Cyclic hexapeptide and ZnO nanoparticles effectively inhibit antibiotic-resistant bacteria in bull semen

Bacterial contamination in bull semen significantly compromises semen quality and fertility, leading to substantial economic losses in livestock breeding. The widespread use of conventional antibiotics in semen extenders has fueled the rise of antibiotic resistance, rendering many treatments ineffective and posing a public health concern. This escalating resistance highlights an urgent need for novel, effective, and non-antibiotic alternatives (ATAs) to maintain semen viability and prevent disease transmission, addressing a critical gap in current animal reproductive health strategies.

Researchers isolated antibiotic-resistant bacteria from Sahiwal bull semen using penicillin and streptomycin selection, followed by identification via 16S rRNA gene sequencing. They then selected Bacillus cereus (Gram-positive) and Proteus mirabilis (Gram-negative) for further analysis. The antimicrobial efficacy of zinc oxide nanoparticles (ZnO NPs) and a cyclic hexapeptide (c-WFW AMP) was evaluated against these strains. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined to assess their potential as antibiotic alternatives.

Analysis of Sahiwal bull semen revealed a high prevalence of antibiotic-resistant bacteria, with Bacillus cereus accounting for 50% of isolates, followed by Proteus mirabilis at 17%, and Enterococcus spp. also at 17%. Other identified resistant strains included Pseudomonas aeruginosa (5%) and Klebsiella variicola (5%). Both tested alternatives demonstrated potent antimicrobial activity. > ZnO NPs effectively inhibited both Bacillus cereus and Proteus mirabilis at an MIC of 60 µg/ml, achieving bactericidal action (MBC) at 80 µg/ml. The c-WFW AMP showed even greater potency, with an MIC of 4 µg/ml against Bacillus spp. and 6 µg/ml against Proteus spp.. Crucially, the c-WFW AMP exhibited bactericidal activity (MBC) at 6 µg/ml for both strains, indicating rapid and complete bacterial elimination.