title: Metallo-beta-lactamase producers in environmental microbiota: new molecular class B enzyme in Janthinobacterium lividum.
abstract: Eleven environmental samples from different sources were screened for the presence of metallo-beta-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-beta-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-beta-lactamase activity was not previously reported), were obtained from 8 samples. In the J. lividum isolate, named JAC1, production of metallo-beta-lactamase activity was elicited upon exposure to beta-lactams. Screening of a JAC1 genomic library for clones showing a reduced imipenem susceptibility led to the isolation of a metallo-beta-lactamase determinant encoding a new member (named THIN-B) of the highly divergent subclass B3 lineage of metallo-beta-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 bla(THIN-B), and inducible production of metallo-beta-lactamase activity, were also detected in the J. lividum type strain DSM1522. Expression of the bla(THIN-B) gene in Escherichia coli resulted in decreased susceptibility to several beta-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-beta-lactamase-producing bacteria are widespread in the environment and identified a new molecular class B enzyme in the environmental species J. lividum.
authors.affiliation: Dipartimento di Biologia Molecolare, Sez. di Microbiologia, Università di Siena, 53100 Siena, Italy. rossolini@unisi.it
authors.forename: G M
authors.initials: GM
authors.lastname: Rossolini
authors.forename: M A
authors.initials: MA
authors.lastname: Condemi
authors.forename: F
authors.initials: F
authors.lastname: Pantanella
authors.forename: J D
authors.initials: JD
authors.lastname: Docquier
authors.forename: G
authors.initials: G
authors.lastname: Amicosante
authors.forename: M C
authors.initials: MC
authors.lastname: Thaller
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004783:Environmental Microbiology; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010802:Phylogeny; D020560:Proteobacteria / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D001618:beta-Lactamases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D047090:beta-Lactams; C425147:beta-lactamase THIN-B; D001618:beta-Lactamases