RECOVERY OF NOSOCOMIAL FECAL FLORA FROM FROZEN STOOL SPECIMENS AND RECTAL SWABS - COMPARISON OF PRESERVATIVES FOR EPIDEMIOLOGIC STUDIES

The recovery of antibiotic-susceptible and -resistant aerobic Gram-neg ative bacilli from stool specimens and from mock rectal swabs after fr eezing (-20C degrees) for as long as 4 weeks was studied using three p reservatives: Cary-Blair (CB) transport medium, buffered glycerol sali ne (BGS), and Para Pak C&S solution (CS). In addition, the recovery of enterococci from rectal swabs was investigated after storage of swabs in Stuart's transport media at 4 degrees C for as long as 4 weeks. Th e log(10) decreases in bacterial counts from seeded stool suspensions frozen in BGS were 0.64 (i.e., fourfold) and 1.16 after 1 and 4 weeks, respectively, which were significantly less (p < .05) than 1 and 4 we ek decreases following freezing in CB (1.57 and 2.85) or in CS (1.50 a nd 2.45). The recovery of Gram-negative bacilli from patients' rectal swabs preserved in BGS was consistent with the results of the experime nts with seeded stool suspensions. There was no detectable decrease in recovery of enterococci from rectal swabs stored at 4 degrees C. BGS performed well as a preservative for freezing stool specimens or recta l swabs for later recovery of nosocomial Gram-negative bacilli; entero cocci survived well in refrigerated rectal swab specimens.