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SUMMARYA molecular epidemiological study was carried out on 60Salmonella dublinisolates identified at the Southern Italy Enterobacteriaceae Center between 1971 and 1985. These included 23 isolates from children with diarrhoea in Palermo obtained during 1984.All isolates from the outbreak of gastroenteritis in children were resistant to chloramphenicol and streptomycin and harboured two plasmids of 50 MDa and 3 MDa molecular weight, whereas the majority of the isolates identified before 1984 were susceptible to these antibiotics and carried only a 50 MDa molecular weight plasmid. FourS. dublinstrains successively identified from cattle (Palermo, Foggia, Portici) and from a child (Palermo) were shown to possess similar antibiotic resistance patterns and plasmid profiles toS. dublinisolates from the outbreak of gastroenteritis in children.The 50 MDa plasmid was shown to be associated with virulence in mice, while it was not possible to assign any genetic function to the 3 MDa plasmid.

Complement-fixing activity of a T strain of Mycoplasma was found to be associated with its lipid components. Heat stability and lability of periodate and ,B-glucosidase treatments led to the conclusion that complement-fixing, active lipids had carboydrate determinants. Periodate treatment of chromatographic fractions of a chloroform-methanol extract showed that only antigens contained in the acetone fraction were periodate labile. Lipids also appeared to be involved in the passive hemagglutination, since the lipid fraction active in complement fixation also combined and blocked the action of antibodies which agglutinated sensitized erythrocytes with strain P108.

The cell membranes of a T-strain of mycoplasma, obtained by ultrasonic disruption, were as effective as whole organisms in eliciting metabolism-inhibiting and complement-fixing antibodies. The soluble fraction separated from cell membranes by centrifugation at 35,000 X g showed a minor ability to elicit an antibody response as measured by metabolism inhibition and complement fixation tests. After a further centrifugation at 100,000 X g, the immunogenic activity of the soluble fraction was completely lost. Immunogenic determinants in mycoplasma membranes could also be demonstrated by adsorption tests; cell membranes were more effective than soluble fractions in adsorbing antibody capacity from the immune sera against whole cells. It has been shown by further experiments that cell membranes have at least two major antigenic determinants, which differ either in chemical nature or in capacity to adsorb and evoke antibodies, characterized by different serological behaviors.