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Antimicrobial Agents and Chemotherapy, April 2003, p. 1382-1390, Vol. 47, No. 4
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.4.1382-1390.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Epidemiology of Rifampin ADP-Ribosyltransferase (arr-2) and Metallo-ß-Lactamase (blaIMP-4) Gene Cassettes in Class 1 Integrons in Acinetobacter Strains Isolated from Blood Cultures in 1997 to 2000

Elizabeth T. S. Houang,1* Yiu-Wai Chu,2 Wai-Sing Lo,1 Ka-Yi Chu,1 and Augustine F. B. Cheng1

Department of Microbiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin,1 Public Health Laboratory Centre, Department of Health, Kowloon, Hong Kong, China2

Received 13 May 2002/ Returned for modification 10 September 2002/ Accepted 23 January 2003

We characterized two new gene cassettes in an Acinetobacter isolate: one harbored the metallo-ß-lactamase (IMP-4) gene blaIMP-4, the other harbored the rifampin ADP-ribosyltransferase (ARR-2) gene arr-2, and both arrayed with the aminoglycoside acetyltransferase [AAC(6')-Ib7] gene cassette aacA4 in two separate class 1 integrons. The epidemiology of these gene cassettes in isolates from blood cultures obtained from 1997 to 2000 was studied. Isolates bearing either the blaIMP-4 or the arr-2 gene cassette or both represented 17.5% (10 of 57) of isolates in 1997, 16.1% (10 of 62) in 1998, 2.5% (1 of 40) in 1999, and 0% (0 of 58) in 2000. These two gene cassettes, probably borne on two separate integrons, were found in at least three genomic DNA groups, with evidence of clonal dissemination in the intensive care unit during 1997 to 1998. Seventeen of the 52 Acinetobacter baumannii (genomic DNA group 2) isolates from 1997 to 2000 harbored intI1, but only one was positive for these gene cassettes, whereas 20 of the 21 intI1-positive isolates of all other genomic DNA groups were positive for either or both of them. Reduced susceptibility to imipenem and rifampin was seen only in isolates harboring the blaIMP-4 and arr-2 cassettes, respectively. The aminoglycoside phosphotransferase [APH(3')-VIa] gene aph(3')-VIa was detected in all 21 isolates for which the MIC of amikacin was >=8 µg/ml, with or without aacA4, whereas aacA4 alone was found in isolates for which the MIC of amikacin was 0.5 to 2 µg/ml. Significant differences between the 17 intI1-positive and 47 intI1-negative isolates belonging to genomic DNA group 3 from 1997 to 1998 in the MICs of amikacin, gentamicin, imipenem, sulfamethoxazole, and ceftazidime were observed (Mann-Whitney test, P < 0.001 to 0.01).


* Corresponding author. Mailing address: Department of Microbiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong, Special Administrative Region, People's Republic of China. Phone: (852) 2632 2304. Fax: (852) 2647 3227. E-mail: ehouang{at}cuhk.edu.hk.


Antimicrobial Agents and Chemotherapy, April 2003, p. 1382-1390, Vol. 47, No. 4
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.4.1382-1390.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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