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標題: 台灣乳牛場病原性大腸桿菌抗藥性及乙內醯胺&;#37238;基因之研究
Study of Antimicrobial Resistance and β-lactamase Gene among Pathogenic Escherichia coli Isolates from Dairy farms in Taiwan
作者: 蔡哲宇
Tsai, Che-Yu
關鍵字: Dairy cow;E. coli;Antimicrobial resistance;beta-lactamases
出版社: 獸醫學系暨研究所
細菌產生抗生素之抗藥性是現代醫學嚴重的問題,對於公共衛生或是動物的健康都帶來很大的威脅。諸多研究均提出人類及動物可能經由食物鏈、直接或間接地接觸到彼此帶有抗藥性基因的細菌,使得抗藥性基因藉以互相的傳播,增加細菌間抗藥性的多樣性。在牧場中,E. coli為乳牛乳房炎、下痢、肺炎及小牛臍帶炎等之常見病原,因此為探討台灣乳牛場中E. coli之抗生素抗藥性以及抗藥性基因的情形,本實驗遂以抗生素敏感性試驗及多重引子聚合&;#37238;連鎖反應(multiplex polymerase chain reaction)方式,偵測目前牧場中使用最多的乙內醯胺類(β-lactam)抗生素的TEM (Temoniera)、SHV (sulphydryl variable)及OXA (oxacillinase)三類乙內醯胺&;#37238;(β-lactamases)抗藥性基因。本實驗自台灣9個地理區的牧場,分別自生乳樣本、下痢牛隻糞便、母牛產後子宮炎分泌物、仔牛臍帶炎病例及牛肺臟病材樣本,共分離出137株E. coli。所挑選的10 種抗生素中,抗藥性最高者為cloxacillin (87.5%)、oxytetracycline (50.0%),其次為ampicillin (35.3%);抗藥性出現率最低的藥物為florfenicol (7.4%)、cefuroxime (9.6%)及ceftiofur (11.%)。Multiplex PCR結果共檢測出76株(55.5%)帶有blaTEM-1抗藥性基因的E. coli;blaTEM-1抗藥性基因親緣關係圖顯示不同樣本來源的抗藥性基因,與其餘樣本的親緣關係相似度約在95%以外,不同樣本及牧場間彼此基因相似度都在97%以上。根據實驗結果顯示,不同牧場之間E. coli的抗藥性呈現多樣性的特徵,以blaTEM-1為實驗結果中常見的抗藥性基因型(55.47%),但並未發現SHV及OXA等相關抗藥性基因。雖然β-lactamase基因在牧場病原性E. coli中並不具有其他的TEM突變型產生,但是具致病性及抗藥性基因的病原性E. coli對於人類的健康及公共衛生仍然是很大的威脅,因此仍須持續地調查其他種類的抗藥性基因在E. coli的分佈情況。總結而言,抗生素敏感性結果顯示E. coli對於oxytetracycline的抗藥性極高(50%),建議現場獸醫師不應該再作為第一線藥物來使用,並且在使用抗生素前應該先對細菌的抗藥性特徵有充份的瞭解,才能達到有效的治療效果並且減少抗藥性細菌產生的可能。動物來源的細菌抗藥性問題已經是全世界都非常重視的議題,因此為了要對台灣牧場中E. coli抗藥性特徵及抗藥性基因的分佈情形有更清楚的瞭解,長期的調查計畫是非常有必要性的。

Antimicrobial resistance is a growing concern for public and animal health in modern medicine. Threats to public health could come from the transfer of pathogens between animals and people via direct contact or indirect contact such as through food. Escherichia coli is one of the most common pathogens which induce such as mastitis, diarrhea, pneumonia, omphalitis in dairy farms. To accurately characterize the relationship between antibiotic use and resistance in dairy farms, epidemiological definitions are needed. The aim of this study was to detect the resistance determinats by use of disk diffusion method and specific oligonucleotide primers for amplifying three β-lactamases genes: blaTEM, blaSHV, and blaOXA-1. In the result of this study, a total of 137 pathogenic E. coli was obtained from raw milk samples, diarrheic feces, omphalitis, uterine infection cases, and lung tissue samples from 63 dairy farms in Taiwan. The result of antibiotic resistance tests was showed with a large proportion of isolates resistant to ampicillin (35.3%), oxytetracycline (50.0%), and cloxacillin (87.5%). Upon testing for β-lactamases genes, the blaTEM-1 was detected in 76 strains (55.5%) from 137 E. coli isolates. However, none of these isolates contained either blaSHV or blaOXA-1 genes. Dendrograms of phylogenetic relationships with blaTEM-1 gene detected from 76 E. coli were very similar (97%-100%), except one (95%) obtained from a fecal sample. According to our results, approximately 90% of strains of E. coli revealed a variety of resistance profiles to the tested antibiotics. Multiplex antimicrobial resistance (≥ 2 antimicrobial) was observed in 77 (56.2%) of E. coli isolates. The prevalence of the antibiotic resistance patterns and the blaTEM-1 gene in our finding was lower than in other researches but the resistant trend was identically. The results may indicate that the susceptibility profile of the causal bacteria should be determined before empirical therapy is started. blaTEM-1 was the predominant β-Lactamase from gram negative isolates worldwide and the most common resistance gene among pathogenic E. coli isolated from dairy farms in Taiwan. Therefore, a long period of surveillance programs is necessary for better understanding about this bacterium and more effective therapy in diseases infected with E. coli.
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