Detection of conjugative R plasmids conferring chloramphenicol resistance in Escherichia coli isolated from domestic and feral pigeons and crows.

A total of 87 domestic pigeons of 2 lots and 184 feral pigeons of 15 lots were examined from 1975 to 1977 for the presence of drug-resistant (especially chloramphenicol resistant) Escherichia coli. 20 (23.0%) of the domestic pigeons of the 2 lots, and 39 (21.2%) of the feral pigeons of 5 lots (33,3%) showed resistant E. coli. Usage of selective media containing chloramphenicol, streptomycin or tetracycline resulted in the increase in isolation frequency of resistant E. coli excepting one lot of domestic pigeons in which isolation of chloramphenicol resistant E. coli was very frequent without selection by the drug. Among a total of 106 resistant E. coli isolates from pigeons, 64 (60.4%) were multiply resistant and 58 of the 64 isolates were resistant to chloramphenicol. 58 (90.6%) of the multiply resistant E. coli carried conjugative R plasmids, including 13 thermosensitive R plasmids. 8 (19.0%) of 42 singly resistant E. coli isolates had conjugative R plasmids. 10 crows of 2 lots were examined similarly. Half of them had resistant E. coli. 15 (78.9%) of a total of 19 resistant E. coli isolates were multiply resistant. Of the 15 multiply resistant E. coli isolates, 5, from 2 Japanese jungle crows, were resistant to chloramphenicol. 11 (73.3%) of the 15 multiply resistant isolates carried conjugative R plasmids, including one thermosensitive R plasmid. Difference of drug resistance status between Salmonella and E. coli isolated from pigeons was discussed.