“…some 0 and K antigens (Orskov et al 1977; Orskov & Orskov, 1985), resistance to serum bactericidal activity (Taylor, 1983;Cross et al 1986), virulence to mice and to chicken embryo (Minshew et al 1978; Van den Bosch, De Graaff & MacLaren, 1979; Bosch, Emody & Ketyi, 1982), aerobactin production (Carbonetti et al 1986), a-haemolysin production (Van den Bosch et al 1981;Welch et al 1981;Cavalieri, Bohach & Snyder, 1984) and mannose resistant haemagglutinin (Evans et al 1980;Hagberg et al 1981;Vaisanen et al 1981). However, these infections not only depend on the intrinsic properties of the strains but also on various hostdependent factors, such as susceptibility linked to an underlying disease (Singer, * Author for reprints.…”