Journal of Applied Microbiology最新文献

Aims: Volatile organic compounds (VOCs) have an important function in plant growth-promoting rhizobacteria (PGPR) development and plant growth. This study aimed to identify VOCs of the PGPR strain, Stutzerimonas stutzeri NRCB010, and investigate their effects on NRCB010 biofilm formation, swarming motility, colonization, and tomato seedling growth.

Methods and results: Solid-phase microextraction and gas chromatography-mass spectrometry were performed to identify the VOCs produced during NRCB010 fermentation. A total of 28 VOCs were identified. Among them, seven (e.g. γ-valerolactone, 3-octanone, mandelic acid, 2-heptanone, methyl palmitate, S-methyl thioacetate, and 2,3-heptanedione), which smell well, are beneficial for plant, or as food additives, and without serious toxicities were selected to evaluate their effects on NRCB010 and tomato seedling growth. It was found that most of these VOCs positively influenced NRCB010 swarming motility, biofilm formation, and colonization, and the tomato seedling growth. Notably, γ-valerolactone and S-methyl thioacetate exhibited the most positive performances.

Conclusion: The seven NRCB010 VOCs, essential for PGPR and crop growth, are potential bioactive ingredients within microbial fertilizer formulations. Nevertheless, the long-term sustainability and replicability of the positive effects of these compounds across different soil and crop types, particularly under field conditions, require further investigation.

Aims: To explore the therapeutic potential of Forsythoside B in treating Streptococcus pneumoniae (S. pneumoniae) infections, focusing on its ability to inhibit pneumolysin activity and protect cells from damage.

Methods and results: Hemolysis tests were used to evaluate Forsythoside B's inhibitory effect on pneumolysin activity, while growth curve analysis assessed its impact on S. pneumoniae growth. Western blotting and oligomerization analysis were conducted to examine its influence on pneumolysin oligomerization. Cytotoxicity assays, including LDH release and live/dead cell staining, evaluated the protective effects of Forsythoside B against pneumolysin-induced damage in A549 cells. Additionally, a mouse model was employed to test the effects on survival rates, lung bacterial load, and inflammation. The results showed that Forsythoside B significantly inhibited pneumolysin activity, reduced its oligomerization, and protected A549 cells from damage without affecting bacterial growth. In the mouse model, it improved survival rates and reduced lung inflammation, indicating its potential as a therapeutic agent against S. pneumoniae infections.

Conclusions: Forsythoside B shows potential as a therapeutic agent for treating pneumonia, particularly in infections caused by S. pneumoniae.

Aims: To identify efficient, broad-spectrum, and non-toxic preservatives for natural agricultural products, eight essential oils were screened for high inhibitory and antioxidant activities against spoilage microbes.

Methods and results: The zone of inhibition test and minimum inhibitory concentration (MIC) assay were performed to assess the antimicrobial activity of eight essential oils against Bacillus subtilis, Staphylococcus aureus, Penicillium, Saccharomyces, and Escherichia coli. Among the eight essential oils, garlic and rose essential oils exhibited the best inhibitory effects, their MICs against the spoilage microbes were 40-640 μl/l and 10-320 μl/l, respectively. In addition, the antioxidant activities of eight essential oils were compared using the DPPH and ABTS radical-scavenging assays and the reducing power assay. Eight essential oils had antioxidant capacity, among which rosemary, thyme, rose, and tea tree essential oils performed the best. Moreover, the combination of thyme and rose exerted stronger antioxidant activity. Therefore, the concentrations of rose and garlic, and thyme essential oils were optimized using response surface methodology to obtain the optimal composite ratios, which were 1254 μl/l, 640 μl/l, and 1228 μl/l for rose, garlic, and thyme, respectively. The DPPH free radical-scavenging rate detected using this formulation was 50.2%, basically consistent with the prediction. Zone of inhibition diameters with the compound essential oil, against five spoilage microbes, were all greater than 45 mm.

Conclusions: The essential oil combination had high antimicrobial, against agricultural product spoilage microbes, and antioxidant activities.

Aims: Cupriavidus isolates are found in environmental and clinical samples and are often resistant to carbapenems, which are last-resort antibiotics. However, their carbapenem-resistance molecular mechanisms remain unknown. This study aimed to (i) characterize and sequence the carbapenem-resistant soil isolate Cupriavidus taiwanensis S2-1-W to uncover its antibiotic resistance determinants; and (ii) clone and characterize a putative novel carbapenemase gene identified in this isolate.

Methods and results: Antibiotic susceptibility testing of C. taiwanensis S2-1-W revealed that it was resistant to most carbapenems, other β-lactams, and aminoglycosides tested. Genome sequencing of this isolate revealed a complex chromosomal resistome that included multidrug efflux pump genes, one aminoglycoside transferase gene, and three β-lactamase genes. Among them, we identified a novel putative class D β-lactamase gene (blaOXA-1206) that is highly conserved among other sequenced C. taiwanensis isolates. Cloning and characterization of blaOXA-1206 confirmed that it encodes for a newly discovered carbapenemase (OXA-1206) that confers resistance to carbapenems and other β-lactams.

Conclusion: Carbapenem-resistance in C. taiwanensis S2-1-W is associated with a newly discovered carbapenemase, OXA-1206.

Aims: This study examined the diversity of arbuscular mycorrhizal fungi (AMF), mean spore density (MSD), and root colonization in relation to factors such as agroclimatic zones, rice varieties and soil types in paddy fields of South India. The aim was to understand how these factors influence AMF association in rice, facilitating their effective use as a biological tool in paddy cultivation.

Methods and results: AMF were identified through light microscopy of spores, while MSD and percentage-root-length colonization (PRLC) were measured using standard methods. Correlation and principal component analyses were performed to explore the interrelationships between AMF characteristics and various environmental, soil, and plant variables. Sixteen AMF species were identified across 29 rice varieties from three agroclimatic zones, 6 soil orders, and 18 soil series over 2 seasons. Notably, 70% of chemicalized rice fields lacked AMF spores, and only 50% exhibited root colonization. This study offers new insights into the role of AMF in rice cultivation.

Conclusion: The AMF diversity and root colonization in relation to environmental variables underscore their significant impact on AMF in particular crop fields.

Aims: The survival of inoculated Escherichia coli on Fuji apples in Washington State orchards was studied, considering evaporative cooling, canopy location, year, and region, with the examination of sunlight exposure and inoculation levels in year 2.

Methods and results: Rifampicin-resistant E. coli was applied to Fuji apples. Initial concentrations for the high-inoculation study were 7.4 ± 0.3 log10 CFU per apple and 3.4 ± 0.3 log10 CFU per apple for the low-inoculation study. Enumeration of E. coli was conducted at 0, 2, 10, 18, 34, 42, 58, 82, 106, and 154 h after inoculation. Results were analyzed using Tukey's honest significance difference test and a log-linear model. Log-linear, Weibull, and biphasic models characterized E. coli die-off patterns for high and low inoculations. The application of evaporative overhead cooling water did not significantly influence E. coli survival on Fuji apples; inoculation level and sunlight exposure were significant factors in a log-linear model. Escherichia coli decreased by 5.5 ± 1.3 and 3.3 ± 0.4 log10 CFU per apple for high and low-inoculated apples, respectively, by 154 h. The biphasic model best explained the die-off pattern for high and low-inoculated Fuji apples.

Conclusions: Overhead evaporative cooling, a useful fruit quality practice, did not impact the survival of generic E. coli on Fuji apple surfaces. The significant impact of sunlight exposure and inoculation levels on die-off highlights the importance of ultraviolet radiation in risk reduction and the need for various inoculum concentrations in preharvest field studies.

Background: The enormous burden of tuberculosis (TB) worldwide is a major challenge to human health, but the costs and risks associated with novel drug discovery have limited treatment options for patients. Repurposing existing antimicrobial drugs offers a promising avenue to expand TB treatment possibilities. This study aimed to explore the activity and synergy of beta-lactams in combination with a beta-lactamase inhibitor, which have been underutilized in TB treatment to date.

Methods: Based on inhibitory concentration, oral bioavailability, and commercial availability, seven beta-lactams (cefadroxil, tebipenem, cephradine, cephalexin, cefdinir, penicillin V, and flucloxacillin), two beta-lactamase inhibitors (avibactam and clavulanate), and three second-line TB drugs (moxifloxacin, levofloxacin, and linezolid) were selected for combination in vitro testing against Mycobacterium tuberculosis H37Rv. Resazurin assays and colony forming unit enumeration were used to quantify drug efficacy, Chou-Talalay calculations were performed to identify drug synergy and Chou-Martin calculations were performed to quantify drug dose reduction index.

Results: The order of activity of beta-lactams was cefadroxil > tebipenem > cephradine > cephalexin > cefdinir > penicillin V > flucloxacillin. The addition of clavulanate improved beta-lactam activity to a greater degree than the addition of avibactam. As a result, avibactam was excluded from further investigations, which focused on clavulanate. Synergy was demonstrated for cefdinir/cephradine, cefadroxil/tebipenem, cefadroxil/penicillin V, cefadroxil/cefdinir, cephalexin/tebipenem, cephalexin/penicillin V, cephalexin/cefdinir, cephalexin/cephradine, and cefadroxil/cephalexin, all with clavulanate. However, combining beta-lactams with moxifloxacin, levofloxacin, or linezolid resulted in antagonistic effects, except for the combinations of penicillin V/levofloxacin, penicillin V/moxifloxacin, and cefdinir/moxifloxacin.

Conclusions: Beta-lactam synergy may provide viable combination therapies for the treatment of TB.