2015.07.28，Professor Sun Baolin Published a paper entitled:“Modulation of ccrAB Expression and SCCmec Excision by an Inverted Repeat Element and SarS in Methicillin-Resistant Staphylococcus aureus” in Antimicrobial Agents and Chemotherapy
Author：Zhang Shijie、Ma Ronghua、Liu Xiaoyu、Zhang Xu、Sun Baolin
Methicillin-resistant Staphylococcus aureus (MRSA) is a notorious human pathogen that can cause a broad spectrum of infections. MRSA strains are resistant to almost the entire family of β-lactam antibiotics due to the acquisition of staphylococcal cassette chromosome mec (SCCmec). The chromosome cassette recombinases A and B encoded by ccrAB genes located on SCCmec play a key role in the excision of SCCmec. Studies have shown that ccrAB genes are only expressed in a minority of cells, suggesting the involvement of a subtle regulatory mechanism in ccrAB expression, which has not been uncovered. Here, we found that an inverted repeat (IR) element, existing extensively and conservatively within the ccrAB promoter of different SCCmec types, played a repressive role in ccrAB expression and SCCmec excision in MRSA strain N315. Substitution of the IR sequence led to a significant increase in ccrAB expression and curing of SCCmec from strain N315 cells. In addition, we identified the transcriptional regulator SarS using DNA-affinity chromatography, and further demonstrated that SarS can bind to the IR sequence and upregulate ccrAB expression and SCCmec excision. These findings reveal a molecular mechanism regulating ccrAB expression and SCCmec excision, and may provide mechanic insights into the lateral transfer of SCCmec and spread of antibiotic resistance in S. aureus.
DOI information: 10.1128/AAC.01041-15