Resistance types in Enterobacter cloacae. Occurrence and resistance to Ampicillin, Carbenicillin, Cephalothin and Mecillinam. Transfer of ampicillin Resistance.

An investigation of the resistance types in Enterobacter cloacae is presented. The frequency of the different resistance types was determined. The strains were divided into three groups according to sensitivity to penicillin derivatives. The ampicillin-carbenicillin-sensitive (A-s/Ca-s) group 1 comprised 20% of the E. cloacae strains received in this laboratory. The ampicillin resistant-carbenicillin-sensitive (A-r/Ca-s) group 2 comprised 38.5% of the strains and the A-r/Ca-r group 3 comprised 41.5% of the strains. Group 3 contained a high proportion of multi-resistant strains. The log 2 IC50 against ampicillin, carbenicillin, cephalothin and mecillinam was determined for 28 strains. The group 3 strains were more ampicillin-resistant than the group 2 ones. Group 1 and 2 did not differ as regards carbenicillin sensitivity. The cephalothin resistance increased from group 1 to group 2 and further on to group 3. Mecillinam sensitivity did not differ between the three groups. The ability to transfer ampicillin resistance was investigated in the 24 A-r strains. The 8 group 2 strains were not able to transfer resistance, while 9 of 16 strains in groups 3 could transfer A-resistance with frequencies ranging from 10-0.2 to 10-5.7. Resistance to sulphonamide, tetracycline and streptomycin was also transferred, often with the same frequency as the ampicillin resistance.