Revealing inducible clindamycin resistance in methicillin-resistant S aureus : A vital diagnostic imperative for effective treatment.

Introduction: The World Health Organization added methicillin-resistant S aureus (MRSA) to the list of "priority pathogens," given its capacity to cause life-threatening infections. Clindamycin is a preferred treatment for non-complicated S aureus-induced skin and soft tissue infections. Its good tissue penetration and oral absorption make it suitable for outpatient therapy. However, the emergence of inducible and constitutive (MLS B ) resistance led to clinical challenges, primarily due to the potential oversight of inducible resistance in routine antimicrobial sensitivity testing.

Materials and methods: This cross-sectional study was conducted at a tertiary care hospital during 2020-2022. A total of 158 MRSA isolates from various clinical specimens were analyzed. The Kirby-Bauer disk diffusion method using cefoxitin disk and D-test were used to identify MRSA and detect inducible clindamycin resistance (ICR), respectively.

Results: Among the 158 MRSA isolates, 34.17% showed constitutive clindamycin resistance (MLS B c), while 22.15% displayed ICR (MLS B i). In addition, 10.13% of isolates demonstrated the MS phenotype, clindamycin, and erythromycin susceptibility, with 53 (33.54%) isolates susceptible to both antibiotics. The relative risk of clindamycin treatment failure was 7.66 times higher if the D-test was not used.

Conclusion: To prevent clindamycin treatment failures, the D-test must be implemented to detect ICR in MRSA isolate. Neglecting simple and cost-effective tests may lead to inaccurate susceptibility reporting, jeopardizing treatment success.