HIGH-LEVELS OF COLICIN RESISTANCE IN ESCHERICHIA-COLI

Colicins are plasmid-encoded antibiotics that are produced by and kill Escherichia coil and other related species. The frequency of colicino geny is high, on average 30% of E. coli isolates produce colicins. Ini tial observations from one collection of 72 strains of E. coil (the EC OR collection) suggest that resistance to colicin killing is also ubiq uitous, with over 70% of strains resistant to one or more colicins. To determine whether resistance is a common trait in E. coli, three addi tional strain collections were surveyed. In each of these collections levels of colicin production were high (from 15 to 50% of the strains produce colicins). Levels of colicin resistance were even higher, with most strains resistant to over 10 colicins. A survey of 137 non-E. co li isolates revealed even higher levels of resistance. We discuss a me chanism (pleiotropy) that could result in the co-occurrence of such hi gh levels of colicin production and colicin resistance.