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The occurrence of extended-spectrum beta-lactamase (ESBL)-producing isolates has increased worldwide. Fecal carriage of ESBL-producing isolates has mainly been detected in nosocomial outbreaks, and few studies have evaluated fecal carriage during nonoutbreak situations and among patients in the community. We have studied the prevalence of ESBLs in 1,239 fecal samples from 849 patients (64.1% of whom were ambulatory) in 1991 and have compared the prevalence data with those obtained in 2003 for 400 fecal samples from 386 patients (75.9% of whom were ambulatory) and 108 samples from independent healthy volunteers. Samples were diluted in saline and cultured in two MacConkey agar plates supplemented with ceftazidime (1 microg/ml) and cefotaxime (1 microg/ml), respectively. Colonies were screened (by the double-disk synergy test) for ESBL production. The clonal relatedness of all ESBL-producing isolates was determined by pulsed-field gel electrophoresis with XbaI digestion; and the ESBLs of all ESBL-producing isolates were characterized by isoelectric focusing, PCR, and sequencing. The rates of fecal carriage of ESBL-producing isolates increased significantly (P < 0.001) in both hospitalized patients and outpatients, from 0.3 and 0.7%, respectively, in 1991, to 11.8 and 5.5%, respectively, in 2003. The rate of occurrence of ESBL-producing isolates among healthy volunteers was 3.7%. All ESBL-producing isolates recovered in 2003 were nonepidemic clones of Escherichia coli. ESBL characterization revealed an increasing diversity of ESBL types: TEM-4 and CTX-M-10 were the only enzymes detected in 1991, whereas TEM-4, TEM-52, SHV-12, CTX-M-9, CTX-M-10, CTX-M-14, and a CTX-M-2-like enzyme were recovered in 2003. The ESBL-producing isolates recovered from outpatients in 2003 corresponded to a CTX-M-9-type cluster (62.5%) and SHV-12 (31.2%), whereas TEM-4 was detected only in hospitalized patients. The frequencies of coresistance in isolates recovered in 2003 were as follows: sulfonamide, 75%; tetracycline, 64.3%; streptomycin, 57.1%; quinolones, 53.5%; and trimethoprim, 50%. The increased prevalence of fecal carriage of ESBL-producing isolates during nonoutbreak situations in hospitalized patients and the establishment of these isolates in the community with coresistance to non-beta-lactam antibiotics, including quinolones, represent an opportunity for these isolates to become endemic.

The sensitivity to cefotaxime and amikacin of 14,272 Gram-negative bacilli (Enterobacteriaceae and non-fermenting Gram-negative bacilli) isolated from clinical samples was studied during the period 1980 to 1985. The minimum inhibitory concentration (MIC) was determined by means of diffusion in agar. Strains were considered resistant to cefotaxime and amikacin if the MIC values were greater than 16 mg/L and greater than 8 mg/L, respectively. The MIC90 reached the critical value for cefotaxime in the case of Citrobacter spp., Escherichia coli, Klebsiella spp., Proteus mirabilis, Salmonella spp. and Shigella spp., and for amikacin in the case of Citrobacter spp., Enterobacter spp., E. coli, Klebsiella spp., P. mirabilis, Proteus vulgaris, Salmonella spp. and Serratia spp. Only Shigella spp. were sensitive to cefotaxime but not to amikacin, and only strains of Enterobacter spp. and Serratia spp. were sensitive to amikacin but not to cefotaxime.