Journal of Applied Microbiology最新文献

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: Cyanobacteria produce and release secondary metabolites in waterways, challenging drinking water treatment plants. Benthic Cyanobacteria, a group of species living at the bottom of waterbodies, have been identified as potential Taste and Odour (T&O) compound and toxin producers. Following an increase in customer T&O complaints about water produced from the SA-L1 Reservoir, this study was conducted to better understand benthic cyanobacetria growth patterns and establish whether the source of detrimental metabolites was pelagic or benthic.

Methods and results: A field-survey was performed from December 2014 to December 2015, during which physical samplers were deployed across a transect (1 m, 2 m, 6 m and 14 m depth). Biofilm and water samples were analysed for microbial community composition, chlorophyll-a (Chl-a), nutrients, T&O and toxins and their associated genes. Seasons and sampling depths impacted benthic communities, Chl-a concentrations and biofilm growth. Spring and autumn were established as peak growth periods for benthic Cyanobacteria. Water geosmin concentrations significantly correlated with the abundance of benthic Cyanobacteria. The potential for cylindrospermopsin and saxitoxin production was detected in this reservoir. Mat detachment mid-spring contributed to T&O dispersion.

Conclusions: Benthic Cyanobacteria are major geosmin contributors in this reservoir. The potential cylindrospermopsin-producer was demonstrated to be benthic, while the saxitoxin producer was identified as pelagic Dolichospermum circinale, which is recruited from bentic mats in spring. Utilities should consider regular monitoring of benthic mats, which provides the necessary evidence to better anticipate benthic and pelagic events, to in turn provide safe and palatable drinking water.

Aims: Pasteurella multocida (Pm) is one of the main pathogens causing bovine respiratory disease in China. The prevention and control measures against Pm are traditionally based on the use of broad-spectrum antibiotics. Previous studies have found that Pm is prone to developing antibiotic resistance and tolerance-related mutations when exposed to low concentrations of antibiotics, ultimately leading to challenges in the prevention and control of Pm. This study aimed to explore the role of the recO gene in Pm in mediating resistance and tolerance to fluoroquinolones.

Methods and results: Highly pathogenic Pm strains (fluoroquinolone-sensitive P3; enrofloxacin-induced resistant P32) were used. RNA-seq screened SOS response-related differentially expressed genes, with recO functionally verified. Its role in Pm's fluoroquinolone resistance/tolerance was clarified via MIC, MBC.The results showed that recO deletion reduced the bacterial tolerance by approximately 10-100-fold after 4 h of exposure to enrofloxacin (ENR) (p < 0.05), decreased the MBC value by 2-fold, and significantly prolonged the time required for resistance development.

Conclusions: In conclusion, inhibiting the expression of the recO gene in Pm not only reduces its resistance to fluoroquinolones but also delays the development of fluoroquinolone resistance. It is hypothesized that the recO gene could serve as a potential target for enhancing the efficacy of fluoroquinolones, thereby improving their antibacterial activity against Pm.

Aims: Targeting bacterial virulence is a promising alternative to traditional antibiotics. In this study, we aimed to identify microbiome-derived factors capable of suppressing virulence traits in pathogenic bacteria.

Methods and results: Eighty-two cell-free extracts (CFEs) applied at 10% (v/v), from human (n = 56) and soil (n = 26) bacterial isolates were screened for effects on planktonic growth, biofilm formation, and virulence using a Galleria mellonella infection model. Growth inhibition was rare, observed only for S. aureus exposed to a Bacillus flexus extract. Anti-biofilm activity was frequent against P. aeruginosa (65/82 CFEs, 79%), less so for S. aureus (20/82, 24%), and absent or reversed for E. coli. Eight CFEs improved larval survival in P. aeruginosa infections; one partly protected against S. aureus, while (47/82, 57%) increased mortality in E. coli-infected larvae. Thirty-eight of 65 anti-biofilm CFEs (58%) for P. aeruginosa tested positive (i.e. observed) in a violacein-based quorum-sensing inhibition assay. One extract (Streptococcus australis) also protected keratinocytes from P. aeruginosa-induced cell loss. Proteomic analysis of P. aeruginosa exposed to S. australis CFE indicated modulation of proteins associated with biofilm regulation and quorum-sensing pathways (e.g. the RsmA/CsrA family), consistent with anti-virulence activity.

Conclusions: Of 82 microbiome-derived CFEs, (65/82, 79%) partially inhibited P. aeruginosa biofilm formation, (20/82, 24%) affected S. aureus, and none inhibited E. coli biofilms. Ten % improved in vivo survival in P. aeruginosa infections, while (47/82, 57%) increased mortality in E. coli-infected larvae. Anti-virulence effects were pathogen-specific and occurred without measurable impacts on planktonic growth under the conditions tested.

Aims: Hyperosmolarity is widely used for food preservation by inhibiting bacterial survival and growth. Therefore, it is of great significance to reveal bacterial osmotic-response mechanism. Biofilm formation presents a significant challenge for the control and prevention of pathogenic bacteria. Our previous study showed that inactivation of the efflux protein TolC in extraintestinal pathogenic Escherichia coli (ExPEC) decreased biofilm formation by affecting curli production in a medium osmolarity-dependent manner. This study aims to explore the role of the two-component CpxA/R system in mediating TolC regulation of ExPEC biofilm formation in response to osmolarity.

Methods and results: Various mutants derived from the parental ExPEC ΔtolC strain were constructed, and their abilities to form biofilms and produce curli fimbriae in different osmotic media were evaluated using crystal violet staining, scanning electron microscopy, Congo red assay, and real-time quantitative PCR. The results showed that the disruption of CpxA/R system by deleting the gene encoding histidine kinase-CpxA or response regulator-CpxR, or by introducing a point mutation at the phosphorylation site of CpxA, significantly compromised the effect of TolC inactivation on ExPEC biofilm formation and curli biosynthesis under both NaCl- and sucrose-induced osmotic stresses.

Conclusions: Our study firstly demonstrate that the CpxAR system mediated the regulation of TolC inactivation on ExPEC biofilm formation and curli production in response to both NaCl- and sucrose-induced osmotic stresses. These findings expand the regulatory network of bacterial biofilm formation and osmotic-responsiveness, contributing to exploring potential targets for preventing and controlling pathogenic bacteria.

This review provides a comprehensive overview of the current landscape in Bacillus spp. fermentation processes for high-value bioproducts such as proteases, amylases, and surfactin in lab-scale bioreactors, highlighting critical process features. An analysis of key findings over the past five years shows that an efficient fermentation requires customized bioreactor conditions dependent on the substrate, strain type, and the target product. Major challenges include overcoming foaming, ensuring oxygen mass transfer, and precisely balancing the growth and production phases. A combined approach using statistical modeling, such as response surface methodology, along with experimental validation in different bioreactor designs is recommended for the process optimization. This integrated strategy can significantly improve the efficiency, predictability, and overall success of Bacillus-based bioprocesses.

Aims: This study investigated colistin resistance in Gram-negative bacteria isolated from wastewater. The research focuses on understanding the genetic mechanisms of mcr-mediated resistance and the role of wastewater as a reservoir for colistin-resistant bacterial pathogens.

Methods and results: The study utilized 16 sewage effluent samples collected from four discharge points (three hospitals and one municipal wastewater treatment plant), during May 2024. Bacterial isolates were obtained using the membrane filtration method, resulting in the recovery of 50 Gram-negative isolates, including Enterobacteriaceae and Aeromonas species. Identification was conducted using MALDI-TOF mass spectrometry. Whole-genome sequencing (WGS) and comprehensive bioinformatics analysis were performed to characterize resistance genes and phylogenetic relationships. Colistin resistance was found in Escherichia coli (mcr-1), Aeromonas veronii (mcr-3), and Enterobacter kobei (mcr-9). Escherichia coli was the predominant species, accounting for 50% of the isolates. WGS revealed predominant resistance profiles across isolates, with E. coli harboring 95 resistance genes, E. kobei 21, and A. veronii. 14. Genomic analysis identified mobile genetic elements (MGEs) like ISCR1 and tnpA, suggesting the potential for horizontal gene transfer. Comparative genomic analysis identified the genetic context of mcr genes, with the mcr-1 gene found on a plasmid in E. coli, mcr-3 on a conjugative plasmid in A. veronii, and mcr-9 on a plasmid in E. kobei.

Conclusions: These findings highlight the role of wastewater in the spread of colistin-resistant bacteria. The presence of mcr genes on mobile elements underscores the need for robust surveillance strategies to monitor the dissemination of these resistance traits in the environment.

Aims: While drinking water disinfection can significantly reduce bacterial populations it does not eradicate all the bacteria present as many cells enter varying levels of dormancy including the viable but non-culturable (VBNC) state. We posit that the VBNC state represents a continuum, with lower and greater levels of stress leading to Shallow and Deep VBNC, respectively, in exposed cells.

Methods and results: We examined the proteomic differences of Escherichia coli that entered varying depths of the VBNC state upon monochloramine disinfection at different doses. Exposure for 1 h to low (17 μM) and high (50 μM) concentrations of monochloramine led to general VBNC outcomes that showed loss of culturability but retention of viability. However, cells exposed to 17 μM monochloramine exhibited high levels of ATP production, while 50 μM exposure resulted in low levels of ATP productions, confirming that the low and high monochloramine doses resulted in a proposed Shallow and Deep VBNC states, respectively. Differentially expressed proteins analyses showed that proteins related to cell motility (LuxS) and arginine biosynthesis (ArgD) were upregulated, while several oxidative stress response proteins (FumC and Mdh) were downregulated in the Shallow VBNC group. Within the Deep VBNC group, multiple DNA translation-related proteins were downregulated as oligopeptides transport proteins (OppA) and periplasmic proteins (YdeI) were upregulated.

Conclusions: Our results confirmed a gradient in VBNC responses of E. coli in response to different monochloramine doses, accompanied by changes in the proteome.