Survival of plasmid-containing strains of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus in phenylmercuric nitrate and thiomersal

Strains of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus harbouring plasmids that confer mercury resistance grew in nutrient broth containing concentrations of phenylmercuric nitrate (PMN) that were inhibitory to isogenic plasmid-less strains. Decimal reduction times of P. aeruginosa and S. aureus in aqueous PMN solution were also increased by the presence of plasmids. The viable count of a plasmid-containing P. aeruginosa strain in Davis and Mingioli's minimal medium (DM) containing 10 microgram ml-1 PMN fell by approximately 99% after 5 h. The count then remained constant for two weeks, when growth recommenced. This pattern of death followed by growth was also observed with the P. aeruginosa strain in DM + 10 microgram ml-1 thiomersal.