Characterization of the metallo-beta-lactamase determinant of Acinetobacter baumannii AC-54/97 reveals the existence of bla(IMP) allelic variants carried by gene cassettes of different phylogeny.
The metallo-beta-lactamase determinant of Acinetobacter baumannii AC-54/97, a clinical isolate from Italy that was previously shown to produce an enzyme related to IMP-1, was isolated by means of a PCR methodology which targets amplification of gene cassette arrays inserted into class 1 integrons. Sequencing revealed that this determinant was an allelic variant (named bla(IMP-2)) of bla(IMP) found in Japanese isolates and that it was divergent from the latter by 12% of its nucleotide sequence, which evidently had been acquired independently. Similar to bla(IMP), bla(IMP-2) was also carried by an integron-borne gene cassette. However, the 59-base element of the bla(IMP-2) cassette was unrelated to those of the bla(IMP) cassettes found in Japanese isolates, indicating a different phylogeny for the gene cassettes carrying the two allelic variants. Expression of the integron-borne bla(IMP-2) gene in Escherichia coli resulted in a significant decrease in susceptibility to a broad array of beta-lactams (ampicillin, carbenicillin, cephalothin, cefoxitin, ceftazidime, cefepime, and carbapenems). The IMP-2 enzyme was purified from an Escherichia coli strain carrying the cloned determinant, and kinetic parameters were determined with several beta-lactam substrates. Compared to IMP-1, the kinetic parameters of IMP-2 were similar overall with some beta-lactam substrates (cefoxitin, ceftazidime, cefepime, and imipenem) but remarkably different with others (ampicillin, carbenicillin, cephaloridine, and meropenem), revealing a functional significance of at least some of the mutations that differentiate the two IMP variants. Present findings suggest that the environmental reservoir of bla(IMP) alleles could be widespread and raise a question about the global risk of their transfer to clinically relevant species.
Riccio
M L
ML
Dipartimento di Biologia Molecolare, Sezione di Microbiologia, Università di Siena, I-53100-Siena, Italy.
Franceschini
N
N
Boschi
L
L
Caravelli
B
B
Cornaglia
G
G
Fontana
R
R
Amicosante
G
G
Rossolini
G M
GM
D000150:Acinetobacter / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D000483:Alleles; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics* / Q000302:isolation & purification; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000032:analysis; D004926:Escherichia coli / Q000187:drug effects; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D001618:beta-Lactamases / Q000235:genetics* / Q000302:isolation & purification; D047090:beta-Lactams
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D047090:beta-Lactams; C000603502:IMP-2 metallo-beta-lactamase, Acinetobacter baumannii; D001618:beta-Lactamases