Prevalence of fluoroquinolone resistance in clinical strains of Campylobacter jejuni isolated in Spain

The purpose of the present study was to investigate the prevalence of resistance to quinolones and other agents in our clinical Campylobacter spp. isolates. With this aim, 60 strains of Campylobacter jejuni and Campylobacter coli isolated from patients (82% children) with diarrhoea in the Residencia Sanitaria Ntra. Sra. del Cristal, Orense (Northwest Spain) between June 1992 and January 1993 were studied. Antimicrobial susceptibility testing was carried out by two different methods: a previously validated commercial broth microdilution technique (for ciprofloxacin, norfloxacin, pefloxacin and 20 other antimicrobial agents), and agar disc diffusion (for nalidixic acid, ciprofloxacin, norfloxacin and 12 other agents). The overall agreement between the two methods was more than 90%. Twenty-two hippurate-positive strains were characterized as being resistant to nalidixic acid (30 mu g disc). All were C. jejuni. Nineteen of the 22 nalidixic acid-resistant C. jejuni strains (16 C. jejuni jejuni 1, two C. jejuni jejuni 2, and one C. jejuni doylei) showed complete cross resistance to fluoroquinolones: ciprofloxacin (10 mu g disc, MIC > 2 mg/L), norfloxacin (10 mu g disc, MIC > 8 mg/L) and pefloxacin (MIC > 4 mg/L); the other three strains showed incomplete cross resistance to fluoroquinolones, two of them were susceptible to norfloxacin (10 mu g disc, MIC less than or equal to 2 mg/L) and the other was susceptible to ciprofloxacin (10 mu g disc, MIC less than or equal to 1 mg/L). Analysis of the antibiogram patterns revealed no significant difference between the 19 fluoroquinolone-resistant (FQR) and the fluoroquinolone-susceptible (FQS) strains with respect to sensitivity to most other antimicrobial agents tested (cephalothin, cefazolin, cefuroxime, vancomycin, aztreonam, gentamicin, tobramycin, nitrofurantoin, imipenem, co-amoxiclav, clindamycin, chloramphenicol, tetracycline, cotrimoxazole, cefotaxime, ceftazidime, amoxycillin, fosfomicin, piperacillin, ticarcillin, novobiocin and kanamycin). A single erythromicin-resistant, quinolone-susceptible strain of C. coli was isolated. Resistance to ampicillin (MIC > 16 mg/L) was found to be more frequent in the FQR strains (36.8%) than in the FQS population (26.6%). Susceptibility to high amounts of the DNA gyrase B inhibitor novobiocin (100 mu g disc) was much more frequent in the FQS strains (72.3%) than in the FQR population (31.3%).