Gentamicin-resistance plasmids in an intensive care unit.

To better understand the role of plasmids and their importance in the endemic antibiotic resistance of Enterobacteriaceae, we began a prospective study of our combined medical intensive care/coronary care unit. An initial culture survey of the patients, ward staff, and environment was followed by a prospective sampling of 139 consecutive new admissions at the time of admission to the unit, and at regular intervals thereafter for the remainder of their stay. All cultures were planted on agar-containing gentamicin. Of the 147 patients studied, 12 (8.2%) were colonized with 20 strains of gentamicin-resistant gram-negative bacilli (GRGNB) at 29 sites. An additional four GRGNB were isolated from the environment. Of the 24 GRGNB strains, 7 (29%) Enterobacteriaceae carried plasmids shown to carry the gentamicin-resistance determinant. Plasmids were further characterized by restriction endonuclease digestion profiles of plasmid DNA purified from E. coli C600 transconjugants or transformants. A 93 kb plasmid introduced to the unit by a Serratia liquefaciens colonizing a patient transferred from another area in the hospital was identical to 93 kb plasmids carried by a C. amalonaticus and an E. aerogenes subsequently colonizing another patient on the unit. A 60 kb plasmid, first From the Division of Infectious Disease, Case Western University School of Medicine, Research, Nursing, and Laboratory Services, Veterans Administration Medical Center, Cleveland, Ohio. Presented in preliminaryform at the annual meeting of the American Thoracic Society, Kansas City, Missouri, 1983. This work was supported by a grant from the Veterans Administration. The authors acknowledge the staff of the intensive care unit for their cooperation; Dr. Carl Vartian for review of the manuscript; Ms. Elizabeth Williams for secretarial assistance; Dr. D. Bobey for aminoglycoside modifying enzyme analysis; and Dr. A.A. Medeiros for p3-lactamase analysis of plasmid-bearing E. coli derivatives. Address reprint requests to David M. Shlaes, MD, PhD, Chief, Infectious Diseases and Microbiology, Cleveland Veterans Administration Medical Center, 10701 East Boulevard, Cleveland, OH 44106. isolated from a S. marcescens colonizing a sink drain was later isolated from an E. cloacae colonizing a patient. Our results indicate that spread of specific R-plasmids may be ne mechanism for dissemination of antibiotic resistance o our MICU/CCU. [Infect Control 1986; 7(7):355-361.]