George A M, Levy S B
J Bacteriol. 1983 Aug;155(2):531-40. doi: 10.1128/jb.155.2.531-540.1983.
Increasing levels of resistance to tetracycline and to a number of other unrelated antibiotics, including chloramphenicol, beta-lactams, puromycin, and nalidixic acid, occurred in Escherichia coli after 50 to 200 generations of growth in the presence of subinhibitory concentrations of tetracycline or chloramphenicol. In the absence of selective pressure, resistances fell to low levels within 100 generations of growth. This amplification of resistance was observed in laboratory and naturally occurring E. coli strains as well as in polA and recA strains. With the exception of previously identified cmlA and cmlB mutations, tetracycline or chloramphenicol resistances were not P1 transducible. Coincident with the emergence of resistance was the appearance of a previously cryptic energy-dependent efflux system for tetracycline. The expression of resistance phenotypes and the tetracycline efflux system were temperature sensitive at 42 degrees C.
在亚抑制浓度的四环素或氯霉素存在下生长50至200代后，大肠杆菌对四环素以及包括氯霉素、β-内酰胺类、嘌呤霉素和萘啶酸在内的许多其他不相关抗生素的耐药水平不断增加。在没有选择压力的情况下，耐药性在100代生长内降至低水平。在实验室菌株、自然发生的大肠杆菌菌株以及polA和recA菌株中均观察到了这种耐药性的扩增。除了先前鉴定出的cmlA和cmlB突变外，四环素或氯霉素耐药性不能通过P1进行转导。与耐药性出现同时发生的是，出现了一种先前隐匿的、能量依赖的四环素外排系统。耐药表型和四环素外排系统的表达在42℃时对温度敏感。
