Serological typing of P. aeruginosa is the most simple and reliable procedure recommended for "in-house" investigations and for studies of suspected outbreaks of infection by this microorganism. It is also a useful procedure in order to know serotype prevalence in a definite geographical area and to obtain indications about the more appropriate composition of polyvalent anti-Pseudomonas vaccines. In the present report, we describe the relatively high frequency of isolation of serogroup 12 from patients in Palermo, Italy. Serogroup 12 is very rare in north-Europe and in the USA, and, as a consequence, it is not included in some vaccine preparations. In Palermo, strains belonging to this serogroup, resistant to a large number of antibiotics, were on the contrary isolated, during more than six years, in different hospitals and from three out-patients. In a Burns Unit, they were in particular responsible for extensive and life-threatening outbreaks.

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SUMMARYThe Lincoln strain of bovine rotavirus, cytocidal for bovine AU-BEK cells, can establish in the same cell cultures in the presence of foetal calf serum (FCS) a persistent infection that depends on selection of highly resistant cells. In fact, after the induction of the carrier state only a small fraction of the cell population was infected. The parental and the carried viruses are not demonstrably different, the cultures are resistant to superinfection by the homologous virus, the cultures can be cured by antiviral serum in the medium and uninfected resistant cell clones can be selected. The presence of FCS was essential during induction and maintenance of persistence. Its effects appear to be exerted not on the control of virus replication in fully sensitive cells but on the proliferation and selection of the resistant cells.

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