We examined the intracellular activities of 11 antimicrobial agents against Legionella pneumophila using a human monocyte-derived cell line, THP-1. Colony counting and microscopic examination of L. pneumophila co-incubated with THP-1 cells (5 × 105 cells/well) were performed. Both extra- and intra-cellular multiplication of L. pneumophila were observed and were dependent on the inoculum of L. pneumophila in the culture; L. pneumophila did not grow in the cell culture medium alone. Light microscopic examination confirmed that extracellular L. pneumophila originated from THP-1 cells disrupted by bacterial multiplication. L. pneumophila multiplied by 3–4 logs after 24 h incubation with THP-1 cells and their number remained stable at 106–107 cfu/mL until 72 h. The results of viability studies using four antimicrobial agents—ciprofloxacin, erythromycin, minocycline and rifampicin—demonstrated that our system was suitable for the intracellular activity assay. We used a concept of ‘minimum extracellular concentration inhibiting intracellular multiplication’ (MIEC) to evaluate the intracellular activity of antimicrobial agents. The MIECs of three β-lactams were markedly higher than their conventional MICs while those of macrolides, quinolones, rifampicin and minocycline were similar to their MICs. Our results suggest that evaluation of the clinical efficacy of drugs against L. pneumophila should include determination of their intracellular activity against the bacteria, which could be measured using our assay system in THP-1 cells.
我们利用人体单核细胞衍生
细胞系 THP-1 研究了 11 种抗菌剂对嗜肺军团菌的细胞内活性。我们对与 THP-1 细胞(5 × 105 个细胞/孔)共培养的嗜肺军团菌进行了菌落计数和显微镜检查。观察到嗜肺叶球菌在细胞外和细胞内繁殖,这取决于
培养基中的嗜肺叶球菌接种量;嗜肺叶球菌不会单独在
细胞培养基中生长。光学显微镜检查证实,细胞外的嗜肺叶球菌来自被细菌繁殖破坏的 THP-1 细胞。使用四种抗菌剂--
环丙沙星、
红霉素、
米诺环素和
利福平进行的存活率研究结果表明,我们的系统适用于细胞内活性检测。我们使用 "抑制细胞内繁殖的最小细胞外浓度"(MI
EC)的概念来评估抗菌剂的细胞内活性。三种β-内酰胺类药物的 MI
ECs 明显高于其常规 MICs,而大环
内酯类、喹诺
酮类、
利福平和
米诺环素的 MI
ECs 与其 MICs 相近。我们的研究结果表明,在评估抗嗜肺病毒药物的临床疗效时,应包括测定这些药物对该细菌的细胞内活性。