A between-species comparison of antimicrobial resistance in enterobacteriain fecal flora

Enterobacteria in fecal flora are often reported to be highly resistant, Es cherichia coli is the main species; resistance data on other species are ra re. To assess the effect of the host's environment, antimicrobial resistanc e was determined in fecal species of the family Enterobacteriaceae from thr ee populations: healthy people (HP)(n = 125) with no exposure to antimicrob ials for 3 months preceding sampling, university hospital patients (UP) (n = 159) from wards where the antibiotic use was 112 defined daily doses (DDD )/bed/month, and geriatric long-term patients (LTP) (n = 74) who used 1.8 D DD/bed/month. The mean length of hospital stay was 5 days for the UP and 22 months for the LTP. The isolates mere identified to at least genus level, and MICs of 16 antimicrobials were determined. From the university hospital , resistance data on clinical Enterobacteriaceae isolates were also collect ed. Resistance data for on average two different isolates per sample (range , 1 to 5) were analyzed: 471 E. coli isolates and 261 other Enterobacteriac eae spp. Resistance was mainly found among E. coli; even in HP, 18% of E. c oli isolates were resistant to two or more antimicrobial groups, with MIC p atterns indicative of transferable resistance. Other fecal enterobacteria w ere generally susceptible, with little typically transferable multiresistan ce. Clinical Klebsiella and Enterobacter isolates were significantly more r esistant than fecal isolates. The resistance patterns at both hospitals mir rored the patterns of antibiotic use, but LTP E, coli isolates were signifi cantly more resistant than those from UP. Conditions permitting an efficien t spread may have been more important in sustaining high resistance levels in the LTP. E. coli was the main carrier of antimicrobial resistance in fec al flora; resistance in other species n as rare in the absence of antimicro bial selection.