INDUCIBLE MACROLIDE RESISTANCE PHENOTYPES AND GENOTYPES IN CLINICAL ISOLATES OF Staphylococcus aureus FROM NNAMDI AZIKIWE UNIVERSITY TEACHING HOSPITAL, NNEWI, SOUTH EAST, NIGERIA

Abstract

Background: The widespread use of macrolide, lincosamide, and streptogramins-B (MLS-B) to treat Staphylococcal infections has caused an increase in resistance to these types of antibiotics.

Aim: The aim of this study is to identify macrolide resistant phenotypes and detect erm genes associated with macrolide resistance in Staphylococcus aureus.

Methodology: A total of 304 Gram positive cocci isolated from different clinical samples received at the Medical Microbiology Laboratory of Nnamdi Azikiwe University Teaching Hospital (NAUTH), Nnewi were used for this study. Oxoid Staphytect agglutination test kits were used to confirm 185 of these isolates as Staphylococcus aureus. Antibiotic sensitivity testing was done on the 185 verified S. aureus isolates while the D-test was used to check for macrolide resistance. Twenty (20) of the D-test positive isolates were tested for the presence of erm A, B, and C genes using a multiplex PCR method.

Results: Results showed that the occurrence of inducible MLS-B phenotype was 23 out of 185 (12.4%) while 46 out of 185 (24.9%) of the isolates displayed the constitutive MLS-B phenotype. Out of the 20 resistant isolates tested for the presence of resistance genes, 8 (40%) tested positive for erm C, while none possessed either erm A or erm B genes. All 8 of the erm C positive isolates were resistant to methicillin (MRSA). The iMLS-B phenotypes were more frequently observed in isolates that tested positive for erm C compared to the cMLS-β phenotype.

Conclusion: This study stresses on the need to be aware that iMLSB and cMLSB phenotypes exist among clinical isolates of S. aureus and that resistant genes are found in some of these isolates. Such isolates should be sought for during routine laboratory investigations in order to avoid possible treatment failure.