Prevalence of Inducible Clindamycin Resistance Among Staphylococcus Aureus Isolates Resistant to Erythromycin

Abstract

BACKGROUND Clindamycin is an effective drug to treat Methicillin-Resistant Staphylococcus Aureus (MRSA). Reporting S. aureus as susceptible to clindamycin without checking for inducible clindamycin resistance may lead to therapeutic failure. Therefore, D-test is used to screen inducible clindamycin resistance. MATERIALS AND METHODS All the S. aureus isolates resistant to erythromycin were taken. Erythromycin (15 μg) disc and clindamycin (2 μg) disc were placed 15 mm apart on Mueller-Hinton agar plates as per CLSI guidelines and incubated at 37°C for 18-24 hours. Flattening of zone (D shape) around clindamycin was taken as D-test positive. RESULTS Out of 270 S. aureus isolates, 80 were resistant to erythromycin. D-test was positive in 29 isolates, out of which 23 were MRSA. These MRSA isolates were also resistant to most of the other routinely used antibiotics. This study showed that inducible clindamycin resistance is as high as 36.2% in erythromycin resistant S. aureus and 10.7% among S. aureus as such. CONCLUSION We conclude that this simple and effective method can be implemented for accurate identification of inducible clindamycin resistance in S. aureus to prevent treatment failure. Clinical laboratories should guide the clinicians about the inducible clindamycin resistance by performing D-test routinely and prevent misuse of antibiotics.