Molecular characterization of resistance to Rifampicin in an emerging hospital-associated Methicillin-resistant Staphylococcus aureus clone ST228, Spain

• Published in: BMC microbiology 2010-03, Vol.10 (1), p.68-68, Article 68
• Main Authors: Mick, Virginie, Domínguez, M Angeles, Tubau, Fe, Liñares, Josefina, Pujol, Miquel, Martín, Rogelio
• Format: Article
• Language: English
• Subjects: Amino acid substitution; Anti-Bacterial Agents; Antibiotics, Antitubercular - pharmacology; Bacteria; Bacterial Proteins - genetics; Bacterial Typing Techniques - methods; Cloning; Colleges & universities; Complications and side effects; Cross infection; Cross Infection - epidemiology; Cross Infection - microbiology; Diffusion; DNA-directed RNA polymerase; Dosage and administration; Drug resistance; Drug resistance in microorganisms; Drug Resistance, Bacterial; Espanya; Genotypes; Health aspects; Hospital de Bellvitge Prínceps d'Espanya; Hospitals; Humans; Infection; Methicillin-Resistant Staphylococcus aureus - drug effects; Methicillin-Resistant Staphylococcus aureus - genetics; Methicillin-Resistant Staphylococcus aureus - isolation & purification; Microbial Sensitivity Tests; Microbiology; Minimum inhibitory concentration; Molecular Epidemiology; Mutation; Nosocomial infections; Nucleic Acid Amplification Techniques - methods; Physiological aspects; Properties; Research article; Resistència als medicaments; Rifampicina; Rifampin; Rifampin - pharmacology; Risk factors; RNA polymerase; RpoB protein; Spain; Spain - epidemiology; Staphylococcal Infections - epidemiology; Staphylococcal Infections - microbiology; Staphylococcus aureus; Staphylococcus infections
• ISSN: 1471-2180; 1471-2180
• DOI: 10.1186/1471-2180-10-68

Methicillin-resistant S. aureus (MRSA) has been endemic in Hospital Universitari de Bellvitge, Barcelona, since 1990. During the 1990-95 period the Iberian clone (ST-247; SCCmec-I) was dominant. Isolates of clonal complex 5 (ST-125; SCCmec-IV) gradually replaced the Iberian clone from 1996 to 2003. A new multiresistant MRSA phenotype showing rifampicin resistance emerged in 2004 and rapidly increased from 25% in 2004 to 45% in 2006. The aims of this study were i) the molecular characterisation of rifampicin resistant MRSA isolates, ii) the study of the rifampicin resistance expression by disk diffusion, microdilution and E-test, and iii) the analysis of the rpoB gene mutations involved in rifampicin resistance. A sample of representative 108 rifampicin-resistant MRSA isolates belonged to a single PFGE genotype, ST-228, SCCmec type I and spa type t041. Of 108 isolates, 104 (96%) had a low-level rifampicin resistance (MICs, 2 to 4 mg/L) and 4 a high-level rifampicin resistance (MICs, 128 - > or = 256 mg/L). Disk diffusion and E-test methods failed to identify a low-level rifampicin resistance in 20 and 12 isolates, respectively. A low-level rifampicin resistance was associated with amino acid substitution 481His/Asn in the beta-subunit of RNA polymerase. Isolates with a high-level rifampicin resistance carried additional mutations in the rpoB gene. The emergence of MRSA clone ST228-SCCmecI, related to the Southern Germany clone, involved a therapeutical challenge for treating serious MRSA infections. Decreased susceptibility to rifampicin in MRSA strains of ST228-SCCmecI was associated with one or two specific mutations in the rpoB gene. One fifth of isolates with low-level rifampicin-resistance were missed by the diffusion methods.