Antibiotic resistance transfer from nonpathogenic to pathogenic bacteria.

Alcaligenes species is a common contaminant of "wet" environmental areas on the surgical ward. Although thought to be a nonpathogenic organism, recent clinical experience on the burn and trauma service has led us to believe that antibiotic resistance transfer may occur between Alcaligenes and Pseudomonas aeruginosa. To evaluate this possibility, germ-free mice were contaminated with Alcaligenes species, which quickly established in the animals' gastrointestinal tracts. These animals then were burned and the wound was seeded with additional Alcaligenes. After 72 hours the average bacterial count was 4.5 X 10(6) cells/gm of tissue, and all animals survived. Ten additional germ-free mice were contaminated with a resistant (Amikacin, tobramycin, gentamicin, and Sisomicin) Alcaligenes species. When a Pseudomonas aeruginosa strain sensitive to these antibiotics was introduced into the environment, it rapidly overgrew the Alcaligenes species but developed resistance to those four antibiotics to which it had been sensitive previously. These animals were then subjected to a 10 second immersion burn, and the wound was seeded with the same strain of Alcaligenes. The Pseudomonas quickly overgrew the Alcaligens on the burn wound and became established, with an average count being 5.2 X 10(8) cells/gm of tissue. When this experiment was repeated, establishing antibiotic sensitive Pseudomonas in the germ-free animals prior to inoculation of resistant Alcaligenes, the R-transfer again occurred but required a longer time.