title: Antibiotic selection pressure resulting in multiple antibiotic resistance and localization of resistance determinants to conjugative plasmids in streptococci.
abstract: The plasmid content, antibiotic susceptibilities, and biochemical traits of fecal streptococci isolated from pigs during a tylosin feeding experiment were analyzed. The presence of tylosin in the feed did not select for a particular streptococcal strain or biochemical type but did select for multiple antibiotic resistance. A DNA probe obtained from Escherichia coli and containing a cloned macrolide-lincosamide-streptogramin B (MLS) resistance determinant from a streptococcal strain of human origin hybridized primarily to large plasmids among MLS-resistant streptococci from antibiotic-fed pigs. Patterns of hybridization were similar among MLS-resistant clinical isolates from human infections and isolates from other antibiotic-fed animals. The results of mating experiments indicated that tylosin selected for localization of the MLS determinants to large conjugative plasmids. These data established (1) a strong sequence homology between MLS resistance genes in isolates from humans and those from farm animals and (2) an increased potential for dissemination of MLS resistance as a consequence of tylosin feeding.
mesh_terms: D000821:Animal Feed; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003227:Conjugation, Genetic; D004269:DNA, Bacterial; D005243:Feces / Q000382:microbiology; D005798:Genes, Bacterial; D006801:Humans; D007933:Leucomycins / Q000494:pharmacology*; D055231:Lincosamides; D018942:Macrolides; D009693:Nucleic Acid Hybridization; D011815:R Factors; D013291:Streptococcus / Q000187:drug effects* / Q000235:genetics; D013552:Swine / Q000382:microbiology; D014769:Virginiamycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D007933:Leucomycins; D055231:Lincosamides; D018942:Macrolides; D014769:Virginiamycin