Diversity of plasmids in Achromobacter xylosoxidans isolates responsible for a seemingly common-source nosocomial outbreak.

Achromobacter xylosoxidans, an uncommon yet highly resistant opportunistic pathogen, was isolated from nine hospitalized patients during an 8-month period. It had been isolated from only seven patients with either nonfatal infection or colonization from 1981 to 1984. From June 1985 to January 1986, A. xylosoxidans was isolated 18 times from seven different sites (sputum, 7 times; urine, 4 times; blood, 3 times; and lung, pleural fluid, wound tissue, and tracheal aspirate, 1 time each). Four patients died, including the three with bacteremia. All but two patients had nosocomial infections and either were on the same ward or were cared for by the same staff members. Eleven A. xylosoxidans strains yielded eight distinct plasmids (8, 21, 23, 26, 38, 50, 51, and 64 megadaltons). Whole-cell peptide patterns of 10 of these strains were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Isolates from the same patient contained the same plasmids and had identical peptide patterns but differed from other strains in both parameters. Plasmids were absent from the two community-acquired isolates. Although nosocomial strains showed similar antibiotic resistance patterns (only moxalactam and ticarcillin-clavulanic acid were uniformly active) and cross-contamination was strongly suggested epidemiologically, results of plasmid and peptide analyses did not support the possibility of a single-strain outbreak.