Programme Hospitalier Recherche Clinique, Institut Pasteur, Inserm, French Public Health Agency.

In one French hospital the rate of resistance to ciprofloxacin in Helicobacter pylori was 3.3% (2 of 60 strains) in 1999. The six resistant clinical strains (four from 1996 and two from 1999) and three ciprofloxacin-selected single-step mutants studied carried one gyrA mutation but none in gyrB. Clinafloxacin and garenoxacin were the most active fluoroquinolones against these mutants. Occurrence of a second gyrA mutation was associated with high MICs of all fluoroquinolones tested.

Summary Helicobacter pylori strains that harbour the Cag pathogenicity island (Cag PAI) induce interleukin (IL)‐8 secretion in gastric epithelial cells, via the activation of NF‐κB, and are associated with severe inflammation in humans. To investigate the influence of Cag PAI‐mediated inflammatory responses on H. pylori adaptation to mice, a selection of H. pylori clinical isolates (n= 12) was cag PAI genotyped and tested in co‐culture assays with AGS gastric epithelial cells, and in mouse colonization studies. Six isolates were shown to harbour a complete cag PAI and to induce NF‐κB activation and IL‐8 secretion in AGS cells. Of the eight isolates that spontaneously colonized mice, six had a cag PAI– genotype and did not induce pro‐inflammatory responses in these cells. Mouse‐to‐mouse passage of the two cag PAI+‐colonizing strains yielded host‐adapted variants that infected mice with bacterial loads 100‐fold higher than those of the respective parental strains (P= 0.001). These mouse‐adapted variants were affected in their capacity to induce pro‐inflammatory responses in host cells, yet no changes in cag PAI gene content were detected between the strains by DNA microarray analysis. This work provides evidence for in vivo selection of H. pylori bacteria with a reduced capacity to induce inflammatory responses and suggests that such bacteria are better adapted to colonize mice.

A total of 198 nonrepetitive clinical strains of Clostridium difficile isolated from different French hospitals in 1991 (n ‫؍‬ 100) and 1997 (n ‫؍‬ 98) were screened for decreased susceptibility to fluoroquinolones by plating onto Wilkins-Chalgren agar containing 16 g of ciprofloxacin per ml. The frequency of decreased susceptibility was 7% (14 of 198) and was identical for the years 1991 and 1997. Serogroups C, H, D, A9, and K accounted for five, four, two, one, and one of the resistant strains, respectively, one strain being nontypeable. Arbitrarily primed PCR typing showed that all resistant strains had unique patterns except two serotype C strains, which could not be clearly distinguished. All isolates with decreased susceptibility carried a mutation either in gyrA (eight mutations, amino acid changes Asp713Val in one, Thr823Ile in six, and Ala1183Thr in one) or in gyrB (six mutations, amino acid changes Asp4263Asn in five and Arg4473Leu in one). These changes are similar to those already described in other species except for Asp713Val, which is novel, and Ala1183Thr, which is exceptional. Attempts to detect the topoisomerase IV parC gene by PCR amplification with universal parC primers or DNA-DNA hybridization under low-stringency conditions were unsuccessful. The susceptibilities of all resistant strains to ciprofloxacin and ethidium bromide were not affected by the addition of reserpine at 20 g/ml. In conclusion, decreased susceptibility to fluoroquinolones in C. difficile is rare in France and is associated with the occurrence of a gyrA or gyrB mutation.Vancomycin and metronidazole are effective antibiotics for the treatment of Clostridium difficile-associated diarrhea (19,24). However, at least 15% of patients relapse after discontinuation of treatment for poorly understood reasons (23, 24). Other treatments may be more effective in preventing relapses.The in vitro activities against C. difficile of older fluoroquinolones like ciprofloxacin and ofloxacin are poor, but those of some new compounds like moxifloxacin are markedly increased (1,3,17,25). Thus, these drugs could become therapeutic alternatives for the treatment of C. difficile-associated diarrhea. Decreased susceptibility to fluoroquinolones in C. difficile has already been described (2, 3, 13, 26), but the data reported are controversial and the genetic mechanisms involved are poorly understood.In the present work, 198 French clinical strains of C. difficile were screened for decreased susceptibility to fluoroquinolones, and the genetic basis of this phenomenon was investigated. MATERIALS AND METHODSBacterial strains. Reference strain ATCC 9689 and 198 nonrepetitive clinical isolates obtained in 1991 (n ϭ 100) and 1997 (n ϭ 98) from 36 French hospitals (7) were studied. Serotyping of the strains had been performed in a previous study (7) by the method of Delmée et al. (12). Serogroups A, C, D, F, G, H, and K accounted for 9, 22, 8, 1, 4, 19, and 14% of the strains, respectively, and 23% of the strains were untypeable. Strains were cultured in...