PLASMID DIVERSITY IN ESCHERICHIA-COLI ISOLATED FROM PROCESSED POULTRYAND POULTRY PROCESSORS

Plasmids of bacteria selected from different bacterial populations bec ause they shared a distinctive antimicrobial resistance phenotype have sometimes had identical restriction fragments. Such identical plasmid s am thought to belong to small and thus epidemic clones because the p lasmid content of unselected resistant isolates has seemed diverse. To survey this presumed diversity and its implications for the lineage o f resistance plasmids we examined the transferability, sizes and EcoR1 restriction fragment sizes of plasmids in both Escherichia coli isola ted randomly from poultry raised by 16 growers as they were being proc essed through two plants and in isolates from the urine of women proce ssing poultry in those plants. Forty two (24%) of 175 resistant isolat es from poultry of 16 growers and 9 (26%) of 34 resistant isolates fro m the poultry processors transferred resistance conjugatively to varie d combinations of antimicrobials. No poultry isolate had both the same expressed and the same transferred combination as any processor's iso late. The DNA bands which could be discerned in electrophoresis gels o f restricted or unrestricted plasmid extracts of isolates or their tra nsconjugants from 156 of the poultry and 24 of the poultry processors appeared diverse. Pairs of related-appearing plasmids were seen in con secutive isolates of poultry from each of two growers and in one pair from different growers. One set of identical appearing plasmids was se en in 3 consecutive isolates from poultry of one grower, others in 2 c onsecutive isolates from a second grower's poultry, in 2 non-consecuti ve isolates of a third grower's, and in single isolates from poultry o f 2 different growers. None of the plasmids from any of the human isol ates appeared related to those from any other human isolate or to thos e of any poultry isolate. These results indicate that resistance plasm ids are highly diverse and that all but two of the exceptions to compl ete diversity in the isolates surveyed hem could be ascribed to cross colonization within flocks of individual poultry growers. Also, while none of the plasmids in the poultry isolates appeared ancestral to any of plasmids in the poultry processors' isolates, their diversity indi cates that those sampled plasmids would be only a very small fraction of the total number of different plasmids in bacteria colonizing poult ry processed at that time or earlier.