Genetic Diversity, Antimicrobial Resistance, and Biofilm Formation in S. agalactiae and S. dysgalactiae Strains Isolated From Milk, Milk Products, and Humans in Sharkia Province, Egypt

Streptococcus spp infections pose a significant public health threat worldwide, contributing to a substantial economic burden. These infections are prevalent among both humans and animals, with potential for zoonotic transmission. Understanding the antimicrobial resistance patterns and genetic diversity of Streptococcus strains is crucial for developing effective prevention and control strategies. A total of 31 Streptococcus isolates isolated from milk (12 isolates), milk products (4 isolates), and humans (15 isolates) in Sharkia Province, Egypt were included in this study, with most exhibiting phenotypic resistance to multiple antibiotics. Antimicrobial resistance was widespread, with 96.8% resistance observed for ampicillin, clindamycin, linezolid, ceftriaxone, meropenem, and tetracycline. No significant differences in resistance profiles were found between S. agalactiae (18 isolates) and S. dysgalactiae (9 isolates). The isolates displayed 13 distinct resistance profiles, with most classified as extensively drug-resistant (80.6%) or pan drug-resistant (9.7%). The tetO gene was most prevalent in isolates from cheese (100%), followed by those from milk (80%) and human (76.9%). Additionally, 81.5%, 66.7%, and 70.4% of isolates were positive for tetO, ermB, and Pbp1A, respectively. Of the isolates, only one (3.2%) was a weak biofilm producer.Phylogenetic analysis revealed a high degree of genetic similarity among the Streptococcus strains, suggesting potential zoonotic transmission. In conclusion, the high prevalence of antimicrobial resistance and the genetic diversity of Streptococcus spp in Sharkia Province highlight the urgent need for effective strategies to combat these infections and prevent their further spread.