药敏试验培养基标准要求

发布时间:

2022-12-27

作者:

做培养基试剂的厂家


药敏试验培养基的选择具有一定的原则和要求,不以个人经验或爱好而更改。为了使临床试验和医疗保健服务水平具备一致的标准,许多国家或机构制定了不同的参照标准。由于参照标准有所差异,故药敏培养基的要求也有所不同。我国药敏试验结果判断标准参照美国CLSI标准文件,则要求除了特殊菌群,K-B法所用的培养基必须是M-H培养基;英国参照的标准BSAC则要求培养基为ISO培养基,而M-H营养琼脂只适用于葡萄球菌的药敏试验。因此在工作中,我们要严谨的参照CLSI,根据不同菌群的需求选择合适、正确的药敏培养基。
 
培养基的成分和质量是保证药敏结果准确性的先决条件。培养基对药敏结果的影响因素具体如下:
 
1、pH:pH的变化可导致抑菌圈直径变大或变小。
2、能拮抗菌药活性的物质:如钙、镁离子能降低氨基糖苷类药物的抗菌活性。
3、厚度:标准厚度为4mm,厚度>4mm,抑菌圈则会变小,<4mm,则会变小。
4、湿度:使用药物平皿前一般先在室温平衡半个小时,使培养基表面干燥,湿度过高不利于细菌的生长或对抗菌药起到稀释作用。
5、硬度:硬度过高不利于抗菌药在琼脂中的扩散,可导致抑菌圈直径变小。
6、营养条件:营养条件太差不利于细菌的生长,抑菌圈直径变大;反之,培养及营养条件太好会让抑菌圈直径变小。
 
将这些原理和原则解说后,针对他们对话中的问题,我一一进行了剖析:
 
根据CLSI,绝大多数细菌药敏试验琼脂均为标准的M-H琼脂,M-H琼脂基本不含有抑制磺胺类药物和四环素类药物抗菌活性的物质,可满足大多数细菌的生长需要,肠球菌对营养要求不高且生长速度较快,因此可选用M-H琼脂(MHA),而不是血平皿。对于大多数细菌,MHA是不需要添加羊血,血液或血清中的蛋白会不同程度结合抗菌药分子,影响了抗菌药物的活性,如羊血中的某些成分可抑制磺胺类药物和四环素类药物抗菌活性,同时也可影响新生霉素、萘夫西林及头孢菌对肠球菌的药敏结果。
 
溶血链球菌、肺炎链球菌等营养要求高的苛养菌则需要使用M-H琼脂+5%脱纤维羊血培养基,也叫M-H药敏试验血琼脂平板(MHBA)。MHBA与普通的分离细菌的血平板或者哥伦比亚血平板(CNA)虽然长相相似,但配方及产业标准(如pH、湿度等)均不一样,是不能相互代替使用的。为了比较肺炎链球菌ATCC49619在MHBA和 CNA培养基上的药敏结果,在其他条件均一致的情况下我们分别用MHBA和CNA做了药敏试验,结果发现,CNA的药敏结果抑菌圈直径偏大,细菌生长情况较差,从而导致“假敏感”结果。
 
因此,作为一名合格的微生物检验人员,我们应该时刻遵守操作规程,牢记标准要求,熟读规则原理,杜绝含糊不清、似是而非,才能确保结果的准确性。
 
 
日水培养基qdrishui.cn

Standard requirements for the culture medium of drug sensitivity test
The selection of medium for drug sensitivity test has certain principles and requirements, and is not changed by personal experience or hobbies. In order to have consistent standards for clinical trials and health care services, many countries or institutions have drawn up different reference standards. Because of the difference in reference standard, the requirements for drug sensitive medium are also different. The criteria for judging the results of drug sensitivity test in our country refer to the CLSI standard documents in the United States. In addition to the special flora, the culture medium used by the K-B method must be the M-H medium; the standard BSAC of the British reference requires the medium as the ISO medium, and the M-H nutritious agar is only suitable for the drug sensitivity test of Staphylococcus. Therefore, in our work, we should carefully consult CLSI and select suitable and correct drug sensitive medium according to the needs of different microbiota.
The composition and quality of the medium are prerequisites for ensuring the accuracy of the results. The factors affecting the sensitivity of the medium are as follows:
1, the change of pH:pH can lead to larger or smaller diameter of bacteriostatic circle.
2, the medium contains substances that are antagonistic to antibacterial activity: calcium and magnesium ions can reduce the antibacterial activity of aminoglycoside drugs.
3, the thickness of the medium: the standard thickness is 4mm, the thickness is >4mm, the inhibition zone will be smaller, and the <4mm will be smaller.
4, the humidity of the culture medium: it is generally balanced at room temperature for half an hour before using the medicine plate, which makes the medium surface dry, and the high humidity of the medium is not conducive to the growth of bacteria or the dilution effect on the antimicrobial agents.
5. Hardness of the medium: excessive hardness is not conducive to the diffusion of antibiotics in agar, which can lead to a smaller diameter of the bacteriostatic circle.
6, nutritional conditions: poor nutrition conditions are not conducive to the growth of bacteria, the diameter of the bacteriostasis circle becomes larger; on the contrary, the cultivation and nutrition conditions will make the diameter of the bacteriostasis circle smaller.
After explaining these principles and principles, I analyze them in the light of their dialogues.
According to CLSI, the overwhelming majority of bacterial susceptibility tests are standard M-H agar, M-H agar does not contain substances that inhibit the antibacterial activity of sulfonamides and tetracycline, and can meet the growth needs of most bacteria. Enterococcus is not high in nutrition and fast in growth. Therefore, M-H agar (MHA) can be used. Not a Petri dish. For most bacteria, MHA does not need to add sheep blood, and the proteins in blood or serum combine with antimicrobial molecules in varying degrees and affect the activity of antibiotics. For example, some of the ingredients in the sheep blood can inhibit the antibacterial activity of sulfonamides and tetracycline, and can also influence the new mycophenycin, naphthalene and cephalosporin. The drug sensitivity of Enterococcus.
The high nutritive bacteria, such as Streptococcus hemolytic streptococcus and Streptococcus pneumoniae, need to use the M-H agar +5% defibrous sheep blood culture medium, and also called the M-H drug sensitive test blood agar plate (MHBA). MHBA is similar to the ordinary separate bacterial blood plate or the Columbia blood plate (CNA), but the formula and industrial standards (such as pH, humidity, etc.) are not the same, and can not be replaced with each other. In order to compare the drug sensitivity results of Streptococcus pneumoniae ATCC49619 on MHBA and CNA medium, we used MHBA and CNA for drug sensitivity test under the same conditions. The results showed that the diameter of the bacteriostasis circle of the drug sensitivity of CNA was large and the growth of the bacteria was poor, thus leading to the "false sensitivity" result.
Therefore, as a qualified microbial inspector, we should always abide by the rules of operation, keep in mind the standard requirements, read the rules of the rules well, avoid ambiguity and specious, so as to ensure the accuracy of the results.