Antimicrobial susceptibilities and genomic characteristics of mupirocin resistant Staphylococcus aureus isolates from Tehran, Iran

The emergence of mupirocin-resistant Staphylococcus aureus strains poses a significant challenge to public health due to limited treatment options and the risk of multidrug resistance. This study aims to investigate the antibiotic susceptibility and molecular characteristics of mupirocin resistant S. aureus isolates. A total of 65 mupirocin-resistant isolates were included in the study. The isolates were characterized using antimicrobial susceptibility testing, biofilm formation assay, staphylococcal cassette chromosome mec typing, multilocus sequence typing, and polymerase chain reaction analysis to detect resistance (mecA, mecC, mupA, erm(A), erm(B), erm(C), tet(M), ant (4')-Ia, aac (6')-Ie/aph (2″), and aph (3')-IIIa) and toxin genes (eta, etb, pvl, and tst). Resistance to mupirocin was observed in 12.5% of the S. aureus isolates collected during the study period. Among the 65 mupirocin-resistant MRSA isolates, 75.4% were classified as HLMUPR and 24.6% as LMUPR. cMLSB and iMLSB phenotypes were identified in 41.5 and 36.9% of the isolates. Our results showed that 49.2, 30.8, and 15.4% of isolates were classified as strong, intermediate, and weak biofilm-forming strains, respectively. Our result revealed that about three-quarters of isolates harbored mecA (100%), tet(M) (76.9%), mupA (75.4%) resistance genes. MLST revealed that the 65 isolates belonged to seven clonal complexes, including CC8 (41.5%), followed by CC22 (20%), CC5 (10.8%), CC30 (10.8%), CC15 (7.7%), CC1 (4.6%) and CC80 (4.6%). The vast majority of S. aureus isolates belonged to CC8/ST239-MRSA (21.5%). Among the 32 strong biofilm producers, the majority (28.1%) belonged to CC8/ST8 MRSA clone. Our result revealed that 39.1% of PVL-positive strains belonged to CC/ST22. The fusidic acid resistance isolates belonged to CC/ST8-MRSA (7.7%), CC8/ST239-MRSA (12.3%), CC/ST22-MRSA (7.7%), and CC30/ST80-MRSA (1.5%) lineages. In conclusion, this study provides valuable insights into the characteristics of mupirocin-resistant S. aureus isolates from Tehran, Iran. The results highlight a high prevalence of HLMUPR in this research. Additionally, the study reveals a diverse genetic landscape, with isolates belonging to various clonal complexes, particularly CC8, CC22, and CC5. The high frequency of biofilm formation and resistance to other antibiotics underscores the need for ongoing surveillance and the development of more effective treatment strategies to combat these multidrug-resistant strains.