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Antimicrob Agents Chemother. 1974 October; 6(4): 492-497
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Transferrable Resistance to Tobramycin in Klebsiella pneumoniae and Enterobacter cloacae Associated with Enzymatic Acetylation of Tobramycin

Barbara H. Minshew1, Randall K. Holmes, Jay P. Sanford and Charles R. Baxter

a Departments of Surgery, Internal Medicine, and Microbiology, University of Texas Southwestern Medical School, Dallas, Texas 75235

ABSTRACT

Among gram-negative bacilli isolated from burn wound cultures, some strains of Enterobacteriaceae were resistant to tobramycin (minimal inhibitory concentration [MIC]≥ 20 µg/ml) but susceptible to gentamicin (MIC ≤ 5 µg/ml). One Klebsiella pneumoniae and two Enterobacter cloacae strains were selected for studies on their mechanisms of resistance to aminoglycoside antibiotics. Resistance to high concentrations of tobramycin (MICs of 25 to 50 µg/ml) was conjugally transferred to a susceptible Escherichia coli strain at rates of 1.2 x 10–4 to 2.8 to 10–4 per donor cell, suggesting that resistance is controlled by R factors. Resistances to tobramycin, kanamycin, and neomycin were cotransferred. Enzymatic activities were present that acetylated tobramycin, gentamicin, and kanamycin in osmotic lysates from the donor and transcipient strains. Enzymatic adenylylation of these aminoglycosides was not observed. The aminoglycoside-acetylating activities from K. pneumoniae and E. cloacae resembled kanamycin acetyltransferase (KAT) in their specificity for aminoglycoside substrates. Not all isolates of bacteria that produce KAT are resistant to tobramycin, but the factors that determine susceptibility or resistance to tobramycin in KAT-producing bacteria have not yet been established.

FOOTNOTES

1 Present address: Department of Surgery, University of Washington, Seattle, Wash. 98195.

Antimicrob Agents Chemother. 1974 October; 6(4): 492-497
Copyright © 1974 American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • McManus, A. T., McManus, W. F., Mason, A. D. Jr, Aitcheson, A. R., Pruitt, B. A. Jr (1985). Microbial Colonization in a New Intensive Care Burn Unit: A Prospective Cohort Study. Arch Surg 120: 217-223 [Abstract]  


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