Letters in Applied Microbiology最新文献

Lactic acid bacteria (LAB) contribute to human health, and LAB functionality has been studied using Caenorhabditis elegans as an alternative host. However, many studies have focused on the efficacy of a single strain of LAB, and few reports have compared various LAB strains. In this study, we examined the effects of 15 strains of LAB isolated from vegetables, meat, and fermented foods on nematode longevity and healthy lifespan. To reduce the frequency of laborious survival observations, we performed a lifespan assay on agar plates containing 2'-deoxy-5-fluorouridine (FUdR), which inhibits egg hatching and prevents generation mixing. Four beneficial strains showed significant lifespan extension and increased spontaneous nematode mobility, regardless of treatment with or without FUdR and the frequency of survival observation. These results suggested increased longevity and an extended healthy lifespan, confirming the reliability of our method. The four strains are expected to show anti-ageing effects besides longevity and have effects on age-related degenerative diseases. Our labor-saving method can be used as an alternative to conventional methods and enable simultaneous screening of multiple strains. Future research could explore factors contributing to lifespan regulation by comparing and verifying differential strain effects on lifespan.

Endophytic microorganisms associated with medicinal plants are of particular interest as they are a potential source of new bioactive chemicals effective against novel emerging and drug-resistant pathogens. Agave americana is a tropical medicinal plant with antibacterial, antifungal, and anticancer properties. We studied the biodiversity of fungal endophytes of A. americana and their antimicrobial production potential. Isolated endophytic fungi were classified into 32 morphotypes (15 from stem and 17 from leaf) based on their cultural and morphological characteristics. Among the fungal crude extracts tested, 82% of isolates from the leaves and 80% of the isolates from the stem showed antibacterial activity against the bacterial strains (Escherichia coli ATTC 25902, Staphylococcus aureus ATTC 14775, and Bacillus subtilis NRRL 5109) tested. Extracts from four fungal isolates from leaves showed antifungal activity against at least one of the fungal strains (Candida albicans ATTC 10231 and Aspergillus fumigatus NRRL 5109) tested. Crude extracts of seven fungal isolates showed a zone of inhibition of more than 11 mm at 10 mgml-1 against both Gram-positive and Gram-negative bacteria tested. Penicillium, Colletotrichum, Curvularia, Pleosporales, Dothideomycetes, and Pleurotus are the main endophytes responsible for bioactive potential. These results indicate that A. americana harbors endophytes capable of producing antimicrobial metabolites.

Dermatomycosis is an infection with global impacts caused especially by dermatophytes and Candida species. Current antifungal therapies involve drugs that face fungal resistance barriers. This clinical context emphasizes the need to discover new antifungal agents. Herein, the antifungal potential of 10 curcumin analogs was evaluated against four Candida and four dermatophyte species. The most active compound, 3,3'-dimethoxycurcumin, exhibited minimum inhibitory concentration values ranging from 1.9‒62.5 to 15.6‒62.5 µg ml-1 against dermatophytes and Candida species, respectively. According to the checkerboard method, the association between DMC and terbinafine demonstrated a synergistic effect against Trichophyton mentagrophytes and Epidermophyton floccosum. Ergosterol binding test indicated DMC forms a complex with ergosterol of Candida albicans, C. krusei, and C. tropicalis. However, results from the sorbitol protection assay indicated that DMC had no effect on the cell walls of Candida species. The in vivo toxicity, using Galleria mellonella larvae, indicated no toxic effect of DMC. Altogether, curcumin analog DMC was a promising antifungal agent with a promising ability to act against Candida and dermatophyte species.

This work reviews biofilm investigation techniques and highlights the benefits and drawbacks of each approach focusing especially on Pseudomonas syringae and may serve as a comprehensive guide for any early-career researchers starting with the topic of biofilm. Each approach with applications of individual microscopy and spectroscopy techniques is summarized together with characterization of Pseudomonas syringae and its role in pathogenesis.

This study aims to isolate microbial strains for producing mono-rhamnolipids with high proportion. Oily sludge is rich in petroleum and contains diverse biosurfactant-producing strains. A biosurfactant-producing strain LP20 was isolated from oily sludge, identified as Pseudomonas aeruginosa based on phylogenetic analysis of 16S rRNA. High-performance liquid chromatography-mass spectrometry results indicated that biosurfactants produced from LP20 were rhamnolipids, mainly containing Rha-C8-C10, Rha-C10-C10, Rha-Rha-C8-C10, Rha-Rha-C10-C10, Rha-C10-C12:1, and Rha-C10-C12. Interestingly, more mono-rhamnolipids were produced by strain LP20 with a relative abundance of 64.5%. Pseudomonas aeruginosa LP20 optimally produced rhamnolipids at a pH of 7.0 and a salinity of 0.1% using glycerol and nitrate. The culture medium for rhamnolipids by strain LP20 was optimized by response surface methodology. LP20 produced rhamnolipids up to 6.9 g L-1, increased by 116%. Rhamnolipids produced from LP20 decreased the water surface tension to 28.1 mN m-1 with a critical micelle concentration of 60 mg L-1. The produced rhamnolipids emulsified many hydrocarbons with EI24 values higher than 56% and showed antimicrobial activity against Staphylococcus aureus and Cladosporium sp. with inhibition rates 48.5% and 17.9%, respectively. Pseudomonas aeruginosa LP20 produced more proportion of mono-rhamnolipids, and the LP20 rhamnolipids exhibited favorable activities and promising potential in microbial-enhanced oil recovery, bioremediation, and agricultural biocontrol.

Strains of Salmonella Enteritidis (SEnt, n = 10) and S. Typhimurium (STm, n = 11), representing clones with high impact on human health, and strains of S. 4,12: b:- (S412B n = 11) and S. Liverpool (SLiv, n = 4), representing clones with minor impact on human health were characterized for 16 growth, stress, and virulence phenotypes to investigate whether systematic differences exist in their performance in these phenotypes and whether there was correlation between performance in different phenotypes. The term serotype was not found to be predictive of a certain type of performance in any phenotype, and surprisingly, on average, strains of SEnt and STm were not significantly better in adhering to and invading cultured intestinal cells than the less pathogenic types. Forest analysis identified desiccation tolerance and the ability to grow at 42°C with high salt as the characters that separated serovars with low human health impact (S412B/SLiv) from serovars with high human health impact (SEnt/STm). The study showed that variation in phenotypes was high even within serovars and correlation between phenotypes was low, i.e. the way that a strain performed phenotypically in one of the tested conditions had a low predictive value for the performance of the strain in other conditions.

This research aimed to determine the relationships between the risk factors for nosocomial multidrug-resistant Acinetobacter baumannii (MDRAB) bacteremia and associated mortality. We analyzed 144 patients treated for A. baumannii bacteremia, including 120 patients with MDRAB bacteremia, from March 2015 to March 2020, in this retrospective study. The overall bacteremia-related mortality rate was 48.6%. The mortality rates were 25.0% and 53.3% for non-MDRAB and MDRAB bacteremia, respectively. Risk factors for the development of MDRAB bacteremia were prior use of cephalosporins [odds ratio (OR): 8.62; P < .001], carbapenems (OR: 15.04; P < .001), or quinolones (OR: 5.02; P = .040); indwelling urinary catheters (OR: 21.38; P < .001); and respiratory tract as the source of bacteremia (OR: 75.33; P < .001). Patients with elective surgeries were inclined to develop non-MDRAB bacteremia (OR: 0.45; P = .029). High scores in the Acute Physiology and Chronic Health Evaluation II (OR: 1.321; P < .001) and Sequential Organ Failure Assessment (OR: 1.326; P < .001) were risk factors for mortality from MDRAB infection. In summary, higher mortality rates occur in patients with MDRAB bacteremia, and risk factors include prior use of cephalosporins, carbapenems, or quinolones. Urinary catheters and the respiratory tract as sources of the infection increase the risk of MDRAB bacteremia.

Antimicrobial susceptibility tests (AST) conducted in vitro offer a range of methods to assess the antimicrobial resistance (AMR) of microorganisms. Escherichia coli, a widely distributed bacterium, is closely linked to the issue of AMR. In this way, the present study aimed to assess the agreement among different in vitro AST methods, including disk diffusion in agar, broth dilution, and agar dilution method. A total of 100 E. coli isolates were analyzed for their resistance levels against six antibiotics: amoxicillin, ceftiofur, ciprofloxacin, chloramphenicol, tetracycline, and sulfamethoxazole + trimethoprim, using the aforementioned AST methods. Standard breakpoint values were employed to classify isolates as resistant, intermediate, or susceptible, and comparisons among the AST methods were conducted by McNemar's test (P < .05). The obtained data demonstrated equivalence among the AST methods, highlighting the reliability of these standardized classical methodologies. This standardization aids in preventing the inappropriate use of antimicrobials and the dissemination of antimicrobial-resistant microorganisms.

The cariogenicity of Streptococcus mutans relates to its ability to form biofilms on dental surfaces. The aim of this work was to develop a flowcell system compatible with time-lapse confocal microscopy to compare the adhesion and accumulation of S. mutans cells on surfaces in unsupplemented media against media containing sucrose or sucralose (a non-metabolized sweetener) over a short period of time. Fluorescent S. mutans 3209/pVMCherry was suspended in unsupplemented media or media supplemented with 1% sucrose or 1% sucralose and passed through a 3D-printed flowcell system. Flowcells were imaged over 60 minutes using a confocal microscope. Image analysis was performed, including a newly developed object-movement-based method to measure biomass adhesion. Streptococcus mutans 3209/pVMCherry grown in 1% sucrose-supplemented media formed small, dense, relatively immobile clumps in the flowcell system measured by biovolume, surface area, and median object centroid movement. Sucralose-supplemented and un-supplemented media yielded large, loose, mobile aggregates. Architectural metrics and per-object movement were significantly different (P < 0.05) when comparing sucrose-supplemented media to either unsupplemented or sucralose-supplemented media. These results demonstrate the utility of a flowcell system compatible with time-lapse confocal microscopy and image analysis when studying initial biofilm formation and adhesion under different nutritional conditions.

Antibiotic resistance in Citrobacter freundii is a public health concern. This study evaluated the closed genome of a C. freundii isolated from the stool of a hospitalized patient initially related to a Salmonella outbreak. Confirmation of the isolate was determined by whole-genome sequencing. Nanopore sequencing was performed using a MinION with a Flongle flow cell. Assembly using SPAdes and Unicycler yielded a closed genome annotated by National Center for Biotechnology Information Prokaryotic Genome Annotation Pipeline. Genomic analyses employed MLST 2.0, ResFinder4.1, PlasmidFinder2.1, and VFanalyzer. Phylogenetic comparison utilized the Center for Food Safety and Applied Nutrition (CFSAN)-single nucleotide polymorphism pipeline and Genetic Algorithm for Rapid Likelihood Inference. Antimicrobial susceptibility was tested by broth microdilution following Clinical and Laboratory Standards Institute criteria. Multi-locus sequence type in silico analysis assigned the C. freundii as sequence type 64 and the blaCMY-41 gene was detected in resistome investigation. The susceptibility to antibiotics, determined using Sensititre® plates, revealed resistance to aztreonam, colistin, cefoxitin, amoxicillin/clavulanic acid, sulfisoxazole, ampicillin, and streptomycin. The genetic relatedness of the C. freundii CFSAN077772 with publicly available C. freundii genomes revealed a close relationship to a C. freundii SRR1186659, isolated in 2009 from human stool in Tanzania. In addition, C. freundii CFSAN077772 is nested in the same cluster with C. freundii clinical strains isolated in Denmark, Mexico, Myanmar, and Canada, suggesting a successful intercontinental spread.