Emergence of Teicoplanin and Linezolid Resistance in Clinical Isolates of Methicillin-Resistant and -Susceptible Staphylococcus aureus

Abstract

Methicillin-resistant Staphylococcus aureus (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 S. aureus (MSSA) and MRSA isolates to last-line agents, including teicoplanin, linezolid, and daptomycin. A total of 134 S. aureus strains isolated from skin and soft tissue infections (SSTIs) were confirmed by detecting the nuc gene via PCR. MRSA and MSSA were identified by cefoxitin disk diffusion and confirmed by mecA 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 (p < 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 S. aureus 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.