Servicio de Microbiología y Enfermedades Infecciosas, Hospital General Universitario Gregorio Marañón, C/Doctor Esquerdo 46, 28007 Madrid, Spain
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Abstract |
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Introduction |
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The in vitro activity of the older quinolones against anaerobic bacteria has been reported to be moderate or poor, so they have not been considered for use in treating CDAD. However, these antimicrobials have rarely been involved in the induction of the disease. A few reports have associated ciprofloxacin use with cases of CDAD,4 but the low frequency of cases reported suggests that their ability to induce CDAD is low.
Recently, some new quinolones have become available. The spectrum of these new drugs has broadened, and some are active against anaerobes.5 Data on their in vitro activities specifically against C. difficile are limited to studies including a wide range of different anaerobe species in which C. difficile is often represented by only a few isolates.57 Our study examines the in vitro activities of new and established quinolones against C. difficile in order to assess their potential utility in the treatment of CDAD and their possible role as inducers of the disease.
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Materials and methods |
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Antimicrobial agents were kindly provided by the following manufacturers: levofloxacin, Hoechst Marion Roussel (Kansas City, KS, USA); grepafloxacin, GlaxoWellcome (London, UK); trovafloxacin, Pfizer (New York, NY, USA); ciprofloxacin, Bayer (Leverkusen, Germany). Ofloxacin was purchased from Sigma Laboratories (St Louis, MO, USA). All agents were prepared and stored according to the manufacturers' instructions.
Antimicrobial susceptibility testing was performed by the agar dilution method, on brucella blood agar, according to the National Committee for Clinical Laboratory Standards (NCCLS).8 Strains were tested with an inoculum of 105 cfu applied with a multipoint inoculator. Plates were incubated at 37°C for 48 h in anaerobic conditions (80% nitrogen, 10% hydrogen, 10% carbon dioxide). The MIC was defined as the lowest concentration of the agent that inhibited growth. The appearance of one or two colonies or a barely visible haze was disregarded. Reference strains were included as controls to monitor the antimicrobial susceptibility testing. The breakpoint for resistance (not clearly defined by the NCCLS for the antimicrobials and/or anaerobic bacteria assayed) was 2 mg/L for ciprofloxacin and
4 mg/L for the remaining agents.
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Results |
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Discussion |
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So far, most established quinolones have shown low activity against anaerobes and specifically against C. difficile. New quinolones are now available with more promising activity against anaerobic bacteria.5 No clearly standardized breakpoints have been reported for susceptibility testing of anaerobes, especially when testing new drugs. In selecting breakpoints, we considered breakpoints for other microorganisms or those used by other authors in similar conditions.5,7 In our study, the MIC90 was 8 mg/L for all the antimicrobials tested. C. difficile showed very high rates of resistance to ciprofloxacin, ofloxacin, levofloxacin and grepafloxacin. Trovafloxacin was much more active against C. difficile than the other quinolones, but a third of the isolates tested were resistant to trovafloxacin. Although trovafloxacin has recently been banned in the European Union owing to potential hepatotoxicity, we included it in our study because some other countries are still using it or are planning to introduce it in the near future.
It is not known whether C. difficile, which may, in small numbers, be part of the normal enteric flora, overgrows because of suppression of the susceptible flora by antimicrobials or whether it is acquired exogenously after the reduction of the indigenous flora which may, normally, act as a barrier to infection. To our knowledge, with one exception,9 there are no reports of CDAD being induced by the new quinolones, although it is possible that, because of their broader antibacterial spectrum and hence their potential reduction of the normal flora, they might be more likely to induce CDAD. As shown by our results, these new drugs do not have good anti-clostridial activity. A recent study indicates that trovafloxacin can suppress bowel flora without causing overgrowth of C. difficile after 17 days of follow-up.10 However, in the intensive care unit of our hospital, two patients who were given trovafloxacin 300 mg/day orally for 21 days to treat lower respiratory tract infection both had severe episodes of diarrhoea in which toxigenic C. difficile was isolated from stool samples (on day 6 in one patient and on day 15 in the other). In both cases, anti-clostridial therapy was introduced, with a favourable clinical outcome (unpublished data).
In our opinion, none of the antimicrobials studied offers a reliable therapeutic option for CDAD. Their role as potential inducers of CDAD, resulting from both their lack of favourable activity against C. difficile and their wide spectrum of antimicrobial activity, which includes many anaerobic bacteria, remains unknown.
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Acknowledgments |
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Notes |
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References |
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2 . Kyne, L., Merry, C., O'Connell, B., Keane, C. & O'Neill, D (1998). Community-acquired Clostridium difficile infection. Journal of Infection 36, 2878.[ISI][Medline]
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4 . Hillman, R. J., Rao, G. G., Harris, J. R. & Taylor-Robinson, D. (1990). Ciprofloxacin as a cause of Clostridium difficile-associated diarrhoea in an HIV antibody-positive patient. Journal of Infection 21, 2057.[ISI][Medline]
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6 . Wexler, H. M., Molitoris, E., Reeves, D. & Finegold, S. M. (1994). In vitro activity of DU-6859a against anaerobic bacteria. Antimicrobial Agents and Chemotherapy 38, 25049.[Abstract]
7 . Woodcock, J. M., Andrews, J. M., Boswell, F. J., Brenwald, N. P. & Wise, R. (1997). In vitro activity of BAY 12-8039, a new fluoroquinolone. Antimicrobial Agents and Chemotherapy 41, 1016.[Abstract]
8 . National Commitee for Clinical Laboratory Standards. (1997). Methods for Antimicrobial Susceptibility Testing of Anaerobic BacteriaFourth Edition: Approved Standard M11-A4. NCCLS, Villanova, PA.
9 . Inagaki, Y., Yamamoto, N., Chida, T., Okamura, N. & Tanaka, M. (1995). The effect of DU-6859a, a new potent fluoroquinolone, on faecal microflora in human volunteers. Japanese Journal of Antibiotics 48, 36879.[Medline]
10 . van Nispen, C. H., Hoepelman, A. I., Rozenberg-Arska, M., Verhoef, J., Purkins, L. & Willavize, S. A. (1998). A double-blind, placebo-controlled, parallel group study of oral trovafloxacin on bowel microflora in healthy male volunteers. American Journal of Surgery 176, 27S31S.[ISI][Medline]
Received 30 June 2000; returned 21 August 2000; revised 25 September 2000; accepted 26 October 2000