1 Clinical Microbiology, Central Hospital, S-351 85 Växjö, Sweden; 2 LEO Pharma, DK-2750 Ballerup, Denmark
Received 27 December 2002; returned 5 January 2003; revised 2 April 2003; accepted 2 April 2003
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Abstract |
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Keywords: cross-resistance, associated resistance, Escherichia coli
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Introduction |
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Most susceptibility surveys report only overall percentage resistance/susceptibility rates. Few publish information on cross-resistance or give details of associated resistance profiles. This paper presents detailed information on the resistance profiles of the 2478 E. coli isolates from the ECO·SENS Project, and on the distribution of different phenotypes in 16 European countries and Canada.
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Materials and methods |
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The analysis comprised the quantitative in vitro susceptibility data for the range of antimicrobials shown in Table 1 against E. coli (n = 2478) from the ECO·SENS Project involving 17 countries (for a list of countries see Table 2). Details of the study procedures have been published previously.1,2
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In vitro susceptibility was determined by agar disc diffusion performed to the standards of the Swedish Reference Group for Antibiotics.5 The zone diameter distributions and breakpoints used were as published previously.2
Cross-resistance was defined as the increased resistance to two or more drugs within the same class of antibiotics, and was considered to be due to a common resistance mechanism.
Associated resistance was defined as the increased resistance to two or more drugs of different drug classes, and was considered to be due to unrelated resistance mechanisms.
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Results |
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With the exception of fosfomycin, resistance to any agent was associated with increased resistance to the other agents tested. This was naturally more pronounced for related drugs (complete or partial cross-resistance) but was also clearly evident among drugs totally unrelated to each other. Thus, gentamicin resistance was 28.6% in E. coli resistant to ciprofloxacin but only 0.3% in susceptible E. coli. Similarly, ampicillin resistance was 69% in E. coli resistant to sulfamethoxazole compared with 12.1% in susceptible organisms (Table 1).
The most common and most pronounced multiple resistance profiles in each country are shown in Table 2. Ampicillin/sulfamethoxazole resistance was the most common phenotype, which was present in 8.7% of isolates and in all countries. The second most common was ampicillin/sulfamethoxazole/trimethoprim/trimethoprimsulfamethoxazole, which was present in 6.4% of isolates and in all countries. The third most common profile was sulfamethoxazole/trimethoprim/trimethoprimsulfamethoxazole, which was present in 2.0% of isolates and in 15 of 17 countries.
There were 21 isolates with resistance to seven or more antimicrobials, 10 of which were from Spain. The maximum number of resistances in any isolate was nine, one in Spain and two in Portugal. There were 15 strains resistant to ciprofloxacin and gentamicin (including other resistances), eight from Spain, three from Portugal, and one each from Belgium, Germany, Greece and Switzerland.
Resistance to cephalosporins, as measured by cefadroxil (closely related to cefalexin in type and activity) was seen in 53 of the E. coli isolates. None exhibited evidence of extended-spectrum ß-lactamases. However, three were resistant to cefotaxime and ceftazidime and were tentatively thought to be producers of AmpC.
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Discussion |
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It would thus seem logical that the high use of ampicillin, any sulphonamide, trimethoprim or the combination of sulphonamide and trimethoprim selects for resistance to any and all of these drugs. The fact that high consumers of co-amoxiclav (e.g. the UK and Ireland) have the highest rates of ampicillin and sulfamethoxazole resistance could indicate that this drug, by the partial cross-resistance that is easily observed (Table 2), selects for the same phenotypes and to the same or a higher degree as ampicillin and/or amoxicillin used alone. Comparing resistance frequencies and antimicrobial consumption in Denmark and Sweden, the same sort of cross-selective relationship seems true for sulfamethoxazole (21.2% resistance in Denmark versus 16.6% resistance in Sweden) and trimethoprim (10.6% and 8.3%, respectively) and the combination (8.2% and 8.3%, respectively). Sulphonamides are still commonly used in Denmark in lower urinary tract infections, but never in Sweden, where they have been off the market for more than 20 years. In Sweden sulphonamides have been replaced by trimethoprim, which has not occured in Denmark.
Fluoroquinolone resistance is an increasing problem in some European countries.4,7 Our results show that a multiple-resistant phenotype involving fluoroquinolone resistance is now present in most countries in Europe, and that this phenotype is selected for not only by the use of quinolones, but also by the use of ampicillin/amoxicillin, sulfamethoxazole and trimethoprimsulfamethoxazole.
Multiple ß-lactam resistance (i.e. ampicillin, co-amoxiclav, cefadroxil and mecillinam) was uncommon. Co-amoxiclav and mecillinam seemed reasonably well protected against the most common type of ampicillin resistance, which is most probably the TEM1 ß-lactamase. However, as previously discussed, co-amoxiclav is affected to some degree by the TEM1 enzyme, a fact that makes breakpoint setting a difficult matter. However, for mecillinam, which is almost exclusively used for uncomplicated urinary tract infection, the effect of the TEM1 enzyme can more easily be disregarded.8
In conclusion, the ECO·SENS Project shows that the frequency of antimicrobial resistance, as well as of multiple resistance in E. coli, shows a geographical gradient, being greater in southern Europe, particularly in Spain and Portugal, than in northern Europe. It also shows that resistance to any agent is associated with increased resistance to all other agents tested, fosfomycin being the only exception. This was naturally more pronounced for related drugs (complete or partial cross-resistance), but was also clearly evident among drugs totally unrelated to each other.
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Acknowledgements |
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Footnotes |
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References |
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2
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Kahlmeter, G. (2000). The ECO·SENS Project: a prospective, multinational, multicentre epidemiological survey of the prevalence and antimicrobial susceptibility of urinary tract pathogensinterim report. Journal of Antimicrobial Chemotherapy 46, Suppl. S1, 1522.
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Howard, A. J., Magee, J. T., Fitzgerald, K. A. et al. (2001). Factors associated with antibiotic resistance in coliform organisms from community urinary tract infection in Wales. Journal of Antimicrobial Chemotherapy 47, 30513.
4 . Daza, R., Gutierrez, J. & Piedrola, G. (2001). Antibiotic susceptibility of bacterial strains isolated from patients with community-acquired urinary tract infections. International Journal of Antimicrobial Agents 18, 2115.[CrossRef][ISI][Medline]
5 . The Swedish Reference Group of Antibiotics. (1997). Antimicrobial susceptibility testing in Sweden. Scandinavian Journal of Infectious Diseases, Suppl. 105, 531. [updates available at http://www.srga.org (2 April 2003, date last accessed)].
6 . Ames, S. G. (1989). The success of plasmid-encoded resistance genes in clinical bacteria. An examination of plasmid-mediated ampicillin and trimethoprim resistance genes and their resistance mechanisms. Journal of Medical Microbiology 28, 7383[ISI][Medline]
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Goettsch, W., van Pelt, W., Nagelkerke, N. et al. (2000). Increasing resistance to fluoroquinolones in E. coli from urinary tract infections in The Netherlands. Journal of Antimicrobial Chemotherapy 46, 2238.
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Sugakoff, W. & Jarlier, V. (2000). Comparative potency of mecillinam and other ß-lactam antibiotics against Escherichia coli strains producing different ß-lactamases. Journal of Antimicrobial Chemotherapy 46, Suppl. S1, 914.