Antimicrobial Agents and Chemotherapy, March 2001, p. 837-844, Vol. 45, No. 3
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.3.837-844.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
-Lactamase Producers in Environmental
Microbiota: New Molecular Class B Enzyme in
Janthinobacterium lividum
Dipartimento di Biologia Molecolare, Sez. di Microbiologia, Università di Siena, 53100 Siena,1 Istituto di Microbiologia, Università "La Sapienza," 00185 Rome,2 Dipartimento di Scienze e Tecnologie Biomediche, Università di L'Aquila. 67100 L'Aquila,3 and Dipartimento di Biologia, II Università di Roma "Tor Vergata," 00133 Rome,4 Italy
Received 24 July 2000/Returned for modification 27 November 2000/Accepted 21 December 2000
Eleven environmental samples from different sources were screened
for the presence of metallo-
-lactamase-producing bacteria by using a
selective enrichment medium containing a carbapenem antibiotic and
subsequently testing each isolate for production of EDTA-inhibitable
carbapenemase activity. A total of 15 metallo-
-lactamase-producing isolates, including 10 Stenotrophomonas maltophilia
isolates, 3 Chryseobacterium spp., one Aeromonas
hydrophila isolate, and one Janthinobacterium lividum
isolate (a species in which production of metallo-
-lactamase
activity was not previously reported), were obtained from 8 samples. In
the J. lividum isolate, named JAC1, production of
metallo-
-lactamase activity was elicited upon exposure to
-lactams. Screening of a JAC1 genomic library for clones showing a
reduced imipenem susceptibility led to the isolation of a
metallo-
-lactamase determinant encoding a new member (named THIN-B)
of the highly divergent subclass B3 lineage of metallo-
-lactamases.
THIN-B is most closely related (35.6% identical residues) to the L1
enzyme of S. maltophilia and more distantly related to the
FEZ-1 enzyme of Legionella gormanii (27.8% identity) and
to the GOB-1 enzyme of Chryseobacterium meningosepticum (24.2% identity). Sequences related to
blaTHIN-B, and inducible production of
metallo-
-lactamase activity, were also detected in the J. lividum type strain DSM1522. Expression of the
blaTHIN-B gene in Escherichia coli
resulted in decreased susceptibility to several
-lactams, including
penicillins, cephalosporins (including cephamycins and oxyimino
cephalosporins), and carbapenems, revealing a broad substrate
specificity of the enzyme. The results of this study indicated that
metallo-
-lactamase-producing bacteria are widespread in the
environment and identified a new molecular class B enzyme in the
environmental species J. lividum.
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