Bovine blood products modulate the effect of ophthalmic antibiotics against common bacterial pathogens in dogs with infectious keratitis.

Bacterial keratitis is a common condition that can result in serious complications including vision impairment and loss of the eye if not treated aggressively. Topical blood products are often utilized concurrently with topical antibiotics for their known anti-collagenolytic properties. These blood products contain albumin that could affect the antibiotic efficacy due to drug-protein binding. In this study, serum and plasma were harvested from 10 healthy bovines, utilizing fresh and frozen (1 month at -20 °C) aliquots for the experiment. Albumin and alpha-2 macroglobulin levels were quantified using species-specific ELISA kits. 30 bacterial isolates (10 Staphylococcus pseudintermedius, 10 Streptococcus canis, 10 Pseudomonas aeruginosa), isolated from canine patients with infectious keratitis were tested with blank plates as well as commercial susceptibility plates (Sensititre™ JOEYE2) to assess the minimal inhibitory concentration (MIC) of 17 different antibiotics in the absence (control) or presence of serum or plasma (fresh or frozen) from bovines (4 test groups). Mean bovine albumin levels ranged from 1.98 to 2.00 mg/ml. The median bovine alpha-2 macroglobulin levels were similar between frozen serum (4,403 ng/ml [range 3,542-5,499 ng/ml]) and frozen plasma (4,959 ng/ml [range 3,305-5,447 ng/ml]). No bacteriological susceptibility differences were noted between fresh and frozen samples for either serum or plasma. Bovine serum/plasma had direct antimicrobial effects in selected bacterial isolates (up to 49% with frozen plasma for Staphylococcus pseudintermedius). When compared with control, bovine serum/plasma increased MICs (1.33-4-fold) or decreased MICs (0.5-0.75 fold) depending on the specific antibiotic and bacterial isolate. In practice, clinicians should consider using bovine serum/plasma over other species' blood products (equine or canine) given direct antimicrobial effects, good anti-collagenolytic potential, and lesser impact on antimicrobial susceptibility to topical antibiotics. Serum and plasma can alter antibiotic efficacy (antibiotic-protein binding from high levels of albumin); therefore, serum/plasma should be applied last and spaced ≥15 min after topical antibiotics.