Chemical composition and antioxidant and anticandidal activities of essential oils from different wild Moroccan Thymus species

Samples of the aerial parts of Thymus broussonetii, T. ciliatus, T. leptobotrys, T. maroccanus, T. pallidus, T. satureioides, and T. serpyllum collected from different natural regions in southern and south-western Morocco were analyzed for their qualitative and quantitative essential oil profiles. In total, 46 compounds, representing more than 99% of the oils, were characterized. Monoterpenes, both hydrocarbons (12.9-58.0%) and oxygenated monoterpenes (38.8-81.1%), were the principal classes of compounds for most of the thyme species studied. Cluster analysis allowed the classification of the species into three main groups: a carvacrol group (Group I), comprising the species T. maroccanus and T. leptobotrys, a linalyl acetate and (E)-nerolidol group (Group II), represented by T. serpyllum, and a thymol and/or carvacrol, γ-terpinene, and p-cymene group (Group III), composed of T. satureioides, T. broussonetii, T. ciliatus, and T. pallidus. The essential oils were screened for their antioxidant and anticandidal activities. The data showed that the oils obtained from T. leptobotrys and T. maroccanus (carvacrol group) possessed the highest antioxidant activities as assessed by the determination of the DPPH free radical-scavenging ability and the ferric-reducing potential. The anticandidal assays indicated that the highest activity was noticed for the essential oil isolated from T. leptobotrys.     

椒样薄荷、薄荷和苏格兰留兰香精油与抗生素的协同抑菌功能

以开花期的椒样薄荷（Mentha×piperita）、薄荷（M.haplocalyx）和苏格兰留兰香（M.×gentilis）叶片部位提取的精油为研究对象,通过GC-MS分析,并采用纸片扩散法研究了3种精油单独使用及与抗生素联合使用时对金黄色葡萄球菌、蜡状芽孢杆菌、大肠杆菌、绿脓杆菌和肺炎克雷伯氏菌的抑制情况。结果表明,（1）椒样薄荷与薄荷精油中含量最高的成分为薄荷醇、薄荷酮和异薄荷酮,苏格兰留兰香精油的主要成分为香芹酮和柠檬烯。薄荷和苏格兰留兰香精油符合欧洲药典与ISO标准,椒样薄荷需要继续改良以提高其精油品质与抑菌功能。（2）精油单独使用时,Pseudomonas aeruginosa ATCC15442对椒样薄荷精油和薄荷精油敏感;P.aeruginosa ATCC27853对薄荷精油和苏格兰留兰香精油敏感。精油与抗生素联合使用时抑菌范围和强度均有所改变：绿脓杆菌的2个菌株对精油与抗生素的组合最为敏感,其中,椒样薄荷精油与头孢他啶的组合对P.aeruginosa ATCC15442显示出最强的增效作用,薄荷精油与头孢他啶混合之后对P.aeruginosa ATCC27853出现拮抗作用。Staphylococcus aureus ATCC25923对所有精油以及精油与抗生素混合物均有抗性。（3）椒样薄荷、薄荷和苏格兰留兰香精油的不同成分及其含量差异不仅对精油品质有影响,而且影响精油对测试菌种的抑制作用,可考虑将其作为薄荷属植物品质育种的参考指标。     

椒样薄荷、薄荷和苏格兰留兰香精油与抗生素的协同抑菌功能

以开花期的椒样薄荷(Mentha × piperita)、薄荷(M. haplocalyx)和苏格兰留兰香(M. × gentilis)叶片部位提取的精油为研究对象, 通过GC-MS分析, 并采用纸片扩散法研究了3种精油单独使用及与抗生素联合使用时对金黄色葡萄球菌、蜡状芽孢杆菌、大肠杆菌、绿脓杆菌和肺炎克雷伯氏菌的抑制情况。结果表明, (1) 椒样薄荷与薄荷精油中含量最高的成分为薄荷醇、薄荷酮和异薄荷酮, 苏格兰留兰香精油的主要成分为香芹酮和柠檬烯。薄荷和苏格兰留兰香精油符合欧洲药典与ISO标准, 椒样薄荷需要继续改良以提高其精油品质与抑菌功能。(2) 精油单独使用时, Pseudomonas aeruginosa ATCC 15442对椒样薄荷精油和薄荷精油敏感; P. aeruginosa ATCC 27853对薄荷精油和苏格兰留兰香精油敏感。精油与抗生素联合使用时抑菌范围和强度均有所改变: 绿脓杆菌的2个菌株对精油与抗生素的组合最为敏感, 其中, 椒样薄荷精油与头孢他啶的组合对P. aeruginosa ATCC 15442显示出最强的增效作用, 薄荷精油与头孢他啶混合之后对P. aeruginosa ATCC 27853出现拮抗作用。Staphylococcus aureus ATCC 25923对所有精油以及精油与抗生素混合物均有抗性。(3) 椒样薄荷、薄荷和苏格兰留兰香精油的不同成分及其含量差异不仅对精油品质有影响, 而且影响精油对测试菌种的抑制作用, 可考虑将其作为薄荷属植物品质育种的参考指标。     

Chemical composition and antimicrobial activity of Cymbopogon citratus and Cymbopogon giganteus essential oils alone and in combination

As part of ongoing research on the chemical composition and the antimicrobial properties of Burkinabe plants essential oils alone and in combination, essential oils (EOs) from leaves of Cymbopogon citratus and Cymbopogon giganteus from Burkina Faso were analyzed by GC-FID and GC-MS. Five constituents, which accounted for 96.3% of the oil, were identified in the EO of C. citratus. Geranial (48.1%), neral (34.6%) and myrcene (11.0%) were the major constituents. For C. giganteus a total of eight compounds were identified which represented 86.0% of the oils extracted. The dominant compounds were limonene (42%) and a set of monoterpene alcohols: trans-p-mentha-1(7),8-dien-2-ol (14.2%), cis-p-mentha-1(7),8-dien-2-ol (12%), trans-p-mentha-2,8-dien-1-ol (5.6%) and cis-p-mentha-2,8-dien-1-ol (5.2%). The EOs were tested against nine bacteria by using disc diffusion and microdilution methods. C. giganteus EO showed antimicrobial effects against all microorganisms tested whereas C. citratus EO failed to inhibit Pseudomonas aeruginosa. The antimicrobial activity of combinations of the two EOs was quantified by the checkerboard method. Combinations of the two EOs exerted synergistic, additive and indifferent antimicrobial effects. Results of the present investigation provide evidence that the combinations of plant EOs could be assessed for synergistic activity in order to reduce their minimum effective dose.     

Chemical composition and synergistic effect of three Moroccan lavender EOs with ciprofloxacin against foodborne bacteria: a promising approach to modulate antimicrobial resistance

The aim of this study was to determine the chemical profile of the essential oils (EOs) of three Moroccan lavender species (Lavandula pedunculata, LP; Lavandula angustifolia, LA; and Lavandula maroccana, LM) and to investigate, for the first time, the synergistic effect of the optimal mixture of the EOs with conventional antibiotic ciprofloxacin against three pathogenic foodborne bacteria. Gas chromatography/mass spectrometry analysis showed that eucalyptol (39·05%), camphor (24·21%) and borneol (8·29%) were the dominant compounds of LA-EO. LP-EO was characterized by the abundance of camphor (74·51%) and fenchone (27·06%), whereas carvacrol (42·08%), camphor (17·95%) and fenchone (12·05%) were the main constituents of LM-EO. EOs alone or combined showed a remarkable antimicrobial activity against the tested bacteria with minimum inhibitory concentrations (MICs) ranging from 3·53 to 15·96 mg ml⁻¹. The optimal mixture, calculated using a mixture design, corresponded to 19% LA, 38% LP and 43% LM. All combination of the EOs and the best EO mixture with ciprofloxacin exhibited a total synergism with fractional inhibitory concentration index values ranging from 0·27 to 0·37. The best EO mixture showed the highest gain of 128-fold, especially against Salmonella spp., more than that found testing the EOs separately. These findings should be taken into consideration for a possible application in the pharmaceutical and food industries.     

In vitro activity of antibiotic combinations against multidrug-resistant strains of Acinetobacter baumannii and the effects of their antibiotic resistance determinants

Various combinations of antibiotics are reported to show synergy in treating nosocomial infections with multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii). Here, we studied hospital-acquired outbreak strains of MDR A. baumannii to evaluate optimal combinations of antibiotics. One hundred and twenty-one strains were grouped into one major and one minor clonal group based on repetitive PCR amplification. Twenty representative strains were tested for antibiotic synergy using Etest(?). Five strains were further analyzed by analytical isoelectric focusing and PCR to identify β-lactamase genes or other antibiotic resistance determinants. Our investigation showed that the outbreak strains of MDR A. baumannii belonged to two dominant clones. A combination of colistin and doxycycline showed the best result, being additive or synergistic against 70% of tested strains. Antibiotic additivity was observed more frequently than synergy. Strains possessing the same clonality did not necessarily demonstrate the same response to antibiotic combinations in vitro. We conclude that the effect of antibiotic combinations on our outbreak strains of MDR A. baumannii seemed strain-specific. The bacterial response to antibiotic combinations is probably a result of complex interactions between multiple concomitant antibiotic resistance determinants in each strain.     

Chemical Constituent,Antimicrobial Activity,and Synergistic Effect of the Stem,Leaf, and Flower Essential Oil of the Artemisia fragrans Willd. from Khoy

Artemisia fragrans is commonly used as a folk medicine as antispasmodic, anti-pyretic, anti-inflammatory, and abortifacient agents. The villagers use its pungent odor to repel rodents, mites, and pests, as well as its essential oil and smoke after burning to treat lung infections after uprooting the plant. Herein, we extracted the essential oils (EOs) of different parts of the plant and analyzed their chemical compositions and antibacterial activities. The chemical analysis led to the identification of 73, 59, and 57 compounds in the EOs of the stem, leaf, and flower, respectively. All of the EOs exhibited antibacterial activities against both G+ and G− bacteria. The EOs of the leaf and flower were more effective against tested bacteria, except B. anthracis and P. aeruginosa, compared to that of the stem. The binary combination of the EOs (stem and flower) or (stem and leaf) showed a synergistic effect. Statistical analysis indicated EOs of leaf and flower are more potent than that of the stem. These findings suggest the application of leaf and flower of the plant, which not only can prevent its uprooting but also ensure better therapeutic function.     

Activity and synergistic interactions of stilbenes and antibiotic combinations against bacteria in vitro

The synergistic antibacterial activity of two stilbenes [3,4??,5-trihydroxystilbene (1) and 3,5-dihydroxy-4-isopropylstilbene(2)] purified from a Bacillus sp. N strain associated with entomopathogenic nematode Rhabditis (Oscheius) in combination with ciprofloxacin and cefotaxime was investigated. The activity of the stilbenes and standard antibiotics on bacteria were determined using the macrodilution method. The minimum inhibitory concentration and minimum bactericidal concentration of the stilbenes was compared with that of the standard antibiotics. The antibacterial activities of stilbenes against pathogenic bacteria were assessed using the checkerboard and time-kill methods to evaluate the synergistic effects of stilbenes in treatment with ciprofloxacin or cefotaxime. The results of the present study showed that the combination effects of both stilbenes with ciprofloxacin were synergistic (FIC index <0.5). Whereas stilbene 2 with cefotaxime recorded additive. Furthermore, time-kill study showed that the growth of the tested bacteria was completely attenuated with 12?C24?h of treatment with 50:50 ratios of stilbenes and antibiotics. These results suggest that stilbenes combined with antibiotics may be microbiologically beneficial and not antagonistic. These findings have potential implications in delaying the development of resistance as the antibacterial effect is achieved with lower concentrations of both drugs (antibiotics and stilbenes). The in vitro synergistic activity of stilbenes and antibiotics against bacteria is reported here for the first time.     

Synergistic effect of Myrtus communis L. essential oils and conventional antibiotics against multi-drug resistant Acinetobacter baumannii wound isolates

Acinetobacter baumannii is a rapidly emerging, highly resistant clinical pathogen with increasing prevalence. In recent years, the limited number of antimicrobial agents available for treatment of infections with multi-drug resistant (MDR) strains reinforced tendency for discovery of novel antimicrobial agents or treatment strategies. The aim of the study was to determine antimicrobial effectiveness of three Myrtus communis L. essential oils, both alone and in combination with conventional antibiotics, against MDR A. baumannii wound isolates. The results obtained highlighted the occurrence of good antibacterial effect of myrtle oils when administered alone. Using checkerboard method, the combinations of subinhibitory concentrations of myrtle essential oils and conventional antibiotics, i.e. polymixin B and ciprofloxacine were examined. The results proved synergism among M. communis L. essential oils and both antibiotics against MDR A. baumannii wound isolates, with a FIC index under or equal 0.50. Combination of subinhibitory concentrations of essential oils and ciprofloxacin most frequently reduced bacterial growth in synergistic manner. The similar has been shown for combination with polymyxin B; furthermore, the myrtle essential oil resulted in re-sensitization of the MDR wound isolates, i.e. MICs used in combination were below the cut off for the sensitivity to the antibiotic. Time-kill curve method confirmed efficacy of myrtle essential oil and polymyxin B combination, with complete reduction of bacterial count after 6 h. The detected synergy offers an opportunity for future development of treatment strategies for potentially lethal wound infections caused by MDR A. baumannii.     

Analysis of Chemical Composition and Assessment of Antioxidant,Cytotoxic and Synergistic Antibacterial Activities of Essential Oils from Different Plant Parts of Piper boehmeriifolium

The essential oils (EOs) from leaves, stems, and whole plant of Piper boehmeriifolium were analyzed using GC/FID and GC/MS. The main constituents of P. boehmeriifolium EOs were β‐caryophyllene, caryophyllene oxide, β‐elemene, spathulenol, germacrene D, β‐selinene, and neointermedeol. The antioxidant potential of the EOs were determined using DPPH^?, ABTS^?+ and FRAP assays. In ABTS^?+ assay, the leaf oil exhibited a remarkable activity with an IC₅₀ value of 7.36 μg/mL almost similar to BHT (4.06 μg/mL). Furthermore, the antibacterial activity of the oils as well as their synergistic potential with conventional antibiotics were evaluated using microdilution and Checkerboard assays. The results revealed that the oils from different parts of P. boehmeriifolium inhibited the growth of all tested bacteria and the minimum inhibitory concentrations were determined to be 0.078 – 1.250 mg/mL. In combination with chloramphenicol or streptomycin, the oils showed significant synergistic antibacterial effects in most cases. Besides, the results of MTT assay indicated that the oil of the whole plant exhibited significant cytotoxic activities on human hepatocellular carcinoma cells (HepG2) and human breast cancer cells (MCF‐7). In summary, the P. boehmeriifolium oils could be regarded as a prospective source for pharmacologically active compounds.     

Synthesis and anti Methicillin resistant Staphylococcus aureus activity of substituted chalcones alone and in combination with non-beta-lactam antibiotics

A total of 30 chalcone analogues was synthesized via a base catalyzed Claisen Schmidt condensation and screened for their in vitro antibacterial activity against Methicillin-sensitive Staphylococcus aureus (MSSA) and Methicillin-resistant Staphylococcus aureus (MRSA) alone or in combination with non beta-lactam antibiotics namely ciprofloxacin, chloramphenicol, erythromycin, vancomycin, doxycycline and gentamicin. In the checkerboard technique, fractional inhibitory concentration indices (FICI) show that the following combinations like ciprofloxacin with 25 (4'-bromo-2-hydroxychalcone); doxycycline with 21 (4-hydroxychalcone); doxycycline with 25; and doxycycline with 4 (2',2-dihydroxychalcone) were synergistic against MRSA. In term SAR study, the relationship between chalcone structure and their antibacterial activity against S. aureus and synergy with tested antibiotics were discussed. Possible mechanisms for antibacterial activity of chalcones alone as well as the synergistic effect in combinations were proposed by molecular modeling studies, respectively. Combinations of chalcones with conventional antibiotics could be an effective alternative in the treatment of infection caused by MRSA.     

The antimicrobial activity of four commercial essential oils in combination with conventional antimicrobials

Aims:  Due to the emergence of multi-drug resistance, alternatives to conventional antimicrobial therapy are needed. This study aims to investigate the in vitro pharmacological interactions between essential oils (considered valuable as natural therapeutic treatments) and conventional antimicrobials (ciprofloxacin/amphotericin B) when used in combination.
Methods and Results:  Interactions of the essential oils ( Melaleuca alternifolia , Thymus vulgaris , Mentha piperita and Rosmarinus officinalis ) when combined with ciprofloxacin against Staphylococcus aureus indicate mainly antagonistic profiles. When tested against Klebsiella pneumoniae the isobolograms show antagonistic, synergistic and additive interactions depending on the combined ratio. The R. officinalis/ ciprofloxacin combination against K. pneumoniae displayed the most favourable synergistic pattern. The interactions of M. alternifolia (tea tree), T.   vulgaris (thyme), M. piperita (peppermint) and R. officinalis (rosemary) essential oils with amphotericin B indicate mainly antagonistic profiles when tested against Candida albicans.
Conclusion:  While a number of interactions show complete antagonism, others show varied (synergistic, additive and/or antagonistic) interactions, thus the efficacy is dependent on the ratio in which the two components co-exist.
Significance and Impact of the Study:  The predominant antagonistic interactions noted here, suggests that some natural therapies containing essential oils should be used with caution when combined with antibiotics.     

Novel strategies of essential oils,chitosan, and nano- chitosan for inhibition of multi-drug resistant: E. coli O157:H7 and Listeria monocytogenes

Despite the wide range of available antibiotics, food borne bacteria demonstrate a huge spectrum of resistance. The current study aims to use natural components such as essential oils (EOs), chitosan, and nano-chitosan that have very influential antibacterial properties with novel technologies like chitosan solution/film loaded with EOs against multi-drug resistant bacteria. Two strains of Escherichia coli O157:H7 and three strains of Listeria monocytogenes were used to estimate antibiotics resistance. Ten EOs and their mixture, chitosan, nano-chitosan, chitosan plus EO solutions, and biodegradable chitosan film enriched with EOs were tested as antibacterial agents against pathogenic bacterial strains. Results showed that E. coli O157:H7 51,659 and L. monocytogenes 19,116 relatively exhibited considerable resistance to more than one single antibiotic. Turmeric, cumin, pepper black, and marjoram did not show any inhibition zone against L. monocytogenes; Whereas, clove, thyme, cinnamon, and garlic EOs exhibited high antibacterial activity against L. monocytogenes with minimum inhibitory concentration (MIC) of 250–400 μl 100^?1 ml and against E. coli O157:H7 with an MIC of 350–500 μl 100^?1 ml, respectively. Among combinations, clove, and thyme EOs showed the highest antibacterial activity against E. coli O157:H7 with MIC of 170 μl 100^?1 ml, and the combination of cinnamon and clove EOs showed the strongest antibacterial activity against L. monocytogenes with an MIC of 120 μl 100^?1 ml. Both chitosan and nano-chitosan showed a promising potential as an antibacterial agent against pathogenic bacteria as their MICs were relatively lower against L. monocytogenes than for E. coli O157:H7. Chitosan combined with each of cinnamon, clove, and thyme oil have a more effective antibacterial activity against L. monocytogenes and E. coli O157:H7 than the mixture of oils alone. Furthermore, the use of either chitosan solution or biodegradable chitosan film loaded with a combination of clove and thyme EOs had the strongest antibacterial activity against L. monocytogenes and E. coli O157:H7. However, chitosan film without EOs did not exhibit an inhibition zone against the tested bacterial strains.     

Synergistic larvicidal and repellent effects of essential oils of three Origanum species on Rhipicephalus annulatus tick

Ticks are of great economic importance worldwide, both because they represent major obstacles to livestock productivity and because of their ability to transmit diseases to humans and animals. Although synthetic acaricides are the most common method for tick control, their overuse has led to the development of resistance as well as unacceptable residual levels in animal products and in the environment in general. There is therefore an urgent need to identify alternative treatments. Among such alternative approaches for tick control is plant essential oil (EO) therapy. In the present study, we investigated the synergistic effect of EOs of three oregano species—Origanum onites, O. majorana and O. minutiflorum—against Rhipicephalus annulatus larvae. Gas chromatography–mass spectrometry profiles of the three EOs revealed that carvacrol was their major component, with a concentration of 86.2% in O. majorana, 79.1% in O. minutiflorum and 77.4% in O. onites. The results of larvicidal assays revealed that the doses that lead to the death of 50% of the ticks (LC₅₀) were 22.99, 25.08 and 27.06 µL/mL for O. majorana, O. minutiflorum and O. onites EOs, respectively, whereas the doses that lead to the death of 99% (LC₉₉) were 41.26, 43.62 and 48.96 µL/mL. In addition, the LC₅₀ and LC₉₉ of the three oils combined was lower (viz., 4.01 and 6.97 µL/mL) than that of each oil alone. The tested EOs were also able to repel larvae of R. annulatus to varying degrees, with O. onites oil exhibiting the greatest repellent effect, as shown by the lowest RC₅₀ dose, followed by O. minutiflorum and O. majorana. Interestingly, this means that the oil that was least effective in killing the larvae was the most effective in repelling them. The calculated synergistic factor of any combination was higher than 1 which means that combinations have a synergistic effect. In conclusion, the combination of all three oils showed higher toxic and repellent activities than either oil separately or combinations of any two oils, suggesting synergistic effects with low doses. Further studies including field trials and the establishment of the mode of action and side effects are urgently needed to expand on these findings, and other tick stages such as adults should also be tested.

     

Odoriferous Therapy: A Review Identifying Essential Oils against Pathogens of the Respiratory Tract

This review explores the body of scientific information available on the antimicrobial properties of essential oils against pathogens responsible for respiratory infections and critically compares this to what is recommended in the Layman's aroma‐therapeutic literature. Essential oils are predominantly indicated for the treatment of respiratory infections caused by bacteria or viruses (total 79.0 %), the efficacy of which has not been confirmed through clinical trials. When used in combination, they are often blended for presumed holistic synergistic effects. Of the essential oils recommended, all show some degree of antioxidant activity, 50.0 % demonstrate anti‐inflammatory effects and 83.3 % of the essential oils showed antihistaminic activity. Of the essential oils reviewed, 43.8 % are considered non‐toxic while the remaining essential oils are considered slightly to moderately toxic (43.7 %) or the toxicity is unknown (12.5 %). Recommendations are made for further research into essential oil combinations.     

Effects of essential oils on methane production and fermentation by, and abundance and diversity of, rumen microbial populations

Five essential oils (EOs), namely, clove oil (CLO), eucalyptus oil (EUO), garlic oil (GAO), origanum oil (ORO), and peppermint oil (PEO), were tested in vitro at 3 different doses (0.25, 0.50, and 1.0 g/liter) for their effect on methane production, fermentation, and select groups of ruminal microbes, including total bacteria, cellulolytic bacteria, archaea, and protozoa. All the EOs significantly reduced methane production with increasing doses, with reductions by 34.4%, 17.6%, 42.3%, 87%, and 25.7% for CLO, EUO, GAO, ORO, and PEO, respectively, at 1.0 g/liter compared with the control. However, apparent degradability of dry matter and neutral detergent fiber also decreased linearly with increasing doses by all EOs except GAO. The concentrations of total volatile fatty acids were not affected by GAO, EUO, or PEO but altered linearly and quadratically by CLO and ORO, respectively. All the EOs also differed in altering the molar proportions of acetate, propionate, and butyrate. As determined by quantitative real-time PCR, all the EOs decreased the abundance of archaea, protozoa, and major cellulolytic bacteria (i.e., Fibrobacter succinogenes, Ruminococcus flavefaciens, and R. albus) linearly with increasing EO doses. On the basis of denaturing gradient gel electrophoresis analysis, different EOs changed the composition of both archaeal and bacterial communities to different extents. The Shannon-Wiener diversity index (H') was reduced for archaea by all EOs in a dose-dependent manner but increased for bacteria at low and medium doses (0.25 and 0.50 g/liter) for all EOs except ORO. Due to the adverse effects on feed digestion and fermentation at high doses, a single EO may not effectively and practically mitigate methane emission from ruminants unless used at low doses in combinations with other antimethanogenic compounds.     

Activity of the Antimicrobial Peptide and Thanatin Analog S-thanatin on Clinical Isolates of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> Resistant to Conventional Antibiotics with Different Structures

The treatment of infections caused by bacteria resistant to the vast majority of antibiotics is a challenge worldwide. To evaluate the effect of S-thanatin (an analog of thanatin, a cationic antimicrobial peptide isolated from the hemipteran insect Podisus maculiventris) against microbial resistant to antibiotics, we studied its bactericidal kinetics, synergistic effect, resistance, and activity on clinical isolates of Klebsiella pneumoniae resistant to conventional antibiotics with different structures. The bactericidal rate of S-thanatin was more than 99% against K. pneumoniae ATCC 700603 when bacterial cultures were monitored for 60 min. The peptide was synergistic with β-lactam cefepime in most of the clinical MDR isolates tested (7/8). An average value of FIC was 0.3708. No synergy was found between the peptide and amoxicillin, gentamycin, tetracycline, or ciprofloxacin in all bacteria tested. A total of 48 isolates of K. pneumoniae with different resistance spectrum tested was susceptible to S-thanatin. The MICs were 6.25–25 μg/ml. No significant difference in the MICs of S-thanatin between the sensitive isolates and the resistant isolates to single antibiotic was observed (P > 0.05). The resistance of K. pneumoniae ATCC 700603 to S-thanatin was slightly higher, when cultured at sub-inhibitory concentration for 5 days. S-thanatin may be an attractive candidate for developing into an antimicrobial agent.     

Annual trends in antibiotic resistance of nosocomial Acinetobacter baumannii strains and the effect of synergistic antibiotic combinations

Acinetobacter baumannii is becoming increasingly resistant to antibiotics often requiring combination therapy. Annual changes of resistance to selected antimicrobials of 150 A. baumannii strains, isolated as nosocomial pathogens between 1994 and 2000 were investigated. The synergistic effects of antimicrobials were studied using a microdilution checkerboard technique in eight selected isolates resistant to third-generation cephalosporins and beta-lactam/beta-lactamase inhibitor combinations and to at least one aminoglycoside. Rates of resistance of cefepime, ceftazidime, ampicillin/sulbactam, amikacin and ciprofloxacin (before 1996 and between 1996-2000) were 29.7% - 72.6, 37.8% - 81.4%, 35.1% - 72.6%, 8.1% - 56.6%, 5.4% - 46.0% respectively (p < 0.001 for each one). Synergy was observed in at least one of the combinations of antibiotics from seven of eight isolates (87%), no antagonism was detected with any combination. Ceftazidime-amikacin (50%) and ampicillin/sulbactam-tobramycin (50%) were the most effective combinations. Due to the effectiveness of sulbactams to Acinetobacter, ampicillin/sulbactam-tobramycin combination is recommended as the first line of choice.     

Positive antibacterial co-action between hop (Humulus lupulus) constituents and selected antibiotics

The research reported here deals with co-action of the hop (Humulus lupulus)-derived anti-bacterial compounds, lupulone and xanthohumol, with several antibiotics. Among the antibiotics investigated for their co-action, polymyxin B sulfate, tobramycin and ciprofloxacin had a positive co-action in inhibiting selected test bacteria. The disc/well-diffusion assay and the minimum inhibitory concentration test (MIC) were employed to determine co-action. Both Gram-positive and Gram-negative bacteria were used in the evaluation. There was some co-action against all Gram-positive bacteria tested. Surprisingly, there was some positive co-action even against certain Gram-negative bacteria but not against others. Particularly, there was no co-action against E.coli. An antibacterial cream with lupulone, neomycin and polymyxin B sulfate was prepared and showed co-action. Ideas for other practical applications of this effect are put forth. The mechanism of the synergistic effect is briefly discussed but no attempt was made to prove it experimentally.     

Activity and interactions of antibiotic and phytochemical combinations against Pseudomonas aeruginosa in vitro

In this study the in vitro activities of seven antibiotics (ciprofloxacin, ceftazidime, tetracycline, trimethoprim, sulfamethoxazole, polymyxin B and piperacillin) and six phytochemicals (protocatechuic acid, gallic acid, ellagic acid, rutin, berberine and myricetin) against five P. aeruginosa isolates, alone and in combination are evaluated. All the phytochemicals under investigation demonstrate potential inhibitory activity against P. aeruginosa. The combinations of sulfamethoxazole plus protocatechuic acid, sulfamethoxazole plus ellagic acid, sulfamethoxazole plus gallic acid and tetracycline plus gallic acid show synergistic mode of interaction. However, the combinations of sulfamethoxazole plus myricetin shows synergism for three strains (PA01, DB5218 and DR3062). The synergistic combinations are further evaluated for their bactericidal activity against P. aeruginosa ATCC strain using time-kill method. Sub-inhibitory dose responses of antibiotics and phytochemicals individually and in combination are presented along with their interaction network to suggest on the mechanism of action and potential targets for the phytochemicals under investigation. The identified synergistic combinations can be of potent therapeutic value against P. aeruginosa infections. These findings have potential implications in delaying the development of resistance as the antibacterial effect is achieved with lower concentrations of both drugs (antibiotics and phytochemicals).