నైరూప్య

Detection of constitutive- and inducible-clindamycin-resistance in clinical isolates of Staphylococcus aureus from a Federal Teaching Hospital in Abakaliki, Nigeria

Ejikeugwu Chika*, Nwezeagu Felix Joseph, Edeh Chijioke, Eze Peter

Infections caused by Staphylococcus aureus are usually treated with clindamycin. However, when treatment is directed against S. aureus isolates harbouring gene that mediate inducible clindamycin resistance, treatment failure is bound to occur. In this study, the occurrence of constitutive- and inducible-clinamycin resistance was phenotypically evacuated in clinical isolates of Staphylococcus aureus from a Federal Teaching Hospital in Abakaliki, Nigeria. A total of 39 non-duplicate clinical isolates of S. aureus were used in this study; and the isolates were subjected to antimicrobial susceptibility testing using cefoxitin (30 µg), bacitracin (10 µg), erythromycin (15 µg), oxacillin (1 µg), clindamycin (2 µg), gentamicin (10 µg), mupirocin (5 µg) and cloxacillin (5 µg). D-test was performed on all the S. aureus strains to detect constitutive- and inducible-clindamycin resistance (iMLSB) phenotypes. The multiple antibiotic resistance nature of the iMLSB phenotypes as calculated using multiple antibiotic resistance index (MARI) formular. Among the 39 clinical isolates of S. aureus studied, 76.9% (30/39) showed resistance to clindamycin, while 74.4% (29/39) showed resistance to erythromycin. Also, all the S. aureus isolates were completely resistant to cloxacillin and mupirocin. A total of 6 (15.4) S. aureus isolates showed inducible-clindamycin resistance (iMLSB) while 20.5% S. aureus isolates (n=8) were confirmed constitutive-clindamycin resistance (cMLSB) phenotypes by the D-test technique. On average, the S. aureus isolates that were positive for iMLSB had MARI of 0.7; and this indicates a high level of multiple antibiotic resistance profile of the isolates. The result of this study has shown that cMLSB and iMLSB occur in clinical isolates of S. aureus from this part of the world. Further molecular characterization of the genetic factors responsible for cMLSB and iMLSB in clinical isolates of S. aureus is necessitated. Since routine antibiotic susceptibility studies cannot detect either cMLSB or iMLSB in clinical isolates of S. aureus, it is important for Nigerian hospital laboratories to include the D-test protocol in their practice.