O'Brien T F, DiGiorgio J, Parsonnet K C, Kass E H, Hopkins J D
Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115.
Vet Microbiol. 1993 Jun;35(3-4):243-55. doi: 10.1016/0378-1135(93)90149-2.
Plasmids of bacteria selected from different bacterial populations because they shared a distinctive antimicrobial resistance phenotype have sometimes had identical restriction fragments. Such identical plasmids are thought to belong to small and thus epidemic clones because the plasmid content of unselected resistant isolates has seemed diverse. To survey this presumed diversity and its implications for the lineage of resistance plasmids we examined the transferability, sizes and EcoR1 restriction fragment sizes of plasmids in both Escherichia coli isolated randomly from poultry raised by 16 growers as they were being processed through two plants and in isolates from the urine of women processing poultry in those plants. Forty two (24%) of 175 resistant isolates from poultry of 16 growers and 9 (26%) of 34 resistant isolates from the poultry processors transferred resistance conjugatively to varied combinations of antimicrobials. No poultry isolate had both the same expressed and the same transferred combination as any processor's isolate. The DNA bands which could be discerned in electrophoresis gels of restricted or unrestricted plasmid extracts of isolates or their transconjugants from 156 of the poultry and 24 of the poultry processors appeared diverse. Pairs of related-appearing plasmids were seen in consecutive isolates of poultry from each of two growers and in one pair from different growers. One set of identical-appearing plasmids was seen in 3 consecutive isolates from poultry of one grower, others in 2 consecutive isolates from a second grower's poultry, in 2 non-consecutive isolates of a third grower's, and in single isolates from poultry of 2 different growers. None of the plasmids from any of the human isolates appeared related to those from any other human isolate or to those of any poultry isolate. These results indicate that resistance plasmids are highly diverse and that all but two of the exceptions to complete diversity in the isolates surveyed here could be ascribed to cross colonization within flocks of individual poultry growers. Also, while none of the plasmids in the poultry isolates appeared ancestral to any of plasmids in the poultry processors' isolates, their diversity indicates that those sampled plasmids would be only a very small fraction of the total number of different plasmids in bacteria colonizing poultry processed at that time or earlier.
从不同细菌群体中挑选出的细菌质粒，因其具有独特的抗微生物耐药表型，有时会有相同的限制性片段。这种相同的质粒被认为属于小型的、因而具有流行性的克隆，因为未挑选的耐药菌株的质粒含量似乎多种多样。为了调查这种假定的多样性及其对抗性质粒谱系的影响，我们检测了从16个养殖户饲养的家禽中随机分离出的大肠杆菌以及在这两家工厂加工家禽的女性尿液中分离出的大肠杆菌中质粒的转移性、大小和EcoR1限制性片段大小。来自16个养殖户家禽的175个耐药菌株中有42个（24%），来自家禽加工人员的34个耐药菌株中有9个（26%）通过接合作用将耐药性转移到了不同的抗菌药物组合中。没有一个家禽分离株与任何加工人员的分离株具有相同的表达和转移组合。在来自156只家禽和24名家禽加工人员的分离株或其转接合子的限制性或非限制性质粒提取物的电泳凝胶中可以分辨出的DNA条带看起来多种多样。在来自两个养殖户的家禽的连续分离株中以及来自不同养殖户的一对分离株中发现了成对的外观相关的质粒。在来自一个养殖户家禽的3个连续分离株中发现了一组外观相同的质粒，在来自第二个养殖户家禽的2个连续分离株中、在第三个养殖户的2个非连续分离株中以及在来自2个不同养殖户家禽的单个分离株中也发现了其他外观相同的质粒。来自任何人类分离株的质粒都与来自任何其他人类分离株的质粒或任何家禽分离株的质粒无关。这些结果表明，抗性质粒高度多样，并且在这里调查的分离株中，除了两个例外，所有完全多样性的例外情况都可归因于个体家禽养殖户鸡群内的交叉定植。此外，虽然家禽分离株中的质粒没有一个似乎是家禽加工人员分离株中任何质粒的祖先，但它们的多样性表明，那些抽样的质粒只是当时或更早加工的家禽中定殖细菌中不同质粒总数的极小一部分。
