Characterization of fusC elements in fusidic acid resistant Staphylococcus aureus and Staphylococcus hominis
Date Issued
2016
Date
2016
Author(s)
Lin, Yu-Tzu
Abstract
Fusidic acid is an antibiotic used in treatment against staphylococcal infection. Resistance to fusidic acid in Staphylococcus aureus is caused by alternation of drug target site or by protection of drug target site. In this study, we analyzed the resistance determinants in 46 fusidic acid-resistant methicillin-resistant S. aureus isolates collected from 2008 to 2010, and performed genotyping. The results showed that fusC (59%) was more common than fusA mutations (41%). The most frequent mutation sites in fusA includes L461K (N = 8) and H457Q/L461F (N = 6). Two major genotypes, spa type t037-ST239-SCCmec type III (83%) and t002-ST5- SCCmec type II (11%), were found. A novel SCC structure, termed SCCfusC, was integrated into the rlmH gene and located upstream of SCCmec and was present in all but one (26/27) fusC-carrying MRSA isolates. The SCCfusC also contained speG, which contributed to the polyamine resistance. This is the first report about MRSA isolates that carry both fusC and speG. The fusC carriage in S. hominis was more frequent than other coagulase-negative staphylococci (CoNS). To understand the flanking region of fusC in S. hominis, 31 fusC-positive S. hominis isolates were collected and analyzed the structure of fusC element. The results showed that 14 isolates carried SCCfusC, 3 carried SCC476 and 8 carried new SCC structure, SCC3390. By PFGE and MLST analysis, the S. hominis population showed a limited clonality. Moreover, the SCCfusC was found in other species of CoNS including S. hominis, S. epidermidis, S. haemolyticus and S. capitis, suggesting that SCCfusC may transfer between different species of staphylococci. In this study, there were 5 vancomycin-intermediate S. aureus (VISA) isolates recovered from a same patient. The first three isolates (NTUH-9383, NTUH-471, and NTUH-1230) were MRSA but the latest two (NTUH-6319 and NTUH-7203) were methicillin-susceptible S. aureus (MSSA) and exhibited the characteristics of small colony variants (SCVs). Two MSSA isolates also displayed resistance to daptomycin. Whole genome sequencing of NTUH-9383 and NTUH-7203 indicated that there were 13 differences, including the presence or loss of SCCmec, 8 point mutations (including mprF, cls2, clpX and fabF), a single nucleotide insertion and three IS256 insertions. The most significant difference between NTUH-6319 and NTUH-7203 was the point mutation in fabF encoding fatty acid synthesis enzyme, which may possibly correspond to small colony of NTUH-7203. By high-resolution micrographs, both NTUH-6319 and NTUH-7203 displayed the features of SCV, abnormal intercellular substance. The overall findings suggested that daptomycin treatment may cause the formation of SCV after steps of a serial of changes.
Subjects
Staphylococcus aureus
Staphylococcus hominis
fusidic acid
small colony variants
Type
thesis
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