Metallo-beta-lactamase producers in environmental microbiota: New molecular class B enzyme in Janthinobacterium lividum

Eleven environmental samples from different sources were screened for the p resence of metallo-beta -lactamase-producing bacteria by using a selective enrichment medium containing a carbapenem antibiotic and subsequently testi ng each isolate for production of EDTA-inhibitable carbapenemase activity. A total of 15 metallo-beta -lactamase-producing isolates, including 10 Sten otrophomonas maltophilia isolates, 3 Chlyseobacterium spp,, one Aeromonas h ydrophila isolate, and one Janthinobacterium lividum isolate (a species in which production of metallo-beta -lactamase activity was not previously rep orted), 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 -la ctamase determinant encoding a new member (named THIN-B) of the highly dive rgent subclass B3 lineage of metallo-beta -lactamases. THIN-B is most close ly related (35.6% identical residues) to the L1 enzyme of S, maltophilia an d 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 re sulted in decreased susceptibility to several beta -lactams, including peni cillins, cephalosporins (including cephamycins and oxyimino cephalosporins) , and carbapenems, revealing a broad substrate specificity of the enzyme. T he results of this study indicated that metallo-beta -lactamase-producing b acteria are widespread in the environment and identified a new molecular cl ass B enzyme in the environmental species J, lividum.