Characterizations of the endolysin Lys84 and its domains from phage qdsa002 with high activities against Staphylococcus aureus and its biofilms

Bacteriophage endolysin Ply113 as a potent antibacterial agent against polymicrobial biofilms formed by enterococci and Staphylococcus aureus

Antibiotic resistance in Enterococcus faecium, Enterococcus faecalis, and Staphylococcus aureus remains a major public health concern worldwide. Furthermore, these microbes frequently co-exist in biofilm-associated infections, largely nullifying antibiotic-based therapy. Therefore, it is imperative to develop an efficient therapeutic strategy for combating infections caused by polymicrobial biofilms. In this study, we investigated the antibacterial and antibiofilm activity of the bacteriophage endolysin Ply113 in vitro. Ply113 exhibited high and rapid lytic activity against E. faecium, E. faecalis, and S. aureus, including vancomycin-resistant Enterococcus and methicillin-resistant S. aureus isolates. Transmission electron microscopy revealed that Ply113 treatment led to the detachment of bacterial cell walls and considerable cell lysis. Ply113 maintained stable lytic activity over a temperature range of 4-45°C, over a pH range of 5.0-8.0, and in the presence of 0-400 mM NaCl. Ply113 treatment effectively eliminated the mono-species biofilms formed by E. faecium, E. faecalis, and S. aureus in a dose-dependent manner. Ply113 was also able to eliminate the dual-species biofilms of E. faecium-S. aureus and E. faecalis-S. aureus. Additionally, Ply113 exerted potent antibacterial efficacy in vivo, distinctly decreasing the bacterial loads in a murine peritoneal septicemia model. Our findings suggest that the bacteriophage endolysin Ply113 is a promising antimicrobial agent for the treatment of polymicrobial infections.

Rapid Screening and Comparison of Chimeric Lysins for Antibacterial Activity against Staphylococcus aureus Strains

Chimeric lysins composed of various combinations of cell wall-lysing (enzymatic) and cell-wall-binding (CWB) domains of endolysins, autolysins, and bacteriocins have been developed as alternatives to or adjuvants of conventional antibiotics. The screening of multiple chimeric lysin candidates for activity via E. coli expression is not cost effective, and we previously reported on a simple cell-free expression system as an alternative. In this study, we sufficiently improved upon this cell-free expression system for use in screening activity via a turbidity reduction test, which is more appropriate than a colony reduction test when applied in multiple screening. Using the improved protocol, we screened and compared the antibacterial activity of chimeric lysin candidates and verified the relatively strong activity associated with the CHAP (cysteine, histidine-dependent amidohydrolase/peptidase) domain of secretory antigen SsaA-like protein (ALS2). ALS2 expressed in E. coli showed two major bands, and the smaller one (subprotein) was shown to be expressed by an innate downstream promoter and start codon (ATG). The introduction of synonymous mutations in the promoter resulted in clearly reduced expression of the subprotein, whereas missense mutations in the start codon abolished antibacterial activity as well as subprotein production. Interestingly, most of the S. aureus strains responsible for bovine mastitis were susceptible to ALS2, but those from human and chicken were less susceptible. Thus, the simple and rapid screening method can be applied to select functional chimeric lysins and define mutations affecting antibacterial activity, and ALS2 may be useful in itself and as a lead molecule to control bovine mastitis.

Characterization and Genomic Analysis of a Novel Lytic Phage DCp1 against Clostridium perfringens Biofilms

Clostridium perfringens (C. perfringens) is one of the foremost pathogens responsible for diarrhea in foals. As antibiotic resistance increases, phages that specifically lyse bacteria are of great interest to us with regard to C. perfringens. In this study, a novel C. perfringens phage DCp1 was isolated from the sewage of a donkey farm. Phage DCp1 had a non-contractile short tail (40 nm in length) and a regular icosahedral head (46 nm in diameter). Whole-genome sequencing indicated that phage DCp1 had a linear double-stranded DNA genome with a total length of 18,555 bp and a G + C content of 28.2%. A total of 25 ORFs were identified in the genome, 6 of which had been assigned to functional genes, others were annotated to encode hypothetical proteins. The genome of phage DCp1 lacked any tRNA, virulence gene, drug resistance gene, or lysogenic gene. Phylogenetic analysis indicated that phage DCp1 belonged to the family Guelinviridae, Susfortunavirus. Biofilm assay showed that phage DCp1 was effective in inhibiting the formation of C. perfringens D22 biofilms. Phage DCp1 could completely degrade the biofilm after 5 h of interaction. The current study provides some basic information for further research on phage DCp1 and its application.

Beyond the Risk of Biofilms: An Up-and-Coming Battleground of Bacterial Life and Potential Antibiofilm Agents

Microbial pathogens and their virulence factors like biofilms are one of the major factors which influence the disease process and its outcomes. Biofilms are a complex microbial network that is produced by bacteria on any devices and/or biotic surfaces to escape harsh environmental conditions and antimicrobial effects. Due to the natural protective nature of biofilms and the associated multidrug resistance issues, researchers evaluated several natural anti-biofilm agents, including bacteriophages and their derivatives, honey, plant extracts, and surfactants for better destruction of biofilm and planktonic cells. This review discusses some of these natural agents that are being put into practice to prevent biofilm formation. In addition, we highlight bacterial biofilm formation and the mechanism of resistance to antibiotics.

The Mechanism of Bacterial Resistance and Potential Bacteriostatic Strategies

Bacterial drug resistance is rapidly developing as one of the greatest threats to human health. Bacteria will adopt corresponding strategies to crack the inhibitory effect of antibiotics according to the antibacterial mechanism of antibiotics, involving the mutation of drug target, secreting hydrolase, and discharging antibiotics out of cells through an efflux pump, etc. In recent years, bacteria are found to constantly evolve new resistance mechanisms to antibiotics, including target protective protein, changes in cell morphology, and so on, endowing them with multiple defense systems against antibiotics, leading to the emergence of multi-drug resistant (MDR) bacteria and the unavailability of drugs in clinics. Correspondingly, researchers attempt to uncover the mystery of bacterial resistance to develop more convenient and effective antibacterial strategies. Although traditional antibiotics still play a significant role in the treatment of diseases caused by sensitive pathogenic bacteria, they gradually lose efficacy in the MDR bacteria. Therefore, highly effective antibacterial compounds, such as phage therapy and CRISPER-Cas precision therapy, are gaining an increasing amount of attention, and are considered to be the treatments with the moist potential with regard to resistance against MDR in the future. In this review, nine identified drug resistance mechanisms are summarized, which enhance the retention rate of bacteria under the action of antibiotics and promote the distribution of drug-resistant bacteria (DRB) in the population. Afterwards, three kinds of potential antibacterial methods are introduced, in which new antibacterial compounds exhibit broad application prospects with different action mechanisms, the phage therapy has been successfully applied to infectious diseases caused by super bacteria, and the CRISPER-Cas precision therapy as a new technology can edit drug-resistant genes in pathogenic bacteria at the gene level, with high accuracy and flexibility. These antibacterial methods will provide more options for clinical treatment, and will greatly alleviate the current drug-resistant crisis.

Endolysin, a Promising Solution against Antimicrobial Resistance

Antimicrobial resistance (AMR) is a global crisis for human public health which threatens the effective prevention and control of ever-increasing infectious diseases. The advent of pandrug-resistant bacteria makes most, if not all, available antibiotics invalid. Meanwhile, the pipeline of novel antibiotics development stagnates, which prompts scientists and pharmacists to develop unconventional antimicrobials. Bacteriophage-derived endolysins are cell wall hydrolases which could hydrolyze the peptidoglycan layer from within and outside of bacterial pathogens. With high specificity, rapid action, high efficiency, and low risk of resistance development, endolysins are believed to be among the best alternative therapeutic agents to treat multidrug resistant (MDR) bacteria. As of now, endolysins have been applied to diverse aspects. In this review, we comprehensively introduce the structures and activities of endolysins and summarize the latest application progress of recombinant endolysins in the fields of medical treatment, pathogen diagnosis, food safety, and agriculture.