Mays T D, Smith C J, Welch R A, Delfini C, Macrina F L
Antimicrob Agents Chemother. 1982 Jan;21(1):110-8. doi: 10.1128/AAC.21.1.110.
Resistance to tetracycline and lincosamide antibiotics was transferred en bloc from a strain of Bacteroides fragilis (V503) to a plasmidless strain of Bacteroides uniformis (V528) during in vitro filter matings. Resistance transfer was detected at frequencies of 10(-5) to 10(-6) drug-resistant progeny per input donor cell and was dependent on cell-to-cell contact of donors and recipients. Transfer was insensitive to DNase and was not mediated by chloroform- or filter-sterilized donor broth cultures. A determinant for resistance to cefoxitin in V503 was not transferred in this system. V503 contained a 3.7 x 10(6)-dalton plasmid (pVA503). Drug-resistant progeny of V503 x V528 matings usually contained pVA503, but up to 20% of the total progeny of such crosses were plasmid free. Filter blot DNA hybridization studies (Southern method) confirmed that pVA503 was not integrated into the host chromosome of the plasmidless progeny. Drug-resistant progeny from V503 x V528 matings (with or without pVA503) conjugally transferred clindamycin resistance an tetracycline resistance to a suitable recipient strain. None of the drug resistance determinants of V503 were affected by treatment with standard plasmid curing regimens, and methods designed to detect very large plasmid molecules failed to suggest the involvement of extrachromosomal DNA in this resistance transfer system. The well-characterized Bacteroides R plasmid, pBF4 (conferring clindamycin resistance), was found to share hybridizing sequences with bulk cellular V503 DNA when examined by filter blot hybridization. Similarly sized sequences were found in drug-resistant progeny recovered from matings. Neither of the two pBF4 derivatives carrying deletions that abolished clindamycin resistance hybridized with V503 DNA.
在体外滤膜交配过程中，脆弱拟杆菌（V503）菌株对四环素和林可酰胺类抗生素的耐药性被整体转移至无质粒的单形拟杆菌（V528）菌株。耐药性转移的检测频率为每输入一个供体细胞产生10^(-5)至10^(-6)个耐药后代，且依赖于供体和受体细胞间的接触。转移对DNA酶不敏感，也不是由氯仿或滤膜除菌的供体肉汤培养物介导的。V503中对头孢西丁的耐药决定簇在该系统中未被转移。V503含有一个3.7×10^6道尔顿的质粒（pVA503）。V503×V528交配产生的耐药后代通常含有pVA503，但此类杂交后代总数中高达20%不含质粒。滤膜印迹DNA杂交研究（Southern法）证实pVA503未整合到无质粒后代的宿主染色体中。V503×V528交配产生的耐药后代（无论有无pVA503）将克林霉素耐药性和四环素耐药性接合转移至合适的受体菌株。V503的任何耐药决定簇都不受标准质粒消除方案处理的影响，且旨在检测非常大的质粒分子的方法未表明该耐药转移系统中有染色体外DNA参与。通过滤膜印迹杂交检测发现，特征明确的拟杆菌R质粒pBF4（赋予克林霉素耐药性）与V503大量细胞DNA有杂交序列。在交配获得的耐药后代中也发现了大小相似的序列。携带消除克林霉素耐药性缺失的两种pBF4衍生物均未与V503 DNA杂交。
