Search

The Enterobacter species E. aerogenes, E. cloacae, and E. hafnia were examined for resistance to penicillin and cephalosporin derivatives. All were resistant to benzyl penicillin, ampicillin, 6 [d(-)alpha-amino-p-hydroxyphenylacetamido] penicillanic acid, cephaloridine, cephalothin, and cephalexin. A significant number were sensitive to carbenicillin and 6 [d(-)alpha-carboxy-3-thienylacetamido] penicillanic acid. No differences among the three species were noted. The beta-lactamase activity was cell-bound, and was not released by osmotic shock, toluene treatment, or diphenylamine treatment. It was rarely released into the growth medium. The beta-lactamase activity was primarily directed against cephalosporin derivatives. Synthesis of beta-lactamase was chromosomally mediated. Resistance to ampicillin seemed to be partly related to entry of the molecule into the bacteria since exposure to ethylenediaminetetraacetate lowered the minimal inhibitory concentration.

In vivo interbacterial transfer of R factor was observed in two patients. Resistance to ampicillin, tetracycline, streptomycin, and chloramphenicol was transferred from Escherichia coli in the intestine of a patient with shigellosis to a Shigella sonnei strain. In a second patient with partial ureteral obstruction, a resistant E. coli strain transferred ampicillin, tetracycline, and streptomycin resistance to a Proteus mirabilis strain.