Metabolically deficient dwarf-colony mutants of Escherichia coli: deficiency and resistance to antibiotics of strains isolated from urine culture.

Sixteen metabolically deficient dwarf-colony mutants of Escherichia coli were isolated from urine culture and represented about 2% of all E. coli isolated during the same period. In 14 cases, mutants were isolated from debilitated patients: elderly persons or patients in the terminal stages of a chronic disease. In 15 of these subjects, deficient dwarf-colony mutants appeared to be the true cause of urinary tract infection, since there was leukocyturia and important bacteriuria, and organisms were obtained in pure culture. Study of metabolic deficiencies on Davis synthetic medium and nutritive agar resulted in the identification of eleven deficiencies in cysteine, two in thiamine, two in thymidine, and one in glutamine. Study of resistance to antibiotics revealed that nine were susceptible to all antibiotics, three were resistant to tetracycline alone, two were resistant to two antibiotics (chloramphenicol-tetracycline, streptomycin-tetracycline), and two were resistant to three antibiotics (ampicillin-chloramphenicol-tetracycline, ampicillin-streptomycin-tetracycline). Resistance was coded for by conjugative plasmids in five strains.