中文摘要：

为调查和分析猪肠道菌的氨基糖苷类药物耐药机制，用PCR及序列分析方法检测鉴定2个猪肠道菌中4种16S rRNA甲基化酶耐药基因rmtAr、mtBr、mtC和armA和10种氨基糖苷钝化酶基因，用接合试验研究rmtB基因和10种氨基糖苷钝化酶基因的水平转移机制，用微量稀释法测定携带rmtB基因的分离菌及其接合子对20种抗菌药物的敏感性。结果，从分离的152株猪肠道菌中共检测到49株（32.3%）rmtB阳性菌，其中48株为大肠埃希氏菌，1株为阴沟肠杆菌，未检出其它16S rRNA甲基化酶编码基因。49株rmtB阳性菌中检测到7种氨基糖苷类钝化酶基因，检出率从高到低依次是aac（3）-Ⅱ（87.8%）、aph（3′）-Ⅶ（79.6%）、aph（3′）-Ⅱ（77.6%）、aadA1（34.7%）、aac（6′）-Ib（14.3%）a、ac（3）-Ⅳ（10.2%）和aph（4）-Ⅰ（8.2%）。46株rmtB阳性菌可以通过接合试验将rmtBa、ac（3）-Ⅱ、aph（3′）-Ⅶ、aph（3′）-Ⅱ和aadA基因传递给受体菌E.coliC600和E.coli488 Rifr，接合率从3.0×10^-6-4.6×10^-13不等。所有rmtB阳性菌株及其接合子对卡那霉素、阿米卡星、妥布霉素、西梭米星、萘替米星、庆大霉素6种氨基糖苷类抗生素均高度耐药（MIC≥512μg.mL-1）。研究结果表明，rmtB基因和氨基糖苷钝化酶基因广泛存在于两猪场，它们共同介导猪源肠道菌对庆大霉素、阿米卡星等氨基糖苷类药物的高度耐药。rmtB基因与aac（3）-Ⅱ、aph（3′）-Ⅶ、aph（3′）-Ⅱ和aadA基因位于同一接合性质粒上，共同传播氨基糖苷类的耐药性。

英文摘要：

Abstract： To investigate the resistance to aminoglycosides in Enterobacteriaceae isolated from two pig farms, Enterobacteriaceae isolated from two pig farms were screened for the presence of the rmtA, rmtB, arrnA,rmtC genes and 10 aminoglycosides modifying enzyme genes by PCR and se- quencing. Conjugation experiments were carried out to study the horizontal transfer mechanism of rmtB and 10 AME genes. All isolates and their transconjugants were tested for susceptibility to 20 antimicrobial agents by the broth microdilution method. Of 152 Enterobacteriaceae isolates re- covered from two pigs, 49 strains（32.3%） were positive for the rmtB gene, including 48 strains of Escherichia coli and a single isolate of Enterobacter cloacae. No other kind of the 16S rRNA methylasegenes was detected. 7 AMES genes including aac（3）-Ⅱ、aph（3′）-Ⅶ、aph（3′）-Ⅱ, aadA1 ,aac （ 6＇） -Ib, aac （ 3 ） -Ⅳ and aph （ 4 ） - Ⅰ were presented in 49 rmtB-positive isolates. The present rate of the 7 AMES genes were ordered as 93.5% （aac（3）-Ⅱ）, 79.6% （aph（3＇）-Ⅱ）, 77.6%（aph（3＇）-Ⅶ） ,34. 5%（aad A1）,14. 3%（aac（ 6＇）-Ib）,10. 2%（aac（3）-Ⅳ）and 8.2%（aph （ 4 ） -Ⅰ）. Total of 46 rmtB-positive isolates transferred their rrntB, aac （3） - Ⅱ , aph （3＇） - Ⅶ ,aph （3＇）-Ⅱ and aad A1 easily to recipients of E. coli C600 and E. coli 488 Rifr. Conjugative transfer frequencies varied from 3.0 × 10^-6 to 4.6 × 10^-13 transconjugants per recipient. All 49 rmtB-positive isolates and 46 transconjugants showed extraordinarily high-level resistance to 4,6-substituted deoxystreptamine （MICs, 〉512ug·mL^-1） and other aminoglycosides . The results indicated that 16S rRNA methylases RmtB and 10 AMEs were widely spread in veterinary clinical isolates from two pig farms. They mediated the high-level resistance to 4, 6-substituted deoxystreptamine and other aminoglycosides. They located on the conjugated plasmid and transfer resistance of aminogly