Microbiology-Sgm最新文献

Foodborne infections pose an increasing public health challenge worldwide. The problem has been aggravated by the dissemination of antimicrobial resistance genes among zoonotic pathogens, which results in a sharp increase in antibiotic resistance rate recorded among the major foodborne pathogens. To obtain an overview of the extent to which food products purchased in the markets in Hong Kong were contaminated by foodborne pathogens, we collected 95 raw meat samples from wet markets and isolated 236 bacterial strains of various species, with Escherichia coli being the most dominant species (131 strains). Contamination of food products by multiple foodborne pathogens was commonly observed. These include both Gram-positive and Gram-negative bacteria that exhibit various levels of resistance, with some possessing multiple clinically important antibiotic resistance genes. Seventeen bacterial strains of various species isolated from three food samples were comprehensively analysed by the Oxford Nanopore R10.4 technology. Novel conjugative plasmids carrying antimicrobial resistance gene-bearing mobile genetic elements were commonly detectable in the test strains. Some of the plasmids were shown to have originated from other environmental sources or other bacterial species, indicating that raw foods in the local market may serve as a reservoir of resistance-encoding genetic elements from which such elements are disseminated to various microbial pathogens. These findings suggest a need to perform periodic but comprehensive surveillance of multidrug-resistant bacterial pathogens and the major antimicrobial resistance genes in common food products, so as to disrupt the transmission routes of such organisms and the resistance-encoding genetic elements that they harbour.

Candidozyma auris is an emerging opportunistic yeast that is important because of its multidrug resistance, persistence in healthcare environments and ability to cause outbreaks. Since its discovery in 2009 in Japan, it has rapidly spread worldwide and is now recognized as a major global public health threat and was recognized by the World Health Organization (WHO) in 2022 as a critical priority fungal pathogen. Distinct phylogeographic clades demonstrate simultaneous emergence on different continents, suggesting ecological or environmental triggers. Clinical management is complicated by frequent resistance to fluconazole, reduced susceptibility to amphotericin B and echinocandins, and frequent misidentification by traditional laboratory methods. Continued genomic surveillance, improved diagnostics and new antifungal strategies are urgently needed, supported by enhanced infection prevention and control procedures.

Unlike most rhizobia, Sinorhizobium meliloti produces spermidine (Spd) in addition to putrescine (Put) and homospermidine (HSpd) as soluble intracellular polyamines. To investigate their roles, we analysed S. meliloti Rm8530 mutants lacking hss (homospermidine synthase, smc04016) or casdh (carboxyspermidine dehydrogenase, smb21630), as well as a double mutant. Biochemical and phenotypic characterization confirmed that hss and casdh are responsible for HSpd and Spd synthesis, respectively, and showed that these structurally similar molecules exert both distinct and overlapping physiological functions. The hss and hss casdh mutants exhibited reduced swimming motility, which was fully restored by HSpd or hss complementation, but not by Spd or casdh. In contrast, swarming motility defects in the double mutant were rescued by either gene or polyamine. Biofilm formation and exopolysaccharide production were largely unaffected. The hss mutant grew normally in minimal medium and formed effective symbioses with alfalfa, whereas the casdh mutant showed slightly delayed growth and reduced nitrogen fixation. The double mutant displayed a pronounced growth lag and significantly lower plant biomass and nitrogen fixation. The expression of hss and casdh was lower in the quorum-sensing-competent strain Rm8530 than in the quorum sensing-deficient strain 1021, with hss expressed about tenfold higher than casdh despite Spd being more abundant in the cells. These results highlight complementary and partially interchangeable roles of spermidine and homospermidine across S. meliloti growth and symbiotic functions.

The emergence of antibiotic-resistant pathogenic bacteria poses a major and growing public health risk. Because antibiotics act on specific molecular targets, bacteria may evolve resistance mechanisms that alter or bypass these targets. This work investigated the antimicrobial effects of carbon monoxide-releasing molecules (CORMs) and their potential for co-administration with a variety of commonly used antibiotics against Escherichia coli. CORMs, commonly transition metal carbonyls, release carbon monoxide under certain conditions. Interestingly, CORMs have been shown to exert antimicrobial activity against bacteria both in vitro and in vivo. However, to effectively treat patients with antibiotic-resistant infections, combination therapies involving two or more antimicrobial agents may be a useful approach. Herein, we report the antimicrobial activity of CORM-2 and CORM-3 against E. coli and, importantly, that sub-inhibitory concentrations of either compound in combination with antibiotics showed a significant increase in efficacy of the conventional antibiotics as assessed by inhibition of bacterial growth and reduced viability. Furthermore, administration of sub-inhibitory concentrations of CORMs increased the antimicrobial activity of multiple antibiotics with a range of modes of action when measured by E-tests and microdilution broth assays. The minimal bactericidal concentrations were reduced 2- to 8-fold and 10- to 63-fold for CORM-2 and CORM-3, respectively. Drug interactions between CORMs and antibiotics were also assessed using checkerboard microdilution methods, providing evidence that CORM activity is synergistic with a wide range of conventional antibiotics tested with fractional inhibitory concentration indices between 0.31 and 0.45. These findings demonstrate the antibacterial activity of CORMs and their synergy with a range of commonly used antibiotics, opening potential avenues for CORMs to be used as adjuvants to traditional antibiotic treatments.

Cationic peptides, particularly those rich in arginine and/or lysine residues, are usually promising antimicrobial agents effective at low concentrations in laboratory settings. However, their applicability in pharmaceutics and biotechnology is currently limited due to their susceptibility to biological enzymatic processes and (in some cases) toxicity to host cells. To address this, we screened eight linear arginine-rich peptides for their haemolytic properties and antimicrobial activity using a set of computational and experimental assays. Inspired by our previous results on R4F4, we then designed three modified peptides based on an R4F4 backbone, R4F4-C16, D-R4F4 and cyclic R4F4, and one based on R4 (R4-C16). Amongst the tested linear peptides containing only natural amino acids, R4F4 exhibited the strongest antibacterial activity; however, this effect was reduced in the presence of human serum and trypsin. Conversely, our study demonstrated that cyclization and substitution to its d-amino acid enantiomer significantly enhanced stability and activity of R4F4, whilst in the presence of proteases. As revealed by fluorescence imaging, microscopy RNA sequencing analysis, the mode of action involves complex and dynamic events. This multifaceted antimicrobial mechanism integrates alterations in membrane permeability, modulation of intracellular reactive oxygen species levels and changes in transcriptomic signature profiles. At the molecular level, notable changes were observed in the bacterial expression of genes associated with metabolic pathways and biological processes. Furthermore, R4F4-derived peptides showed substantial antibiofilm activity in preventing the formation and disruption of mature biofilms, together with good cytocompatibility, highlighting the potential for clinical applicability. In conclusion, this study emphasizes the importance of optimizing the stability of peptide-based antimicrobials, particularly those rich in arginine, and highlights the advantages of incorporating d-amino acids and cyclization for enhanced performance. This information will prove useful in the future design of antimicrobial peptides. In addition, the molecular perspective on peptide-induced gene expression changes, as identified by RNA-seq, broadens our understanding of antimicrobial peptides' activities and provides a clearer picture of their versatile mechanisms.

Paracoccus denitrificans is a metabolically versatile alphaproteobacterium first isolated in 1910 by Martinus Beijerinck. Similarities between the aerobic respiratory chain and membrane composition of P. denitrificans and those of eukaryotic mitochondria have stimulated the use of P. denitrificans as a model for oxidative phosphorylation. The organism has also been used extensively as a model for studies of denitrification, cytochrome c biogenesis, lithotrophy using thiosulphate as a source of energy, methylotrophy, and carbon metabolism more broadly. Through the application of structural biology and modern genome-based approaches, work on P. denitrificans continues to make significant contributions across multiple areas of microbiology.

This study describes an alternative role of the general stress response (GSR) regulated by Sigma B, via the two-component system RsbKY, which is methylated via RsbM, in motility regulation for the peritrichously flagellated, motile, foodborne pathogen Bacillus cereus. Using a set of Sigma B-related mutants, we found reduced surface spreading on low-agar plates for all mutants compared to the WT of B. cereus ATCC 14579. The GSR mutants still contained flagella similar to WT in the samples taken from the edge of colonies with reduced surface spreading. Using cell trajectory analysis of selected mutants and WT, we found that the Sigma B-controlled Hpr-like phosphocarrier bc1009 mutant had a reduced duration of the run phase, resulting in an overall lower persistence and coverage of the surface area over a given time. Indeed, prolonged incubation of low-agar 'swimming' plates resulted in full coverage by all GSR mutants, indicating functional motility, but reduced efficiency. Proteome analysis of samples from low-agar plates showed overall lower expression levels of motility-related proteins and, in particular, significantly lower values for proteins related to the C-ring, involved in the regulation of the run-and-tumble motion of bacteria. The bc1009 mutant showed an additional downregulation of a subset of methyl-accepting chemotaxis proteins, involved in the activation of the key chemotaxis regulators CheA and CheY. We propose a new chemotaxis model, in which CheA and CheY are still key regulators, but an additional regulatory role on the run-and-tumble motion is proposed for the Sigma B-regulated Hpr-like protein Bc1009 via the unique two-component system RsbKY.

The VIM-1 metallo-β-lactamase enzyme, encoded within class 1 integrons, is found in Gram-negative clinical isolates worldwide and has been linked to outbreaks of bacterial pathogens in nosocomial settings. Six vim-1+ clinical isolates, from the genera Escherichia, Klebsiella and Enterobacter, were obtained from Kingston, Ontario, Canada. Whole-genome sequencing revealed that vim-1 was plasmid-borne in all strains and situated as the first gene in In916 or In110 integrons. Analysis of related plasmids suggested that these vim-1-containing plasmids are globally disseminated and have spread via horizontal gene transfer and autochthonous vertical spread within Ontario. Interestingly, the MICs of ertapenem and meropenem, two clinically relevant carbapenem antibiotics, against these six isolates varied more than tenfold, suggesting that the effects of VIM-1 are dependent on the genomic content of the host microbe. Introducing vim-1 into three common Enterobacterales laboratory strains was not sufficient to confer resistance to ertapenem and meropenem. Instead, adaptive laboratory evolution of the vim-1 ⁺ laboratory strains revealed that vim-1-mediated carbapenem resistance in these strains was dependent on epistatic interactions with ompC mutations, likely due to decreased outer membrane permeability to these antibiotics. Together, these results provide additional support for the role of gene epistasis in modulating the antimicrobial resistance phenotypes of acquired resistance genes, as well as previous results suggesting that the presence of a β-lactamase gene is insufficient to confer strong resistance to carbapenems without being paired with reduced outer membrane permeability.

Bacteriophages are key drivers of bacterial evolution, particularly through their integration as prophages within host genomes. However, the diversity and host specificity of prophages in relevant pathogens such as Enterobacter species remain poorly characterized. In this study, we revealed the diversity of prophages, mapped their distribution and explored their relationships with their bacterial hosts. We analysed 3,661 prophage sequences identified from the genomes of 20 different Enterobacter species. This analysis uncovered an extensive hidden diversity, comprising 1,617 phage genera and 2,423 phage species - nearly 80% of which were singletons - highlighting an exceptionally rich prophage landscape. We found substantial variation in prophage species richness across host species and isolation sources, with Enterobacter kobei and environmental isolates exhibiting the highest richness. Prophage populations showed strong host specificity and limited cross-species transmission. Moreover, prophages exhibited geographic structuring and significant congruence between host and prophage phylogenies, as well as with the ecological lifestyles of their bacterial hosts. Although we found phages of the same species infecting different host species, these events were infrequent. Finally, bacterial genomes encoded diverse defence systems, mainly PDC-S07, RM type I-II and gabija, whereas only 8.9% of prophages encoded anti-defence systems, mostly anti-CBASS and anti-RM. Overall, this study provides new insights into the diversity of Enterobacter prophages and underscores their ecological and clinical relevance in shaping host adaptation and phage-host dynamics.

The modern antibiotic era began in the early twentieth century, but humans have long used materials from the natural world to attempt to treat the symptoms of infection. In this primer, we will discuss the rationale for attempting to reconstruct historical infection remedies in order to assess their antimicrobial activity and how this approach could aid the discovery of molecular cocktails with potential for development into novel treatments for infection.