalian cell cytotoxicity values. The antibiotic has therapeutic in vivo efficacy when dosed subcutaneously in multiple murine models of established bacterial infections, including thigh infection with MRSA and blood septicemia with S. pneumoniae , as well as when dosed orally in an antibiotic-induced Clostridioides difficile infection model. MCC5145 exhibited reduced nephrotoxicity at microbiologically active doses in mice compared to vancomycin. MCC5145 also showed improved activity against biofilms compared to vancomycin, both in vitro and in vivo, and a low propensity to select for drug resistance. Characterization of drug action using a transposon library bioinformatic platform showed a mechanistic distinction from other glycopeptide antibiotics.

5-Fluorouracil blocks quorum-sensing of biofilm-embedded methicillin-resistant Staphylococcus aureus in mice

Antibiotic-resistant pathogens often escape antimicrobial treatment by forming protective biofilms in response to quorum-sensing communication via diffusible autoinducers. Biofilm formation by the nosocomial pathogen methicillin-resistant Staphylococcus aureus (MRSA) is triggered by the quorum-sensor autoinducer-2 (AI-2), whose biosynthesis is mediated by methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN) and S-ribosylhomocysteine lyase (LuxS). Here, we present a high-throughput screening platform for small-molecular inhibitors of either enzyme. This platform employs a cell-based assay to report non-toxic, bioavailable and cell-penetrating inhibitors of AI-2 production, utilizing engineered human cells programmed to constitutively secrete AI-2 by tapping into the endogenous methylation cycle via ectopic expression of codon-optimized MTAN and LuxS. Screening of a library of over 5000 commercial compounds yielded 66 hits, including the FDA-licensed cytostatic anti-cancer drug 5-fluorouracil (5-FU). Secondary screening and validation studies showed that 5-FU is a potent quorum-quencher, inhibiting AI-2 production and release by MRSA, Staphylococcus epidermidis, Escherichia coli and Vibrio harveyi. 5-FU efficiently reduced adherence and blocked biofilm formation of MRSA in vitro at an order-of-magnitude-lower concentration than that clinically relevant for anti-cancer therapy. Furthermore, 5-FU reestablished antibiotic susceptibility and enabled daptomycin-mediated prevention and clearance of MRSA infection in a mouse model of human implant-associated infection.

The force awakens: The dark side of mechanosensing in bacterial pathogens

For many bacteria, the ability to sense physical stimuli such as contact with a surface or a potential host cell is vital for survival and proliferation. This ability, and subsequent attachment, confers a wide range of benefits to bacteria and many species have evolved to take advantage of this. Despite the impressive diversity of bacterial pathogens and their virulence factors, mechanosensory mechanisms are often conserved. These include sensing impedance of flagellar rotation and resistance to type IV pili retraction. There are additional mechanisms that rely on the use of specific membrane-bound adhesins to sense either surface proximity or shear forces. This review aims to examine these mechanosensors, and how they are used by pathogenic bacteria to sense physical features in their environment. We will explore how these sensors generate and transmit signals which can trigger modulation of virulence-associated gene expression in some of the most common bacterial pathogens: Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli and Vibrio species.

Memory CD8+ T Cells Balance Pro- and Anti-inflammatory Activity by Reprogramming Cellular Acetate Handling at Sites of Infection

Serum acetate increases upon systemic infection. Acutely, assimilation of acetate expands the capacity of memory CD8⁺ T cells to produce IFN-γ. Whether acetate modulates memory CD8⁺ T cell metabolism and function during pathogen re-encounter remains unexplored. Here we show that at sites of infection, high acetate concentrations are being reached, yet memory CD8⁺ T cells shut down the acetate assimilating enzymes ACSS1 and ACSS2. Acetate, being thus largely excluded from incorporation into cellular metabolic pathways, now had different effects, namely (1) directly activating glutaminase, thereby augmenting glutaminolysis, cellular respiration, and survival, and (2) suppressing TCR-triggered calcium flux, and consequently cell activation and effector cell function. In vivo, high acetate abundance at sites of infection improved pathogen clearance while reducing immunopathology. This indicates that, during different stages of the immune response, the same metabolite-acetate-induces distinct immunometabolic programs within the same cell type.

Expression of a Shiga-Like Toxin during Plastic Colonization by Two Multidrug-Resistant Bacteria, Aeromonas hydrophila RIT668 and Citrobacter freundii RIT669, Isolated from Endangered Turtles (Clemmys guttata)

Aeromonas hydrophila RIT668 and Citrobacter freundii RIT669 were isolated from endangered spotted turtles (Clemmys guttata). Whole-genome sequencing, annotation and phylogenetic analyses of the genomes revealed that the closest relative of RIT668 is A. hydrophila ATCC 7966 and Citrobacter portucalensis A60 for RIT669. Resistome analysis showed that A. hydrophila and C. freundii harbor six and 19 different antibiotic resistance genes, respectively. Both bacteria colonize polyethylene and polypropylene, which are common plastics, found in the environment and are used to fabricate medical devices. The expression of six biofilm-related genes—biofilm peroxide resistance protein (bsmA), biofilm formation regulatory protein subunit R (bssR), biofilm formation regulatory protein subunit S (bssS), biofilm formation regulator (hmsP), toxin-antitoxin biofilm protein (tabA) and transcriptional activator of curli operon (csgD)—and two virulence factors—Vi antigen-related gene (viaB) and Shiga-like toxin (slt-II)—was investigated by RT-PCR. A. hydrophila displayed a > 2-fold increase in slt-II expression in cells adhering to both polymers, C. freundii adhering on polyethylene displayed a > 2-fold, and on polypropylene a > 6-fold upregulation of slt-II. Thus, the two new isolates are potential pathogens owing to their drug resistance, surface colonization and upregulation of a slt-II-type diarrheal toxin on polymer surfaces.

Evolution of Multi-Resistance to Vancomycin, Daptomycin, and Linezolid in Methicillin-Resistant Staphylococcus aureus Causing Persistent Bacteremia

The genomic evolution in vivo in persistent infection was critical information for understanding how methicillin-resistant Staphylococcus aureus (MRSA) was adapted to host environments with high antibiotic selective pressure. Thirty-two successive MRSA blood isolates with incremental non-susceptibility to vancomycin (VISA), daptomycin (DRSA), and/or linezolid (LRSA) were isolated from a patient failing multiple courses of antimicrobial therapy during 1,356 days of bacteremia. Whole genome sequencing (WGS) for all consecutive isolates were conducted to characterize the evolutionary pathways, resistance-associated mutations and their temporal relationship with antimicrobial treatment. The WGS-based phylogeny categorized the isogenic strains into three major clades, I (22 isolates), II (7 isolates), and III (3 isolates), respectively, harboring a median (range) of 7 (1–30), 62 (53–65), and 118 (100–130) non-synonymous mutations when compared to the very first isolate. Clade I strains were further grouped into early and late subclades, which, respectively, shared the most recent common ancestor with Clade III strains at day 393.7 and Clade II strain at day 662.5. Clade I and Clade III strains were characterized, respectively, with high rates of VISA (9/22, 40.9%) and VISA-and-DRSA phenotype (2/3, 66.7%). Linezolid-resistance including VISA-DRSA-and-LRSA phenotype was exclusively identified in Clade II strains after eight courses of linezolid treatment. The LRSA displayed a small colony variant phenotype and were associated with G2576T mutations in domain V region of 23S rRNA. Substantial loss of mobile elements or alleles mediating resistance or virulence were identified during the evolution of multi-resistance. However, the gene loss might not be correlated to the development of VISA, DRSA, or LRSA phenotype. In conclusion, MRSA in persistent bacteremia was adapted to harsh host environment through multiple pathways involving both resistance-associated mutations and extensive gene loss.

Acrylic microparticles increase daptomycin intracellular and in vivo anti-biofilm activity against Staphylococcus aureus

Daptomycin (DAP) is a cyclic lipopeptide antibiotic with potential clinical application in orthopedic infections caused by staphylococci. However, it failed to eradicate Staphylococcus aureus in vitro, in intracellular infection studies, as well as in vivo in an experimental model of implant-associated biofilm infections. In this study, the antimicrobial effect of DAP encapsulated in poly(methyl methacrylate)-Eudragit (PMMA-EUD) microparticles (DAP-MPs) on intracellular S. aureus was evaluated in human osteoblast cells using fluorescence in situ hybridization (FISH) analysis. Encapsulated DAP was able to reduce the amount of intracellular S. aureus by 73% compared to blank microparticles (MPs). Then, the advantage of treating with DAP-MPs versus free DAP was evaluated in a murine model of implant-associated biofilm infection. Free DAP showed a >3 log₁₀ decrease in planktonic and adherent bacteria but failed to eradicate adherent methicillin-resistant S. aureus (MRSA), whereas DAP-MPs showed a clearance of planktonic MRSA, significantly reduced adherent MRSA by more than 3 log₁₀ and cured the infection in 60%. This was linked to the prolonged higher DAP concentration within the tissue cage fluid compared to free DAP. To our knowledge, this study provides the first evidence for the high intracellular and in vivo anti-biofilm efficacy of DAP-MPs to target staphylococcal infections.

Immunomimetic Designer Cells Protect Mice from MRSA Infection

Many community- and hospital-acquired bacterial infections are caused by antibiotic-resistant pathogens. Methicillin-resistant Staphylococcus aureus (MRSA) predisposes humans to invasive infections that are difficult to eradicate. We designed a closed-loop gene network programming mammalian cells to autonomously detect and eliminate bacterial infections. The genetic circuit contains human Toll-like receptors as the bacterial sensor and a synthetic promoter driving reversible and adjustable expression of lysostaphin, a bacteriolytic enzyme highly lethal to S. aureus. Immunomimetic designer cells harboring this genetic circuit exhibited fast and robust sense-and-destroy kinetics against live staphylococci. When tested in a foreign-body infection model in mice, microencapsulated cell implants prevented planktonic MRSA infection and reduced MRSA biofilm formation by 91%. Notably, this system achieved a 100% cure rate of acute MRSA infections, whereas conventional vancomycin treatment failed. These results suggest that immunomimetic designer cells could offer a therapeutic approach for early detection, prevention, and cure of pathogenic infections in the post-antibiotic era.

Video Abstract

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A closed-loop gene network with bacterial sense-and-destroy actuation

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Direct diagnosis of implant-associated infections through blood biomarkers

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Early prevention of MRSA infection, as well as biofilm formation, in vivo

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Curing acute MRSA infections as an alternative to antibiotic therapy

Lipid moieties on lipoproteins of commensal and non-commensal staphylococci induce differential immune responses

Lipoproteins (Lpp) of Gram-positive bacteria are major players in alerting our immune system. Here, we show that the TLR2 response induced by commensal species Staphylococcus aureus and Staphylococcus epidermidis is almost ten times lower than that induced by noncommensal Staphylococcus carnosus, and this is at least partially due to their different modifications of the Lpp lipid moieties. The N terminus of the lipid moiety is acylated with a long-chain fatty acid (C17) in S. aureus and S. epidermidis, while it is acylated with a short-chain fatty acid (C2) in S. carnosus. The long-chain N-acylated Lpp, recognized by TLR2-TLR1 receptors, silences innate and adaptive immune responses, while the short-chain N-acetylated Lpp, recognized by TLR2-TLR6 receptors, boosts it.

A Human Biofilm-Disrupting Monoclonal Antibody Potentiates Antibiotic Efficacy in Rodent Models of both Staphylococcus aureus and Acinetobacter baumannii Infections

Many serious bacterial infections are antibiotic refractory due to biofilm formation. A key structural component of biofilm is extracellular DNA, which is stabilized by bacterial proteins, including those from the DNABII family. TRL1068 is a high-affinity human monoclonal antibody against a DNABII epitope conserved across both Gram-positive and Gram-negative bacterial species. In the present study, the efficacy of TRL1068 for the disruption of biofilm was demonstrated in vitro in the absence of antibiotics by scanning electron microscopy. The in vivo efficacy of this antibody was investigated in a well-characterized catheter-induced aortic valve infective endocarditis model in rats infected with a methicillin-resistant Staphylococcus aureus (MRSA) strain with the ability to form thick biofilms, obtained from the blood of a patient with persistent clinical infection. Animals were treated with vancomycin alone or in combination with TRL1068. MRSA burdens in cardiac vegetations and within intracardiac catheters, kidneys, spleen, and liver showed significant reductions in the combination arm versus vancomycin alone (P < 0.001). A trend toward mortality reduction was also observed (P = 0.09). In parallel, the in vivo efficacy of TRL1068 against a multidrug-resistant clinical Acinetobacter baumannii isolate was explored by using an established mouse model of skin and soft tissue catheter-related biofilm infection. Catheter segments infected with A. baumannii were implanted subcutaneously into mice; animals were treated with imipenem alone or in combination with TRL1068. The combination showed a significant reduction of catheter-adherent bacteria versus the antibiotic alone (P < 0.001). TRL1068 shows excellent promise as an adjunct to standard-of-care antibiotics for a broad range of difficult-to-treat bacterial infections.

New Insight into Daptomycin Bioavailability and Localization in Staphylococcus aureus Biofilms by Dynamic Fluorescence Imaging

Staphylococcus aureus is one of the most frequent pathogens responsible for biofilm-associated infections (BAI), and the choice of antibiotics to treat these infections remains a challenge for the medical community. In particular, daptomycin has been reported to fail against implant-associated S. aureus infections in clinical practice, while its association with rifampin remains a good candidate for BAI treatment. To improve our understanding of such resistance/tolerance toward daptomycin, we took advantage of the dynamic fluorescence imaging tools (time-lapse imaging and fluorescence recovery after photobleaching [FRAP]) to locally and accurately assess the antibiotic diffusion reaction in methicillin-susceptible and methicillin-resistant S. aureus biofilms. To provide a realistic representation of daptomycin action, we optimized an in vitro model built on the basis of our recently published in vivo mouse model of prosthetic vascular graft infections. We demonstrated that at therapeutic concentrations, daptomycin was inefficient in eradicating biofilms, while the matrix was not a shield to antibiotic diffusion and to its interaction with its bacterial target. In the presence of rifampin, daptomycin was still present in the vicinity of the bacterial cells, allowing prevention of the emergence of rifampin-resistant mutants. Conclusions derived from this study strongly suggest that S. aureus biofilm resistance/tolerance toward daptomycin may be more likely to be related to a physiological change involving structural modifications of the membrane, which is a strain-dependent process.

Preventing Implant-Associated Infections by Silver Coating

Implant-associated infections (IAIs) are a dreaded complication mainly caused by biofilm-forming staphylococci. Implant surfaces preventing microbial colonization would be desirable. We examined the preventive effect of a silver-coated titanium-aluminum-niobium (TiAlNb) alloy. The surface elicited a strong, inoculum-dependent activity againstStaphylococcus epidermidisandStaphylococcus aureusin an agar inhibition assay. Gamma sterilization and alcohol disinfection did not alter the effect. In a tissue cage mouse model, silver coating of TiAlNb cages prevented perioperative infections in an inoculum-dependent manner and led to a 100% prevention rate after challenge with 2 × 10(6)CFU ofS. epidermidisper cage. InS. aureusinfections, silver coating had only limited effect. Similarly, daptomycin or vancomycin prophylaxis alone did not preventS. aureusinfections. However, silver coating combined with daptomycin or vancomycin prophylaxis thwarted methicillin-resistantS. aureusinfections at a prevention rate of 100% or 33%, respectively. Moreover, silver release from the surface was independent of infection and occurred rapidly after implantation. On day 2, a peak of 82 μg Ag/ml was reached in the cage fluid, corresponding to almost 6× the MIC of the staphylococci. Cytotoxicity toward leukocytes in the cage was low and temporary. Surrounding tissue did not reveal histological signs of silver toxicity.In vitro, no emergence of silver resistance was observed in several clinical strains of staphylococci upon serial subinhibitory silver exposures. In conclusion, our data demonstrate that silver-coated TiAlNb is potent for prevention of IAIs and thus can be considered for clinical application.

A High-Affinity Native Human Antibody Disrupts Biofilm from Staphylococcus aureus Bacteria and Potentiates Antibiotic Efficacy in a Mouse Implant Infection Model

Many serious bacterial infections are difficult to treat due to biofilm formation, which provides physical protection and induces a sessile phenotype refractory to antibiotic treatment compared to the planktonic state. A key structural component of biofilm is extracellular DNA, which is held in place by secreted bacterial proteins from the DNABII family: integration host factor (IHF) and histone-like (HU) proteins. A native human monoclonal antibody, TRL1068, has been discovered using single B-lymphocyte screening technology. It has low-picomolar affinity against DNABII homologs from important Gram-positive and Gram-negative bacterial pathogens. The disruption of established biofilm was observedin vitroat an antibody concentration of 1.2 μg/ml over 12 h. The effect of TRL1068in vivowas evaluated in a murine tissue cage infection model in which a biofilm is formed by infection with methicillin-resistantStaphylococcus aureus(MRSA; ATCC 43300). Treatment of the established biofilm by combination therapy of TRL1068 (15 mg/kg of body weight, intraperitoneal [i.p.] administration) with daptomycin (50 mg/kg, i.p.) significantly reduced adherent bacterial count compared to that after daptomycin treatment alone, accompanied by significant reduction in planktonic bacterial numbers. The quantification of TRL1068 in sample matrices showed substantial penetration of TRL1068 from serum into the cage interior. TRL1068 is a clinical candidate for combination treatment with standard-of-care antibiotics to overcome the drug-refractory state associated with biofilm formation, with potential utility for a broad spectrum of difficult-to-treat bacterial infections.

A novel point mutation promotes growth phase-dependent daptomycin tolerance in Staphylococcus aureus

Recalcitrance of genetically susceptible bacteria to antibiotic killing is a hallmark of bacterial drug tolerance. This phenomenon is prevalent in biofilms, persisters, and also planktonic cells and is associated with chronic or relapsing infections with pathogens such as Staphylococcus aureus. Here we report the in vitro evolution of an S. aureus strain that exhibits a high degree of nonsusceptibility to daptomycin as a result of cyclic challenges with bactericidal concentrations of the drug. This phenotype was attributed to stationary growth phase-dependent drug tolerance and was clearly distinguished from resistance. The underlying genetic basis was revealed to be an adaptive point mutation in the putative inorganic phosphate (Pi) transporter gene pitA. Drug tolerance caused by this allele, termed pitA6, was abrogated when the upstream gene pitR was inactivated. Enhanced tolerance toward daptomycin, as well as the acyldepsipeptide antibiotic ADEP4 and various combinations of other drugs, was accompanied by elevated intracellular concentrations of Pi and polyphosphate, which may reversibly interfere with critical cellular functions. The evolved strain displayed increased rates of survival within human endothelial cells, demonstrating the correlation of intracellular persistence and drug tolerance. These findings will be useful for further investigations of S. aureus drug tolerance, toward the development of additional antipersister compounds and strategies.

Evaluation of High-Dose Daptomycin Versus Vancomycin Alone or Combined with Clarithromycin or Rifampin Against Staphylococcus aureus and S. epidermidis in a Novel In Vitro PK/PD Model of Bacterial Biofilm

INTRODUCTION

Medical device infections are associated with significant morbidity and mortality. These difficult-to-treat infections often result in antibiotic failure and resistance. Combination therapy is often required, however, the most optimal combination is unknown. We evaluated the in vitro activity of daptomycin (DAP) or vancomycin (VAN) alone and in combination with rifampin (RIF) or clarithromycin (CLA) against strains of Staphylococcus aureus and S. epidermidis grown in biofilm on 3 prosthetic device materials.

METHODS

One methicillin-resistant S. aureus (MRSA R5266), one heteroresistant vancomycin-intermediate S. aureus (hVISA R3640), and one methicillin-resistant S. epidermidis (MRSE R461) strain was evaluated in a CDC biofilm reactor with titanium, Teflon®, and steel coupons. Regimens simulated included DAP 10 mg/kg/day, and VAN 1 g q12h alone or in combination with RIF 600 mg q24h or CLA 250 mg q12h. Additional regimens including DAP 12 mg/kg/day or VAN ± RIF 450 mg q12h were evaluated against the hVISA strain.

RESULTS

DAP + RIF or VAN + RIF demonstrated enhanced activity against R3640 in embedded biofilm (EB) cells in all materials versus DAP or VAN alone (P ≤ 0.040). Only DAP + RIF demonstrated sustained bactericidal activity (≥3.80 log10 CFU/cm2 reduction from baseline) against EB and planktonic cells of R5266 and EB cells of R461 in all 3 materials. Of interest, CLA did not appear to enhance DAP or VAN killing activities, and the addition of RIF prevented the emergence of resistance to DAP or VAN in all organisms.

CONCLUSION

Using an in vitro bacterial biofilm model containing three common prosthetic device materials, DAP + RIF and VAN + RIF were the most effective regimens. DAP + RIF displayed the greatest activity and represents a promising combination to evaluate for treatment of biofilm-associated staphylococcal infections.

Foreign Body Infection Models to Study Host-Pathogen Response and Antimicrobial Tolerance of Bacterial Biofilm

The number of implanted medical devices is steadily increasing and has become an effective intervention improving life quality, but still carries the risk of infection. These infections are mainly caused by biofilm-forming staphylococci that are difficult to treat due to the decreased susceptibility to both antibiotics and host defense mechanisms. To understand the particular pathogenesis and treatment tolerance of implant-associated infection (IAI) animal models that closely resemble human disease are needed. Applications of the tissue cage and catheter abscess foreign body infection models in the mouse will be discussed herein. Both models allow the investigation of biofilm and virulence of various bacterial species and a comprehensive insight into the host response at the same time. They have also been proven to serve as very suitable tools to study the anti-adhesive and anti-infective efficacy of different biomaterial coatings. The tissue cage model can additionally be used to determine pharmacokinetics, efficacy and cytotoxicity of antimicrobial compounds as the tissue cage fluid can be aspirated repeatedly without the need to sacrifice the animal. Moreover, with the advance in innovative imaging systems in rodents, these models may offer new diagnostic measures of infection. In summary, animal foreign body infection models are important tools in the development of new antimicrobials against IAI and can help to elucidate the complex interactions between bacteria, the host immune system, and prosthetic materials.

Comparison of the antibiotic activities of Daptomycin, Vancomycin, and the investigational Fluoroquinolone Delafloxacin against biofilms from Staphylococcus aureus clinical isolates

Biofilm-related infections remain a scourge. In an in vitro model of biofilms using Staphylococcus aureus reference strains, delafloxacin and daptomycin were found to be the most active among the antibiotics from 8 different pharmacological classes (J. Bauer, W. Siala, P. M. Tulkens, and F. Van Bambeke, Antimicrob. Agents Chemother. 57:2726-2737, 2013, doi:10.1128/AAC.00181-13). In this study, we compared delafloxacin to daptomycin and vancomycin using biofilms produced by 7 clinical strains (S. aureus epidemic clones CC5 and CC8) in order to rationalize the differences observed between the antibiotics and strains. The effects of the antibiotics on bacterial viability (resazurin reduction assay) and biomass (crystal violet staining) were measured and correlated with the proportion of polysaccharides in the matrix, the local microenvironmental pH (micro-pH), and the antibiotic penetration in the biofilm. At clinically meaningful concentrations, delafloxacin, daptomycin, and vancomycin caused a ≥25% reduction in viability against the biofilms formed by 5, 4, and 3 strains, respectively. The antibiotic penetration within the biofilms ranged from 0.6 to 52% for delafloxacin, 0.2 to 10% for daptomycin, and 0.2 to 1% for vancomycin; for delafloxacin, this was inversely related to the polysaccharide proportion in the matrix. Six biofilms were acidic, explaining the high potency of delafloxacin (lower MICs at acidic pH). Norspermidine and norspermine (disassembling the biofilm matrix) drastically increased delafloxacin potency and efficacy (50% reduction in viability for 6 biofilms at clinically meaningful concentrations) in direct correlation with its increased penetration within the biofilm, while they only modestly improved daptomycin efficacy (50% reduction in viability for 2 biofilms) and penetration, and they showed marginal effects with vancomycin. Delafloxacin potency and efficacy against biofilms are benefited by its penetration into the matrix and the local acidic micro-pH.

Effect of brominated furanones on the formation of biofilm by Escherichia coli on polyvinyl chloride materials

To study the influence of brominated furanones on the biofilm (BF) formation by Escherichia coli (E. coli) on polyvinyl chloride (PVC) material, and to provide new ways of surface modification of materials to clinically prevent biomaterial centered infection. Three brominated furanones, dissolved in ethanol, furanone-1(3,4-dibromo-5-hydroxyl-furanone), furanone-2(4-bromo-5-(4-methoxypheny)-3-(methylamino)-furanone), and furanone-3(3,4-dibromo-5,5-dimethoxypheny-2(5H)-furanone) with representative chemical structure, were coated on the surfaces of separate PVC materials (1 × 1 cm), respectively. The surface-modified PVC materials were incubated with E. coli and for controls, 75 % ethanol-treated PVC materials were used. This treatment played as control group. The cultivation incubations were for 6, 12, 18, and 24 h. The thickness of bacterial BF and bacterial community quantity unit area on the PVC materials was determined by confocal laser scanning microscopy (CLSM), and the surface structure of bacterial BF formation was examined by scanning electron microscopy (SEM). The results of CLSM indicated the thickness of bacterial BF and bacterial community quantity unit area on PVC materials treated with furanone-3 were significantly lower than that of control at all time points (P < 0.05), whereas, the differences between furanone-1 and furanone-2 groups and control group were not significantly different (P > 0.05). The results of SEM indicated that after 6 h incubation, the quantity of bacterial attachment to the surface of PVC material treated with furanone-3 was lower than the control group. By 18 h incubation there was completely formed BF structure on the surface of control PVC material. However, there was no significant BF formation on the surface of PVC material treated with furanone-3. The impact of different brominated furanones on SA biofilm formation on the surface of PVC materials are different, furanone-3 can inhibit E. coli biofilm formation on the surface of PVC material.

Bacteria-surface interactions

The interaction of bacteria with surfaces has important implications in a range of areas, including bioenergy, biofouling, biofilm formation, and the infection of plants and animals. Many of the interactions of bacteria with surfaces produce changes in the expression of genes that influence cell morphology and behavior, including genes essential for motility and surface attachment. Despite the attention that these phenotypes have garnered, the bacterial systems used for sensing and responding to surfaces are still not well understood. An understanding of these mechanisms will guide the development of new classes of materials that inhibit and promote cell growth, and complement studies of the physiology of bacteria in contact with surfaces. Recent studies from a range of fields in science and engineering are poised to guide future investigations in this area. This review summarizes recent studies on bacteria-surface interactions, discusses mechanisms of surface sensing and consequences of cell attachment, provides an overview of surfaces that have been used in bacterial studies, and highlights unanswered questions in this field.

Staphylococcus aureus in the house fly: temporospatial fate of bacteria and expression of the antimicrobial peptide defensin

House flies disseminate numerous species of bacteria acquired during feeding and breeding activities in microbe-rich habitats. Previous house fly surveys have detected the pathogen Staphylococcus aureus Rosenbach 1884, which causes cutaneous and septic infections in mammals, and enterotoxic food poisoning. We assessed the fate of GFP-expressing S. aureus (GFP-S. aureus) in the house fly alimentary canal with microscopy and by culture of whole flies and excreta. Furthermore, the concurrent expression of the antimicrobial peptide gene defensin was measured in the crop, proventriculus, midgut, and fat body. As soon as 4 h postingestion (PI), GFP-S. aureus were visualized as cocci or diplococci in the hindgut and rectum of flies fed approximately equal 10(5) colony forming units. Bacteria persisted up to 6 h PI but significantly decreased. Excretion of viable GFP-S. aureus peaked at 2 h PI and, although significantly less, continued up to 4 h PI. defensin was highly upregulated locally in the alimentary canal and systemically in fat body at 2, 4, and 6 h PI making this study the first to report, to our knowledge, an epithelial and systemic response to a bacterium with lysine-type peptidoglycan in flies exposed via feeding. While flies harbored S. aureus for up to 6 h PI, the highest probability of vectoring biologically relevant amounts of bacteria occurred 0-2 h PI. The combined effects of excretion, digestion and antimicrobial effectors likely contribute to loss of ingested bacteria. Nonetheless, house flies are relevant vectors for S. aureus up to 2 h PI and environmental reservoirs up to 6 h PI.

Antimicrobial properties of 8-hydroxyserrulat-14-en-19-oic acid for treatment of implant-associated infections

Treatment options are limited for implant-associated infections (IAI) that are mainly caused by biofilm-forming staphylococci. We report here on the activity of the serrulatane compound 8-hydroxyserrulat-14-en-19-oic acid (EN4), a diterpene isolated from the Australian plant Eremophila neglecta. EN4 elicited antimicrobial activity toward various Gram-positive bacteria but not to Gram-negative bacteria. It showed a similar bactericidal effect against logarithmic-phase, stationary-phase, and adherent Staphylococcus epidermidis, as well as against methicillin-susceptible and methicillin-resistant S. aureus with MICs of 25 to 50 μg/ml and MBCs of 50 to 100 μg/ml. The bactericidal activity of EN4 was similar against S. epidermidis and its Δica mutant, which is unable to produce polysaccharide intercellular adhesin-mediated biofilm. In time-kill studies, EN4 exhibited a rapid and concentration-dependent killing of staphylococci, reducing bacterial counts by >3 log(10) CFU/ml within 5 min at concentrations of >50 μg/ml. Investigation of the mode of action of EN4 revealed membranolytic properties and a general inhibition of macromolecular biosynthesis, suggesting a multitarget activity. In vitro-tested cytotoxicity on eukaryotic cells was time and concentration dependent in the range of the MBCs. EN4 was then tested in a mouse tissue cage model, where it showed neither bactericidal nor cytotoxic effects, indicating an inhibition of its activity. Inhibition assays revealed that this was caused by interactions with albumin. Overall, these findings suggest that, upon structural changes, EN4 might be a promising pharmacophore for the development of new antimicrobials to treat IAI.

Extensive in vivo resilience of persistent Salmonella

Chronic infections caused by persistent pathogens represent an important health problem. Here, we establish a simple practical mouse Salmonella infection model for identifying bacterial maintenance functions that are essential for persistency. In this model, a substantial fraction of Salmonella survived even several days of treatment with a potent fluoroquinolone antibiotic indicating stringency of the model. Evaluation of twelve metabolic defects revealed dramatically different requirements for Salmonella during persistency as compared to acute infections. Disrupted synthesis of unsaturated/cyclopropane fatty acids was the only defect that resulted in rapid Salmonella clearance suggesting that this pathway might contain suitable targets for antimicrobial chemotherapy of chronic infection.

Inhibition of biofilm formation by esomeprazole in Pseudomonas aeruginosa and Staphylococcus aureus

Staphylococcus aureus and Pseudomonas aeruginosa are common nosocomial pathogens responsible for biofilm-associated infections. Proton pump inhibitors (PPI), such as esomeprazole, may have novel antimicrobial properties. The objective of this study was to assess whether esomeprazole prevents sessile bacterial growth and biofilm formation and whether it may have synergistic killing effects with standard antibiotics. The antibiofilm activity of esomeprazole at 0.25 mM was tested against two strains each of S. aureus and P. aeruginosa. Bacterial biofilms were prepared using a commercially available 96-peg-plate Calgary biofilm device. Sessile bacterial CFU counts and biomass were assessed during 72 hours of esomeprazole exposure. The killing activities after an additional 24 hours of vancomycin (against S. aureus) and meropenem (against P. aeruginosa) treatment with or without preexposure to esomeprazole were also assessed by CFU and biomass analyses. P. aeruginosa and S. aureus strains exposed to esomeprazole displayed decreased sessile bacterial growth and biomass (P < 0.001, each parameter). After 72 h of exposure, there was a 1-log(10) decrease in the CFU/ml of esomeprazole-exposed P. aeruginosa and S. aureus strains compared to controls (P < 0.001). After 72 h of exposure, measured absorbance was 100% greater in P. aeruginosa control strains than in esomeprazole-exposed strains (P < 0.001). Increased killing and decreased biomass were observed for esomeprazole-treated bacteria compared to untreated controls exposed to conventional antibiotics (P < 0.001, each parameter). Reduced biofilm growth after 24 h was visibly apparent by light micrographs for P. aeruginosa and S. aureus isolates exposed to esomeprazole compared to untreated controls. In conclusion, esomeprazole demonstrated an antibiofilm effect against biofilm-producing S. aureus and P. aeruginosa.

Daptomycin and tigecycline have broader effective dose ranges than vancomycin as prophylaxis against a Staphylococcus aureus surgical implant infection in mice

Vancomycin is widely used for intravenous prophylaxis against surgical implant infections. However, it is unclear whether alternative antibiotics used to treat methicillin-resistant Staphylococcus aureus (MRSA) infections are effective as prophylactic agents. The aim of this study was to compare the efficacies of vancomycin, daptomycin, and tigecycline as prophylactic therapy against a methicillin-sensitive S. aureus (MSSA) or MRSA surgical implant infection in mice. MSSA or MRSA was inoculated into the knee joints of mice in the presence of a surgically placed medical-grade metallic implant. The efficacies of low- versus high-dose vancomycin (10 versus 110 mg/kg), daptomycin (1 versus 10 mg/kg), and tigecycline (1 versus 10 mg/kg) intravenous prophylaxis were compared using in vivo bioluminescence imaging, ex vivo bacterial counts, and biofilm formation. High-dose vancomycin, daptomycin, and tigecycline resulted in similar reductions in bacterial burden and biofilm formation. In contrast, low-dose daptomycin and tigecycline were more effective than low-dose vancomycin against the implant infection. In this mouse model of surgical implant MSSA or MRSA infection, daptomycin and tigecycline prophylaxis were effective over a broader dosage range than vancomycin. Future studies in humans will be required to determine whether these broader effective dose ranges for daptomycin and tigecycline in mice translate to improved efficacy in preventing surgical implant infections in clinical practice.

Impact of extracellular nuclease production on the biofilm phenotype of Staphylococcus aureus under in vitro and in vivo conditions

Recent studies suggest that extracellular DNA promotes biofilm formation in Staphylococcus aureus and, conversely, that extracellular nucleases limit the ability to form a biofilm. S. aureus produces at least two extracellular nucleases, and in the study described in this report, we examined the impact of each of these nucleases on biofilm formation under both in vitro and in vivo conditions. Our results demonstrate that both nucleases impact biofilm formation in the clinical isolate UAMS-1. Under certain in vitro conditions, this impact is negative, with mutation of either or both of the nuclease genes (nuc1 and nuc2) resulting in an enhanced capacity to form a biofilm. However, this effect was not apparent in vivo in a murine model of catheter-associated biofilm formation. Rather, mutation of either or both nuclease genes appeared to limit biofilm formation to a degree that could be correlated with increased susceptibility to daptomycin.