Infect Chemother.  2009 Jun;41(3):165-173. 10.3947/ic.2009.41.3.165.

Detection and Characterization of Integrons in Nontyphoid Salmonella Clinical Isolates

• Lee JE
• Park SJ
• Kim SH
• Kim MN
• Lee NY
• Lee BK
• Lee SO
• Kim YS
• Woo JH
• Choi SH

• KMID: 1782319
• DOI: http://doi.org/10.3947/ic.2009.41.3.165

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.

Keyword

Salmonella; Integrons; Antibiotic resistance

MeSH Terms

Agar
Ampicillin
Chloramphenicol
Drug Resistance, Microbial
Electrophoresis, Gel, Pulsed-Field
Enteritis
Humans
Integrases
Integrons
Polymerase Chain Reaction
Prevalence
Salmonella
Sprains and Strains
Streptomycin
Sulfamethoxazole
Tetracycline
Trimethoprim
Agar
Ampicillin
Chloramphenicol
Integrases
Streptomycin
Sulfamethoxazole
Tetracycline
Trimethoprim

Figure

• 

  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.

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