Antibiotic resistance and molecular characterization of clinical isolates of methicillin-resistant coagulase-negative staphylococci isolated from bacteremic patients in oncohematology O. Bouchami & W. Achour & M. A. Mekni & J. Rolo & A. Ben Hassen Received: 22 September 2010 / Accepted: 18 January 2011 # Institute of Microbiology, Academy of Sciences of the Czech Republic, v.v.i. 2011 Abstract Polymerase chain reaction (PCR) amplification of antibiotic resistance genes as well as staphylococcal cassette chromosome mec (SCCmec) typing and pulsed- field gel electrophoresis (PFGE) of SmaI macrorestriction fragments of genomic DNA were used to characterize 45 methicillin-resistant coagulase-negative staphylococci (MRCoNS) isolates responsible of bacteremia recovered in patients at the Bone Marrow Transplant Centre of Tunisia in 1998–2007. Among the 45 MRCoNS isolates, Staphylococcus epidermidis was the most prevalent species (75.6%) followed by Staphylococcus haemolyticus (22.2%) and Staphylococcus hominis (2.2%). Extended susceptibil- ity profiles were generated for MRCoNS against 16 antimicrobial agents. Out of 45 mecA-positive strains, 43 (95.6%) were phenotypically methicillin-resistant and two (4.4%) were methicillin-susceptible. The msr(A) was the most prevalent gene (13 isolates; 48.1%) among erythromycin-resistant isolates. The erm(C) was found alone in seven (25.9%) or in combination with both erm (A) and erm(B) in two (7.4%) isolates. The aac(6′)-Ie-aph (2″)-Ia was the most prevalent gene among aminoglycoside- resistant isolates, detected alone in 14 isolates (33.3%) isolates, in combination with ant(4′)-Ia in 18 (42.8%) isolates, in combination with aph(3′)-IIIa in four (9.5%) or with both ant(4′)-Ia and aph(3′)-IIIa in two (4.7%) isolates. The ant(4′)- Ia was detected in three (7.1%) isolates and the aph(3′)-IIIa in one (2.4%) isolate. Among tetracycline-resistant isolates, six (85.7%) strains harbored the tet(K) gene and one (14.3%) strain carried tet(K) and tet(M) genes. SCCmec types IV (31%) and III (24.5%), the most prevalent types detected, were found to be more resistant to non-β-lactam antibiotics. A wide diversity of isolates was observed by PFGE among MRCoNS. Abbreviations CoNS Coagulase-negative staphylococci CVC Central venous catheter MLS B Resistance to macrolides, lincosamides, and streptogramin B (other than erythromycin) MRCoNS Methicillin-resistant coagulase-negative staphylococci PCR Polymerase chain reaction PFGE Pulsed-field gel electrophoresis SCCmec Staphylococcal cassette chromosome mec Coagulase-negative staphylococci (CoNS) are the largest cause of bloodstream and central venous catheter (CVC)- related bloodstream infections among patients with hemato- logical disorders. To a large extent, this results from their ability to accumulate antibiotic resistance determinants (Worth and Slavin 2009). Methicillin-resistant staphylococ- cal strains have acquired and integrated into their genome the staphylococcal cassette chromosome mec (SCCmec), which O. Bouchami : W. Achour : M. A. Mekni Laboratory Department, Centre National de Greffe de Moelle Osseuse, Tunis, Tunisia J. Rolo : A. B. Hassen Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa (ITQB/UNL), Oeiras, Portugal O. Bouchami (*) Service des laboratoires, Centre National de Greffe de Moelle Osseuse, Rue Djebel Lakhdhar, Bab Saadoun, 1006 Tunis, Tunisia e-mail: onsboucham@yahoo.fr Folia Microbiol DOI 10.1007/s12223-011-0017-1