The main biological features and resistance to antibacterial drugs of Streptococcus agalactiae isolated from the cow’s milk

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Abstract

Background and Aim. The main goal of our research, as stated in the article, was to study the phenotypic characteristics of strains of S. agalactiae isolated from milk, identify and evaluate the effectiveness of the main groups of antibiotics recommended for use in veterinary medicine, including those provided by EUCAST.

Materials and Methods. The study of the phenotypic characteristics of S. agalactiae and the research on antibiotic resistance were carried out at the base of the Microbiology Laboratory of the Biotechnology Research Institute of Kostanay State University named after A. Baitursynov in 2023, using mastitis milk samples brought to the microbiology laboratory. The biological characteristics of streptococci in the milk samples were identified using classical microbiological methods. The antibiotic susceptibility testing was performed using the disk diffusion method in Mueller-Hinton agar.

Results. The results of the study indicate that out of 631 milk samples from animals in the region’s dairy farms, 35 of them were found to be S. agalactiae isolates. The text you provided seems to report the results of a study that investigated 631 samples of raw milk for mastitis, identifying 35 S. agalactiae isolates. It details the antibiotic susceptibility of these isolates, indicating a high susceptibility to benzylpenicillin (90.4%), amoxicillin (80.9%), kanamycin (76.1%), and moderate susceptibility to ampicillin and neomycin. However, the isolates demonstrated lower susceptibility to doxycycline (47.6%), tylosin (42.8%), gentamicin, and erythromycin (33.3%).

Conclusion. Thus, various mechanisms of antibiotic resistance and ways of their acquisition by bacteria significantly complicate the process of selecting effective antibiotic therapy both in agroindustrial organizations and in medical institutions. The mechanisms of acquired and natural antibiotic resistance are inherently complex and vary from species to species, from strain to strain of microorganisms. Basically, intraspecific and interspecific acquisition of antibiotic resistance genes is carried out through horizontal transfer - conjugation, transformation, and transduction.