Characterization of antibiotic resistance genes among staphylococci isolated from ready-to-eat food

• Main Authors: Yu-Ting Wang, 王鈺婷
• Other Authors: Lee-Jene Teng
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/8z7thh

博士 === 國立臺灣大學 === 醫學檢驗暨生物技術學研究所 === 107 === This study investigated antibiotic resistance of staphylococci isolated from 1128 samples of high-circulating RTE foods in Taiwan. A total of 111 Staphylococcus aureus and 709 coagulase-negative staphylococci (CoNS) comprising 23 species were isolated. The prevalence of S. aureus differed in various category of RTE foods, highest in fresh-cut fruits/vegetables (20.5%) and lowest in low-water activity (LWA) foods (0.7%). The overall staphylococcal contamination was highest in fresh-cut fruits/vegetables (62.2%), in which multiple isolates (up to 10) or species (up to 6) in single sample were frequently found. Distinct distribution of species contributed to unique feature in each category. Prevalence of antibiotic-resistant S. aureus was higher in fresh-cut fruits/vegetables samples (14.2% in 127) compared to other food categories (0-7.1%). A total of 4 MRSA carrying SCCmec type IV or VT were identified (3.6% in 111), in which 3 belonged to sequence type ST59 and one was ST5. Of 41 methicillin-resistant CoNS (5.8% in 709) isolates, S. epidermidis with SCCmec containing mec complex class B and ccrA2B2 complex was most frequent. Among CoNS species, prevalence of methicillin resistance was highest in S. cohnii (2/5), but the combination of mec complex and ccr complex in SCCmec did not appear in S. aureus. In addition to S. saprophyticus and S. cohnii carrying known intrinsic genes (fusD and fusF) conferring low-level resistance to fusidic acid, low-level fusidic acid resistance also commonly found in S. xylosus, S. kloosii and S. sciuri. Novel fusB-family determinants were identified in S. xylosus, S. sciuri and S. kloosii. Owing to mobile genetic elements were not found in the neighboring region of these novel fusB-family determinants, suggesting these novel fusB-family determinants could be immobile. Other kinds of antibiotic resistance and the corresponding determinants were also found in RTE food-isolated staphylococci, including penicillin (blaZ)、tetracycline (tetK、tetL、tetM)、erythromycin (ermA、ermB、ermC、msrA/B、ermT)、gentamicin (aacA-aphD)、fusidic acid (fusB、fusC) and trimethoprim/sulfamethoxazole (dfrA、dfrG). Among CoNS species contributing main composition of staphylococcal community on RTE food, S. epidermidis and S. warneri exhibited higher rate of antibiotic resistance and carried various resistance gene compared to other species. Compared to other categories, higher contamination rate of staphylococci carrying resistance genes (including mecA) was found in fresh-cut fruits/vegetables, suggesting fresh-cut fruits/vegetables had higher potential in transmitting antibiotic resistance. Owing to S. cohnii displaying highly virulent in clinical and frequently carrying SCCmec which could not found in S. aureus, long-read sequencing was applied to discover SCCmec structures in S. cohnii isolated from rice cake (strain RC35) and ice desserts (strain I-104 and I-112), and three novel SCCmec composites were found. A composite SCCmec-SCC structure in strain RC35 was composed of an entire SCCmec TUS33 previously found in S. saprophyticus strain TSU33 isolated from human urinary tract infection, the SCCWC28 in S. cohnii WC28 isolated from wound specimens, and a series of ORFs including staphyloxanthin crtOPQMN operon common in some staphylococcal species. The structure in strain I-104 included an SCCI-104-up carrying ccrA1B3 complex, both which and is upstream 8 kb region displayed high identity to part of SCCAI16 found in S. pseudintermedius isolated from dog, and a composite SCCmec-SCC structure found in strain RC35. The strain I-112 harbored an SCCmec (an SCCmecTSU33 and the 3’ portion of SCCI-104-up), followed by a large SCC containing ccrA1B7 complex, the genes for virulence and resistance to antibiotics and environmental stimuli, and the tail region shared by SCCRC35. The region surrounding the class A mec complex was conserved in the above strains. Moreover, the tail regions of SCCmec-SCC composites in 3 MR-S. cohnii contained crtOPQMN operon, which was also found in S. cohnii isolated from clinical settings and healthy people’s hands and MR-S. saprophyticus isolates from ready-to-eat foods. The colony appearance of S. cohnii containing crtOPQMN operon displayed significant yellow. Absorbance at 465 nm was significantly higher in pigment extracted from S. cohnii carrying crtOPQMN operon than that from S. cohnii without crtOPQMN operon. Compared to S. cohnii ATCC49330 without crtOPQMN operon, S. cohnii RC35 displayed notably more resistant under treatment of 1.5% hydrogen peroxide, suggesting crtPOQMN operon could be functional. This is the first description of novel SCCmec composites in food-isolated S. cohnii, in which the copresence of SCCmecTUS33 and SCCWC28 and novel SCC structure was found. This study first identified crtOPQMN operon on SCC structure, suggesting crtOPQMN operon could transmit among some staphylococci and provide the ability to defense host innate immune system.