Occurrence and characteristics of class 1, 2 and 3 integrons in Escherichia coli, Salmonella and Campylobacter spp. in the Netherlands.
OBJECTIVE
To determine the occurrence and transmission of class 1, 2 and 3 integrons in multidrug-resistant or sulfamethoxazole-resistant Salmonella from human and animal sources and in Campylobacter spp. and Escherichia coli from broilers isolated in the Netherlands in 2004.


METHODS
PCR, restriction fragment length polymorphism (RFLP) and DNA sequencing were used to detect integrase genes and gene cassettes within 234 E. coli isolates, 40 Campylobacter isolates and 228 Salmonella isolates.


RESULTS
Class 1 integrons were found in 76% of the E. coli and in 43% of the Salmonella isolates. Class 2 integrons were found in 11% of the E. coli and 1% of the Salmonella isolates. No class 1 or 2 integrons were detected in the Campylobacter isolates, and no class 3 integrons were detected in any of the bacterial species examined. The 22 different integrons detected harboured 20 different gene cassettes. The cassette arrays dfrA1-aadA1 and dfrA1-sat2-aadA1 were most frequently associated with class 1 and 2 integrons, respectively. For the first time linF was found to be associated with a class 2 integron as part of the linF-sat2-aadA1 cassette. The gene cassettes found within the integrons explain only a part of the resistance profile of the isolates. Conjugation experiments demonstrated transfer of class 1 and 2 integrons.


CONCLUSIONS
Our data demonstrate the importance of integrons for the occurrence and transmission of multidrug resistance. Identical predominant class 1 and 2 integrons in E. coli and Salmonella serovars indicate horizontal transfer between these species.
van Essen-Zandbergen
Alieda
A
Central Institute for Animal Disease Control Lelystad (CIDC-Lelystad), Wageningen UR, PO Box 2004, 8203 AA Lelystad, The Netherlands.
Smith
Hilde
H
Veldman
Kees
K
Mevius
Dik
D
D000818:Animals; D002167:Campylobacter / Q000187:drug effects / Q000235:genetics*; D002169:Campylobacter Infections / Q000453:epidemiology / Q000382:microbiology; D002645:Chickens; D003227:Conjugation, Genetic / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology; D006801:Humans; D019426:Integrases / Q000235:genetics; D032023:Integrons / Q000235:genetics*; D009426:Netherlands / Q000453:epidemiology; D012150:Polymorphism, Restriction Fragment Length; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012475:Salmonella / Q000187:drug effects / Q000235:genetics*; D012480:Salmonella Infections / Q000453:epidemiology / Q000382:microbiology
D004269:DNA, Bacterial; D019426:Integrases