Equine platelet lysate exhibits bacteriostatic effects against gram-negative clinical bacterial isolates.

Overview

• This research investigated the antimicrobial effects of equine platelet lysate (PL) on antibiotic-resistant gram-negative bacterial isolates from horses.
• The study found that equine PL significantly inhibited bacterial growth compared to both control and traditional antibiotics, showing promise as an alternative treatment against resistant infections.

Background and Significance

• Antibiotic resistance is a major medical concern driving the search for alternative or adjunctive therapies to traditional antibiotics.
• Platelet lysate (PL) is a blood-derived product made by lysing platelets, releasing various growth factors and proteins with potential antimicrobial properties.
• Equine PL is being studied for its ability to inhibit growth of clinically relevant, antibiotic-resistant bacterial strains isolated from horses.

Objective

• To compare in vitro the effects of equine PL against classic antibiotic treatments on the growth of antibiotic-resistant gram-negative bacterial isolates from clinical equine sources.
• The hypothesis was that PL would exhibit an antimicrobial or bacteriostatic effect even on bacteria resistant to common antibiotics.

Methods

• Platelets were collected via apheresis from nine healthy donor horses.
• Platelet lysate was prepared by subjecting platelets to two freeze-thaw cycles to induce lysis and release platelet contents.
• PL from groups of three donors was pooled to create three batches for testing.
• Three clinical isolates belonging to the Enterobacteriaceae family (gram-negative bacteria) were selected for assays:
• Enterobacter cloacae complex (ECC)
• Enterobacter hormachei
• Morganella morganii
• Growth curve and time-kill assays were performed using treatments:
• 40% volume/volume (v/v) equine PL
• Phosphate-buffered saline (PBS) as a negative control
• Antibiotics corresponding to resistance profiles: ceftiofur, gentamicin, and trimethoprim-sulfamethoxazole (TMS)
• The growth rate, measured as changes in optical density (mOD/min), and viable bacterial counts (log fold change) were recorded and statistically compared across treatments over 16 hours.

Results

• Bacterial growth rates in the presence of PL were markedly reduced compared to controls and antibiotics:
• ECC: Growth rate with PL ranged from 0.93–1.72 mOD/min, versus 5.50 mOD/min for PBS and 5.84 for ceftiofur.
• E. hormachei: PL 0.92–1.58 mOD/min, PBS 5.27, gentamicin 5.13.
• M. morganii: PL 1.94–2.39, PBS 3.96, TMS 4.04.
• PL showed a mild bactericidal effect within 1 hour post-treatment characterized by a negative log fold change in viable bacteria:
• ECC: PL -0.28 to -0.79; PBS 0.42; ceftiofur 0.1
• E. hormachei: PL -0.18 to -0.36; PBS 0.61; gentamicin 0.46
• M. morganii: PL -0.09 to -0.26; PBS 0.36; TMS 0.11
• Interestingly, antibiotics to which the isolates were resistant failed to reduce bacterial growth or viability, emphasizing the effectiveness of PL despite bacterial resistance.

Conclusions

• Equine platelet lysate at 40% concentration exhibits a clear bacteriostatic effect on antibiotic-resistant gram-negative clinical isolates.
• PL significantly reduces the growth rate and viable bacterial counts compared to both untreated controls and classical antibiotics when bacteria show resistance.
• This finding suggests PL could be a promising candidate for alternative or adjunctive antimicrobial therapy against resistant bacterial infections in veterinary or potentially human medicine.
• Further research is needed to understand the mechanisms of PL antibacterial action and to evaluate clinical efficacy and safety in vivo.