Comparative Assessment of Azithromycin and Erythromycin for Identifying Inducible Clindamycin Resistance in Staphylococcus aureus

Background Staphylococcus aureus remains a significant pathogen responsible for a wide range of infections. Clindamycin is frequently employed as an effective alternative for treating Staphylococcal infections. However, the emergence of antimicrobial resistance, particularly inducible clindamycin resistance (ICR), poses a substantial therapeutic challenge. Routine detection of ICR is crucial to prevent therapeutic failures and ensure appropriate use of clindamycin. Identifying a suitable substitute for erythromycin in resource-limited settings could enhance the reliability and feasibility of ICR detection in clinical laboratories. This study aimed to assess whether azithromycin could serve as a reliable alternative inducer for the detection of ICR in S. aureus and to compare its results with the standard erythromycin-induced D-test. Material and methods A cross-sectional comparative study was carried out in a tertiary care hospital setting. A total of 216 non-duplicate clinical isolates of Staphylococcus aureus were subjected to the D-test using both erythromycin and azithromycin in combination with clindamycin. The erythromycin-induced clindamycin resistance test, as recommended by the Clinical and Laboratory Standards Institute (CLSI), served as the reference method. Interpretation of azithromycin-induced D-test results was based on adapted CLSI criteria used for erythromycin. Result Of the 216 Staphylococcus aureus isolates tested, the iMLSB phenotype was most common with 52.31% isolates (n=113), followed by 12.03% cMLSB (n=26) and macrolide-streptogramin (MS) (17.21%, n=37). Our findings show 100% agreement between the test method (using azithromycin) and the reference method (using erythromycin) for the determination of ICR. Conclusion This study demonstrates that azithromycin may be a viable alternative to erythromycin for detecting inducible clindamycin resistance in clinical isolates of Staphylococcus aureus. Incorporating azithromycin in routine susceptibility testing could offer a practical substitute, particularly in settings where erythromycin is unavailable.