2 BACTERICIDAL TARGETS FOR PENICILLIN IN PNEUMOCOCCI - AUTOLYSIS-DEPENDENT AND AUTOLYSIS-INDEPENDENT KILLING MECHANISMS
2 BACTERICIDAL TARGETS FOR PENICILLIN IN PNEUMOCOCCI - AUTOLYSIS-DEPENDENT AND AUTOLYSIS-INDEPENDENT KILLING MECHANISMS
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DOI：
10.1128/aac.34.1.33
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发表时间：
1990-01-01
影响因子：
4.9
通讯作者：
TOMASZ, A
中科院分区：
文献类型：
--
作者：
MOREILLON, P;MARKIEWICZ, Z;TOMASZ, A
据推测，青霉素（以及其他细胞壁抑制剂）主要通过触发其主要自溶酶（N-乙酰胞壁酰-L-丙氨酸酰胺酶;称为酰胺酶）杀死肺炎球菌，导致大量细胞壁降解。三种类型的实验表明，只有部分的这种杀伤是由于细胞裂解酰胺酶。(i)酰胺酶的特异性抑制剂对青霉素诱导的裂解的抑制仅在一定程度上保护肺炎球菌免于被杀死，20倍，或100倍。大于MIC。(ii)通过质粒插入或缺失（Lyt-）完全消除酰胺酶的突变体仍然被杀死，尽管速度比野生型Lyt+菌株慢（每6小时3至4个对数单位而不是4至5个对数单位，即，比野生型慢约1个对数单位; P < 0.001）。(iii)一个新的突变（cid），它不是针对酰胺酶基因的，进一步降低了对缺乏酰胺酶的突变体的杀伤至每6小时1个对数单位（Lyt-CidP-表型）。将酰胺酶基因重新引入Lyt-Cid-细胞中部分恢复了青霉素诱导的裂解，但仅略微增加了杀伤率（从Lyt-Cid-细胞中的每6小时1个对数单位增加到Lyt+ Cid-细胞中的每6小时2个对数单位）。我们得出结论，青霉素通过两种不同的机制杀死肺炎球菌;一种涉及酰胺酶的触发（每6小时约1个对数单位的杀伤），另一种是酰胺酶独立的机制，负责每6小时3至4个对数单位的杀伤。在Lyt+ Cid-细胞中，在生长的细菌中原位触发酰胺酶活性显著降低，表明在Cid基因产物和酰胺酶之间存在一些调节相互作用。
It has been assumed that penicillin (and also other cell wall inhibitors) kill pneumococci predominantly by triggering their major autolytic enzyme (an N-acetylmuramoyl-L-alanine amidase; referred to as amidase), resulting in massive cell wall degradation. Three types of experiments suggest that only part of this killing is due to cell lysis by amidase. (i) Suppression of penicillin-induced lysis by specific inhibitors of amidase protected pneumococci only marginally from killing in spite of prolonged exposure to concentrations of penicillin that were 10 .times., 20 .times., or 100 .times. greater than the MIC. (ii) Mutants from which the amidase was completely eliminated by plasmid insertion or deletion (Lyt-) were still killed, albeit at a slower rate than the wild-type Lyt+ strains (3 to 4 log units instead of 4 to 5 log units per 6 h, i.e., about 1 log unit slower than the wild type; P < 0.001). (iii) a new mutation (cid), which was not to the amidase gene, further reduced killing of mutants lacking amidase to 1 log unit per 6 h (Lyt- CidP- phenotype). Reintroduction of the amidase gene into Lyt- Cid- cells partially restored penicillin-induced lysis but increased only slightly the rate of killing (from 1 log unit per 6 h in Lyt- Cid- cells to 2 log units per 6 h in Lyt+ Cid- cells). We conclude that penicillin kills pneumococci by two distinct mechanisms; one that involves the triggering of the amidase (about 1 log unit of killing per 6 h) and another, amidase-independent mechanism that is responsible for 3 to 4 log units of killing per 6 h. Triggering of the amidase activity in situ in growing bacteria was significantly reduced in Lyt+ Cid- cells, indicating that there is some regulatory interaction between the cid gene product and the amidase.