Suerbaum S, Friedrich S, Leying H, Opferkuch W
Medizinische Mikrobiologie und Immunologie, Ruhr-Universität Bochum, Germany.
Zentralbl Bakteriol. 1994 Aug;281(2):146-57. doi: 10.1016/s0934-8840(11)80565-7.
The amount of capsular polysaccharide expression has been shown to be the major determinant of serum resistance in Escherichia coli K1. E. coli K92, like K1, is a polymer of sialic acid molecules. It differs from K1 by containing both alpha (2.8) and alpha (2.9) linkages. Four strains of E. coli K92 were tested for serum resistance. Three strains were serum-resistant (50% normal human serum), one strain was moderately serum-sensitive. The serum-resistant strains expressed significantly more capsular polysaccharide than did the serum-sensitive strain. For each of the serum-resistant strains, six mutants were isolated by selection for resistance against infection with a K92-specific bacteriophage. All of the mutants expressed less capsular polysaccharide than the respective wild-type strains. All mutants were more sensitive to serum killing than the wild-type strains. In all groups, the mutants with lowest expression of capsular polysaccharide were highly serum-sensitive. Changes of outer membrane proteins or lipopolysaccharide patterns that were present in some mutants did not correlate with serum resistance properties of the mutants. Furthermore, it was investigated whether the presence of active serum had an influence on capsule expression. In the serum-sensitive strain, the presence of serum induced a significant and concentration-dependent increase of capsule expression. Serum had no effect on capsule expression by the serum-resistant strains. We conclude from the data that the expression of K92 capsular polysaccharide determines serum resistance in the strains examined.
荚膜多糖的表达量已被证明是大肠杆菌K1血清抗性的主要决定因素。大肠杆菌K92与K1一样，是唾液酸分子的聚合物。它与K1的不同之处在于同时含有α（2,8）和α（2,9）连接。对四株大肠杆菌K92进行了血清抗性测试。三株具有血清抗性（50%正常人血清），一株对血清中度敏感。血清抗性菌株表达的荚膜多糖明显多于血清敏感菌株。对于每一株血清抗性菌株，通过选择对K92特异性噬菌体感染具有抗性的菌株，分离出六个突变体。所有突变体表达的荚膜多糖均少于各自的野生型菌株。所有突变体对血清杀伤的敏感性均高于野生型菌株。在所有组中，荚膜多糖表达量最低的突变体对血清高度敏感。一些突变体中存在的外膜蛋白或脂多糖模式的变化与突变体的血清抗性特性无关。此外，还研究了活性血清的存在是否对荚膜表达有影响。在血清敏感菌株中，血清的存在诱导了荚膜表达的显著且浓度依赖性增加。血清对血清抗性菌株的荚膜表达没有影响。我们从这些数据得出结论，K92荚膜多糖的表达决定了所检测菌株的血清抗性。
