Erythromycin resistance in coagulase-negative staphylococci clinical isolates

• Main Authors: Hsin Li, 李鑫
• Other Authors: Lee-Jene Teng
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/yzax5p

碩士 === 國立臺灣大學 === 醫學檢驗暨生物技術學研究所 === 107 === Coagulase-negative staphylococci (CoNS) are normal inhabitants of human skin and mucous membranes. They had long been considered as culture contaminants, but have become the major cause of nosocomial blood stream infection, mainly because of catheter-related infections. CoNS are often resistant to many antibiotics, such as erythromycin. In our study, 418 clinical isolates identified as CoNS by VITEK 2 or MALDI-TOF were collected from NTUH from 2015 to 2016 and identified with molecular methods, 414 of which were successfully identified as CoNS. We then analyzed their MLSB phenotype with double disk diffusion test, erythromycin resistance genes with PCR, and MIC values with agar dilution test. 263 of 414 (63.5%) isolates were resistant to erythromycin, and the four species S. epidermidis, S. capitis, S. haemoylticus and S. hominis subsp. hominis more often collected had higher resistant rate then average, resulting in the high resistant rate of CoNS. The major resistant phenotype was cMLSB (54.0%), and the major resistant genes were ermC (38.4%) and msrA/B (33.5 %). High level resistance to erythromycin was found in erm-carrying isolates (>256 μg/ml) whereas low level resistance to erythromycin in msrA/B-carrying isolates (32~64 μg/ml). Furthermore, 3 isolates of S. epidermidis (SE05, SE06 and SE07) carried the rare ermT, and compared with the known ermT-carrying plasmids our team had solved by PCR mapping. Plasmids of SE05 and SE07 resembled that of SE01, featuring the rep gene inserted by IS431. Plasmid of SE06 was composed of two sections: plasmid of SE03 (ermT, aadD and rep gene) and pHSSA1278 of S. aureus containing fosB gene. Results of S1-PFGE and southern blot indicated that there were more than one plasmids carrying ermT gene in SE05 and SE06, and their sizes were far larger then the solved 5kb-plasmids. We speculated that those 5kb plasmids may form from larger plasmids. PFGE analysis of 7 ermT-carrying S. epidermidis isolates showed that even though they were all CC5 lineage, they belonged to 6 different pulsotypes. Furthermore, during species identification we found one isolate, the NTUH_8064285, couldn’t be correctly identified by several methods, and was differentiated from known staphylococcal species on the basis of 16S rRNA, dnaJ, gap, groEL, tuf and rpoB gene sequences and MLSA. These results indicated that NTUH_8064285 may be new staphylococcal species, and that it’s closely related to S. haemolyticus.