Characterization of maltocin S16, a phage tail‐like bacteriocin with antibacterial activity againstStenotrophomonas maltophiliaandEscherichia coli

The world of phage tail-like bacteriocins: State of the art and biotechnological perspectives

In the struggle for resources, bacteria have developed different systems of competition, including the type VI secretion system (T6SS) and phage tail-like bacteriocins (PTLBs), that act by killing other bacterial species or strains from the same species. The emergence of antimicrobial resistance (AMR) is an urgent global health problem. In this context, the need to develop new antimicrobial agents has put PTLBs in the spotlight. This review focuses on the most relevant aspects of PTLBs such as their structural features, biology, the technological tools to improve their application, and the most importantly their patents.

Expression and Antagonistic Activity Against Plant Pathogens of the Phage Tail-like Protein from Burkholderia multivorans WS-FJ9

Microorganisms exert antagonistic effects on pathogens through different mechanisms, thereby achieving biological control of plant diseases. Many Burkholderia strains can produce complex secondary metabolites and substances that have toxic effects on host cells. The phage tail-like bacteriocins (tailocins) is a compound with antibacterial activity. However, its function in B. multivorans has not yet been reported. This article explores the ability of B. multivorans WS-FJ9 to antagonise plant pathogenic fungi and oomycetes, screening the potential tailocins in the strain WS-FJ9 and verifying their function, to reveal its novel antimicrobial mechanisms. We found that WS-FJ9 had strong antagonistic effects on the plant pathogenic fungi Phomopsis macrospore and Sphaeropsis sapinea, and the pathogenic oomycete Phytophthora cinnamomi. The phage tail-like protein Bm_67459 was predicted from the WS-FJ9 strain genome. The Bm_67459 cDNA encoded 111 amino acid sequence, and the relative molecular weight was approximately 11.69 kDa, the theoretical isoelectric point (pI) was 5.49, and it was a hydrophilic protein. Bm_67459 had no transmembrane helix region or signal peptide, and it belonged to the Phage_TAC_7 super family. qRT-PCR results showed that Bm_67459 gene expression was significantly upregulated during contact between WS-FJ9 and P. cinnamomi. The purified Bm_67459 protein significantly inhibited P. cinnamomi mycelial growth at 10 μg·mL-1. In summary, the WS-FJ9 strain had broad-spectrum anti-phytopathogenic activity, and the tailocin Bm_67459 was an important effector against the plant pathogen P. cinnamomi, which helps to reveal the antagonistic mechanism of this strain at the molecular level and provides excellent strain resources for the biological control of plant diseases.

Biochemical characterisation and production kinetics of high molecular-weight (HMW) putative antibacterial proteins of insect pathogenic Brevibacillus laterosporus isolates

BACKGROUND

Bacterial genomes often encode structures similar to phage capsids (encapsulins) and phage tails which can be induced spontaneously or using genotoxic compounds such as mitomycin C. These high molecular-weight (HMW) putative antibacterial proteins (ABPs) are used against the competitive strains under natural environment. Previously, it was unknown whether these HMW putative ABPs originating from the insect pathogenic Gram-positive, spore-forming bacterium Brevibacillus laterosporus (Bl) isolates (1821L, 1951) are spontaneously induced during the growth and pose a detrimental effect on their own survival. Furthermore, no prior work has been undertaken to determine their biochemical characteristics.

RESULTS

Using a soft agar overlay method with polyethylene glycol precipitation, a narrow spectrum of bioactivity was found from the precipitated lysate of Bl 1951. Electron micrographs of mitomycin C- induced filtrates showed structures similar to phage capsids and contractile tails. Bioactivity assays of cell free supernatants (CFS) extracted during the growth of Bl 1821L and Bl 1951 suggested spontaneous induction of these HMW putative ABPs with an autocidal activity. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of spontaneously induced putative ABPs showed appearance of ~ 30 kDa and ~ 48 kDa bands of varying intensity across all the time intervals during the bacterial growth except in the initial hours. Statistically, spontaneously induced HMW putative ABPs of Bl 1951 exhibited a significant decrease in the number of viable cells of its producer strain after 18 h of growth in liquid. In addition, a significant change in pH and prominent bioactivity of the CFS of this particular time period was noted. Biochemically, the filtered supernatant derived from either Bl 1821L or Bl 1951 maintained bioactivity over a wide range of pH and temperature.

CONCLUSION

This study reports the spontaneous induction of HMW putative ABPs (bacteriocins) of Bl 1821L and Bl 1951 isolates during the course of growth with potential autocidal activity which is critically important during production as a potential biopesticide. A narrow spectrum of putative antibacterial activity of Bl 1951 precipitate was found. The stability of HMW putative ABPs of Bl 1821L and Bl 1951 over a wide range of pH and temperature can be useful in expanding the potential of this useful bacterium beyond the insecticidal value.

Effect of Stenotrophomonas maltophilia on Tuberculosis

Tuberculosis (TB) is an important infectious disease suffered by many countries, including China. In this stage, accurate diagnosis and treatment are key measures for the prevention and control of TB. Stenotrophomonas maltophilia is a global emerging Gram-negative, multidrug-resistant (MDR) organism characterized by its high contribution to the increase in crude mortality rates. By single cell preparation and strain identification, we isolated S. maltophilia from stored cultures of Mycobacterium tuberculosis (Mtb). We found that S. maltophilia could not be removed from sputum by alkali treatment or inhibited by antibiotic mixture added to MGIT 960 indicator tubes. When co-cultured with Mtb on a Löwenstein-Jensen (L-J) slant, it could inhibit the growth of Mtb and liquefy the medium. More seriously, it was resistant to 10 of the 12 anti-TB drugs, including isoniazid and rifampin, and made the mixed samples display multidrug-resistant Mtb (MDR-TB) results in the drug sensitivity test, which might change a treatment regimen and increase disease burden. Following, we conducted a small-scale surveillance which showed that the isolation rate of S. maltophilia in TB patients was 6.74%, but these patients had no special characteristics and the presence of S. maltophilia was hidden. The effect of S. maltophilus on TB and its mechanism are unclear and require more attention. IMPORTANCE China is a high-burden country for tuberculosis (TB), multidrug-resistant/rifampicin-resistant tuberculosis (MDR/RR-TB), and HIV-associated TB. Increasing the positive rate of culture and the accuracy of antibiotic susceptibility testing (AST) are important for diagnosis, treatment, and control of TB. In our study, we found that the isolation rate of Stenotrophomonas maltophilia in TB patients was not neglectable and that this bacterium affects the isolation and AST results of TB. Due to a lack of relevant research, the impact of S. maltophilia on the course and outcome of TB is unclear. However, the characteristics of S. maltophilia that increase disease mortality require attention. Therefore, in the clinical testing of TB, in addition to mycobacteria, it is recommended to increase the detection of co-infected bacteria and improve the awareness of TB clinicians of these bacteria.

An Overview of the Potentialities of Antimicrobial Peptides Derived from Natural Sources

Antimicrobial peptides (AMPs) are constituents of the innate immune system in every kind of living organism. They can act by disrupting the microbial membrane or without affecting membrane stability. Interest in these small peptides stems from the fear of antibiotics and the emergence of microorganisms resistant to antibiotics. Through membrane or metabolic disruption, they defend an organism against invading bacteria, viruses, protozoa, and fungi. High efficacy and specificity, low drug interaction and toxicity, thermostability, solubility in water, and biological diversity suggest their applications in food, medicine, agriculture, animal husbandry, and aquaculture. Nanocarriers can be used to protect, deliver, and improve their bioavailability effectiveness. High cost of production could limit their use. This review summarizes the natural sources, structures, modes of action, and applications of microbial peptides in the food and pharmaceutical industries. Any restrictions on AMPs' large-scale production are also taken into consideration.

Phage-tail-like bacteriocins as a biomedical platform to counter anti-microbial resistant pathogens

Phage Tail Like bacteriocins (PTLBs) has been an area of interest in the last couple of years owing to their varied application against multi-drug resistant (MDR), anti-microbial resistant (AMR) pathogens and their evolutionary link with the dsDNA virus and bacteriophages. PTLBs are defective phages derived from Myoviridae and Siphoviridae phages, PTLBs are distinguished into R-type (Rigid type) characterized by a non-flexible contractile nanotube resembling Myoviridae phage contractile tails, and F-type (Flexible type) with a flexible non-contractile rod-like structure similar to Siphoviridae phages. In this review, we have discussed the structural association, mechanism, and characterization of PTLBs. Moreover, we have elucidated the symbiotic biological function and application of PTLBs against MDR and XDR pathogens and highlighted the evolutionary role of PTLBs. The difficulties that must be overcome to implement PTLBs clinically are also discussed. It is imperative that these issues be addressed by academics in future studies before being implemented in clinical settings. This article is novel in its way as it will not only provide us with a gateway that acts as a novel strategy for scholars to mitigate and control the uprising issue of AMR pathogens but also promote the development of clinical studies for PTLBs.

The Potential of Phage Therapy against the Emerging Opportunistic Pathogen Stenotrophomonas maltophilia

The isolation and characterization of bacteriophages for the treatment of infections caused by the multidrug resistant pathogen Stenotrophomonas maltophilia is imperative as nosocomial and community-acquired infections are rapidly increasing in prevalence. This increase is largely due to the numerous virulence factors and antimicrobial resistance genes encoded by this bacterium. Research on S. maltophilia phages to date has focused on the isolation and in vitro characterization of novel phages, often including genomic characterization, from the environment or by induction from bacterial strains. This review summarizes the clinical significance, virulence factors, and antimicrobial resistance mechanisms of S. maltophilia, as well as all phages isolated and characterized to date and strategies for their use. We further address the limited in vivo phage therapy studies conducted against this bacterium and discuss the future research needed to spearhead phages as an alternative treatment option against multidrug resistant S. maltophilia.

Physicochemical properties and mode of action of a novel bacteriocin BM1122 with broad antibacterial spectrum produced by Lactobacillus crustorum MN047

Bacteriocins are defined as ribosomally synthesized antibacterial peptides/proteins that either kill or inhibit the growth of other bacteria. In the present study, the physicochemical properties, mode of action, and potential use in food preservation of a novel bacteriocin BM1122 from Lactobacillus crustorum MN047 were studied. It exhibited a broad inhibitory spectrum against selected Gram-positive and Gram-negative bacteria. Kinetic curves revealed efficient time-dependent bactericidal activity. Moreover, BM1122 possessed low hemolytic activity and good thermal stability between 60 and 120 °C. It was resistant to a wide range of pH (2 to 11) and proteinases. The scanning and transmission electron microscopy showed that BM1122 led to plasmolysis of Staphylococcus aureus and pore formation in Escherichia coli. Flow cytometric analysis demonstrated that BM1122 destroyed cell membrane integrity. Additionally, BM1122 could also inhibit biofilm formation and disturb the normal cell cycles of S. aureus and E. coli. Finally, BM1122 may enhance the inhibition of S. aureus and E. coli on beef meat stored at 4 °C for a duration of 10 days. These findings indicated that BM1122 had the potential for use as a natural preservative in the food industry. PRACTICAL APPLICATION: Fresh raw meats are highly perishable products. Bacteriocin BM1122 with a broad antibacterial spectrum can inhibit the growth of microorganisms in beef meat during refrigerated storage.