JAC Advance Access originally published online on January 25, 2006
Journal of Antimicrobial Chemotherapy 2006 57(3):569-572; doi:10.1093/jac/dkl002
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Reduction in fluoroquinolone susceptibility among non-typhoidal strains of Salmonella enterica isolated from Finnish patients
1 Antimicrobial Research Laboratory, Department of Bacterial and Inflammatory Diseases, National Public Health Institute, Kiinamyllynkatu 13, 20521 Turku, Finland; 2 Department of Medicine, Turku University Hospital, Kiinamyllynkatu 4-8, 20520 Turku, Finland; 3 Enteric Bacteria Laboratory, Department of Bacterial and Inflammatory Diseases, National Public Health Institute, Mannerheimintie 166, 00300 Helsinki, Finland
* Corresponding author. Tel: +358-2-3316600; Fax: +358-2-331-6699; E-mail: antti.hakanen{at}utu.fi
Received 19 October 2005; returned 6 December 2005; revised 11 December 2005; accepted 23 December 2005
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
Objectives: The proportion of Salmonella isolates with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, especially in South-east Asia. The present study was performed to evaluate the incidence of and changes in quinolone resistance in Salmonella isolates of either foreign or domestic origin in Finland.
Methods: A total of 1004 Salmonella isolates collected from Finnish patients between 2000 and 2004 were analysed for ciprofloxacin susceptibility. Of these isolates, 504 were of domestic origin and 500 were of foreign origin, collected from travellers to 43 different countries. The Salmonella collection consisted of 89 different serotypes. All isolates belonged to non-typhoidal Salmonella enterica.
Results: Of all isolates, 3 (0.3%) were ciprofloxacin-resistant (MIC 
4 mg/L) and 214 (21.3%) exhibited reduced susceptibility to ciprofloxacin (MIC 0.125–2 mg/L). The annual proportion of reduced susceptibility varied between 3 and 15% among the domestic Salmonella isolates (P = 0.123). Between 2000 and 2004, the annual proportion of reduced susceptibility increased significantly (from 23 to 39%; P = 0.001) among all foreign isolates as well as among those from Spain alone (from 4 to 73%; P < 0.001). Among the isolates from Thailand, reduced ciprofloxacin susceptibility remained at a constantly high level (52–66%) throughout the study.
Conclusions: Our results show that reduced fluoroquinolone susceptibility in S. enterica is not restricted to South-east Asia alone but continues to grow rapidly in many parts of the world including countries of the European Union.
Keywords: salmonella , quinolones , ciprofloxacin , drug resistance , enteric bacteria
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
The proportion of Salmonella strains with reduced susceptibility to fluoroquinolones has increased during recent years in many countries.1,2 This is of concern, since, according to several reports, treatment failures may occur when fluoroquinolones are used to treat infections caused by strains with reduced susceptibility to this antimicrobial group.1,3,4
Fluoroquinolone susceptibility of Salmonella enterica isolates has been surveyed in the National Public Health Institute, Finland, since 1995 by analysing Salmonella isolates from Finnish patients who acquired the disease either at home (i.e. domestic isolates) or abroad (i.e. foreign isolates). During these annual surveys, a significant increase was observed between 1995 and 1999 in the annual proportions of reduced fluoroquinolone susceptibility among domestic Salmonella isolates (from 0 to 4.1%) as well as among those of foreign origin (from 3.9 to 23.5%).5,6 The increase was most prominent among the isolates from travellers returning from South-east Asia, especially Thailand.6 The present study was performed to evaluate the subsequent incidence of and changes in quinolone resistance in Salmonella isolates of either foreign or domestic origin in Finland. Special efforts were made to define the countries presently associated with reduced fluoroquinolone susceptibility of salmonellas.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
We included in this study a total of 1004 Salmonella isolates collected between 2000 and 2004 from Finnish patients seeking medical assistance for gastroenteritis. Starting in January each year, we consecutively collected 100 foreign and 100 domestic isolates, which account for 7–9% of the total annual Salmonella isolates in Finland. The aim was to include only epidemiologically unrelated strains. An isolate was designated to be of foreign origin if the patient had reported travel abroad during 1 month before the specimen date. All other isolates were designated to be of domestic origin. Epidemiological information regarding potential travelling and the travel destination was collected from the forms accompanying each isolate sent to the Enteric Bacteria Laboratory of the National Public Health Institute, Helsinki, which serves as the National Salmonella Reference Centre in Finland. Isolates recovered from distinct sources were determined to be epidemiologically unrelated. For each Salmonella outbreak recognized, only one isolate representing the epidemic strain was included.
The MICs of ciprofloxacin for the isolates were determined by the standard plate agar dilution method according to the National Committee for Clinical Laboratory Standards (presently the Clinical and Laboratory Standards Institute) guidelines.7 Mueller-Hinton II agar (BBL, Becton Dickinson and Company, Cockeysville, MD, USA) was used as the culture medium. Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, E. coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853 were used as controls in testing for susceptibility.
The breakpoint value for reduced ciprofloxacin susceptibility was chosen as 0.125 mg/L on the basis of earlier publications.1,6,8 This breakpoint value is supported by histogram and scatterplot analyses combined with sequencing data.1,6,8
Data analysis
The susceptibility data were analysed by using the WHONET5 computer program (available from http://www.who.int/drugresistance/whonetsoftware/en/). In statistical analyses, data were summarized with numbers and proportions of Salmonella isolates. Logistic regression with year as a covariate was used when modelling the trend over years. Differences between groups were studied with interactions in the model, but final analysis was performed for each group separately. Predicted values with 95% confidence intervals were used when plotting the trend. P values < 0.05 were interpreted as significant. The data were analysed using SAS PROC GENMOD (SAS system for Windows, release 8).
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
Of the 1004 Salmonella isolates studied, 500 were classified as being of foreign origin and 504 were classified as being of domestic origin. Of all isolates, 98% were from stools and 2% were from extraintestinal sources. The Salmonella collection consisted of 89 different serotypes. All isolates belonged to non-typhoidal S. enterica. The most common serotypes among the Salmonella isolates from travellers were Salmonella Enteritidis and Salmonella Typhimurium, accounting for 36 and 7% of those isolates, respectively. The proportion of Salmonella Enteritidis among the foreign isolates was 34% in 2000, 48% in 2001, 41% in 2002, 25% in 2003 and 31% in 2004. Among the domestic salmonellas, Salmonella Typhimurium and Salmonella Enteritidis were the most common serotypes, accounting for 36 and 17% of the isolates, respectively. The proportion of Salmonella Typhimurium among the domestic isolates was 25% in 2000, 36% in 2001, 45% in 2002, 21% in 2003 and 52% in 2004.
Of the 500 foreign isolates, the country where salmonellosis was acquired was identified for 496 isolates, collected from travellers to 43 different countries. The origin of two isolates was traced to a continental level, while the origin of two isolates remained unknown. The majority of the isolates classified as being of foreign origin were from travellers to Asia, Europe or Africa (Table 1). The most common countries of origin were Thailand with 169 (34%) isolates, Spain with 123 (25%) isolates, Egypt with 42 (8%) isolates and India with 28 (6%) isolates.
|
Of all 1004 Salmonella isolates, 3 (0.3%) were ciprofloxacin-resistant (MIC
4 mg/L) and 214 (21.3%) exhibited reduced susceptibility to ciprofloxacin (MIC 0.125–2 mg/L). These isolates with reduced susceptibility consisted of 173 foreign isolates and 41 domestic isolates. Between 2000 and 2004, the annual proportion of reduced susceptibility increased from 23% (23/101) to 39% (39/99) (P = 0.001) among the foreign isolates and from 8% (8/104) to 10% (10/100) (P = 0.123) among the domestic isolates (Figure 1).
|
The 217 Salmonella isolates with reduced ciprofloxacin susceptibility included 26 different serotypes. The most common serotypes were Salmonella Enteritidis (26% of isolates), Salmonella Hadar (19%) and Salmonella Virchow (12%). Of all 267 Salmonella Enteritidis isolates included in the study, 57 (21%) showed reduced susceptibility to ciprofloxacin.
The isolates with reduced ciprofloxacin susceptibility were obtained from travellers returning from 21 different countries, the majority of the isolates being from Thailand (n = 98), Spain (n = 26) and Egypt (n = 11). The geographic distribution of these isolates to the continental level is shown in Table 1. Between 2000 and 2004, the annual proportion of reduced ciprofloxacin susceptibility increased from 4% (1/25) to 73% (8/11) (P < 0.001) among the isolates from Spain (Figure 1), and from 0% (0/6) to 31% (5/16) (P = 0.094) among the isolates from Egypt (Figure 1).
Among the isolates with reduced ciprofloxacin susceptibility from Thailand, Spain and Egypt, 20, 3 and 6 different serotypes, respectively, were identified. These findings exclude the presence of only one or very few clones of fluoroquinolone non-susceptible Salmonella strains. Of the 26 Salmonella isolates with reduced susceptibility from Spain, 23 belonged to Salmonella Enteritidis, 13 of them being of phage type 1. Of the 98 Salmonella isolates with reduced susceptibility from Thailand, 10 (10%) belonged to Salmonella Enteritidis, three of them being of phage type 1.
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
We show here that the annual proportion of reduced ciprofloxacin susceptibility among Salmonella isolates from Finnish travellers increased significantly (from 23 to 39%) between 2000 and 2004. The majority of the travellers acquired Salmonella isolates with reduced susceptibility in Thailand, where their frequency remained at a constantly high level (52–66%) throughout the study period, having increased dramatically between 1995 and 1999.6 In Spain, Salmonella isolates with reduced susceptibility had already existed in the late 1990s6 but increased significantly (from 4 to 73%) between 2000 and 2004. Among the isolates from Egypt, Salmonella isolates with reduced ciprofloxacin susceptibility emerged in 2001, after which they rapidly increased. This increase did not reach statistical significance in the present study but, so far, the number of quinolone-resistant isolates from Egypt has been small. These results are alarming, since they show that the reduced fluoroquinolone susceptibility in salmonellas continues to grow rapidly in many parts of the world, including countries of the European Union and Africa.
The factors behind the rapidly increased quinolone resistance among Salmonella isolates have aroused a lot of speculation. Previous studies have shown that reduced fluoroquinolone susceptibility in salmonellas is usually associated with a point mutation leading to an amino acid change in their quinolone resistance determining region of the gyrA gene.4,6,8 Resistance based on mutations in gyrase genes may have gone forward by selection pressure caused by the use of antimicrobial agents, either in human medicine or in agriculture. Alternatively, quinolone resistance may be due to decreased permeability or the presence of efflux pump mechanisms. Exposure of Salmonella isolates to low concentrations of fluoroquinolones has been shown to lead to activation of the efflux pump system, and a reduction in susceptibility, even when there are no mutations in gyrA.9 Thus, one can speculate that the finding that quinolone resistance in S. enterica has rapidly increased in South-east Asia and in certain parts of Europe may, at least partly, be due to the presence of a high selection pressure in those areas. The epidemiology of quinolone resistance in S. enterica resembles the recent epidemiology of fluoroquinolone resistance in the Campylobacter species. Fluoroquinolone resistance first became manifest among Campylobacter isolates from South-east Asia and Spain and was soon followed by an increase in resistance in the isolates from other countries.10,11
Salmonella Enteritidis was the most common serotype among the foreign Salmonella isolates, and Salmonella Enteritidis was also most commonly associated with reduced ciprofloxacin susceptibility. However, the increase in reduced ciprofloxacin susceptibility observed here among the foreign isolates was not due to a change in the proportion of Salmonella Enteritidis, which did not increase during the years.
Although our aim was to include only epidemiologically unrelated strains, our study design did not allow us to check whether patients inhabiting different localities in Finland had visited the same geographical area in the same tourist group. Therefore, it remains possible that some of the foreign isolates may have been epidemiologically related. There is some evidence that, in Europe, clonal expansion may account for high levels of quinolone resistance in Salmonella Enteritidis, particularly isolates of phage type 1.12 Also in the present study, Salmonella Enteritidis was the predominant serovar among the quinolone-resistant isolates from Spain, and phage type 1 was the predominant phage type. The situation was quite different among the isolates from Thailand, where only a minority (10%) of the quinolone-resistant isolates belonged to Salmonella Enteritidis.
The increasing quinolone resistance in salmonellas may have serious clinical consequences. Although antimicrobial treatment is commonly not needed in gastroenteritis caused by non-typhoidal salmonellas, effective therapy is necessary in invasive infections. If such an infection is caused by a Salmonella strain with reduced fluoroquinolone susceptibility, treatment with a fluoroquinolone may not be a safe alternative.1,3,4
In conclusion, reduced ciprofloxacin susceptibility increased significantly among all foreign Salmonella isolates as well as among those from Spain alone. Among the isolates from Thailand, reduced ciprofloxacin susceptibility remained at a constantly high level throughout the study. Our results show that reduced fluoroquinolone susceptibility in S. enterica is not restricted to South-east Asia alone, but continues to grow rapidly in many parts of the world. This may lead to clinical consequences.
|
Transparency declarations |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
None to declare.
|
Acknowledgements |
|---|
We are indebted to Erkki Nieminen for technical assistance, Tarja Heiskanen, Liisa Immonen and Minna Lamppu for laboratory assistance, and Kirsi Mäkisalo for collecting the travelling data if it did not accompany the strain. None of the authors received any financial support for the study.
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionTransparency declarationsReferences |
|---|
1. Mølbak K, Baggesen DL, Aarestrup FM et al. An outbreak of multidrug-resistant, quinolone-resistant Salmonella enterica serotype typhimurium DT104. N Engl J Med 1999; 341: 1420–5.
2. Threlfall EJ, Frost JA, Ward LR et al. Increasing spectrum of resistance in multiresistant Salmonella typhimurium. Lancet 1996; 347: 1053–4.[Web of Science][Medline]
3. Helms M, Vastrup P, Gerner-Smidt P et al. Excess mortality associated with antimicrobial drug-resistant Salmonella typhimurium. Emerg Infect Dis 2002; 8: 490–5.[Web of Science][Medline]
4.
Piddock LJV, Griggs DJ, Hall MC et al. Ciprofloxacin resistance in clinical isolates of Salmonella typhimurium obtained from two patients. Antimicrob Agents Chemother 1993; 37: 662–6.
5.
Hakanen A, Siitonen A, Kotilainen P et al. Increasing fluoroquinolone resistance in salmonella serotypes in Finland during 1995-1997 J Antimicrob Chemother 1999; 43: 145–8.
6. Hakanen A, Kotilainen P, Huovinen P et al. Reduced fluoroquinolone susceptibility in Salmonella enterica serotypes in travelers returning from Southeast Asia. Emerg Infect Dis 2001; 7: 996–1003.[Web of Science][Medline]
7. National Committee for Clinical Laboratory Standards. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically—Sixth Edition: Approved standard M7-A6. NCCLS, Wayne, PA, USA, 2003.
8.
Hakanen A, Kotilainen P, Jalava J et al. Detection of decreased fluoroquinolone susceptibility in salmonellas and validation of nalidixic acid screening test. J Clin Microbiol 1999; 37: 3572–7.
9. Cebrián L, Rodríguez JC, Escribano I et al. Characterization of Salmonella spp. mutants with reduced fluoroquinolone susceptibility: importance of efflux pump mechanisms. Chemotherapy 2005; 51: 40–3.[CrossRef][Web of Science][Medline]
10. Engberg J, Aarestrup FM, Taylor DE et al. Quinolone and macrolide resistance in Campylobacter jejuni and C. coli: resistance mechanisms and trends in human isolates. Emerg Infect Dis 2001; 7: 24–34.[Web of Science][Medline]
11. Hakanen A, Jousimies-Somer H, Siitonen A et al. Fluoroquinolone resistance in Campylobacter jejuni isolates in travelers returning to Finland: association of ciprofloxacin resistance to travel destination. Emerg Infect Dis 2003; 9: 267–70.[Web of Science][Medline]
12.
Kilmartin D, Morris D, O'Hare C et al. Clonal expansion may account for high levels of quinolone resistance in Salmonella enterica serovar Enteritidis. Appl Environ Microbiol 2005; 71: 2587–91.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  M. Gunell, M. A. Webber, P. Kotilainen, A. J. Lilly, J. M. Caddick, J. Jalava, P. Huovinen, A. Siitonen, A. J. Hakanen, and L. J. V. Piddock Mechanisms of Resistance in Nontyphoidal Salmonella enterica Strains Exhibiting a Nonclassical Quinolone Resistance Phenotype Antimicrob. Agents Chemother., September 1, 2009; 53(9): 3832 - 3836. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Kehrenberg, A. de Jong, S. Friederichs, A. Cloeckaert, and S. Schwarz Molecular mechanisms of decreased susceptibility to fluoroquinolones in avian Salmonella serovars and their mutants selected during the determination of mutant prevention concentrations J. Antimicrob. Chemother., May 1, 2007; 59(5): 886 - 892. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||