Increasing antibiotic resistances and a lack of new antibiotics render the treatment of Gram-negative bacterial infections increasingly difficult. Therefore, additional approaches are being investigated. Macrolides are not routinely used against Gram-negative bacteria due to lack of evidence of in vitro effectiveness. However, it has been shown that Pseudomonas spp. are susceptible to macrolides in liquid RPMI-1640 and clinical data suggest improvement in patients' outcomes. So far, these findings have been hardly applicable to the clinical setting due to lack of routine low-complexity antimicrobial susceptibility testing (AST) for macrolides. We therefore optimized and compared broth microdilution and disk diffusion AST. Multidrug-resistant Gram-negative bacteria (Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Pseudomonas aeruginosa) were tested for azithromycin susceptibility by disk diffusion and broth microdilution in Mueller-Hinton and RPMI-1640 media. Azithromycin susceptibility of Enterobacteriaceae and a subgroup of P. aeruginosa increased significantly on RPMI-1640 agar compared to Mueller-Hinton agar. Further, a significant correlation (Kendall, τ, p) of zone diameters and minimal inhibitory concentrations (MICs) was found on RPMI-1640 agar for E. coli (-0.4279, 0.0051), E. cloacae (-0.3783, 0.0237) and P. aeruginosa (-0.6477, <0.0001). Performing routine disk diffusion AST on RPMI-1640 agar may lead to the identification of additional therapeutic possibilities for multidrug-resistant bacterial infections in the routine clinical diagnostic setting.

中文翻译：

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通过纸片扩散测试评估 RPMI-1640 琼脂上多重耐药革兰氏阴性菌对阿奇霉素的敏感性增加。


抗生素耐药性的增加和新抗生素的缺乏使得革兰氏阴性细菌感染的治疗变得越来越困难。因此，正在研究其他方法。由于缺乏体外有效性的证据，大环内酯类药物并不常规用于对抗革兰氏阴性菌。然而，已经表明假单胞菌属。对液体 RPMI-1640 中的大环内酯类药物敏感，临床数据表明患者的预后有所改善。到目前为止，由于缺乏大环内酯类药物的常规低复杂性抗菌药物敏感性测试（AST），这些发现很难应用于临床。因此，我们优化并比较了肉汤微量稀释法和纸片扩散 AST。通过纸片扩散和肉汤微量稀释在 Mueller-Hinton 和 RPMI-1640 介质中测试多重耐药革兰氏阴性菌（大肠杆菌、阴沟肠杆菌、肺炎克雷伯菌、铜绿假单胞菌）对阿奇霉素的敏感性。与 Mueller-Hinton 琼脂相比，RPMI-1640 琼脂上肠杆菌科和铜绿假单胞菌亚群的阿奇霉素敏感性显着增加。此外，在 RPMI-1640 琼脂上发现大肠杆菌 (-0.4279, 0.0051)、阴沟肠杆菌 (-0.3783, 0.0237) 和铜绿假单胞菌（-0.6477，<0.0001）。在 RPMI-1640 琼脂上进行常规纸片扩散 AST 可能会导致在常规临床诊断环境中识别多重耐药细菌感染的其他治疗可能性。