Identification of a novel broad-spectrum endolysin, Ply0643, with high antibacterial activity in mouse models of streptococcal bacteriaemia and mastitis

Streptococcal arginine deiminase system defences macrophage bactericidal effect mediated by XRE family protein XtrSs

The arginine deiminase system (ADS) has been identified in various bacteria and functions to supplement energy production and enhance biological adaptability. The current understanding of the regulatory mechanism of ADS and its effect on bacterial pathogenesis is still limited. Here, we found that the XRE family transcriptional regulator XtrSs negatively affected Streptococcus suis virulence and significantly repressed ADS transcription when the bacteria were incubated in blood. Electrophoretic mobility shift (EMSA) and lacZ fusion assays further showed that XtrSs directly bind to the promoter of ArgR, an acknowledged positive regulator of bacterial ADS, to repress ArgR transcription. Moreover, we provided compelling evidence that S. suis could utilize arginine via ADS to adapt to acid stress, while ΔxtrSs enhanced this acid resistance by upregulating the ADS operon. Moreover, whole ADS-knockout S. suis increased arginine and antimicrobial NO in the infected macrophage cells, decreased intracellular survival, and even caused significant attenuation of bacterial virulence in a mouse infection model, while ΔxtrSs consistently presented the opposite results. Our experiments identified a novel ADS regulatory mechanism in S. suis, whereby XtrSs regulated ADS to modulate NO content in macrophages, promoting S. suis intracellular survival. Meanwhile, our findings provide a new perspective on how Streptococci evade the host's innate immune system.

Endolysin NC5 improves early cloxacillin treatment in a mouse model of Streptococcus uberis mastitis

Streptococcus uberis frequently causes bovine mastitis, an infectious udder disease with significant economic implications for dairy cows. Conventional antibiotics, such as cloxacillin, sometimes have limited success in eliminating S. uberis as a stand-alone therapy. To address this challenge, the study objective was to investigate the VersaTile engineered endolysin NC5 as a supplemental therapy to cloxacillin in a mouse model of bovine S. uberis mastitis. NC5 was previously selected based on its intracellular killing and biofilm eradicating activity. To deliver preclinical proof-of-concept of this supplemental strategy, lactating mice were intramammarily infected with a bovine S. uberis field isolate and subsequently treated with cloxacillin (30.0 μg) combined with either a low (23.5 μg) or high (235.0 μg) dose of NC5. An antibiotic monotherapy group, as well as placebo treatment, was included as controls. Two types of responders were identified: fast (n = 17), showing response after 4-h treatment, and slow (n = 10), exhibiting no clear response at 4 h post-treatment across all groups. The high-dose combination therapy in comparison with placebo treatment impacted the hallmarks of mastitis in the fast responders by reducing (i) the bacterial load 13,000-fold (4.11 ± 0.78 Δlog10; p < 0.001), (ii) neutrophil infiltration 5.7-fold (p > 0.05), and (iii) the key pro-inflammatory chemokine IL-8 13-fold (p < 0.01). These mastitis hallmarks typically followed a dose response dependent on the amount of endolysin added. The current in vivo study complements our in vitro data and provides preclinical proof-of-concept of NC5 as an adjunct to intramammary cloxacillin treatment. KEY POINTS: • Engineered endolysin NC5 was preclinically evaluated as add-on to cloxacillin treatment. • Two types of mice (slow and fast responding) were observed. • The add-on treatment decreased bacterial load, neutrophil influx, and pro-inflammatory mediators.

A novel chimeric endolysin Cly2v shows potential in treating streptococci-induced bovine mastitis and systemic infections

Streptococcus species are important pathogens implicated in bovine mastitis, causing considerable economic losses within the global dairy industry. With the development of multidrug-resistant bacteria, it is crucial to develop novel antibiotic alternatives. Here, we constructed a novel chimeric endolysin, Cly2v, which comprises the Ply2741 CHAP domain (1-155aa) and the PlyV12 CBD domain (146-314aa). Biochemical characterization analysis indicated that Cly2v exhibits a melting temperature of 50.7°C and retains stable bactericidal activity at pH = 3-10. In vitro experiments demonstrated that Cly2v exhibited more efficient bactericidal activity against Streptococcus compared to the parental endolysin Ply2741. Cly2v (25 μg/mL) can effectively inhibit and reduce biofilms formed by Streptococcus, resulting in a 68 and 44% reduction in OD590nm for S. agalactiae X2 and S. uberis 002-1 biofilms. Notably, in a mouse mastitis model, treatment with Cly2v (50 μg/gland) led to a reduction in bacterial load by 2.16 log10CFU/ml and decreased inflammatory cytokine levels in mammary tissue. To our knowledge, this represents the first application of a chimeric endolysin in the treatment of early-stage mouse mastitis induced by streptococci. Additionally, in a systemic infection model, treatment with Cly2v (400 μg/mouse) provided protection rates of up to 100 and 78% against S. agalactiae ATCC13813 infections when challenged for 1 h and 3 h, respectively. Furthermore, a significant reduction in bacterial loads was observed in the blood and organs compared to the PBS group. In summary, Cly2v possesses significant potential as an alternative antibiotic for the treatment of streptococci-induced bovine mastitis and systemic infections.

Bacteriophage as a potential biotherapeutics to combat present-day crisis of multi-drug resistant pathogens

The rise of Multi-Drug Resistant (MDR) bacterial pathogens to most, if not all, currently available antibacterial agents has become a global threat. As a consequence of the antibiotic resistance epidemic, phage therapy has emerged as a potential alternative to conventional antibiotics. Despite the high therapeutic advantages of phage therapy, they have not yet been successfully used in the clinic due to various limitations of narrow host specificity compared to antibiotics, poor adhesion on biofilm surface, and susceptibility to both human and bacterial defences. This review focuses on the antibacterial effect of bacteriophage and their recent clinical trials with a special emphasis on the underlying mechanism of lytic phage action with the help of endolysin and holin. Furthermore, recent clinical trials of natural and modified endolysins and some marketed products have also been emphasized with future prospective.

Bacteriophage-derived endolysins as innovative antimicrobials against bovine mastitis-causing streptococci and staphylococci: a state-of-the-art review

Bacteriophage-encoded endolysins, peptidoglycan hydrolases breaking down the Gram-positive bacterial cell wall, represent a groundbreaking class of novel antimicrobials to revolutionize the veterinary medicine field. Wild-type endolysins exhibit a modular structure, consisting of enzymatically active and cell wall-binding domains, that enable genetic engineering strategies for the creation of chimeric fusion proteins or so-called 'engineered endolysins'. This biotechnological approach has yielded variants with modified lytic spectrums, introducing new possibilities in antimicrobial development. However, the discovery of highly similar endolysins by different groups has occasionally resulted in the assignment of different names that complicate a straightforward comparison. The aim of this review was to perform a homology-based comparison of the wild-type and engineered endolysins that have been characterized in the context of bovine mastitis-causing streptococci and staphylococci, grouping homologous endolysins with ≥ 95.0% protein sequence similarity. Literature is explored by homologous groups for the wild-type endolysins, followed by a chronological examination of engineered endolysins according to their year of publication. This review concludes that the wild-type endolysins encountered persistent challenges in raw milk and in vivo settings, causing a notable shift in the field towards the engineering of endolysins. Lead candidates that display robust lytic activity are nowadays selected from screening assays that are performed under these challenging conditions, often utilizing advanced high-throughput protein engineering methods. Overall, these recent advancements suggest that endolysins will integrate into the antibiotic arsenal over the next decade, thereby innovating antimicrobial treatment against bovine mastitis-causing streptococci and staphylococci.

Ultrashort lipo-tetrapeptide with potent antibacterial activity and local therapeutic effect against Staphylococcus aureus

OBJECTIVES

Mastitis in dairy cows is a common infectious disease on dairy farms and a major danger to the dairy industry. The harmful bacteria with the greatest clinical isolation rate are Staphylococcus aureus. As a result, bacterial mastitis in dairy cows can lead to decreased milk output, quality, and costs. Traditional antibiotics are currently used to treat mastitis in dairy cows. Nonetheless, long-term usage of high doses of antibiotics increases the risk of the establishment of drug-resistant strains, and the problem of drug residues is becoming more prevalent. We investigated the antibacterial effects of varying molecular side chain length lipopeptides on Staphylococcus aureus ATCC25923 and GS1311 using five tetrapeptide ultrashort lipopeptides developed and synthesised in this study.

METHODS

To evaluate the application value of the synthesized lipopeptides in the prevention and treatment of mastitis, the lipopeptides with the best antibacterial action were chosen for safety testing and a mouse mastitis model treatment test.

RESULTS

Three of the lipopeptides produced have strong antibacterial properties. Within the drug's safe concentration range, C16KGGK has an excellent antibacterial action and can have a therapeutic influence on mastitis induced by Staphylococcus aureus infection in mice.

CONCLUSION

The findings of this study can be used to develop new antibacterial medications and their therapeutic application in the treatment of mastitis in dairy cows.

Antibacterial effect of synthetic ultra-short lipopeptide on Streptococcus agalactiae and its active on bacterial mastitis in mice

Streptococcus agalactiae mastitis is one of the significant threats to the milk industry. The traditional antibiotic treatment method is easy to cause the emergence of resistant strains, and the problem of drug residue is increasingly severe. In this study, we designed and synthesized five lipopeptides. The antibacterial activity of different molecular structure lipopeptides against Streptococcus agalactiae was detected. Furthermore, the mouse mastitis model was established using Streptococcus agalactiae. The lipopeptides with better antibacterial effect were selected for the treatment experiment to evaluate the application value in the treatment of mastitis. The results showed that 4 of the synthesized lipopeptides had specific antibacterial activity. SLP3 and SLP4 have an excellent antibacterial effect and can treat murine mastitis caused by Streptococcus agalactiae infection within the safe concentration range. The results of this study can provide an excellent experimental basis for new antibiotics and clinical application in the treatment of dairy cow mastitis.