BMC Microbiology最新文献

Background: Outer membrane protein OmpA is composed of two domains, an N-terminal β-barrel structure embedded in the outer membrane and a C-terminal globular domain noncovalently associated with the peptidoglycan layer in periplasm. Stenotrophomonas maltophilia KJ is a clinical isolate. In our recent study, we disclosed that KJ∆OmpA_{299 - 356,} an OmpA C-terminal deletion mutant, compromised menadione tolerance. Furthermore, the involvement of σ^E, σ^N, and ompO in the ∆ompA_{299 - 356}-mediated phenotype was proposed. In that study, we hypothesized that there was an unidentified σ^N-regulated candidate responsible for ∆ompA_{299 - 356}-mediated menadione tolerance decrease, and the candidate was disclosed in this study.

Methods and results: Transcriptome analysis of wild-type KJ and KJ∆OmpA_{299 - 356} revealed that a five-gene cluster, smlt4023-smlt4019 (annotated as nagPIBAF), was upregulated in KJ∆OmpA_{299 - 356}. Reverse transcription-PCR (RT-PCR) confirmed the presence of the nagPIBAF operon. The expression of the nagPIBAF operon was negatively regulated by NagI and σ^N, and triggered by N-acetylglucosamine. In-frame deletion mutant construction and menadione tolerance assay demonstrated that nagP, nagB, and nagA upregulation in KJ∆OmpA_{299 - 356} connected with ∆ompA_{299 - 356}-mediated menadione tolerance decrease. The intracellular reactive oxygen species (ROS) level assay further verified that in the presence of external oxidative stress such as menadione treatment, nagPIBAF operon upregulation and ompO inactivation synergistically increased intracellular ROS levels, which exceeded the capacity of bacterial oxidative stress alleviation systems and resulted in a decrease of menadione tolerance.

Conclusions: Loss of interaction between OmpA C-terminus and peptidoglycan causes envelope stress and activates σ^E regulon. ompO and rpoN are downregulated in response to σ^E activation. rpoN downregulation further derepresses nagPIBAF operon, which can favor the metabolism route of glycolysis, TCA cycle, and electron transport chain. nagPIBAF upregulation and OmpO downregulation synergistically increase intracellular ROS levels and result in menadione tolerance decrease.

Clinical trial number: Not applicable.

The gut microbiota of insects plays a pivotal role in digesting food, supplying nutrients, and synthesizing enzymes, particularly those capable of degrading lignocellulosic biomass-a key factor in waste management. In Karnataka, India, the larvae of Holotrichia serrata and Leucopholis coneophora are major crop pests. However, the potential of their gut bacterial communities to degrade lignocellulose has yet to be fully explored. This study aimed to isolate and evaluate lignocellulose-degrading bacteria from these larvae. Seventeen cellulolytic bacterial strains were successfully isolated from the fermentation chamber of white grubs, most of which belonged to the Firmicutes and γ-Proteobacteria classes. Notable genera included Bacillus, Enterobacter, and Klebsiella. Among these, Bacillus toyonensis strain LC3B1 exhibited remarkable cellulolytic activity, with a cellulolytic index of 1.93 ± 0.037. This strain demonstrated the highest degradation on groundnut husk powder (33.25 ± 0.823%), followed by paddy straw powder (31.45 ± 0.608%) and corncob powder (28.15 ± 1.56%), highlighting its potential for effective agricultural residue degradation. FTIR analysis of carboxymethyl cellulose (CMC) hydrolyzed by LC3B1 revealed various decomposition products, including ketones, aldehydes, alcohols, and carboxylic acids. Scanning electron microscopy (SEM) of the treated biomass revealed significant morphological changes, such as pore formation and tunneling within the substrate. The broad cellulolytic capabilities observed across bacteria from white grub gut microbiota, including members of the Bacillaceae, Enterobacteriaceae, and Pseudomonadaceae families, underscore their potential as valuable resources for lignocellulosic biomass degradation, biofuel production, and sustainable waste management strategies. This study highlights the promise of insect gut microbiota as a reservoir for environmentally beneficial microbial applications.

Background: Microorganisms are the biotic foundation for nutrient cycling across ecosystems, and their assembly is often based on the nutrient availability of their environment. Though previous research has explored the seasonal lake turnover and geochemical cycling within the Salton Sea, California's largest lake, the microbial community of this declining ecosystem has been largely overlooked. We collected seawater from a single location within the Salton Sea at 0 m, 3 m, 4 m, 5 m, 7 m, 9 m, 10 m, and 10.5 m depths in August 2021, December 2021, and April 2022.

Results: We observed that the water column microbiome significantly varied by season (R² = 0.59, P = 0.003). Temperature (R² = 0.27, P = 0.004), dissolved organic matter (R² = 0.13, P = 0.004), and dissolved oxygen (R² = 0.089, P = 0.004) were significant drivers of seasonal changes in microbial composition. In addition, several halophilic mixotrophs and other extremotolerant bacteria were consistently identified in samples across depths and time points, though their relative abundances fluctuated by season. We found that while sulfur cycling genes were present in all metagenomes, their relative coverages fluctuated by pathway and season throughout the water column. Sulfur oxidation and incomplete sulfur oxidation pathways were conserved in the microbiome across seasons.

Conclusions: Our work demonstrates that the microbiome within the Salton Seawater has the capacity to metabolize sulfur species and utilize multiple trophic strategies, such as alternating between chemorganotrophy and chemolithoautrophy, to survive this harsh, fluctuating environment. Together, these results suggest that the Salton Sea microbiome is integral in the geochemical cycling of this ever-changing ecosystem and thus contributes to the seasonal dynamics of the Salton Sea. Further work is required to understand how these environmental bacteria are implicated relationship between the Salton Sea's sulfur cycle, dust proliferation, and respiratory distress experienced by the local population.

Background: The isolation and culture of Mycobacterium ulcerans (Mu) as a primary diagnostic modality for Buruli ulcer (BU) disease are limiting due to their low sensitivity and slow-growing nature. M. ulcerans cultures can also be overgrown with other bacteria and fungi. Culture, however, remains an important tool for the study of persisting viable M. ulcerans, drug susceptibility tests, and other molecular assays to improve management of the disease. The challenge of contamination with other fast-growing bacteria necessitates decontamination of clinical samples prior to culturing, but current methods may be too harsh, resulting in low yields of M. ulcerans. We aimed to evaluate a Tika-Kic decontamination process for M. ulcerans that uses supplements to stimulate M. ulcerans growth to improve recovery.

Methods: Swab and Fine Needle Aspirate (FNA) samples were collected from 21 individuals with confirmed BU at baseline (week 0) and weeks 2 and 4 after initiating antibiotic treatment. Samples were decontaminated with Tika-Kic decontamination medium and the modified Petroff (NaOH) methods then inoculated each into Mycobacterium Growth Indicator Tube (MGIT) or Löwenstein Jensen (LJ) medium. Time to growth detection and confirmation by qPCR as well as the proportion of positive cultures for all three methods and the proportion of positive cultures for all three time points were documented. Common contaminating bacteria were also isolated and identified.

Results: The proportion of M. ulcerans positive cultures obtained was higher for Tika-MGIT samples [14/43 (32%)] compared to Petroff-MGIT samples [10/43 (23%)] and Petroff-LJ samples [8/43 (19%)]. Baseline samples had a higher isolate proportion [17 (53%)] compared to samples collected after treatment initiation [9 (28%) for week 2 and 6 (19%) for week 4]. Contaminating bacteria isolated include Burkholderia cepacia, Pseudomonas aeruginosa, Pasteurella pneumotropica, Proteus mirabilis, Morganella morganii, Staphylococcus aureus and Enterococcus.

Conclusion: Our study shows an advantage for culturing Mycobacterium ulcerans from clinical samples using the Tika-Kic decontamination and growth medium. Further research is needed to refine sample processing to improve M. ulcerans recovery.

Rotavirus is a major cause of pediatric gastroenteritis, for which effective treatments are limited. This study investigates the antioxidant and antiviral potential of lactoferrin, Geobacillus stearothermophilus, and Lactobacillus delbrueckii subsp. lactis against Rotavirus infection. In this study, Geobacillus stearothermophilus and Lactobacillus delbrueckii subsp. lactis were isolated from Hammam Pharon soil and milk cheese, respectively, and identified using molecular techniques with accession numbers PP758390 and PP758383. The antioxidant effect against DPPH showed that lactoferrin exhibited the strongest scavenging ability, followed by Geobacillus stearothermophilus and Lactobacillus delbrueckii subsp. lactis. In vivo experiments involved administering lactoferrin, Geobacillus stearothermophilus, and Lactobacillus delbrueckii subsp. lactis in the drinking water of young mice for three days, followed by Rotavirus infection on the fourth day and sacrifice on the fifth day. The results demonstrated that lactoferrin significantly reduced the pathogenic effects of Rotavirus, as indicated by the normalization of inflammatory cytokines (TNF-α and IL-6) in the serum (p ≤ 0.001). Histological examination of small intestinal sections from Rotavirus-infected mice revealed extensive destruction of villus structures, while mice treated with lactoferrin showed no pathological changes compared to the control group. Geobacillus stearothermophilus-treated mice exhibited less pathological alteration and Lactobacillus delbrueckii subsp. lactis-treated mice showed mild pathological changes. Additionally, molecular docking studies indicated that bacteriocin (a bacterial protein) exhibited the highest binding affinity for the Rotavirus outer membrane protein (VP6) at -261.92 kcal/mol, outperforming lactoferrin (-229.32 kcal/mol). Additionally, bacteriocin's active compounds, turimicin (-7.9 kcal/mol) and lactin (-6.5 kcal/mol), also showed strong binding to VP6, suggesting their potential as therapeutic agents against Rotavirus. In conclusion, this study highlights the significant antiviral potential of lactoferrin against Rotavirus, demonstrating its ability to mitigate pathological changes and normalize inflammatory responses in infected mice. The findings also suggest that bacteriocins, particularly those with high binding affinities to Rotavirus proteins, could serve as promising candidates for therapeutic interventions against Rotavirus infections.

Background: Considering the efficacy of antimicrobial photodynamic therapy (PDT) in inactivating bacteria, this study reports that zinc hydroxide chloride nanosheets (ZHC-NSs) are useful for this purpose.

Materials & methods: The characterization of ZHC-NSs was performed using microscopic and spectroscopic techniques. The irritation test, acute toxicity test, and genotoxicity test of ZHC-NSs were evaluated and their effects on human pulp fibroblast cells (HPFC) viability, intracellular reactive oxygen species (ROS) levels, and antibacterial activity of ZHC-NSs (1-8 mg ml^-1) alone or in light conditions were investigated.

Results: The ZHC-NSs structure showed a crystalline form and their sheets' thickness had an average size of 129.6 ± 19.50 nm. ZHC-NSs did not severely damage internal organs and were not genotoxic. The cytotoxic effect of ZHC-NSs on HPFC was concentration-dependent so that ZHC-NSs at higher concentrations (4 and 8 mg ml^-1) killed half of the HPFC cells. When ZHC-NSs were used in combination with a 980 nm diode laser, namely ZHC-NS^©, ROS production increased and led to enhanced antibacterial activity against Streptococcus mutans in planktonic and biofilm form. A statistically significant difference was found between ZHC-NSs without laser irradiation and photoexcited ZHC-NSs.

Conclusion: ZHC-NSs^© with the potential ability to produce ROS could be effective in complementary treatment against S. mutans.

Background: Dairy cow mastitis is a common and prevalent disease arose by various complicated pathogeny, which poses serious threat to the health of cows, safety of dairy product and economic benefits for pastures. Due to the high stealthiness and long incubation period, subclinical mastitis (SM) of cows causes enormous economic losses. Besides the infection by exogenous pathogenic microorganisms, previous studies demonstrated that gastrointestinal microbial dysbiosis is one of the crucial causes for occurrence and development of mastitis based on the theory of entero-mammary axis. Whereas, limited researches have been conducted on potential pathological metabolic mechanisms underlying the relationship between gut microbiota and SM in cows.

Results: The differences in blood parameters, gut microbiome, plasma and fecal metabolome between healthy and SM cows were compared by performing 16 S rDNA sequencing and non-targeted metabolomic analysis in the current study. The content of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and activity of catalase (CAT), total antioxidant capacity(T-AOC) were significantly decreased, while malondialdehyde (MDA) concentration was dramatically increased in serum of SM cows in comparison with healthy cows. The gut of cows with SM harbored more abundant Cyanobacteria, Proteobacteria, Succinivibrio and Lactobacillus_iners. Moreover, the abundance of Paraprevotella, Coprococcus, Succiniclasticum, Desulfovibrio and Bifidobacterium_pseudolongum were observably reduced in the gut of SM cows. Furthermore, higher abundance of pro-inflammatory metabolites were observed in feces (9(S)-HPODE, 25-hydroxycholesterol, dodecanedioic acid, etc.) and plasma (9-hydroxy-10,12-octadecadienoic acid, 13,14-dihydro PGF1α, 5,6-dehydro arachidonic acid, myristic acid, histamine, etc.) of SM cows. The abundance of certain metabolites with anti-inflammatory and antioxidant properties (mandelic acid, gamma-tocotrienol, deoxycholic acid, etc.) were notably decreased in feces or plasma of cows with SM.

Conclusions: The intestinal microbial composition and metabolic profiles of healthy and SM cows were significantly distinct, that were characterized by decreased abundance of intestinal symbiotic bacteria, potential probiotics and anti-inflammatory, antioxidant compounds, along with increased abundance of potential pro-inflammatory bacteria, lipid metabolites, and the occurrence of oxidative stress in cows suffered from SM. The results of this study further enriched our understanding of the correlations between gut microbiota and metabolic profiles and SM, which provided insight into the formulation of management strategies for SM in cows.

Phage therapy is an effective strategy to combat multidrug resistance in bacteria and has been increasingly utilized to protect animals from bacterial infections. This study involved the isolation and purification of a novel myoviruses phage, vB_AceP_PAc, from a drug-resistant bacterial strain Aeromonas caviae. Genome sequence analysis based on nucleotide sequences revealed that vB_AceP_PAc shared significant similarity with the genomes of 10 other Aeromonas phages, with the highest coverage rate of 52% with phiA047. Intraperitoneal injection of 1 × 10⁷ CFU/mL (100 µL/mouse) A. caviae AC-CY resulted in diarrhea in mice three days later. At this time, oral administration of 1 × 10⁹ PFU/mL (100 µL/mouse) vB_AceP_PAc effectively alleviated the diarrhea induced by Pseudomonas aeruginosa infection in the mice. Furthermore, oral administration of 1 × 10⁹ PFU/ml vB_AceP_PAc (100 µl/mouse) in healthy mice significantly reduced inflammatory cytokine levels, increased tight junction molecule levels, and improved intestinal barrier function. Moreover, the consumption of vB_AceP_PAc by health mice led to a significant increase in the abundance of Lactobacillaceae in the gut, while the expression of CD3⁺CD4⁺/CD3⁺CD8⁺ was minimally affected. Overall, the findings of this study confirmed the promising potential of bacteriophage vB_AceP_PAc in treating diarrhea caused by A. caviae.