EVALUATION OF COLICINS FOR INHIBITORY ACTIVITY AGAINST DIARRHEAGENIC ESCHERICHIA-COLI STRAINS, INCLUDING SEROTYPE O157-H7

Twenty-four Escherichia coli strains producing standard colicins were evaluated for inhibitory activity against 27 diarrheagenic E. coli str ains of serotypes O15:H-, 026:(Hll, H-), and O111:(H8, H11, H-), inclu ding O157:H7, representing diarrheagenic E. coli clones, 3, 4, 8, 9, a nd 10, Overlay techniques were used to assess inhibition on Luria agar and Luria agar supplemented with 0.25 mu g of mitomycin C per mi to i nduce colicin production, As a group, the A colicins (Col) El to E8, K , and N inhibited 23 to 25 (85.2 to 92.6%) of the 27 diarrheagenic str ains on mitomycin C-containing agar, whereas the most active group B c olicins, Col D and Ia, inhibited 9 and 12 (33.3 and 44.4%), of the dia rrheagenic strains, respectively, Col G and EI and Mcc B17 inhibited 2 2 to 27 (81.5 to 100%) of the diarrheagenic strains on Luria agar but were suppressed on mitomycin C-containing agar medium, All O157:H7 str ains evaluated were sensitive to Col El to E8, K, and N on mitomycin C -containing agar and to Col G and H and Mcc B17 on Luria agar, Sensiti vity to colicins of the selected set of diarrheagenic strains was in t he order diarrheagenic E. coli clone 9 > 4 > 3 > 10 > 8 and was not re stricted to strains of a single clone or serotype, Strain 8C from clon e 8 was resistant to most test colicins, There is potential for using colicins in foods and agriculture to inhibit sensitive diarrheagenic E . coli strains,including serotype O157:H7.