Novel pentadecenyl tetrazole enhances susceptibility of methicillin-resistant Staphylococcus aureus biofilms to gentamicin

Challenges and Opportunities of Nontraditional Approaches to Treating Bacterial Infections

Due to increasing rates of antimicrobial-resistant infections and the current inadequacy of the antibiotic pipeline, there is increasing interest in nontraditional approaches to antibacterial therapies. We define "traditional" agents as small-molecule agents that directly target bacterial components to exert a bacteriostatic or bactericidal effect, and "nontraditional approaches" as antimicrobial therapeutics that work through other means (ie, not a small molecule and/or utilizes a nontraditional target). Due to their atypical features, such therapies may be less susceptible to the emergence of resistance than traditional antibiotics. They include approaches such as monoclonal antibodies, virulence disruptors, immunomodulators, phage therapies, microbiome-based therapies, antibiotic potentiators, and antisense approaches. This article discusses both the developmental and regulatory advantages and challenges associated with each of these technologies. By identifying existing regulatory and developmental gaps, we hope to provide a sense of where focusing resources may provide the greatest impact on successful product development.

Small-Molecule Potentiators for Conventional Antibiotics against Staphylococcus aureus

Antimicrobial resistance constitutes a global health problem, while the discovery and development of novel antibiotics is stagnating. Methicillin-resistant Staphylococcus aureus, responsible for the establishment of recalcitrant, biofilm-related infections, is a well-known and notorious example of a highly resistant micro-organism. Since resistance development is unavoidable with conventional antibiotics that target bacterial viability, it is vital to develop alternative treatment options on top. Strategies aimed at more subtle manipulation of bacterial behavior have recently attracted attention. Here, we provide a literature overview of several small-molecule potentiators for antibiotics, identified for the treatment of Staphylococcus aureus infection. Typically, these potentiators are not bactericidal by themselves and function by reversing resistance mechanisms, by attenuating Staphylococcus aureus virulence, and/or by interfering with quorum sensing.

Hyperoside inhibits biofilm formation of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a common pathogen in hospital-acquired infection and is readily able to form biofilms. Due to its high antibiotic resistance, traditional antibacterial treatments exert a limited effect on P. aeruginosa biofilm infections. It has been indicated that hyperoside inhibits P. aeruginosa PAO1 (PAO1) biofilm formation without affecting growth. Therefore, the current study examined the biofilm formation and quorum sensing (QS) system of PAO1 in the presence of hyperoside. Confocal laser scanning microscopy analysis demonstrated that hyperoside significantly inhibited biofilm formation. It was also observed that hyperoside inhibited twitching motility in addition to adhesion. Data from reverse transcription-quantitative polymerase chain reaction indicated that hyperoside inhibited the expression of lasR, lasI, rhlR and rhlI genes. These results suggest that the QS-inhibiting effect of hyperoside may lead to a reduction in biofilm formation. However, the precise mechanism of hyperoside on P. aeruginosa pathogenicity remains unclear and requires elucidation in additional studies.

Acyldepsipeptide antibiotics as a potential therapeutic agent against Clostridium difficile recurrent infections

Alternative antimicrobial therapies based on acyldepsipeptides may hold promising results, based on the fact that they have shown to efficiently eradicate persister cells, stationary cells and cell in biofilm structures of several pathogenic bacteria from the infected host. Clostridium difficile infection is considered the result of extensive hospital use of expanded-spectrum antibiotics, which cause dysbiosis of the intestinal microbiota, enhancing susceptibility to infection and persistence. Considering the urgent need for the development of novel and efficient antimicrobial strategies against C. difficile, we review the potential application to treat C. difficile infections of acyldepsipeptides family of antibiotics, its mechanism of action and current developmental stages.

Subinhibitory concentrations of metronidazole increase biofilm formation in Clostridium difficile strains

Resistance mechanism to metronidazole is still poorly understood, even if the number of reports on Clostridium difficile strains with reduced susceptibility to this antibiotic is increasing. In this study, we investigated the ability of the C. difficile strains 7032994, 7032985 and 7032989, showing different susceptibility profiles to metronidazole but all belonging to the PCR ribotype 010, to form biofilm in vitro in presence and absence of subinhibitory concentrations of metronidazole. The quantitative biofilm production assay performed in presence of metronidazole revealed a significant increase in biofilm formation in both the susceptible strain 7032994 and the strain 7032985 exhibiting a reduced susceptibility to this antibiotic, while antibiotic pressure did not affect the biofilm-forming ability of the stable-resistant strain 7032989. Moreover, confocal microscopy analysis showed an abundant biofilm matrix production by the strains 7032994 and 7032885, when grown in presence of metronidazole, but not in the stable-resistant one. These results seem to demonstrate that subinhibitory concentrations of metronidazole are able to enhance the in vitro biofilm production of the above-mentioned PCR ribotype 010 C. difficile strains, susceptible or with reduced susceptibility to this antibiotic, suggesting a possible role of biofilm formation in the multifactorial mechanism of metronidazole resistance developed by C. difficile.

Prevention of cell-surface attachment and reduction of penicillin-binding protein 2a (PBP2a) level in methicillin-resistant Staphylococcus aureus biofilms by Acalypha wilkesiana

BACKGROUND

Formation of biofilm is known to enhance the virulence of methicillin-resistance Staphylococcus aureus (MRSA), which is associated with persistent infections in hospital settings. The biofilm layer essentially forms a protective barrier encapsulating the bacterial colony and thus reduces the effectiveness of chemotherapeutics. We have isolated 9EA-FC-B bioactive fraction from Acalypha wilkesiana Müll. Arg. that reverses ampicillin resistant in MRSA through inhibition of the antibiotic resistant protein, penicillin-binding protein 2a (PBP2a). In this study, we aimed to investigate the effects of 9EA-FC-B on MRSA biofilm forming capacity.

METHODS

Inhibition of biofilm production and microtiter attachment assays were employed to study the anti-biofilm activity of 9EA-FC-B, while latex agglutination test was performed to investigate the effect on PBP2a in the biofilm matrix. We also attempted to characterise the chemical components of the fraction using high performance liquid chromatography (HPLC) and phytochemical analysis.

RESULTS

Fraction 9EA-FC-B and ampicillin exhibited similar inhibitory effect on MRSA's biofilm production at their respective minimum inhibitory concentrations (81.56% vs 84.49%, respectively). However, the test fraction was more effective in suppressing cell surface attachment (90.85%) compared to ampicillin (37.8%). Interestingly, ampicillin enhanced the level PBP2a and in the contrary 9EA-FC-B attenuated the production of the resistant protein in the bioflim matrix. HPLC and phytochemical analysis revealed that 9EA-FC-B fraction is a complex mixture containing tannins, saponins, sterol/steroids, and glycosides.

CONCLUSIONS

Bioactive fraction 9EA-FC-B inhibited the production of MRSA biofilm by preventing the initial cell-surface attachment and reducing the amount PBP2a in the matrix. PBP2a found in the biofilm matrix is believed to have a role in the development of virulence in MRSA.

Biocompatible nanocarrier fortified with a dipyridinium-based amphiphile for eradication of biofilm

Annihilation of bacterial biofilms is challenging owing to their formidable resistance to therapeutic antibiotics and thus there is a constant demand for development of potent antibiofilm agents that can abolish established biofilms. In the present study, the activity of a dipyridinium-based cationic amphiphile (compound 1) against established bacterial biofilms and the subsequent development of a compound 1-loaded nanocarrier for potential antibiofilm therapy are highlighted. Solution-based assays and microscopic analysis revealed the antagonistic effect of compound 1 on biofilms formed by Staphylococcus aureus MTCC 96 and Pseudomonas aeruginosa MTCC 2488. In combination studies, compound 1 could efficiently potentiate the action of tobramycin and gentamicin on P. aeruginosa and S. aureus biofilm, respectively. A human serum albumin (HSA)-based nanocarrier loaded with compound 1 was generated, which exhibited sustained release of compound 1 at physiological pH. The compound 1-loaded HSA nanocarrier (C1-HNC) displayed the signature membrane-directed activity of the amphiphile on target bacteria, efficiently eliminated established bacterial biofilms, and was observed to be nontoxic to a model human cell line. Interestingly, compound 1 as well as the amphiphile-loaded HSA nanocarrier could eradicate established S. aureus biofilm from the surface of a Foley's urinary catheter. On the basis of its biocompatibility and high antibiofilm activity, it is conceived that the amphiphile-loaded nanocarrier may hold potential in antibiofilm therapy.

Antibacterial activity of Taxodium ascendens Diterpenes against Methicillin-resistant Staphylococcus aureus

One new and seven known diterpenes were identified from an antibacterial chromatographic fraction of Taxodium ascendens. Of these, demethylcryptojaponol (2), 6-hydroxysalvinolone (3), hydroxyferruginol (4), and hinokiol (5) demonstrated potent activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). These compounds represent a class of synthetically accessible compounds that could be further developed for treatment of drug-resistant bacterial infections.

Antibacterial chromene and chromane stilbenoids from Hymenocardia acida

Six chromene stilbenoids and one chromane stilbenoid were isolated from the African tree Hymenocardia acida. Several were moderately active against methicillin-resistant Staphylococcus aureus clinical isolate MRSA-108, including hymenocardichromanic acid, which was active at 8 μg/ml. None had IC50 values <20 μM in antiproliferation assays against several human cancer cell lines.

Biological evaluation of hyperforin and its hydrogenated analogue on bacterial growth and biofilm production

Bacterial biofilms are organized communities of microorganisms, embedded in a self-produced matrix, growing on a biotic surface and resistant to many antimicrobial agents when associated with a medical device. These biofilms require the development of new strategies for the prevention and treatment of infectious disease, including the potential use of natural products. One interesting natural product example is Hypericum, a plant genus that contains species known to have antimicrobial properties. The major constituent of Hypericum perforatum is an unstable compound named hyperforin (1); for this reason it was not believed to play a significant role in the pharmacological effects. In this investigation a hydrogenated hyperforin analogue (2) was tested on several ATCC and clinical isolate strains, in their planktonic and biofilm form (Staphylococcus aureus, MRSA, and Enterococcus faecalis). Compound 2 was effective against planktonic and biofilm cultures, probably due to higher stability, showing the percentage of cells killed in the range from 45% to 52%. These results are noteworthy from the point of view of future development of these polyprenylated phloroglucinols as potential antibiotics.

Biofilm formation by Clostridium difficile

Clostridium difficile infection (CDI) is a major healthcare-associated disease worldwide. Recurring infections and increasing antibiotic resistance have complicated treatment of CDI. While C. difficile spores are important for transmission and persistence of CDI, other factors such as gut colonization and formation of bacterial communities in the gut may also contribute to pathogenesis and persistence, but have not been well investigated. Recently, we reported that important clinical C. difficile strains are able to form composite biofilms in vitro. C. difficile biofilm formation is a complex process, modulated by several different factors, including cell surface components and regulators. We also reported that bacteria within biofilms are more resistant to high concentrations of vancomycin, the antibiotic of choice for treatment of CDI. Here we summarize our recent findings and discuss the implications of biofilm formation by this anaerobic gut pathogen in disease pathogenesis and treatment.

Multiple factors modulate biofilm formation by the anaerobic pathogen Clostridium difficile

Bacteria within biofilms are protected from multiple stresses, including immune responses and antimicrobial agents. The biofilm-forming ability of bacterial pathogens has been associated with increased antibiotic resistance and chronic recurrent infections. Although biofilms have been well studied for several gut pathogens, little is known about biofilm formation by anaerobic gut species. The obligate anaerobe Clostridium difficile causes C. difficile infection (CDI), a major health care-associated problem primarily due to the high incidence of recurring infections. C. difficile colonizes the gut when the normal intestinal microflora is disrupted by antimicrobial agents; however, the factors or processes involved in gut colonization during infection remain unclear. We demonstrate that clinical C. difficile strains, i.e., strain 630 and the hypervirulent strain R20291, form structured biofilms in vitro, with R20291 accumulating substantially more biofilm. Microscopic and biochemical analyses show multiple layers of bacteria encased in a biofilm matrix containing proteins, DNA, and polysaccharide. Employing isogenic mutants, we show that virulence-associated proteins, Cwp84, flagella, and a putative quorum-sensing regulator, LuxS, are all required for maximal biofilm formation by C. difficile. Interestingly, a mutant in Spo0A, a transcription factor that controls spore formation, was defective for biofilm formation, indicating a possible link between sporulation and biofilm formation. Furthermore, we demonstrate that bacteria in clostridial biofilms are more resistant to high concentrations of vancomycin, a drug commonly used for treatment of CDI. Our data suggest that biofilm formation by C. difficile is a complex multifactorial process and may be a crucial mechanism for clostridial persistence in the host.