Emergence of Teicoplanin and Linezolid Resistance in Clinical Isolates of Methicillin-Resistant and -Susceptible <i>Staphylococcus aureus</i>

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA), a critical pathogen according to the World Health Organization, requires new treatments and resistance surveillance. This study compared the antibiotic susceptibility of clinical methicillin-susceptible <i>S. aureus</i> (MSSA) and MRSA isolates to last-line agents, including teicoplanin, linezolid, and daptomycin. A total of 134 <i>S. aureus</i> strains isolated from skin and soft tissue infections (SSTIs) were confirmed by detecting the <i>nuc</i> gene via PCR. MRSA and MSSA were identified by cefoxitin disk diffusion and confirmed by <i>mecA</i> gene amplification. Antibiotic susceptibility was initially screened by the Kirby-Bauer disk diffusion method, with minimum inhibitory concentrations (MICs) of last-resort antibiotics (teicoplanin, linezolid, and daptomycin) precisely determined by broth microdilution. Multidrug-resistant (MDR) phenotypes were defined as resistance to ≥2 non-β-lactam antimicrobial classes for MRSA and ≥3 for MSSA. Statistical analyses were conducted with chi-square and Fisher's exact tests. MRSA isolates exhibited significantly greater resistance than MSSA to cefazolin, gentamicin, amikacin, azithromycin, tetracycline, clindamycin, ciprofloxacin, and teicoplanin (<i>p</i> < 0.05). While daptomycin remained highly effective (96.3% susceptibility), concerning rates of non-susceptibility were observed for linezolid (41%) and teicoplanin (15.7%), primarily among MRSA isolates. Overall, MDR was prevalent in 41.7% of the <i>S. aureus</i> isolates. Daptomycin and cefazolin remain effective against MRSA and MSSA SSTIs, respectively. However, emerging resistance to last-line agents such as teicoplanin and linezolid is alarming and necessitates enhanced surveillance, prudent antibiotic use, and increased antimicrobial research to counter the growing threat of antibiotic resistance.