An Antimicrobial Metabolite from Bacillus sp.: Significant Activity Against Pathogenic Bacteria Including Multidrug-Resistant Clinical Strains

Anti-Staphylococcus aureus effects of natural antimicrobial peptides and the underlying mechanisms

Staphylococcus aureus can cause localized infections such as abscesses and pneumonia, as well as systemic infections such as bacteremia and sepsis. Especially, methicillin-resistant S. aureus often presents multidrug resistance, which becomes a major clinical challenge. One of the most common reasons for methicillin-resistant S. aureus antibiotic resistance is the presence of biofilms. Natural antimicrobial peptides derived from different species have shown effectiveness in combating S. aureus biofilms. In this review, we summarize the inhibitory activity of antimicrobial peptides against S. aureus planktonic cells and biofilms. We also summarize the possible inhibitory mechanisms, involving cell adhesion inhibition, membrane fracture, biofilm disruption and DNA disruption. We believe this can provide the basis for further research against S. aureus biofilm-associated infections.

Antimicrobial peptides from Bacillus spp. and strategies to enhance their yield

Antibiotic resistance is a growing concern that is affecting public health globally. The search for alternative antimicrobial agents has become increasingly important. Antimicrobial peptides (AMPs) produced by Bacillus spp. have emerged as a promising alternative to antibiotics, due to their broad-spectrum antimicrobial activity against resistant pathogens. In this review, we provide an overview of Bacillus-derived AMPs, including their classification into ribosomal (bacteriocins) and non-ribosomal peptides (lipopeptides and polyketides). Additionally, we delve into the molecular mechanisms of AMP production and describe the key biosynthetic gene clusters involved. Despite their potential, the low yield of AMPs produced under normal laboratory conditions remains a challenge to large-scale production. This review thus concludes with a comprehensive summary of recent studies aimed at enhancing the productivity of Bacillus-derived AMPs. In addition to medium optimization and genetic manipulation, various molecular strategies have been explored to increase the production of recombinant antimicrobial peptides (AMPs). These include the selection of appropriate expression systems, the engineering of expression promoters, and metabolic engineering. Bacillus-derived AMPs offer great potential as alternative antimicrobial agents, and this review provides valuable insights on the strategies to enhance their production yield, which may have significant implications for combating antibiotic resistance. KEY POINTS: • Bacillus-derived AMP is a potential alternative therapy for resistant pathogens • Bacillus produces two main classes of AMPs: ribosomal and non-ribosomal peptides • AMP yield can be enhanced using culture optimization and molecular approaches.

Mass spectrometric analysis of bioactive conditioned media of bacteria isolated from reptilian gut

Aim

To determine whether selected gut bacteria of crocodile exhibit antibacterial properties.

Materials & methods

Two bacteria isolated from Crocodylus porosus gut were used, namely: Pseudomonas aeruginosa and Aeromonas dhakensis. Conditioned media were tested against pathogenic bacteria and metabolites were analyzed using liquid chromatography-mass spectrometry.

Results & conclusion

Antibacterial assays revealed that conditioned media showed potent effects against pathogenic Gram-positive and Gram-negative bacteria. LC-MS revealed identity of 210 metabolites. The abundant metabolites were, N-Acetyl-L-tyrosine, Acetaminophen, Trans-Ferulic acid, N, N-Dimethylformamide, Pyrocatechol, Cyclohexanone, Diphenhydramine, Melatonin, Gamma-terpinene, Cysteamine, 3-phenoxypropionic acid, Indole-3-carbinol, Benzaldehyde, Benzocaine, 2-Aminobenzoic acid, 3-Methylindole. These findings suggest that crocodile gut bacteria are potential source of novel bioactive molecules that can be utilized as pre/post/antibiotics for the benefit of human health.

Purification and Characterization of Novel Anti-MRSA Peptides Produced by Brevibacillus sp. SPR-20

Methicillin-resistant Staphylococcus aureus (MRSA) is listed as a high-priority pathogen because its infection is associated with a high mortality rate. It is urgent to search for new agents to treat such an infection. Our previous study isolated a soil bacterium (Brevibacillus sp. SPR-20), showing the highest antimicrobial activity against S. aureus TISTR 517 and MRSA strains. The present study aimed to purify and characterize anti-MRSA substances produced by SPR-20. The result showed that five active substances (P1-P5) were found, and they were identified by LC-MS/MS that provided the peptide sequences of 14-15 residues. Circular dichroism showed that all peptides contained β-strand and disordered conformations as the major secondary structures. Only P1-P4 adopted more α-helix conformations when incubated with 50 mM SDS. These anti-MRSA peptides could inhibit S. aureus and MRSA in concentrations of 2-32 μg/mL. P1 (NH₂-VVVNVLVKVLPPPVV-COOH) had the highest activity and was identified as a novel antimicrobial peptide (AMP). The stability study revealed that P1 was stable in response to temperature, proteolytic enzymes, surfactant, and pH. The electron micrograph showed that P1 induced bacterial membrane damage when treated at 1× MIC in the first hour of incubation. The killing kinetics of P1 was dependent on concentration and time. Mechanisms of P1 on tested pathogens involved membrane permeability, leakage of genetic material, and cell lysis. The P1 peptide at a concentration up to 32 μg/mL showed hemolysis of less than 10%, supporting its safety for human erythrocytes. This study provides promising anti-MRSA peptides that might be developed for effective antibiotics in the post-antibiotic era.

Identification and Characterization of a Potential Antimicrobial Peptide Isolated from Soil Brevibacillus sp. WUL10 and Its Activity against MRSA Pathogens

Methicillin-resistant Staphylococcus aureus (MRSA) is a severe threat to public health globally. The development of novel agents has encountered the repeated mechanism of drug resistance. This study aimed to investigate an anti-MRSA substance isolated from a promising soil bacterium. The result showed that an isolate (WUL10) was in the Brevibacillus genus. The minimum inhibitory concentration (MIC) of the purified substance was 1 µg/mL against S. aureus TISTR 517 and MRSA strains. This substance showed the bactericidal effect at the concentration of 1–2 µg/mL against these bacterial indicators. The activity of the substance retained more than 95% when encountering high temperatures and a wide range of pH, but it was sensitive to proteolytic enzymes and SDS. It was identified as a novel antimicrobial peptide (KVLVKYLGGLLKLAALMV-COOH) with the predicted structure of α-helix. The substance could rupture the cell wall of the tested pathogen. MIC and MBC of the synthesized peptide were 16 and 64 µg/mL, respectively. The difference in the activity between the isolated and synthetic peptides might be from the synergistic effects of other AMPs in the purified substance. This novel AMP would provide an advantage for further development of anti-MRSA substances to manage the situation of antibiotic resistance.

Enhanced Antibacterial Activity of Brevibacillus sp. SPR19 by Atmospheric and Room Temperature Plasma Mutagenesis (ARTP)

Antibiotic resistance is a major health concern worldwide. In our previous study, some bacterial isolates exhibited antibacterial activity against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). However, the production of antibacterial substances by native microorganisms is limited by biosynthetic genes. This study aimed to improve the antibacterial activity of SPR19 using atmospheric and room temperature plasma mutagenesis (ARTP). The results showed that SPR19 belonged to the Brevibacillus genus. The growth curves and production kinetics of antibacterial substances were investigated. Argon-based ARTP was applied to SPR19, and the 469 mutants were preliminarily screened using agar overlay method. The remaining 25 mutants were confirmed by agar well diffusion assay against S. aureus TISTR 517 and MRSA isolates 142, 1096, and 2468. M285 exhibited the highest activity compared to the wild-type strain (10.34–13.59%) and this mutant was stable to produce the active substances throughout 15 generations consistently. The antibacterial substances from M285 were tolerant to various conditions (heat, enzyme, surfactant, and pH) while retaining more than 90% of their activities. Therefore, Brevibacillus sp. SPR19 is a potential source of antibacterial substances. ARTP mutagenesis is a powerful method for strain improvement that can be utilized to treat MRSA infection in the future.

Characterization of the antimicrobial activity produced by Bacillus sp. isolated from wetland sediment

Bacteria of the genus Bacillus sp. present the potential for inhibiting various pathogens, making them a promising starting point in the search for new antimicrobial substances. In this study, bacteria were isolated from sediment samples from humid areas of a Natural Conservation Unit in the state of Rio Grande do Sul, Brazil. The isolate Bacillus sp. sed 1.4 was selected for production of antimicrobial activity, and was characterized by MALDI-TOF and 16S rDNA sequencing. Phylogenetic analysis showed that Bacillus sed 1.4 was closely related to Bacillus altitudinis and Bacillus pumilus. The cell-free supernatant was partially purified using ammonium sulfate precipitation, gel filtration chromatography (Sephadex G-200) and an ultrafiltration membrane. Partial purification resulted in specific activity of 769.23 AU/mg, with a molecular mass of approximately 148 kDa. This antimicrobial substance showed stability at 100°C for 5 min, and was inactivated by proteolytic enzymes. An antimicrobial effect against Listeria species was observed. Considering the importance of the Listeria genus in the area of food safety, this antimicrobial activity should be further explored, specifically in the field of dairy products and with a focus on food biopreservation studies.

The potentials of secondary metabolites from Bacillus cereus SN7 and Vagococcus fluvialis CT21 against fish pathogenic bacteria

One of the major factors that affect the total production of fisheries is the declining number of catches and aquaculture production due to the high pathogenicity in aquatic environment. This enforces the need to find anti-pathogenic agents that could solve the problem. In addition, the application of potential Bacillus cereus SN7 and Vagococcus fluvialis CT21 isolated and identified from the sea water of Siak, Riau, Indonesia need to be optimally exploited. The aim of this study, therefore, is to determine the component of bioactive compounds present in Bacillus cereus SN7 and Vagococcus fluvialis CT21, and also to explore their intrinsic potential as a biological control agent in fisheries, especially for inhibiting the growth of pathogenic bacteria (Vibrio alginolyticus, Aeromonas hydrophila and Pseudomonas aeruginosa). The method used was experimental, where the ethyl acetate crude extracts of both samples were analyzed for their phytochemical content, followed by thin layer chromatography analysis and Liquid Chromatography Mass Spectrometry. In addition, anti-pathogenic activity test was performed using the Kirby-Bauer method, minimum inhibitory and bactericidal concentration analysis. The results showed alkaloids, flavonoids, and saponins were the potential bioactive components in the crude extracts of Bacillus cereus SN7 and Vagococcus fluvialis CT21. Furthermore, the anti-pathogenic activity test demonstrated the ability for both bacteria to inhibit three types of pathogens with the following inhibitory zone values: Vibrio alginolyticus (10-11 mm), Aeromonas hydrophila (8-12 mm), and Pseudomonas aeruginosa (8-10 mm). In conclusion secondary metabolite compounds produced by Bacillus cereus SN7 and Vagococcus fluvialis CT21 possess the capacity to inhibit pathogenic bacteria. Hence, both samples are potential candidates for anti-pathogen development, especially in fisheries.

Microbial symbionts of insects as a source of new antimicrobials: a review

To stop the antimicrobial resistance crisis, there is an urgent need for increased investment in antimicrobial research and development. Currently, many researchers are focussing on insects and their microbiota in the search for new antimicrobials. This review summarizes recent literature dedicated to the antimicrobial screening of insect symbionts and/or their metabolites to uncover their value in early drug discovery. We summarize the main steps in the methodology used to isolate and identify active insect symbionts and have noted substantial variation among these studies. There is a clear trend in isolating insect Streptomyces bacteria, but a broad range of other symbionts has been found to be active as well. The microbiota of many insect genera and orders remains untargeted so far, which leaves much room for future research. The antimicrobial screening of insect symbionts has led to the discovery of a diverse array of new active biomolecules, mainly peptides, and polyketides. Here, we discuss 15 of these symbiont-produced compounds and their antimicrobial profile. Cyphomycin, isolated from a Streptomyces symbiont of a Cyphomyrmex fungus-growing ant, seems to be the most promising insect symbiont-derived antimicrobial so far. Overall, insect microbiota appears to be a promising search area to discover new antimicrobial drug candidates.

Soil-Associated Bacillus Species: A Reservoir of Bioactive Compounds with Potential Therapeutic Activity against Human Pathogens

Soil hosts myriads of living organisms with the extensive potential to produce bioactive compounds. Bacteria are the major soil inhabitants that represent a rich reservoir for antibiotic production along with their role in recycling nutrients and maintenance of the soil ecosystem. Here, from 55 tested soil samples, we isolated and identified a novel antibiotic-producing bacterial strain with a phylogenetically closest match to Bacillus subtilis sp. based on BLASTN search of GenBank for the 16S rRNA gene sequence. We characterized this novel strain through microscopic, biochemical, and molecular techniques, combined with testing its potential antimicrobial activity. Chemical studies revealed that the antibiotic produced by this strain is a glycopeptide. It exhibited profound activity against both methicillin-resistant Staphylococcus aureus (MRSA) and Candida albicans. The antibiotic is optimally produced at 37 °C after 28 h of growth. The biocompatibility of the extracted antibiotic was tested over a wide range of factors including temperature, pH, surfactants, and metal salts. To confirm its therapeutic potential, a sterile solution of the antibiotic was tested in vivo against bacteria-induced keratitis in rats where significant healing activity was recorded. Hence, this soil Bacillus strain may lead to the development of novel antibiotics for the treatment of human pathogens.

Antimicrobial activities of Bacillus velezensis strains isolated from stingless bee products against methicillin-resistant Staphylococcus aureus

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have reached epidemic proportions globally. Therefore, there is an urgent need for a continuous supply of antibiotics to combat the problem. In this study, bacteria initially identified as species belonging to the Bacillus amyloliquefaciens operational group were re-identified based on the housekeeping gene, gyrB. Cell-free supernatants (CFS) from the strains were used for antimicrobial tests using the agar well diffusion assay against MRSA and various types of pathogenic bacteria. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and physicochemical characteristics of the CFS were determined. Based on gyrB sequence analysis, five strains (PD9, B7, PU1, BP1 and L9) were identified as Bacillus velezensis. The CFS of all B. velezensis strains showed broad inhibitory activities against Gram-negative and -positive as well as MRSA strains. Strain PD9 against MRSA ATCC 33742 was chosen for further analysis as it showed the biggest zone of inhibition (21.0 ± 0.4 mm). The MIC and MBC values obtained were 125 μl/ml. The crude antimicrobial extract showed bactericidal activity and was stable at various temperatures (40–80°C), pH (4–12), surfactants (Tween 20, Tween 80, SDS and Triton X-100) and metal ions (MgCI_2, NaCI_2, ZnNO₃ and CuSO₄) when tested. However, the crude extract was not stable when treated with proteinase K. All these properties resembled the characteristics of peptides. The antimicrobial compound from the selected strain was purified by using solvent extraction method and silica gel column chromatography. The purified compound was subjected to High Performance Liquid Chromatography which resulted in a single peak of the anti-MRSA compound being detected. The molecular weight of the anti-MRSA compound was determined by using SDS-PAGE and zymogram. The size of the purified antimicrobial peptide was approximately ~ 5 kDa. The antimicrobial peptide produced from B. velezensis strain PD9 is a promising alternative to combat the spread of MRSA infections in the future.

Ultrastructural changes in methicillin-resistant Staphylococcus aureus (MRSA) induced by a novel cyclic peptide ASP-1 from Bacillus subtilis: A scanning electron microscopy (SEM) study

Increasing antimicrobial resistance among Staphylococcus aureus necessitates a new antimicrobial with a different site of action. We have isolated a novel cyclic peptide-1 (ASP-1) from Bacillussubtilis with potent activity against methicillin-resistant S. aureus (MRSA) at a minimum inhibitory concentration (MIC) of 8-64μg/ml. Scanning electron micrographs demonstrated drastic changes in the cellular architecture of ASP-1 treated cells of S. aureus ATCC 29213 and an MRSA clinical isolate at MICs, with damages to the cell wall, membrane lysis and probable leakage of cytoplasmic contents at minimum bactericidal concentrations. The ultrastructure alterations induced by ASP-1 have also been compared with those of oxacillin-treated MRSA cells at its MIC using scanning electron microscopy.

Bacteriocin isolated from the natural inhabitant of Allium cepa against Staphylococcus aureus

Extensive usage of antibiotics has led to the emergence of drug-resistant strains of pathogens and hence, there is an urgent need for alternative antimicrobial agents. Antimicrobial Peptides (AMPs) of bacterial origin have shown the potential to replace some conventional antibiotics. In the present study, an AMP was isolated from Bacillus subtilis subsp. spizizenii strain Ba49 present on the Allium cepa, the common onion and named as peptide-Ba49. The isolated AMP was purified and characterized. The purified peptide-Ba49, having a molecular weight of ~ 3.3 kDa as determined using mass spectroscopy, was stable up to 121 °C and in the pH range of 5-10. Its interaction with protein degrading enzymes confirmed the peptide nature of the molecule. The peptide exhibited low minimum inhibitory concentration (MIC) against Staphylococcus aureus and its (Methicillin-resistant Staphylococcus aureus) MRSA strains (MIC, 2-16 µM/mL). Further, time kill kinetic assay was performed and analysis of the results of membrane depolarization and permeabilization assays (TEM, DiBAC₄ (3) and PI) suggested peptide-Ba49 to be acting through the change in membrane potential leading to disruption of S. aureus membrane. Additionally, cytotoxicity studies of peptide-Ba49, carried out using three mammalian cell lines viz. HEK 293T, RAW 264.7, and L929, showed limited cytotoxicity on these cell lines at a concentration much higher than its MIC values. All these studies suggested that the AMP isolated from strain Ba49 (peptide-Ba49) has the potential to be an alternative to antibiotics in terms of eradicating the pathogenic as well as drug-resistant microorganisms.

Isolation and Characterization of Fengycins Produced by Bacillus amyloliquefaciens JFL21 and Its Broad-Spectrum Antimicrobial Potential Against Multidrug-Resistant Foodborne Pathogens

The continuing emergence and development of pathogenic microorganisms that are resistant to antibiotics constitute an increasing global concern, and the effort in new antimicrobials discovery will remain relevant until a lasting solution is found. A new bacterial strain, designated JFL21, was isolated from seafood and identified as B. amyloliquefaciens. The antimicrobial substance produced by B. amyloliquefaciens JFL21 showed low toxicity to most probiotics but exhibited strong antimicrobial activities against multidrug-resistant foodborne pathogens. The partially purified antimicrobial substance, Anti-JFL21, was characterized to be a multiple lipopeptides mixture comprising the families of surfactin, fengycin, and iturin. Compared with commercially available polymyxin B and Nisin, Anti-JFL21 not only could exhibit a wider and stronger antibacterial activity toward Gram-positive pathogens but also inhibit the growth of a majority of fungal pathogens. After further separation through gel filtration chromatography (GFC), the family of surfactin, fengycin, and iturin were obtained, respectively. The results of the antimicrobial test pointed out that only fengycin family presented marked antimicrobial properties against the indicators of L. monocytogenes, A. hydrophila, and C. gloeosporioides, which demonstrated that fengycins might play a major role in the antibacterial and antifungal activity of Anti-JFL21. Additionally, the current study also showed that the fengycins produced by B. amyloliquefaciens JFL21 not only maintained stable anti-Listeria activity over a broad pH and temperature range, but also remained active after treatment with ultraviolet sterilization, chemical reagents, and proteolytic enzymes. Therefore, the results of this study suggest the new strain and its antimicrobials are potentially useful in food preservation for the biological control of the multidrug-resistant foodborne pathogens.

Promising Anti-MRSA Activity of Brevibacillus sp. Isolated from Soil and Strain Improvement by UV Mutagenesis

Antibiotic-resistant infection is a major health problem, and a limited number of drugs are currently approved as antibiotics. Soil bacteria are promising sources in the search for novel antibiotics. The aim of the present study is to isolate and assess soil bacteria with anti-MRSA activity and improve their capabilities by UV mutagenesis. Soil samples from the upper south of Thailand were screened for antibacterial activity using the cross-streak method. Agar well diffusion was used to examine the activity of isolates against a spectrum of human pathogens. The most active isolate was identified by 16S rRNA sequencing, and the production kinetics and stability were investigated. The most promising isolate was mutated by UV radiation, and the resulting activity and strain stability were studied. The results show that isolates from the cross-streak method could inhibit Staphylococcus aureus TISTR 517 (94 isolates) and Escherichia coli TISTR 887 (67 isolates). Nine isolates remained active against S. aureus TISTR 517 and MRSA, and eight isolates inhibited the growth of E. coli TISTR 887 as assessed using agar well diffusion. The most active strain was Brevibacillus sp. SPR-20, which had the highest activity at 24 h of incubation. The active substances in culture supernatants exhibited more than 90% activity when subjected to treatments involving various heat, enzymes, surfactants, and pH conditions. The mutant M201 showed significantly higher activity (109.88–120.22%) and strain stability compared to the wild-type strain. In conclusion, we demonstrate that soil Brevibacillus sp. is a potential resource that can be subjected to UV mutagenesis as a useful approach for improving the production of anti-MRSA in the era of antibiotic resistance.

Diversity and Bioactive Potential of Actinobacteria from Unexplored Regions of Western Ghats, India

The search for novel bioactive metabolites continues to be of much importance around the world for pharmaceutical, agricultural, and industrial applications. Actinobacteria constitute one of the extremely interesting groups of microorganisms widely used as important biological contributors for a wide range of novel secondary metabolites. This study focused on the assessment of antimicrobial and antioxidant activity of crude extracts of actinobacterial strains. Western Ghats of India represents unique regions of biologically diverse areas called “hot spots”. A total of 32 isolates were obtained from soil samples of different forest locations of Bisle Ghat and Virjapet situated in Western Ghats of Karnataka, India. The isolates were identified as species of Streptomyces, Nocardiopsis, and Nocardioides by cultural, morphological, and molecular studies. Based on preliminary screening, seven isolates were chosen for metabolites extraction and to determine antimicrobial activity qualitatively (disc diffusion method) and quantitatively (micro dilution method) and scavenging activity against DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals. Crude extracts of all seven isolates exhibited fairly strong antibacterial activity towards MRSA strains (MRSA ATCC 33591, MRSA ATCC NR-46071, and MRSA ATCC 46171) with MIC varying from 15.62 to 125 μg/mL, whereas showed less inhibition potential towards Gram-negative bacteria Salmonella typhi (ATCC 25241) and Escherichia coli (ATCC 11775) with MIC of 125–500 μg/mL. The isolates namely S1A, SS5, SCA35, and SCA 11 inhibited Fusarium moniliforme (MTCC 6576) to a maximum extent with MIC ranging from 62.5 to 250 μg/mL. Crude extract of SCA 11 and SCA 13 exhibited potent scavenging activities against DPPH and ABTS radicals. The results from this study suggest that actinobacterial strains of Western Ghats are an excellent source of natural antimicrobial and antioxidant compounds. Further research investigations on purification, recovery, and structural characterization of the active compounds are to be carried out.

Residual antibacterial activity of canine hair treated with five mousse products against Staphylococcus pseudintermedius in vitro

BACKGROUND

Topical therapy alone can be effective in the treatment of canine pyoderma. Topical products are commercially available as shampoos, sprays, wipes and mousses. To date, no studies have evaluated the efficacy of commercially available mousse products in the treatment of canine pyoderma.

OBJECTIVE

To determine the residual antibacterial activity of canine hairs treated with mousse products containing different active ingredients.

ANIMALS

Fifteen client-owned dogs with no history of dermatological disease.

METHODS AND MATERIALS

Dogs were treated once with five mousse products [(i) 2% chlorhexidine and 1% ketoconazole, (ii) 2% chlorhexidine and 2% miconazole, (iii) 3% chlorhexidine and 0.5% climbazole, (iv) 2% salicylic acid 10% ethyl lactate and (v) phytosphingosine HCl 0.05%; control]. Hair samples were collected from each treatment area before application, one hour after application and on days 2, 4, 7, 10 and 14 post-treatment. Collected hairs were weighed and plated on Mueller-Hinton agar plates streaked with a Staphylococcus pseudintermedius isolate showing no antimicrobial resistance. Plates were incubated for 24 h and bacterial growth inhibition zones around the hairs were measured.

RESULTS

Mousses 1, 2 and 3 created significant inhibition zones up to Day 10 when compared to pre-treatment samples. On Day 14, only mousse 3 produced a significant zone of inhibition when compared to the pre-treatment sample. Mousses 4 and 5 showed no statistical difference between any of the samples.

CONCLUSIONS AND CLINICAL IMPORTANCE

These results suggest that three of the mousse products had residual activity in inhibiting S. pseudintermedius growth in vitro for at least 10 days.

Antimicrobial and Cytotoxic Properties of Bioactive Metabolites Produced by Streptomyces cavourensis YBQ59 Isolated from Cinnamomum cassia Prels in Yen Bai Province of Vietnam

The endophytic actinomycete strain YBQ59 was isolated from Cinnamomum cassia Prels in Yen Bai province (21°53'14″N; 104°35'9″E) of northern Vietnam. Based on analysis of morphological, physiological characteristics and 16S rRNA gene sequence (GenBank Acc. No. MF950891), the strain YBQ59 possessed high similarity to Streptomyces cavourensis subsp. cavourensis strain NRRL 2740, therefore assigned as S. cavourensis YBQ59. The ethyl acetate extract of the YBQ59 culture broth isolated eight pure secondary metabolites, identified as 1-monolinolein (1), bafilomycin D (2), nonactic acid (3), daidzein (4), 3'-hydroxydaidzein (5), 5,11-epoxy-10-cadinanol (6), prelactone B (7), and daucosterol (8). Compounds 1, 3-8 were reported for the first time from S. cavourensis. Compounds 1-5 exhibited antimicrobial activities against both methicillin-resistant Staphylococcus aureus ATCC 33591 (MRSA) and methicillin-resistant Staphylococcus epidermidis ATCC 35984 (MRSE) among which the compound 1 revealed the strongest effects with minimum inhibitory concentrations of 8.5 and 14.6 µg/mL, respectively. The compound 2 showed high potential effect against MRSA (MIC of 11.1 µg/mL) but less effect against MRSE (MIC of 30.3 µg/mL). The cytotoxicity of the compounds 1-7 was investigated against human lung adenocarcinoma EGFR-TKI-resistant cells, among which compounds 1, 2, and 5 exhibited the strong effect against A549 cells with IC₅₀ values of 3.6, 6.7, and 7.8 µM, respectively. Taken together, the experimental findings in this study suggested that the compounds 1 and 2 could be reproducible metabolites applicable for inhibition of both drug-resistant bacteria and cancer cell lines.

Bacteriocinogenic properties of Escherichia coli P2C isolated from pig gastrointestinal tract: purification and characterization of microcin V

The aim of this study was to isolate and investigate the bacteriocinogenic and probiotic potential of new Gram-negative isolates. Of 22 bacterial isolates from pig intestine and chicken crops, ten isolates had demonstrated a good activity, and the most potent five strains were identified as four E. coli and one as Proteus sp. No virulence factors were detected for E. coli strains isolated from pig intestine. The semi-purified microcins proved to be resistant to temperature and pH variation, but sensitive to proteolytic enzymes. Of particular interest, strain E. coli P2C was the most potent, free of virulence genes and sensitive to tested antibiotics. Purification procedure revealed the presence of a single pure peak having a molecular mass of 8733.94 Da and matching microcin V (MccV). The sequence obtained by LC-MS/MS confirmed the presence of MccV. Purified MccV showed a good activity against pathogenic coliforms, especially E. coli O₁K₁H₇ involved in avian colibacillosis. The present study provides evidence that E. coli strains isolated from pig intestine produce microcin-like substances. E. coli P2C is a safe MccV producer that could be a good candidate for its application as novel probiotic strain to protect livestock and enhance growth performance.

Structural Elucidation and Molecular Docking of a Novel Antibiotic Compound from Cyanobacterium Nostoc sp. MGL001

Cyanobacteria are rich source of array of bioactive compounds. The present study reports a novel antibacterial bioactive compound purified from cyanobacterium Nostoc sp. MGL001 using various chromatographic techniques viz. thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Further characterization was done using electrospray ionization mass spectroscopy (ESIMS) and nuclear magnetic resonance (NMR) and predicted structure of bioactive compound was 9-Ethyliminomethyl-12-(morpholin - 4 - ylmethoxy) -5, 8, 13, 16–tetraaza–hexacene - 2, 3 dicarboxylic acid (EMTAHDCA). Structure of EMTAHDCA clearly indicated that it is a novel compound that was not reported in literature or natural product database. The compound exhibited growth inhibiting effects mainly against the gram negative bacterial strains and produced maximum zone of inhibition at 150 μg/mL concentration. The compound was evaluated through in silico studies for its ability to bind 30S ribosomal fragment (PDB ID: 1YRJ, 1MWL, 1J7T, and 1LC4) and OmpF porin protein (4GCP, 4GCQ, and 4GCS) which are the common targets of various antibiotic drugs. Comparative molecular docking study revealed that EMTAHDCA has strong binding affinity for these selected targets in comparison to a number of most commonly used antibiotics. The ability of EMTAHDCA to bind the active sites on the proteins and 30S ribosomal fragments where the antibiotic drugs generally bind indicated that it is functionally similar to the commercially available drugs.