犬源大肠杆菌分离株对四环素类药物耐药性的检测

Detection of Resistance of Dog-derived Escherichia coli Isolates to Tetracyclines

用微量肉汤倍比稀释法测定四环素类等抗菌药物对53株犬源大肠杆菌分离株的最小抑菌浓度（MIC）,用PCR和DNA测序方法检测犬源大肠杆菌中四环素耐药基因（tet基因）,了解tet基因的流行情况、分析试验菌对四环素类药物的耐药机制。结果表明：25%的分离菌呈多重耐药现象,最多对8种药物耐药。分离菌对四环素类中的土霉素、四环素、多西环素耐药率高,耐药率介于69.8%~86.1%。基因检测结果显示,犬源大肠杆菌中共检测到5种tet基因,分别为tet A、tet B、tet C、tet G、tet L基因,都属于外排泵基因,未检测到核糖体保护基因。其中tet G基因的检出率最高,共检出39株（检出率达70%）,有40个菌株同时检出2种或2种以上tet基因,有3株同时检测到4种tet基因,仅有4株未检测到任何tet基因。研究表明：犬源大肠杆菌对常用抗菌药物的耐药情况十分严重,tet基因的携带率高,主动外排是犬源大肠杆菌对四环素类耐药的主要机制。

The MICs of tetracyclines and other antibacterial agents against 53 strains of Escherichia coli isolated from dogs were determined by using broth microdilution, and the presence of tetracycline-resistant genes （tet genes） in these strains was investiga- ted through PCR and DNA sequencing. The aims of this study are to understand the prevalence of tet genes in the tested strains, and to analyze their resistant mechanism to tetracyclines. The results showed that 25% of E. coli isolates from dogs expressed multidrug resistance phenotypes, and were resistant to at most 8 kinds of antibacterial drugs. The resistant rate of the tested isolates to oxytetra- cycline, tetracycline and doxycycline was high, and ranged from 69.8% to 86.1%. PCR and DNA sequencing indicated that 5 tet genes （tetA ,tetB ,tetC ,tetG andtetL） were detected in dog-derived E. coli isolates, and they all belonged to efflux-pump genes; while ribosomal protection genes were not found. Among the tet genes detected, the detected rate of tetG gene was the highest （73.60%, 39/53）. Furthermore, 40 strains carried two or more than two tet genes each; 3 strains carried four tet genes each; only 4 strains did not carry anytet gene. These results revealed that the resistance of dog-derived E. coli isolates to the common antibacte- rial agents was very serious, and the detected rate of tet genes was high, suggesting that active efflux is the main mechanism of re- sistance of dog-derived E. coli isolatesto tetracyclines.