Emergence of fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli in subjects from Finland

Evolution of susceptibilities of Campylobacter spp. to quinolones and macrolides

Erythromycin, new macrolides, and quinolones are alternatives for the treatment of Campylobacter infections. Concerns related to the emergence of resistance to both groups of drugs have been raised. We studied the evolution of antimicrobial susceptibilities of 275 clinical isolates of microorganisms of the genus Campylobacter isolated in our institution during a 5-year period (1988 to 1992). The microorganisms studied were C. jejuni (n = 230), C. coli (n = 42), and C. fetus (n = 3). The overall resistance rates (determined by the agar dilution method and the recommendations of the National Committee for Clinical Laboratory Standards) were as follows: erythromycin, 2.3%; clarithromycin, 2.3%; azithromycin, 1.9%; ciprofloxacin, 28.5%; norfloxacin, 31%; ofloxacin, 26.3%; and nalidixic acid, 36.8%. The evolution of resistance (percent resistance in 1988 versus percent resistance in 1992) was as follows: erythromycin, 2.6 versus 3.1; clarithromycin, 2.6 versus 3.1; azithromycin, 2.6 versus 3.1; ciprofloxacin, 0 versus 49.5; norfloxacin, 2.6 versus 55.5; ofloxacin, 0 versus 45.6; nalidixic acid, 2.6 versus 56.8. Our data show stable macrolide activity against Campylobacter spp. and the rapid development of quinolone resistance over the last 5 years.

Bacterial resistance to fluoroquinolones: lessons to be learned

Resistance to fluoroquinolone antibacterials has emerged in a limited form, largely amongst certain specific species and often restricted to single clones of these pathogens. Mediated by chromosomal mutation, the major mechanisms are alterations in gyrase subunits and reduced penetration associated with decreased outer membrane protein production. Resistance is most commonly seen to emerge amongst pathogens with higher than average initial MICs, particularly affected species being Pseudomonas aeruginosa and the staphylococci. Resistance is more likely to be encountered when such pathogens are exposed to concentrations at or below the MIC, which may result either from underdosage, the presence of the organism in a sequestered site, e.g. bone or prostate, or from confounding factors such as the presence of pus, indwelling prostheses or interactions which reduce absorption from the gastrointestinal tract. Repetitive use of these agents and continued use of fluoroquinolone precursors, such as nalidixic acid, may also contribute to resistance emergence. Most resistance is appearing amongst hospitalised patients and much of the apparent burden reflects horizontal cross-infection of many patients by a single resistant clone. There is very limited data linking increasing community use of fluoroquinolones with resistance emergence amongst pathogens such as Escherichia coli. In the main, the emergence of resistance can be anticipated and perhaps prevented or avoided for the sorts of risk groups and pathogens described. The use of adequate dosage by appropriate routes of administration in suitable patients and implementation of surveillance procedures for those at risk will minimise such problems. Policies for the effective use of these valuable agents should be part of everyday practice in hospitals.

Azithromycin resistance in Campylobacter jejuni and Campylobacter coli

The MICs of erythromycin, azithromycin and ciprofloxacin were determined for 60 human fecal isolates of Campylobacter. Of these, 30 strains selected on the basis of their resistance to erythromycin by disk diffusion were highly resistant to both erythromycin and azithromycin. Nine of these selected isolates were resistant to ciprofloxacin. The remaining 30 strains were non-selected, consecutive isolates of Campylobacter susceptible to erythromycin by disk diffusion and were shown to be two- to five-fold more susceptible to azithromycin than to erythromycin as determined by MIC testing.

Plasmid profiles and antimicrobial susceptibility of Campylobacter jejuni isolated from Israeli children with diarrhea

Thirty Campylobacter jejuni (C. jejuni) strains isolated from stools of Israeli children with enteritis were tested for sensitivity to eight antimicrobial agents (MIC) and the presence of plasmids. It was found that all the isolates were sensitive to ciprofloxacin, ofloxacin, furazolidone and erythromycin. Of the 30 strains tested, 21 (70%) were found to be tetracycline-resistant, a relatively high resistance rate as compared with data from other countries and previous reports from Israel. Plasmids were detected in 17 out of 30 C. jejuni isolates (55.6%). A total of nine different plasmid profiles could be distinguished; six profiles were represented by one strain each. Of the 21 tetracycline-resistant strains, plasmids were found in 17 isolates (80%) carrying from 1-2 to 5 plasmids of various sizes. No plasmids were found in tetracycline-sensitive strains, with the exception of one isolate which contained a 24.4 MDa plasmid and was co-trimoxazole-resistant. Our studies indicate a relatively high percentage of tetracycline-resistant C. jejuni isolates in the Tel Aviv area. In 80% of these strains, various plasmid profiles were detected.

Susceptibilities of beta-lactamase-positive and -negative strains of Campylobacter coli to beta-lactam agents

The percentages of susceptibility of 28 strains of Campylobacter coli to beta-lactam agents were 96% for amoxicillin and ampicillin, 57% for ticarcillin, 4% for cefoxitin and cefuroxime, 61% for cefotaxime, and 11% for ceftazidime. None of the strains were susceptible to penicillin G, piperacillin, cefazolin, cephalothin, cefamandole, and cefoperazone. All strains were susceptible to imipenem and ciprofloxacin, and 21% were susceptible to erythromycin. A beta-lactamase was detected in 68% of the strains by cefinase disks and by the nitrocefin method. The beta-lactamase-positive strains were significantly less susceptible to amoxicillin, ampicillin, and ticarcillin than the beta-lactamase-negative strains (P < or = 0.003). Clavulanic acid (0.25 microgram/ml) but not sulbactam and tazobactam (2 micrograms/ml) lowered to susceptible levels the amoxicillin and ampicillin MICs of the only strain of C. coli resistant to amoxicillin, ampicillin, and ticarcillin.

In vitro susceptibility of quinolone-resistant Campylobacter jejuni to new macrolide antibiotics

The MICs of erythromycin and three new macrolide antibiotics were determined for 36 quinolone-susceptible and 106 quinolone-resistant Campylobacter jejuni. The MIC90 values of azithromycin, clarithromycin, roxithromycin and erythromycin were 0.5, 4, 16 and 4 mg/l respectively. No difference was found between macrolide activity against the quinolone-susceptible and the quinolone-resistant strains. Clarithromycin and especially azithromycin might eventually replace erythromycin for the treatment of Campylobacter jejuni infections in view of their pharmacological properties.

The epidemiology of bacterial resistance to quinolones

The new fluoroquinolones have been in use for nearly 10 years in the treatment of community- and nosocomially-acquired infections. Resistant clones may be selected during therapy and disseminate if favourable epidemiological conditions prevail. Resistance to the fluoroquinolones is still rare in common pathogens with 97 to 100% of strains remaining susceptible. Resistance has been reported in methicillin-susceptible Staphylococcus aureus, Campylobacter jejuni/coli, Salmonella, Shigella and Escherichia coli. Among nosocomial pathogens, the incidence of fluoroquinolone resistance varies between bacterial species, countries and periods of study, and is dependent on local epidemiological factors and antibiotic policies. The highest incidence of resistance is observed in Serratia and Acinetobacter spp., and particularly in methicillin-resistant S. aureus. Surveillance programmes are needed to follow up trends in resistance to the fluoroquinolones and their possible association with clinical failures.

Emergence of resistance to erythromycin and fluoroquinolones in thermotolerant Campylobacter strains isolated from feces 1987-1991

During the period 1987 to 1991 a retrospective study was performed to determine the resistance of thermotolerant Campylobacter species isolated from feces to erythromycin and fluoroquinolones. Of the 672 strains studied, 614 (91.3%) were identified as Campylobacter jejuni and 58 (8.7%) as Campylobacter coli. During the study period the rate of resistance of Campylobacter jejuni to erythromycin remained relatively stable (0.9-3.5%), while resistance of Campylobacter coli to erythromycin emerged later (1989) with much higher rates (14.8-33%). Overall, 11.8% and 10.7% of Campylobacter jejuni strains isolated after 1987 were resistant to nalidixic acid and ciprofloxacin respectively, resistance increasing from 2.3% in 1988 to 32% in 1991. In 1991 the first strains of Campylobacter coli with resistance to these fluoroquinolones were detected (rates 29% and 26% respectively). Of the strains resistant to nalidixic acid, only 10.9% were susceptible to ciprofloxacin.