Letters in Applied Microbiology最新文献

Faecal contamination of surface waters has the potential to spread not only pathogenic organisms but also antimicrobial resistant organisms. During the bathing season of 2021, weekly water samples, from six selected coastal bathing locations (n = 93) and their freshwater tributaries (n = 93), in Northern Ireland (UK), were examined for concentrations of faecal indicator bacteria Escherichia coli and intestinal enterococci. Microbial source tracking involved detection of genetic markers from the genus Bacteroides using PCR assays for the general AllBac marker, the human HF8 marker and the ruminant BacR marker for the detection of human, and ruminant sources of faecal contamination. The presence of beta-lactamase genes blaOXA-48, blaKPC, and blaNDM-1 was determined using PCR assays for the investigation of antimicrobial resistance genes that are responsible for lack of efficacy in major broad-spectrum antibiotics. The beta-lactamase gene blaOXA-48 was found in freshwater tributary samples at all six locations. blaOXA-48 was detected in 83% of samples that tested positive for the human marker and 69% of samples that tested positive for the ruminant marker over all six locations. This study suggests a risk of human exposure to antimicrobial resistant bacteria where bathing waters receive at least episodically substantial transfers from such tributaries.

The increasing resistance to polymyxins in Acinetobacter baumannii has made it even more urgent to develop new treatments. Anti-virulence compounds have been researched as a new solution. Here, we evaluated the modification of virulence features of A. baumannii after acquiring resistance to polymyxin B. The results showed lineages attaining unstable resistance to polymyxin B, except for Ab7 (A. baumannii polymyxin B resistant lineage), which showed stable resistance without an associated fitness cost. Analysis of virulence by a murine sepsis model indicated diminished virulence in Ab7 (A. baumannii polymyxin B resistant lineage) compared with Ab0 (A. baumannii polymyxin B susceptible lineage). Similarly, downregulation of virulence genes was observed by qPCR at 1 and 3 h of growth. However, an increase in bauE, abaI, and pgAB expression was observed after 6 h of growth. Comparison analysis of Ab0, Ab7, and Pseudomonas aeruginosa suggested no biofilm formation by Ab7. In general, although a decrease in virulence was observed in Ab7 when compared with Ab0, some virulence feature that enables infection could be maintained. In light of this, virulence genes bauE, abaI, and pgAB showed a potential relevance in the maintenance of virulence in polymyxin B-resistant strains, making them promising anti-virulence targets.

Alternative strategies for controlling Staphylococcus aureus and other pathogens have been continuously investigated, with nisin, a bacteriocin widely used in the food industry as a biopreservative, gaining increasing attention. In addition to its antimicrobial properties, bacteriocins have significant effects on genome functionality even at inhibitory concentrations. This study investigated the impact of subinhibitory concentrations of nisin on S. aureus. Culturing in the presence of 0.625 μmol l-1 nisin, led to the increased relative expression of hla, saeR, and sarA, genes associated with virulence while expression of the sea gene, encoding staphylococcal enterotoxin A (SEA), decreased. In an in vivo experiment, Galleria mellonella larvae inoculated with S. aureus cultured in the presence of nisin exhibited 97% mortality at 72 h post-infection, compared to over 40% of larvae mortality in larvae infected with S. aureus. A comprehensive understanding of the effect of nisin on the transcriptional response of virulence genes and the impact of these changes on the virulence of S. aureus can contribute to assessing the application of this bacteriocin in food and medical contexts.

Sleeplessness (insomnia) is a potential symptom of depression. A probiotic NVP1704 alleviates depression-like behavior and neuroinflammation in mice. Therefore, to understand whether NVP1704 could be effective against sleeplessness in vivo, we exposed immobilization stress (IS) in mice, then orally administered NVP1704 for 5 days, and assayed depression/anxiety-like behavior in the open field, elevated plus maze, and tail suspension tests, sleeping latency time, and sleep duration, euthanized then by exposure to CO2, and analyzed their related biomarkers. Oral administration of NVP1704 decreased IS-induced depression/anxiety-like behavior and sleeping latency time and increased IS-suppressed sleeping duration. NVP1704 increased IS-suppressed expression of γ-aminobutyric acid (GABA), GABAA receptor α1 (GABAARα1) and α2 subunits (GABAARα2), serotonin, 5-HT receptors (5-HT1AR and 5-HT1BR), and melatonin receptors (MT1R and MT2R) in the prefrontal cortex and thalamus. NVP1704 also increased the IS-suppressed GABAARα1-positive cell population in the prefrontal cortex and decreased IS-induced corticosterone, TNF-α, and IL-6 expression and the NF-κB+Iba1+ cell population in the brain and myeloperoxidase, TNF-α, and IL-6 expression and the NF-κB+CD11c+ cell population in the colon. Based on these findings, NVP1704 may alleviate depression/anxiety/sleeplessness-like behaviors through the upregulation of serotonergic and GABAergic systems and downregulation of NF-κB activation.

Lactoferrin is an antimicrobial glycoprotein that demonstrates a broad-spectrum of activity against a wide variety of clinical pathogens. This study investigated the potential of bovine lactoferrin (bLf) against multidrug resistant Staphylococcus capitis (S. capitis) strains. Growth curve analysis and time-kill curves demonstrated that at 750 µg ml-1 lactoferrin significantly inhibited (50.6%, P < 0.05) the growth of most isolates tested (90%), and this effect was based on a bacteriostatic mechanism. At the same concentration, bLf also significantly inhibited (30%, P < 0.05) biofilm formation in 40% of strains tested. Combinations of bLf with selected antibiotics were assessed for enhanced antimicrobial activity using growth curves. BLf combined with β-lactam antibiotics reduced the growth of S. capitis strains, however, the effects were not significant. BLf displays antimicrobial effects against multidrug resistant S. capitis isolates, but with strain-specific effects.

The dairy industry generates substantial wastewater, which is commonly treated using integrated anaerobic hydrolysis and aerated biofilm reactors. However, the bacterial composition and functional differences within the generated floccules remain unclear. In this study, we employed 16S rRNA and metagenomic sequencing to compare bacterial communities and enzyme gene profiles between suspended floccules from the hydrolysis ponds and the aeration ponds. Results revealed that the bacterial phyla Firmicutes, Proteobacteria, and Bacteroidetes dominated the wastewater treatment system and the relative abundance of these bacterial phyla varied in each pond. Additionally, the aeration ponds exhibited higher bacterial operational taxonomic units and enzyme gene abundance. Network analysis demonstrated a more complex bacterial network structure in the hydrolysis ponds compared to the aeration ponds. Furthermore, enzyme gene abundance revealed higher metabolic enzyme genes in the hydrolysis ponds, while signal transduction enzyme genes were more abundant in the aeration ponds. Notably, the top 10 bacterial genera, primarily Hydromonas in the hydrolysis ponds and Ferruginibacter in the aeration ponds, exhibited distinct contributions to signal transduction enzyme genes. Hydromonas dominated the metabolic enzyme genes in both ponds. These findings provide crucial insights for optimizing dairy wastewater treatment technologies.

Neocosmospora solani causes Fusarium wilt disease and root rot, which are serious problems worldwide. To determine the growth inhibition of Neocosmospora solani by Trichoderma hamatum volatile organic compounds (VOCs), the major chemical components of Trichoderma hamatum VOCs and the differences in their contents at different times were analysed, and the activity of these components was evaluated. The antifungal activity of Trichoderma hamatum was measured by a screening test, as Trichoderma hamatum exhibited strong antagonism against Neocosmospora solani in vitro. The double plate technique was used to verify the activity of Trichoderma hamatum VOCs, and the inhibition rate was 63.77%. Neocosmospora solani mycelia were uneven and expanded, the contents of the cells leaked, and the mycelia shrank and presented a diaphragm in the hyphae upon Trichoderma hamatum VOCs treatment. Trichoderma hamatum VOCs and their contents at different times were analysed by using gas chromatography-mass spectrometry. 6-Pentyl-2H-pyran-2-one clearly presented in greater amounts than the other components on day 3, 4, 5, and 6. VOCs from Trichoderma hamatum exhibited evident effects on the percentage of healthy fruit after day 3. Moreover, Trichoderma hamatum can improve the biological control of diseases caused by soilborne pathogens, and can be applied in biocontrol fields.

Aeromonas dhakensis is reported as an emerging pathogenic species within the genus Aeromonas and is widely distributed in tropical coastal areas. This study provided a detailed description and characterization of a strain of A. dhakensis (202108B1) isolated from diseased Ancherythroculter nigrocauda in an inland region of China. Biochemical tests identified the isolate at the genus level, and the further molecular analysis of concatenated housekeeping gene sequences revealed that the strain belonged to the species A. dhakensis. The isolated A. dhakensis strain was resistant to five antibiotics, namely, penicillin, ampicillin, clindamycin, cephalexin, and imipenem, while it was susceptible to or showed intermediate resistance to most of the other 15 tested antibiotics. The isolated strain of A. dhakensis caused acute hemorrhagic septicemia and tissue damage in artificially infected A. nigrocauda, with a median lethal dose of 7.76 × 104 CFU/fish. The genome size of strain 202108B1 was 5 043 286 bp, including 1 chromosome and 4 plasmids. This is the first detailed report of the occurrence of infection caused by an A. dhakensis strain causing infection in an aquaculture system in inland China, providing important epidemiological data on this potential pathogenic species.

Salmonella is a common cause of human foodborne illness, which is frequently associated with consumption of contaminated or undercooked poultry meat. Serotype Infantis is among the most common serotypes isolated from poultry meat products globally. Isolates of serotype Infantis carrying the pESI plasmid, the most dominant strain of Infantis, have been shown to exhibit oxidizer tolerance. Therefore, 16 strains of Salmonella with and without pESI carriage were investigated for susceptibility to biocide chemical processing aids approved for use in US poultry meat processing: peracetic acid (PAA), cetylpyridinium chloride (CPC), calcium hypochlorite, and sodium hypochlorite. Strains were exposed for 15 s to simulate spray application and 90 min to simulate application in an immersion chiller. All strains tested were susceptible to all concentrations of PAA, CPC, and sodium hypochlorite when applied for 90 min. When CPC, calcium hypochlorite, and sodium hypochlorite were applied for 15 s to simulate spray time, strains responded similarly to each other. However, strains responded variably to exposure to PAA. The variation was not statistically significant and appears unrelated to pESI carriage. Results highlight the necessity of testing biocide susceptibility in the presence of organic material and in relevant in situ applications.

Non-antibiotic adjuncts may improve Helicobacter pylori infection control. Our aim was to emphasize curcumin benefits in controlling H. pylori infection. We discussed publications in English mostly published since 2020 using keyword search. Curcumin is the main bioactive substance in turmeric. Curcumin inhibited H. pylori growth, urease activity, three cag genes, and biofilms through dose- and strain-dependent activities. Curcumin also displayed numerous anticancer activities such as apoptosis induction, anti-inflammatory and anti-angiogenic effects, caspase-3 upregulation, Bax protein enhancement, p53 gene activation, and chemosensitization. Supplementing triple regimens, the agent increased H. pylori eradication success in three Iranian studies. Bioavailability was improved by liposomal preparations, lipid conjugates, electrospray-encapsulation, and nano-complexation with proteins. The agent was safe at doses of 0.5->4 g daily, the most common (in 16% of the users) adverse effect being gastrointestinal upset. Notably, curcumin favorably influences the intestinal microbiota and inhibits Clostridioides difficile. Previous reports showed the inhibitory effect of curcumin on H pylori growth. Curcumin may become an additive in the therapy of H. pylori infection, an adjunct for gastric cancer control, and an agent beneficial to the intestinal microbiota. Further examination is necessary to determine its optimal dosage, synergy with antibiotics, supplementation to various eradication regimens, and prophylactic potential.