Rationale for use of antimicrobial combinations

Antimicrobial Drug-Drug Interactions in the Treatment of Infectious Keratitis

PURPOSE

Infectious keratitis is a serious disease requiring immediate, intensive, and broad-spectrum empiric treatment to prevent vision loss. Given the diversity of organisms that can cause serious corneal disease, current guidelines recommend treatment with several antimicrobial agents simultaneously to provide adequate coverage while awaiting results of microbiology cultures. However, it is currently unknown how the use of multiple ophthalmic antimicrobial agents in combination may affect the efficacy of individual drugs.

METHODS

Using a panel of 9 ophthalmic antibiotics, 3 antifungal agents, and 2 antiacanthamoeba therapeutics, fractional inhibitory concentration testing in the standard checkerboard format was used to study 36 antibiotic-antibiotic combinations, 27 antibiotic-antifungal combinations, and 18 antibiotic-antiacanthamoeba combinations against both Staphylococcus aureus and Pseudomonas aeruginosa for synergistic, additive, neutral, or antagonistic drug-drug interactions.

RESULTS

We demonstrate that while most combinations resulted in no change in antimicrobial efficacy of individual components, the combination of erythromycin + polyhexamethylene biguanide was found to be antagonistic toward P. aeruginosa . Conversely, 18 combinations toward S. aureus and 15 combinations toward P. aeruginosa resulted in additive or synergistic activity, including 4 with improved activity toward both species.

CONCLUSIONS

Understanding how drug-drug interactions may affect drug efficacy is critical to selecting the appropriate combination therapy and improving clinical outcomes of this blinding disease.

CpxA/R-Controlled Nitroreductase Expression as Target for Combinatorial Therapy against Uropathogens by Promoting Reactive Oxygen Species Generation

The antibiotic resistances emerged in uropathogens lead to accumulative treatment failure and recurrent episodes of urinary tract infection (UTI), necessitating more innovative therapeutics to curb UTI before systematic infection. In the current study, the combination of amikacin and nitrofurantoin is found to synergistically eradicate Gram-negative uropathogens in vitro and in vivo. The mechanistic analysis demonstrates that the amikacin, as an aminoglycoside, induced bacterial envelope stress by introducing mistranslated proteins, thereby constitutively activating the cpxA/R two-component system (Cpx signaling). The activation of Cpx signaling stimulates the expression of bacterial major nitroreductases (nfsA/nfsB) through soxS/marA regulons. As a result, the CpxA/R-dependent nitroreductases overexpression generates considerable quantity of lethal reactive intermediates via nitroreduction and promotes the prodrug activation of nitrofurantoin. As such, these actions together disrupt the bacterial cellular redox balance with excessively-produced reactive oxygen species (ROS) as "Domino effect", accelerating the clearance of uropathogens. Although aminoglycosides are used as proof-of-principle to elucidate the mechanism, the synergy between nitrofurantoin is generally applicable to other Cpx stimuli. To summarize, this study highlights the potential of aminoglycoside-nitrofurantoin combination to replenish the arsenal against recurrent Gram-negative uropathogens and shed light on the Cpx signaling-controlled nitroreductase as a potential target to manipulate the antibiotic susceptibility.

MicroRNA therapeutics and nucleic acid nano-delivery systems in bacterial infection: a review

Bacteria that have worked with humans for thousands of years pose a major threat to human health even today, as drug resistance has become a prominent problem. Compared to conventional drug therapy, nucleic acid-based therapies are a promising and potential therapeutic strategy for diseases in which nucleic acids are delivered through a nucleic acid delivery system to regulate gene expression in specific cells, offering the possibility of curing intractable diseases that are difficult to treat at this stage. Among the many nucleic acid therapeutic ideas, microRNA, a class of small nucleic acids with special properties, has made great strides in biology and medicine in just over two decades, showing promise in preclinical drug development. In this review, we introduce recent advances in nucleic acid delivery systems and their clinical applications, highlighting the potential of nucleic acid therapies, especially miRNAs extracted from traditional herbs, in combination with the existing set of nucleic acid therapeutic systems, to potentially open up a new line of thought in the treatment of cancer, viruses, and especially bacterial infectious diseases.

The antimicrobial efficacy of copper, cobalt, zinc and silver nanoparticles: alone and in combination

With the advent of nanotechnology, there has been an extensive interest in the antimicrobial potential of metals. The rapid and widespread development of antimicrobial-resistant and multidrug-resistant bacteria has prompted recent research into developing novel or alternative antimicrobial agents. In this study, the antimicrobial efficacy of metallic copper, cobalt, silver and zinc nanoparticles was assessed againstEscherichia coli(NCTC 10538),S. aureus(ATCC 6538) along with three clinical isolates ofStaphylococcus epidermidis(A37, A57 and A91) and three clinical isolates ofE. coli(Strains 1, 2 and 3) recovered from bone marrow transplant patients and patients with cystitis respectively. Antimicrobial sensitivity assays, including agar diffusion and broth macro-dilution to determine minimum inhibitory and bactericidal concentrations (MIC/MBC) and time-kill/synergy assays, were used to assess the antimicrobial efficacy of the agents. The panel of test microorganisms, including antibiotic-resistant strains, demonstrated a broad range of sensitivity to the metals investigated. MICs of the type culture strains were in the range of 0.625-5.0 mg ml^-1. While copper and cobalt exhibited no difference in sensitivity between Gram-positive and Gram-negative microorganisms, silver and zinc showed strain specificity. A significant decrease (p< 0.001) in the bacterial density ofE. coliandS. aureuswas demonstrated by silver, copper and zinc in as little as two hours. Furthermore, combining metal nanoparticles reduced the time required to achieve a complete kill.

Antibiotic Adjuvants: A Versatile Approach to Combat Antibiotic Resistance

The problem of antibiotic resistance is on the rise, with multidrug-resistant strains emerging even to the last resort antibiotics. The drug discovery process is often stalled by stringent cut-offs required for effective drug design. In such a scenario, it is prudent to delve into the varying mechanisms of resistance to existing antibiotics and target them to improve antibiotic efficacy. Nonantibiotic compounds called antibiotic adjuvants which target bacterial resistance can be used in combination with obsolete drugs for an improved therapeutic regime. The field of "antibiotic adjuvants" has gained significant traction in recent years where mechanisms other than β-lactamase inhibition have been explored. This review discusses the multitude of acquired and inherent resistance mechanisms employed by bacteria to resist antibiotic action. The major focus of this review is how to target these resistance mechanisms by the use of antibiotic adjuvants. Different types of direct acting and indirect resistance breakers are discussed including enzyme inhibitors, efflux pump inhibitors, inhibitors of teichoic acid synthesis, and other cellular processes. The multifaceted class of membrane-targeting compounds with poly pharmacological effects and the potential of host immune-modulating compounds have also been reviewed. We conclude with providing insights about the existing challenges preventing clinical translation of different classes of adjuvants, especially membrane-perturbing compounds, and a framework about the possible directions which can be pursued to fill this gap. Antibiotic-adjuvant combinatorial therapy indeed has immense potential to be used as an upcoming orthogonal strategy to conventional antibiotic discovery.

Molecular Detection of Tetracycline-Resistant Genes in Multi-Drug-Resistant Escherichia coli Isolated from Broiler Meat in Bangladesh

This study aimed to estimate the antimicrobial resistance (AMR) patterns and tetracycline-resistant gene profiles of Escherichia coli (E. coli) from broiler meat and livers sourced from live bird markets (LBMs) and supermarkets (SMs) in Chattogram, Bangladesh. In total, 405 samples were collected from SMs and LBMs, comprising muscle (n = 215) and liver (n = 190) samples. Disc diffusion tests were used to determine antimicrobial susceptibility profiles. PCR was used to identify E. coli and tetracycline-resistant genes. Over half (57%) of the chicken product samples were positive for E. coli. The AMR profiling of these isolates showed that the highest prevalence of resistance was against sulphamethoxazole-trimethoprim (89%), followed by tetracycline (87%), ampicillin (83%), and ciprofloxacin (61%). Among the antimicrobials listed by the World Health Organization as critically important, E. coli isolates were found to be resistant to cephalexin (37%), gentamicin (32%), and colistin sulfate (21%). A large proportion of E. coli demonstrated multi-drug resistance (MDR). Most (84%) of the tetracycline-resistant isolates encoded tetA. Of the remaining isolates, 0.5% encoded tetC, 6.0% encoded two genes, and 3.6% of isolates were tetD, which was newly identified by this study in Bangladesh. Broiler products in Bangladesh are frequently contaminated with multi-drug-resistant E. coli, with differential carriage of tetracycline genes. The prevalence of tetracycline resistance among E. coli indicates a concern for poultry health and welfare regarding the management of colibacillosis. It also indicates growing public health risks of AMR among broiler-associated pathogens, which can be transferred to humans via the food chain. Appropriate control measures should be developed and implemented, focused on the rational use of antimicrobials in poultry farming systems, to mitigate risk from this drug-resistant zoonotic pathogen from foods of animal origin and to protect public health.

In Vitro Assessment of the Combination of Antibiotics against Some Integron-Harbouring Enterobacteriaceae from Environmental Sources

One strategy for combating antimicrobial resistance in many infections is to combine antibacterial compounds to create combinations that outperform each molecule alone. In this study, we examine and study the inhibitory effect of combining two drugs belonging to different antibiotic classes to obtain a possible potentiating effect against some Enterobacteriaceae isolates harbouring integrons recovered from rivers and effluents of hospital and wastewater treatment plants in Eastern Cape Province, South Africa. These integrons could easily enable the isolates to acquire genes that confer additional resistance against conventional antibiotics. The minimum inhibitory concentration of the various antibiotics was determined using the broth microdilution, while the checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs). A total of 26.3% (10/38) of the interactions were categorised as synergistic, while 73.7% (28/38) were indifferent. None of the combinations were antagonistic. The time–kill assays revealed all the synergistic interactions as bactericidal. Therefore, the combinations of gentamicin with tetracycline, ciprofloxacin, and ceftazidime against multidrug-resistant (MDR) Klebsiella pneumoniae, tetracycline–ceftazidime combination against MDR Escherichia coli, colistin combinations with ceftazidime and gentamicin, and tetracycline–gentamicin combinations against MDR Citrobacter freundii may be future therapeutic alternatives. Hence, the synergistic combinations reported in this study must be assessed further in vivo before their clinical applications.

Bacterial Toxin-Triggered Release of Antibiotics from Capsosomes Protects a Fly Model from Lethal Methicillin-Resistant Staphylococcus aureus (MRSA) Infection

Antibiotic resistance is a severe global health threat and hence demands rapid action to develop novel therapies, including microscale drug delivery systems. Herein, a hierarchical microparticle system is developed to achieve bacteria-activated single- and dual-antibiotic drug delivery for preventing methicillin-resistant Staphylococcus aureus (MRSA) bacterial infections. The designed system is based on a capsosome structure, which consists of a mesoporous silica microparticle coated in alternating layers of oppositely charged polymers and antibiotic-loaded liposomes. The capsosomes are engineered and shown to release their drug payloads in the presence of MRSA toxins controlled by the Agr quorum sensing system. MRSA-activated single drug delivery of vancomycin and synergistic dual delivery of vancomycin together with an antibacterial peptide successfully kills MRSA in vitro. The capability of capsosomes to selectively deliver their cargo in the presence of bacteria, producing a bactericidal effect to protect the host organism, is confirmed in vivo using a Drosophila melanogaster MRSA infection model. Thus, the capsosomes serve as a versatile multidrug, subcompartmentalized microparticle system for preventing antibiotic-resistant bacterial infections, with potential applications to protect wounds or medical device implants from infections.

Synergistic Antimicrobial Metal Oxide-Doped Phosphate Glasses; a Potential Strategy to Reduce Antimicrobial Resistance and Host Cell Toxicity

The emergence of antimicrobial resistant strains bacteria and a decline in the discovery of new antibiotics has led to the idea of combining various antimicrobials to treat resistant strains and/or polymicrobial infections. Metal oxide-doped glasses have been extensively investigated for their antimicrobial potential; however to date, most experiments have focused on single metal species in isolation. The present study investigates the antimicrobial potential of sodium calcium phosphates (P₂O₅)₅₀(Na₂O)₂₀(CaO)_30-X(MO)_X, where M is cobalt, copper, or zinc as single species. In addition, this work studied the effect of co-doping glasses containing two different metal ions (Co + Cu, Co + Zn, and Cu + Zn). The antimicrobial efficacy of all glasses was tested against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacterial strains, as well as a fungal strain (Candida albicans). Minimum inhibitory and bactericidal concentrations and time kill/synergy assays were used to assess the antimicrobial activity. An enhanced antimicrobial effect, at 5 mg/mL concentration, was exhibited by cobalt, copper, and zinc oxide glasses alone and in combinations. A synergistic antimicrobial effect was observed by Cu + Co and Cu + Zn against E. coli and Cu + Zn against S. aureus.

Effects of drinking water supplementation with Lactobacillus reuteri, and a mixture of reuterin and microcin J25 on the growth performance, caecal microbiota and selected metabolites of broiler chickens

Background

Since the overuse of antibiotics in animal production has led to a selection of antibiotic-resistant pathogens that affect humans and animals as well. Scientists are therefore searching for novel natural alternatives to antibiotics. In this study Lactobacillus reuteri and a combination of reuterin and microcin J25 (RJ) were evaluated as promoters of growth and modulators of the cecal microbiota and metabolite profiles in broiler chickens. One-day-old Cobb 500 male broilers were distributed to 8 treatments: negative control (without antibiotic), positive control (bacitracin), three concentrations of RJ and three doses of L. reuteri plus glycerol. The birds (2176, 34 per pen, 8 pens per treatment) were reared for 35 d.

Results

The body weight of the bacitracin and 5 mmol/L reuterin combined with 0.08 μmol/L microcin J25 (10RJ) treatment group was significantly higher than that of the negative control group (P < 0.05). L. reuteri had no significant effect on broiler growth. MiSeq high-throughput sequencing of 16S rRNA showed clustering of cecal microbial operational taxonomic unit diversity according to treatment. The influence of bacitracin and 10RJ on bacterial community overall structure was similar. They promoted Ruminococcaceae, Lachnospiraceae and Lactobacillaceae, increased the relative abundance of Faecalibacterium and decreased the abundance of Bacteroides and Alistipes, while the negative control condition favored Bacteroidaceae and Rikenellaceae. Furthermore, 10RJ increased the concentration of short-chain fatty acid in the cecum and changed the metabolome overall.

Conclusions

These overall suggest that 10RJ can promote a host-friendly gut environment by changing the cecal microbiome and metabolome. This combination of natural antimicrobial agents in the drinking water had a positive effect on broiler growth and may be suitable as an alternative to antibiotic growth promoters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00683-6.

Ceragenins and Antimicrobial Peptides Kill Bacteria through Distinct Mechanisms

Ceragenins are a family of synthetic amphipathic molecules designed to mimic the properties of naturally occurring cationic antimicrobial peptides (CAMPs). Although ceragenins have potent antimicrobial activity, whether their mode of action is similar to that of CAMPs has remained elusive. Here, we reported the results of a comparative study of the bacterial responses to two well-studied CAMPs, LL37 and colistin, and two ceragenins with related structures, CSA13 and CSA131. Using transcriptomic and proteomic analyses, we found that Escherichia coli responded similarly to both CAMPs and ceragenins by inducing a Cpx envelope stress response. However, whereas E. coli exposed to CAMPs increased expression of genes involved in colanic acid biosynthesis, bacteria exposed to ceragenins specifically modulated functions related to phosphate transport, indicating distinct mechanisms of action between these two classes of molecules. Although traditional genetic approaches failed to identify genes that confer high-level resistance to ceragenins, using a Clustered Regularly Interspaced Short Palindromic Repeats interference (CRISPRi) approach we identified E. coli essential genes that when knocked down modify sensitivity to these molecules. Comparison of the essential gene-antibiotic interactions for each of the CAMPs and ceragenins identified both overlapping and distinct dependencies for their antimicrobial activities. Overall, this study indicated that, while some bacterial responses to ceragenins overlap those induced by naturally occurring CAMPs, these synthetic molecules target the bacterial envelope using a distinctive mode of action. IMPORTANCE The development of novel antibiotics is essential because the current arsenal of antimicrobials will soon be ineffective due to the widespread occurrence of antibiotic resistance. The development of naturally occurring cationic antimicrobial peptides (CAMPs) for therapeutics to combat antibiotic resistance has been hampered by high production costs and protease sensitivity, among other factors. The ceragenins are a family of synthetic CAMP mimics that kill a broad spectrum of bacterial species but are less expensive to produce, resistant to proteolytic degradation, and seemingly resistant to the development of high-level resistance. Determining how ceragenins function may identify new essential biological pathways of bacteria that are less prone to the development of resistance and will further our understanding of the design principles for maximizing the effects of synthetic CAMPs.

Antibiotic resistance in agriculture: Perspectives on upcoming strategies to overcome upsurge in resistance

Antibiotic resistance is a massive problem rising constantly and spreading rapidly since the past decade. The major underlying mechanism responsible for this problem is an overuse or severe misuse of antibiotics. Regardless of this emerging global threat, antibiotics are still being widely used, not only for treatment of human infections, but also to a great extent in agriculture, livestock and animal husbandry. If the current scenario persists, we might enter into a post-antibiotic era where drugs might not be able to treat even the simplest of infections. This review discusses the current status of antibiotic utilization and molecular basis of antibiotic resistance mechanisms acquired by bacteria, along with the modes of transmittance of the resultant resistant genes into human pathogens through their cycling among different ecosystems. The main focus of the article is to provide an insight into the different molecular and other strategies currently being studied worldwide for their use as an alternate to antibiotics with an overall aim to overcome or minimize the global problem of antibiotic resistance.

Venturicidin A, A Membrane-active Natural Product Inhibitor of ATP synthase Potentiates Aminoglycoside Antibiotics

Despite the remarkable advances due to the discovery and development of antimicrobials agents, infectious diseases remain the second leading cause of death worldwide. This fact underlines the importance of developing new therapeutic strategies to address the widespread antibiotic resistance, which is the major contributing factor for clinical failures of the current therapeutics. In a screen for antibiotic adjuvants, we identified a natural product from actinomycetes, venturicidin A (VentA), that potentiates the aminoglycoside antibiotic gentamicin against multidrug-resistant clinical isolates of Staphylococcus, Enterococcus, and Pseudomonas aeruginosa. Furthermore, the combination of gentamicin and VentA was bactericidal and rapidly eradicated methicillin-resistant S. aureus (MRSA). The molecular mechanism of gentamicin potentiation activity is attributed to uncoupling of ATP synthesis by VentA from electron transport presumably by blocking the proton flow through ATP synthase, which results in an elevated concentration of extracellular protons and subsequent anticipated raise in gentamicin uptake. The disruption of the proton flux was characterized by perturbed membrane potential in MRSA. These results demonstrate that inhibition of ATP synthase along with the subsequent membrane dysregulation, as shown here with VentA, complements aminoglycoside antibiotics against MDR bacteria, and that this approach may be employed to combat bacterial resistance.

Understanding effect of interaction of nanoparticles and antibiotics on bacteria survival under aquatic conditions: Knowns and unknowns

The review provides a comprehensive overview of the available state-of-the-art of nanoparticles (NPs) and antibiotics (ABs) occurrence and their fate in the natural aquatic settings by addressing different research questions and the challenges faced while addressing those questions. Firstly, understand the interaction of NPs and ABs with themselves in addition to other matrix components (presence of natural organic matter, bacteria, biofilms, other anthropogenic pollutants and metals from natural sources). Secondly, summarize the bactericidal activity of NP and AB due to reactive oxygen species (ROS) production. The complete information was gathered from database and analysed as per the conjectured questions under laboratory versus environmental-relevant conditions (1. Fate of NPs and ABs, and 2. Will the presence of NPs and ABs alone and their mixtures influence the ROS concentration and antibacterial activity), and proposed six reactions to describe the fate of NP and AB in natural aquatic settings. However, laboratory-based studies revealed that NP and AB fate largely depend on the ionic strength, organic matter content and pH of the matrix whereas field based information is missing about this. The former was performed at sterile conditions using sophisticated instruments and standard protocol as compared to latter and can't be replicated under natural aquatic settings due to lack of: (i) accurate environmental concentration of NPs and ABs, (ii) knowledge of bacterial type and their concentration, (iii) optimized protocol and tracking systems. The author's recommendation is to verify the proposed reactions experimentally by using the frequently found pairs of NPs and ABs in the natural aquatic settings. Further, ranked them on their decreasing order of toxicity and informed regulatory bodies for further action. Overall research is needed in the suggested directions to reduce uncertainty behind the impacts of NPs and ABs on the aquatic settings and their role in bactericidal activity.

Mimicking in-vivo exposures to drug combinations in-vitro: anti-tuberculosis drugs in lung lesions and the hollow fiber model of infection

Here, we evaluate protocol requirements to mimic therapeutically relevant drug concentrations at the site of infection (i.e. lung lesion) in an in-vitro hollow fibre model of infection using pulmonary tuberculosis as a paradigm. Steady-state pharmacokinetic profiles in plasma, lung tissue and lung lesion homogenate were simulated for isoniazid, rifampicin and pyrazinamide and moxifloxacin. An R-shiny User Interface was developed to support conversion of in-vivo pharmacokinetic C_MAX, T_MAX and T_1/2 estimates into pump settings. A monotherapy protocol mimicking isoniazid in lung lesion homogenate (isoniazid C_MAX = 1,200 ng/ml, T_MAX = 2.2 hr and T_1/2 = 4.7 hr), and two combination therapy protocols including drugs with similar (isoniazid and rifampicin (C_MAX = 400 ng/ml)) and different half-lives (isoniazid and pyrazinamide (C_MAX = 28,900 ng/ml and T_1/2 = 8.0 hr)) were implemented in a hollow-fiber system. Drug levels in the perfusate were analysed using ultra-high-performance liquid chromatographic-tandem mass spectrometric detection. Steady state pharmacokinetic profiles measured in the hollow fiber model were similar to the predicted in-vivo steady-state lung lesion homogenate pharmacokinetic profiles. The presented approach offers the possibility to use pharmacological data to study the effect of target tissue exposure for drug combinations. Integration with pharmacokinetics modelling principles through a web interface will provide access to a wider community interested in the evaluation of efficacy of anti-tubercular drugs.

Drug combinations: a strategy to extend the life of antibiotics in the 21st century

Antimicrobial resistance threatens a resurgence of life-threatening bacterial infections and the potential demise of many aspects of modern medicine. Despite intensive drug discovery efforts, no new classes of antibiotics have been developed into new medicines for decades, in large part owing to the stringent chemical, biological and pharmacological requisites for effective antibiotic drugs. Combinations of antibiotics and of antibiotics with non-antibiotic activity-enhancing compounds offer a productive strategy to address the widespread emergence of antibiotic-resistant strains. In this Review, we outline a theoretical and practical framework for the development of effective antibiotic combinations.

Efficacy of a 14-day quadruple-therapy regimen for third-line Helicobacter pylori eradication

PURPOSE

To assess the efficacy of amoxicillin, tetracycline, high-dose metronidazole, and a proton-pump inhibitor for third-line Helicobacter pylori eradication.

METHODS

We enrolled 70 consecutive patients who had registered, failed to respond to two rounds of H. pylori eradication, and undergone endoscopy for H. pylori culture. Seven patients were lost to follow-up. Patients were treated according to the results of antibiotic-susceptibility testing reports (cultured group, n=39). Those who failed the H. pylori culture were prescribed 14-day quadruple therapy containing esomeprazole 40 mg twice daily, amoxicillin 1 g twice daily, tetracycline 500 mg four times daily, and metronidazole 500 mg three times daily (empirical group, n=24). A follow-up urea breath test was performed 8 weeks later.

RESULTS

Antibiotic-resistance rates were 79.5% (clarithromycin), 94.9% (levofloxacin), 66.7% (metronidazole), 2.6% (amoxicillin), and 0 (tetracycline). Eradication rates attained by the cultured and empirical group were 89.7% (95% CI 72.7%-97.1%) and 58.3% (95% CI 36.6%-77.9%) in per-protocol analysis (P=0.004) and 81.4% (95% CI 66.6%-91.6%) and 51.8% (95% CI 31.9%-71.3%) in intention-to-treat analysis (P=0.014), respectively. Culture-guided therapy was the only clinical factor influencing the efficacy of H. pylori eradication (OR 0.16, 95% CI 0.04-0.60; P=0.006). Despite the high metronidazole-resistance rate (66.7%) after two treatment failures, the eradication rate in patients with this condition was 84%.

CONCLUSION

Empirical 14-day modified quadruple therapy is not acceptable as an alternative third-line rescue H. pylori treatment. The success rate of third-line susceptibility-guided treatment was near 90%. This report is valuable as a reminder to medical practitioners that rather than a try-and-see approach, susceptibility-guided therapy should always be considered whenever possible for patients who have undergone several treatment failures.

Inhibition of Bacterial Growth by Peptide-Conjugated Morpholino Oligomers

Morpholino oligomers (MOs) are antisense molecules designed for sequence-specific binding of target mRNA. In bacteria, inhibition is hypothesized to occur by preventing translation initiation. Cell-penetrating peptides may be conjugated to the 5'- or 3'-termini of an MO to enhance cellular entry and therefore inhibition. Here we describe the three standard microbiological assays to assess in vitro antibacterial MO efficacy.

Daptomycin in combination with other antibiotics for the treatment of complicated methicillin-resistant Staphylococcus aureus bacteremia

PURPOSE

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as one of the most important nosocomial pathogens. Resistance to antibiotic therapy has been known to emerge especially in clinically complex scenarios, resulting in challenges in determining optimal treatment of serious MRSA. Daptomycin, in combination with other antibiotics, has been successfully used in the treatment of these infections, with the aims of resulting in reducing the prevention of antimicrobial resistance and increased killing compared with daptomycin monotherapy.

METHODS

This article reviews all the published studies that used daptomycin combination therapy for the treatment of bacteremia and associated complicated infections caused by gram-positive organisms, including MRSA. We discuss the rationale of combination antibiotics and the mechanisms that enhance the activity of daptomycin, with special focus on the role of β-lactam antibiotics.

FINDINGS

There are limited clinical data on the use of daptomycin in combination with other antibiotics. Most of this use was as successful salvage therapy in the setting of failing primary, secondary, or tertiary therapy and/or relapsing infection. Synergy between β-lactams and daptomycin is associated with several characteristics, including increased daptomycin binding and β-lactam-mediated potentiation of innate immunity, but the precise molecular mechanism is unknown.

IMPLICATIONS

Use of daptomycin in combination with other antibiotics, especially β-lactams, offers a promising treatment option for complicated MRSA bacteremia in which emergence of resistance during treatment may be anticipated. Because it is currently not possible to differentiate complicated from uncomplicated bacteremia at the time of presentation, combination therapy may be considered as first-line therapy, with de-escalation to monotherapy in uncomplicated cases and cases with stable pharmacologic and surgical source control.

Something old, something new: revisiting natural products in antibiotic drug discovery

Antibiotic discovery is in crisis. Despite a growing need for new drugs resulting from the increasing number of multi-antibiotic-resistant pathogens, there have been only a handful of new antibiotics approved for clinical use in the past 2 decades. Faced with scientific, economic, and regulatory challenges, the pharmaceutical sector seems unable to respond to what has been called an “apocalyptic” threat. Natural products produced by bacteria and fungi are genetically encoded products of natural selection that have been the mainstay sources of the antibiotics in current clinical use. The pharmaceutical industry has largely abandoned these compounds in favor of large libraries of synthetic molecules because of difficulties in identifying new natural product antibiotics scaffolds. Advances in next-generation genome sequencing, bioinformatics, and analytical chemistry are combining to overcome barriers to natural products. Coupled with new strategies in antibiotic discovery, including inhibition of resistance, novel drug combinations, and new targets, natural products are poised for a renaissance to address what is a pressing health care crisis.

Randomized comparison of two non-bismuth-containing second-line rescue therapies for Helicobacter pylori

BACKGROUND

 Classical second-line anti-Helicobacter pylori includes proton-pump inhibitor, tetracycline, metronidazole, and bismuth salts, but alternative therapies are required owing to the restricted availability of the latter. Levofloxacin-containing triple therapy is recommended but is expensive. Besides, quinolone resistance in an endemic tuberculosis infection area like Taiwan is concerned. The low in vitro antibiotic resistance to amoxicillin and tetracycline in Taiwanese H. pylori strains implies that in vivo esomeprazole/amoxicillin/tetracycline (EAT) second-line rescue therapy may be effective. This study compared the efficacy of esomeprazole/amoxicillin/levofloxacin (EAL) and EAT second-line eradication therapies and determines the clinical factors influencing the efficacy of salvage regimens.

MATERIALS AND METHODS

One hundred and twenty-eight patients who failed H. pylori eradication using the standard triple therapy for 7 days are randomly assigned to either EAL group (esomeprazole 40 mg twice daily, amoxicillin 1 g twice daily, and levofloxacin 500 mg once daily) for 7 days or EAT group (esomeprazole 40 mg twice daily, amoxicillin 1 g twice daily, tetracycline 500 mg four times daily) for 14 days. Follow-up endoscopy or urea breath test was performed 8 weeks later to assess treatment response.

RESULTS

The eradication rates of EAL and EAT groups were 78.1 versus 75.0%, p = .676 (in intention-to-treat analysis) and 80.3 versus 80%, p = .0964 (per-protocol analysis). Both groups exhibited similar drug compliance (95.3 vs 96.9%, p = .952) but more adverse events in the EAT group (6.3 vs 12.5%, p = .225).

CONCLUSIONS

Despite low in vitro drug resistances to amoxicillin and tetracycline, the efficacy of 14-day EAT regimens attained an unacceptable report card of 75% eradication rates in intention-to-treat analysis and was not even superior to the 7-day EAL regimen. Drug-drug interaction between combined antibiotics should be considered other than in vivo drug resistances.

Discovering new antimicrobial agents

Although there has been a relentless increase in resistance to antimicrobial agents amongst important bacterial pathogens throughout the world, it is well known that the number of new antimicrobial agents being brought to the market has undergone a steady decline in the past several decades. There are a number of reasons for this, which are detailed in this article, but there is also a great deal of continuing research to find new effective antimicrobials, much of it now being carried out in academic centres and especially in small biotechnology companies, rather than by large pharma. Whilst classic screening methods and chemical modification of known antimicrobial agents continue to produce potential leads for new antimicrobial agents, a number of other approaches are being investigated. These include the search for potentiators of the activity of known antimicrobial agents and the development of hybrid agents, novel membrane-active drugs, and inhibitors of bacterial virulence and pathogenesis. A number of new bacterial targets are also being exploited, as are bacteriophages and their lytic enzymes. Given the amount of investigation presently underway, it is clear that although the antibiotic pipeline is not as promising as it was half a century ago, it is far from dry.

In vitro activity of ceftaroline alone and in combination against clinical isolates of resistant gram-negative pathogens, including beta-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa

Ceftaroline is a novel broad-spectrum cephalosporin that exhibits bactericidal activity against many gram-positive and -negative pathogens. However, the activity of ceftaroline cannot be solely relied upon for eradication of multidrug-resistant gram-negative isolates, such as Pseudomonas aeruginosa and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, which represent a current clinical concern. As drug combinations might be beneficial by potential synergy, we evaluated the in vitro activity of ceftaroline combined with meropenem, aztreonam, cefepime, tazobactam, amikacin, levofloxacin, and tigecycline. Susceptibility testing was performed for 20 clinical P. aeruginosa isolates, 10 ESBL-producing Escherichia coli isolates, 10 ESBL-producing Klebsiella pneumoniae isolates, and 10 AmpC-derepressed Enterobacter cloacae isolates. Time-kill experiments were performed for 10 isolates using antimicrobials at one-fourth the MIC. Ceftaroline exhibited a MIC range of 0.125 to 1,024 microg/ml and was reduced 2- to 512-fold by combination with tazobactam (4 microg/ml) for ESBL-producing strains. In time-kill experiments, ceftaroline plus amikacin was synergistic against 90% of the isolates (and indifferent for one P. aeruginosa isolate). Ceftaroline plus tazobactam was indifferent for E. cloacae and P. aeruginosa strains but synergistic against 100% of E. coli and K. pneumoniae isolates. Combinations of ceftaroline plus meropenem or aztreonam were also synergistic for all E. coli and E. cloacae isolates, respectively, but indifferent against 90% of the other isolates. Finally, combinations of ceftaroline plus either tigecycline, levofloxacin, or cefepime were indifferent for 100% of the isolates. No antagonism was observed with any combination. Ceftaroline plus amikacin appeared as the most likely synergistic combination. This represents a promising therapeutic option, and further studies are warranted to elucidate the clinical value of ceftaroline combinations against resistant gram-negative pathogens.

Antimicrobial use and bacterial resistance in neonatal patients

The neonatal population is at extremely high risk for developing infections. Because of the premature infant's prolonged length of stay, these patients may receive several courses of antibiotics while hospitalized. Although the number of antibiotics used in this population is limited, the dosing regimens must be carefully prescribed and adjusted to account for changing pharmacokinetic parameters. In addition, the development of antimicrobial resistance should always be a concern. The neonatal nurse can help ensure antimicrobial regimens are given appropriately and monitor these regimens for efficacy and toxicity.

Genetic diversity among Enterococcus faecalis

Enterococcus faecalis, a ubiquitous member of mammalian gastrointestinal flora, is a leading cause of nosocomial infections and a growing public health concern. The enterococci responsible for these infections are often resistant to multiple antibiotics and have become notorious for their ability to acquire and disseminate antibiotic resistances. In the current study, we examined genetic relationships among 106 strains of E. faecalis isolated over the past 100 years, including strains identified for their diversity and used historically for serotyping, strains that have been adapted for laboratory use, and isolates from previously described E. faecalis infection outbreaks. This collection also includes isolates first characterized as having novel plasmids, virulence traits, antibiotic resistances, and pathogenicity island (PAI) components. We evaluated variation in factors contributing to pathogenicity, including toxin production, antibiotic resistance, polymorphism in the capsule (cps) operon, pathogenicity island (PAI) gene content, and other accessory factors. This information was correlated with multi-locus sequence typing (MLST) data, which was used to define genetic lineages. Our findings show that virulence and antibiotic resistance traits can be found within many diverse lineages of E. faecalis. However, lineages have emerged that have caused infection outbreaks globally, in which several new antibiotic resistances have entered the species, and in which virulence traits have converged. Comparing genomic hybridization profiles, using a microarray, of strains identified by MLST as spanning the diversity of the species, allowed us to identify the core E. faecalis genome as consisting of an estimated 2057 unique genes.

Overview of infectious diseases, Part 2

The choice of drug therapy in the treatment of infectious disease depends on many factors, including the probable sensitivity of likely pathogens and previous efficacy of the agent. Pharmacokinetic factors are crucial since good in vitro results cannot predict in vivo success unless the drug is present in effective concentration at the infection site. Combination therapy can be used in certain situations to improve the chances of clinical success. Part 3 of this series will conclude the discussion of drug therapy. The general manifestations of and recovery process from infectious diseases will also be discussed.

Have the new beta-lactams rendered the aminoglycosides obsolete for the treatment of serious nosocomial infections?

Hospital-acquired infections are often due to multi-resistant gram-negative bacilli. When treating these infections, the physician must use potent antibiotics that have broad spectrums of activity. Aminoglycosidic aminocyclitols and the newer beta-lactam antibiotics are particularly valuable in the management of hospital-acquired infections. This article discusses the role of both classes of antibiotics in this setting.

Antimicrobial combinations in the therapy of infections due to gram-negative bacilli

Antimicrobial combinations are used most frequently to provide broad-spectrum coverage; however, they are also frequently employed to enhance antimicrobial activity (synergism). Although there is extensive in vitro documentation of synergism for many antibiotic combinations, a clear advantage for these combinations has been difficult to demonstrate in clinical studies. Several types of combinations have been useful in clinical medicine and frequently result in synergism. These include combinations of a cell wall-active agent with an aminoglycosidic aminocyclitol, combinations of a beta-lactamase inhibitor with a beta-lactam, and combinations of agents that inhibit sequential steps in a metabolic pathway. Given its spectrum of activity, aztreonam will often be used with clindamycin or a beta-lactam antibiotic. Combinations of beta-lactams may be synergistic via several mechanisms. However, these combinations also exhibit significant potential for antagonism when used against gram-negative bacilli and, therefore, require careful evaluation prior to clinical use.