Affiliation:
1. Laboratory of Cellular Biology1 and
2. Laboratory of Bacteriology and Medical Mycology,2
3. Istituto Superiore di Sanità Rome, and Institute of Microbiology, University of Rome, “La Sapienza,”3 Rome, Italy
Abstract
ABSTRACT
The presence and genetic content of integrons were investigated for 37 epidemiologically unrelated multiple-drug-resistant strains of
Salmonella enterica
serotype Typhimurium from humans. All isolates were resistant to ampicillin, chloramphenicol, kanamycin, streptomycin, sulfonamides, and trimethoprim, as well as to tetracycline and/or nalidixic acid; 20% of them were also resistant to gentamicin and amikacin. Three different class 1 integrons (In-t1, In-t2, and In-t3) were identified by Southern blot hybridization, PCR, and DNA sequencing, and these integrons were found to carry the
aadB
,
catB3
,
oxa1
,
aadA1a
,
aacA4
, and
aacC1
gene cassettes. Integrons In-t1 (
aadB
and
catB3
) and In-t2 (
oxa1
and
aadA1a
) were both located on a conjugative IncFI plasmid of 140 kb. In-t3 (
aacA4
,
aacC1
, and
aadAIa
) was located on an IncL/M plasmid of 100 kb which was present, in association with the IncFI plasmid, in gentamicin- and amikacin-resistant isolates. Despite the extensive similarity at the level of the antibiotic resistance phenotype, integrons were not found on the prototypic IncFI plasmids carried by epidemic
Salmonella
strains isolated during the late 1970s. The recent appearance and the coexistence of multiple integrons on two conjugative plasmids in the same
Salmonella
isolate are examples of how mobile gene cassettes may contribute to the acquisition and dissemination of antibiotic resistance.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
112 articles.
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