Isolates of the Iberian clone exhibited resistance against almost all antibiotics available for MRSA ACY-1215 order therapy including clindamycin, erythromycin, gentamicin, tobramycin, tetracycline, ciprofloxacin and rifampicin. From 1996 to 2003, the Iberian clone was gradually replaced by isolates of Clonal Complex 5 (ST125 and variants; find more SCCmec type IV) related to the Paediatric clone (ST5; SCCmec type IV) [4]. Unlike the Iberian clone, these strains showed only consistent resistance to tobramycin and ciprofloxacin combined with variable resistance to clindamycin and/or erythromycin. Similar trends have been observed in other hospitals in Spain and in other countries such as

France, Germany, Belgium or Portugal, with involvement of different clonal lineages [5–10]. MRSA isolates resistant to clindamycin, erythromycin, gentamicin, tobramycin, and ciprofloxacin were detected in 2004. These isolates showed reduced susceptibility to rifampicin (RIF-R), according to the Clinical and Laboratory Standards Institute (CLSI) criteria [11]. This new phenotype buy VE-822 of multiresistance differed from that of the Iberian clone on the low level RIF-R and on the tetracycline susceptibility. The frequency of the RIF-R

MRSA isolates rapidly increased from 2004 to 2006: 25% (59/237) of all MRSA clinical isolates in 2004, 33% (67/206) in 2005, and 45% (116/256) in 2006. The percentage of RIF-R MRSA decreased to 30% (111/378) in 2007 and 25% in 2008 (75/300). Gefitinib cell line Rifampicin

cannot be used as a single agent to treat MRSA infections because of the rapid selection of resistant mutants [12, 13]. However, combinations of rifampicin with other anti-staphylococcal agents such as quinolones [14] or fusidic acid [15] could prevent the emergence of rifampicin resistance during therapy [16]. Rifampicin interacts specifically with the RNA polymerase beta-subunit encoded by the gene rpoB [12]. Rifampicin resistance in S. aureus, as in other bacteria, is associated with mutations in particular regions (cluster I and II) of the gene rpoB [13, 17]. The objectives of the present study were: i) to characterise a collection of MRSA isolates expressing this new multiresistant pattern, and to determine whether they represented a novel genotype or they were the current representatives of a previously detected clone, ii) to determine the different levels of the rifampicin resistance by disk diffusion, microdilution and E-test, and iii) to analyse mutations in the rpoB gene related to rifampicin resistance. Methods Hospital setting The Hospital Universitari de Bellvitge in Barcelona, Spain, is a nearly 900-bed tertiary care teaching centre. It is the reference hospital for a geographical area with a population of approximately 1 million inhabitants.