Gradual pediocin PA-1 resistance in Enterococcus faecalis confers cross-protection to diverse pore-forming cationic antimicrobial peptides displaying changes in cell wall and mannose PTS expression

Potential and application of tandem mass spectrometry (MS/MS) in the analysis and identification of novel bacteriocins: a review

Bacteriocins are antimicrobial peptides synthesised ribosomally by Gram-positive or Gram-negative bacteria to gain a competitive advantage. The majority of bacteriocins are derived from Gram-positive bacteria, with lactic acid bacteria being the most common source. Because they are considered ‘natural’, there is currently significant development of bacteriocins for application as food preservative agents. As a preservative agent, bacteriocin activity is highly dependent on purity, down to the amino acid profile and sequence. Therefore, bacteriocin identification is important. Currently, MS is a cutting-edge tool in bacteriocin identification. This method has high selectivity, sensitivity and resolution. To the best of our knowledge, systematic reviews focusing on the application of MS for bacteriocin identification are currently limited. In light of this, the objective of this study is to provide a comprehensive review and summary of MS technologies in bacteriocin research, with a particular focus on the discovery and characterisation of novel sources of bacteriocin. Additionally, studies related to the discovery of bacteriocins from various sources, their role as antimicrobial agents, and their synthesis are emphasised. Thus, this study presents a comprehensive analysis of the advantages, limitations, and future perspectives of the methods employed.

Phenotypic and molecular characterization of clinically isolated antibiotics-resistant S. aureus (MRSA), E. coli (ESBL) and Acinetobacter 1379 bacterial strains

Antibiotic-resistant bacteria causing nosocomial infections pose a significant global health concern. This study focused on examining the lipid profiles of both non-resistant and clinically resistant strains of Staphylococcus aureus (MRSA 1418), E. coli (ESBL 1384), and Acinetobacter 1379. The main aim was to investigate the relationship between lipid profiles, hydrophobicity, and antibiotic resistance so as to identify the pathogenic potential and resistance factors of strains isolated from patients with sepsis and urinary tract infections (UTIs). The research included various tests, such as antimicrobial susceptibility assays following CLSI guidelines, biochemical tests, biofilm assays, and hydrophobicity assays. Additionally, gas chromatography mass spectrometry (GC-MS) and GC-Flame Ionization Detector (GC-FID) analysis were used for lipid profiling and composition. The clinically isolated resistant strains (MRSA-1418, ESBL-1384, and Acinetobacter 1379) demonstrated resistance phenotypes of 81.80%, 27.6%, and 63.6%, respectively, with a multiple antibiotic resistance index of 0.81, 0.27, and 0.63. Notably, the MRSA-1418 strain, which exhibited resistance, showed significantly higher levels of hemolysin, cell surface hydrophobicity, biofilm index, and a self-aggregative phenotype compared to the non-resistant strains. Gene expression analysis using quantitative real-time PCR (qPCR). Indicated elevated expression levels of intercellular adhesion biofilm-related genes (icaA, icaC, and icaD) in MRSA-1418 (pgaA, pgaC, and pgaB) and Acinetobacter 1379 after 24 h compared to non-resistant strains. Scanning electron microscopy (SEM) was employed for structural investigation. These findings provide valuable insights into the role of biofilms in antibiotic resistance and suggest potential target pathways for combating antibiotic-resistant bacteria.

A novel of new class II bacteriocin from Bacillus velezensis HN-Q-8 and its antibacterial activity on Streptomyces scabies

Potato common scab is a main soil-borne disease of potato that can significantly reduce its quality. At present, it is still a challenge to control potato common scab in the field. To address this problem, the 972 family lactococcin (Lcn972) was screened from Bacillus velezensis HN-Q-8 in this study, and an Escherichia coli overexpression system was used to obtain Lcn972, which showed a significant inhibitory effect on Streptomyces scabies, with a minimum inhibitory concentration of 10.58 μg/mL. The stability test showed that Lcn972 is stable against UV radiation and high temperature. In addition, long-term storage at room temperature and 4°C had limited effects on its activity level. The antibacterial activity of Lcn972 was enhanced by Cu²⁺ and Ca²⁺, but decreased by protease K. The protein was completely inactivated by Fe²⁺. Cell membrane staining showed that Lcn972 damaged the cell membrane integrity of S. scabies. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations revealed that the hyphae of S. scabies treated with Lcn972 were deformed and adhered, the cell membrane was incomplete, the cytoplasm distribution was uneven, and the cell appeared hollow inside, which led to the death of S. scabies. In conclusion, we used bacteriocin for controlling potato common scab for the first time in this study, and it provides theoretical support for the further application of bacteriocin in the control of plant diseases.

Enterococcus spp. as a Producer and Target of Bacteriocins: A Double-Edged Sword in the Antimicrobial Resistance Crisis Context

Enterococcus spp. are one of the most frequent producers of bacteriocins (enterocins), which provides them with an advantage to compete in their natural environment, which is the gut of humans and many animals. The enterocins’ activity against microorganisms from different phylogenetic groups has raised interest in Enterococcus spp. in different contexts throughout the last decades, especially in the food industry. Nevertheless, some species can also cause opportunistic life-threatening infections and are frequently multidrug-resistant (MDR). Vancomycin-resistant Enterococcus (VRE), in particular, are an ongoing global challenge given the lack of therapeutic options. In this scenario, bacteriocins can offer a potential solution to this persistent threat, either alone or in combination with other antimicrobials. There are a handful of studies that demonstrate the advantages and applications of bacteriocins, especially against VRE. The purpose of this review is to present a current standpoint about the dual role of Enterococcus spp., from important producers to targets needed to be controlled, and the crucial role that enterocins may have in the expansion of enterococcal populations. Classification and distribution of enterocins, the current knowledge about the bacteriocinome of clinical enterococci, and the challenges of bacteriocin use in the fight against VRE infections are particularly detailed.

Physiological and Transcriptional Response of Xanthomonas oryzae pv. oryzae to Berberine, an Emerging Chemical Control

Berberine, a botanical drug, has great ability to inhibit the growth of Xanthomonas oryzae pv. oryzae. However, the antibacterial mechanism of berberine against X. oryzae pv. oryzae remains poorly understood. In this study, we investigated the physiological and transcriptional response of X. oryzae pv. oryzae to berberine. When strain X. oryzae pv. oryzae GX13 was treated with berberine (10 µg/ml), the hypersensitive response in tobacco, virulence to rice, pathogen population in the rice xylem, production of extracellular polysaccharide (EPS), and activity of extracellular hydrolases decreased, but the levels of pyruvate and ATP increased. Moreover, biofilm formation was inhibited, and the cell membrane was damaged. Transcriptome sequencing analysis showed downregulated expression of gspD, gspE, and gspF, involved in the type II secretion system (T2SS); hrcC, hrcJ, hrcN, and others, involved in the type III secretion system (T3SS); gumB and gumC, associated with EPS; zapE, ftsQ, and zapA, associated with cell division; lpxH, lpxK, kdtA, and others, associated with the membrane; and pyk, pgk, and mdh, encoding pyruvate kinase, phosphoglycerate kinase, and malate dehydrogenase, respectively. Upregulated expression was observed for nuoA, nuoB, and nuoH, encoding the NADH dehydrogenase complex, and atpF, atpC, and atpB, encoding ATP synthase. An adenylate cyclase (CyaA) fusion assay showed that berberine affects type three effector protein secretion via the T3SS and reduces effector translocation in X. oryzae pv. oryzae. It is speculated that the negative growth and virulence phenotypes of berberine-treated X. oryzae pv. oryzae GX13 may involve differentially expressed genes associated with cytoarchitecture and energy metabolism, and these effects on primary cell function may further dampen virulence and result in differential expression of T3SS- and T2SS-related genes.

Phenotypic comparison and DNA sequencing analysis of a wild-type and a pediocin-resistant mutant of Listeria ivanovii

Listeria ivanovii is one of the two pathogenic species within the genus Listeria, the other being Listeria monocytogenes. In this study, we generated a stable pediocin resistant mutant Liv-r1 of a L. ivanovii strain, compared phenotypic differences between the wild-type and the mutant, localised the pediocin-induced mutations in the chromosome, and analysed the mechanisms behind the bacteriocin resistance. In addition to pediocin resistance, Liv-r1 was also less sensitive to nisin. The growth of Liv-r1 was significantly reduced with glucose and mannose, but less with cellobiose. The cells of Liv-r1 adsorbed less pediocin than the wild-type cells. Consequently, with less pediocin on the cell surface, the mutant was also less leaky, as shown as the release of intracellular lactate dehydrogenase to the supernatant. The surface of the mutant cells was more hydrophobic than that of the wild-type. Whole genome sequencing revealed numerous changes in the Liv-r1 chromosome. The mutations were found e.g., in genes encoding sigma-54-dependent transcription regulator and internalin B, as well as in genes involved in metabolism of carbohydrates such as glucose and cellobiose. Genetic differences observed in the mutant may be responsible for resistance to pediocin but no direct evidence is provided.

Bacteriocins: Classification, synthesis, mechanism of action and resistance development in food spoilage causing bacteria

Huge demand of safe and natural preservatives has opened new area for intensive research on bacteriocins to unravel the novel range of antimicrobial compounds that could efficiently fight off the food-borne pathogens. Since food safety has become an increasingly important international concern, the application of bacteriocins from lactic acid bacteria that target food spoilage/pathogenic bacteria without major adverse effects has received great attention. Different modes of actions of these bacteriocins have been suggested and identified, like pore-forming, inhibition of cell-wall/nucleic acid/protein synthesis. However, development of resistance in the food spoilage and pathogenic bacteria against these bacteriocins is a rising concern. Emergence and spread of mutant strains resistant to bacteriocins is hampering food safety. It has spurred an interest to understand the bacteriocin resistance phenomenon displayed by the food pathogens, which will be helpful in mitigating the resistance problem. Therefore, present review is focused on the different resistance mechanisms adopted by food pathogens to overcome bacteriocin.

Apigenin Impacts the Growth of the Gut Microbiota and Alters the Gene Expression of Enterococcus

Apigenin is a major dietary flavonoid with many bioactivities, widely distributed in plants. Apigenin reaches the colon region intact and interacts there with the human gut microbiota, however there is little research on how apigenin affects the gut bacteria. This study investigated the effect of pure apigenin on human gut bacteria, at both the single strain and community levels. The effect of apigenin on the single gut bacteria strains Bacteroides galacturonicus, Bifidobacterium catenulatum, Lactobacillus rhamnosus GG, and Enterococcus caccae, was examined by measuring their anaerobic growth profiles. The effect of apigenin on a gut microbiota community was studied by culturing a fecal inoculum under in vitro conditions simulating the human ascending colon. 16S rRNA gene sequencing and GC-MS analysis quantified changes in the community structure. Single molecule RNA sequencing was used to reveal the response of Enterococcus caccae to apigenin. Enterococcus caccae was effectively inhibited by apigenin when cultured alone, however, the genus Enterococcus was enhanced when tested in a community setting. Single molecule RNA sequencing found that Enterococcus caccae responded to apigenin by up-regulating genes involved in DNA repair, stress response, cell wall synthesis, and protein folding. Taken together, these results demonstrate that apigenin affects both the growth and gene expression of Enterococcus caccae.

Focal Targeting of the Bacterial Envelope by Antimicrobial Peptides

Antimicrobial peptides (AMPs) are utilized by both eukaryotic and prokaryotic organisms. AMPs such as the human beta defensins, human neutrophil peptides, human cathelicidin, and many bacterial bacteriocins are cationic and capable of binding to anionic regions of the bacterial surface. Cationic AMPs (CAMPs) target anionic lipids [e.g., phosphatidylglycerol (PG) and cardiolipins (CL)] in the cell membrane and anionic components [e.g., lipopolysaccharide (LPS) and lipoteichoic acid (LTA)] of the cell envelope. Bacteria have evolved mechanisms to modify these same targets in order to resist CAMP killing, e.g., lysinylation of PG to yield cationic lysyl-PG and alanylation of LTA. Since CAMPs offer a promising therapeutic alternative to conventional antibiotics, which are becoming less effective due to rapidly emerging antibiotic resistance, there is a strong need to improve our understanding about the AMP mechanism of action. Recent literature suggests that AMPs often interact with the bacterial cell envelope at discrete foci. Here we review recent AMP literature, with an emphasis on focal interactions with bacteria, including (1) CAMP disruption mechanisms, (2) delocalization of membrane proteins and lipids by CAMPs, and (3) CAMP sensing systems and resistance mechanisms. We conclude with new approaches for studying the bacterial membrane, e.g., lipidomics, high resolution imaging, and non-detergent-based membrane domain extraction.

Contribution of Cell Surface Hydrophobicity in the Resistance of Staphylococcus aureus against Antimicrobial Agents

Staphylococcus aureus is found in a wide variety of habitats, including human skin, where many strains are commensals that may be clinically significant or contaminants of food. To determine the physiological characteristics of resistant strain of Staphylococcus aureus against pediocin, a class IIa bacteriocin, a resistant strain was compared with wild type in order to investigate the contribution of hydrophobicity to this resistance. Additional clumping of resistant strain relative to wild type in light microscopy was considered as an elementary evidence of resistance attainment. A delay in log phase attainment was observed in resistant strain compared to the wild type strain. A significant increase in cell surface hydrophobicity was detected for resistant strain in both hexadecane and xylene indicating the contribution of cell surface hydrophobicity as adaptive reaction against antimicrobial agents.