Antibiotic resistance: is the end of an era near?

High Prevalence of blaOXA-48 and blaNDM-Producing Carbapenem-Resistant Klebsiella pneumoniae Isolated from Clinical Samples in Shahid Rajaei Hospital in Tehran, Iran

Background: Due to the increasing antibiotic resistance, treating infections caused by Klebsiella pneumoniae has become more challenging. Objectives: The present study aimed to investigate the prevalence of blaOXA-48 and blaNDM producing carbapenem-resistant K. pneumoniae isolated from clinical samples in Shahid Rajaei hospital in Tehran, Iran. Methods: Various clinical samples were collected from 1,186 patients admitted with open heart surgery in two wards (ICU and surgery) in Shahid Rajaei Heart Hospital in Tehran, Iran. Klebsiella pneumoniae isolates were identified by standard microbiologic tests. Antimicrobial susceptibility of isolates were determined by disk diffusion and E-test methods. A modified carbapenem inactivation method (mCIM) was performed to detect the presence of carbapenemase. Antibiotic resistance genes were detected using conventional polymerase chain reaction (PCR) by primers targeting blaOXA-48, blaSPM, blaIMP, blaVIM, and blaNDM genes. Results: A total of 131 clinical isolates of K. pneumoniae were isolated and 45.8% (60/131) of them were resistant to carbapenem. Klebsiella pneumoniae isolates showed the highest resistance rate (100%) to ceftriaxone, ceftazidime, cefazolin, and cefepime and the maximum sensitivity to tigecycline (96.7%). The carbapenemase-encoding blaOXA-48 and blaNDM-1 genes were detected in 96.7% and 66.7% of isolates, respectively. Eight different clusters of the isolates, considering a ≥ 80% homology cut-off, were shown with the same rep-PCR pattern. Clusters A, B, C, D, E, F, G, and H included 20, 11, 7, 6, 6, 3, 2, and 2 members, respectively. Conclusions: The RAPD-PCR method reveals the clonal relationship between isolates and may help improve infection control procedures.

Phototherapy and optical waveguides for the treatment of infection

With rapid emergence of multi-drug resistant microbes, it is imperative to seek alternative means for infection control. Optical waveguides are an auspicious delivery method for precise administration of phototherapy. Studies have shown that phototherapy is promising in fighting against a myriad of infectious pathogens (i.e. viruses, bacteria, fungi, and protozoa) including biofilm-forming species and drug-resistant strains while evading treatment resistance. When administered via optical waveguides, phototherapy can treat both superficial and deep-tissue infections while minimizing off-site effects that afflict conventional phototherapy and pharmacotherapy. Despite great therapeutic potential, exact mechanisms, materials, and fabrication designs to optimize this promising treatment option are underexplored. This review outlines principles and applications of phototherapy and optical waveguides for infection control. Research advances, challenges, and outlook regarding this delivery system are rigorously discussed in a hope to inspire future developments of optical waveguide-mediated phototherapy for the management of infection and beyond.

Inactivation of carbapenem-resistant Klebsiella pneumoniae by photo-Fenton: Residual effect, gene evolution and modifications with citric acid and persulfate

The photo-Fenton process application to eliminate carbapenem-resistant Klebsiella pneumoniae, an antibiotic-resistant priority pathogen, was evaluated. Initially, reagents concentration effect was tested and under suitable conditions (5 mg L^-1 of Fe²⁺ and 50 mg L^-1 of H₂O₂) complete bacteria inactivation by action of hydroxyl radical and UVA plus hydrogen peroxide was achieved at 120 min. The process presented a strong residual disinfecting effect when light was turned off at only 20 min. Besides, the cultivability of treated K. pneumoniae in a selective medium containing carbapenem antibiotics was considered. bla-KPC, gene responsible for the resistance, evolution was also assessed. The bacteria response to carbapenem antibiotics was higher as the treatment time increased. In turn, bla-KPC gene remained when K. pneumoniae was completely inactivated (120 min); nevertheless, treatment times longer than 120 min diminished bla-KPC presence. Finally, the photo-Fenton process and its modifications (citric acid addition or persulfate anion instead hydrogen peroxide) were applied to a real hospital wastewater in Colombia. In such complex matrix, the conventional photo-Fenton system reached a moderate disinfection (∼3.5 log-units at 300 min). Meanwhile, in presence of citric acid total inactivation was completed at the same time. Interestingly, the H₂O₂ substitution by persulfate strongly accelerated the microorganism elimination, achieving the 6-log-units reduction after only 60 min of process action. Thus, the effective elimination of K. pneumoniae from water by the modified photo-Fenton evidenced the potential applicability of this process to limit the proliferation of antibiotic resistant bacteria.

Comparative Pharmacokinetics and Preliminary Pharmacodynamics Evaluation of Piscidin 1 Against PRV and PEDV in Rats

Antimicrobial peptide (Piscidin-1) is an effective natural polypeptide, which has great influence and potential on porcine epidemic diarrhea virus (PEDV) and pseudorabies virus (PRV). As an alternative antibiotic substitute, Piscidin-1 was subjected for pharmacokinetics study with three administration routes (i.v, i.m, and p.o) after a single dose of 2 mg/kg in rats and preliminary pharmacodynamics including antiviral activity in cell against PEDV and PRV. Based on 50 percent tissue culture infective dose (TCID₅₀), there were about 2 and 10% virus survived ratios for Piscidin-1 against PRV and PEDV, respectively. The plaque test showed 1 and 2 μg/ml Piscidin-1 could eliminate 95% PRV and 85% PEDV, respectively. The main pharmacokinetics parameters of C_max, AUC_0−∞, Ke, t_1/2, T_max, MRT, and Cl_b in plasma were not applicable value, 25.9 μg^*h/ml, 0.041 h⁻¹, 16.97 h, not available value, 22.77 h, 0.067 L/h^*kg after i.v administration, 2.37 μg/ml, 18.95 μg^*h/ml, 0.029 h⁻¹, 23.50 h, 0.33 h, 30.12 h, 0.095 L/h^*kg after i.m administration and 0.73 μg/ml, 9.63 μg^*h/ml, 0.036 h⁻¹, 19.46 h, 0.50 h, 26.76 h, 0.171 L/h^*kg after p.o administration. The bioavailability values after i.m and p.o administrations were calculated as 73.17 and 37.18%, respectively. The i.m administration was selected for pharmacokinetics study in ileum content against PEDV. The main pharmacokinetic parameters of C_max, AUC_0−∞, Ke, t_1/2, T_max, MRT, and Cl_b in ileum content were 1.67 μg/ml, 78.40 μg^*h/ml, 0.034 h⁻¹, 20.16 h, 8.12 h, 36.45 h, 0.026 L/h^*kg. The C_max values in plasma (2.37 μg/ml) and ileum content (1.67 μg/ml) were higher than the effective inhibitory concentration determined in the plaque test, and this indicates that Piscidin-1 might have effective inhibition effect against PRV and PEDV after administration of 2 mg/kg i.m. The results of this study represent the first investigations toward the pharmacokinetic characteristics of piscidin-1 in plasma upon three different administration routes, among which i.m. resulted in the highest bioavailability (73.17%). Furthermore, the pharmacokinetics study of ileum content indicated Piscidin-1 might have good effect against PEDV and could be regarded as an alternative antibiotic in clinical veterinary in the future study.

Highly effective photodynamic inactivation of E. coli using gold nanorods/SiO2 core-shell nanostructures with embedded verteporfin

The potential of gold nanorods post-coated with a 20 nm silica shell loaded with verteporfin (Au NRs@SiO2-VP) as efficient near-infrared nanostructures for photodynamic therapy under continuous wave and pulsed-mode excitation to eradicate a virulent strain of E. coli associated with urinary tract infection is described.

Role of phenylalanine and valine10 residues in the antimicrobial activity and cytotoxicity of piscidin-1

Piscidin-1 (Pis-1) is a linear antibacterial peptide derived from mast cells of aquacultured hybrid striped bass that comprises 22 amino acids with a phenylalanine-rich amino-terminus. Pis-1 exhibits potent antibacterial activity against pathogens but is not selective for distinguishing between bacterial and mammalian cells. To determine the key residues for its antibacterial activity and those for its cytotoxicity, we investigated the role of each Phe residue near the N-terminus as well as the Val¹⁰ residue located near the boundary of the hydrophobic and hydrophilic sectors of the helical wheel diagram. Fluorescence dye leakage and tryptophan fluorescence experiments were used to study peptide-lipid interactions, showing comparable depths of insertion of substituted peptides in different membranes. Phe² was found to be the most deeply inserted phenylalanine in both bacterial- and mammalian-mimic membranes. Each Phe was substituted with Ala or Lys to investigate its functional role. Phe² plays key roles in the cytotoxicity as well as the antibacterial activities of Pis-1, and Phe⁶ is essential for the antibacterial activities of Pis-1. We also designed and synthesized a piscidin analog, Pis-V10K, in which Lys was substituted for Val¹⁰, resulting in an elevated amphipathic α-helical structure. Pis-V10K showed similar antibacterial activity (average minimum inhibitory concentration (MIC)  = 1.6 µM) to Pis-1 (average MIC  = 1.5 µM). However, it exhibited much lower cytotoxicity than Pis-1. Lys¹⁰-substituted analogs, Pis-F1K/V10K, Pis-F2K/V10K, and Pis-F6K/V10K in which Lys was substituted for Phe retained antibacterial activity toward standard and drug-resistant bacterial strains with novel bacterial cell selectivity. They exert anti-inflammatory activities via inhibition of nitric oxide production, TNF-α secretion, and MIP-1 and MIP-2 production. They may disrupt the binding of LPS to toll-like receptors, eventually suppressing MAPKs-mediated signaling pathways. These peptides may be good candidates for the development of peptide antibiotics with potent antibacterial activity but without cytotoxicity.

Polymethylmethacrylate doped with porphyrin and silver nanoparticles as light-activated antimicrobial material

Light-activated antimicrobial materials based on polymethylmethactylate doped with porphyrin and silver nanoparticles were prepared and studied.

Light based anti-infectives: ultraviolet C irradiation, photodynamic therapy, blue light, and beyond

Owing to the worldwide increase in antibiotic resistance, researchers are investigating alternative anti-infective strategies to which it is supposed microorganisms will be unable to develop resistance. Prominent among these strategies, is a group of approaches which rely on light to deliver the killing blow. As is well known, ultraviolet light, particularly UVC (200-280 nm), is germicidal, but it has not been much developed as an anti-infective approach until recently, when it was realized that the possible adverse effects to host tissue were relatively minor compared to its high activity in killing pathogens. Photodynamic therapy is the combination of non-toxic photosensitizing dyes with harmless visible light that together produce abundant destructive reactive oxygen species (ROS). Certain cationic dyes or photosensitizers have good specificity for binding to microbial cells while sparing host mammalian cells and can be used for treating many localized infections, both superficial and even deep-seated by using fiber optic delivered light. Many microbial cells are highly sensitive to killing by blue light (400-470 nm) due to accumulation of naturally occurring photosensitizers such as porphyrins and flavins. Near infrared light has also been shown to have antimicrobial effects against certain species. Clinical applications of these technologies include skin, dental, wound, stomach, nasal, toenail and other infections which are amenable to effective light delivery.

Antimicrobial photodynamic therapy with decacationic monoadducts and bisadducts of [70]fullerene: in vitro and in vivo studies

BACKGROUND

Antimicrobial photodynamic therapy uses photosensitizers designed to bind to microorganisms and generate reactive oxygen species when illuminated with visible light.

MATERIALS & METHODS

We synthesized a highly water-soluble [70]fullerene monoadduct, C70[>M(C3N6(+)C3)2]-(I(-))10 (LC17), and bisadduct, C70[>M(C3N6(+)C3)2][>M(C3N6C3)2] (LC18), both with a well-defined decacationic quaternary ammonium iodide moiety with ten positive charges per C70 to give water solubility and bacterial binding. We determined the antimicrobial effects against human pathogens, Gram-positive (Staphylococcus aureus) and Gram-negative species (Escherichia coli and Acinetobacter baumannii) when activated by UVA or white light.

RESULTS

White light was more effective with LC17, while UVA light was more effective with LC18. Both compounds were effective in a mouse model of Gram-negative third-degree burn infections determined by bioluminescence imaging.

DISCUSSION & CONCLUSION

We propose that the attachment of an additional deca(tertiary-ethylenylamino)malonate arm to C70 allowed the moiety to act as a potent electron donor and increased the generation yield of hydroxyl radicals under UVA illumination.

Denis TG, Xuan Y, Huang YY, Tanaka M, Zadlo A, Sarna T, Hamblin MR. Paradoxical potentiation of methylene blue-mediated antimicrobial photodynamic inactivation by sodium azide: role of ambient oxygen and azide radicals

Sodium azide (NaN(3)) is widely employed to quench singlet oxygen during photodynamic therapy (PDT), especially when PDT is used to kill bacteria in suspension. We observed that addition of NaN(3) (100 μM or 10 mM) to gram-positive Staphylococcus aureus and gram-negative Escherichia coli incubated with methylene blue (MB) and illuminated with red light gave significantly increased bacterial killing (1-3 logs), rather than the expected protection from killing. A different antibacterial photosensitizer, the conjugate between polyethylenimine and chlorin(e6) (PEI-ce6), showed reduced PDT killing (1-2 logs) after addition of 10mM NaN(3). Azide (0.5mM) potentiated bacterial killing by Fenton reagent (hydrogen peroxide and ferrous sulfate) by up to 3 logs, but protected against killing mediated by sodium hypochlorite and hydrogen peroxide (considered to be a chemical source of singlet oxygen). The intermediacy of N(3)() was confirmed by spin-trapping and electron spin resonance studies in both MB-photosensitized reactions and Fenton reagent with addition of NaN(3). We found that N(3)() was formed and bacteria were killed even in the absence of oxygen, suggesting the direct one-electron oxidation of azide anion by photoexcited MB. This observation suggests a possible mechanism to carry out oxygen-independent PDT.

Type I and Type II mechanisms of antimicrobial photodynamic therapy: an in vitro study on gram-negative and gram-positive bacteria

BACKGROUND AND OBJECTIVES

Antimicrobial photodynamic therapy (APDT) employs a non-toxic photosensitizer (PS) and visible light, which in the presence of oxygen produce reactive oxygen species (ROS), such as singlet oxygen ((1) O(2), produced via Type II mechanism) and hydroxyl radical (HO(.), produced via Type I mechanism). This study examined the relative contributions of (1) O(2) and HO(.) to APDT killing of Gram-positive and Gram-negative bacteria.

STUDY DESIGN/MATERIALS AND METHODS

Fluorescence probes, 3'-(p-hydroxyphenyl)-fluorescein (HPF) and singlet oxygen sensor green reagent (SOSG) were used to determine HO(.) and (1) O(2) produced by illumination of two PS: tris-cationic-buckminsterfullerene (BB6) and a conjugate between polyethylenimine and chlorin(e6) (PEI-ce6). Dimethylthiourea is a HO(.) scavenger, while sodium azide (NaN(3)) is a quencher of (1) O(2). Both APDT and killing by Fenton reaction (chemical generation of HO(.)) were carried out on Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Proteus mirabilis, and Pseudomonas aeruginosa).

RESULTS

Conjugate PEI-ce6 mainly produced (1) O(2) (quenched by NaN(3)), while BB6 produced HO(.) in addition to (1) O(2) when NaN(3) potentiated probe activation. NaN(3) also potentiated HPF activation by Fenton reagent. All bacteria were killed by Fenton reagent but Gram-positive bacteria needed a higher concentration than Gram-negatives. NaN(3) potentiated Fenton-mediated killing of all bacteria. The ratio of APDT killing between Gram-positive and Gram-negative bacteria was 2 or 4:1 for BB6 and 25:1 for conjugate PEI-ce6. There was a NaN(3) dose-dependent inhibition of APDT killing using both PEI-ce6 and BB6 against Gram-negative bacteria while NaN(3) almost failed to inhibit killing of Gram-positive bacteria.

CONCLUSION

Azidyl radicals may be formed from NaN(3) and HO(.). It may be that Gram-negative bacteria are more susceptible to HO(.) while Gram-positive bacteria are more susceptible to (1) O(2). The differences in NaN(3) inhibition may reflect differences in the extent of PS binding to bacteria (microenvironment) or differences in penetration of NaN(3) into cell walls of bacteria.

Ultraviolet C irradiation: an alternative antimicrobial approach to localized infections?

This review discusses the potential of ultraviolet C (UVC) irradiation as an alternative approach to current methods used to treat localized infections. It has been reported that multidrug-resistant microorganisms are equally sensitive to UVC irradiation as their wild-type counterparts. With appropriate doses, UVC may selectively inactivate microorganisms while preserving viability of mammalian cells and, moreover, is reported to promote wound healing. UVC is also found in animal studies to be less damaging to tissue than UVB. Even though UVC may produce DNA damage in mammalian cells, it can be rapidly repaired by DNA repair enzymes. If UVC irradiation is repeated excessively, resistance of microorganisms to UVC inactivation may develop. In summary, UVC should be investigated as an alternative approach to current methods used to treat localized infections, especially those caused by multidrug-resistant microorganisms. UVC should be used in a manner such that the side effects would be minimized and resistance of microorganisms to UVC would be avoided.

Photodynamic inactivation of bacteria using polyethylenimine-chlorin(e6) conjugates: Effect of polymer molecular weight, substitution ratio of chlorin(e6) and pH

BACKGROUND AND OBJECTIVES

Antimicrobial photodynamic therapy (APDT) is a novel technique to treat local infections. Previously we reported that the attachment of chlorin(e6) to polyethylenimine (PEI) polymers to form PEI-ce6 conjugates is an effective way to improve ce6 PDT activity against bacteria. The aim of this work was to explore how the polymer molecular weight, substitution ratio (SR) of ce6 and pH value affect the PDT efficacy.

STUDY DESIGN/MATERIALS AND METHODS

We have synthesized PEI-ce6(10) (MW = 60,000, SR = 1) and PEI-ce6(11) (MW = 60,000, SR = 5) and compared these with the previous PEI-ce6(9) (MW = 10,000, SR = 1). We tested the PDT efficacy of these three conjugates against Gram-negative E. coli and Gram-positive bacteria (S. aureus and E. fecalis) at three different pH values (5.0, 7.4, 10.0) that may affect the charge on both the bacterial cells and on the conjugate (that has both basic and acidic groups).

RESULTS

PEI-ce6(9) and PEI-ce6(10) were the most effective against these tested bacteria. The PDT effect of all three conjugates depended on pH values. The effective order was pH = 10.0 > pH = 7.4 > pH = 5.0 on E. coli. For S. aureus and E. fecalis the order was pH = 5.0 > pH = 10.0 > pH = 7.4. PEI-ce6(11) PDT activity was worse than PEI-ce6(10) activity which is probably connected to the fact that ce6 molecules are self-quenched within the PEI-ce6(11) molecule. Ce6 quenching within the PEI-ce6 molecules was proved by analyzing fluorescence spectra of PEI-ce6 conjugates at different pH values. There were no differences in bacterial uptake between different pH values in three PEI-ce6 conjugates.

CONCLUSION

We assume high pH (rather than low pH as was hypothesized) disaggregates the conjugates, so the higher pH was more effective than the lower pH against E. coli. But for Gram-positive bacteria, low pH was more effective possibly due to more overall positive charge on the conjugate.

Stable synthetic cationic bacteriochlorins as selective antimicrobial photosensitizers

Photodynamic inactivation is a rapidly developing antimicrobial treatment that employs a nontoxic photoactivatable dye or photosensitizer in combination with harmless visible light to generate reactive oxygen species that are toxic to cells. Tetrapyrroles (e.g., porphyrins, chlorins, bacteriochlorins) are a class of photosensitizers that exhibit promising characteristics to serve as broad-spectrum antimicrobials. In order to bind to and efficiently penetrate into all classes of microbial cells, tetrapyrroles should have structures that contain (i) one or more cationic charge(s) or (ii) a basic group. In this report, we investigate the use of new stable synthetic bacteriochlorins that have a strong absorption band in the range 720 to 740 nm, which is in the near-infrared spectral region. Four bacteriochlorins with 2, 4, or 6 quaternized ammonium groups or 2 basic amine groups were compared for light-mediated killing against a gram-positive bacterium (Staphylococcus aureus), a gram-negative bacterium (Escherichia coli), and a dimorphic fungal yeast (Candida albicans). Selectivity was assessed by determining phototoxicity against human HeLa cancer cells under the same conditions. All four compounds were highly active (6 logs of killing at 1 microM or less) against S. aureus and showed selectivity for bacteria over human cells. Increasing the cationic charge increased activity against E. coli. Only the compound with basic groups was highly active against C. albicans. Supporting photochemical and theoretical characterization studies indicate that (i) the four bacteriochlorins have comparable photophysical features in homogeneous solution and (ii) the anticipated redox characteristics do not correlate with cell-killing ability. These results support the interpretation that the disparate biological activities observed stem from cellular binding and localization effects rather than intrinsic electronic properties. These findings further establish cationic bacteriochlorins as extremely active and selective near-infrared activated antimicrobial photosensitizers, and the results provide fundamental information on structure-activity relationships for antimicrobial photosensitizers.

Photodynamic therapy for localized infections--state of the art

Photodynamic therapy (PDT) was discovered over 100 years ago by observing the killing of microorganisms when harmless dyes and visible light were combined in vitro. Since then it has primarily been developed as a treatment for cancer, ophthalmologic disorders and in dermatology. However, in recent years interest in the antimicrobial effects of PDT has revived and it has been proposed as a therapy for a large variety of localized infections. This revival of interest has largely been driven by the inexorable increase in drug resistance among many classes of pathogen. Advantages of PDT include equal killing effectiveness regardless of antibiotic resistance, and a lack of induction of PDT resistance. Disadvantages include the cessation of the antimicrobial effect when the light is turned off, and less than perfect selectivity for microbial cells over host tissue. This review will cover the use of PDT to kill or inactivate pathogens in ex vivo tissues and in biological materials such as blood. PDT has been successfully used to kill pathogens and even to save life in several animal models of localized infections such as surface wounds, burns, oral sites, abscesses and the middle ear. A large number of clinical studies of PDT for viral papillomatosis lesions and for acne refer to its antimicrobial effect, but it is unclear how important this microbial killing is to the overall therapeutic outcome. PDT for periodontitis is a rapidly growing clinical application and other dental applications are under investigation. PDT is being clinically studied for other dermatological infections such as leishmaniasis and mycobacteria. Antimicrobial PDT will become more important in the future as antibiotic resistance is only expected to continue to increase.