Surface Properties of Klebsiella and E Coli: Role of Capsular Polysaccharide in Protection Against Phagocytosis

Abstract

Klebsiellae are Gram negative capsulate bacteria which are important pathogens, causing bacteremia, pneumonia and wound infection. The K21 serotype of Klebsiella is not homogeneous but consists of strains producing one or other of two chemically distinct types of capsular polysaccharide (K21a and K21b); K21b is more commonly encountered among clinical isolates [1]. We have investigated the role of the capsule of Klebsiella pneumoniae (K21b) as a determinant of pathogenicity by examining the resistance to phagocytic uptake and killing by polymorphonuclear leucocytes (PMNLs) of the native bacteria and a spontaneously derived capsule-less mutant. In addition, we have investigated the role of the antigenically similar colanic acid capsule produced by E coli DH1 transformed by plasmid pLV213 which carries the rcs gene [2]. The capsules are hydrophilic, negatively charged polysaccharides whose influences upon the surface properties of the bacteria can be determined by phase partitioning [3]. The various strains of bacteria provide particulates with varying surface properties, and allow correlations between these physicochemical properties and the biological properties of resistance to phagocytosis to be examined. Avoidance of phagocytosis is a strong virulence factor, which can be associated with altered surface properties, such as those detected by phase partitioning [4].