Characterization of high-level quinolone resistance in Campylobacter jejuni

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.

Mechanisms of resistance to quinolones

Mechanisms of resistance to the quinolones have been described for several bacterial species, but mainly for Escherichia coli and Staphylococcus aureus. Two principal mechanisms have been described: 1) alteration of the DNA gyrase, which is the target site of the quinolones; and 2) diminished accumulation in the cell as a result of either decreased uptake or increased efflux. Alteration of DNA gyrase is usually the result of a mutation in the gyrA, or more rarely, the gyrB gene. All substitutions in subunit A of the gyrase are located in the 67 to 106 amino-acid domain and are clustered around Ser-83 in E. coli and Ser-84 in S. aureus. A decrease in uptake has been described for Gram-negative bacteria such as Enterobacteriaceae and Pseudomonas aeruginosa. It has almost always been correlated with a modified electrophoretic profile of outer membrane proteins of the quinolone-resistant mutants. In E. coli, a decrease in OmpF seemed to be linked to the activation of the micF operon in most of the mutants described. These mutants were cross-resistant to unrelated antibiotics, such as trimethoprim, chloramphenicol, tetracycline, and some beta-lactams. In all these mutants the normal or enhanced efflux of quinolones increased the level of resistance. Enhanced efflux has been described as the second mechanism of resistance in S. aureus. Acquired resistance to the quinolones was thought, until recently, to result from chromosomal mutation. Plasmid-mediated resistance associated with an enhanced efflux has been described in S. aureus, but this needs to be confirmed. When a high level of resistance is observed, 2 or 3 mechanisms may be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Quinolones in the treatment of acute bacterial diarrhoeal diseases

Acute bacterial diarrhoea is still an important disease, especially in developing countries. Resistance to antibiotics among enteric pathogens is relatively common in many parts of the world. The quinolones are active in vitro against these organisms, and achieve high stool concentrations. Because of these features, quinolones have been used in the treatment of acute diarrhoeal diseases caused by various bacteria. They appear to be effective in the therapy of shigellosis and travellers' diarrhoea, as well as in the prevention of diarrhoeal disease in travellers. However, their role in the treatment of salmonella gastroenteritis has not been established yet.

Antimicrobial susceptibilities of Campylobacter jejuni and Campylobacter coli isolated in Sweden: a 10-year follow-up report

Resistance to erythromycin and doxycycline and more recently to fluoroquinolones has been reported to occur in Campylobacter spp. both in vitro and in patients treated with these antibiotics. The frequency of resistance to 14 antimicrobial agents in Campylobacter jejuni and Campylobacter coli isolated from patients infected in Sweden or abroad is described. For some agents, a comparison of susceptibility in strains of Campylobacter spp. isolated in 1978 with those isolated in 1988 is made. No general increase in in vitro resistance to antibiotics commonly used for the treatment of human gastroenteritis caused by C. jejuni or C. coli has occurred during the last 10 years in Sweden, which might be a consequence of strict antibiotic control. The numbers of strains from 1988 to 1989 resistant to ciprofloxacin and to norfloxacin included in this study (0.7 and 1.4%, respectively) are still fewer than those that were resistant to erythromycin (7.3%) or doxycycline (12.4%). There is, however, since 1989 to 1990 an indication of increasing resistance to these antibiotics.

Rapid emergence of quinolone resistance in Campylobacter jejuni in patients treated with norfloxacin

15/60 subjects from one center, who all took part in a multicenter double-blind, placebo-controlled study to evaluate the effect of norfloxacin on acute enteritis, had norfloxacin sensitive strains of Campylobacter jejuni in pre-study stool specimens. Eight of the 15 subjects received active drug. In 3 of these 8, high-level quinolone resistant Campylobacter strains of the same serotype as in pre-treatment samples were isolated 4-90 days after the initiation of treatment.

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

The in vitro susceptibilities of 102 human campylobacter strains isolated between 1978 and 1980 and 100 strains isolated in 1990 to ciprofloxacin, norfloxacin, erythromycin, gentamicin, and doxycycline were examined. The biotypes and heat-stable serotypes of the strains as well as antimicrobial treatments and travel history of the campylobacter-positive patients were also studied. The results indicated that susceptibility to erythromycin, gentamicin, and doxycycline has remained the same during the past 10 years. No gentamicin-resistant strains were found. Resistance to erythromycin was 3% in both groups of strains. However, the number of norfloxacin-resistant strains increased from 4 to 11% in the follow-up period, and ciprofloxacin-resistant strains, which had not occurred 10 years ago, composed 9% of the strains isolated in 1990. Thus, the increase of fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli has been significant in Finland in the past 10 years.