In vitro antibacterial effects of statins against bacterial pathogens causing skin infections

With financial considerations impeding research and development of new antibiotics, drug repurposing (finding new indications for old drugs) emerges as a feasible alternative. Statins are extensively prescribed around the world to lower cholesterol, but they also possess inherent antimicrobial properties. This study identifies statins with the greatest potential to be repurposed as topical antibiotics and postulates a mechanism of action for statins’ antibacterial activity. Using broth microdilution, the direct antibacterial effects of all seven parent statins currently registered for human use and three selected statin metabolites were tested against bacterial skin pathogens Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Serratia marcescens. Simvastatin and pitavastatin lactone exerted the greatest antibacterial effects (minimum inhibitory concentrations of 64 and 128 μg/mL, respectively) against S. aureus. None of the statins tested were effective against E. coli, P. aeruginosa, or S. marcescens, but simvastatin hydroxy acid acid might be active against S. aureus, E. coli, and S. marcescens at drug concentrations >?256 μg/mL. It was found that S. aureus may exhibit a paradoxical growth effect when exposed to simvastatin; thus, treatment failure at high drug concentrations is theoretically probable. Through structure-activity relationship analysis, we postulate that statins’ antibacterial action may involve disrupting the teichoic acid structures or decreasing the number of alanine residues present on Gram-positive bacterial cell surfaces, which could reduce biofilm formation, diminish bacterial adhesion to environmental surfaces, or impede S. aureus cell division.     

Mucosal immunization against respiratory bacterial pathogens

Bacterial respiratory diseases remain a major cause of morbidity and mortality throughout the world. The young and the elderly are particularly susceptible to the pathogens that cause these diseases. Therapeutic approaches remain dependent upon antibiotics contributing to the persistent increases in antibiotic resistance. The main causes of respiratory disease discussed in this review are Mycobacterium tuberculosis, Corynebacterium diphtheriae, Bordatella pertussis, Streptococcus pneumoniae, non-typeable Haemophilus influenzae, Moraxella catarrhalis and Pseudomonas aeruginosa. All these organisms initiate disease at the mucosal surface of the respiratory tract and thus the efficacy of the host's response to infection needs to be optimal at this site. Vaccines available for diseases caused by many of these pathogens have limitations in accessibility or efficacy, highlighting the need for improvements in approaches and products. The most significant challenges in both therapy and prevention of disease induced by bacteria in the respiratory tract remain the development of non-injectable vaccines and delivery systems/immunization regimens that improve mucosal immunity.     

In vitro activity of quinupristin/dalfopristin against selected bacterial pathogens isolated in Italy

Objectives: To evaluate the activity of quinupristin/dalfopristin, a new injectable streptogramin, against 732 clinical strains recently isolated in Italy.
Methods: Susceptibility tests were performed according to NCCLS-guided MIC methodology. Pathogens included in the evaluation included 108 Staphylococcus aureus isolates, 124 coagulase-negative staphylococcal isolates, 158 Streptococcus pyogenes isolates, 30 Streptococcus agalactiae isolates, 30 β-hemolytic streptococcal isolates, 18 Streptococcus sanguis isolates, 80 Streptococcus pneumoniae isolates, 69 Enterococcal isolates, 40 Haemophilus influenzae isolates, 30 Moraxella catarrhalis isolates and, finally, 30 Gram-positive and 25 Gram-negative anaerobes.
Results: Quinupristin/dalfopristin inhibited Staphylococcus aureus and other Staphylococcus spp., irrespective of their oxacillin or erythromycin resistance phenotypes. Similarly, streptococci were fully inhibited by quinupristin/dalfopristin. Enterococcus faecalis was not included in the spectrum of this streptogramin, while isolates of Enterococcus faecium were inhibited by the new compound. Respiratory pathogens such as H. influenzae and M. catarrhalis were inhibited by quinupristin/dalfopristin as well as all Gram-negative anaerobes tested.
Conclusions: These findings suggest a putative role for quinupristin/dalfopristin in the empirical treatment of severe nosocomial and community-acquired infections caused by pathogens often displaying resistance to multiple antibiotics. This drug may provide an alternative to glycopeptide compounds.     

A novel membrane fusion-mediated plant immunity against bacterial pathogens

Plants have developed their own defense strategies because they have no immune cells. A common plant defense strategy involves programmed cell death (PCD) at the infection site, but how the PCD-associated cell-autonomous immunity is executed in plants is not fully understood. Here we provide a novel mechanism underlying cell-autonomous immunity, which involves the fusion of membranes of a large central vacuole with the plasma membrane, resulting in the discharge of vacuolar antibacterial proteins to the outside of the cells, where bacteria proliferate. The extracellular fluid that was discharged from the vacuoles of infected leaves had both antibacterial activity and cell death-inducing activity. We found that a defect in proteasome function abolished the membrane fusion associated with both disease resistance and PCD in response to avirulent bacterial strains but not to a virulent strain. Furthermore, RNAi plants with a defective proteasome subunit PBA1 have reduced DEVDase activity, which is an activity associated with caspase-3, one of the executors of animal apoptosis. The plant counterpart of caspase-3 has not yet been identified. Our results suggest that PBA1 acts as a plant caspase-3-like enzyme. Thus, this novel defense strategy through proteasome-regulating membrane fusion of the vacuolar and plasma membranes provides plants with a mechanism for attacking intercellular bacterial pathogens.     

Comparative in vitro activity of ertapenem against bacterial pathogens isolated from patients with lower respiratory tract infections

This study compared the in vitro activity of ertapenem, ceftriaxone, cefepime, ciprofloxacin and amoxicillin–clavulanate against 381 aerobic and facultative bacterial pathogens isolated from 320 patients with acute bacterial exacerbation of chronic bronchitis or community-acquired pneumonia. Streptococcus pneumoniae and Haemophilus influenzae accounted for 54.6% of the isolates. The ertapenem MIC was ≤2 mg/L for 98.4% of isolates and ≥8 mg/L for 1.0% (all methicillin-resistant Staphylococcus aureus ). Ertapenem had the most potent activity against Enterobacteriaceae, Moraxella catarrhalis , and methicillin-susceptible S. aureus , and its activity against H. influenzae and H. parainfluenzae , all strains of which were susceptible, was not altered by β -lactamase production. Only one S. pneumoniae strain, a penicillin-resistant isolate, was resistant to ertapenem. Ertapenem was highly active in vitro against pyogenic bacteria recovered from patients with community-acquired lower respiratory tract infections.     

Antimicrobial activity of octenidine against multidrug-resistant Gram-negative pathogens

Multidrug-resistant (MR) Gram-negative (GN) pathogens pose a major and growing threat for healthcare systems, as therapy of infections is often limited due to the lack of available systemic antibiotics. Well-tolerated antiseptics, such as octenidine dihydrochloride (OCT), may be a very useful tool in infection control to reduce the dissemination of MRGN. This study aimed to investigate the bactericidal activity of OCT against international epidemic clones of MRGN. A set of five different species (Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Acinetobacter baumannii, and Pseudomonas aeruginosa) was studied to prove OCT efficacy without organic load, under “clean conditions” (0.3 g/L albumin) and under “dirty conditions” (3 g/L albumin + 3 mL/L defibrinated sheep blood), according to an official test norm (EN13727). We used five clonally unrelated isolates per species, including a susceptible wild-type strain, and four MRGN isolates, corresponding to either the 3MRGN or 4MRGN definition of multidrug resistance. A contact time of 1 min was fully effective for all isolates by using different OCT concentrations (0.01% and 0.05%), with a bacterial reduction factor of >5 log₁₀ systematically observed. Growth kinetics were determined with two different wild-type strains (A. baumannii and K. pneumoniae), proving a time-dependent efficacy of OCT. These results highlight that OCT may be extremely useful to eradicate emerging highly resistant Gram-negative pathogens associated with nosocomial infections.     

In vitro activity of daptomycin in combination with low-dose colistin against a diverse collection of Gram-negative bacterial pathogens

The activity of colistin in combination with daptomycin was assessed using 30 Gram-negative type strains and multidrug-resistant isolates with defined mechanisms of resistance. Daptomycin minimum inhibitory concentrations (MICs) were determined with and without sub-inhibitory concentrations of colistin. The activity of daptomycin was not affected with respect to Escherichia coli, Klebsiella pneumoniae or Pseudomonas aeruginosa. For colistin-susceptible Acinetobacter baumannii, sensitisation factors ranged from 8 to 128 (median 32), with the daptomycin MIC being reduced to the Clinical and Laboratory Standards Institute (CLSI) enterococci susceptibility breakpoint of 4 μg/ml for the ATCC 19606 type strain. A combination of daptomycin and colistin may be useful for the treatment of A. baumannii but not infections due to other Gram-negative species.     

Azthreonam: in vitro activity against urinary pathogens

The in vitro activity of azthreonam, a novel monocyclic beta-lactam antibiotic, was investigated for Gram negative urinary pathogens by determining the susceptibilities of 105 consecutive isolates from specimens submitted to the Auckland Hospital microbiology laboratory. All were sensitive or of intermediate sensitivity by disc diffusion testing. Minimum inhibitory concentrations (MICs) were 0.25 mg/l for 97 per cent of Enterobacteriaceae and ranged from 2-16 mg/l for Pseudomonas aeruginosa. Of antibiotics tested routinely in this laboratory only tobramycin showed comparable potency.     

Antioxidant activity of 7,8-dihydroxyflavone provides neuroprotection against glutamate-induced toxicity

Glutamate, an excitatory neurotransmitter in the central nervous system, plays an important role in neurological disorders. Previous studies have shown that excess glutamate can cause oxidative stress in a hippocampal HT-22 cell line. 7,8-Dihydroxyflavone (7,8-DHF), a member of the flavonoid family, is a selective tyrosine kinase receptor B (TrkB) agonist that has neurotrophic effects in various neurological diseases such as stroke and Parkinson's disease. In this study, we found that there is no TrkB receptor in HT-22 cells. Despite this, our data demonstrate that 7,8-DHF still protects against glutamate-induced toxicity in HT-22 cells in a concentration-dependent manner, indicating that 7,8-DHF prevents cell death through other mechanisms rather than TrkB receptors in this cell model. We further show that 7,8-DHF increases cellular glutathione levels and reduces reactive oxygen species (ROS) production caused by glutamate in HT-22 cells. Finally, our data demonstrate that 7,8-DHF protects against hydrogen peroxide and menadione-induced cell death, suggesting that 7,8-DHF has an antioxidant effect. In summary, although 7,8-DHF is considered as a selective TrkB agonist, our results demonstrate that 7,8-DHF can still confer neuroprotection against glutamate-induced toxicity in HT-22 cells via its antioxidant activity.     

NLR-mediated control of inflammasome assembly in the host response against bacterial pathogens

The host response against diverse bacterial pathogens involves activation of specialized immune cells and elaboration of pro-inflammatory cytokines that help to coordinate appropriate host defense. Members of the interleukin-1 (IL-1) cytokine family, IL-1β and IL-18, are central players in this process. Extracellular release of the mature, active form of these cytokines requires their processing by the cysteine protease caspase-1, which therefore serves as a key regulator of the inflammatory response. In addition to its role in secretion of pro-inflammatory cytokines, caspase-1 is also required for a form of cell death, recently termed pyroptosis, that occurs in macrophages infected by certain bacterial pathogens. Caspase-1 itself is synthesized as a pro-enzyme, which must first be activated by autocatalytic cleavage. This activation requires recruitment of caspase-1 into multiprotein complexes known as inflammasomes. The Nod-like receptor (NLR) family of cytosolic proteins play an important role in detecting inflammatory stimuli and subsequently mediate inflammasome assembly. A common feature of NLR proteins that trigger inflammasome assembly in response to bacterial infection is that they appear to sense membrane perturbation or delivery of bacterial components into the cytosol through bacterial pore-forming toxins or bacterial secretion systems. This review will discuss the recent developments regarding caspase-1 activation in response to bacterial infection, cross-talk between caspase-1 and other pathways involved in regulating cell death, and recent findings that a number of bacterial pathogens possess mechanisms to inhibit caspase-1 activation.     

Lipoproteins of bacterial pathogens

Bacterial lipoproteins are a set of membrane proteins with many different functions. Due to this broad-ranging functionality, these proteins have a considerable significance in many phenomena, from cellular physiology through cell division and virulence. Here we give a general overview of lipoprotein biogenesis and highlight examples of the roles of lipoproteins in bacterial disease caused by a selection of medically relevant Gram-negative and Gram-positive pathogens: Mycobacterium tuberculosis, Streptococcus pneumoniae, Borrelia burgdorferi, and Neisseria meningitidis. Lipoproteins have been shown to play key roles in adhesion to host cells, modulation of inflammatory processes, and translocation of virulence factors into host cells. As such, a number of lipoproteins have been shown to be potential vaccines. This review provides a summary of some of the reported roles of lipoproteins and of how this knowledge has been exploited in some cases for the generation of novel countermeasures to bacterial diseases.     

Comparative in vitro activity of norfloxacin against urinary tract pathogens

The in vitro activity of norfloxacin (MK366) against 477 aerobic gram-negative and gram-positive clinical isolates was compared to that of nalidixic acid, nitrofurantoin, ampicillin, cephalexin, trimethoprim, sulfamethoxazole, and the combination trimethoprim-sulfamethoxazole. Norfloxacin was more active than the other agents against all gram-negative organisms tested. Minimal inhibitory concentrations (MICs) ofPseudomonas aeruginosa were ? 0.125–32 mg/l with 90 % inhibited (MIC90) by 4 mg/l; MICs of theEnterobacteriaceae includingSerratia marcescens were ? 0.125–8 mg/l with an MIC90 of ? 4 mg/l. There was also excellent activity against the grampositive cocci includingStaphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus and the enterococci, with MICs ? 0.125–4 mg/l and an MIC90 ? 4 mg/l. Only 8 of 477 organisms were norfloxacin-resistant (MIC ? 16 mg/l): 3 of 100Pseudomonas aeruginosa, 3 of 10Pseudomonas maltophilia and 2 of 15Streptococcus bovis strains. In contrast, 97 % of the gram-positive cocci and 49 % of the gram-negative bacilli were nalidixic acid-resistant (MIC ? 32 mg/l). Norfloxacin shows excellent activity against a wide range of bacteria and merits further study as a urinary antibacterial agent.     

CEACAM3: an innate immune receptor directed against human-restricted bacterial pathogens

Carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) is an immunoglobulin-related glycoprotein exclusively expressed on granulocytes. In contrast to other members of the CEACAM family, CEACAM3 does not support cell-cell adhesion, but rather mediates the opsonin-independent recognition and elimination of a restricted set of human-specific Gram-negative bacterial pathogens including Neisseria gonorrhoeae, Haemophilus influenzae, and Moraxella catarrhalis. Within the last 4 years, molecular determinants of CEACAM3 function and CEACAM3-initiated signaling pathways have been elucidated. Sequence comparison between CEACAM3 and other CEACAM family members points to a chimeric origin of this receptor with the bacteria-binding extracellular domain and the function-promoting intracellular domain derived from different genes. This review summarizes the current knowledge about the structure-function relationship of CEACAM3 and tries to combine these molecular aspects with a plausible scenario concerning the evolutionary origin of this phagocyte receptor in the light of host-pathogen adaptation.     

Interleukin-17 in host defence against bacterial,mycobacterial and fungal pathogens

The mammalian immune system is intricately regulated, allowing for potent pathogen-specific immunity to be rapidly activated in response to infection with a broad and diverse array of potential pathogens. As a result of their ability to differentiate into distinct effector lineages, CD4 T cells significantly contribute to pathogen-specific adaptive immune responses. Through the production of effector cytokines, CD4 T helper (Th) cells orchestrate the precise mobilization of specific immune cells to eradicate infection. The protective effects of the newly identified lineage of Th17 cells against pathogens like Klebsiella pneumoniae, Citrobacter rodentium and Candida albicans indicate the capacity of Th17 cells to confer protection against extracellular bacterial and fungal pathogens, filling a critical void in host immunity not covered by the classically described Th1 lineage that activates immunity to intracellular pathogens or the Th2 lineage that is important in protection against mucosal parasitic pathogens. Host defence by Th17 cells extends beyond protection against extracellular bacterial and fungal pathogens, as demonstrated in infections against intracellular bacteria like Listeria monocytogenes and Salmonella enterica, as well as Mycobacterium tuberculosis. Herein, we summarize both experimental data from mouse infection models and epidemiological studies in humans that demonstrate the protective effects of interleukin-17 and Th17 CD4 T cells in immunity to bacterial, mycobacterial and fungal pathogens.     

Inhibitory activity of a standardized elderberry liquid extract against clinically-relevant human respiratory bacterial pathogens and influenza A and B viruses

Background  

Black elderberries (Sambucus nigra L.) are well known as supportive agents against common cold and influenza. It is further known that bacterial super-infection during an influenza virus (IV) infection can lead to severe pneumonia. We have analyzed a standardized elderberry extract (Rubini, BerryPharma AG) for its antimicrobial and antiviral activity using the microtitre broth micro-dilution assay against three Gram-positive bacteria and one Gram-negative bacteria responsible for infections of the upper respiratory tract, as well as cell culture experiments for two different strains of influenza virus.     

Immunoregulatory functions of interleukin 18 and its role in defense against bacterial pathogens

Interleukin-18 (IL-18) is a proinflammatory cytokine that belongs to the IL-1 cytokine family, due to its structure, receptor family and signal transduction pathways. Similarly to IL-1beta, IL-18 is synthesized as a precursor requiring caspase-1 for cleavage into an active IL-18 molecule. However, with regard to its capacity to induce the production of Th1 cytokines and to enhance cell-mediated cytotoxicity, IL-18 is also related to IL-12. Produced mainly by antigen-presenting cells, IL-18 is a pleiotropic factor involved in the regulation of both innate and acquired immune responses, playing a key role in autoimmune, inflammatory, and infectious diseases. This review summarizes recent advances in the understanding of IL-18 structure, processing, receptor expression, and immunoregulatory functions and emphasizes the critical role of this cytokine in bacterial infections. It focuses on the participation of this cytokine in the defense against intracellular bacteria, including Listeria, Shigella, Salmonella, and Mycobacterium tuberculosis. Since this cytokine may be particularly useful in immunoprophylactic and immunotherapeutic interventions in which the cellular response is most desirable, the potential therapeutic aspects of IL-18 is also discussed.     

In vitro activity of dermaseptin S1 derivatives against genital pathogens

Savoia D, Donalisio M, Civra A, Salvadori S, Guerrini R. In vitro activity of dermaseptin S1 derivatives against genital pathogens. APMIS 2010; 118: 674–80. The aim of this study was to evaluate the biological activity of nine dermaseptin‐S1 (DRS‐S1) derivatives (synthesized by solid‐phase methods and purified) against different pathogens causing genital infections (Trichomonas vaginalis, Herpes simplex virus, Papillomavirus). The in vitro activity on T. vaginalis was determined by counting the protozoon in a hemocytometer after vital staining with trypan blue; antiviral activity of the compounds was tested on monolayers of Vero cells for Herpes simplex virus‐1 (GFP) and on 293TT cells for human papillomavirus (HPV‐16) pseudovirions (GFP). The cytotoxicity of the derivatives was assessed by evaluating both the hemolytic activity and the effect on Vero and 293TT cells. The DRS‐S1 longer peptides demonstrated a superior activity on T. vaginalis but also a certain cytopathic effect. The compounds with 29 amino acids exhibited activity against the two viruses tested at concentrations not toxic to cells. The results obtained show that some of the synthetic peptides assessed have inhibitory activity against the pathogens tested, indicating a potential for the development of new molecules for use as topical microbicides to prevent the sexual transmission of microorganisms.