Changes in sensitivity patterns to selected antibiotics in Clostridium difficile in geriatric in-patients over an 18-month period

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Abstract
Clostridium difficile-associated disease continues to be a major problem in hospitals and long-term care facilities throughout the developed world. Administration of certain antibiotics such as amoxycillin, oral cephalosporins and clindamycin is associated with the greatest risk of developing C. difficile disease. The two antibiotics used for treatment of C. difficile disease are vancomycin and metronidazole, to which there is currently very little resistance. Randomly selected isolates (186) from 90 patients being investigated during an 18-month epidemiological study into the disease were tested for their susceptibility to vancomycin, metronidazole, amoxycillin, clindamycin, cefoxitin and ceftriaxone by the NCCLS agar dilution method. There was a narrow range of MIC for the two treatment agents (vancomycin and metronidazole), from 0.5 to 4 μg ml−1, with no evidence of resistance. All strains were resistant to cefoxitin (MIC 64–256 μg ml−1), the antibiotic used in most selective media. All strains were of similar sensitivity to amoxycillin (MIC90= 4 μg ml−1). Most strains were resistant to ceftriaxone (MIC ≥ 64 μg ml−1) or of intermediate resistance (MIC ≥ 32 μg ml−1), with only two sensitive strains (MIC 16 μg ml−1). Clindamycin resistance was common, with 67 % of strains resistant (MIC ≥ 8 μg ml−1), 25 % with intermediate resistance (MIC ≥ 4 μg ml−1) and only 8 % sensitive (MIC ≤ 2 μg ml−1). Twelve isolates from six different patients had very high resistance to clindamycin (MIC ≥ 128 μg ml−1). Multiple isolates from the same patient, taken at different times, showed changes in susceptibility patterns over time. The only major change in susceptibility over the time-period was in clindamycin resistance; some strains appeared to become more resistant while others became less resistant. No differences were seen in the MIC50 and MIC90 of the different S-types of C. difficile identified, although some S-types were present in very small numbers. There was no correlation between the antibiotics prescribed and susceptibility.