Emergence of gentamicin-resistant Klebsiella in a general hospital.

Gentamicin had been in use in a general hospital for over 7 years before any gentamicin-resistant Klebsiella were observed. In 1974 and 1975, nine different gentamicin-resistant serobiotypes of Klebsiella were isolated from 35 patients. The first strain to appear had R-factor-mediated gentamicin resistance, and it infected 19 patients during a period of almost 2 years, spreading largely by case-to-case infection in patients with urinary catheters. It appeared to lose the capacity to transfer its gentamicin resistance after it had infected five of the patients. We had previously isolated on the same ward a gentamicin-susceptible Klebsiella of identical type, and it was found to be capable of acquiring an R-factor for gentamicin resistance. All of the other types of gentamicin-resistant Klebsiella infected few patients and did not persist in the hospital; four of them had R-factor-mediated resistance to gentamicin and all four, as did the original strain, cotransferred kanamycin, neomycin, and tobramycin resistance. Every gentamicin-resistant Klebsiella was susceptible to amikacin and netilmicin.