Detection and Characterization of Integrons in Nontyphoid Salmonella Clinical Isolates

Jung Eun Lee; Su Jin Park; Sung Han Kim; Mi-Na Kim; Nam Yong Lee; Bok Kwon Lee; Sang-Oh Lee; Yang Soo Kim; Jun-Hee Woo; Sang-Ho Choi

doi:10.3947/ic.2009.41.3.165

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Lee, Park, Kim, Kim, Lee, Lee, Lee, Kim, Woo, and Choi: Detection and Characterization of Integrons in Nontyphoid Salmonella Clinical Isolates

Original Article

Infection and Chemotherapy

Infection and Chemotherapy 2009; 41(3): 165-173.

Published online: 30 June 2009

DOI: https://doi.org/10.3947/ic.2009.41.3.165

Detection and Characterization of Integrons in Nontyphoid Salmonella Clinical Isolates

Jung Eun Lee^1,², Su Jin Park^1,², Sung Han Kim, M.D.^1,², Mi-Na Kim, M.D.³, Nam Yong Lee, M.D.⁴, Bok Kwon Lee, Ph.D.⁵, Sang-Oh Lee, M.D.^1,², Yang Soo Kim, M.D.^1,², Jun-Hee Woo, M.D.^1,², Sang-Ho Choi, M.D.^1,²

¹Center for Antimicrobial Resistance and Microbial Genomics, University of Ulsan, Seoul, Korea.

²Department of Infectious Diseases, Asan Medical Center, Seoul, Korea.

³Department of Laboratory Medicine, University of Ulsan College of Medicine, Seoul, Korea.

⁴Department of Laboratory Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

⁵Division of Enteric Bacterial Infection, Korean Center for Disease Control and Prevention, Seoul, Korea.

Correspondence author: Sang-Ho Choi, M.D. Department of Infectious Diseases, Asan Medical Center, Asanbyeongwon-gil 86, Songpa-gu, Seoul 138-736, Korea. Tel: +82-2-3010-3304, Fax: +82-2-3010-6970, sangho@amc.seoul.kr

Received 23 February 2009 Accepted 24 March 2009

(open-access):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Nontyphoid Salmonella (NTS) is a leading cause of human food-borne enteritiS. It has been known that integron, a naturally occurring gene capture and expression element, plays an important role in the development and dissemination of multidrug-resistance. In this study, we investigated the prevalences and molecular characteristics of integrons in NTS clinical strains.

Materials and Methods

Between 1995-96 and 2000-03, a total 261 NTS clinical strains comprising 39 serotypes were collected from clinical specimens. All strains were serotyped, and the MICs of ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim were determined by agar dilution method. Integrons were detected by PCR amplification of integrase genes, and gene cassettes were determined by PCR and sequencing. Conjugation experiments were performed using E. coli J53 as a recipient. The clonal relationship was analyzed by pulsed-field gel electrophoresis (PFGE).

Results

Of the 261 strains tested, class 1 integrons were present in 21 strains (8.0%). Class 2 and class 3 integrons were not found. The integron-positive rate was higher in S. Typhimurium (24.2% [8/33]) than in S. Enteritidis (2.0% [3/153]). Overall rates of antimicrobial resistance were higher in integron-positive strains. dhfr12-orfF-aadA2 gene cassette was detected in 5 strains, aadA2 in 4 strains, dhfr17-orfF-aadA5 in 2 strains, and addA1 in 1 strain. Ten integron-positive transconjugants were successfully selected. Among 8 integron-positive strains of S. Typhimurium, 7 had similar PFGE patterns.

Conclusion

This study suggests that integrons are already playing a significant role in antimicrobial resistance in NTS. Continuous monitoring is needed to detect the emergence and spread of integron-mediated antimicrobial resistance.

Keywords: Salmonella, Integrons, Antibiotic resistance

Figures and Tables

Figure 1

Polymerase chain reaction fragments from the cassette regions of class 1 integrons. M, Molecular weight Marker (1 kb ladder); S. Enteritidis (Lanes 1-3); S. Typhimurium (Lanes 4-11); S. Heidelberg (Lanes 12, 13); S. Montevideo (Lanes 14, 15); S. Dubulin (Lane 16); S. Sinstorf (Lane 17); S. Cuckmere (Lane 18); S. salamae (Lane 19); S. Othmarschen (Lane 20); S. Haifa (Lane 21).

Figure 2

Pulsed-field gel electrophoresis patterns of chromosomal DNA restriction fragments resolved in 1.0% Seakem Gold agarose in 0.5×TBE buffer for Salmonella DNA digestion with XbaI. M, ladder size marker; S. Enteritidis (Lanes 1-3); S. Typhimurium (Lanes 4-11); S. Heidelberg (Lanes 12,13); S. Montevideo (Lanes 14,15); S. Dubulin (Lane 16); S. Sinstorf (Lane 17); S. salamae (Lane 18); S. Cuckmere (Lane 19); S. Othmarschen (Lane 20); S. Haifa (Lane 21); ND, not deteremind.

Table 1

Antibiotic Resistance Patterns of 261 Nontyphoid Salmonella strains

Abbreviations: AMC, ampicillin; CHP, chloramphenicol; SM, streptomycin; SMX, sulfamethoxazole; TC, tetracycline; TMP, trimethoprim; NA, nalidixic acid

Table 2

Antibiotic Resistance Patterns According to the Presence or Absence of Integron

Abbreviations : AMC, ampicillin; CHP, chloramphenicol; SM, streptomycin; SMX, sulfamethoxazole; TC, tetracycline; TMP, trimethoprim; NA, nalidixic acid; MDR, multidrug resistance (defined as resistance to more than 3 classes of antibiotics)

Table 3

Distribution of Class 1 Integron Gene Cassette and Antibiotic Resistance Patterns of 21 Integron-carrying Strains

Abbreviations : RDNC, reacts but dose not conform to any standard phage type; A, ampicillin; C, chloramphenicol; S, streptomycin; S, sulfamethoxazole; T, tetracycline; Tm, trimethoprim; N, nalidixic acid

Table 4

Antibiotic Resistance Patterns and MICs for 10 Conjugated Strains and Their Transconjugants

Abbreviations: RDNC, reacts but dose not conform to any standard phage type; A or AMC, ampicillin; C or CHP, chloramphenicol; or SM, streptomycin; Su or SMX, sulfamethoxazole; T or TC, tetracycline, Tm or TMP, trimethoprim

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