School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales 2052, Australia.
School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales 2052, Australia.
Cont Lens Anterior Eye. 2023 Jun;46(3):101819. doi: 10.1016/j.clae.2023.101819. Epub 2023 Feb 1.
Tolerance to antibiotics may occur due to changes in bacterial growth patterns and can be a precursor to development of resistance. However, there is a lack of information on the ability of ocular bacteria isolates to develop tolerance. This paper explores the tolerance to 8 different antibiotics of 61 microbial keratitis isolates of Pseudomonas aeruginosa from Australia and India using the MBC/MIC ratio, with tolerance defined by a ratio ≥ 32, and tolerance to ciprofloxacin by an agar diffusion assay.
Antibiotics used were ciprofloxacin, levofloxacin, gentamicin, tobramycin, piperacillin, imipenem, ceftazidime and polymyxin B. Isolates were sourced from microbial keratitis infections in Australia and India. Minimum bactericidal and minimum inhibitory concentration (MBC and MIC) were obtained using broth microdilution and compared to breakpoints from the Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) to determine bacterial susceptibility. Tolerance was assessed as MBC/MIC ≥ 32. An alternative method for tolerance detection (TD) was assessed with 13P. aeruginosa sensitive isolates by agar disk diffusion assay of ciprofloxacin followed by application of glucose to the agar and observation of re-growth of colonies.
Thirty-three isolates were resistant to imipenem, 20 to ciprofloxacin, 14 to tobramycin and piperacillin, 12 to levofloxacin and ceftazidime, 8 to gentamicin, and 5 to polymyxin B. The percentage of strains resistant to levofloxacin (7 vs 30 %; p = 0.023), gentamicin (0 vs 24 %; p = 0.005) and tobramycin (4 vs 33 %; p = 0.004) was significantly greater in isolates from India.On average, strains from India exhibited notably greater MIC and MBC values compared to strains obtained from Australia. Out of 61 isolates, none displayed an MBC/MIC ratio ≥ 32. However, three sensitive isolates had low tolerance, nine had medium tolerance and one had high tolerance to ciprofloxacin with the TDtest.
This study used two methods to determine whether P. aeruginosa strains could show tolerance to antibiotics. Using the MBC/MIC criteria no strain was considered tolerant to any of the eight antibiotics used. When 13 strains were tested for tolerance against ciprofloxacin, the most commonly used monotherapy for keratitis, one had high tolerance and nine had medium tolerance. This demonstrates the capacity of P. aeruginosa to develop tolerance which may result in therapeutic failures if inappropriate dosing regimens are used to treat keratitis.
由于细菌生长模式的变化，抗生素可能会产生耐药性，这可能是耐药性发展的前兆。然而，关于眼部细菌分离株产生耐药性的能力的信息却很缺乏。本研究使用 MBC/MIC 比值来探讨澳大利亚和印度的 61 株铜绿假单胞菌眼部微生物角膜炎分离株对 8 种不同抗生素的耐药性，将比值≥32 定义为耐药，采用琼脂扩散试验测定对环丙沙星的耐药性。
使用的抗生素为环丙沙星、左氧氟沙星、庆大霉素、妥布霉素、哌拉西林、亚胺培南、头孢他啶和多黏菌素 B。分离株来自澳大利亚和印度的微生物角膜炎感染。采用肉汤微量稀释法获得最低杀菌浓度（MBC）和最低抑菌浓度（MIC），并与临床实验室标准化协会（CLSI）和欧洲抗菌药物敏感性试验委员会（EUCAST）的折点进行比较，以确定细菌的敏感性。耐药性评估为 MBC/MIC≥32。用 13 株铜绿假单胞菌敏感株进行琼脂扩散试验检测对环丙沙星的耐药性，然后在琼脂上涂葡萄糖，观察菌落重新生长，用这种替代方法（TD 法）检测耐药性。
33 株对亚胺培南耐药，20 株对环丙沙星耐药，14 株对妥布霉素和哌拉西林耐药，12 株对左氧氟沙星和头孢他啶耐药，8 株对庆大霉素耐药，5 株对多黏菌素 B 耐药。印度分离株对左氧氟沙星（7%比 30%；p=0.023）、庆大霉素（0%比 24%；p=0.005）和妥布霉素（4%比 33%；p=0.004）的耐药率显著高于澳大利亚分离株。与澳大利亚分离株相比，印度分离株的平均 MIC 和 MBC 值明显更高。在 61 株分离株中，没有一株的 MBC/MIC 比值≥32。然而，TD 试验显示，3 株敏感株对环丙沙星有低耐药性，9 株有中耐药性，1 株有高耐药性。
本研究使用两种方法来确定铜绿假单胞菌是否对抗生素产生耐药性。使用 MBC/MIC 标准，没有一株菌被认为对 8 种抗生素中的任何一种有耐药性。当对 13 株对环丙沙星（治疗角膜炎最常用的单药治疗）的耐药性进行测试时，有一株菌具有高耐药性，9 株菌具有中耐药性。这表明铜绿假单胞菌有产生耐药性的能力，如果使用不当的剂量方案治疗角膜炎，可能会导致治疗失败。
