LJM 1993-2820 1819-6357 Libyan Journal of Medicine Vol. 5, January 2010, pp. 1–2 sici xxx PUBMED Abbreviation Libyan Journal of Medicine LETTER TO THE EDITOR Detection of inducible clindamycin resistance (MLSB<sub>i</sub>) among methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) from Libya Letter to the Editor <para>Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) first emerged as nosocomial pathogens in the early 1960s are of great concern to public health and highly reported in human clinical samples <citationref linkend="CIT0001">1</citationref>. There are major international concerns about rising levels of MRSA and multi-drug resistant <i>S. aureus</i> owing to the difficulties of treating infections and the ease with which MRSA spreads within hospitals <citationref linkend="CIT0002">2</citationref>. Until recently, most infections of MRSA were acquired primarily in hospital settings, but now MRSA is responsible for both hospital and community-acquired infections <citationref linkend="CIT0001">1</citationref>. The objective of this study was to investigate MRSA collected isolates for MLSB phenotypes, in particular inducible clindamycin resistance (MLSB<sub>i</sub>).</para> <para>MRSA collected isolates of hospital-origin were further investigated at the Microbiology Department, Biotechnology Research Centre, Tripoli, Libya. One hundred and twenty-eight MRSA isolates were confirmed at species level as <i>S. aureus</i> by culturing onto mannitol salt agar (MSA) and API Staph test strips (bioMerieux). Confirmation as MRSA was by latex agglutination test for PBP2a and disc diffusion method against cefoxitin in accordance with British Society of Antimicrobials and Chemotherapy guidelines (BSAC) as described by Andrews <citationref linkend="CIT0003">3</citationref>. Isolates were also tested against erythromycin, clindamycin, and synercid for the characterization of MLSB phenotypic isolates. <i>D</i>-tests were performed on isolates exhibiting erythromycin resistance, to assay for the presence of inducible clindamycin resistance (MLSB<sub>i</sub> phenotype) as described by Fiebelkorn et al. <citationref linkend="CIT0004">4</citationref>.</para> <para>Of the 128 tested MRSA isolates, 24.2% (<i>n</i>=31) were resistant to clindamycin, 63.2% (<i>n</i>=81) isolates were resistant to erythromycin, and 17.9% (<i>n</i>=23) were resistant to synercid. Twelve isolates (9.3%) exhibited MLSB<sub>c</sub> (constitutive) phenotype and <i>D</i>-tests identified six isolates (4.6%) with inducible resistance to clindamycin (MLSB<sub>i</sub> phenotype).</para> <para>Clindamycin is an efficient and economic lincosamide drug used for the treatment of staphylococci infection <citationref linkend="CIT0005">5</citationref>. One macrolide resistance mechanism, modification of a drug binding site on the ribosome, results in resistance to macrolides, azalides, lincosamides, and group (B) streptogramins (MLSB). MLSB phenotypes can be either constitutive (MLSB<sub>c</sub>) or inducible (MLSB<sub>i</sub>). The inducible resistance to clindamycin (MLSB<sub>i</sub>) in MRSA can severely compromise therapy and can result in failure of clindamycin treatment of MRSA infections when non-suitable therapy (e.g. erythromycin) is given <citationref linkend="CIT0006">6</citationref>. MLSB<sub>i</sub> strains can be successfully treated with clindamycin; however MLSB<sub>i</sub> can complicate therapy when MLSB<sub>i</sub> phenotype-switching into MLSB<sub>c</sub> occurs possibly due to mutation, in the absence of macrolide inducers <citationref linkend="CIT0006">6</citationref>. Clindamycin can still be used for MRSA infections in our hospitals. <citationref linkend="CIT0007">7</citationref> However, susceptibility testing for the detection of inducible resistance to clindamycin should be routinely performed <citationref linkend="CIT0007">7</citationref> <citationref linkend="CIT0008">8</citationref>.<br/> <br/> <i>Mohamed O. Ahmed</i> <br/>Department of Microbiology<br/>Biotechnology Research Centre<br/>Tripoli, Libya<br/>and<br/>Department of Veterinary Microbiology and Parasitology<br/>Faculty of Veterinary Medicine<br/>AlFateh University<br/>Tripoli, Libya<br/>Email: mhmd73@lttnet.net<br/> <br/> <i>Mohamed H. Alghazali and Abdelalbaset</i> <i>R. Abuzweda</i> <br/>Department of Microbiology<br/>Biotechnology Research Centre<br/>Tripoli, Libya<br/> <br/> <i>Samira G. Amri</i> <br/>Burns and Plastic Surgery Centre<br/>Tripoli, Libya<br/> </para> </section1> <ackno> <title>Acknowledgements Thanks to Dr. Mohamed El Sherif the director of National Authority for Scientific Research, Tripoli, Libya for the unlimited support and Dr. Keith E. Baptiste from the University of Copenhagen, Denmark. References Robinson JO Pearson JC Christiansen KJ Coombs GW Murray RJ. Community-associated versus healthcare-associated methicillin-resistant Staphylococcus aureus bacteraemia: a 10-year retrospective review Eur J Clin Microbiol Infect Dis. 2009 28 353 61 Gould IM. The clinical significance of methicillin-resistant Staphylococcus aureus J Hosp Infect. 2005 61 277 82 Andrews JM. BSAC standardized disc susceptibility testing method (version 5) J Antimicrob Chemother. 2006 58 511 29 Fiebelkorn KR Crawford SA McElmeel ML Jorgensen JH. 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