Antimicrobial resistance in human oral and intestinal anaerobic microfloras.

In the present study we determined the resistance patterns of anaerobic bacteria from human saliva and stool specimens and investigated whether there were significant differences in resistance between outpatients and hospitalized patients, regardless of whether they had received antimicrobial agents. No bacterial strains resistant to ampicillin, piperacillin, cefoxitin, cefuroxime, imipenem, clindamycin, doxycycline, chloramphenicol, or metronidazole were isolated from the saliva samples. However, resistance to ampicillin, cefoxitin, and cefuroxime was found in strains from 70% of the fecal samples (mainly Bacteroides thetaiotaomicron, Clostridium innocuum, and Bacteroides ovatus). Resistance to both ampicillin and cefuroxime was frequently found in 19% of the isolated strains (mainly B. thetaiotaomicron, B. ovatus, and Bacteroides vulgatus). No strains that were resistant to imipenem, chloramphenicol, or metronidazole were found. Hospitalization and/or intake of antimicrobial agents was associated with an increase in the relative number of resistant anaerobic intestinal bacteria. The percentage of resistant anaerobic strains encountered, compared with the total number of anaerobic bacteria in the normal fecal microflora, was between 5.2 and 14.8%, with the lower value associated with the outpatient group. Two-thirds of the resistant strains from this group had a relative frequency of less than 1% of the total anaerobic flora, while one-third of the strains were present at a level of greater than 1%; for the hospitalized patients, two-thirds of the strains were present at a level of greater than 1%, and one-third of the strains were present at a level of less than 1% (P < 0.001). Patients who had received antimicrobial agents for 6 days or more (n=20) had an average of 1.6 resistant anaerobic strains each, while patients treated for 3 to 5 days (n = 30) had a mean number of 0.87 resistant strains each ( P < 0.05).