Synergistic interaction of eugenol with antibiotics against Gram negative bacteria

Eugenol, the principal chemical component of clove oil from Eugenia aromatica has been long known for its analgesic, local anesthetic, anti-inflammatory, and antibacterial effects. The interaction of the eugenol with ten different hydrophobic and hydrophilic antibiotics was studied against five different Gram negative bacteria. The MIC of the combination was found to decrease by a factor of 5–1000 with respect to their individual MIC. This synergy is because of the membrane damaging nature of eugenol, where 1 mM of its concentration is able to damage nearly 50% of the bacterial membrane. Eugenol was also able to enhance the activities of lysozyme, Triton X-100 and SDS in damaging the bacterial cell membrane. The hydrophilic antibiotics such as vancomycin and β-lactam antibiotics which have a marginal activity on these gram negative bacteria exhibit an enhanced antibacterial activity when pretreated with eugenol. Reduced usage of antibiotics could be employed as a treatment strategy to slow down the onset of antibiotic resistance as well as decrease its toxicity. Experiments performed with human blood cells indicated that the concentration of eugenol used for the combination studies were below its cytotoxic values. Pharmacodynamic studies of the combinations need to be performed to decide on the effective dosage.     

Biological consequences of improving the structural stability of hairpins that have antimicrobial activity

Designing new antimicrobial peptides (AMPs) focuses heavily on the activity of the peptide and less on the elements that stabilize the secondary structure of these peptides. Studies have shown that improving the structure of naturally occurring AMPs can affect activity and so here we explore the relationship between structure and activity of two non‐naturally occurring AMPs. We have used a backbone‐cyclized peptide as a template and designed an uncyclized analogue of this peptide that has antimicrobial activity. We focused on beta‐hairpin‐like structuring features. Improvements to the structure of this peptide reduced the activity of the peptide against gram‐negative, Escherichia coli but improved the activity against gram‐positive, Corynebacterium glutamicum. Distinctions in structuring effects on gram‐negative versus gram‐positive activity were also seen in a second peptide system. Structural improvements resulted in a peptide that was more active than the native against gram‐positive bacterium but less active against gram‐negative bacterium. Our results show that there is not always a correlation between improved hairpin‐structuring and activity. Other factors such as the type of bacteria being targeted as well as net positive charge can play a role in the potency of AMPs. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.     

Antibacterial activity and chemical composition of Turkish propolis

The antibacterial activities of propolis samples have been examined in vitro, according to the principles accepted for the determination of a similar activity of antibiotics with the use of solid and liquid media. It has been found that propolis extracts showed antibacterial activity through a range of commonly encountered gram positive cocci (S. aureus, beta hem. Streptococus), but had weak activity against gram negative bacteria (E. coli, P. aeruginosa). GC/MS analysis showed that propolis samples contain a variety of chemical compounds including aromatic compounds, fatty acid esters and sesquiterpenes.     

Antimicrobial potentiality of a phenothiazine group of antipsychotic drug-prochlorperazine

The antipsychotic drug, prochlorperazine (Pcp), was tested for its antimicrobial efficacy against 103 strains belonging to both gram positive and gram negative bacteria. The drug was found to possess maximum activity against Staphylococcus aureus, Vibrio cholerae and Shigella spp. Pcp was moderately active against E. coli but most of the strains belonging to Bacillus spp, Klebsiella spp, Salmonella spp and Lactobacillus spp were found to be resistant to this drug. The drug was tested for its mode of antibacterial activity against Shigella dysenteriae 1 and it was found to be bacteriostatic in action. In in vivo studies, Pcp offered significant protection to Swiss albino mice at concentrations of 0.75 micro g/g (P < 0.01) and 1.5 microg/g (P < 0.001) body weight when challenged with 50 median lethal dose of Salmonella typhimurium NCTC 74. Thus the result depicts that prochlorperazine may emerge as a strong antimicrobial drug to replace the conventional antibiotics and to overcome the problem of drug resistance.     

Sperm‐duct gland secretion of the grass goby Zosterisessor ophiocephalus exhibits antimicrobial activity

The grass goby Zosterisessor ophiocephalus sperm‐duct gland extract displayed antimicrobial activity against gram‐positive and gram‐negative bacteria. This suggests that sperm‐duct gland mucins might be functional in protecting eggs and possibly parents from pathogens, an activity of great adaptive value for Z. ophiocephalus, which lays eggs in mud nests.     

Antibacterial activity of Penicillium spp. strains isolated in extreme environments

Penicillium spp. isolated from the sediments of ponds in continental Antarctica have been studied and compared with species obtained from similar environments in the Apennines of the Liguria region, in northwestern Italy. The antibacterial activity exhibited by some strains was evaluated against standard strains using both liquid and solid media. The preliminary data suggest an antibacterial activity similar to β-lactam antibiotics. Accepted: 24 October 1999     

Design and Synthesis of Heterocyclic Conjugated Peptides as Novel Antimicrobial Agents

Antimicrobial peptides have been recognized as a novel class of antibiotics and several candidates are currently in clinical trials. In the present study, new antimicrobial compounds were synthesized by coupling quinazolinone moiety with the fragments of elastin sequences VP, GVP, VGVP and GVGVP. They were evaluated for their antibacterial activity against both gram positive and gram negative bacterial strains. We are here reporting that heterocyclic conjugated tetra peptide and penta peptide showed enhanced antibacterial activity compare to the conventional antimicrobial drugs.     

A chlorinated phenylpyrrole antibiotic fromActinoplanes

Two chlorophenyl-containing antibiotics have been isolated from a strain ofActinoplanes (ATCC 33002). Antibiotic A 15104 Y is a chlorinated phenylpyrrole compound whose structure has been confirmed by chemical synthesis. Antibiotic A 15104 Z is a chlorophenol derivative for which a structural formula is proposed on the basis of its physicochemical properties. A 15104 Y shows antimicrobial activity against Gram-positive, Gram-negative, and acid-fast bacteria, yeasts, fungi, and protozoa, while A 15104 Z possesses a low activity against Gram-positive bacteria andTrichophyton. A 15104 Y has a weak activity in curing experimentally infected mice, at a dose that is one-fifth the LD₅₀ for the same species. This is the first example of a chloropyrrole derivative isolated from an actinomycete.     

Antibiotic‐Potentiating Activity of Phanostenine Isolated from Cissampelos sympodialis Eichler

Cissampelos sympodialis Eichler is well studied and investigated for its antiasthmatic properties, but there are no data in the literature describing antibacterial properties of alkaloids isolated from this botanical species. This work reports the isolation and characterization of phanostenine obtained from roots of C. sympodialis and describes for the first time its antimicrobial and antibiotic modulatory properties. Phanostenine was first isolated from Cissampelos sympodialis and its antibacterial activities were determined. Chemical structures of the alkaloid isolate were determined using spectroscopic and chemical analyses. Phanostenine was also tested for its antibacterial activity against standard strains and clinical isolates of Escherichia coli and Staphylococcus aureus. Minimal inhibitory concentration (MIC) was determined in a microdilution assay and for the evaluation of antibiotic resistance‐modifying activity. MIC of the antibiotics was determined in the presence or absence of phanostenine at sub‐inhibitory concentrations. The evaluation of antibacterial activity by microdilution assay showed activity for all strains with better values against S. aureus ATCC 12692 and E. coli 27 (787.69 mm ). The evaluation of aminoglycoside antibiotic resistance‐modifying activity showed reduction in the MIC of the aminoglycosides (amikacin, gentamicin and neomycin) when associated with phanostenine, MIC reduction of antibiotics ranging from 21 % to 80 %. The data demonstrated that phanostenine possesses a relevant ability to modify the antibiotic activity in vitro. We can suggest that phanostenine presents itself as a promising tool as an adjuvant for novel antibiotics formulations against bacterial resistance.     

Recombinant expression and purification of the antimicrobial peptide magainin‐2

Magainin‐2 (MAG2) is a polycationic antimicrobial peptide isolated from the skin of the African clawed frog Xenopus laevis. It has a wide spectrum of antimicrobial activities against gram‐positive and gram‐negative bacteria, fungi, and induces osmotic lysis of protozoa. MAG2 also possesses antiviral and antitumoral properties. These activities make this peptide a promising candidate for therapeutic applications. Recombinant expression systems are necessary for the affordable production of large amounts of the biologically active peptide. In this work, MAG2 has been cloned to the N‐terminal of a family III carbohydrate‐binding module fused to the linker sequence (LK‐CBM3) from Clostridium thermocellum; a formic acid recognition site was introduced between the two modules for chemical cleavage of the peptide. The recombinant protein MAG2‐LK‐CBM3 was expressed in Escherichia coli BL21 (DE3) and MAG2 was successfully cleaved and purified from the fusion partner LK‐CBM3. Its functionality was confirmed by testing its activity against gram‐negative bacteria. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2013     

Antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20

Aims: The aim of this study was to determine the antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20 against several micro‐organisms, including Gram‐positive and Gram‐negative bacteria, yeasts and filamentous fungi. Methods and Results: Antimicrobial and antiadhesive activities were determined using the microdilution method in 96‐well culture plates. The biosurfactant showed antimicrobial activity against all the micro‐organisms assayed, and for twelve of the eighteen micro‐organisms (including the pathogenic Candida albicans, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus agalactiae), the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were achieved for biosurfactant concentrations between 25 and 50 mg ml^?1. Furthermore, the biosurfactant showed antiadhesive activity against most of the micro‐organisms evaluated. Conclusions: As far as we know, this is the first compilation of data on antimicrobial and antiadhesive activities of biosurfactants obtained from lactobacilli against such a broad group of micro‐organisms. Although the antiadhesive activity of biosurfactants isolated from lactic acid bacteria has been widely reported, their antimicrobial activity is quite unusual and has been described only in a few strains. Significance and Impact of the Study: The results obtained in this study regarding the antimicrobial and antiadhesive properties of this biosurfactant opens future prospects for its use against micro‐organisms responsible for diseases and infections in the urinary, vaginal and gastrointestinal tracts, as well as in the skin, making it a suitable alternative to conventional antibiotics.     

Effect of Macrolide Antibiotics on Macrophage Functions

Macrolide antibiotics have a variety of actions other than antimicrobial activities. Recently, it has been suggested that macrolide antibiotics act as immunomodulators. In this study, we evaluated the effects of macrolide antibiotics on macrophage functions. For the macrophage, we used the mouse macrophage cell line J774.1. The following effects of macrolide antibiotics on macrophage functions were evaluated: the effect of macrolide antibiotics on macrophage growth; the phagocytosis of beads; cytocidal activity against Candida albicans; and chemotaxis to lipopolysaccharide (LPS). Macrolide antibiotics except for azithromycin significantly stimulated the growth of the macrophage. In addition, pretreatment with macrolide antibiotics except for roxithromycin significantly stimulated the macrophage phagocytosis of beads, macrophage chemotaxis to LPS, and macrophage cytocidal activity against Candida albicans. These results suggest that macrolide antibiotics stimulate macrophage functions.     

In vitro activity of honey,total alkaloids of Sophora alopecuroides and matrine alone and in combination with antibiotics against multidrug-resistant Pseudomonas aeruginosa isolates

Natural products, including honey, total alkaloids of Sophora alopecuroides (TASA) and matrine have been used in combination with antibiotics against various pathogenic bacteria. However, there are limited data on the antibacterial activity of these natural products in combination against multidrug-resistant Pseudomonas aeruginosa strains. The in vitro activity of honey, TASA and matrine alone and in combination with antibiotics against P. aeruginosa isolates was investigated. In this study, four biofilm-producing P. aeruginosa isolates, which were resistant to multiple antibiotics, were used. These natural products were not the most effective single agent against four isolates. The fractional inhibitory concentration index method revealed the synergistic effect of matrine and TASA-honey in combination with ciprofloxacin (Cip) against all tested isolates. When these combinations were used, the resistance of isolates to Cip was decreased significantly (six to eightfold reduction in the minimum inhibitory concentration of Cip. The disk diffusion method showed that all isolates were resistant to β-lactams. Combinations of these antibiotics with TASA and matrine changed slightly the activity of either antibiotic used as a single agent. All isolates produced metallo-β-lactamase enzymes (MBL). Pretreatment isolates with Cip-matrine and Cip-TASA-honey resulted in a statistically downregulated expression of the mexA gene. These natural products can be used against overactivating MexAB-OprM but not MBL-producing P. aeruginosa isolates.     

Preferred conformations and flexibility of aminoacyl side chain of penicillins

Possible conformations of penicillin G; d and l isomers of ampicillin; α-amino-α-methyl-benzyl penicillins and 3- pyridyl methyl penicillin have been studied by an energy minimization procedure using empirical potential functions. The preferred conformations of these antibiotics have been correlated with their biological activity. The conformational requirement of the antibiotic to be active against Gram-positive and Gram-negative (β-lactamase-negative) bacterial strains seems to be the same. The reduced activity of penicillin G against Gram-negative bacteria has been attributed to its lower ability to permeate the outer membrane. The flexibility of the sidechains of these antibiotics is also shown to be important for the desired biological activity.     

Complete genome sequence of a newly isolated lytic bacteriophage,EFAP‐1 of Enterococcus faecalis,and antibacterial activity of its endolysin EFAL‐1

Aims: In this work, we aimed to identify an effective treatment of infections caused by Enterococcus spp. strains resistant to conventional antibiotics. Methods and Results: We report the isolation and characterization of a new lytic bacteriophage, designated bacteriophage EFAP‐1, that is capable of lysing Enterococcus faecalis bacteria that exhibit resistance to multiple antibiotics. EFAP‐1 has low sequence similarity to all known bacteriophages. Transmission electron microscopy confirmed that EFAP‐1 belongs to the Siphoviridae family. A putative lytic protein of EFAP‐1, endolysin EFAL‐1, is encoded in ORF 2 and was expressed in Escherichia coli. Recombinant EFAL‐1 had broad‐spectrum lytic activity against several Gram‐positive pathogens, including Ent. faecalis and Enterococcus faecium. Conclusions: The complete genome sequence of the newly isolated enterococcal lytic phage was analysed, and it was demonstrated that its recombinant endolysin had broad lytic activity against various Gram‐positive pathogens. Significance and Impact of the Study: Bacteriophage EFAP‐1 and its lytic protein, EFAL‐1, can be utilized as potent antimicrobial agents against Enterococcus spp. strains resistant to conventional antibiotics in hospital infections and also as environmental disinfectants to control disease‐causing Enterococcus spp. in dairy farms.     

Antibacterial activity and synergy of antibiotics with sanguisorbigenin isolated from Sanguisorba officinalis L. against methicillin-resistant Staphylococcus aureus

The present study evaluated the antibacterial activity and the synergy of the sanguisorbigenin (SGB) from the dried root of Sanguisorba officinalis L. combined with β-lactam antibiotics against methicillin-resistant Staphylococcus aureus. A total of six strains of reference strain and clinical isolates were used to determine the antibacterial activity using a broth microdilution assay, and the synergistic effects were determined using a checkerboard assay. To analyse the mechanism of synergy, we conducted the level of penicillin-binding protein 2a by western blot. In addition, quantitative RT-PCR was performed to analyse the mecA gene expression. The minimal inhibitory concentration values of SGB against six strains of S. aureus were in the range of 12·5–50 μg ml⁻¹, and there were synergy, or partial synergy effects when SGB was combined with antibiotics. Furthermore, when treated with SGB, the level of penicillin-binding protein 2a and the expression of the mecA gene was reduced significantly. In conclusion, this study demonstrated that SGB is a potential natural antibacterial agent against methicillin-resistant S. aureus that represents a considerable burden on the healthcare system worldwide, and may an exceptionally modulator of β-lactam antibiotics.     

Identification and evaluation of quercetin as a potential inhibitor of naphthoate synthase from Enterococcus faecalis

Enterococcus faecalis is a gram‐positive, rod‐shape bacteria responsible for around 65% to 80% of all enterococcal nosocomial infections. It is multidrug resistant (MDR) bacterium resistant to most of the first‐line antibiotics. Due to the emergence of MDR strains, there is an urgent need to find novel targets to develop new antibacterial drugs against E. faecalis. In this regard, we have identified naphthoate synthase (1,4‐dihydroxy‐2‐naphthoyl‐CoA synthase, EC: 4.1.3.36; DHNS) as an anti‐E. faecalis target, as it is an essential enzyme for menaquinone (vitamin K₂) synthetic pathway in the bacterium. Thus, inhibiting naphtholate synthase may consequently inhibit the bacteria's growth. In this regard, we report here cloning, expression, purification, and preliminary structural studies of naphthoate synthase along with in silico modeling, molecular dynamic simulation of the model and docking studies of naphthoate synthase with quercetin, a plant alkaloid. Biochemical studies have indicated quercetin, a plant flavonoid as the potential lead compound to inhibit catalytic activity of EfDHNS. Quercetin binding has also been validated by spectrofluorimetric studies in order to confirm the bindings of the ligand compound with EfDHNS at ultralow concentrations. Reported studies may provide a base for structure‐based drug development of antimicrobial compounds against E. faecalis.