Journal of Applied Microbiology最新文献

Aims: Most chemically defined media for Bacillus are developed with a focus on an individual species. To broaden the applicability, this study aimed to formulate a chemically defined medium that supports the growth of multiple food-relevant Bacillus species. Specifically, it was the aim to support growth of both food fermentation strains from the Bacillus subtilis clade as well as pathogenic strains from the Bacillus cereus clade.

Methods and results: We developed a new chemically defined medium, named Pafoba, using thirteen Bacillus strains: two from the Bacillus cereus clade and eleven strains from the Bacillus subtilis clade, representing seven species. Medium optimisation involved substituting ammonium chloride and sodium chloride with ammonium sulphate and trisodium citrate, enriching glucose, iron, and phosphate concentrations, and applying nutrientomission assays to identify growth requirements. All strains exhibited growth on Pafoba. Ten strains reached a comparable or higher maximum optical density (OD600) on Pafoba medium compared to Brain Heart Infusion broth. Strain-specific nutrient requirements were identified, including a biotin dependency for Bacillus subtilis strain PRO64, and essential amino acid requirements in Bacillus mycoides and Bacillus cereus strains.

Conclusions: The Pafoba medium supports consistent growth across diverse Bacillus species, making it suitable for both fundamental studies and practical applications such as detection and isolation of Bacillus spp. in food-related contexts.

Gram-negative bacterial infections are increasingly becoming resistant to available antibiotic treatment options. The World Health Organization attributed over 1 million deaths to bacterial antimicrobial resistance (AMR) in 2021. While there is a crisis in terms of the available effective antibiotic repertoire, there is also a simultaneous decline in novel drug discovery. In this scenario, the search for alternative or complementary therapeutic options is not only relevant, but also urgently needed. Bacterial virulence factors have been proposed as alternative therapeutic targets since there is lesser propensity for emergence of resistance to these effector molecules. Type 1 fimbriae or FimH of Enterobacteriaceae constitute such a potential target, as these structures are crucial for the initial adhesion and colonization by binding mannose-rich host cell-surface receptors. Additionally, FimH has been associated with multiple diseases, including urinary tract infections (UTIs) and Crohn's disease (CD). The elucidation of Escherichia coli FimH crystal structure has opened the possibility for structure-based drug design to combat these diseases. Many mannose-based compounds are being tried as alternative therapeutics against UTIs and CD with a few molecules showing promise. In this review, we discuss the role of FimH in different diseases, its potential and scope for structure-based development of different mannose-based compounds, and other advanced FimH-blocking therapeutics in preventing these infections.

Aims: Copper-rich shape memory alloys (Cu-SMAs) combine unique mechanical properties and catalytic redox activity, supporting the development of advanced endodontic files to improve patient treatments. This study evaluated the bactericidal activity of CuAlBe and CuAlNi wires combined with H2O2-containing solutions against Enterococcus faecalis, a resilient bacterial species frequently associated with persistent root canal infections.

Methods and results: Activity was assessed on planktonic bacteria through CFU counts and on a 2-week-old monospecies biofilm grown on hydroxyapatite discs using SYTO9/propidium iodide staining and fluorescence confocal microscopy. Both Cu-SMAs combined with H2O2 and ascorbic acid (AA) reduced bacterial viability of planktonic cells by 6 log₁₀ after 1-min exposure. In biofilms, CuAlNi/H₂O₂/AA caused cell permeabilization and lysis within 15 min at the wire-biofilm interface. Prolonged exposure led to a time-dependent spatial expansion of bactericidal effects. Diffusing H₂O₂ reacted with Cu²⁺ from the alloy, sustaining a Fenton-like reaction. Gas bubbles formed along the wire generated a convective flow dispersing the reactive mixture millimetres away from the wire surface.

Conclusions: CuAlNi/H₂O₂/AA combination couples radical generation and convection, enabling deep biofilm eradication beyond the wire/solution interface.

Aims: Biofilms formed by Salmonella are a significant concern in the poultry industry due to their role in pathogen persistence. However, there is a lack of data observing the expression of biofilm related genes in different Salmonella serovars. The aim of this study was to investigate the expression patterns of key biofilm-associated genes across three Salmonella serovars, namely Salmonella Typhimurium, Kentucky, and Reading, throughout their biofilm growth cycles.

Methods and results: The expressions of csgD, bapA, bcsA, adrA, and luxS were analyzed in cultures representing different biofilm growth phases: 12 h and 24 h planktonic cells, 4-day old biofilms, and 5-day old biofilms under nutrient deprivation. The findings from this study revealed that only S. Reading exhibited upregulation of these genes at the 24 h planktonic stage at a maximum of 9.58-fold. In contrast, a downregulation of all five genes was noted in the 4-day old biofilms for all serovars. Most notably, bapA was downregulated by 3 765-fold in S. Typhimurium. Upon subjecting the biofilms to nutrient deprivation, there was a notable recovery in the activity of these genes across all serovars with the exception of csgD in S. Typhimurium.

Conclusion: These results suggest that expression of biofilm-associated genes is stimulated by nutrient availability even at biofilm maturity and may vary among different serovars.

Antimicrobial resistance (AMR) is one of the most critical public health threats of the 21st century and is projected to become a leading cause of mortality by 2050. The World Health Organization (WHO) recognizes AMR as a top priority in its 2030 research agenda, emphasizing the need to find new antibiotics and innovative therapies. Research on antimicrobial peptides (AMPs) offers a promising alternative given their rapid, membrane-mediated mode of action and low probability of resistance development. Advances in artificial intelligence (AI) now enable large-scale analysis of biological data, prediction of antimicrobial activity and optimization of peptide designs. Deep-learning and machine-learning models, open-access databases and cutting-edge protein-structure prediction algorithms provide unprecedented opportunities to accelerate the discovery and development of AMPs. Beyond discovery, AI aids in predicting three-dimensional peptide structures, which is essential for understanding their mechanisms of action. Here, we highlight recent progress in integrating AI into the fight against AMR, focusing on the design and prediction of peptides as new antimicrobial agents.

Aims: Soil bacterial communities are a crucial biological indicator of soil health and crop performance; however, their response to climate change remains poorly understood. Wild blueberry farms are experiencing unprecedented temperature changes, which may exacerbate microbial responses and potentially harm the crop. Here, we aimed to elucidate the response of bacterial communities in wild blueberry fields to warming.

Methods and results: We employed passive and active open-top chambers to simulate climate warming scenarios, which elevated atmospheric temperatures by 1.2 and 3.3 °C, respectively. Soils in the active warming treatment exhibited significantly lower water content than in ambient conditions. Overall soil bacterial diversity and richness under the warming (passive and active) treatments and ambient controls did not demonstrate significant differences after two years of warming. However, we found significantly higher bacterial evenness and diversity under warming treatments in the early growing season (June). Our study found pronounced seasonal shifts in the evenness and diversity of bacteria in wild blueberry soils, suggesting that the variation in bacterial community structure may be more influenced by seasonal changes in temperature and plant activity than by warming treatments.

Conclusion: Our study reveals the limited impact of warming on overall soil bacterial diversity in a temperate crop, but the seasonal dynamics of bacterial diversity and composition are sensitive to warming. The increased bacterial evenness and diversity under warming treatments in June could be attributed to advanced plant phenology, indicating a potential future shift in seasonal dynamics of bacterial activity under global warming.

Aims: This work aims (i) to evaluate in vitro the antibacterial and antibiofilm activities of an extract collected from a hazelnut by-product (skins) against spoilage bacteria and foodborne pathogens and (ii) to assess its effects on the microbiological quality and sensory/technological characteristics of beef burgers.

Methods and results: The antibacterial properties of hazelnut skin extract (HSE) at concentrations ranging from 2.5 to 20 mg mL-1 were evaluated using a modified protocol based on the method described by the Clinical and Laboratory Standards Institute. In parallel, the biofilm-eradicating potential was assessed according to the Innovotech guidelines, which describe a standardized method for biofilm disruption studies. In vivo experiments were also conducted on beef burgers containing 2% and 4% HSE, along with untreated controls. Each sample underwent microbiological and physicochemical analyses at 0, 3 and 6 days of refrigerated storage.During in vitro assays, HSE exhibited greater antibacterial activity against Gram-positive bacteria, with growth inhibition occurring at lower concentrations. Conversely, in vivo tests revealed no statistically significant differences in microbiological parameters between control and HSE-treated burgers. Furthermore, adding different concentrations of HSE to the treated samples did not significantly affect the pH, although it altered the acidification dynamics, which occurred earlier on day 3 in burgers containing 4% HSE. Finally, both concentrations of HSE resulted in significant differences in weight loss and colour.

Conclusions: In light of these findings, further studies are required to enhance HSE bioavailability in food matrices and to minimize its impact on their sensory/technological properties.

Aim: Bacterial vaginosis (BV) is the most common vaginal disorder in women of reproductive age. Current therapies are limited by poor activity against biofilms and high recurrence rates (>50%), demonstrating that new antimicrobials are required. Drug repurposing is an attractive approach for the discovery of new antimicrobials, so we aimed to screen repurposed libraries for activity against the key BV pathobiont Gardnerella vaginalis.

Methods and results: Two drug libraries from Medicines for Malaria Venture comprising 640 compounds were screened against G. vaginalis and various Lactobacilli species. Initial screening identified 16 G. vaginalis-selective compounds, of which 10 showed ≥90% inhibition of planktonic growth whilst sparing Lactobacillus crispatus. Subsequent assays revealed that three candidates displayed activity against pre-formed G. vaginalis biofilms; MMV1634360 (an antiproliferative compound with reported anticancer and antifungal activity), MMV1582487 (originally developed as an Escherichia coli aminopeptidase N inhibitor) and MMV1582497 (a thymidylate kinase inhibitor developed for Mycobacterium tuberculosis). All three produced >2-log reduction in viable cell counts at 10 µM (p<0.05 for all compounds).Further cytotoxicity testing in VK2/E6E7 vaginal epithelial cells excluded MMV1634360 and MMV1582497 due to off-target effects, leaving MMV1582487 as a leading candidate. MMV1582487 demonstrated further activity against a high biofilm-forming G. vaginalis clinical isolate with >4log10 CFU/mL reduction in viable cell counts at 10 µM (p<0.001), and synergy with existing antibiotic therapy.

Conclusions: We demonstrate that MMV1582487 is a selective, non-cytotoxic, anti-biofilm candidate against G. vaginalis, supporting it's potential as a novel therapeutic option for BV.

Aims: This study aimed to characterize a colistin- and carbapenem-resistant Pseudomonas aeruginosa ST1560 strain isolated from Guanabara Bay, Brazil, and to investigate the molecular mechanisms underlying its resistance phenotype.

Methods and results: Six surface water samples from Guanabara Bay were collected, yielding 71 P. aeruginosa subjected to antimicrobial susceptibility testing. Three isolates exhibited elevated minimal inhibitory concentrations (MICs) to colistin (≥512, 64, and 8 mg/L) in the absence of mcr genes (1-10). Among these, only strain CCVSU 5861 demonstrated carbapenemase confirmed by Blue Carba test. This strain was selected for whole-genome sequencing (Illumina). Genomic analysis identified the presence of blaKPC-2 and blaOXA-395, along with additional resistance determinants associated with aminoglycosides and fosfomycin. Genes involved in lipopolysaccharide modification, (arnA, arnT, and basS) were also detected, likely contributing to colistin resistance. The blaKPC-2 gene was located adjacent to the mobile genetic element ISKpn6, suggesting potential horizontal gene transfer.

Conclusions: The P. aeruginosa ST1560 displays a complex multidrug resistance profile, including resistance to both colistin and carbapenems. This phenotype appears to be mediated by a combination of acquired resistance genes and chromosomal mechanisms. The localization of blaKPC-2 within a mobile genetic element underscores the risk of dissemination in aquatic environments.

Aims: This study reports the first documented cases of Castellaniella spp. infection in dogs, describing associated clinical and pathological findings and characterizing a novel species within this genus.

Methods and results: Pleural effusions from two dogs presenting with acute respiratory distress and systemic illness were evaluated via cytology, bacterial culture, and next-generation sequencing. Both cases exhibited neutrophilic-macrophagic inflammation with intracellular gram-negative rods, primarily within macrophages. Bacterial culture failed to identify the organisms. Metagenomic analysis identified organisms belonging to the genus Castellaniella in both cases. In case 2, an unclassified Castellaniella species was detected, suggesting the presence of a previously undescribed species within the genus. Both dogs died shortly after presentation, and necropsy and histopathology findings were described.

Conclusions: Castellaniella spp. warrant consideration as potential emerging pathogens in domestic animals, challenging their previous classification as non-pathogenic environmental bacteria. The identification of a novel species also underscores the genus's genetic diversity and adaptive potential.