Published online by Cambridge University Press: 14 April 2009
A study was made of the R factors from two multiply drug resistant wild type isolates of Pseudomonas aeruginosa from a Birmingham hospital (Lowbury et al. 1969) from which, in contrast to other strains from the same source (Chandler & Krishnapillai, 1974a), drug resistance was not transferable to Escherichia coli K12 or Salmonella typhimurium. Transfer of drug resistance occurred at a low frequency to Shigella flexneri, although drug resistance in this species was subsequently non-transferable.
In P. aeruginosa there are several features of these two R factors which distinguish them from the group 1 and 2 R factors described previously (Chandler & Krishnapillai, 1974a). Although coding for resistance to neomycin and tetracycline, they did not express this resistance in two strains of P. aeruginosa examined, in contrast to the wild type strains they were isolated in.
The control of transfer of the two R factors is different to the group 1 and 2 R factors in that derepression of transfer could be demonstrated following physiological treatments or mutagenesis. The R factors of this third group were compatible with the group 2 R factors, but did not repress their pilus synthesis on the basis of R factor specific phage plating.