Resistance Types in Escherichia Coli

An investigation of the resistance types in lactose fermenting E. coli is presented. The frequency and sensitivity to beta-lactam antibiotics of different resistance types was investigated. The strains were divided into three groups according to sensitivity to penicillin derivatives. Group 1 contained the ampicillin-carbenicillin sensitive (A-s/Ca-s), group 2 the ampicillin resistant-carbenicillin sensitive (A-r/Ca-s) and group 3 the ampicillin-carbenicillin resistant (A-r/Ca-r). A-s/Ca-r were not observed. One third of the A-r strains were sensitive to carbenicillin. The distribution of resistance types was different in the three groups. Group 1 was dominated by the usual sensitive E. coli. Group 3 contained a very high proportion of multiresistant types. The IC50 against ampicillin, carbenicillin and cephalothin of 55 strains was determined. Group 3 (A-r/Ca-r, 25 strains) was much more ampicillin resistant than group 2 (A-r/Ca-s, 16 strains). Group 2 was less sensitive to carbenicillin than group 1 (A-s/Ca-s, 14 strains). Group 3 did not differ significantly from group 1 with respect to cephalothin sensitivity, while group 2 was much more resistant than the others.