Incompatibility Reactions of R Plasmids Isolated from Escherichia coli of Animal Origin

Abstract

The incompatibility reactions of a group of 90 R plasmids, isolated from the fecal Escherichia coli of calves, pigs, and chickens, have been determined against reference plasmids of the incompatibility groups F 11 , I, N, P, and W. Twenty plasmids belonged to incompatibility groups F 11 , I, N, or P. Forty-nine plasmids were compatible with all of the five reference plasmids. Eight plasmids exhibited marked incompatibility with representatives of two or more of the above groups, whereas two strains showed incompatibility reactions consistent with the coexistence of two compatible plasmids. In addition, 19 plasmids remain untyped because they showed intermediate reactions with one or more reference plasmids.

Naturally occurring plasmids exhibiting incompatibility with members of incompatibility groups I and P

“…Bacterial strains and plasmids. Many of the bacterial strains and plasmids used in this work and the relevant aspects of their genotypes have been described previously (11). A number of strains harboring plasmids belonging to a number of incompatibility groups were obtained from N. Datta.…”

“…Media and antibiotics. The culture media and antibiotics used have been described in detail previously (11).…”

“…In early studies, in which the group of 90 R plasmids were checked for incompatibility against a large num-ber of standard plasmids, the plasmid transfers were accomplished by mating on solid media, and transconjugants were tested for incompatibility as described previously (11). However, in more detailed studies of a number of plasmids, the following methods were used.…”

“…Table 1 shows the marker loss observed when standard group P and I plasmids were introduced into strains of JP990 which carried the eight plasmids exhibiting incompatibility with groups I and P. The other four plasmids showing multiple incompatibility with other groups will not be discussed further in this paper. The method used in these experiments for testing incompatibility has been described previously (11) and involves a selection for transconjugants possessing one of the plasmid-coded resistance markers of the donor and the chromosomally treated gene for nalidixic acid resistance of the recipient. Loss of the resident plasmid can occur during purification on selective medium or during subsequent overnight growth on unselective medium.…”

“…Whereas the majority of plasmids that have been tested exhibit incompatibility with members of only a single incompatibility group, some exceptions to this rule have been observed (7,15,27). In a previous report, we described the testing of 90 R plasmids isolated from fecal Escherichia coli of animal origin for incompatibility with standard plasmids of groups FIl, I, N, P, and W (11). Only 20 of these plasmids could be grouped into one or another of these standard groups, and 4 exhibited incompatibility with members of two groups, namely, Ia and P. With the availability of an increased range of standard plasmids, the 90 R plasmids were checked for incompatibility reactions with standard plasmids of the additional groups FI, ly, M, S, T, C, L, J, H, A, and K. The bulk of the plasmids still remained untypable (data not shown), 3 plasmids were identified that belonged to incompat-ibility group T, and 12 plasmids were now found to be incompatible with members of more than a single incompatibility group.…”