Priming of the murine mammary gland with Staphylococcus chromogenes IM reduces bacterial growth of Streptococcus uberis: a proof-of-concept study

Characterization and therapeutic potential of newly isolated bacteriophages against Staphylococcus species in bovine mastitis

Bovine mastitis, primarily caused by Staphylococcus aureus, significantly affects the dairy industry by reducing milk production and quality. The rise of antibiotic-resistant bacteria has prompted the need for alternative treatments. The three newly isolated bacteriophages, OPT-SA02, OPT-SC01, and OPT-SX11, were isolated from chicken fecal and sewage samples in South Korea. These bacteriophages were characterized via physiological and genomic analyses, identifying their therapeutic potential against S. aureus-induced mastitis. The bacteriophages were identified as members of the Herelleviridae family, exhibiting stability across broad pH (2-12) and temperature (37-70°C) ranges, as well as strong antibacterial activity at low multiplicity of infection (MOI) levels. Genomic analysis revealed that the conservation of lysis-related genes (holin and endolysin) is responsible for their lytic capabilities. Additionally, protein structural predictions revealed multi-domain structures in their endolysins, enhancing their lytic potential. These findings suggest that OPT-SA02, OPT-SC01, and OPT-SX11 show significant promise as alternative treatments for bovine mastitis.IMPORTANCEBovine mastitis, caused by pathogens such as Staphylococcus aureus and Staphylococcus xylosus, remains a major challenge in dairy farming, leading to significant economic losses and reduced milk quality. The increasing prevalence of antibiotic-resistant strains further complicates treatment, emphasizing the need for alternative strategies. This study identifies three newly isolated bacteriophages with effective antibacterial activity against these pathogens and provides comprehensive genomic and structural insights into their mechanisms. Genomic characterization revealed conserved lytic cassettes and genetic diversity within related bacteriophages, offering a deeper understanding of their evolutionary relationships and potential applications. Furthermore, protein structure analysis of the endolysin derived from these bacteriophages identified multi-domain architectures with preserved catalytic cores, underscoring their lytic efficacy against bacterial cell walls. These findings advance the understanding of the genetic and structural mechanisms of bacteriophage-mediated lysis and highlight their potential as sustainable tools for managing bovine mastitis and improving milk quality in dairy farming.

Non-aureus Staphylococci Cause the Spontaneous Cure or Persistent Infection of Major Bovine Mastitis Pathogens in the Murine Mammary Glands

The microbial ecology in mastitis involves the interactions between bacteria and the mammary gland environment. Poor mastitis control, for which understanding these microbial relationships is crucial, increases the risk of mastitis and co-infections. The aim of this study was to determine the pathogenesis and bacterial ecology of murine mammary glands following intramammary infection (IMI) with S. aureus (AU), S. agalactiae (SA), and four isolates of selected non-aureus staphylococci (NAS), as well as co-infections of AU or SA with NAS. Selected NAS demonstrated resistance to growth inhibition after co-culture with AU and SA and were proven to be protective in vitro against AU and SA. Both single infections and co-infections of AU, SA, two selected isolates of S. hominis (NAS1 and NAS2), and two selected isolates of S. chromogens (NAS3 and NAS4) were injected into the murine mammary glands at 105 CFU/mL. After 72 h of inoculation, the results showed that AU, AU-NAS2, and AU-NAS3 expressed severe inflammation with clinical signs of mastitis. The persistence of AU was found for AU, NAS3, and AU-NAS3, whereas the persistence of SA was found for SA-NAS1, SA-NAS3, and SA-NAS, although single SA could not persist. Interestingly, NAS2 in both the single- and co-IMIs with AU or SA resulted in a spontaneous cure 72 h after the IMI. In conclusion, some NAS have beneficial results because they can eliminate S. aureus and S. agalactiae, but some NAS have negative effects because they can support persistent S. agalactiae infection. These results may be used to explain both the advantages and disadvantages of NAS on farms with poor mastitis control. In addition, the beneficial S. hominis may initiate natural live antibiotics and reduce antibiotic resistance problems.

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.

Staphylococcal mastitis in dairy cows

Bovine mastitis is one of the most common diseases of dairy cattle. Even though different infectious microorganisms and mechanical injury can cause mastitis, bacteria are the most common cause of mastitis in dairy cows. Staphylococci, streptococci, and coliforms are the most frequently diagnosed etiological agents of mastitis in dairy cows. Staphylococci that cause mastitis are broadly divided into Staphylococcus aureus and non-aureus staphylococci (NAS). NAS is mainly comprised of coagulase-negative Staphylococcus species (CNS) and some coagulase-positive and coagulase-variable staphylococci. Current staphylococcal mastitis control measures are ineffective, and dependence on antimicrobial drugs is not sustainable because of the low cure rate with antimicrobial treatment and the development of resistance. Non-antimicrobial effective and sustainable control tools are critically needed. This review describes the current status of S. aureus and NAS mastitis in dairy cows and flags areas of knowledge gaps.

Metabolites of non-aureus staphylococci affect the ability of Staphylococcus aureus to adhere to and internalize into bovine mammary epithelial cells

This study investigated whether cell-free supernatants (SN) from four bovine non-aureus staphylococcal (NAS) isolates prevent Staphylococcus aureus adhesion to and internalization into bovine mammary epithelial cells (MAC-T cells) and if so, to determine whether such effects were potentially associated with the S. aureus accessory gene regulator (agr) system. Overall, we demonstrated that all SN obtained from the NAS isolates promoted adhesion of a S. aureus agr+ strain to, yet reduced the internalization into MAC-T cells, while similar effects were not observed for its agr- mutant strain. Our findings provide novel anti-virulence strategies for treating and controlling bovine S. aureus mastitis.