Letters in Applied Microbiology最新文献

Botryosphaeria dothidea is an important pathogenic fungal, which cause the serious threats to crop and the substantial economic losses. Plant essential oils (EOs) have the strong antifungal activity, and induce fruit resistance to microorganisms. The antifungal activity and mechanism of Mentha spicata EOs and major compounds against B. dothidea, and the extending shelf life of Actinidia chinensis fruit were investigated. The results showed that estragole was a most abundant in M. spicata EOs compounds. M. spicata EOs, D-carvone, estragole and fenchone exhibited strong inhibitory effects on B. dothidea. M. spicata EOs and fenchone had significantly increased the electrical conductivity of B. dothidea solution, and caused to loss of nucleic acid and soluble protein. M. spicata EOs and estragole suppressed the cellulase and peroxidase of B. dothidea, however, fenchone promoted the xylanase activity. B. dothidea proliferation on A. chinensis fruit was inhibited by M. spicata EOs and major compounds during day 3 to 7 in situ. M. spicata EOs and fenchone promoted the A. chinensis fruit cellulase activity, however, the xylanase activity significantly reduced. The peroxidase activity of A. chinensis fruit increased by estragole. This study showed that M. spicata EOs has great potential as antifungal agent used for fruit postharvest.

In recent years, misdiagnosis or delayed diagnosis of Chlamydia psittaci (C. psittaci) infections has led to frequent outbreaks of severe public health events, such as severe pneumonia and respiratory distress, drawing increasing attention. Rapid and simple detection methods are vital for early intervention to reduce severity and mortality. In this study, we designed highly specific RPA primers and crRNA (CRISPR RNA) based on the highly conserved CPSIT_0429 gene in the C. psittaci genome, and preliminarily established a nucleic acid detection method for C. psittaci using the RPA-CRISPR/Cas12a system. In the two-step assay, the combination of the CPSIT_0429-F1/R1 primer pair and CPSIT_0429-crRNA2 achieved a detection limit of 2 × 10° copies/μL. Incorporating 20% glycerol enabled a one-tube assay with a limit of 2 × 102 copies/μL. Furthermore, the method showed no cross-reactivity with common respiratory pathogens such as Influenza virus, SARS-CoV-2, and Streptococcus pneumoniae, demonstrating excellent specificity. Both the two-step and one-tube methods were compared with qPCR-verified C. psittaci positive samples. The results indicated that both assays showed high consistency with qPCR results. The RPA-CRISPR/Cas12a detection method is rapid, accurate, highly sensitive, and specific, providing a reliable platform for early diagnosis and clinical management of C. psittaci infections.

This study investigated antibacterial effects of Cinnamomum loureirii essential oil (CLEO) against three foodborne microorganisms: Escherichia coli, Staphylococcus aureus, Pseudomonas putida. GC-MS showed trans-cinnamaldehyde was CLEO's major constituent (91.18%). CLEO's minimum inhibition concentrations (MICs) were 1, 0.25, 2 mg mL-1 for E.coli, S.aureus, P.putida, respectively. With rising CLEO concentration, nucleic acid and alkaline phosphatase (AKR) leakage of three bacteria increased gradually; S. aureus had higher leakage at 1/2MIC. This demonstrated CLEO disrupts cell wall/membrane integrity, affects cell structure, changes membrane permeability of bacterial proteins. Scanning/transmission electron microscopy (SEM/TEM) showed obvious bacterial morphological/ultrastructural changes, affecting normal cell division, further confirming CLEO-induced cell wall/membrane damage. Additionally, CLEO exhibited antibiofilm activity at sub-MIC levels, inhibiting three bacteria's biofilm formation. Under 2 × MIC, inhibition rates of E. coli, S. aureus, P. putida were 85.21%, 31.29%, 72.36%, respectively. Overall, CLEO is a promising natural antibacterial agent/multifunctional food additive for food and pharmaceutical industries.

Group B Streptococcus (GBS) is a major cause of maternal and neonatal infections, complicated by increasing antimicrobial resistance and high virulence. In this study, from 235 vaginal swabs, 45 GBS isolates were identified and screened; 12 representative isolates (strong biofilm producers with the complete virulence gene profile) were selected for downstream analyses. Molecular analysis showed high prevalence of virulence genes (fbsA 95.5%, lmb 91.1%, pavA 88.8%, fbsB 86.6%) and biofilm-related genes (pil-1 88.8%, pil-2a 91.1%, pil-2b 84.4%). Subsequently, a Bifidobacterium bifidum (designated B. bifidum BB-6; GenBank accession number PX474696) isolated from human breast milk was used to prepare a cell-free supernatant (CFS). GC-MS analysis of the CFS of B. bifidum identified several bioactive compounds, including acetic acid, propionic acid and lactic acid. Checkerboard assays indicated synergism between CFS and penicillin/vancomycin, with a fractional inhibitory concentration index (FICI) of ≤0.5 in most cases. Sub-minimum inhibitory concentration (sub-MIC) of CFS significantly inhibited biofilm formation (P < 0.01), and quantitative real-time PCR (qRT-PCR) revealed downregulation of virulence (fbsB down -4.40-fold) and biofilm genes (pil-2b down -5.49-fold). These results highlight the therapeutic potential of B. bifidum CFS against GBS, warranting further studies to isolate active compounds and evaluate safety and efficacy in vivo.

Bacillus spp. can colonize various plant tissues, promoting growth and providing biocontrol. Bacillus amyloliquefaciens GZY63 exhibits strong antagonistic activity against anthracnose pathogens in Camellia oleifera. However, its potential as a biocontrol agent in Ca. oleifera remains underexplored, mainly because knowledge regarding its colonization behavior in this host plant is limited. In this study, we used a chloramphenicol-resistant GFP-tagged GZY63 strain to assess the colonization patterns of the bacterium in Ca. oleifera through quantitative Polymerase Chain Reaction (qPCR). In particular, we investigated the bacterium's colonization dynamics across three Ca. oleifera varieties, with a focusing on differences between the root and foliar inoculation methods. The results revealed that root inoculation of B. amyloliquefaciens GZY63 resulted in significantly higher colonization efficiency and more rapid bacterial translocation to leaf tissues than its foliar inoculation. Moreover, the colonization efficiency varied among the three Ca. oleifera varieties, indicating that host genotype influences the bacterium's endophytic compatibility. Although the underlying biochemical factors and regulatory mechanisms remain unclear, our results provide valuable insights into host-microbe interactions in Ca. oleifera. These findings provide a theoretical basis for optimizing the application of B. amyloliquefaciens GZY63 as biocontrol agent in Ca. oleifera and underscore the importance of selecting compatible host genotypes for effective microbial inoculation.

Continuous cultivation can lead to soil nutrient imbalances and have adverse effects on soil rhizosphere microorganisms. This study investigated the impact of continuous cultivation of Salvia miltiorrhiza on rhizosphere soil microbial communities by comparing four planting durations: CK (no cultivation), D1 (annual planting), D2 (two consecutive years), and D3 (three consecutive years). High-throughput sequencing technology was used to analyze changes in rhizosphere soil microbial communities. The results revealed that the planted soil of Salvia miltiorrhiza exhibited lower abundances of beneficial bacteria such as Bacillus and Acidothermus compared to CK. The pathogenic fungus Fusarium was found to found to have the highest abundance in D2 soil. Linear discriminant analysis effect size analysis at the genus level identified several biomarkers, including g_Candidatus_Solibacter, g_Sphingomonas, g_RB41, and g_Chitinophaga as bacterial markers, while g_Talaromyces, g_Thermomyces, g_Trichothecium, g_Solicoccozyma, and g_Pseudopithomyces as fungal markers. Correlation analysis between these microbial markers and environmental factors showed that total nitrogen had a significant positive correlation with bacteria g_Candidatus_Solibacter and fungi g_Solicoccozyma, but a significant negative correlation with bacteria g_Sphingomonas and g_RB41. Soil organic matter showed a negative correlation with g_Sphingomonas; g_Candidatus Solibacter was negatively correlated with g_Sphingomonas.

Fungal pathogens continue to pose a significant challenge to global agriculture, food security, and public health, resulting in substantial crop losses, food spoilage, and the accumulation of harmful mycotoxins. The extensive reliance on synthetic chemical fungicides raises serious concerns, including the emergence of resistant fungal strains, ecotoxicity, and adverse health effects. This review highlights the potential of Bacillus spp. and Lactobacillus (LAB) in the development of natural antifungal agents. These bacterial genera are known for the production of a wide range of bioactive metabolites, such as cell-free supernatants (CFS) with potent antifungal properties, volatile organic compounds (VOCs), phenolic acids, and lipopeptides. Lactobacillus-derived compounds, particularly phenyl lactic acid, play a dual role in inhibiting fungal growth while also improving food quality and safety. Similarly, Bacillus spp. produce lipopeptides and volatile organic compounds (VOCs) that are effective against a wide range of airborne and soilborne plant pathogens. Recent studies also highlight Bacillus-mediated green synthesis of nanoparticles (e.g. silver, zinc oxide, and selenium) with potent antifungal activity. These eco-friendly nanomaterials inhibit fungal growth, disrupt biofilms, and enhance plant defenses, offering a targeted and sustainable alternative to chemical fungicides. This review advocates the integration of bacterial antifungal strategies into sustainable agriculture and post-harvest management systems.

Avian pathogenic E. coli (APEC) is a leading cause of colibacillosis in poultry worldwide. Molecular genotyping using polymerase chain reaction (PCR) is a rapid and effective way to separate Avian Pathogenic E. coli (APEC) from commensal E. coli in poultry. This study assessed the accuracy of four different molecular genotyping panels in a head-to-head comparison, using 250 APEC isolates from diseased birds and 106 fecal E. coli (AFEC) isolates from healthy birds. The cut-off value of all four panels was observed and optimal cut-off values with sensitivity and specificity were suggested in this study. The results found that the APECtyper panel had the highest sensitivity (81.2%) being significantly different to the other 3 panels, while the 9-gene panel demonstrated the highest specificity (89.6%). The cut-off of the 13-gene panel was optimized with a predicted probability of 12%, balancing sensitivity (57.2%) and specificity (75.5%), which was used in this study. Overall, three of the four panels except the 13-gene panel showed good performance with distinct strengths. This research provides valuable insights, but further studies are needed to confirm the reliability and reproducibility of these assays across different geographical regions, various poultry populations, and diverse field conditions.

Forage from four locations (blocks) was inoculated with 150 000 CFU/g Lactiplantibacillus plantarum DSM26571, Lactococcus lactis NCIMB30117, and Enterococcus lactis 22502 (LPEL); 150 000 CFU/g Lactococcus lactis DSM22501 and Lentilactobacillus buchneri DSM11037 (LB); or distilled water (CON), packed full (D100; 264 kg DM/m3) or half (D50; 132 kg DM/m3) density, and ensiled for 7, 14, 60, or 90 d. Data were analyzed as a randomized complete block with fixed (packing density, bacterial inoculation, storage length, and their interactions) and random (block) effects. An interaction between inoculation and storage length was observed for pH. At early storage lengths, LPEL had the lowest pH, without differences afterwards. A three-way interaction was observed for lactic acid concentration; D100 was greater than D50. An interaction between packing density and bacterial inoculation was observed for acetic acid concentration; D50-LPEL and D50-LB had the lowest acetic acid concentrations. Bacterial inoculants had minor effects, although the homofermentative inoculant decreased pH. Greater packing density increased organic acids. Thus, a combination of greater packing density and homofermentative microbial inoculants may improve fermentation and minimize storage losses. Further research is warranted to better characterize changes in the microbial community of alfalfa silage with different microbial inoculants and ensiled at different packing densities.

The presence of multidrug-resistant Escherichia coli strains in healthy cattle represents a major threat to public health because they can act as a reservoir of resistance genes. Little is known about the antimicrobial susceptibility profile and genetic characteristics of E. coli strains isolated from healthy calves in Panama and Central America. We conducted a cross-sectional study evaluating isolates from healthy calves in Panama. Antimicrobial susceptibility was determined against 15 antibiotics, and strains were classified as resistant, intermediate, or susceptible. 120 E. coli isolates were obtained, of which 61% were resistant to at least one antibiotics analyzed, while only 39% were susceptible. The most frequent resistance was to tetracycline (36%) and ampicillin (34%). Fifteen percent of the isolates (18/120) were multidrug-resistant, and 2% presented an extended spectrum β-lactamase phenotype; blaTEM (22%) and blaCTX-M (10%) genes were detected, with the Extended-Spectrum β-lactamases phenotype observed in isolates carrying blaCTX-M. Plasmid-mediated quinolone resistance gene qnrA (10%), qnrB (13%), and qnrS (23%) were detected among the isolates. Our results suggest that a significant proportion of antimicrobial resistance occurs in intestinal strains of E. coli isolated from healthy calves in Panama.