Hawkey P M, Birkenhead D, Kerr K G, Newton K E, Hyde W A
Department of Microbiology, University of Leeds, UK.
J Antimicrob Chemother. 1993 Jan;31(1):47-55. doi: 10.1093/jac/31.1.47.
The susceptibility of Xanthomonas maltophilia strains to beta-lactams is known to vary according to the type of growth media used. We have assayed the divalent cation content of various susceptibility testing media and correlated this with the susceptibility to imipenem of 30 strains of X. maltophilia, by calculating the IC50. No correlation was found with Ca++ and Mg++ content (r = 0.005, P = 0.99), but a highly significant correlation with the Zn++ content (7.7-42.7 mumol/L) of the medium was found (r = 0.93, P = 0.003). The effect of Zn++ on the susceptibility of X. maltophilia to imipenem was further investigated by adding varying amounts of zinc sulphate to Oxoid Mueller-Hinton agar which has a low Zn++ content (14.2 mumol/L). A highly significant correlation between the Zn++ content and the IC50 was observed (r = 0.95, P = 0.001). Some variability was seen from one series of IC50 determinations to another and samples of ultra-pure water were processed in exactly the same fashion as the agar media and then assayed for cation content. No significant increase in Ca++ or Mg++ content of the water were observed but water autoclaved in universal containers with metal caps and rubber washers acquired up to 40 mumol/L of Zn++. Studies of the correlation between in-vitro sensitivity tests and the clinical performance of beta-lactams used against X. maltophilia will need to take account of the Zn++ content of the susceptibility testing media used.
嗜麦芽窄食单胞菌菌株对β-内酰胺类药物的敏感性已知会因所用生长培养基的类型而异。我们测定了各种药敏试验培养基中的二价阳离子含量，并通过计算半数抑制浓度（IC50）将其与30株嗜麦芽窄食单胞菌对亚胺培南的敏感性进行关联。未发现与Ca++和Mg++含量存在相关性（r = 0.005，P = 0.99），但发现与培养基中Zn++含量（7.7 - 42.7 μmol/L）存在高度显著相关性（r = 0.93，P = 0.003）。通过向Zn++含量较低（14.2 μmol/L）的Oxoid Mueller-Hinton琼脂中添加不同量的硫酸锌，进一步研究了Zn++对嗜麦芽窄食单胞菌对亚胺培南敏感性的影响。观察到Zn++含量与IC50之间存在高度显著相关性（r = 0.95，P = 0.001）。从一系列IC50测定到另一系列会观察到一些变异性，并且以与琼脂培养基完全相同的方式处理超纯水样品，然后测定阳离子含量。未观察到水中Ca++或Mg++含量有显著增加，但在带有金属盖和橡胶垫圈的通用容器中高压灭菌的水获得了高达40 μmol/L 的Zn++。针对嗜麦芽窄食单胞菌进行的体外敏感性试验与所用β-内酰胺类药物临床疗效之间相关性的研究将需要考虑所用药敏试验培养基的Zn++含量。
