[01] Kumurya A. S., Department of Medical Laboratory Science, Faculty of Allied Health Sciences, Bayero University, Kano, Nigeria.

Background: Macrolide (MLSB) resistance is the most widespread and clinically important mechanism of resistance encountered with Gram-positive organisms. Resistance may be constitutive (cMLSB phenotype) or inducible (iMLSB phenotype). The iMLSB phenotypes are not differentiated by using standard susceptibility test methods, but can be distinguished by erythromycin-clindamycin disk approximation test (D-test) and demonstration of resistance genes by molecular methods. Aims: To demonstrate in vitro iMLSB in erythromycin-resistant (ER) and clindamycin-susceptible (CLI-S) clinical isolates of Staphylococcus aureus and interpretation of susceptibility tests to guide therapy. Materials and Methods: One hundred isolates of Staphylococcus aureus were recovered from various clinical specimens. All the Staphylococcus aureus were identified by conventional microbiological methods including colony morphology, Gram stain, catalase, slide coagulase and tube coagulase. Polymerase chain reaction (PCR) was used to amplify both the S. aureus specific sequence gene and mecA gene of 100 isolates with the amplicon size of 107 and 532 bp respectively. Antibiotic susceptibility testing was performed by Kirby Bauer disc diffusion method. Erythromycin-resistant isolates were examined for iMLSB by using double disk approximation test (D-test) at 15 mm disk separation. Results: All the isolates (n=100) expressed S. aureus specific sequence gene in their PCR products. Only 5 isolates (5.0%) were confirmed as Methicillin resistant Staphylococcus aureus (MRSA) based on the detection of mecA gene. Seven percent of Staphylococcus aureus were ER among which 4.0% were Methicillin susceptible Staphylococcus aureus (MSSA) and 3.0% were MRSA. The inducible MLSB (iMLSB) phenotype was detected in 3 MRSA isolates and all the 4 erythromycin-resistant MSSA strains were positive for the cMLSB phenotypes. Sixty per cent of iMLSB phenotypes were observed to be methicillin-resistant. All the isolates (MSSA and MRSA) were susceptible to vancomycin. Conclusions: The identification of multi-resistant MSSA with in vitro inducible clindamycin resistance at our health institutions raises concern of clindamycin treatment failures with methicillin-resistant infections. It is recommended that microbiology laboratories should include the D-test for inducible resistance to clindamycin in the routine antibiotic susceptibility testing.

D-Test, Inducible Clindamycin Resistance, Staphylococcus aureus

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