Plasmids and hospital acquired infections.

One hundred multiply resistant gram-negative bacilli isolated in a routine clinical microbiology laboratory over a six month period have been examined for their ability to transfer their resistance pattern, or part of it, to a sensitive recipient Escherichia coli and for plasmid carriage. Sixty-six of these transferred resistance and plasmids were isolated from 40. The importance of investigating the occurrence and spread of plasmids in providing epidemiological data for the control of hospital infection is emphasised.