1. 15th International Symposium on Staphylococci and Staphylococcal Infections 26th-30th August Lyon, France
Prevalence and mechanism of resistance among Staphylococcus aureus to MLSB antibiotics in Greece
Styliani Sarrou1, Apostolos Liakopoulos1, Eleanna Drougka 2,3, Iris Spiliopoulou2,3, Efi Petinaki1
 1 Department of Microbiology, University Hospital of Larissa, Larissa, Greece;2 Department of Microbiology, School of Medicine, University of Patras, Patras, Greece; 3 National Reference Laboratory for Staphylococci, Patras, Greece;
Objectives: To determine the rate and the molecular basis of resistance among Staphylococcus aureus in MLSB antibiotics (macrolides, lincosamides and streptogramins B) in Greece.
Introductions: There are three mechanisms involved in erythromycin resistance: (i) the use of an energy-dependent efflux (msrA gene), (ii) production of inactivating enzymes (ere genes) and (iii) alteration of 23S rRNA methylases erythromycin resistance (erm genes). This third mechanism of resistance is also associated with the cross resistance to other macrolides, lincosamides and type B streptogramin (MLS B ) (1).On the other hand, lincomycin resistance is due either to 23S rRNA alteration (erm genes) either to enzyme inactivation (lnu genes), while, streptogramin B resistance is due to efflux proteins (vga genes), 23S rRNA alteration (erm genes) and enzyme inactivation (vat genes) (2).
Materials-Methods: A total of 709 S. aureus consecutively isolated from clinical specimens during 2011 in two tertiary Greek care hospitals [University Hospital of Larissa-Central Greece (UHL) and University Hospital of Patras, Southwestern Greece, (UHP)] were included. Identification and susceptibility testing was performed by the automated Vitek II System. Double disk synergy and Hodge tests were performed in order to distinguish M, L and MLSB inducible phenotypes. The detection of erm, ere,msrA, lnu, vat and vga genes was assessed by PCR (3). The clonality of isolates was determined by pulse field gel electrophoresis and multi locus sequence typing (4,5).
Results: Among 329 S. aureus (151 MRSA and 178 MSSA), originated from UHL, 134 (89 MRSA and 45 MSSA) exhibited resistance to erythromycin (41%), and 121 (85 MRSA and 36 MSSA) to clindamycin (36.7%). In more details, 54 MRSA and 8 MSSA exhibited the MLSB constitutive phenotype, 31 MRSA and 27 MSSA exhibited the MLSB inducible phenotype, 4 MRSA and 10 MSSA exhibited the M phenotype and 1 MSSA exhibited L phenotype.
ER CCR ER CCR
Among 380 S. aureus (162 MRSA and 218 MSSA) from the UHP, only 36 MRSA (9.4%) were resistant to erythromycin; 6, 13 and 17 exhibited MLSB inducible, MLSB constitutive and M phenotypes respectively. Genes ermA and ermC correlated with MLSB, phenotype, either inducible or constitutive, msra with M phenotype, while lnuB gene described for the first time in S. aureus, correlated with L-phenotype. No coexistence of two genes was observed in any isolate. Molecular typing revealed that the majority of erythromycin-resistant MRSA belonged to ST239 and ST80 that predominate in our institutions.
Conclusions: Significant differences on the resistance rates to MLSB antibiotics were observed between the Central and Southwestern Greece. In Central Greece, this resistance rate dramatically increased from 16.4% in 2000 to 41% in 2011 (6), a result that partially could be explained by the extensive usage of clindamycin to treat soft and skin staphylococcal infections.
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