Identification and phylogenetic analysis of multidrug resistance, caries-related  Streptcoccus mutans in Sulaymaniyah City, Iraqi Kurdistan Region

Streptococcus mutans plays a key role in the oral ecosystem through dental plaque formation and initiation of dental caries, the foremost oral health problem around the world. This study aimed to determine antimicrobial resistance patterns and to investigate the phylogenetic relationships of local multidrug-resistant (MDR) S. mutans isolated from dental caries in Kurdish patients in Sulaymaniyah city, Iraqi Kurdistan Region. Dental plaque samples were collected from 160 adult Kurdish patients diagnosed with dental caries who attended the dental clinic of the College of Dentistry, University of Sulaimani. Isolation and identification of S. mutans were carried out using conventional culture methods, Gram staining, and the automated biochemical testing, followed by molecular confirmation using conventional PCR. Antimicrobial susceptibility testing of the confirmed isolates was performed using VITEK® 2 system against seventeen antimicrobial agents. MDR isolates (resistant to ≥ 3 antimicrobial categories) were further subjected to partial sequencing of gtfD gene, and phylogenetic analysis (Neighbor-Joining method) was conducted by comparison with global reference strains. Out of the 160 samples analysed, 112 S. mutans isolates were identified, of which 13 (11.6%) were classified as MDR. Partial gtfD gene sequences of the MDR isolates were successfully obtained and submitted to the GenBank database. Phylogenetic analysis revealed the presence of multiple well-supported clusters, including a distinct in dependent clade as well as closely related clades showing genetic similarity to international reference strains. These findings suggest that the studied isolates represent both globally disseminated S. mutans lineages and region-specific genetic variants. This study demonstrates a considerably high prevalence of S. mutans among adult Kurdish patients with dental caries and highlights variable antimicrobial resistance patterns. The observed phylogenetic relatedness between local MDR isolates and strains from diverse geographical regions indicates overall genetic stability of S. mutans, with evidence of localized microevolutionary diversification. The coexistence of globally related strains and locally evolving lineages suggests ongoing international dissemination coupled with regional adaptation, underscoring the importance of continuous localized molecular surveillance and region-specific antimicrobial stewardship strategies.