Barker J, Scaife H, Brown M R
Department of Biomedical Sciences, Sheffield Hallam University, United Kingdom.
Antimicrob Agents Chemother. 1995 Dec;39(12):2684-8. doi: 10.1128/AAC.39.12.2684.
The antimicrobial susceptibilities of Legionella pneumophila isolates grown either in U937 human monocytic cells or in Acanthamoeba polyphaga were studied after release from the host cells without further subculture. Time-survival studies showed that exposure of L. pneumophila cells, gown exclusively in vitro, to 5 micrograms of rifampin per ml resulted in at least 99% killing after 6 h and no detectable survivors at 24 h. Similar rates of killing were observed for in vitro-grown cells tested by exposure to ciprofloxacin. Conversely, time-survival studies revealed that macrophage-grown and amoeba-grown cells were ca. 1,000-fold more resistant to the activities of both drugs. Macrophage-grown cells treated with 5 micrograms of rifampin per ml showed 70 and 62% survival after 6 and 24 h, respectively. Intracellularly grown legionellae were also highly resistant to erythromycin (8 microgram/ml). After 24 h of exposure to the drug, there was 70 and 60% survival for amoeba-grown and macrophage-grown legionellae, respectively, whereas in vitro-grown cells showed a 2-log10 reduction in viable count. when intracellularly grown L. pneumophila cells were subcultured in broth for 48 h, they reverted to the phenotype characteristic of in vitro growth. Morphologically, the cells were larger than their intracellularly grown counterparts and resistance characteristics were lost. The susceptibilities of the subcultured cells to all three drugs were similar to those of Legionella cells grown exclusively in vitro. In view of these findings, the successful treatment of Legionnaires disease may be related as much to the resistance phenotype induced by intramacrophage growth as to the ability of the antibiotic to enter phagocytic cells.
对从宿主细胞释放后未经进一步传代培养的嗜肺军团菌分离株进行了抗菌药敏性研究，这些分离株分别在U937人单核细胞或多噬棘阿米巴中生长。时间存活研究表明，仅在体外生长的嗜肺军团菌细胞暴露于每毫升5微克利福平后，6小时后至少99%被杀死，24小时后无存活菌检出。通过暴露于环丙沙星测试的体外生长细胞也观察到类似的杀灭率。相反，时间存活研究表明，在巨噬细胞中生长和在阿米巴中生长的细胞对这两种药物的活性的抗性大约高1000倍。每毫升5微克利福平处理的巨噬细胞生长的细胞在6小时和24小时后的存活率分别为70%和62%。细胞内生长的军团菌对红霉素（8微克/毫升）也具有高度抗性。暴露于该药物24小时后，在阿米巴中生长和在巨噬细胞中生长的军团菌的存活率分别为70%和60%，而体外生长的细胞活计数减少了2个对数级。当细胞内生长的嗜肺军团菌细胞在肉汤中传代培养48小时后，它们恢复到体外生长的表型特征。形态上，这些细胞比细胞内生长的对应细胞大，并且失去了抗性特征。传代培养细胞对所有三种药物的药敏性与仅在体外生长的军团菌细胞相似。鉴于这些发现，军团病的成功治疗可能与巨噬细胞内生长诱导的抗性表型以及抗生素进入吞噬细胞的能力同样相关。
