Lowest Minimum Inhibitory Concentration Research Articles

Quantitative Analysis of Swertiamarin Content from Fagraea fragrans Leaf Extract using HPLC Technique and its Correlation to Antibacterial Activity

The rise in drug resistance poses escalating challenges for antibacterial medications, leading to an urgent demand for the exploration and innovation of new antibacterial drugs. Fagraea fragrans Roxb., belonging to the Gentianaceae family, is one of the common herbal medicines which can be found abundantly in Southeast Asia. The secoiridoid glucoside swertiamarin, one of the major compounds in F. fragrans leaf, exhibits antimicrobial effects. To guarantee the medicinal effectiveness of F. fragrans leaves, it is essential to identify a standardized analytical method for quantifying the active compound. In this study, the optimized HPLC method following ICH guideline was validated for the quantitative analysis of swertiamarin content in F. fragrans leaf in terms of linearity (y = 5733.5x - 369.1; R2 = 0.9999), accuracy (93.57-96.39% recovery), precision (0.91% RSD for repeatability precision; 1.19% RSD for intermediate precision), limit of detection (0.73 µg/mL), limit of quantitation (2.23 µg/mL), specificity (peak purity index = 0.999995) and robustness (% RSD <1).The maximum wavelength of swertiamarin was found to be at 238 nm. The amount of swertiamarin content in F. fragrans leaf extract conducted from the validated HPLC method was found to be 0.0259 ± 0.0005 g/100 g crude drug. The leaf extract exhibited antimicrobial activity against clinical isolates of Enterobacter cloacae, Klebsiella pneumonia, and Escherichia coli at 0.125 mg/mL, and Pseudomonas aeruginosa at 0.5, showing minimum inhibitory concentration (MIC) values. Whereas swertiamarin exhibited even lower MIC values. The developed HPLC analysis effectively determines swertiamarin content as a chemical marker to ensure the antimicrobial potential of F. fragrans leaves.

Synthesis, characterization, antibacterial efficacy, and Cytotoxicity of monoclinic KMg3(Al0.5B0.5)Si3O10F2: A novel material for anticariogenic applications

Fluorophlogopite is a well-known fluorosilicate glass-ceramic derivative known for its bioactivity, machinability and optimal mechanical properties. There is limited information regarding its antibacterial and biocompatible properties. This research paper presents the synthesis and characterization of a novel Boron-doped Fluorphlogopite [KMg3(Al0.5B0.5)Si3O10F2] aiming to improve its antibacterial properties intended for anticariogenic applications. The combustion synthesis method was employed, with oxalyl dihydrazide (ODH) (C2H6N4O2) serving as the fuel. X-ray Diffraction (XRD) analyses unveiled a monoclinic crystal system, showcasing a P21 space group, and an average crystallite size of approximately 28 nm. Morphological scrutiny divulged clustered, irregularly shaped, cluster-like structures. The energy gap was determined to be around 4.97 ± 0.0062 eV. Fourier-Transform Infrared (FTIR) spectroscopy depicted the presence of characteristic bonds. BET analysis indicated the presence of a large surface area and porous structure (mesopores), which may contribute to lower MIC and MBC values, enhancing antibacterial effectiveness. The antibacterial activity, evaluated via agar well diffusion, yielded an 8 mm zone of inhibition. Furthermore, the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) against S mutans were determined to be 2 mg/ml and 16 mg/ml, respectively. The biocompatibility of the synthesized KMg3(Al0.5B0.5)Si3O10F2 was assessed through the MTT assay, indicating non-toxic behavior at a concentration of 12 μg/ml with 98 % cell viability, while showing moderate toxicity with 61 % viable cells at its highest concentration of 200 μg/ml.

Antimicrobial Activity, Cytotoxicity, and Qualitative Phytochemistry of Leaf, stem bark, and root bark extracts from Prunus africana (Hook. F.) Kalkman

The rise of resistant strains poses a significant public health risk, particularly, in sub-Saharan Africa, where over 50% of global infectious disease-associated deaths occur, highlighting the urgent need for novel, safe, affordable, and accessible antimicrobials. Accordingly, we investigated the antimicrobial activity, cytotoxicity, and qualitative phytochemistry of the aqueous, hydroethanolic, and acetonic leaf, stem bark, and root bark extracts of Prunus africana (Hook. F.) Kalkman, based on its ethnomedicinal information. The results showed the aqueous root bark and aqueous/acetonic stem bark extracts demonstrated significant (p<0.05) antimicrobial efficacy against S. aureus at 800 µg/ml, outperforming other extracts and the reference antibiotic. Growth inhibition zones for most extracts on S. aureus showed a concentration-dependent increase, though not significantly (p>0.05) different. The acetonic root bark extract, particularly at 800 µg/ml, exhibited superior inhibitory effects against B. cereus compared to other extracts (p<0.05), although the positive control antibiotic significantly (p<0.05) outperformed all plant extracts. Notably, none of the studied extracts affected P. aeruginosa and E. coli, while varying effects were observed against C. albicans. Further we observed that the hydroethanolic and aqueous stem bark extracts' exceptionally low Minimum Inhibitory and Bactericidal Concentrations (MICs and MBCs) against S. aureus (3.125 µg/ml). Conversely, the acetonic leaf extract showed higher MIC and MBC values against S. aureus (100 µg/ml). Cytotoxicity assessments using brine shrimp nauplii revealed the percentage mortalities caused by Vincristine and aqueous root/stem bark extracts at 1000 µg/ml, were significantly (p<0.05) higher than those caused by other extracts (Median lethal concentrations (LC50) of 513 µg/ml to 24327.82 µg/ml). Qualitative phytochemistry identified alkaloids in root bark and stem bark extracts, flavonoids, phenols, quinones, steroids, and terpenoids across all samples, with saponins in acetonic root bark and all three leaf extracts, and glycosides in acetonic stem bark, hydroethanolic root bark, and acetonic leaf extracts. These findings highlight the diverse antimicrobial and cytotoxic properties of P. africana extracts, suggesting potential therapeutic applications and emphasise the need for further exploration.

An In Vitro Study to Evaluate the Antimicrobial Activity of a Zinc Citrate, Sodium Fluoride, Alum and Xylitol-Based Toothpaste Formulation.

Periodontitis is a prevalent condition significantly affecting oral health. Comorbid conditions, such as diabetes, can heighten the severity of periodontal disease and overall oral health. Therefore, to enhance oral health and manage comorbid conditions, comprehensive periodontal care is essential. This approach could involve using toothpaste containing antimicrobial ingredients in routine oral care. This paper presents the results of an in vitro study analysing the antimicrobial properties of the test formulation containing zinc citrate, alum, sodium fluoride, and xylitol-based toothpaste(Stolin-R).These ingredients work together to help in providing comprehensive oral care by controlling growth of bacteria majorly responsible for periodontal disease and thus maintaining optimal oral hygiene. To determine the antimicrobial properties of zinc citrate, alum, sodium fluoride, and xylitol-based toothpaste formulationagainst key periodontal pathogens through in vitro analyses. The antimicrobial efficacy of test formulationis evaluated through minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-dependent antibacterial assessment against key periodontal pathogens, including Porphyromonas gingivalis, Tannerella forsythia, Fusobacterium nucleatum, Prevotella intermedia, Streptococcus mutans, and Bacteroides fragilis. The test formulationdemonstrated potent antimicrobial effectiveness against Bacteroides fragilis, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia, Streptococcus mutans, and Tannerella forsythia, by exhibiting low MIC and MBC. Additionally, significant bacterial reduction, exceeding 99.99%, was observed within five minutes, emphasising its potential as an effective adjunct in combating periodontal infection. Zinc citrate, alum, sodium fluoride, and xylitol-based toothpaste formulation demonstrates significant antimicrobial activity against key periodontal pathogens, suggesting its potential as an effective agent for maintaining oral health and combating gingival infection.

Influence of low-cost Thai leucoxene minerals on the growth, bioactive compounds, and antibacterial activities of Chrysanthemum indium L. cuttings in in vitro culture

The effects of low-cost Thai leucoxene mineral (LM) at different concentrations (10, 20, 30, 40, 50, and 60 mg/L) on the growth and antibacterial properties of Chrysanthemum indium L. cuttings under in vitro were evaluated. The primary chemical composition of LM was approximately 86% titanium dioxide (TiO2), as determined by dispersive X-ray spectroscopy. The crystalline structure, shape, and size were investigated by X-ray diffraction and scanning electron microscopy. LM at 40 and 50 mg/L significantly increased plant height, leaf number, node number, and fresh and dry weight. These growth-promoting properties were accompanied by improved chlorophyll and carotenoid contents and antioxidant enzyme activities and reduced malondialdehyde levels. Additionally, LM treatment at 40 and 50 mg/L had positive effects on antibacterial activity, as indicated by the lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values. The high levels of phenolic compounds in the plants contributed to the MIC and MBC values. In conclusion, these findings provide evidence for the effectiveness of LM in enhancing the growth of Chrysanthemum plants in in vitro culture and improving their antibacterial abilities.

Silencing of Resistance Mechanism in Vancomycin-Resistance Enterococci Using Antisense RNA of vanA Gene

The World Health Organization has included the problem of antibiotic resistance among the top 10 important health problems in the world. Treatment of infectious diseases has become more difficult due to the spread of antibiotic resistance between bacteria via transposable elements. Vancomycin-resistant enterococci (VRE) are of critical medical and public health importance due to their association with serious nosocomial infections and high risk of death. One of the most important features of VREs is that they have multiple antibiotic resistance and treatment options are reduced. Therefore, new treatment methods are needed. The vanA gene constitutes the building block of the vancomycin resistance mechanism and causes high resistance to vancomycin. In this study, it was aimed to investigate the neutralization of the vancomycin resistance mechanism by creating vanA antisense RNA (asRNA). The vanA positive VRE50 strain in our culture collection which was isolated from the clinical sample, was used to amplify the vanA gene by polymerase chain reaction (PCR). The amplified vanA amplicon was inserted inversely into the pUC19 plasmid by means of the enzyme cutting sites in the primers used. The resulting plasmid was combined with the pAT392 plasmid which can replicate in gram-positive bacteria and a fusion plasmid was created. The fusion plasmid whose orientation was confirmed, was transferred to the wild strain VRE50 by electroporation method. Minimum inhibitory concentration (MIC) values of transformed VRE (tVRE50) and wild type VRE50 strains used as control were determined by the E-Test method. The vancomycin MIC value of the wild type VRE50 strain was determined as 1024 µg/mL and that of the tVRE50 strain was 32 µg/mL and it was determined that the vancomycin resistance of the tVRE50 strain decreased with asRNA (antisense RNA). Antisense RNA technology is an important method for neutralizing the expression of genes. This study showed that neutralization of the vancomycin resistance gene may provide a lower MIC value in a vancomycin-resistant enterococcus strain and lead to increased susceptibility. This new approach provides a new method for VRE treatment by neutralizing the vancomycin resistance mechanism. The result obtained in this study needs to be supported by in vivo tests.

Molecular insights into quercetin-enhanced crystalline silver nanoparticles: Implications for breast cancer cell cytotoxicity and antibacterial action in Kyllinga nemoralis

Amidst the ongoing global health crisis posed by cancer and antibiotic-resistant infections, innovative solutions are in high demand. The utilization of Kyllinga nemoralis leaf (KNL) extracts for synthesizing silver nanoparticles (AgNPs) represents a novel approach, with the potential to deliver profound advancements in healthcare, benefitting society on a broad scale. Successful synthesis of AgNPs by KNL extracts for treating breast cancer cells, specifically MDA-MB-231 cells, is recorded in this report. The adsorption mechanism of quercetin (Q) on Ag and its optimized structural characteristics were computed at the DFT level. According to FTIR analysis, quercetin, one of the flavonoids found in KNL extract, acts as a reducing and stabilizing agent for the conversion of Ag+ ions to Ag0, and carboxylates serve as ligands that cap the AgNPs. The small-sized (7 nm), spherical particles, which are uniform in size and monodispersed, exhibit regulation over the size of the AgNPs due to being shielded by enough flavonoids and gallic acid absorbed into the extract. The observed negative zeta potential of −20 mV indicates the moderate stability of the AgNPs colloid. It is noted that AgNPs prepared at higher concentrations of KNL extract showed lower minimum inhibitory concentration (MIC) values (80 µg/mL) and larger inhibition zones (22 mm) against Pseudomonas aeruginosa. The cell viability rate of MDA-MB-231 cell lines decreases with increasing concentration of AgNPs. The antibacterial and anticancer activity of AgNPs is observed in a size-dependent manner. This research raises the possibility of using plant-based, small-sized AgNPs therapeutically for breast cancer and as antibacterial agents.

A carrier-free injectable hydrogel self-assembled using natural thymol and glycyrrhizin for MRSA-infected wound healing in rats

A carrier-free, self-assembled, injectable hydrogel was developed as wound dressing to deal with skin wound bleeding, bacterial infections, and wound healing. Natural thymol (THY) and glycyrrhizin were used to construct THY-loaded glycymicelles (THY@glycymicelles), which greatly improved the aqueous solubility of THY. Optimal THY@glycymicelles had a high encapsulation efficiency of THY and a uniform nanoparticle size. Interestingly, THY@glycymicelles could reversibly transform into THY@glycyrrhizin hydrogel (THY@glycygel) by adjusting neutral pH to skin pH (pH ∼ 4.9), and vice versa. THY@glycygel had a dense porous sponge microstructure and showed many excellent features, including injectable, hemostatic, antibacterial, and anti-inflammatory properties. In vitro antibacterial evaluation, THY@glycygel showed lower minimum inhibitory concentration to three tested bacteria than free THY. In terms of antibacterial mechanism, THY@glycygel could destroy the bacterial cell wall and membrane, increasing the extracellular alkaline phosphatase release, and inhibiting biofilm. THY@glycygel had strong hemostatic ability and exhibited great potential for antimicrobial activity and improving wound healing infected by methicillin-resistant Staphylococcus aureus (MRSA). Mechanisms including antimicrobial, promoting hair follicle growth, improving epidermis remolding and collagen deposition, decreasing inflammatory cytokine levels, and increasing growth factor levels promoted the MRSA-infected skin wound healing process of THY@glycygel. Totally, this novel hydrogel has great potential as wound dressing.

Antibiotic potentiating effect of Bauhinia purpurea L. against multidrug resistant Staphylococcus aureus.

Bauhinia purpurea L. is a medium-sized tree from the family Fabaceae. The plant is traditionally used as medicine by different tribes in Sikkim. The present study aimed to evaluate the modulation in minimum inhibitory concentration (MIC) of the bark methanol extract of Bauhinia purpurea L. against the clinical isolates of multidrug resistant Staphylococcus aureus. The synergistic activity of the test plant extract with different classes of antibiotics was also evaluated. The methanol extract of Bauhinia purpurea exhibited modulation by a 16-fold reduction in the MIC of clindamycin against both resistant and susceptible isolates, followed by penicillin and gentamicin, whereas a maximum of only a 4-fold MIC reduction was observed with ciprofloxacin. The lowest minimum inhibitory concentration and minimum bactericidal concentration showed by the plant extract was 0.48 and 0.97 mg/mL, respectively. The methanol extract of Bauhinia purpurea exhibited synergistic activity with penicillin, gentamicin, ciprofloxacin, and clindamycin against most of the tested isolates of multidrug-resistant Staphylococcus aureus (MDR-SA). Gas chromatography-mass spectrometry analysis of Bauhinia purpurea L. bark methanol extract revealed 16 phytocompounds. The results provide an insight into the potential antibacterial property of the plant extract in terms of its antibiotic MIC modulation and synergistic properties with the selected antibiotics. This is the first report of the antibiotic potentiation property of Bauhinia purpurea L., collected from Sikkim, India.

Combined effect of brazilin-rich extract and lawsone methyl ether against infection-causing bacteria

Bacterial contamination and infection widely affect the food, pharmaceutical and biomedical industries. Additionally, these bacteria developed resistance to synthetic antibiotics causing public health danger, globally. Natural plant extracts (NPE) are suitable alternatives to synthetic antibiotics to tackle antimicrobial resistance problems. Furthermore, a blend or combination of different NPEs exerts a wide spectrum of antimicrobial activity. Therefore, the combined effect of brazilin-rich extract (BRE) and lawsome methyl ether (LME) against infection-causing common bacteria were evaluated. BRE had a lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against most of the Gram-negative bacteria (Salmonella typhi, Salmonella typhimurium and Pseudomonas aeruginosa) while LME was active against most of the Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, and Staphylococcus epidermidis). The combination of BRE and LME at 2:1 and 1:1 concentration significantly reduced the MIC value of each compound as compared to either BRE or LME concentration alone (P < 0.05). Further time-kill kinetics revealed a 3.0–3.5 log reduction in Gram-positive bacteria and a 2.5–3.0 log reduction in Gram-negative bacteria during 120 min of incubation, respectively. Therefore, a combination of BRE and LME was recommended as natural antibacterial to synthetic antibiotics for food and pharmaceutical applications.

Comparative Study of Toxic Terpenoidal Aldehydes and Lactone Derivatives from the European Polypore Bondarzewia mesenterica.

Two unprecedented isomeric secondary metabolites named vibralactones Z5 (1a) and Z6 (1b), in addition to eleven known compounds (2-12), were isolated from solid-state rice culture medium of Bondarzewia mesenterica (Bondarzewiaceae). Chemical structures of the isolated compounds were established via spectral analyses. The new lactone derivatives were weakly active against Staphylococcus aureus without any significant cytotoxicity, while the molecules containing an aldehyde functionality showed significant antimicrobial and cytotoxic effects. For instance, erinacine P (7) and (+)-isovelleral (8) and erinacine P (7) were cytotoxic against all tested cell lines at IC50 values in the ranges of 3.5-14.2 and 2.8-30.2 μM, respectively. In addition, they revealed moderate antimicrobial activity with the lowest minimum inhibitory concentration (MIC) values recorded against Mucor hiemalis (8.3 μg/mL), Pichia anomala, and Rhodotorula glutinis at 16.6 μg/mL.

Potential applications of biosurfactants produced by different Pseudomonas syringae: A comparative study on interfacial activity, antimicrobial efficacy, and cytotoxicity

Finding novel biocompatible compounds with adequate interfacial activity and low toxicity still represents a great challenge for the scientific community. In this context, this work aims to compare for the first time the potential applications of biosurfactants produced by three Pseudomonas syringae pathovars: P. syringae pv tabaci (TA), P. syringae pv tomato (TO) and P. syringae pv syringae (SY). Isolated lipopeptides proved excellent emulsifying activity against a great variety of hydrocarbons and vegetable oils. The lowest minimum inhibitory concentrations against the pathogenic strain Staphylococcus aureus were observed for the biosurfactants produced by TA and SY (0.375 mg/mL). Non-cytotoxic effects were observed for concentrations of up to 10 mg/mL for these BS, and they proved differential cytotoxicity against cancer cell lines. These results open perspectives for the application of these surfactants as low-toxic bioemulsifiers and biotherapeutics.

Genomic context as well as sequence of both psr and penicillin-binding protein 5 contributes to β-lactam resistance in Enterococcus faecium.

The findings of this study shed light on ampicillin resistance in Enterococcus faecium clade A strains. They underscore the significance of alterations in the amino acid sequence of penicillin-binding protein 5 (PBP5) and the pivotal role of the psr region in PBP5 expression and ampicillin resistance. Notably, the presence of a full-length psrB leads to reduced PBP5 expression and lower minimum inhibitory concentrations (MICs) of ampicillin compared to the presence of a shorter psrA, regardless of the pbp5 allele involved. Additionally, clade B E. faecium strains exhibit lower AMP MICs when both psr alleles from clades A and B are present, although it is important to consider other distinctions between clade A and B strains that may contribute to this effect. It is intriguing to note that the divergence between clade A and clade B E. faecium and the subsequent evolution of heightened AMP MICs in hospital-associated strains appear to coincide with changes in Pbp5 and psr. These changes in psr may have resulted in an inactive Psr, facilitating increased PBP5 expression and greater ampicillin resistance. These results raise the possibility that a mimicker of PsrB, if one could be designed, might be able to lower MICs of ampicillin-resistant E. faecium, thus potentially resorting ampicillin to our therapeutic armamentarium for this species.

The microenvironment in antibiotic susceptibility testing.

Antibiotic susceptibility testing (AST) by agar diffusion has been repeatedly standardized and, in most cases, gives results which predict clinical success when antibiotic treatment is based on such results. The formation of the inhibition zone is due to a transition from planktonic to biofilm mode of growth. The kinetics of the interaction of antibiotics with bacteria is similar during AST by agar diffusion and during administration of antibiotics to the patients. However, the Mueller-Hinton agar (MHA) recommended for AST agar diffusion test is fundamentally different from the composition of the interstitial fluid in the human body where the infections take place and human cells do not thrive in MH media. Use of RPMI 1640 medium designed for growth of eucaryotic cells for AST of Pseudomonas aeruginosa against azithromycin results in lower minimal inhibitory concentration, compared to results obtained by MHA. The reason is that the RPMI 1640 medium increases uptake and reduces efflux of azithromycin compared to MHA. During treatment of cystic fibrosis patients with azithromycin, mutational resistance occur which is not detected by AST with MHA. Whether this is the case with other antibiotics and bacteria is not known but it is of clinical importance to be studied.

Phytochemistry and antimicrobial activity of Moroccan Origanum compactum and Ruta montana essential oils against nosocomial bacteria

Introduction: Healthcare-associated infections are a global public health issue with farreaching individual and economic repercussions. The microorganism’s multi-resistance frequently increases the risk that can be lowered by using biomolecules of medicinal plant essential oils (EOs). This study investigated the phytochemical components and antimicrobial potential of the EOs of Moroccan Origanum compactum and Ruta montana gathered from Taza Region. Methods: The EOs’ chemical analysis was performed by GC/MS and their antimicrobial effects were assessed by the microplate dilution method against eight nosocomial resistantbacterial strains. Results: The main constituents of O. compactum EO were Thymol (29.56%), carvacrol (26.44%), γ-terpinene (18.86%) and p-cymene (12.01%), while those of R. montana EO were 2-undecanone (85.76%), 2-nonanone (3.95%), 2-decanone (3.67%) and 2-dodecanone (1.94%). The O. compactum EO had important antimicrobial effects on all bacteria experienced. The lower minimum inhibitory concentration (MIC) values were obtained for the tested Staphylococcus species (0.062%, 0.125% (v/v)) while the highest one (2% (v/v)) was obtained for Klebsiella pneumonia and Pantoea spp. The R. montana EO showed MIC values of 4% (v/v) for Pantoea spp. and 8% (v/v) for the other tested strains except K. pneumonia for which no effect was shown. Conclusion: Therefore, these EOs, especially the O. compactum one, have an interesting antibacterial potential against nosocomial infections and might be used to develop new antimicrobial agents.

Antibiotic Susceptibility of Staphylococcus Aureus with VanA and MecA Genes.

Staphylococcus aureus (S.aureus) is an emerging antibiotic resistant bacterium responsible for various infections in human. Resistance to methicillin and vancomycin are of prime concern in S. aureus. The study aims to determine the minimum inhibitory concentration (MIC) of Vancomycin and evaluate the existence of mecA and vanA genes, associated with antibiotic resistance. Clinical specimens from three Kathmandu hospitals were processed and S. aureus was identified using conventional microbiological procedures. MRSA was phenotypically identified with cefoxitin (30µg) disc diffusion, while vancomycin susceptibility was assessed using the Ezy MICTM stripes. The mecA and vanA genes were detected by polymerase chain reaction (PCR). Out of 266 S. aureus samples from various clinical specimen subjected for analysis, 77 (28.9%) were found methicillin-resistant (MRSA) and 10 (3.8%) were observed vancomycin-resistant (VRSA). Vancomycin resistant isolates showed a significant correlation between resistance to ampicillin, chloramphenicol, and cefoxitin. The mecA gene was found in 39 of the MRSA isolates, having 50.64% of MRSA cases, while the vanA gene was detected in 4 of the VRSA cases, constituting 40% of VRSA occurrences. The strains with higher vancomycin minimum inhibitory concentration values (≥ 1.5 μg/ml) displayed increased resistance rates to various antibiotics compared to strains with lower minimum inhibitory concentration values (< 1.5 μg/ml). The presence of vanA genes was strongly associated (100%) with vancomycin resistance, while the 10.3% mecA gene was identified from MRSA having resistance towards vancomycin also.

In vitro activity of omadacycline against clinical isolates of Nocardia.

Nocardiosis typically requires a prolonged treatment duration of ≥6 months and initial combination therapy with 2-3 antibiotics. First-line regimens for nocardiosis are associated with considerable toxicity; therefore, alternative therapies are needed. Omadacycline is an aminomethylcycline with broad antimicrobial activity whose in vitro activity against Nocardia species has not been formally assessed. The in vitro potency of omadacycline was evaluated against 300 Nocardia clinical isolates by broth microdilution. The most common Nocardia species tested were N. cyriacigeorgica (21%), N. nova (20%), and N. farcinica (12%). The most common specimens were respiratory (178 isolates, 59%) and wound (57 isolates, 19%). Omadacycline minimum inhibitory concentrations (MICs) across all Nocardia species ranged from 0.06 µg/mL to 8 µg/mL, with an MIC50 of 2 µg/mL and MIC90 of 4 µg/mL. The lowest MICs were found among N. paucivorans (MIC50 = 0.25 µg/mL, MIC90 = 0.25 µg/mL), N. asiatica (MIC50 = 0.25 µg/mL, MIC90 = 1 µg/mL), N. abscessus complex (MIC50 = 0.5 µg/mL, MIC90 = 1 µg/mL), N. beijingensis (MIC50 = 0.5 µg/mL, MIC90 = 2 µg/mL), and N. otitidiscaviarum (MIC50 = 1 µg/mL, MIC90 = 2 µg/mL). The highest MICs were found among N. farcinica (MIC50 = 4 µg/mL, MIC90 = 8 µg/mL). In vitro potency differed by species among Nocardia clinical isolates. Further studies are warranted to evaluate the potential clinical utility of omadacycline for nocardiosis.

Effects of Maturation on Antibacterial Properties of Vietnamese Mango (Mangifera indica) Leaves.

This study, for the first time, has investigated the relationships between alterations of mangiferin contents in mango leaves at different maturity stages and their antibacterial properties. Leaves were classified into six different maturity stages based on their color: (1) young dark reddish brown, (2) young yellow, (3) young light green, (4) mature green, (5) old dark green, and (6) old yellow leaves. Ethanol extracts were then examined against Gram-positive and Gram-negative bacteria, applying broth dilution and agar well diffusion methods. In addition, we also measured the mangiferin contents in leaves at different stages for the purpose of evaluating how the changes in this phytochemistry value affects their activities against bacteria. The results showed that extracts from leaves at young ages had better antibacterial properties than those from old leaves, as evidenced by the lower minimum inhibitory concentrations and larger inhibitory zones. In addition, we also found that the contents of mangiferin were significantly decreased followed the maturation process. These results suggest that mango leaves at young stages, especially dark reddish brown and young yellow leaves, are preferable for application in bacterial infections and other therapies related to mangiferin's constituents.

ANTIBACTERIAL ACTIVITY OF RICINNUS COMMUNIS: IN VITRO STUDY

Ricinnus communis herb produces significant antimicrobial activity particularly against Gram negative bacteria, in comparison with standard antibiotics. Four bacterial genera were selected two Gram negative (Escherichia coli, and Pseudomonas aeruginosa); and two Gram positive (Staphylococcus aureus, Enterococcus fecalis). These bacterial isolates were incubated and subsequently adding Ricinus communis extracts which were prepared as alcoholic and aqueous solutions .The MIC (Minimal Inhibitory Concentration)was determined for ten isolates of each bacteria . Results showed that the MIC of aqueous extracts ranged between 8-32mg/ml for all selected bacteria while the MIC of the alcoholic extract ranged between 8-16mg/ml. Moreover; the lowest MIC of alcoholic extract was 8mg/ml while the lowest MIC for aqueous extract was 16mg/ml. In conclusion, the alcoholic and aqueous extract generates specific MIC, but the alcoholic extracts produce more particular effects by lower MIC (8 mg/ml). Thus; a topical application of these extracts are useful as alternative antimicrobial remedy regarding the sensitive bacteria.

Bigger problems from smaller colonies: emergence of antibiotic-tolerant small colony variants of Mycobacterium avium complex in MAC-pulmonary disease patients.

Mycobacterium avium complex (MAC) is a group of slow-growing mycobacteria that includes Mycobacterium avium and Mycobacterium intracellulare. MAC pulmonary disease (MAC-PD) poses a threat to immunocompromised individuals and those with structural pulmonary diseases worldwide. The standard treatment regimen for MAC-PD includes a macrolide in combination with rifampicin and ethambutol. However, the treatment failure and disease recurrence rates after successful treatment remain high. In the present study, we investigated the unique characteristics of small colony variants (SCVs) isolated from patients with MAC-PD. Furthermore, revertant (RVT) phenotype, emerged from the SCVs after prolonged incubation on 7H10 agar. We observed that SCVs exhibited slower growth rates than wild-type (WT) strains but had higher minimum inhibitory concentrations (MICs) against multiple antibiotics. However, some antibiotics showed low MICs for the WT, SCVs, and RVT phenotypes. Additionally, the genotypes were identical among SCVs, WT, and RVT. Based on the MIC data, we conducted time-kill kinetic experiments using various antibiotic combinations. The response to antibiotics varied among the phenotypes, with RVT being the most susceptible, WT showing intermediate susceptibility, and SCVs displaying the lowest susceptibility. In conclusion, the emergence of the SCVs phenotype represents a survival strategy adopted by MAC to adapt to hostile environments and persist during infection within the host. Additionally, combining the current drugs in the treatment regimen with additional drugs that promote the conversion of SCVs to RVT may offer a promising strategy to improve the clinical outcomes of patients with refractory MAC-PD.