Characterization of drug-resistant Streptococcus spp. from food and human sources and in vitro antibacterial assessment of an oregano nanoemulsion

Abstract

Abstract Objectives This study aimed to characterize drug-resistant Streptococcus spp. isolated from food and human sources in Upper Egypt, focusing on their virulence and antimicrobial resistance profiles, and to evaluate the in vitro antibacterial activity of an oregano essential oil nanoemulsion. Materials and methods A total of 440 food and human samples were collected in Aswan, Upper Egypt, and screened using conventional microbiological methods. Molecular confirmation was performed by detecting the tuf gene, followed by species identification using the 16 S rRNA and spn9802 genes. Selected virulence ( scpB , Rib , Lmb , and cylE ) and resistance ( aac6-aph2 , pbp1A , and tetO ) genes were detected by PCR. Antimicrobial susceptibility testing and the multiple antibiotic resistance (MAR) index were determined. The antibacterial activity of the oregano nanoemulsion was assessed using inhibition zone assays at varying concentrations. Results Streptococcus spp. were detected in 22% of samples, with higher prevalence in throat swabs (34%) and raw milk (21.9%). Predominant species included S. agalactiae , S. pyogenes , S. dysgalactiae , S. pneumoniae , and S. uberis . Virulence genes were variably distributed, with scpB (33%) and cylE (31.8%) most frequent. Resistance genes were moderately detected, particularly tetO (21.2%). Most isolates were resistant to β-lactams but fully susceptible to ceftaroline and fosfomycin; the mean MAR index was 0.477. The oregano nanoemulsion showed concentration-dependent antibacterial activity. Conclusion Drug-resistant Streptococcus spp. from food and human sources in Upper Egypt carry important virulence and resistance determinants. The oregano essential oil nanoemulsion demonstrated promising in vitro antibacterial activity, suggesting potential as a natural antimicrobial; however, further in vivo and safety studies are required.