Class 1 integrons lacking qacEDelta1 and sul1 genes in Escherichia coli isolates of food, animal and human origins.
OBJECTIVE
To study the frequency and diversity of class 1 integrons lacking the 3'-conserved segment (CS) in intI1-positive Escherichia coli isolates of different origins.


METHODS
The presence of intI1 was previously detected in 84 E. coli isolates of food (21 isolates), animal (32) and healthy-human volunteer (31) origins. The qacEDelta1-sul1 genes were analyzed by PCR and those isolates that lacked these genes were included in this work. The genetic structure of class 1 integrons was determined, using the PCR and sequencing primer-walking strategy. Isolates and plasmids were typed.


RESULTS
Class 1 integrons lacking the 3'-CS were found in 13 of the 84 intI1-positive E. coli isolates (15.5%) of food, animal, and human origins. All 13 isolates showed unrelated patterns by REP-PCR. The following gene cassette arrangements were identified inside the class 1 integrons of these 13 strains: dfrA1; dfrA5; dfrA12-orfF-aadA2-cmlA1-aadA1-qacH-IS440-sul3; dfrA12-orfF-aadA2-cmlA1-aadA1-IS440-sul3; estX-psp-aadA2-cmlA1-aadA1-qacH-IS440-sul3; and a new arrangement estX-psp-aadA2-cmlA1Delta-IS1294-DeltacmlA1-aadA1-qacH-IS440-sul3 that contain the IS1294 into the cmlA1 gene (included in GenBank, number EU704128). Complete or truncated mef(B) gene was detected upstream of sul3 gene in this type of integrons. Plasmids were identified in four of the studied strains by PCR-replicon-typing, detecting different combinations of IncY, I1, FIC, FII, FIB plasmids. Non-classic integrons were located into plasmids of 100-150 kb in four studied strains.


CONCLUSIONS
Occurrence and diversity of class 1 integrons lacking 3'-CS among the studied intI1-positive E. coli isolates of different origins were relatively high. The sul3 gene was detected in most of class 1 integrons lacking 3'-CS.
Sáenz
Y
Y
Area de Bioquímica y Biología Molecular, Universidad de La Rioja, Logroño, Spain.
Vinué
L
L
Ruiz
E
E
Somalo
S
S
Martínez
S
S
Rojo-Bezares
B
B
Zarazaga
M
M
Torres
C
C
D000818:Animals; D017124:Conserved Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005516:Food Microbiology; D006801:Humans; D019426:Integrases / Q000235:genetics / Q000378:metabolism*; D032023:Integrons / Q000235:genetics* / Q000502:physiology
D029968:Escherichia coli Proteins; C091882:Sul1 protein, E coli; D019426:Integrases; C115006:integron integrase IntI1