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Lee, Kang, Oh, Jeong, Kim, Seol, Cho, and Lee: Antimicrobial Resistance and Integrons Found in Commensal Escherichia coli Isolates from Healthy Humans
Original Article

J Bacteriol Virol 2006;36(3):133-139.

Published online: 18 February 2006

DOI: https://doi.org/10.4167/jbv.2006.36.3.133

Antimicrobial Resistance and Integrons Found in Commensal Escherichia coli Isolates from Healthy Humans

Je Chul Lee, Hee Young Kang, Jae Young Oh, Jae Ho Jeong, Jungmin Kim, Sung Yong Seol, Dong Taek Cho, Yoo Chul Lee∗,

Department of Microbiology, Kyungpook National University School of Medicine, Daegu 700-422, Korea

∗Corresponding author: Yoo Chul Lee. Department of Microbiology, Kyungpook National University School of Medicine, 101, Dongin-dong, Jung-gu, Daegu, 700-422, Korea. Phone: +82-53-420-4843, Fax: +82-53-427-5664, e-mail: yclee@knu.ac.kr

Received 28 June 2006       Accepted 26 July 2006

Copyright © 2006 Journal of Bacteriology and Virology

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

The emergence and spread of antimicrobial resistance among the pathogenic and commensal Enterobacteriaceae are of great concern worldwide. We characterized the antimicrobial resistance and integrons found in commensal Escherichia coli from healthy humans in the community. Class 1 integrase (intl1) and class 2 integrase (intl2) genes were identified in 22 (13.3%) and 2 (1.2%) of 165 E. coli isolates, respectively. dfrA17-aadA5 and dfrA1-aadA2 were the most common class 1 integrons. The prevalence of each type of class 1 integron among commensal E. coli isolates during 2001∼2003 was similar to that of clinical E. coli isolates from hospital-acquired infections during 1994∼1999. The resistant rates of commensal E. coli isolates carrying intl1 to ampicillin, streptomycin, gentamicin, sulfamethoxazole, trimethoprim, chloramphenicol, and tetracycline were significantly higher than those of intl1-negative E. coli isolates (p<0.05). Integrons were directly associated with multidrug resistance in commensal E. coli isolates. It is hypothesized that multidrug-resistant Enterobacteriaceae from hospital-acquired infections are a potential reservoir for integrons associated with resistance genes found in commensal E. coli isolates in the community.

Keywords: Integron, Commensal fecal flora, Multiresistance, Escherichia coli

References

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Figure 1.
PCR amplification of gene cassette regions of class 1 and 2 integrons. Lane 1–6, class 1 integron carrying dfrA17-aadA5, dfrA1-aadA2, dfrA12-orfF-aadA2, dfrA5, dfrA7, and aadA1, respectively. Lane 7, class 2 integron carrying dfrA1-sat-aadA1. Lane M, lambda DNA fragments digested with HindIII.
jbv-36-133f1.tif
Figure 2.
Multiplicity of antimicrobial resistance and its association with the presence of integrons in commensal E. coli isolates. E. coli isolates were examined for antimicrobial susceptibility to 15 agents.
jbv-36-133f2.tif
Table 1.
Characterization of integrons found in commensal E. coli isolates
Cassette array No. of isolates No. of isolates that carry integrons at
Conjugative plasmids Non-conjugative plasmids Chromosome
Class 1 integrons        
dfrA17-aadA5 6 6 0 0
dfrA1-aadA2 5 3 2 0
dfrA12-orfF-aadA2 1 1 0 0
dfrA5 1 1 0 0
dfrA7 2 0 2 0
aadA1 2 0 0 2
No cassettes 5 1 3 1
Class 2 integrons        
dfrA1-sat-aadA1 2 0 0 2
Total 24 12 7 5
Table 2.
Antimicrobial susceptibility of commensal E. coli isolates according to the presence of integrons
Antimicrobial agent No. (%) of isolates P
Total (n=165) intl-positive (n=24) intl-negative (n=141)
β-lactams        
 Ampicillin 72 (43.6) 18 (75.0) 54 (38.3) 0.001∗
 Piperacillin 28 (17.0) 6 (25.0) 22 (15.6) 0.257
 Cephalothin 9 (5.5) 1 (4.2) 8 (5.7) 0.764
 Cefamandole 6 (3.6) 0 6 (4.3) 0.303
 Ceftazidime 0 0 0  
Aminoglycosides        
 Streptomycin 58 (35.2) 17 (70.8) 41 (29.1) < 0.001∗
 Kanamycin 6 (3.6) 2 (8.3) 4 (2.8) 0.184
 Gentamicin 3 (1.8) 2 (8.3) 1 (0.7) 0.010∗
 Tobramycin 3 (1.8) 1 (4.2) 2 (1.4) 0.352
Fluoroquinolones        
 Ciprofloxacin 2 (1.2) 0 2 (1.4) 0.557
 Norfloxacin 3 (1.8) 2 (8.3) 1 (0.7) 0.184
Antifolates        
 Sulfamethoxazole 42 (25.4) 18 (75.0) 24 (17.0) < 0.001∗
 Trimethoprim 23 (13.9) 16 (66.7) 7 (5.0) < 0.001∗
Chloramphenicol 16 (9.70) 12 (50.0) 4 (2.8) < 0.001∗
Tetracycline 64 (38.8) 18 (75.0) 46 (32.6) < 0.001∗

∗ Asterisk indicates statistical significance

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