Prevalence, Virulence Genes, Antibiotic Resistance and Pathogenicity of Streptococcus Agalactiae in Rabbits (Oryctolagus Cuniculus)

This study was conducted from July 2022 to November 2023 at rabbit farms in the Damietta governorate, Egypt. It aimed to investigate the presence of Streptococcus agalactiae, identify some virulence genes, assess the in-vitro susceptibility of this organism to various antimicrobials, and examine the impact of S. agalactiae experimental infection on weaned rabbits. For this purpose, a total of 408 samples were analyzed, including skin, uteri, and milk. These samples comprised 100 apparently healthy rabbits, 224 diseased rabbits, and 84 freshly deceased rabbits. S. agalactiae was isolated at the following rates: 10% (10 out of 100) from apparently healthy rabbits, 15.6% (35 out of 224) from diseased rabbits, and 16.7% (14 out of 84) from freshly dead rabbits. The isolates were identified through 16S rRNA sequencing. Additionally, S. agalactiae isolates tested positive by PCR for the Sip surface protein (sip) and contained virulent genes related to protease immunity protein (rip). The antibiotic susceptibility test conducted using the disc diffusion method revealed that S. agalactiae isolates were sensitive to gentamicin (86%), penicillin-G (80%), erythromycin (78%), ciprofloxacin (74%), cefotaxime (72%), and cephradine (70%). However, the isolates exhibited resistance to ampicillin (76%), trimethoprim/sulfamethoxazole (72%), streptomycin (68%), and amoxicillin (42%). The pathogenicity test conducted on 65 rabbits, inoculated via intramuscular and intranasal routes, showed that S. agalactiae was highly pathogenic, resulting in 45% and 15% mortality rates, respectively. The examination revealed hemorrhage throughout the internal organs, including the heart, spleen, liver, and kidneys, alongside severe congestion, multifocal hemorrhage, and lung swelling. In conclusion, this study emphasizes the significance of S. agalactiae as a pathogen in rabbit farms. Further research is needed to develop a vaccine to prevent such infections.