Abstract: subspecies (subsp.) is an important facultative pathogen in horses and can cause severe infections in other species including humans. Facing the post-antibiotic era, novel antimicrobials are needed for fighting bacterial infections. Bacteriophages (phages) are the natural predators of bacteria and discussed as a promising antimicrobial treatment option. The objective of this study was to isolate and characterize subsp. specific phages for the first time and to evaluate their efficacy and . In total, 13 phages with lytic activity were isolated and host ranges were determined. Two phages with broad host ranges and high efficiency of plating (vB_SeqZP_LmqsRe26-2 (lytic activity: 30/37 bacterial isolates) and vB_SeqZP_LmqsRe26-3 (lytic activity: 29/37 bacterial isolates)) and one phage with relatively low efficiency of plating (vB_SeqZP_LmqsRe26-1) were selected for further characterization, including electron microscopy and whole genome sequencing. In planktonic killing assays at two tested multiplicities of infection (MOI 1 and MOI 10), significant bacterial growth reduction was observed when the phages vB_SeqZP_LmqsRe26-2 and vB_SeqZP_LmqsRe26-3 were added. These phages were subsequently co-incubated with clinical subsp. isolates in an equine endometrial explant model but did not achieve bacterial growth reduction at MOI 1 and MOI 10. However, helium ion microscopy revealed presence of particles adherent to the bacteria on the explant after incubation (25 h), suggesting possible phage-bacteria interactions. In conclusion, phages against subsp. were successfully isolated and characterized. Promising results were observed in but no significant reduction was detected in experiments, requiring additional investigations. However, after further adaptations (e.g., optimization of MOIs and phage administration or use of phage-antibiotic combination), phages could be a potential antimicrobial tool for future therapeutic use in subsp. infections, although the available results do not currently support the therapeutic usage.
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Overview
This study isolated and characterized bacteriophages specific to Streptococcus equi subspecies zooepidemicus, a pathogen affecting horses and other species including humans.
The research evaluated the antibacterial effectiveness of these phages in laboratory and tissue models, identifying promising results in culture but limited efficacy in an ex vivo tissue model.
Background and Objectives
Pathogen: Streptococcus equi subsp. zooepidemicus is a facultative pathogen primarily affecting horses but also capable of infecting other animals and humans, causing severe infections.
Challenge: Rising antibiotic resistance necessitates alternative antimicrobial strategies.
Proposed Solution: Bacteriophages (phages), viruses that infect and kill bacteria, present a promising alternative treatment option.
Study Goal: To isolate and characterize phages specific to S. equi subsp. zooepidemicus and assess their antibacterial efficacy both in vitro (planktonic bacterial culture) and ex vivo (equine endometrial tissue model).
Phage Isolation and Characterization
Isolation: Thirteen distinct bacteriophages with lytic activity against S. equi subsp. zooepidemicus were isolated.
Host Range Testing: The susceptibility of 37 bacterial isolates to these phages was determined.
Selection for Detailed Study:
Two phages with broad host range and high efficiency of plating (EOP):
vB_SeqZP_LmqsRe26-2 (lytic against 30/37 isolates)
vB_SeqZP_LmqsRe26-3 (lytic against 29/37 isolates)
One phage with relatively lower plating efficiency:
vB_SeqZP_LmqsRe26-1
Characterization Techniques: Electron microscopy was used to study phage morphology, and whole genome sequencing was performed to analyze phage genetic material.
In Vitro Efficacy Testing
Experimental Design: Planktonic killing assays were conducted with multiplicities of infection (MOI) of 1 and 10, indicating the ratio of phages to bacterial cells.
Results: The two selected phages with broad host range (vB_SeqZP_LmqsRe26-2 and vB_SeqZP_LmqsRe26-3) caused significant reduction in bacterial growth.
Ex Vivo Efficacy Testing
Model Used: An equine endometrial explant model was employed to evaluate phage activity in a tissue environment closer to real infection sites.
Results: Despite co-incubation of phages with clinical isolates of S. equi subsp. zooepidemicus at MOIs 1 and 10, no significant bacterial growth reduction was observed.
Helium Ion Microscopy Findings: Imaging revealed phage particles adhering to bacteria after 25 hours, suggesting potential phage-bacteria interactions despite lack of observed bacterial killing.
Conclusions and Future Directions
Successes: Phages specific to S. equi subsp. zooepidemicus were successfully isolated and shown to kill bacteria effectively in planktonic cultures.
Limitations: The lack of significant bacterial reduction in ex vivo tissue suggests the need for further optimization.
Potential Improvements:
Adjusting MOI values and administration methods to enhance phage penetration and activity in tissues.
Exploring phage-antibiotic combination therapies for synergistic effects.
Implications: While current results do not yet support therapeutic use of these phages in infections caused by S. equi subsp. zooepidemicus, they hold promise as future antimicrobial agents pending additional research.
Cite This Article
APA
Köhne M, Hüsch R, Tönissen A, Schmidt M, Müsken M, Böttcher D, Hirnet J, Plötz M, Kittler S, Sieme H.
(2024).
Isolation and characterization of bacteriophages specific to Streptococcus equi subspecies zooepidemicus and evaluation of efficacy ex vivo.
Front Microbiol, 15, 1448958.
https://doi.org/10.3389/fmicb.2024.1448958
Unit for Reproductive Medicine - Clinic for Horses, University of Veterinary Medicine, Foundation, Hannover, Germany.
Hüsch, Ronja
Unit for Reproductive Medicine - Clinic for Horses, University of Veterinary Medicine, Foundation, Hannover, Germany.
Tönissen, Anna
Unit for Reproductive Medicine - Clinic for Horses, University of Veterinary Medicine, Foundation, Hannover, Germany.
Schmidt, Matthias
Department of Technical Biogeochemistry, Helmholtz Centre for Environmental Research -UFZ, Leipzig, Germany.
Müsken, Mathias
Central Facility for Microscopy, Helmholtz Centre for Infection Research - HZI, Braunschweig, Germany.
Böttcher, Denny
Institute for Veterinary Pathology, Faculty of Veterinary Medicine, Leipzig University, Leipzig, Germany.
Hirnet, Juliane
Institute of Food Quality and Food Safety, University of Veterinary Medicine, Foundation, Hannover, Germany.
Plötz, Madeleine
Institute of Food Quality and Food Safety, University of Veterinary Medicine, Foundation, Hannover, Germany.
Kittler, Sophie
Institute of Food Quality and Food Safety, University of Veterinary Medicine, Foundation, Hannover, Germany.
Sieme, Harald
Unit for Reproductive Medicine - Clinic for Horses, University of Veterinary Medicine, Foundation, Hannover, Germany.
Conflict of Interest Statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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